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The objective of our study was to evaluate the effects of feeding triglyceride and fatty acid (FA) supplements enriched in palmitic acid (PA; C16:0) on production and nutrient digestibility responses of mid-lactation dairy cows. Fifteen Holstein cows (137 ± 49 d in milk) were randomly assigned to a treatment sequence in a 3 × 3 Latin square design. Treatments consisted of a control diet (CON; no added PA) or 1.5% FA added as either a FA supplement (PA-FA) or a triglyceride supplement (PA-TG). The PA supplements replaced soyhulls, and diets were balanced for glycerol content. Periods were 21 d in length with sample and data collection occurring during the final 5 d. Compared with CON, PA treatments increased dry matter (66.5 vs. 63.9%) and neutral detergent fiber (NDF) apparent digestibility (42.0 vs. 38.2%). Although PA treatments tended to increase 18-carbon FA apparent digestibility (79.1 vs. 77.9%), PA treatments decreased 16-carbon (63.1 vs. 75.8%) and total FA (72.0 vs. 76.5%) apparent digestibilities compared with CON. The PA treatments increased milk fat content (3.60 vs. 3.41%), milk fat yield (1.70 vs. 1.60 kg/d), yield of 16-carbon milk FA (570 vs. 471 g/d), 3.5% fat-corrected milk (47.6 vs. 46.5 kg/d), and energy-corrected milk (47.4 vs. 46.6 kg/d) compared with CON. The PA treatments did not affect dry matter intake (28.5 vs. 29.2 kg/d), milk yield (47.0 vs. 47.4 kg/d), milk protein yield (1.42 vs. 1.45 kg/d), milk lactose yield (2.29 vs. 2.31 kg/d), yield of <16-carbon milk FA (360 vs. 370 g/d), yield of >16-carbon milk FA (642 vs. 630 g/d), body weight (720 vs. 723 kg), or body condition score (3.14 vs. 3.23). We did not observe differences in digestibilities of dry matter, NDF, and 18-carbon FA between PA-TG and PA-FA. In contrast, PA-FA increased 16-carbon (68.6 vs. 57.6%) and total FA apparent digestibility (73.8 vs. 70.1%) compared with PA-TG. This resulted in PA-FA supplementation increasing the apparent digestibility of the PA supplement by ∼10 percentage points compared with PA-TG. Compared with PA-TG, PA-FA increased 16-carbon FA intake by 60 g/d, absorbed 16-carbon FA by 86 g/d, and absorbed total FA by 85 g/d. Compared with PA-TG, PA-FA increased dry matter intake (29.1 vs. 27.8 kg/d), yield of 16-carbon milk FA (596 vs. 545 g/d), and tended to increase milk yield (47.6 vs. 46.4 kg/d), milk fat yield (1.70 vs. 1.66 kg/d), and 3.5% fat-corrected milk (48.1 vs. 47.2 kg/d). In conclusion, the production response of dairy cows to PA tended to be greater for a FA supplement compared with a triglyceride supplement. Overall, PA increased NDF digestibility, milk fat yield, energy-corrected milk, and feed efficiency in mid-lactation dairy cows.
Fat supplements are added to dairy cow diets to increase dietary energy density, feed efficiency, yields of milk and milk fat, and to improve energy balance (
). Individual fatty acids (FA) can have different effects, and recently, considerable research has focused on palmitic acid (C16:0) supplementation. This FA has been reported to increase milk yield, milk fat concentration and yield, and the efficiency of milk production compared with a control diet (
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.
Long-term palmitic acid supplementation interacts with parity in lactating dairy cows: production responses, nutrient digestibility, and energy partitioning.
). Because the supplements described in the above-mentioned studies were similar in FA composition, understanding factors (e.g., basal diet composition, characteristics of fat supplements) that are associated with variations in production responses may allow for more precise feeding recommendations.
The degree of esterification of fat supplements has been suggested as a factor that may affect FA digestibility, and consequently, production responses of dairy cows (
); therefore, these previous studies suggested that lipolysis in the small intestine maybe a rate-limiting step in digestion of triglyceride (TG) sources of fat. Recently, we observed that feeding a C16:0 TG supplement (77% C16:0 and 5% C18:0) reduced total FA digestibility by 8.7% units compared with a Ca-salts of palm FA (
Short communication: Comparison of a palmitic acid-enriched triglyceride supplement and calcium salts of palm fatty acids supplement on production responses of dairy cows.
observed that total FA digestibility was reduced ∼8 percentage points when a saturated TG supplement containing 72% C16:0 and 5% C18:0 was fed, compared with a control diet. However, the decrease in FA digestibility observed by
Short communication: Comparison of a palmitic acid-enriched triglyceride supplement and calcium salts of palm fatty acids supplement on production responses of dairy cows.
Effects of saturation and esterification of fat sources on site and extent of digestion in steers: Digestion of fatty acids, triglycerides, and energy.
). A possible factor affecting variation in FA digestibility due to feeding TG fat supplements in previous studies is differences in the FA profile of the supplements examined. To our knowledge, most published studies evaluating the effect of C16:0 supplementation on dairy cow responses were conducted utilizing FA rather than TG supplements. Because the FA profile of fat supplements seems to be an important factor affecting FA digestibility, evaluating the effect of the degree of esterification in supplements with similar FA profiles is of importance.
The objective of our study was to evaluate the effects of commercially available C16:0 supplements fed either as FA or TG supplements on nutrient digestibility and production responses of mid-lactation dairy cows. We hypothesized that a C16:0 supplement fed as FA would have higher digestibility than the TG supplement, but that the differences would be smaller than previously reported in the literature due to differences in the FA profile of the supplements.
MATERIALS AND METHODS
Design and Treatments
All experimental procedures were approved by the Institutional Animal Care and Use Committee at Michigan State University, East Lansing. Fifteen mid-lactation Holstein cows at the Michigan State University Dairy Field Laboratory were randomly assigned to treatment sequence in replicated 3 × 3 Latin squares with 21-d periods. All animals received a common diet containing no supplemental fat during a 14-d preliminary period to obtain baseline values for response variables. At the beginning of the trial, mean DIM, BW, and ECM (mean ± SD) were 137 ± 49 d, 700 ± 52 kg, and 48.1 ± 6.1 kg/d, respectively.
Treatments were a control diet (CON; no added PA) or 1.5% of FA added either as a FA supplement (PA-FA) or a triglyceride supplement (PA-TG). Chemical composition and characteristics of the PA supplements are presented in Table 1. The PA supplements replaced soyhulls in the diets, which were formulated to meet the requirements of the average cow in the group (
; Table 2). Both fat-supplemented diets were balanced for glycerol concentration; glycerol was not added to our CON treatment. Although it is important to consider a possible different metabolic fate for the glycerol fed in the diet or released from TG in the intestine (or both), it is unlikely that it affected our results due to the very small amount required to balance dietary glycerol content between the PA-TG and PA-FA diets. The DM concentration was determined twice weekly for forages and diets were adjusted when necessary. A basal diet mix (containing forage sources, corn grain, high-moisture corn, soybean meal, and mineral mix) was mixed daily in a mixer wagon. Then, the soyhulls, the fat supplements, and the basal diet were mixed in a tumble mixer for each experimental diet. Cows were housed in tiestalls throughout the experiment and milked twice daily (0400 and 1500 h). Access to feed was blocked from 0800 to 1000 h for collection of orts and offering of new feed. Cows were fed 115% of expected intake at 1000 h daily. Water was available ad libitum in each stall and stalls were bedded with sawdust and cleaned twice daily.
Table 1Physical characterization and composition of triglyceride (PA-TG) and fatty acid (PA-FA) palmitic acid supplements fed in treatment diets (n = 3)
Vitamin and mineral mix contained 34.1% dry ground shelled corn, 25.6% white salt, 21.8% calcium carbonate, 9.1% Biofos (The Mosaic Co., Plymouth, MN), 3.9% magnesium oxide, 2% soybean oil, and <1% of each of the following: manganese sulfate, zinc sulfate, ferrous sulfate, copper sulfate, iodine, cobalt carbonate, vitamin E, vitamin A, vitamin D, and selenium.
2.0
2.0
2.0
Limestone
0.60
0.60
0.60
Sodium bicarbonate
0.71
0.71
0.71
Nutrient composition, % of DM
NDF
31.0
29.9
29.9
CP
16.7
16.6
16.6
Starch
26.0
25.9
26.0
Total fatty acids
3.37
4.83
4.83
16:0
0.55
1.70
1.85
18:0
0.08
0.16
0.11
cis-9 18:1
0.59
0.79
0.71
cis-9,cis-12 18:2
1.72
1.75
1.74
cis-9,cis-12,cis-15 18:3
0.19
0.19
0.19
1 CON = control diet, no addition of palmitic acid; PA-TG = palmitic acid fed as triglyceride; PA-FA = palmitic acid fed as free fatty acid.
4 Vitamin and mineral mix contained 34.1% dry ground shelled corn, 25.6% white salt, 21.8% calcium carbonate, 9.1% Biofos (The Mosaic Co., Plymouth, MN), 3.9% magnesium oxide, 2% soybean oil, and <1% of each of the following: manganese sulfate, zinc sulfate, ferrous sulfate, copper sulfate, iodine, cobalt carbonate, vitamin E, vitamin A, vitamin D, and selenium.
Samples and data for production results were collected during the last 5 d of each treatment period (d 17 to 21). Samples of all diet ingredients (0.5 kg) and orts from each cow (12.5%) were collected daily and composited by period for analysis. Milk yield was recorded, and 2 milk samples were collected at each milking. One aliquot was collected in a sealed tube with preservative (bronopol tablet, D&F Control Systems, San Ramon, CA) and stored at 4°C for milk component analysis. The second aliquot was stored without preservative at −20°C until analyzed for FA composition.
For apparent digestibility measurements, fecal samples (∼400 g) were collected every 15 h during the last 5 d of each period resulting in 8 samples per cow per period, representing every 3 h of a 24-h period to account for diurnal variation. Feces were stored at −20°C until samples were dried and composited on equal DM basis for each cow period. Body weight was measured 3 times per week and 4 trained investigators determined BCS on a 5-point scale in 0.25 increments on the last day of each period (
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). Samples of feed ingredients, orts, and feces were analyzed for ash, NDF, indigestible NDF, CP, starch, and FA concentration as described by
, method Ca 14–56), and gross energy with bomb calorimetry by Eurofins Global Inc. (Des Moines, IA). Digestibility of supplemental fat was estimated with a Lucas test. The intake of FA from the basal diet was subtracted from that in each supplemented diet to calculate supplemental FA intake. Fecal output of undigested basal FA was estimated using FA digestibility measured when cows were fed the control diet and that value was used for each specific cow. We did not observe a period effect for total FA digestibility (P = 0.30), so we applied the FA digestibility when cows received the control diets to when they received treatment diets during other periods. Fecal output of basal FA was subtracted from fecal output of total FA when cows were fed the supplemented diets. Digestibility of supplemental fat was estimated with a Lucas test by regressing supplemental FA intake by supplemental FA absorbed. The slope of each regression is the estimated apparent digestibility coefficient of each fat supplement.
Individual milk samples were analyzed for fat, true protein, and lactose concentrations by mid-infrared spectroscopy (
, method 972.160) by the Michigan Herd Improvement Association (Universal Lab Services, Lansing, MI). Yields of 3.5% FCM, ECM, and milk components were calculated using milk yield and component concentrations for each milking, summed for a daily total, and averaged for each collection period. Milk samples used for analysis of FA composition were composited based on milk fat yield (d 17–21 of each period). Milk lipids were extracted, and FAME prepared according to our methods previously described by
The FA yield response to additional FA intake (FAYR-INT) was calculated as
FAYR-INT (%) = [(FA yield for PA supplemented diet – FA yield for CON)/(FA intake for PA supplemented diet – FA intake for CON)] × 100.
The FA yield response to additional absorbed FA (FAYR-ABS) was calculated as
FAYR-ABS (%) = [(FA yield for PA supplemented diet – FA yield for CON)/(absorbed FA for PA supplemented diet – absorbed FA for CON)] × 100.
Statistical Analysis
All data were analyzed using the mixed model procedure of SAS (version 9.4, SAS Institute, Cary, NC). Data were analyzed using the following model:
Yijkl = μ + C(S)i(j) + Sj + Pk + Tl + eijkl,
where Yijkl = the dependent variable, μ = the overall mean, C(S)i(j) = random effect of cow nested in sequence (i = 1 to 15), Sj = random effect of treatment sequence (j = 1 to 6), Pk = fixed effect of period (k = 1 to 3), Tl = fixed effect of treatment (l = 1 to 3), and eijkl = residual error. The interaction between period and treatment was initially included in the model but was removed because it was not significant (all P > 0.20). Two preplanned contrasts were used to evaluate (1) the overall effect of PA supplemented treatments [CON vs. PA; 1/2 (PA-TG + PA-FA)], and (2) the effect of PA supplement (PA-TG vs. PA-FA). Contrasts were declared significant at P ≤ 0.05 and trends at 0.05 < P ≤ 0.10.
RESULTS
Compared with CON, PA treatments did not affect DMI (P = 0.13) but increased DM digestibility (P < 0.01) and NDF digestibility (P < 0.01, Table 3). The PA treatments increased 16-carbon and total FA intake (both P < 0.01) and tended to increase 18-carbon FA intake (P = 0.06) compared with CON. The PA treatments decreased 16-carbon and total FA apparent digestibilities (both P < 0.01) but tended to increase 18-carbon FA apparent digestibility (P = 0.10). Also, compared with CON, PA treatments increased absorbed 16-carbon, 18-carbon, and total FA (all P < 0.05). Compared with PA-TG, PA-FA increased DMI (P = 0.05), but we did not observe differences in digestibilities of DM, NDF, or 18-carbon FA between PA-TG and PA-FA (all P > 0.50). In contrast, PA-FA increased 16-carbon (P < 0.01) and total FA apparent digestibility (P = 0.02) compared with PA-TG. Compared with PA-TG, PA-FA increased 16-carbon FA intake by 60 g/d (P < 0.01) and increased absorbed 16-carbon FA by 86 g/d (P < 0.01) and absorbed total FA by 85 g/d (P < 0.01). We estimated that the apparent digestibility of the basal diet (without supplemental fat) was 76.2% (Figure 1A). Additionally, by using a Lucas test we estimated that PA-FA increased apparent digestibility of supplemental fat by ∼10 percentage points compared with PA-TG (69.5 vs. 59.0% for PA-FA and PA-TG, respectively; Figure 1B).
Table 3Nutrient intake and apparent digestibility and absorbed 16-carbon, 18-carbon, and total fatty acids (FA) for cows fed treatment diets (n = 15)
CON = control diet, no addition of palmitic acid; PA-TG = palmitic acid fed as triglyceride supplement; PA-FA = palmitic acid fed as free fatty acid supplement.
P-values associated with contrasts: (1) the effect of PA treatments [CON vs. PA; 1/2(PA-TG + PA-FA)], and (2) the effect of palmitic acid fed as triglycerides or free fatty acids (PA-TG vs. PA-FA).
CON
PA-TG
PA-FA
CON vs. PA
PA-TG vs. PA-FA
Intake, kg/d
DM
29.2
27.8
29.1
0.77
0.13
0.05
NDF
9.01
8.29
8.69
0.27
0.01
0.08
Intake, g/d
Total FA
990
1,370
1,410
37.2
<0.01
0.13
16-Carbon
180
500
560
14.2
<0.01
<0.01
18-Carbon
770
820
810
23.8
0.06
0.45
Digestibility, %
DM
63.9
66.5
66.4
0.37
<0.01
0.71
NDF
38.2
42.1
41.8
0.38
<0.01
0.59
Total FA
76.5
70.1
73.8
1.10
<0.01
0.02
16-Carbon
75.8
57.6
68.6
1.83
<0.01
<0.01
18-Carbon
77.9
78.6
79.6
1.08
0.10
0.52
Absorbed, g/d
Total FA
763
957
1,041
29.3
<0.01
<0.01
16-Carbon
141
288
374
11.8
<0.01
<0.01
18-Carbon
605
646
640
19.7
0.05
0.77
1 CON = control diet, no addition of palmitic acid; PA-TG = palmitic acid fed as triglyceride supplement; PA-FA = palmitic acid fed as free fatty acid supplement.
2 P-values associated with contrasts: (1) the effect of PA treatments [CON vs. PA; 1/2(PA-TG + PA-FA)], and (2) the effect of palmitic acid fed as triglycerides or free fatty acids (PA-TG vs. PA-FA).
Figure 1Lucas test to estimate the apparent fatty acid (FA) digestibility of the basal diet (A) and palmitic acid-enriched supplements (B) fed as triglycerides (PA-TG, triangles and dashed line) or fatty acids (PA-FA, circles and solid line). To estimate the FA digestibility of the basal diet, a Lucas test was used regressing basal FA intake by basal FA absorbed for each cow when they received the control diet. To estimate the digestibility of the supplements, the intake of FA from the basal diet was subtracted from that in each supplemented diet to calculate the supplemental FA intake. Fecal output of undigested basal FA was estimated using FA digestibility measured when cows were fed the control diet and that value was used for individual cows. Fecal output of basal FA was subtracted from fecal output of total FA when cows were fed the supplemented diets. The slopes (i.e., apparent digestibility of supplemental fat) were 0.762 ± 0.089, 0.590 ± 0.019, and 0.695 ± 0.021 for control, PA-TG, and PA-FA, respectively, and intercepts were not different from zero (P > 0.59).
Compared with CON, PA treatments did not affect milk yield (P = 0.67; Table 4). In contrast, PA treatments increased milk fat content (P < 0.01), milk fat yield (P < 0.01), 3.5% FCM (P = 0.01), and ECM (P = 0.04) compared with CON. Additionally, the PA treatments increased feed efficiency (ECM/DMI; P < 0.01), but reduced BW change (P = 0.01) compared with CON. Compared with PA-TG, PA-FA tended to increase milk yield (P = 0.06), milk fat yield (P = 0.10), and 3.5% FCM (P = 0.09). We did not observe differences in concentrations or yields of milk protein and lactose, or in feed efficiency, between PA-TG and PA-FA (all P < 0.10). The PA-FA increased BW change (P = 0.05) and BCS (P = 0.03) compared with PA-TG.
Table 4Milk yield, milk composition, BW, and BCS for cows fed treatment diets (n = 15)
CON = control diet, no addition of palmitic acid; PA-TG = palmitic acid fed as triglyceride supplement; PA-FA = palmitic acid fed as free fatty acid supplement.
P-values associated with contrasts: (1) the effect of PA treatments [CON vs. PA; 1/2(PA-TG + PA-FA)], and (2) the effect of palmitic acid fed as triglycerides or free fatty acid (PA-TG vs. PA-FA).
ECM = [(0.327 × kg of milk) + (12.95 × kg of milk fat) + (7.20 × kg of milk protein).
46.7
47.0
47.6
0.94
0.04
0.14
Milk composition
Fat, kg/d
1.60
1.66
1.70
0.02
<0.01
0.10
Fat, %
3.41
3.61
3.59
0.09
<0.01
0.47
Protein, kg/d
1.45
1.40
1.43
0.03
0.15
0.52
Protein, %
3.10
3.04
3.04
0.02
<0.01
0.39
Lactose, kg/d
2.31
2.27
2.30
0.06
0.46
0.76
Lactose, %
4.89
4.88
4.86
0.03
0.39
0.22
ECM/DMI
1.59
1.69
1.64
0.03
<0.01
0.78
BW, kg
723
719
725
17.9
0.80
0.15
BW change, kg/d
0.65
0.25
0.50
0.19
0.01
0.05
BCS
3.14
3.15
3.23
0.03
0.17
0.03
BCS change
0.07
0.008
0.06
0.03
0.12
0.15
1 CON = control diet, no addition of palmitic acid; PA-TG = palmitic acid fed as triglyceride supplement; PA-FA = palmitic acid fed as free fatty acid supplement.
2 P-values associated with contrasts: (1) the effect of PA treatments [CON vs. PA; 1/2(PA-TG + PA-FA)], and (2) the effect of palmitic acid fed as triglycerides or free fatty acid (PA-TG vs. PA-FA).
3 3.5% FCM = [(0.4324 × kg of milk) + (16.216 × kg of milk fat)].
4 ECM = [(0.327 × kg of milk) + (12.95 × kg of milk fat) + (7.20 × kg of milk protein).
Milk FA are derived from 2 sources: <16 carbon FA from de novo synthesis in the mammary gland and >16 carbon FA originating from extraction from plasma. Mixed-source FA (16-carbon) originate from de novo synthesis in the mammary gland and extraction from plasma. Compared with CON, PA treatments reduced the concentration of <16-carbon and >16-carbon (all P < 0.01; Table 5) but increased 16-carbon milk FA (P < 0.01). On a yield basis, PA treatments increased 16-carbon milk FA (P < 0.01) due primarily to the increase in concentration and yield of C16:0 (P < 0.01; Table 6). In contrast, PA treatments did not affect the yield of <16-carbon milk FA (P = 0.23) or >16-carbon milk FA (P = 0.56). Additionally, PA treatments increased yield of cis-9 C18:1 (P < 0.01). Compared with PA-TG, PA-FA increased the concentration and yield of 16-carbon FA (both P < 0.01) primarily due to the greater increase in concentration and yield of C16:0 (P < 0.01). In contrast, PA-FA decreased the concentration (P < 0.01) and yield (P = 0.03) of >16-carbon milk FA due to a lower yield of cis-9 C18:1 (P = 0.01) compared with PA-TG. The FAYR-INT was 18.4 and 23.8% for PA-TG and PA-FA, respectively. The FAYR-ABS was 36.0 and 36.1% for PA-TG and PA-FA, respectively.
CON = control diet, no addition of palmitic acid; PA-TG = palmitic acid fed as triglyceride supplement; PA-FA = palmitic acid fed as free fatty acid supplement.
P-values associated with contrasts: (1) the effect of PA treatments [CON vs. PA; 1/2(PA-TG + PA-FA)], and (2) the effect of palmitic acid fed as triglycerides or free FA (PA-TG vs. PA-FA).
De novo FA originate from mammary de novo synthesis (<16 carbons), preformed FA originate from extraction from plasma (>16 carbons), and 16-carbon FA originate from both sources (C16:0 plus cis-9 C16:1).
A total of approximately 80 individual FA were quantified. Only select FA are reported in the table.
g/100 g of FA
C4:0
3.41
3.43
3.42
0.06
0.71
0.88
C6:0
2.22
2.08
2.04
0.05
<0.01
0.38
C8:0
1.28
1.13
1.11
0.03
<0.01
0.26
C10:0
3.05
2.54
2.52
0.11
<0.01
0.53
C12:0
3.49
2.85
2.82
0.11
<0.01
0.68
C14:0
11.6
10.1
10.1
0.18
<0.01
0.79
C16:0
30.1
33.4
36.3
0.26
<0.01
<0.01
cis-9 C16:1
1.38
1.42
1.54
0.04
<0.01
<0.01
C18:0
11.0
11.1
9.8
0.31
<0.01
<0.01
trans-6 to -8 C18:1
0.28
0.29
0.25
0.006
0.08
<0.01
trans-9 C18:1
0.23
0.23
0.20
0.004
<0.01
<0.01
trans-10 C18:1
0.51
0.43
0.42
0.03
<0.01
0.94
trans-11 C18:1
1.03
1.00
0.85
0.03
<0.01
<0.01
cis-9 C18:1
18.6
19.2
18.3
0.39
0.37
<0.01
cis-11 C18:1
0.60
0.58
0.57
0.02
0.24
0.81
cis-9,cis-12 C18:2
2.62
2.51
2.37
0.05
<0.01
<0.01
cis-9,trans-11 C18:2
0.42
0.40
0.36
0.01
<0.01
0.05
cis-9,cis-12,cis-15 C18:3
0.35
0.32
0.31
0.008
<0.01
0.13
1 CON = control diet, no addition of palmitic acid; PA-TG = palmitic acid fed as triglyceride supplement; PA-FA = palmitic acid fed as free fatty acid supplement.
2 P-values associated with contrasts: (1) the effect of PA treatments [CON vs. PA; 1/2(PA-TG + PA-FA)], and (2) the effect of palmitic acid fed as triglycerides or free FA (PA-TG vs. PA-FA).
3 De novo FA originate from mammary de novo synthesis (<16 carbons), preformed FA originate from extraction from plasma (>16 carbons), and 16-carbon FA originate from both sources (C16:0 plus cis-9 C16:1).
4 A total of approximately 80 individual FA were quantified. Only select FA are reported in the table.
CON = control diet, no addition of palmitic acid; PA-TG = palmitic acid fed as triglyceride supplement; PA-FA = palmitic acid fed as free fatty acid supplement.
P-values associated with contrasts: (1) the effect of PA treatments [CON vs. PA; 1/2(PA-TG + PA-FA)], and (2) the effect of palmitic acid fed as triglycerides or free fatty acids (PA-TG vs. PA-FA).
De novo fatty acids originate from mammary de novo synthesis (<16 carbons), preformed fatty acids originate from extraction from plasma (>16 carbons), and 16-carbon fatty acids originate from both sources (C16:0 plus cis-9 C16:1).
A total of approximately 80 individual fatty acids were quantified. Only select fatty acids are reported in the table.
g/d
C4:0
51.5
53.8
54.4
2.66
0.12
0.76
C6:0
33.8
32.7
32.6
1.89
0.29
0.95
C8:0
19.6
17.8
18.5
1.19
0.19
0.85
C10:0
46.7
44.1
44.8
3.03
0.49
0.98
C12:0
53.4
45.0
49.1
3.36
0.15
0.16
C14:0
165
159
161
8.9
0.44
0.93
C16:0
454
523
571
23.9
<0.01
<0.01
cis-9 C16:1
20.9
22.4
24.3
0.89
<0.01
<0.01
C18:0
164
173
155
7.9
0.92
<0.01
trans-6 to -8 C18:1
4.2
4.6
4.0
0.21
0.28
<0.01
trans-9 C18:1
3.4
3.5
3.1
0.12
0.43
<0.01
trans-10 C18:1
7.6
6.7
6.7
0.52
<0.01
0.96
trans-11 C18:1
15.4
15.8
13.4
0.80
0.15
<0.01
cis-9 C18:1
276
300
287
11.2
<0.01
0.01
cis-11 C18:1
9.0
9.1
9.1
0.42
0.54
0.73
cis-9,cis-12 C18:2
39.0
39.1
37.1
1.55
0.19
0.01
cis-9,trans-11 C18:2
6.4
6.3
5.8
0.29
0.21
0.07
cis-9,cis-12,cis-15 C18:3
5.4
5.1
4.9
0.23
<0.01
0.14
1 CON = control diet, no addition of palmitic acid; PA-TG = palmitic acid fed as triglyceride supplement; PA-FA = palmitic acid fed as free fatty acid supplement.
2 P-values associated with contrasts: (1) the effect of PA treatments [CON vs. PA; 1/2(PA-TG + PA-FA)], and (2) the effect of palmitic acid fed as triglycerides or free fatty acids (PA-TG vs. PA-FA).
3 De novo fatty acids originate from mammary de novo synthesis (<16 carbons), preformed fatty acids originate from extraction from plasma (>16 carbons), and 16-carbon fatty acids originate from both sources (C16:0 plus cis-9 C16:1).
4 A total of approximately 80 individual fatty acids were quantified. Only select fatty acids are reported in the table.
Changes in intake and nutrient digestibility due to supplemental fat may affect, positively or negatively, digestible energy available for milk production, body reserves, or both (
). In this regard, understanding factors that influence FA digestibility are useful in developing strategies for diet formulation and provide information critical for optimal FA supplementation. The digestibility of fat supplements fed as TG has been shown to be lower than the digestibility of fat supplements fed as FA (
Effects of saturation and esterification of fat sources on site and extent of digestion in steers: Digestion of fatty acids, triglycerides, and energy.
). However, the TG supplements in most previous studies contained higher proportions of C18:0 as the major FA. Therefore, these results might not only be influenced by the degree of esterification, but also by the FA profile of the supplement fed. Although considerable research has recently examined the effect of C16:0 supplements, to our knowledge, most published studies with dairy cows used FA rather than TG supplements. Due to the importance of FA digestibility when evaluating fat supplements, we conducted the current experiment to examine the effects of degree of esterification of C16:0 supplements on production responses of dairy cows. The use of enriched C16:0 supplements with similar FA profile in the present experiment allowed us to compare the effects of degree of esterification while minimizing potential confounding effects of large differences in other FA in the supplements.
Overall, PA treatments did not affect DMI, which agrees with results from studies feeding enriched (≥85%) sources of C16:0 in which DMI has not been reduced compared with a control diet (
observed that saturated hydrogenated FA supplements did not affect DMI. In our current study, PA-TG decreased DMI compared with PA-FA, whereas we recently observed lower DMI for a Ca-salts of palm FA supplement compared with a PA-TG supplement (
Short communication: Comparison of a palmitic acid-enriched triglyceride supplement and calcium salts of palm fatty acids supplement on production responses of dairy cows.
suggested that esterification of FA to glycerol may alter the sensing mechanism in the upper duodenum by which FA inhibit DMI. Reasons for the differences between our results and the above-mentioned studies may include differences in the FA profiles of the supplements and, possibly, the production level of the cows studied. Further research is needed to evaluate these inconsistent results and to elucidate the mechanisms regulating feed intake when FA and TG supplements are fed.
When fed at typical inclusion rates (≤3% of diet DM), fat supplements minimally influence the digestibility of large aggregated fractions, such as DM digestibility, even when the digestibility of total FA differs markedly (
). In our study, PA treatments increased both NDF and DM digestibility compared with CON. This increased NDF digestibility agrees with previous studies feeding C16:0 as a FA supplement (
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.
Short communication: Comparison of a palmitic acid-enriched triglyceride supplement and calcium salts of palm fatty acids supplement on production responses of dairy cows.
). Although the mechanisms for this effect on fiber digestion due to feeding C16:0 are unknown, possible factors include an increase in retention time driven by an increase in cholecystokinin secretion (
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.
suggested that the FA profile of supplemental fat may affect NDF digestibility because we observed that feeding a FA blend with high content of C16:0 (80% C16:0) and a FA blend with 45% C16:0 and 35% cis-9 C18:1 increased NDF digestibility compared with a nonfat control diet and a diet supplemented with a FA blend with 40% C16:0 and 40% C18:0.
We observed that compared with CON, PA treatments reduced the digestibility of 16-carbon FA and total FA. Although
reported that feeding a highly enriched C16:0 supplement had positive effects on 16-carbon and total FA digestibilities of low-producing cows, other studies with high-producing cows have observed reductions in FA digestibility when feeding similar supplements (
Long-term palmitic acid supplementation interacts with parity in lactating dairy cows: production responses, nutrient digestibility, and energy partitioning.
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. Although total flow of FA at the duodenum affects FA digestibility (
Nutrient digestibility and milk production responses to increasing levels of palmitic acid supplementation vary in cows receiving diets with or without whole cottonseed.
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.
). In our study, although the intake of 16-carbon FA was slightly over 500 g/d for the PA treatments and we observed that PA treatments reduced FA digestibility, this reduction was similar to that observed by
. Although the exact mechanisms for the reduction in FA digestibility as FA intake increases are unknown, potential causes have been suggested and include competition for absorption sites and limits in emulsification (
Effects of saturation and esterification of fat sources on site and extent of digestion in steers: Digestion of fatty acids, triglycerides, and energy.
observed reduced intestinal digestibility of 16-carbon, 18-carbon, and total FA when a partially hydrogenated tallow TG supplement was fed, compared with a partially hydrogenated tallow FA supplement. Therefore, lipolysis in the small intestine might be a rate-limiting step to TG supplement digestion; because several lipases are only active at the distal end of the small intestine, they may be unable to hydrolyze large amounts of duodenal TG when these supplements are fed, therefore possibly limiting intestinal digestibility (
). In our study, we observed that PA-TG reduced total FA digestibility compared with PA-FA. However, the decrease in FA digestibility was smaller than that previously reported by the above-mentioned studies. We propose that this inconsistency is due to differences in the FA profile of the supplements being evaluated.
reported lower intestinal hydrolysis in sheep for tallow compared with coconut oil, olive oil, and corn oil. This was attributed to lower lipase activity resulting from lower solubility and poor emulsification of tallow due to its FA profile. Therefore, the lower solubility of TG enriched with C18:0 may increase the need for emulsification compounds to form micelles and reduce the time of action for intestinal lipases and FA absorption. Additionally, in our meta-analysis evaluating the digestibility of individual FA using duodenally cannulated cows, we determined that as the amount of C18:0 reaching the duodenum increased, the digestibility of C18:0 linearly decreased across nonsupplemented and fat-supplemented diets encompassing a wide range of C18:0 duodenal flows (
Short communication: Comparison of a palmitic acid-enriched triglyceride supplement and calcium salts of palm fatty acids supplement on production responses of dairy cows.
for their TG supplements. Although we did not measure it in our study, it is possible that our PA-TG supplement could have been partially hydrolyzed in the rumen, resulting in less intact TG reaching the intestine compared with previous studies that fed partially or fully hydrogenated tallow. This hypothesis deserves further investigation. Overall, our results indicate that the degree of esterification is a major factor affecting digestibility of supplemental fat, and the magnitude of the response is influenced by the FA profile of the supplement.
Overall, we observed that PA treatments did not affect milk yield, but increased 3.5% FCM and ECM compared with CON. Although studies with C16:0 supplements have reported some contradictory results regarding milk yield, most have shown that these supplements increase 3.5% FCM and ECM (e.g.,
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, PA treatments reduced milk protein content in our study, but milk protein yield was not affected. Reductions in milk protein content, absent changes in milk protein yield, were consistently observed when responses to several sources of supplemental fat were reviewed (
). In contrast, we observed that PA-FA tended to increase milk yield and 3.5% FCM compared with PA-TG. These results are likely due to the increased DMI and FA digestibility for the PA-FA treatment, compared with PA-TG. This would also explain the differences we observed in BW gain between PA-FA (0.50 kg/d) compared with PA-TG (0.25 kg/d). As discussed by
, depending on the stage of lactation and energy balance, an increase in diet energy density via dietary FA supplements could increase milk production, milk fat yield, and body reserves as long as dietary FA supplements do not reduce DMI or negatively affect the digestibility of other nutrients.
Most of our short-term studies involving C16:0 supplements (fed at 1.5 to 2.0% diet DM) to mid-lactation cows have indicated increases in milk fat yield of ∼100 g/d (
Long-term palmitic acid supplementation interacts with parity in lactating dairy cows: production responses, nutrient digestibility, and energy partitioning.
observed that feeding a C16:0 supplement (1.5% diet DM) over a 10-wk period increased milk fat yield by ∼150 g/d. In our study, PA treatments increased milk fat content (+0.20 percentage points) and milk fat yield (+80 g/d) compared with CON, but the increase in milk fat yield tended to be greater for PA-FA than for PA-TG. When we calculated the FAYR based on FA intake, the results indicated a greater FA transfer for PA-FA than for PA-TG (18.4 and 23.8% for PA-TG and PA-FA, respectively). However, when we calculated FAYR based on absorbed FA, transfer efficiency was similar for both supplements (36.0 and 36.1% for PA-TG and PA-FA, respectively). Using duodenal infusions of C16:0,
reported an apparent FAYR of 46.7% for C16:0, whereas the transfer efficiency from diet to milk fat ranged from 16 to 24% in studies feeding C16:0-enriched supplements (
). Therefore, differences in milk fat responses between PA-FA and PA-TG are likely explained by differences in FA digestibility rather than the extraction and incorporation of these FA into milk fat.
The increase in milk fat associated with our PA treatments occurred due to an increase in the yield of 16-carbon milk FA. This finding agrees with several previous studies that fed C16:0 supplements (
suggested that an increase in the availability of C16:0 for lipid synthesis in mammary epithelial cells may increase the activity of glycerol-3-phosphate acyltransferase in the mammary gland, therefore increasing the proportion of C16:0 acylated at sn-1 at the expense of sn-2. Other FA would counterbalance the decrease in the amount of C16:0 at sn-2. This could explain why our PA treatments increased the yield of mixed-source FA without reducing the yield of de novo and preformed FA not only by increasing TG synthesis, but also by changing the FA interpositional distribution in the TG. Additionally, we observed that PA-TG increased the yield of preformed FA, compared with PA-FA, and this was mainly the result of increased cis-9 C18:1. Increased milk cis-9 C18:1 associated with C16:0 supplementation likely occurs to maintain milk fluidity (
In conclusion, feeding C16:0 supplements increased NDF digestibility, milk fat yield, 3.5% FCM, ECM, and feed efficiency of mid-lactation dairy cows. Also, the production responses of dairy cows to C16:0 tended to be greater for a FA compared with a TG supplement, which occurred due to the lower FA digestibility of PA-TG compared with PA-FA.
ACKNOWLEDGMENTS
We thank the Michigan Alliance for Animal Agriculture (East Lansing, MI) and Al Ames (NutriLinx LLC, Hardwick, VT) for financial support of this study. We acknowledge C. Preseault, Y. Sun, J. L. Garver, S. E. Schmidt, M. Western, K. Wu, K. Spaans, J. L. Spaans, and T. N. Bryant (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 PhD fellowship from Coordenação de Aperfoiçamento de Pessoal de Nivel Superior (CAPES) from the Brazilian Ministry of Education (Brasilia, DF, Brazil).
REFERENCES
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Effects of diet on short-term regulation of feed intake by lactating dairy cows.
Long-term palmitic acid supplementation interacts with parity in lactating dairy cows: production responses, nutrient digestibility, and energy partitioning.
Short communication: Comparison of a palmitic acid-enriched triglyceride supplement and calcium salts of palm fatty acids supplement on production responses of dairy cows.
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.
Effects of saturation and esterification of fat sources on site and extent of digestion in steers: Digestion of fatty acids, triglycerides, and energy.
Nutrient digestibility and milk production responses to increasing levels of palmitic acid supplementation vary in cows receiving diets with or without whole cottonseed.
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