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Altering the ratio of dietary palmitic and oleic acids affects nutrient digestibility, metabolism, and energy balance during the immediate postpartum in dairy cows

  • Author Footnotes
    * Current address: Perdue Agribusiness, Salisbury, MD 21804
    J. de Souza
    Footnotes
    * Current address: Perdue Agribusiness, Salisbury, MD 21804
    Affiliations
    Department of Animal Science, Michigan State University, East Lansing 48824
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  • Author Footnotes
    † Current address: Cargill, Inc., 15407 McGinty Rd W, Wayzata, MN 5539
    C.M. Prom
    Footnotes
    † Current address: Cargill, Inc., 15407 McGinty Rd W, Wayzata, MN 5539
    Affiliations
    Department of Animal Science, Michigan State University, East Lansing 48824
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  • A.L. Lock
    Correspondence
    Corresponding author
    Affiliations
    Department of Animal Science, Michigan State University, East Lansing 48824
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  • Author Footnotes
    * Current address: Perdue Agribusiness, Salisbury, MD 21804
    † Current address: Cargill, Inc., 15407 McGinty Rd W, Wayzata, MN 5539
Open ArchivePublished:December 23, 2020DOI:https://doi.org/10.3168/jds.2020-19312

      ABSTRACT

      This article is the second from an experiment that determined the effects of altering the dietary ratio of palmitic (C16:0) and oleic (cis-9 C18:1) acids on digestibility, production, and metabolic responses of dairy cows during the immediate postpartum. This article elaborates on the effect of these diets on nutrient digestibility, energy balance, and metabolism. Fifty-six multiparous cows were used in a randomized complete block design and randomly assigned to 1 of 4 treatments fed from 1 to 24 d in milk. The treatments were: (1) control (CON) diet not supplemented with fatty acids (FA); (2) diet supplemented with a FA blend containing 80% C16:0 and 10% cis-9 C18:1 (80:10); (3) diet supplemented with a FA blend containing 70% C16:0 and 20% cis-9 C18:1 (70:20); and (4) diet supplemented with a FA blend containing 60% C16:0 and 30% cis-9 C18:1 (60:30). The FA supplement blends were added at 1.5% of diet dry matter by replacing soyhulls in the CON diet. Three preplanned contrasts were used to compare treatment differences: (1) CON versus FA-supplemented diets, (80:10 + 70:20 + 60:30)/3; (2) the linear effect of cis-9 C18:1 inclusion in diets; and (3) the quadratic effect of cis-9 C18:1 inclusion in diets. The FA-supplemented diets increased digestibility of dry matter, neutral detergent fiber, 18-carbon FA, and total FA compared with CON. We observed a tendency for an interaction between treatment and time for the digestibility of 18-carbon and total FA because the difference in digestibility between CON and 60:30 treatments tended to increase over time. Increasing dietary cis-9 C18:1 increased linearly the digestibility of dry matter, neutral detergent fiber, 16-carbon, 18-carbon, and total FA. Interestingly, total absorbed FA was positively related to milk, milk fat yield, energy-corrected milk, plasma insulin, and albumin, and negatively related to plasma nonesterified FA (NEFA) and body weight loss. The FA-supplemented diets increased intake of digestible energy, metabolizable energy, and net energy for lactation compared with CON. Compared with CON, FA-supplemented diets increased milk energy output and tended to increase negative energy balance. Increasing dietary cis-9 C18:1 increased intake of digestible energy, metabolizable energy, and net energy for lactation. Although increasing dietary cis-9 C18:1 did not affect milk energy output and energy for maintenance, increasing dietary cis-9 C18:1 improved energy balance. Compared with CON, FA-supplemented diets increased plasma insulin, but we did not observe differences between CON and FA-supplemented diets for NEFA and albumin. Increasing cis-9 C18:1 in FA treatments linearly decreased plasma NEFA and tended to linearly increase insulin and β-hydroxybutyrate. During the carryover period, no treatment differences in blood metabolites were observed. Our results indicate that feeding FA supplements containing C16:0 and cis-9 C18:1 during the immediate postpartum period increased nutrient digestibility, energy intake, and milk energy output compared with a non-fat-supplemented control diet. Increasing dietary cis-9 C18:1 increased energy intake, reduced markers of body fat mobilization, and improved energy balance during the immediate postpartum.

      Key words

      INTRODUCTION

      Lactogenesis, uterine involution, and pronounced changes in endocrine function and energy balance create a unique set of challenges that trigger major adaptive changes in the metabolic function of dairy cows during early lactation (
      • Bradford B.J.
      • Yuan K.
      • Farney J.K.
      • Mamedova L.K.
      • Carpenter A.J.
      Invited review: Inflammation during the transition to lactation: New adventures with an old flame.
      ). Therefore, dairy cows undergo large metabolic adaptations in glucose, AA, fatty acid (FA), and mineral metabolism to support lactation and avoid metabolic dysfunction immediately postpartum (
      • Overton T.R.
      • McArt J.A.A.
      • Nydam D.V.
      A 100-year review: Metabolic health indicators and management of dairy cattle.
      ). The major nutritional challenge in early lactation is to meet the increasing requirements for energy and key nutrients while feed intake is limited. As part of the metabolic adaptive mechanisms, body fat reserves are mobilized around parturition, due to reduced plasma insulin concentration (
      • Zachut M.
      • Honig H.
      • Striem S.
      • Zick Y.
      • Boura-Halfon S.
      • Moallem U.
      Periparturient dairy cows do not exhibit hepatic insulin resistance, yet adipose-specific insulin resistance occurs in cows prone to high weight loss.
      ), low insulin sensitivity of extra-hepatic tissues (
      • Bell A.W.
      Regulation of organic nutrient metabolism during transition from late pregnancy to early lactation.
      ), and increased catecholamine-stimulated lipolysis (
      • Contreras G.A.
      • Strieder-Barboza C.
      • Raphael W.
      Adipose tissue lipolysis and remodeling during the transition period of dairy cows.
      ). Increased mobilization of body reserves results in increased plasma nonesterified fatty acid (NEFA) concentrations (
      • González F.D.
      • Muiño R.
      • Pereira V.
      • Campos R.
      • Benedito J.L.
      Relationship among blood indicators of lipomobilization and hepatic function during early lactation in high-yielding dairy cows.
      ), which can alter immune function and increase the risk and severity of both metabolic and infectious diseases (
      • Sordillo L.M.
      • Contreras G.A.
      • Aitken S.L.
      Metabolic factors affecting the inflammatory response of periparturient dairy cows.
      ;
      • Sordillo L.M.
      Nutritional strategies to optimize dairy cattle immunity.
      ). Furthermore, the control of feed intake is likely dominated by hepatic oxidation of NEFA during the immediate postpartum period (
      • Allen M.S.
      • Bradford B.J.
      • Oba M.
      Board-invited review: The hepatic oxidation theory of the control of feed intake and its application to ruminants.
      ), and therefore, the increased NEFA supply to the liver can further decrease energy intake, thereby intensifying negative energy balance (
      • Allen M.S.
      • Piantoni P.
      Metabolic control of feed intake: Implications for metabolic disease of fresh cows.
      ). Thus, considering that nutrient status plays a critical role during early lactation, nutrition-based management strategies to increase energy intake and minimize negative energy balance are important to the health and productivity of dairy cattle.
      Supplemental fat can be used as a strategy to increase energy intake, but limited research is available, and results are inconsistent regarding the effects of FA supplementation on energy balance and metabolism in early-lactation cows.
      • Piantoni P.
      • Lock A.L.
      • Allen M.S.
      Saturated fat supplementation interacts with dietary forage neutral detergent fiber content during the immediate postpartum period in Holstein cows: Energy balance and metabolism.
      observed that feeding a saturated FA supplement [37% palmitic acid (C16:0) + 46% stearic acid (C18:0)] at 2.0% of diet DM during the first 4 wk postpartum interacted with forage NDF level on the response of dairy cows; when the FA supplement was fed in a low forage diet (20% of forage NDF), it increased energy intake and energy balance and reduced body fat mobilization at the expense of milk yield. The high forage diet with supplemental FA increased DMI and tended to decrease BCS loss compared with the same diet without FA supplementation. In a recent study with early-lactation cows, feeding a C16:0-enriched supplement at 1.5% of diet DM during the first 24 d postpartum increased the yield of milk fat, ECM, and BW loss; did not affect DMI; and resulted in a more negative energy balance in dairy cows (
      • de Souza J.
      • Lock A.L.
      Effects of timing of palmitic acid supplementation on production responses of early-lactation dairy cows.
      ;
      • de Souza J.
      • Strieder-Barboza C.
      • Contreras G.A.
      • Lock A.L.
      Effects of timing of palmitic acid supplementation during early lactation on nutrient digestibility, energy balance, and metabolism of dairy cows.
      ). Therefore, the FA profile of supplemental fat is a major factor affecting production responses and metabolism of early-lactation cows.
      In postpeak cows, we recently observed that feeding an FA blend with a high content of C16:0 (80% C16:0) increased milk energy output and energy partitioning toward milk, whereas feeding a FA blend containing 45% C16:0 and 35% oleic acid (cis-9 C18:1) increased energy allocated to BW and the partitioning of energy to BW compared with a control diet not supplemented with FA (
      • de Souza J.
      • Preseault C.L.
      • Lock A.L.
      Altering the ratio of dietary palmitic, stearic, and oleic acids in diets with or without whole cottonseed affects nutrient digestibility, energy partitioning, and production responses of dairy cows.
      ). Interestingly, feeding cis-9 C18:1 not only increased BW gain in postpeak cows but also increased plasma insulin compared with control diets and other FA supplements (
      • de Souza J.
      • Preseault C.L.
      • Lock A.L.
      Altering the ratio of dietary palmitic, stearic, and oleic acids in diets with or without whole cottonseed affects nutrient digestibility, energy partitioning, and production responses of dairy cows.
      ,
      • de Souza J.
      • St-Pierre N.R.
      • Lock A.L.
      Altering the ratio of dietary C16:0 and cis-9 C18:1 interacts with production level in dairy cows: effects on production responses and energy partitioning.
      ). Lipolysis and lipogenesis are influenced by circulating insulin concentrations, as well as by the responsiveness and sensitivity of adipose tissue to insulin (
      • De Koster J.D.
      • Opsomer G.
      Insulin resistance in dairy cows.
      ). Thus, increases in plasma insulin or insulin sensitivity during early lactation may lead to decreased body fat mobilization and improvements in energy balance. However, to our knowledge, the effect of feeding cis-9 C18:1 alone or in combination with other FA has not been evaluated in early lactation cows.
      Therefore, we hypothesized that increasing the amount of cis-9 C18:1 in supplemental fat would reduce milk energy output due to differences in milk fat yield responses, and that feeding cis-9 C18:1 would reduce body reserve mobilization and improve energy balance in early lactation. Our objective was to determine the effects of altering the dietary ratio of C16:0 and cis-9 C18:1 on nutrient digestibility, metabolism, and energy balance of early lactation dairy cows during the immediate postpartum period.

      MATERIALS AND METHODS

      All experimental procedures were approved by the Institutional Animal Care and Use Committee at Michigan State University (East Lansing). This article is the second from an experiment that evaluated the effects of altering the dietary ratio of C16:0 and cis-9 C18:1 on production and metabolic responses of early lactation dairy cows. This article focuses on the effect of these diets on nutrient digestibility, energy intake and balance, and plasma metabolites and hormones. The companion paper (
      • de Souza J.
      • Prom C.M.
      • Lock A.L.
      Altering the ratio of dietary palmitic and oleic acids impacts production responses during the immediate postpartum and carryover periods in dairy cows.
      ) describes treatment effects on DMI, yield of milk and milk components, BW and BCS, and milk FA profile.

      Design and Treatment Diets

      Fifty-six multiparous Holstein cows at the Michigan State University Dairy Cattle Teaching and Research Center were used in a randomized complete block design. Cows were blocked into 14 blocks by BCS (up to 0.50-unit difference using the 1 = thin, 5 = fat scale in 0.25 increments), previous lactation 305-d mature-equivalent milk yield (within 2,000 kg), and parity (up to 1 lactation difference). The BCS used to block cows was the last measurement before parturition. Cows within each block were randomly assigned to 1 of 4 treatments fed from 1 to 24 DIM. Each cow was housed in the same tiestall, assigned by parturition order, throughout the entire period. The treatments were combinations of 2 commercially available FA supplements that differed in FA profile, which were blended to achieve different ratios of C16:0 and cis-9 C18:1 in the FA supplement blends (Nutracor and Nutracal, Wawasan Agrolipids, Johor, Malaysia). The treatments were: (1) control (CON) diet not supplemented with FA; (2) diet supplemented with a FA blend containing 80% C16:0 and 10% cis-9 C18:1 (80:10); (3) diet supplemented with a FA blend containing 70% C16:0 and 20% cis-9 C18:1 (70:20); and (4) diet supplemented with a FA blend containing 60% C16:0 and 30% cis-9 C18:1 (60:30). The FA supplement blends were added at 1.5% of diet DM, replacing soyhulls in the CON diet. Treatment diets were mixed daily in a tumble-mixer and were fed from the morning following parturition. From d 25 to 63 postpartum (carryover period), all cows were offered a common diet, mixed daily in a mixer wagon. Treatment diets contained 23% forage NDF, 24.6% starch, and 16.7% CP. Carryover diet contained 20.3% forage NDF, 27.6% starch, and 16.9% CP. The ingredient and nutrient composition of the diets fed as TMR, including the close-up ration for reference, as well as a summary of all health incidents during the treatment period are reported in the companion article (
      • de Souza J.
      • Prom C.M.
      • Lock A.L.
      Altering the ratio of dietary palmitic and oleic acids impacts production responses during the immediate postpartum and carryover periods in dairy cows.
      ).

      Data and Sample Collection

      Milk yield, amount of feed offered and refused, BW, and BCS were recorded, and samples of milk, feed ingredients, and orts were collected and stored as described in
      • de Souza J.
      • Prom C.M.
      • Lock A.L.
      Altering the ratio of dietary palmitic and oleic acids impacts production responses during the immediate postpartum and carryover periods in dairy cows.
      . Samples and body measurements were collected or recorded on the same day of the week during the entire experiment, so that all collection days are ± 3 d.
      On d 5, 12, and 19 postpartum, fecal samples (500 g) were collected every 6 h, representing every 6 h of a 24-h period to account for diurnal variation, for nutrient digestibility analysis. Feces were stored in sealed plastic cups at −20°C until dried, ground, and composited per cow per sampling day. Blood samples were collected on d 5, 12, 19, and 33 postpartum by venipuncture of coccygeal vessels within 1 h before feeding. Blood was collected into 2 evacuated tubes, 1 containing potassium EDTA, and the other containing potassium oxalate with sodium fluoride as a glycolytic inhibitor. Both were centrifuged at 2,000 × g for 15 min at 4°C immediately after sample collection, and plasma was harvested and stored at −20°C until analysis.

      Sample Analysis

      Diet ingredients, orts, and fecal samples were dried at 55°C in a forced-air oven for 72 h for DM determination. Dried samples were ground with a Wiley mill (1-mm screen; Arthur H. Thomas, Philadelphia, PA). Feed ingredients and orts were analyzed for NDF, CP, starch, and FA concentrations as described by
      • Boerman J.P.
      • de Souza J.
      • Lock A.L.
      Milk production and nutrient digestibility responses to increasing levels of stearic acid supplementation of dairy cows.
      . Fecal samples were analyzed for NDF and FA concentrations as described by
      • Boerman J.P.
      • de Souza J.
      • Lock A.L.
      Milk production and nutrient digestibility responses to increasing levels of stearic acid supplementation of dairy cows.
      . Gross energy (GE) was assayed by bomb calorimeter (Parr Instrument Inc., Moline, IL) in all samples. Indigestible NDF was used as an internal marker to estimate fecal output to determine the apparent total-tract digestibility of nutrients (
      • Cochran R.C.
      • Adams D.C.
      • Wallace J.D.
      • Galyean M.L.
      Predicting the digestibility of different diets with internal markers: Evaluation of four potential markers.
      ). Indigestible NDF was estimated as NDF after a 240-h in vitro fermentation (
      • Goering H.K.
      • Van Soest P.J.
      Forage Fiber Analyses (Apparatus, Reagents, Procedures, and Some Applications). Agricultural Handbook no. 379.
      ). Serum concentrations of NEFA, BHB, and albumin were determined using an Olympus AU640e chemistry analyzer (Olympus America, Center Valley, PA) at the Diagnostic Center for Population and Animal Health of Michigan State University (Lansing, MI) with intra- and interassay CV <3%. Serum insulin concentrations were determined by ELISA (Bovine Insulin ELISA; Mercodia AB, Uppsala, Sweden) with intra- and interassay CV <3%.
      Energy intake and balance were calculated using equations (
      • NRC (National Research Council)
      Nutrient Requirements of Dairy Cattle.
      ) according to
      • Harvatine K.J.
      • Allen M.S.
      Effects of fatty acid supplements on milk yield and energy balance of lactating dairy cows.
      . Digestible energy (DE) intake = GE intake × GE digestibility. The NEL intake was calculated from DE according to
      • NRC (National Research Council)
      Nutrient Requirements of Dairy Cattle.
      as NEL(intake) = 0.703 × ME (intake) − 0.19 + {[(0.097 × ME(intake) + 0.19)/97] × [ether extract − 3]}; ME(intake) = 1.01 × (DE(intake)) − 0.45] + 0.0046 × (ether extract − 3) (
      • NRC (National Research Council)
      Nutrient Requirements of Dairy Cattle.
      ). Milk energy output (Mcal/d) was calculated according to
      • NRC (National Research Council)
      Nutrient Requirements of Dairy Cattle.
      as milk energy output (Mcal/d) = [9.29 × fat (kg) + 5.63 × true protein (kg) + 3.95 × lactose (kg)], where each component was based on the average output of a cow during the week. The NEm (Mcal/d) was calculated as 0.08 Mcal/kg × BW (kg)0.75 and energy balance (Mcal/d) determined as NEL intake (Mcal/d) − milk NEL (Mcal/d) − NEL maintenance requirement (Mcal/d) (
      • NRC (National Research Council)
      Nutrient Requirements of Dairy Cattle.
      ). The efficiency of energy utilization for milk was calculated as milk energy output/ DE intake (NEL milk/DEI). The efficiency of energy utilization for production was calculated as milk (energy output + energy for maintenance)/DE intake (NEL production/DEI).

      Statistical Analysis

      Data were analyzed as a complete block design. Cow was considered the experimental unit (14 cows per treatment and 14 blocks). All weekly data were analyzed using the MIXED procedure of SAS v.9.2 (SAS Institute Inc., Cary, NC) with the week being the repeated measurement.
      The model used for the treatment period (1–24 DIM) included:
      Yijkl = μ + Bi + C(BiFk)j + Fk + Tl + FkTl + eijkl,


      where Yijkl is the dependent variable, μ = overall mean, Bi = random effect of block, C(BiFk)j = random effect of cow within block and treatment diet, Fk = fixed effect of treatment during the treatment period, Tl = fixed effect of time, FkTl = fixed effect of treatment during the treatment by time interaction, and eijkl = residual error.
      Unless otherwise specified, first-order autoregressive was the covariate structure used for analysis because it resulted in the lowest BIC for most of the variables measured. A reduced model was used for analysis of blood metabolites variables collected in the carryover period without the effect of time in the model because a single time point was collected. Normality of the residuals was checked with normal probability and box plots and homogeneity of variances with plots of residuals vs. predicted values. Significance was declared at P ≤ 0.05 for main effects and P ≤ 0.10 for interactions. Tendencies were declared at P ≤ 0.10 for main effects and P ≤ 0.15 for interactions. Three preplanned contrasts were used to compare treatment differences: (1) CON versus FA-supplemented diets, (80:10 + 70:20 + 60:30)/3; (2) the linear effect of cis-9 C18:1 inclusion in diet; and (3) the quadratic effect of cis-9 C18:1 inclusion in diet.

      RESULTS

      Nutrient Digestibility

      The FA-supplemented diets did not affect DMI (P = 0.14; Table 1) but tended to increase NDF intake (P = 0.06) compared with CON. Also, compared with CON, FA-supplemented diets increased intake of 16-carbon (P < 0.01), 18-carbon (P < 0.01), and total FA (P < 0.01). The FA-supplemented diets increased digestibility of DM (P = 0.02), NDF (P < 0.01), 18-carbon (P < 0.01), and total FA (P < 0.01) compared with CON. Additionally, compared with CON, FA-supplemented diets increased absorbed 16-carbon (P < 0.01), 18-carbon (P < 0.01), and total FA (P < 0.01).
      Table 1Nutrient intake and total-tract nutrient digestibility for cows fed treatment diets during the treatment period (d 1 to 24 postpartum)
      ItemTreatment
      Treatments were: CON (control; no supplemental fat); 80:10 [1.5% of fatty acid (FA) supplement blend to provide ~80% C16:0 and 10% cis-9 C18:1]; 70:20 (1.5% of FA supplement blend to provide ~70% C16:0 and 20% cis-9 C18:1); and 60:30 (1.5% of FA supplement blend to provide ~60% C16:0 and 30% cis-9 C18:1).
      SEMContrast
      P-values associated with contrasts of treatment effects: CON vs. FAT [control vs. FA-supplemented diets: (80:10 + 70:20 + 60:30)/3]; and linear and quadratic effects of cis-9 C18:1 inclusion in supplemental fat.
      P-value
      Trt = treatment.
      CON80:1070:2060:30CON vs. FATLinearQuadraticTimeTrt × Time
      Intake, kg
       DM20.320.720.921.80.480.140.030.51<0.010.97
       NDF4.745.005.175.320.250.060.150.34<0.010.53
      Intake, g/d
       Total FA31666964368831.7<0.01<0.01<0.01<0.010.36
       16-carbon5431126625613.7<0.01<0.01<0.01<0.010.30
       18-carbon25333836041717.7<0.01<0.010.42<0.010.30
      Digestibility, %
       DM69.269.970.271.00.520.02<0.010.980.420.14
       NDF37.639.939.941.30.76<0.01<0.010.530.430.17
       Total FA82.382.583.884.90.97<0.01<0.010.120.460.15
       16-carbon78.277.779.681.11.180.360.040.370.600.29
       18-carbon85.788.088.588.70.92<0.01<0.010.980.250.10
      Absorbed FA, g/d
       Total FA26855453858526.5<0.01<0.01<0.01<0.010.44
       16-carbon4324621120810.9<0.01<0.01<0.01<0.010.34
       18-carbon22329731937015.7<0.01<0.010.47<0.010.45
      1 Treatments were: CON (control; no supplemental fat); 80:10 [1.5% of fatty acid (FA) supplement blend to provide ~80% C16:0 and 10% cis-9 C18:1]; 70:20 (1.5% of FA supplement blend to provide ~70% C16:0 and 20% cis-9 C18:1); and 60:30 (1.5% of FA supplement blend to provide ~60% C16:0 and 30% cis-9 C18:1).
      2 P-values associated with contrasts of treatment effects: CON vs. FAT [control vs. FA-supplemented diets: (80:10 + 70:20 + 60:30)/3]; and linear and quadratic effects of cis-9 C18:1 inclusion in supplemental fat.
      3 Trt = treatment.
      Increasing dietary cis-9 C18:1 increased 16-carbon (quadratic, P < 0.01), 18-carbon (linear, P < 0.01), and total FA intakes (quadratic, P < 0.01). Additionally, increasing dietary cis-9 C18:1 increased digestibility of DM (linear, P < 0.01), NDF (linear, P < 0.01), 16-carbon (linear, P = 0.04), 18-carbon (linear, P < 0.01), and total FA (linear, P < 0.01). Increasing dietary cis-9 C18:1 increased absorbed 16-carbon (quadratic, P < 0.01), 18-carbon (linear, P < 0.01), and total FA (quadratic, P < 0.01).
      Overall, nutrient digestibility was not affected by time (P > 0.25). We observed a tendency for an interaction between treatment and time for the digestibility of DM (P = 0.14) because the difference in digestibility between CON and 60:30 tended to increase over time (Figure 1). We also observed a tendency for an interaction between treatment and time for the digestibility of 18-carbon (P = 0.10) and total FA (P = 0.15), because the difference in digestibility between CON and 60:30 tended to increase over time (Figure 2).
      Figure thumbnail gr1
      Figure 1Effects of dietary treatments on digestibility of DM (A) and NDF (B) over time during the treatment (1–24 DIM). Diets fed during the treatment period were CON (control diet not supplemented with FA); 80:10 (80% C16:0 + 10% cis-9 C18:1); 70:20 (70% C16:0 + 20% cis-9 C18:1;); and 60:30 (60% C16:0 + 30% cis-9 C18:1). Compared with CON, FA-supplemented diets increased digestibility of DM (P = 0.02) and NDF (P < 0.01). We observed a tendency for an interaction between treatment and time for the digestibility of DM (P = 0.14) because the difference in digestibility between CON and 60:30 tended to increase over time. Additionally, increasing dietary cis-9 C18:1 increased digestibility of DM (linear, P < 0.01) and NDF (linear, P < 0.01). Error bars indicate SEM.
      Figure thumbnail gr2
      Figure 2Effects of dietary treatments on digestibility of 16-carbon (A), 18-carbon (B), and total FA (C) over time during the treatment (1–24 DIM). Diets fed during the treatment period were CON (control diet not supplemented with FA); 80:10 (80% C16:0 + 10% cis-9 C18:1); 70:20 (70% C16:0 + 20% cis-9 C18:1); and 60:30 (60% C16:0 + 30% cis-9 C18:1). The FA-supplemented diets increased digestibility of 18-carbon (P < 0.01) and total FA (P < 0.01) compared with CON. We observed a tendency for an interaction between treatment and time for the digestibility of 18-carbon (P = 0.10) and total FA (P = 0.15) because the difference in digestibility between CON and 60:30 tended to increase over time. Additionally, increasing dietary cis-9 C18:1 increased digestibility of 16-carbon (linear, P = 0.04), 18-carbon (linear, P < 0.01), and total FA (linear, P < 0.01). Error bars indicate SEM.

      Energy Intake and Energy Balance

      The FA-supplemented diets increased intake of DE (P = 0.04; Table 2), ME (P = 0.04), and NEL (P = 0.05) compared with CON. Compared with CON, FA-supplemented diets increased milk energy output (P = 0.04) and tended to make energy balance more negative (P = 0.08). We did not observe treatment differences for the efficiency of energy utilization for milk (P = 0.33) and production (P = 0.74). Overall, DE intake and milk energy output increased over time (P < 0.01), and the differences across treatments were consistent over time for these variables (Figure 3).
      Table 2Energy intake, energy output and balance, and efficiency of energy utilization for cows fed treatment diets during the treatment period (d 1 to 24 postpartum)
      ItemTreatment
      Treatments were: CON (control; no supplemental fat); 80:10 [1.5% of fatty acid (FA) supplement blend to provide ~80% C16:0 and 10% cis-9 C18:1]; 70:20 (1.5% of FA supplement blend to provide ~70% C16:0 and 20% cis-9 C18:1); and 60:30 (1.5% of FA supplement blend to provide ~60% C16:0 and 30% cis-9 C18:1).
      SEMContrast
      P-values associated with contrasts of treatment effects: CON vs. FAT [control vs. FA-supplemented diets: (80:10 + 70:20 + 60:30)/3]; linear and quadratic effects of cis-9 C18:1 inclusion in supplemental fat.
      P-value
      Trt = treatment.
      CON80:1070:2060:30CON vs. FATLinearQuadraticTimeTrt × Time
      Energy intake, Mcal/d
       DE
      Digestible energy (DE) intake = gross energy intake (Mcal/d) × gross energy digestibility.
      59.462.362.564.41.510.040.020.73<0.010.91
       ME
      Metabolizable energy intake = 1.01 × (DE intake − 0.45) + 0.0046 × (ether extract − 3); NRC (2001).
      51.753.554.155.51.110.040.020.86<0.010.87
       NEL
      Net energy of lactation intake: NEL intake = 0.703 × ME intake − 0.19 + {[(0.097 × ME intake + 0.19)/97] × [ether extract − 3]}.
      31.933.734.235.00.630.050.010.99<0.010.75
      Energy output, Mcal/d
       Milk
      Milk NEL (Mcal/d) = milk yield (kg/d) × [(fat % × 0.0929) + (true protein % × 0.0563) + (lactose % × 0.0395)]; NRC (2001).
      33.937.336.436.61.200.040.170.17<0.010.78
       Maintenance
      NEL maintenance (Mcal/d) = 0.08 Mcal/kg × BW (kg)0.75; NRC (2001).
      10.910.710.911.10.200.990.320.29<0.010.05
       Energy balance,
      Energy balance (Mcal/d) = NEL intake (Mcal/d) − milk NEL (Mcal/d) − NEL maintenance requirement (Mcal/d).
      Mcal/d
      −11.7−14.9−13.2−12.70.950.080.770.04<0.010.22
      Efficiency
       NEL milk/DE intake0.5660.5960.5860.5680.020.330.920.090.280.90
       NEL production/DE intake
      NEL production = milk NEL + NEL required for maintenance.
      0.7500.7680.7610.7410.020.740.630.230.020.86
      1 Treatments were: CON (control; no supplemental fat); 80:10 [1.5% of fatty acid (FA) supplement blend to provide ~80% C16:0 and 10% cis-9 C18:1]; 70:20 (1.5% of FA supplement blend to provide ~70% C16:0 and 20% cis-9 C18:1); and 60:30 (1.5% of FA supplement blend to provide ~60% C16:0 and 30% cis-9 C18:1).
      2 P-values associated with contrasts of treatment effects: CON vs. FAT [control vs. FA-supplemented diets: (80:10 + 70:20 + 60:30)/3]; linear and quadratic effects of cis-9 C18:1 inclusion in supplemental fat.
      3 Trt = treatment.
      4 Digestible energy (DE) intake = gross energy intake (Mcal/d) × gross energy digestibility.
      5 Metabolizable energy intake = 1.01 × (DE intake − 0.45) + 0.0046 × (ether extract − 3);
      • NRC (National Research Council)
      Nutrient Requirements of Dairy Cattle.
      .
      6 Net energy of lactation intake: NEL intake = 0.703 × ME intake − 0.19 + {[(0.097 × ME intake + 0.19)/97] × [ether extract − 3]}.
      7 Milk NEL (Mcal/d) = milk yield (kg/d) × [(fat % × 0.0929) + (true protein % × 0.0563) + (lactose % × 0.0395)];
      • NRC (National Research Council)
      Nutrient Requirements of Dairy Cattle.
      .
      8 NEL maintenance (Mcal/d) = 0.08 Mcal/kg × BW (kg)0.75;
      • NRC (National Research Council)
      Nutrient Requirements of Dairy Cattle.
      .
      9 Energy balance (Mcal/d) = NEL intake (Mcal/d) − milk NEL (Mcal/d) − NEL maintenance requirement (Mcal/d).
      10 NEL production = milk NEL + NEL required for maintenance.
      Figure thumbnail gr3
      Figure 3Effects of dietary treatments on digestible energy (DE) intake (A), milk energy output (B), and energy balance (C) over time during the treatment (1–24 DIM). Diets fed during the treatment period were CON (control diet not supplemented with FA); 80:10 (80% C16:0 + 10% cis-9 C18:1); 70:20 (70% C16:0 + 20% cis-9 C18:1); and 60:30 (60% C16:0 + 30% cis-9 C18:1). The FA-supplemented diets increased intake of DE (P = 0.04) and milk energy output (P = 0.04), and tended to reduce energy balance (P = 0.08) compared with CON. Overall, DE intake, milk energy output, and energy balance increased over time (P < 0.01), and the differences across treatments were consistent over time for these variables. Increasing dietary cis-9 C18:1 increased intake of DE (linear, P = 0.02) and improved energy balance (quadratic, P = 0.04). Error bars indicate SEM.
      Increasing dietary cis-9 C18:1 increased intake of DE (linear, P = 0.02), ME (linear, P = 0.02), and NEL (linear P = 0.01). Although increasing dietary cis-9 C18:1 did not affect milk energy output (P > 0.17) or energy for maintenance (P > 0.29), increasing dietary cis-9 C18:1 improved energy balance (quadratic, P = 0.04). Increasing dietary cis-9 C18:1 tended to increase the efficiency of energy utilization for milk (quadratic, P = 0.09) but did not affect energy utilization for production (P > 0.23).

      Plasma Insulin and Metabolites During the Treatment Period

      Compared with CON, FA-supplemented diets increased plasma insulin (P = 0.02; Table 3). We did not observe differences between CON and FA-supplemented diets for plasma NEFA (P = 0.57), BHB (P = 0.14), or albumin (P = 0.11). Increasing cis-9 C18:1 in FA treatments linearly decreased plasma NEFA (P = 0.03; Table 3), tended to linearly increase insulin (P = 0.07) and BHB (P = 0.10), but did not affect albumin (P > 0.10). Also, we tended to observe an interaction between treatment and time for BHB (P = 0.15) due to FA-supplemented diets increasing BHB compared with CON at wk 3 (Figure 4).
      Table 3Plasma insulin and metabolites for cows fed diets during treatment period (d 1 to 24 postpartum)
      ItemTreatment
      Treatments were: CON (control; no supplemental fat); 80:10 [1.5% of fatty acid (FA) supplement blend to provide ~80% C16:0 and 10% cis-9 C18:1]; 70:20 (1.5% of FA supplement blend to provide ~70% C16:0 and 20% cis-9 C18:1); and 60:30 (1.5% of FA supplement blend to provide ~60% C16:0 and 30% cis-9 C18:1).
      SEMContrast
      P-values associated with contrasts of treatment effects: CON vs. FAT [control vs. FA-supplemented diets: (80:10 + 70:20 + 60:30)/3]; linear and quadratic effects of cis-9 C18:1 inclusion in supplemental fat.
      P-value
      Trt = treatment.
      CON80:1070:2060:30CON vs. FATLinearQuadraticTimeTrt × Time
      Insulin, μg/L0.260.270.310.310.010.020.070.550.040.21
      NEFA,
      Nonesterified fatty acids.
      mEq/L
      0.720.840.750.670.050.570.030.87<0.010.56
      BHB, mg/dL10.611.513.314.81.530.140.100.910.370.15
      Albumin, g/dL3.083.273.173.180.060.110.260.48<0.010.96
      1 Treatments were: CON (control; no supplemental fat); 80:10 [1.5% of fatty acid (FA) supplement blend to provide ~80% C16:0 and 10% cis-9 C18:1]; 70:20 (1.5% of FA supplement blend to provide ~70% C16:0 and 20% cis-9 C18:1); and 60:30 (1.5% of FA supplement blend to provide ~60% C16:0 and 30% cis-9 C18:1).
      2 P-values associated with contrasts of treatment effects: CON vs. FAT [control vs. FA-supplemented diets: (80:10 + 70:20 + 60:30)/3]; linear and quadratic effects of cis-9 C18:1 inclusion in supplemental fat.
      3 Trt = treatment.
      4 Nonesterified fatty acids.
      Figure thumbnail gr4
      Figure 4Effects of dietary treatments on (A) plasma insulin, (B) nonesterified fatty acids (NEFA), and (C) BHB over time during the treatment (1–24 DIM) and carryover (25–63 DIM) periods. Data were analyzed separately for the treatment and carryover periods. Diets fed during the treatment period were CON (control diet not supplemented with FA); 80:10 (80% C16:0 + 10% cis-9 C18:1); 70:20 (70% C16:0 + 20% cis-9 C18:1); and 60:30 (60% C16:0 + 30% cis-9 C18:1). The line on wk 3 indicates the start of the carryover period, when all cows were fed a common diet with no supplemental fat added. During the treatment period, compared with CON, FA-supplemented diets increased plasma insulin (P = 0.02). Also, we tended to observe an interaction between treatment and time for BHB (P = 0.15) due to FA-supplemented diets increasing BHB compared with CON at wk 3. Increasing cis-9 C18:1 in FA treatments linearly decreased plasma NEFA (P = 0.03), and tended to linearly increase insulin (P = 0.07) and BHB (P = 0.10). Error bars indicate SEM.

      Plasma Insulin and Metabolites During the Carryover Period

      During the carryover period, blood metabolites were only evaluated at 1 time point (d 33). We did not observe difference between CON and FA-supplemented diets or among the FA treatments for the metabolites evaluated (P > 0.10; Table 4).
      Table 4Plasma insulin and metabolites for cows fed diets during the carryover period
      ItemTreatment
      Treatments were: CON (control; no supplemental fat); 80:10 [1.5% of fatty acid (FA) supplement blend to provide ~80% C16:0 and 10% cis-9 C18:1]; 70:20 (1.5% of FA supplement blend to provide ~70% C16:0 and 20% cis-9 C18:1); and 60:30 (1.5% of FA supplement blend to provide ~60% C16:0 and 30% cis-9 C18:1).
      SEMContrast
      P-values associated with contrasts of treatment effects: CON vs. FAT [control vs. FA-supplemented diets: (80:10 + 70:20 + 60:30)/3]; linear and quadratic effects of cis-9 C18:1 inclusion in supplemental fat.
      CON80:1070:2060:30CON vs. FATLinearQuadratic
      Insulin, μg/L0.380.420.370.380.020.810.380.58
      NEFA,
      Nonesterified fatty acids.
      mEq/L
      0.400.370.410.410.070.760.490.68
      BHB, mg/dL6.495.545.647.360.860.750.130.44
      Albumin, g/dL3.343.413.413.390.060.430.800.96
      1 Treatments were: CON (control; no supplemental fat); 80:10 [1.5% of fatty acid (FA) supplement blend to provide ~80% C16:0 and 10% cis-9 C18:1]; 70:20 (1.5% of FA supplement blend to provide ~70% C16:0 and 20% cis-9 C18:1); and 60:30 (1.5% of FA supplement blend to provide ~60% C16:0 and 30% cis-9 C18:1).
      2 P-values associated with contrasts of treatment effects: CON vs. FAT [control vs. FA-supplemented diets: (80:10 + 70:20 + 60:30)/3]; linear and quadratic effects of cis-9 C18:1 inclusion in supplemental fat.
      3 Nonesterified fatty acids.

      Correlations

      We used Pearson correlation coefficients to assess relationships between production and metabolic variables (Table 5). Interestingly, total absorbed FA was positively related to milk yield (P < 0.01; r = 0.42), milk fat yield (P < 0.01; r = 0.35), ECM yield (P < 0.01; r = 0.37), plasma insulin (P < 0.01; r = 0.28), and plasma albumin (P < 0.01; r = 0.29), and negatively related to plasma NEFA (P = 0.03; r = −0.18) and BW loss (P = 0.08; r = −0.14). We observed that DE intake was positively related to DMI (P < 0.01; r = 0.79), milk yield (P < 0.01; r = 0.60), milk fat yield (P < 0.01; r = 0.29), ECM (P < 0.01; r = 0.29), plasma insulin (P = 0.01; r = 0.22), and plasma albumin (P < 0.01; r = 0.36), and negatively related to plasma NEFA (P < 0.01; r = −0.25) and BHB (P = 0.02; r = −0.19). Milk energy output was positively related to total absorbed FA (P < 0.01; r = 0.49), DE intake (P < 0.01; r = 0.51), milk yield (P < 0.01; r = 0.65), milk fat yield (P < 0.01; r = 0.92), and ECM yield (P < 0.01; r = 0.93). In contrast, energy balance was negatively related to milk yield (P < 0.01; r = −0.33), milk fat yield (P < 0.01; r = −0.81), and ECM yield (P < 0.01; r = −0.72), and positively related to total absorbed FA (P < 0.01; r = 0.24).
      Table 5Correlation coefficients between production variables, plasma metabolites, and energy parameters for cows fed treatment diets (1–24 DIM)
      Item
      NEFA = nonesterified fatty acids; FA = fatty acids; DE = digestible energy.
      Milk yield, kgDMI, kgMilk fat yield, kgMilk fat, %ECM, kgBW loss, kg/dInsulin, μg/LAlbumin, g/dLNEFA, mEq/LBHB, mg/dLTotal FA absorbed, gDE, McalMilk energy output, McalEnergy balance, Mcal
      Milk yield, kg1.000.55
      The Pearson correlation coefficient of the linear relationship between 2 variables. The value for each cow per week was used as independent variables.
      0.41−0.300.48−0.01−0.060.41−0.080.190.420.600.65−0.33
      <0.01
      The P-value associated with the linear relationship between 2 variables.
      <0.01<0.01<0.010.910.45<0.010.310.02<0.01<0.01<0.01<0.01
      DMI, kg1.000.30−0.180.300.260.160.29−0.270.180.520.790.43−0.08
      <0.010.03<0.01<0.010.06<0.01<0.010.03<0.01<0.01<0.010.33
      Milk fat yield, kg1.000.290.81−0.04−0.010.08−0.090.230.350.290.92−0.81
      <0.01<0.010.640.860.300.260.01<0.01<0.01<0.01<0.01
      Milk fat, %1.000.04−0.07−0.02−0.130.100.27−0.09−0.310.08−0.31
      0.650.410.850.100.23<0.010.27<0.010.36<0.01
      ECM, kg1.000.01−0.020.20−0.140.150.370.350.93−0.72
      0.930.850.020.100.10<0.01<0.01<0.01<0.01
      BW loss, kg/d1.000.18−0.16−0.28−0.14−0.14−0.21−0.040.12
      0.020.04<0.010.090.080.010.610.14
      Insulin, μg/L1.00−0.04−0.20−0.150.280.220.010.05
      0.590.010.07<0.010.010.980.54
      Albumin, g/dL1.00−0.01−0.070.290.360.27−0.02
      0.880.42<0.01<0.01<0.010.78
      NEFA, mEq/L1.000.12−0.18−0.25−0.160.08
      0.160.03<0.010.060.32
      BHB, mg/dL1.000.03−0.190.05−0.12
      0.700.020.550.16
      Total FA absorbed,
      The P-value associated with the linear relationship between 2 variables.
      g
      1.000.730.490.24
      <0.01<0.01<0.01
      DE, Mcal1.000.510.02
      <0.010.78
      Milk energy output, Mcal1.00−0.79
      <0.01
      Energy balance, Mcal1.00
      1 NEFA = nonesterified fatty acids; FA = fatty acids; DE = digestible energy.
      2 The Pearson correlation coefficient of the linear relationship between 2 variables. The value for each cow per week was used as independent variables.
      3 The P-value associated with the linear relationship between 2 variables.

      DISCUSSION

      The challenge of meeting nutrient requirements is greater during early lactation than other lactation stages due to an increased risk of negative energy and nutrient balance (
      • NRC (National Research Council)
      Nutrient Requirements of Dairy Cattle.
      ). The enhanced nutrient demand for milk production requires homeorhetic adaptations to support both the increased energy demand of the mammary gland and peripheral tissue metabolism (
      • Bauman D.E.
      • Currie W.B.
      Partitioning of nutrients during pregnancy and lactation: A review of mechanisms involving homeostasis and homeorhesis.
      ). Feeding supplemental fat may be a strategy to increase energy intake and reduce negative energy balance, but inconsistent responses to supplemental fat have been observed (e.g.,
      • Moallem U.
      • Katz M.
      • Arieli A.
      • Lehrer H.
      Effects of peripartum propylene glycol or fats differing in fatty acid profiles on feed intake, production, and plasma metabolites in dairy cows.
      ;
      • Piantoni P.
      • Lock A.L.
      • Allen M.S.
      Saturated fat supplementation interacts with dietary forage neutral detergent fiber content during the immediate postpartum period in Holstein cows: Energy balance and metabolism.
      ;
      • de Souza J.
      • Strieder-Barboza C.
      • Contreras G.A.
      • Lock A.L.
      Effects of timing of palmitic acid supplementation during early lactation on nutrient digestibility, energy balance, and metabolism of dairy cows.
      ). In contrast, research is progressing from feeding traditional animal and plant fats to feeding individual FA and blends of FA, which extends beyond their energy contribution to include potentially structural, metabolic, and physiological effects (
      • Palmquist D.L.
      • Jenkins T.C.
      A 100-Year Review: Fat feeding of dairy cows.
      ). For example, our recent research suggests that altering the dietary ratio of C16:0 and cis-9 C18:1 may alter nutrient partitioning between the mammary gland and adipose tissue in post-peak cows (
      • de Souza J.
      • Preseault C.L.
      • Lock A.L.
      Altering the ratio of dietary palmitic, stearic, and oleic acids in diets with or without whole cottonseed affects nutrient digestibility, energy partitioning, and production responses of dairy cows.
      ;
      • de Souza J.
      • St-Pierre N.R.
      • Lock A.L.
      Altering the ratio of dietary C16:0 and cis-9 C18:1 interacts with production level in dairy cows: effects on production responses and energy partitioning.
      ). Feeding high levels of C16:0 increased milk fat yield and energy partitioning to milk compared with nonfat control diets and other FA supplements (
      • de Souza J.
      • Lock A.L.
      Long-term palmitic acid supplementation interacts with parity in lactating dairy cows: Production responses, nutrient digestibility, and energy partitioning.
      ;
      • Western M.M.
      • de Souza J.
      • Lock A.L.
      Effects of commercially available palmitic and stearic acid supplements on nutrient digestibility and production responses of lactating dairy cows.
      ), whereas feeding cis-9 C18:1 increased total FA digestibility and nutrient partitioning to body reserves in post-peak cows compared with nonfat supplemented control diets and other FA supplements (
      • de Souza J.
      • Preseault C.L.
      • Lock A.L.
      Altering the ratio of dietary palmitic, stearic, and oleic acids in diets with or without whole cottonseed affects nutrient digestibility, energy partitioning, and production responses of dairy cows.
      ;
      • de Souza J.
      • St-Pierre N.R.
      • Lock A.L.
      Altering the ratio of dietary C16:0 and cis-9 C18:1 interacts with production level in dairy cows: effects on production responses and energy partitioning.
      ). Because metabolic state and stage of lactation play a critical role in energy partitioning, we evaluated the effects of altering the dietary ratio of C16:0 and cis-9 C18:1 in supplemental fat blends on nutrient digestibility and metabolic responses of early lactation dairy cows, and production responses are presented in our companion paper (
      • de Souza J.
      • Prom C.M.
      • Lock A.L.
      Altering the ratio of dietary palmitic and oleic acids impacts production responses during the immediate postpartum and carryover periods in dairy cows.
      ).
      In our study, feeding supplemental fat increased total FA digestibility compared with CON. We varied levels of C16:0 (from 0.36 to 1.57% diet DM) and cis-9 C18:1 (from 0.46 to 0.90% diet DM), whereas the other FA were fed at a similar level (Supplemental Table S1, https://doi.org/10.3168/jds.2020-19312). To our knowledge, few studies have measured FA digestibility in early lactation cows.
      • Bines J.A.
      • Brumby P.E.
      • Storry J.E.
      • Fulford R.J.
      • Braithwaite G.D.
      The effect of protected lipids on nutrient intakes, blood and rumen metabolites and milk secretion in dairy cows during early lactation.
      fed increasing levels of tallow in the first 13 wk of lactation and observed a quadratic response in total FA digestibility measured at wk 10 to 12 of lactation.
      • de Souza J.
      • Strieder-Barboza C.
      • Contreras G.A.
      • Lock A.L.
      Effects of timing of palmitic acid supplementation during early lactation on nutrient digestibility, energy balance, and metabolism of dairy cows.
      reported that feeding a C16:0-enriched supplement during the immediate postpartum decreased the digestibility of 16-carbon and total FA; however, the difference between treatments for these variables reduced over time. Variable effects on FA digestibility have been observed in post-peak cows; although
      • Rico D.E.
      • Ying Y.
      • Harvatine K.J.
      Effect of a high-palmitic acid fat supplement on milk production and apparent total-tract digestibility in high- and low-milk yield dairy cows.
      reported that feeding a C16:0 supplement had positive effects on 16-carbon and total FA digestibility, other studies with high-producing cows have observed reductions in FA digestibility when feeding similar supplements (
      • de Souza J.
      • Batistel F.
      • Santos F.A.
      Effect of sources of calcium salts of fatty acids on production, nutrient digestibility, energy balance, and carryover effects of early lactation grazing dairy cows.
      ;
      • Rico J.E.
      • de Souza J.
      • Allen M.S.
      • Lock A.L.
      Nutrient digestibility and milk production responses to increasing levels of palmitic acid supplementation vary in cows receiving diets with or without whole cottonseed.
      ). In a recent meta-analysis,
      • Boerman J.P.
      • Firkins J.L.
      • St-Pierre N.R.
      • Lock A.L.
      Intestinal digestibility of long-chain fatty acids in lactating dairy cows: A meta-analysis and meta-regression.
      observed no reduction in FA digestibility when the duodenal flow of C16:0 increased up to 500 g/d, whereas increasing the duodenal flow of C18:0 to the same level reduced FA digestibility. Additionally, 2 recent studies indicated no difference in FA digestibility between control and a C16:0 supplemented diets when the FA supplement contained at least 10% of cis-9 C18:1 (
      • de Souza J.
      • Preseault C.L.
      • Lock A.L.
      Altering the ratio of dietary palmitic, stearic, and oleic acids in diets with or without whole cottonseed affects nutrient digestibility, energy partitioning, and production responses of dairy cows.
      ;
      • Western M.M.
      • de Souza J.
      • Lock A.L.
      Effects of commercially available palmitic and stearic acid supplements on nutrient digestibility and production responses of lactating dairy cows.
      ). This suggests that although total flow of FA to the duodenum affects FA digestibility (
      • Boerman J.P.
      • Firkins J.L.
      • St-Pierre N.R.
      • Lock A.L.
      Intestinal digestibility of long-chain fatty acids in lactating dairy cows: A meta-analysis and meta-regression.
      ), the profile of FA entering the duodenum is a critical factor affecting FA digestibility (
      • Doreau M.
      • Chilliard Y.
      Digestion and metabolism of dietary fat in farm animals.
      ;
      • de Souza J.
      • Preseault C.L.
      • Lock A.L.
      Altering the ratio of dietary palmitic, stearic, and oleic acids in diets with or without whole cottonseed affects nutrient digestibility, energy partitioning, and production responses of dairy cows.
      ).
      Additionally, in our study we observed a positive linear effect of increasing dietary cis-9 C18:1 on 16-carbon, 18-carbon and total FA digestibility. Similarly, in post-peak cows,
      • de Souza J.
      • St-Pierre N.R.
      • Lock A.L.
      Altering the ratio of dietary C16:0 and cis-9 C18:1 interacts with production level in dairy cows: effects on production responses and energy partitioning.
      observed increases in total FA digestibility with increasing level of cis-9 C18:1 in supplemental fat (from 10 to 30%) replacing C16:0 (from 80 to 60%) with no interactions with cow production level. Although there are indications that feeding cis-9 C18:1 improves FA digestibility, the mechanism involved in these changes is not well understood. In ruminants, micelle formation is critical for transporting FA through the aqueous environment to the enterocyte surface (
      • Davis C.L.
      Fats in Animal Feeds.
      ).
      • Freeman C.P.
      Properties of fatty acids in dispersions of emulsified lipid and bile salt and the significance of these properties in fat absorption in the pig and the sheep.
      examined the amphiphilic properties of polar lipids in bile salt solutions and reported that cis-9 C18:1 had a positive effect on the micellar solubility of C18:0. Additionally, a faster uptake of unsaturated FA compared with saturated FA across the enterocyte plasma membrane and faster re-esterification within the enterocyte has been also proposed as a mechanism explaining differences in digestibility of individual FA (
      • Ockner R.K.
      • Pittman J.P.
      • Yager J.L.
      Differences in the intestinal absorption of saturated and unsaturated long chain fatty acids.
      ). Although we increased dietary cis-9 C18:1 using mainly FA as Ca salts, it is likely that this treatment increased rumen outflow of other 18-carbon FA since it is well established that Ca-salts dissociate to some degree in the rumen (
      • Jenkins T.C.
      • Bridges Jr., W.C.
      Protection of fatty acids against ruminal biohydrogenation in cattle.
      ). Therefore, it is unclear if these results are exclusively associated with an overall effect of 18-carbon FA or a specific FA altering digestibility. Interestingly, in our study we observed that total absorbed FA was positively related to production outcomes (yields of milk, milk fat, and ECM) and negatively related to plasma NEFA and BW loss. In a recent study with postpeak cows, infusing an emulsifier postruminally increased FA digestibility and also the yields of milk fat and ECM (
      • de Souza J.
      • Westerrn M.
      • Lock A.L.
      Abomasal infusion of an exogenous emulsifier improves fatty acid digestibility and milk fat yield of lactating dairy cows.
      ). Therefore, these results highlight the importance of FA digestibility on production and metabolic responses of lactating dairy cows.
      Typically, fat supplements minimally influence the digestibility of large aggregated fractions, such as DM digestibility, even when the digestibility of total FA differs markedly (
      • Grummer R.R.
      Influence of prilled fat and calcium salts of palm oil fatty acids on ruminant fermentation and nutrient digestibility.
      ;
      • Weiss W.P.
      • Wyatt D.J.
      Digestible energy values of diets with different fat supplements when fed to lactating dairy cows.
      ). However, in our study, we observed that FA-supplemented diets consistently increased both NDF and DM digestibilities compared with CON.
      • Piantoni P.
      • Lock A.L.
      • Allen M.S.
      Saturated fat supplementation interacts with dietary forage neutral detergent fiber content during the immediate postpartum and carryover periods in Holstein cows: Production responses and digestibility of nutrients.
      observed that feeding a saturated FA supplement (C16:0 + C18:0) increased NDF digestibility by 4.0% units in a low forage NDF diet but had no effect in a high forage NDF diet during the immediate postpartum period.
      • de Souza J.
      • Strieder-Barboza C.
      • Contreras G.A.
      • Lock A.L.
      Effects of timing of palmitic acid supplementation during early lactation on nutrient digestibility, energy balance, and metabolism of dairy cows.
      reported that feeding a C16:0-enriched supplement during the immediate postpartum increased the digestibility of NDF and DM. With postpeak cows, previous studies have consistently reported that feeding C16:0-enriched supplements increase NDF digestibility compared with nonfat supplemented control diets (
      • Rico J.E.
      • de Souza J.
      • Allen M.S.
      • Lock A.L.
      Nutrient digestibility and milk production responses to increasing levels of palmitic acid supplementation vary in cows receiving diets with or without whole cottonseed.
      ;
      • de Souza J.
      • Lock A.L.
      Long-term palmitic acid supplementation interacts with parity in lactating dairy cows: Production responses, nutrient digestibility, and energy partitioning.
      ) and to other FA supplements (
      • de Souza J.
      • Preseault C.L.
      • Lock A.L.
      Altering the ratio of dietary palmitic, stearic, and oleic acids in diets with or without whole cottonseed affects nutrient digestibility, energy partitioning, and production responses of dairy cows.
      ;
      • Western M.M.
      • de Souza J.
      • Lock A.L.
      Effects of commercially available palmitic and stearic acid supplements on nutrient digestibility and production responses of lactating dairy cows.
      ). Feeding C16:0 may increase NDF digestibility due to an increase in retention time driven by an increase in cholecystokinin secretion (
      • Piantoni P.
      • Lock A.L.
      • Allen M.S.
      Palmitic acid increased yields of milk and milk fat and nutrient digestibility across production level of lactating cows.
      ). Additionally, rumen bacteria typically synthesize C16:0 de novo to produce phosphatidic acid, the precursor for FA components in membranes of Butyrivibrio bacteria (
      • Hackmann T.J.
      • Firkins J.L.
      Electron transport phosphorylation in rumen butyrivibrios: Unprecedented ATP yield for glucose fermentation to butyrate.
      ). However, if dietary C16:0 could be incorporated into rumen bacterial membranes, considerable energy would be spared which may favor bacterial growth (
      • Vlaeminck B.
      • Fievez V.
      • Cabrita A.J.R.
      • Fonseca A.J.M.
      • Dewhurst R.J.
      Factors affecting odd- and branched-chain fatty acids in milk: A review.
      ), potentially increasing NDF digestibility. Therefore, the results of our study with early-lactation cows agree with previous findings in indicating a positive effect of feeding C16:0 on fiber digestibility. Also, in our study, we observed a linear positive effect of increasing dietary cis-9 C18:1 on DM and NDF digestibility. Furthermore, the difference in DM digestibility between the CON and 60:30 treatments tended to increase over time. Feed intake and nutrient digestibility are often negatively related (
      • NRC (National Research Council)
      Nutrient Requirements of Dairy Cattle.
      ). However, in our trial the 60:30 treatment increased both DMI and nutrient digestibility compared with the CON treatment. The NDF digestibility response to dietary cis-9 C18:1 have been inconsistent across studies. For instance,
      • Lopes J.C.
      • Harper M.T.
      • Giallongo F.
      • Oh J.
      • Smith L.
      • Ortega-Perez A.M.
      • Harper S.A.
      • Melgar A.
      • Kniffen D.M.
      • Fabin R.A.
      • Hristov A.N.
      Effect of high-oleic-acid soybeans on production performance, milk fatty acid composition, and enteric methane emission in dairy cows.
      did not observe differences in NDF digestibility when replacing conventional soybean with cis-9 C18:1 enriched soybean, whereas a recent in vitro study reported decreased fiber digestibility when cis-9 C18:1 as a free FA was added to continuous culture fermenters (
      • Sears A.
      • de Souza J.
      • Wenner B.A.
      • Batistel F.
      Palmitic, stearic, and oleic acids differently alter NDF digestibility in a continuous culture system.
      ). In contrast,
      • de Souza J.
      • St-Pierre N.R.
      • Lock A.L.
      Altering the ratio of dietary C16:0 and cis-9 C18:1 interacts with production level in dairy cows: effects on production responses and energy partitioning.
      reported no treatment differences for digestibilities of DM and NDF when feeding different ratios of C16:0 and cis-9 C18:1 for post-peak cows. Therefore, other factors such as level of supplementation, form of delivery of FA, and potential interactions with other FA and dietary factors may influence the response on nutrient digestibility to dietary cis-9 C18:1.
      Increasing energy intake and improving energy balance is one of the main goals of nutritional management during early lactation. In our study, we observed positive correlations between DE intake and yields of milk and ECM and a negative relationship between DE intake and BW loss and plasma NEFA concentration. Overall, FA-supplemented diets increased energy intake including DE, ME, and NEL compared with CON. Previous studies feeding FA supplements around parturition have reported inconsistent results regarding energy intake. Reasons for these inconsistent results regarding the effect of supplemental fat may include different methods to calculate or predict energy intake, duration of the supplementation period, level of supplemental fat in the diet, and most likely the FA profile of supplemental fat.
      • Piantoni P.
      • Lock A.L.
      • Allen M.S.
      Saturated fat supplementation interacts with dietary forage neutral detergent fiber content during the immediate postpartum period in Holstein cows: Energy balance and metabolism.
      reported that cows immediately postpartum had increased energy intake (+ 4.2 Mcal of NEL/d) when fed a saturated FA supplement (C16:0 + C18:0) regardless of dietary forage NDF level partially due to the high DMI in FA-supplemented diets (+1.4 kg of DMI/d).
      • de Souza J.
      • Strieder-Barboza C.
      • Contreras G.A.
      • Lock A.L.
      Effects of timing of palmitic acid supplementation during early lactation on nutrient digestibility, energy balance, and metabolism of dairy cows.
      reported that feeding a C16:0-enriched supplement during the immediate postpartum increased energy intake (+ 3.7 Mcal of NEL/d) partially because of the positive effect of this FA supplement on NDF digestibility. In contrast,
      • Moallem U.
      • Katz M.
      • Arieli A.
      • Lehrer H.
      Effects of peripartum propylene glycol or fats differing in fatty acid profiles on feed intake, production, and plasma metabolites in dairy cows.
      fed a saturated FA supplement (C16:0 + C18:0) during the pre- and postpartum periods and reported that the supplement did not affect predicted energy intake compared with a diet with no supplemental fat. In our study, we observed a positive linear effect of increasing dietary cis-9 C18:1 on energy intake, which was associated with a linear increase in feed intake and nutrient digestibility (NDF and FA) as dietary cis-9 C18:1 increased. As discussed by
      • de Souza J.
      • Strieder-Barboza C.
      • Contreras G.A.
      • Lock A.L.
      Effects of timing of palmitic acid supplementation during early lactation on nutrient digestibility, energy balance, and metabolism of dairy cows.
      , considering the potential effect that individual FA may have on feed intake and nutrient digestibility, measuring energy intake rather than predicting it from dietary composition is vital for determining energy intake and energy balance.
      In our study, the 80:10 treatment increased milk energy output and the efficiency of energy utilization to milk compared with other treatments because of the increase in milk fat yield (
      • de Souza J.
      • Prom C.M.
      • Lock A.L.
      Altering the ratio of dietary palmitic and oleic acids impacts production responses during the immediate postpartum and carryover periods in dairy cows.
      ); however, it also increased plasma NEFA and negative energy balance. Similarly, in early lactation cows, we previously observed that feeding a C16:0-enriched supplement increased ECM and milk energy output, but decreased BW, BCS, and increased NEFA and negative energy balance when fed during the first 24 d after calving (
      • de Souza J.
      • Lock A.L.
      Effects of timing of palmitic acid supplementation on production responses of early-lactation dairy cows.
      ;
      • de Souza J.
      • Strieder-Barboza C.
      • Contreras G.A.
      • Lock A.L.
      Effects of timing of palmitic acid supplementation during early lactation on nutrient digestibility, energy balance, and metabolism of dairy cows.
      ). In contrast, most studies feeding C16:0 supplements to postpeak cows (fed at 1.5 to 2.0% diet DM) have indicated no changes in BW and BCS compared with control diets (
      • Rico J.E.
      • de Souza J.
      • Allen M.S.
      • Lock A.L.
      Nutrient digestibility and milk production responses to increasing levels of palmitic acid supplementation vary in cows receiving diets with or without whole cottonseed.
      ;
      • de Souza J.
      • Lock A.L.
      Long-term palmitic acid supplementation interacts with parity in lactating dairy cows: Production responses, nutrient digestibility, and energy partitioning.
      ;
      • Western M.M.
      • de Souza J.
      • Lock A.L.
      Effects of commercially available palmitic and stearic acid supplements on nutrient digestibility and production responses of lactating dairy cows.
      ). In postpeak cows,
      • Mathews A.T.
      • Rico J.E.
      • Sprenkle N.T.
      • Lock A.L.
      • McFadden J.W.
      Increasing palmitic acid intake enhances milk production and prevents glucose-stimulated fatty acid disappearance without modifying systemic glucose tolerance in mid-lactation dairy cows.
      observed a decrease in glucose-stimulated NEFA disappearance in cows fed C16:0, suggesting the possibility of localized adipose tissue insulin resistance with prolonged C16:0 supplementation. Also, feeding C16:0 in early lactation rapidly increased circulating ceramide, especially C24:0-ceramide (
      • Davis A.N.
      • Phipps Z.C.
      • Zeng Q.
      • de Souza J.
      • Rico J.E.
      • Lock A.L.
      • McFadden J.W.
      Palmitic acid feeding increases plasma ceramide concentrations in Holstein dairy cows during early lactation.
      ), which is inversely associated with glucose clearance rates following an insulin challenge postpartum (
      • Rico J.E.
      • Saed Samii S.
      • Mathews A.T.
      • Lovett J.
      • Haughey N.J.
      • McFadden J.W.
      Temporal changes in sphingolipids and systemic insulin sensitivity during the transition from gestation to lactation.
      ). Because the development of insulin resistance in adipose and skeletal muscle tissues enables the dairy cow to partition nutrients toward the mammary gland during early lactation (
      • Bell A.W.
      Regulation of organic nutrient metabolism during transition from late pregnancy to early lactation.
      ;
      • Bell A.W.
      • Bauman D.E.
      Adaptations of glucose metabolism during pregnancy and lactation.
      ), it is possible that the change in energy partitioning to milk at the expense of body reserves in the immediate postpartum period in the 80:10 treatment may be partially related to changes in insulin resistance. Although lipolysis ensures an adequate supply of energy substrates to tissues around parturition, intense and protracted lipolysis predisposes cows to inflammatory and metabolic diseases by limiting the capacity of adipose tissue for energy buffering and contributing to chronically increased plasma NEFA (
      • Contreras G.A.
      • Strieder-Barboza C.
      • Raphael W.
      Adipose tissue lipolysis and remodeling during the transition period of dairy cows.
      ). Plasma NEFA concentrations greater than 0.7 mmol/L in the immediate postpartum period have been described as a risk factor for the development of clinical diseases postpartum (i.e., clinical ketosis, metritis, displaced abomasum), impaired reproduction in the subsequent breeding period, and early culling from the herd (
      • Ospina P.A.
      • McArt J.A.
      • Overton T.R.
      • Stokol T.
      • Nydam D.V.
      Using nonesterified fatty acids and β-hydroxybutyrate concentrations during the transition period for herd-level monitoring of increased risk of disease and decreased reproductive and milking performance.
      ;
      • Ribeiro E.S.
      • Lima F.S.
      • Greco L.F.
      • Bisinotto R.S.
      • Monteiro A.P.A.
      • Favoreto M.
      • Ayres H.
      • Marsola R.S.
      • Martinez N.
      • Thatcher W.W.
      • Santos J.E.P.
      Prevalence of periparturient diseases and effects on fertility of seasonally calving grazing dairy cows supplemented with concentrates.
      ). We observed that during the first week after calving the number of cows with NEFA concentrations in serum greater than 0.7 mmol/L was similar between CON and 80:10 (54 and 61% for CON and 80:10, respectively). Although the 80:10 treatment increased markers of lipolysis in the immediate postpartum, we observed a pronounced positive carryover effect of this treatment on milk yield (
      • de Souza J.
      • Prom C.M.
      • Lock A.L.
      Altering the ratio of dietary palmitic and oleic acids impacts production responses during the immediate postpartum and carryover periods in dairy cows.
      ). Further studies are needed to understand the mechanism by which C16:0 supplementation increases milk energy output at the expense of body reserves in the immediate postpartum period, and the possible effects of greater BW and BCS losses on health and reproduction of dairy cows.
      One of our hypotheses in this study was that increasing the amount of cis-9 C18:1 in supplemental fat would reduce milk energy output and improve energy balance in early lactation. Interestingly, we observed that increasing dietary cis-9 C18:1 improved energy balance by decreasing BW and BCS losses compared with the 80:10 treatment. The differences in nutrient partitioning are probably driven by insulin, as we observed that increasing cis-9 C18:1 increased plasma insulin concentration. Similarly, previous studies indicated that feeding cis-9 C18:1 not only increased BW gain in postpeak cows but also plasma insulin compared with non-fat-supplemented diets and other FA supplements (
      • de Souza J.
      • Preseault C.L.
      • Lock A.L.
      Altering the ratio of dietary palmitic, stearic, and oleic acids in diets with or without whole cottonseed affects nutrient digestibility, energy partitioning, and production responses of dairy cows.
      ,
      • de Souza J.
      • St-Pierre N.R.
      • Lock A.L.
      Altering the ratio of dietary C16:0 and cis-9 C18:1 interacts with production level in dairy cows: effects on production responses and energy partitioning.
      ). Although to our knowledge this has not been studied in cows, previous studies using rats have observed that cis-9 C18:1 stimulated insulin secretion from pancreatic β-cells (
      • Itoh Y.
      • Kawamata Y.
      • Harada M.
      • Kobayashi M.
      • Fujii R.
      • Fukusumi S.
      • Ogi K.
      • Hosoya M.
      • Tanaka Y.
      • Uejima H.
      • Tanaka H.
      • Maruyama M.
      • Satoh R.
      • Okubo S.
      • Kizawa H.
      • Komatsu H.
      • Matsumura F.
      • Noguchi Y.
      • Shinohara T.
      • Hinuma S.
      • Fujisawa Y.
      • Fujino M.
      Free fatty acids regulate insulin secretion from pancreatic β cells through GPR40.
      ;
      • Fujiwara K.
      • Maekawa F.
      • Yada T.
      Oleic acid interacts with GPR40 to induce Ca2+ signaling in rat islet beta-cells: mediation by PLC and L-type Ca2+ channel and link to insulin release.
      ). Elevated insulin concentrations would reduce plasma NEFA through inhibiting lipolysis or increasing lipogenesis (
      • Vernon R.G.
      Lipid metabolism during lactation: A review of adipose tissue-liver interactions and the development of fatty liver.
      ). In addition, increased concentrations of plasma triglycerides (TAG) could result from increased absorption of dietary FA increasing the supply of TAG-rich lipoproteins available in circulation. As a result, increases in insulin secretion could partition circulating TAG into other tissues and reduce lipolysis from adipose tissues. Furthermore,
      • Yanting C.
      • Yang Q.Y.
      • Ma G.L.
      • Du M.
      • Harrison J.H.
      • Block E.
      Dose- and type-dependent effects of long-chain fatty acids on adipogenesis and lipogenesis of bovine adipocytes.
      reported that cis-9 C18:1 increased adipocyte number and size through enhancing adipogenic commitment and lipogenesis compared with saturated FA (C14:0, C16:0, and C18:0). Also, the latter authors reported that in mature adipocytes treated with FA, the lipid content in adipocytes was affected by FA profile and ranked as cis-9 C18:1 > cis-9 cis-12 C18:2 > C14:0 > C18:0 > C16:0. Although we observed that feeding cis-9 C18:1 decreased plasma NEFA, a tendency for a linear increase in BHB was observed. Importantly, BHB does not only originate from ketogenesis in the liver from FA but also from conversion in the rumen epithelial cell of butyrate to BHB (
      • Weigand E.
      • Young J.W.
      • McGilliard A.D.
      Extent of butyrate metabolism by bovine ruminoreticulum epithelium and the relationship to absorption rate.
      ). Infusion of butyrate in the rumen has been positively related to DMI and plasma BHB (
      • Herrick K.J.
      • Hippen A.R.
      • Kalscheur K.F.
      • Schingoethe D.J.
      • Ranathunga S.D.
      • Anderson J.L.
      • Moreland S.C.
      • van Eys J.E.
      Infusion of butyrate affects plasma glucose, butyrate, and β-hydroxybutyrate but not plasma insulin in lactating dairy cows.
      ). Therefore, in our study, the increase in plasma BHB when feeding cis-9 C18:1 may be related to the greater DMI observed. Of note in our study, increasing cis-9 C18:1 in FA treatments tended to reduce body reserve mobilization despite the increase in milk energy output indicating that this could be a strategy to improve cow energy status and health without decreasing performance. Further research is needed to determine the mechanism by which cis-9 C18:1 may alter energy partitioning in early lactation cows.

      CONCLUSIONS

      Our results indicate that feeding FA supplements containing C16:0 and cis-9 C18:1 during the immediate postpartum period increased nutrient digestibility, energy intake, and milk energy output compared with a non-fat-supplemented control diet. Increasing dietary C16:0 increased energy intake, milk energy output, but also increased markers of body fat mobilization and negative energy balance during the immediate postpartum. Increasing dietary cis-9 C18:1 increased energy intake, reduced markers of body fat mobilization and improved energy balance during the immediate postpartum.

      ACKNOWLEDGMENTS

      We acknowledge Normand St-Pierre (Perdue Agribusiness, Salisbury, MD) for statistical advice in planning and analyzing data from this study. We acknowledge Perdue Agribusiness for financial support and donation of the supplements. We also acknowledge L.C. Worden, M. Western, J. Guy, H. Eerdum, H. Sharrard, T. Kulpinski, A. Negreiro, E. Butler, and B. Goering (all in the Department of Animal Science, Michigan State University), and the staff of the Michigan State University Dairy Cattle Teaching and Research Center for their assistance in this experiment. Jonas de Souza was supported by a Ph.D. fellowship from Coordenação de Aperfoiçamento de Pessoal de Nivel Superior (CAPES) from the Brazilian Ministry of Education (Brasilia, DF, Brazil). Crystal Prom was supported by a pre-doctoral fellowship from USDA NIFA. Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the authors and do not necessarily reflect the view of the US Department of Agriculture. The authors have not stated any conflicts of interest.

      Supplementary Material

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      Linked Article

      • Altering the ratio of dietary palmitic and oleic acids affects production responses during the immediate postpartum and carryover periods in dairy cows
        Journal of Dairy ScienceVol. 104Issue 3
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          The objectives of our study were to determine the effects of altering the dietary ratio of palmitic (C16:0) and oleic (cis-9 C18:1) acids on production and metabolic responses of early-lactation dairy cows during the immediate postpartum period and to evaluate carryover effects of the treatment diets early in lactation. Fifty-six multiparous cows were used in a randomized complete block design and randomly assigned to 1 of 4 treatments (14 cows per treatment) fed from 1 to 24 d in milk (DIM). The treatments were: (1) control (CON) diet not supplemented with fatty acids (FA); (2) diet supplemented with a FA blend containing 80% C16:0 and 10% cis-9 C18:1 (80:10); (3) diet supplemented with a FA blend containing 70% C16:0 and 20% cis-9 C18:1 (70:20); and (4) diet supplemented with a FA blend containing 60% C16:0 and 30% cis-9 C18:1 (60:30).
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