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Feeding lower-protein diets based on red clover and grass or alfalfa and corn silage does not affect milk production but improves nitrogen use efficiency in dairy cows
Department of Agriculture and Environment, Harper Adams University, Newport, Shropshire, TF10 8NB, United KingdomDepartment of Biochemistry and Chemistry, Sylhet Agricultural University, Sylhet-3100, Bangladesh
Reducing the dietary crude protein (CP) concentration can decrease the financial cost and lower the environmental impact of milk production. Two studies were conducted to examine the effects of reducing the dietary CP concentration on animal performance, nutrient digestibility, milk fatty acid (FA) profile, and nitrogen use efficiency (NUE; milk N/N intake) in dairy cows fed legume silage-based diets. Thirty-six multiparous Holstein-Friesian dairy cows that were 76 ± 14 (mean ± SD) days in milk and 698 ± 54 kg body weight were used in a 3 × 3 Latin square design in each of 2 studies, with 3 periods of 28 d. In study 1, cows were fed diets based on a 50:50 ratio of red clover to grass silage [dry matter (DM) basis] containing 1 of 3 dietary CP concentrations: high (H) = 175 g of CP/kg of DM; medium (M) = 165 g of CP/kg of DM; or low (L) = 150 g of CP/kg of DM. In study 2, cows were fed 175 g of CP/kg of DM with a 50:50 ratio of alfalfa to corn silage (H50) or 1 of 2 diets containing 150 g of CP/kg of DM with either a 50:50 (L50) or a 60:40 (L60) ratio of alfalfa to corn silage. Cows in both studies were fed a total mixed ration with a forage-to-concentrate ratio of 52:48 (DM basis). All diets were formulated to meet the MP requirements, except L (95% of MP requirements). In study 1, cows fed L ate 1.6 kg of DM/d less than those fed H or M, but milk yield was similar across treatments. Mean milk protein, fat, and lactose concentrations were not affected by diet. However, the apparent total-tract nutrient digestibility was decreased in cows fed L. The NUE was 5.7 percentage units higher in cows fed L than H. Feeding L also decreased milk and plasma urea concentrations by 4.4 mg/dL and 0.78 mmol/L, respectively. We found no effect of dietary treatment on the milk saturated or monounsaturated FA proportion, but the proportion of polyunsaturated FA was increased, and milk odd- and branched-chain FA decreased in cows fed L compared with H. In study 2, DM intake was 2 kg/d lower in cows receiving L50 than H50. Increasing the alfalfa content and feeding a low-CP diet (L60) did not alter DMI but decreased milk yield and milk protein concentration by 2 kg/d and 0.6 g/kg, respectively, compared with H50. Likewise, milk protein and lactose yield were decreased by 0.08 kg/d in cows receiving L60 versus H50. Diet had no effect on apparent nutrient digestibility. Feeding the low-CP diets compared with H50 increased the apparent NUE by approximately 5 percentage units and decreased milk and plasma urea concentrations by 7.2 mg/dL and 1.43 mmol/L, respectively. Dietary treatment did not alter milk FA profile except cis-9,trans-11 conjugated linoleic acid, which was higher in milk from cows receiving L60 compared with H50. We concluded that reducing CP concentration to around 150 g/kg of DM in red clover and grass or alfalfa and corn silage-based diets increases the apparent NUE and has little effect on nutrient digestibility or milk performance in dairy cows.
The increasing global price of soybean meal in association with tighter regulations on the disposal of slurry and manure, and greater public scrutiny of the sustainability of dairy farming, has led to renewed interest in alternative strategies for feeding protein to dairy cows (
). Two obvious approaches are to increase the use of high-protein homegrown forage legumes and to reduce protein concentrations in the diet of dairy cows (
Alfalfa and red clover are the most popular forage legumes grown globally and are common in dairy cattle diets in North America and northern and western Europe (
). Both alfalfa and red clover silages contain CP levels of approximately 180 to 200 g/kg of DM under typical management conditions. In comparison, grass silage ranges from 100 to 160 and corn silage from 70 to 90 g of CP/kg of DM (
Performance and nutrient utilisation of dairy cows offered silages produced from three successive harvests of either a red clover–perennial ryegrass sward or a perennial ryegrass sward.
). Alfalfa and red clover can be grown in a range of soil types and weather conditions, and produce high DM yields without artificial N fertilizer input (
). Several studies have reported that the inclusion of up to 66% red clover or alfalfa silage in the forage component of dairy cow diets improved DMI, milk yield, and the content of PUFA in milk (
Replacement of grass and maize silages with lucerne silage: Effects on performance, milk fatty acid profile and digestibility in Holstein-Friesian dairy cows.
). The use of red clover compared with grass silage has also been reported to increase the efficiency of microbial protein (MCP) synthesis in the rumen and improve the omasal flow of AA (
Replacement of grass and maize silages with lucerne silage: Effects on performance, milk fatty acid profile and digestibility in Holstein-Friesian dairy cows.
The effect of varying proportion and chop length of lucerne silage in a maize silage-based total mixed ration on diet digestibility and milk yield in dairy cattle.
Feeding diets that are high in CP (>175 g CP/kg DM) can improve the supply of MP to the intestine, but high-CP diets typically result in low nitrogen use efficiency (NUE; milk N/N intake), with increased RDP leading to the production of excess ammonia in the rumen (
Despite the potential negative effects of low-CP diets on intake and performance, it has been reported that the CP concentration in dairy cow diets can be reduced to around 140 to 150 g/kg DM with no negative effects on dairy cow performance, health, or fertility if the diets are formulated appropriately to maximize MCP synthesis and supply sufficient MP (
). However, the effects of low-CP diets that are based on high inclusion rates of red clover or alfalfa silage are unclear. Most studies that have evaluated the inclusion of legume silages have fed CP concentrations of approximately 170 g/kg DM, and limited knowledge exists on the effects of reducing the dietary protein concentration in legume silage-based diets on milk performance and N utilization, particularly for red clover (
Effects of inclusion of whole-crop pea silages differing in their tannin content on the performance of dairy cows fed high or low protein concentrates.
). As a consequence, diets based on forage legume silages can be deficient in digestible undegradable protein or may be imbalanced in AA, which can lead to a reduced milk yield (
We hypothesized that feeding low-protein diets based on legume (red clover or alfalfa) silages or altering the inclusion rate of alfalfa in a low-CP diet of lactating cows would improve NUE without affecting milk performance if the MP supply was maintained. The objective of our 2 studies was to determine the effect of reducing dietary CP concentration in diets based on high-protein forage legumes. The first study (study 1) examined the effects of reducing dietary CP concentration in a red clover and grass silage-based diet on intake, milk performance, diet digestibility, and NUE in dairy cows. The second study (study 2) examined the effects of dietary CP concentration in diets with different proportions of alfalfa and corn silage.
MATERIALS AND METHODS
Animals and Housing
All procedures were performed in accordance with the United Kingdom Animals (Scientific Procedures) Act 1986 (amended 2012) and received local ethical approval (Harper Adams University, Newport, Shropshire, United Kingdom). Study 1 was conducted from October 2018 to January 2019, and study 2 from January to April 2019.
Study 1 used 18 multiparous lactating dairy cows producing (mean ± SD) 45.3 ± 5.72 kg of milk per day. Cows were 71 ± 14 DIM, with BW 690 ± 48 kg, and BCS 2.6 ± 0.31 (where 1 = emaciated and 5 = obese; scored to 0.25 units;
). Study 2 used a separate group of 18 Holstein-Friesian multiparous dairy cows, yielding 46.5 ± 4.78 kg of milk per day. These cows were 81 ± 13 DIM, with a mean BW of 705 ± 59 kg, and BCS of 2.6 ± 0.32. All cows were housed in the same area of an open span building fitted with freestalls and mattresses. Stalls were bedded twice weekly with sawdust and lime, with automatic scrapers that scraped the passageways at 6-h intervals. All cows had constant ad libitum access to fresh drinking water.
Experimental Design
Each study was a 3 × 3 Latin square design with 3 periods and 3 dietary treatments. Experimental periods were 28 d in duration, which included a 21-d adaptation to the diets and a 7-d sampling period. Cows were blocked by milk yield recorded in the week before the start of the study and DIM, and randomly assigned to 1 of 3 dietary treatments in each study. In study 1, the red clover and grass silage-based diets were formulated to supply 3 different concentrations of dietary CP: 175 (high, H), 165 (medium, M), or 150 (low, L) g CP/kg DM. In study 2, the treatment diets were formulated to contain 175 g CP/kg DM with a 50:50 ratio of alfalfa to corn silage (H50), 150 g CP/kg DM with 50:50 alfalfa to corn silage (L50), or 150 g CP/kg DM with 60:40 alfalfa to corn silage (L60).
Diets and Feeding
The animals were fed the diets as a TMR that was formulated to produce an average of 37 kg of milk per day according to
. All diets were formulated to be isoenergetic (ME basis) and to contain a similar MP content, except in study 1, where diet L was predicted to supply 95% of MP requirements. To maintain the MP supply, rumen-protected protein sources (xylose-treated soybean meal and heat-treated rapeseed meal) were used in the formulation of the low-CP diets (Table 1). The forage-to-concentrate ratios in both studies were maintained at 52:48 (DM basis).
Table 1Dietary ingredients and predicted chemical composition of diets based on red clover and grass silage or alfalfa and corn silage, fed to dairy cows in studies 1 and 2
Study 1 based on red clover and grass silage; H = high- (175 g CP/kg DM), M = medium- (165 g CP/kg DM), and L = low-CP diets (150 g CP/kg DM). Study 2 based on alfalfa and corn silage; H50 = 175 g CP/kg DM with 50:50 alfalfa to corn silage, L50 = 150 g CP/kg DM with 50:50 alfalfa to corn silage, and L60 = 150 g CP/kg DM with 60:40 alfalfa to corn silage.
Mineral and vitamin premix (KW Alternative Feeds), providing (g/kg) 220 calcium, 30 phosphorus, 80 magnesium, 80 sodium, (mg/kg) 760 copper, 30 selenium, 1,000,000 IU of vitamin A, 300,000 IU of vitamin D3, 3,000 IU of vitamin E, 2.5 mg/kg vitamin B12, 135 mg/kg biotin.
Predicted composition of diets were calculated using Feed Into Milk (Thomas, 2004). MPE = metabolizable protein-rumen energy limited; MPN = metabolizable protein-rumen nitrogen limited.
(g/kg DM)
Forage:concentrate (DM basis)
0.52
0.52
0.52
0.52
0.52
0.52
ME (MJ/kg DM)
11.9
11.9
11.9
12.0
11.9
11.8
CP
175
165
150
175
150
152
MPE
104
104
98
109
104
104
MPE (% of requirements)
100
100
95
105
100
100
MPN
118
115
106
121
104
104
MPN (% of requirements)
118
111
102
116
100
100
1 Study 1 based on red clover and grass silage; H = high- (175 g CP/kg DM), M = medium- (165 g CP/kg DM), and L = low-CP diets (150 g CP/kg DM). Study 2 based on alfalfa and corn silage; H50 = 175 g CP/kg DM with 50:50 alfalfa to corn silage, L50 = 150 g CP/kg DM with 50:50 alfalfa to corn silage, and L60 = 150 g CP/kg DM with 60:40 alfalfa to corn silage.
2 Xylose-treated soybean meal (KW Alternative Feeds).
3 Heat-treated rapeseed meal (SC Feeds).
4 Mineral and vitamin premix (KW Alternative Feeds), providing (g/kg) 220 calcium, 30 phosphorus, 80 magnesium, 80 sodium, (mg/kg) 760 copper, 30 selenium, 1,000,000 IU of vitamin A, 300,000 IU of vitamin D3, 3,000 IU of vitamin E, 2.5 mg/kg vitamin B12, 135 mg/kg biotin.
5 Predicted composition of diets were calculated using Feed Into Milk (
In study 1, the red clover was fed 50:50 (DM basis) with grass silage. First cuts of both red clover (Trifolium pratense) and grass silages (Lolium perenne) were mown at a leafy stage on May 23 and June 10, 2018, respectively, wilted for 24 h, harvested with a self-propelled, precision chop forage harvester (John Deere 7840i), and ensiled in separate concrete clamps with an additive (Axphast Gold; Biotal) applied at the rate of 2.0 L/t. In study 2, a primary growth of alfalfa (Medicago sativa) was mown at early bloom, wilted for 36 h, harvested using a self-propelled forage harvester on June 2, 2019, and ensiled in a concrete clamp with an additive added at the rate of 2.0 L/t (Axcool Gold, Biotal). The corn silage was harvested on October 26, 2019, using a self-propelled forage harvester and ensiled in a concrete clamp with an additive (Corncool Gold, Biotal) applied at the rate of 2 L/t. The alfalfa silage was fed 50:50 (DM basis) with corn silage in H50 and L50, and increased to 60:40 in L60, the maximum inclusion rate of alfalfa that still provided the same predicted MP supply.
In both studies, dietary ingredients were mixed daily for 10 min using a forage mixer (MixMax 10, Hi-Spec Engineering Limited) calibrated to ±1 kg and fed through roughage intake control feed bins (Insentec B.V.), fitted with automatic animal identification and weighing system calibrated to ±0.1 kg, with a cow per feed bin ratio of 1.2. Fresh feed was delivered once daily at approximately 0800 h at the rate of 1.05 of the previously recorded intakes, with intake calculated daily and refusals collected 3 times weekly before feeding.
Experimental Routine
Forage samples were collected twice weekly and dried in a forced-air oven at 105°C, and the ratio of the forages was adjusted to the desired value. Fresh forages and TMR were sampled daily during the final week of each period, stored at −20°C, and pooled within period before subsequent analyses. Additional TMR samples were collected at 0, 4, 8, and 24 h after feeding and fresh forage at approximately 1000 h on d 22 to 24 of each period for the determination of particle size (PS) distribution. All TMR and forage samples were separated into 6 fractions using a modified Penn State Particle Separator, as described by
Cows were milked twice daily at approximately 0600 and 1600 h in a 40-point internal rotary parlor (GEA AutoRotor Magnum 40). During the final week of each period, milk yield was recorded at each milking, and 4 samples were collected at 2 consecutive morning and evening milkings for subsequent analyses of milk composition. Body weight and BCS were recorded following the afternoon milking at the start of the first experimental period, and then at the end of periods 1, 2, and 3.
In studies 1 and 2, fecal grab samples (approximately 350 g/d per cow) were collected during the final week of each study period from 4 representative cows per treatment at 1000 and 1600 h for 5 consecutive days, and stored at −20°C for subsequent analyses. Blood samples were collected by jugular venipuncture during the final week of each study period from 4 representative cows per treatment into heparinized and fluoride oxalate tubes (Becton Dickinson and Company) over 2 consecutive days at 0800, 0900, 1100, and 1300 h. The samples were centrifuged at 1,600 × g for 15 min at 4°C to separate the plasma. Plasma derived from heparinized tubes was immediately analyzed for ammonia, with further subsamples stored at −20°C for subsequent analysis of urea and BHB, whereas glucose was analyzed using plasma obtained from fluoride oxalate tubes.
In Situ Degradability of the Forages
Three nonlactating Holstein-Friesian cows with a mean BW of 650 ± 28 kg that had previously been fitted with a rumen cannula 10 cm in diameter (Bar Diamond) were housed in a straw-bedded yard and fed a basal ration at maintenance level (
). The ration contained (g/kg, DM basis) 264 alfalfa silage, 176 corn silage, 354 chopped wheat straw, 86 Spey syrup (Trident, AB Agri Ltd.), 32 rapeseed meal, 32 wheat distillers dark grains, 14 soybean meal, 9 palm kernel meal, 3 molasses, 12 magnesium chloride, 12 dry cow minerals, 4 g/kg Provimi LiFT (a package of vitamins and cofactors), and 2 g/kg DM of Vistacell Ultra (a live yeast; AB Vista). Dietary ingredients were mixed with the same forage mixer as the cows in the performance study, and diet was offered daily at 0800 h through individual feed bins (American Calan). All cows had continuous access to fresh drinking water.
The in situ degradability of the silages used in both studies was determined following the method reported by
. In situ nylon bags (Sericol) with a pore size of 42 µm were filled with 8 ± 0.1 g of fresh forage and placed in the rumen of each cow in duplicate 30 min after feeding, and recovered after 4, 8, 16, 24, 48, and 96 h. Following ruminal incubation, the bags were immediately placed in cold water to inhibit further microbial degradation and rinsed for 10 min in the cold rinse cycle of an automatic washing machine (model WAK24210GC, Bosch). For each forage, 0-h time points were also determined using samples without ruminal incubation. All bags were then dried for 48 h in a forced-air oven at 60°C, and the duplicates of the same sample dried residues composited within time point and animal and analyzed for total N.
Chemical Analyses
Subsamples of forage and TMR were bulked by period and dried for 48 h in a forced-air oven at 60°C and analyzed for DM according to
; 934.01, intra-assay CV of 1.18%). Dried feed samples were then ground in a Wiley mill (Thomas Scientific) through a 1.0-mm sieve before analyses for ash (942.05), CP (988.05), and ether extract (920.39), with intra-assay CV of 0.53, 0.80, and 7.52%, respectively (
using heat stable α-amylase for NDF analysis (Sigma; intra-assay CV of 1.87 and 1.05% for NDF and ADF, respectively). Forage ammonia-N and pH were determined using fresh samples following the method of
. Fresh forage samples were also analyzed for their content of lactate, ethanol, acetate, propionate, isobutyrate, and butyrate by Sciantec Analytical (Stockbridge Technology Centre, North Yorkshire, UK) using a water extraction technique followed by high-performance liquid and gas-liquid chromatography.
Milk samples were analyzed for fat, total protein, lactose, and urea by the near-mid-infrared method at National Milk Laboratories (Wolverhampton, UK). Fatty acids in milk were analyzed by extracting milk fat by centrifugation and methylation using sodium methoxide, according to the method of
. The individual milk and feed FAME was determined by gas-liquid chromatography (Hewlett Packard 6890), fitted with a CP-Sil 88 column (100 m × 0.25-mm i.d. × 0.20-um film, Agilent Technologies) as described by
. A mixed reference standard (Sigma-Aldrich) was routinely run, and individual FA calculated.
Fecal samples were composited by cow and period, and dried in a forced-air oven at 60°C until constant weight. The dried fecal samples were then milled (1 mm) using a Cuisinart electric grinder (SG20U) and analyzed for acid-insoluble ash, total N, NDF, ADF, and ash. Blood plasma samples were analyzed for ammonia BHB, glucose, and urea (Randox Laboratories; kit catalog no. AM 1015, RB 1008, GL 1611, and UR 221, respectively, with intra-assay CV of 9.61, 5.94, 1.08, and 5.12%, respectively) using a Cobas Miras Plus Autoanalyzer (ABX Diagnostics).
Calculations
Dry matter intake was calculated from the recorded daily fresh feed intake for each cow and the analyzed DM content of the TMR. Fecal DM output, digested nutrients, and apparent total-tract digestibility coefficients of DM, OM, N, NDF, and ADF were determined using acid-insoluble ash as an internal marker, as per the method of
. The 4% FCM yield was determined by adjusting the milk yield to 40 g of fat per kilogram of milk (4% FCM yield = milk yield × fat %/4), and ECM was computed as (3.14 MJ/kg) = milk yield × [383 × fat (g/kg) × 100 + 242 × protein (g/kg) × 100 + 165.4 × lactose (g/kg) × 100 + 207]/3,140 (
Gaillon P. Chabert Y. A Nordic Proposal for an Energy Corrected Milk (ECM) Formula. Paris, France. EAAP publication 50. Centre for Agricultural Publishing and Documentation (PUDOC),
1991
). Apparent NUE was calculated as milk N/dietary total N intake, with the N secreted in milk determined as total milk protein/6.38. The forage and TMR PS geometric mean (Xm) and standard deviation of Xm were determined using the equations by
where p is the disappearance percentage at t time, a is the immediately soluble fraction, b is the potentially degradable fraction, c is the degradation rate (per hour) of b, and t is the incubation period (h). The effective ruminal degradability (ED) was computed using an 8% per hour rumen passage rate (k) as follows:
ED = a + b [c/(c + k)].
Statistical Analysis
Data from each study were analyzed by ANOVA as a row and column design (
), using GenStat 18th edition (VSN International Ltd.), with diet and period as fixed effects and cow as random effect. All data were checked for normality using descriptive statistics before running the ANOVA model in GenStat. The model used was
Yijk = μ + Di + Pj + Ak + Eijk,
where Yijk and μ represent the dependent variable and total mean, and Di, Pj, Ak, and Eijk as the diet, period, animal, and residual error, respectively. Plasma metabolites and particle fractions were analyzed as repeated-measures ANOVA that included the fixed effect of sampling time in the model, and interactions between diet and sampling time were also assessed. Tukey's test was conducted post hoc to determine treatment means that differed. Results are presented as the least squares means of each treatment and standard error of the mean. Effects were considered significant when P < 0.05, and a tendency was considered when P < 0.10.
RESULTS
Forage and Diet Characteristics
Study 1
We observed that the red clover silage contained a higher DM content than the grass silage but was lower in NDF and total fat (Table 2). Both forages had CP contents above 160 g/kg DM, with the concentration in the red clover being 11 g/kg DM higher than the grass silage. The lactate and acetate contents of the red clover silage were 26.0 and 16.3 g/kg DM lower, respectively, than the grass silage, and the concentrations of ammonia-N were similar in both forages. Both silages also had a similar long-chain PUFA content, with the content of C18:3 cis-9,cis-12,cis-15 in the grass silage being 3.88 g of FA/kg of DM higher than the red clover silage. The Xm of the PS of the grass silage was higher than the red clover silage. Similarly, the fractions of peNDF>4mm and peNDF>8mm were higher in grass silage than in the red clover silage. The DM, OM, NDF, ADF, and ether extract concentrations of the 3 TMR were similar, whereas the CP concentration was higher in H than M or L (Table 3). The total FA content in H was 1.9 g of FA/kg of DM higher than the other diets. The mean Xm, physical effectiveness factor (pef)>4mm, and peNDF>4mm were similar for all 3 diets, but we found a tendency for an interaction (P = 0.06) between diet and sampling time for pef>8mm (Supplemental Table S1, https://doi.org/10.6084/m9.figshare.21878619,
), which was lower at 4 h after the morning feed for diet H, but at 24 h postfeeding was higher in H compared with the other 2 diets.
Table 2Nutrient composition (g/kg DM), fermentation profile, fatty acid content, and particle size distribution of red clover, grass silage, alfalfa silage, and corn silage fed to dairy cows in studies 1 and 2
Table 3Nutrient composition (g/kg DM), fatty acid content, and particle size distribution of diets based on red clover and grass silage or alfalfa and corn silage, fed to dairy cows in studies 1 and 2
Study 1 based on red clover and grass silage; H = high- (175 g CP/kg DM), M = medium- (165 g CP/kg DM), and L = low-CP diets (150 g CP/kg DM). Study 2 based on alfalfa and corn silage; H50 = 175 g CP/kg DM with 50:50 alfalfa to corn silage, L50 = 150 g CP/kg DM with 50:50 alfalfa to corn silage, and L60 = 150 g CP/kg DM with 60:40 alfalfa to corn silage.
Fraction of the diets at 0 h postfeeding; Xm = geometric mean particle size; SDgm = SD of Xm; pef = physical effectiveness factor; peNDF = physically effective fiber.
(% DM)
>44 (mm)
0.00
0.00
0.00
0.00
0.00
0.00
33 to 44 (mm)
2.84
2.49
2.58
1.06
0.78
0.98
19 to 32.9 (mm)
16.0
15.3
14.4
15.8
15.6
17.0
8 to 19 (mm)
45.3
44.8
45.5
45.3
47.8
45.4
4 to 8 (mm)
10.2
9.31
9.94
12.7
13.0
12.9
<4 (mm)
25.7
28.1
27.5
25.2
22.8
23.7
Xm (mm)
12.7
12.3
12.3
12.4
12.7
12.7
SDgm
2.19
2.21
2.19
2.14
2.09
2.13
pef>4 (%)
74.3
71.9
72.5
74.8
77.2
76.3
pef>8 (%)
64.1
62.6
62.5
62.1
64.2
63.4
peNDF>4 (%)
28.4
27.6
27.2
26.0
27.4
27.2
peNDF>8 (%)
24.5
24.1
23.5
21.6
22.8
22.6
1 Study 1 based on red clover and grass silage; H = high- (175 g CP/kg DM), M = medium- (165 g CP/kg DM), and L = low-CP diets (150 g CP/kg DM). Study 2 based on alfalfa and corn silage; H50 = 175 g CP/kg DM with 50:50 alfalfa to corn silage, L50 = 150 g CP/kg DM with 50:50 alfalfa to corn silage, and L60 = 150 g CP/kg DM with 60:40 alfalfa to corn silage.
2 EE = ether extract.
3 Fraction of the diets at 0 h postfeeding; Xm = geometric mean particle size; SDgm = SD of Xm; pef = physical effectiveness factor; peNDF = physically effective fiber.
Our alfalfa silage was lower in DM and OM and higher in NDF and ADF than the corn silage (Table 2). We observed that the CP concentration of the alfalfa silage was nearly twice that of the corn silage. In contrast, the ammonia-N content of our corn silage was 10.4 g/kg of total N higher than the alfalfa silage, and the pH of the alfalfa silage was 0.55 pH units lower. The lactate content of the alfalfa silage was 43.4 g/kg of DM higher than the corn silage, and the content of acetate was 9.4 g/kg of DM lower. We further found that the long-chain PUFA content was higher in the corn silage, with the concentration of C18:2 cis-9,cis-12 being 8.22 g of FA/kg of DM higher than the alfalfa silage. In contrast, the C18:3 cis-9,cis-12,cis-15 content of the corn silage was 4.32 g of FA/kg of DM lower than the alfalfa silage. We observed that the Xm of the PS of our alfalfa silage was higher than that of our corn silage. The DM, OM, NDF, ADF, and ether extract concentrations of the 3 TMR were similar, whereas the CP concentration varied across the treatments (Table 3). The total FA content in H50 was 1.8 g of FA/kg of DM higher than the other 2 diets. We found a tendency (P < 0.10) for the mean Xm, pef, and peNDF to be numerically higher in L50 or L60 compared with H50 (Supplemental Table S2, https://doi.org/10.6084/m9.figshare.21878619,
). In contrast, we found a tendency (P = 0.061) for a higher mean small PS fraction (<4 mm) in H50 compared with L50 or L60, whereas sampling time post-feeding did not affect the mean PS fractions of the diet except for the medium-length (8–19 mm) fraction, which increased (P = 0.050) until 8 h after feeding.
In Situ Forage Degradability
Study 1
We found a tendency for a higher (P = 0.094) soluble fraction (a) of DM in the red clover compared with the grass silage (Table 4). In contrast, the red clover silage had a lower (P = 0.014) potentially degradable DM fraction (b) compared with the grass silage. However, we observed no effect (P > 0.05) of forage on the extent of degradation (a + b) or the rate (c) of the potentially degradable fraction of DM. The ED of DM was 7.12% higher (P = 0.030) in the red clover compared with the grass silage. The soluble fraction of the CP was 101 g/kg of DM higher (P = 0.011) in the grass silage compared with the red clover. In contrast, the potentially degradable fraction of CP was 109 g/kg of DM higher (P = 0.004) than the grass silage. However, we found no effect (P > 0.05) of forage on the extent of degradation or the rate of the potentially degradable fraction of CP, whereas the ED of the CP was 4.5% lower (P = 0.008) in the red clover than the grass silage.
Table 4In situ DM and CP degradability coefficients of red clover, grass silage, alfalfa silage, and corn silage fed to dairy cows in studies 1 and 2
a = soluble fraction; b = potentially rumen-degradable fraction; c = degradation rate of fraction b per hour; ED = effective rumen degradability at 8%/h rumen passage rate.
Study 1
Study 2
Red clover silage
Grass silage
SEM
P-value
Alfalfa silage
Corn silage
SEM
P-value
DM degradation coefficient (g/kg DM)
a
278
246
1.1
0.094
200
406
0.1
<0.001
b
565
611
0.8
0.014
580
457
1.2
0.002
a+b
844
857
0.5
0.124
779
863
0.6
<0.001
c
0.08
0.07
0.007
0.243
0.09
0.06
0.005
0.028
ED
557
520
0.8
0.030
498
608
0.6
<0.001
CP degradation coefficient (g/kg total N)
a
323
424
1.6
0.011
428
538
1.1
0.002
b
549
440
1.3
0.004
422
272
1.1
<0.001
a+b
872
864
0.5
0.318
850
810
0.5
0.004
c
0.10
0.09
0.009
0.416
0.11
0.08
0.008
0.045
ED
627
655
0.4
0.008
672
673
0.3
0.843
1 a = soluble fraction; b = potentially rumen-degradable fraction; c = degradation rate of fraction b per hour; ED = effective rumen degradability at 8%/h rumen passage rate.
Our corn silage had a higher (P < 0.05) soluble fraction of DM compared with the alfalfa silage (Table 4). In contrast, the potentially degradable fraction of the DM was 123 g/kg of DM higher (P < 0.05) in the alfalfa compared with the corn silage. Likewise, the rate of degradation of the potentially degradable fraction of DM was higher (P < 0.05) in the alfalfa compared with the corn silage. We observed a difference in the ED of the DM, which was 22.1% higher (P < 0.001) in the corn than the alfalfa silage. The corn silage also had a higher (P < 0.05) soluble fraction of CP compared with the alfalfa silage. In contrast, the potentially degradable fraction of CP was 150 g of CP/kg of DM higher (P < 0.05) in the alfalfa compared with the corn silage. Similarly, the rate of degradation of the potentially degradable fraction of CP was higher (P < 0.05) in the alfalfa compared with the corn silage. However, the ED of the CP was comparable for both forages.
Feed Intake and Animal Performance
Study 1
The DMI was 1.6 kg/d lower (P = 0.001) in cows receiving L than H or M (Table 5). However, diet had no effect on milk yield, ECM yield, or FCM yield, with means of 34.8, 34.9, and 36.7 kg/d, respectively. Similarly, diet did not (P > 0.05) affect milk protein, fat, or lactose contents. In contrast, the milk urea concentration was 4.4 mg/dL lower (P = 0.018) in cows receiving L than H, with those fed M having an intermediate value. Feed efficiency was 0.1 kg/kg of DM higher (P < 0.05) in cows fed L compared with M, with those receiving H having an intermediate value. Dietary treatment did not affect (P > 0.05) mean BW or BCS, although BCS change was numerically lower in cows fed L compared with M or H.
Table 5Intake, milk performance, BW, and body condition of dairy cows fed diets based on red clover and grass silage or alfalfa and corn silage in studies 1 and 2
Study 1 based on red clover and grass silage; H = high- (175 g CP/kg DM), M = medium- (165 g CP/kg DM), and L = low-CP diets (150 g CP/kg DM). Study 2 based on alfalfa and corn silage; H50 = 175 g CP/kg DM with 50:50 alfalfa to corn silage, L50 = 150 g CP/kg DM with 50:50 alfalfa to corn silage, and L60 = 150 g CP/kg DM with 60:40 alfalfa to corn silage.
a,b Means within a row within a study with different superscripts differ (P < 0.05).
1 Study 1 based on red clover and grass silage; H = high- (175 g CP/kg DM), M = medium- (165 g CP/kg DM), and L = low-CP diets (150 g CP/kg DM). Study 2 based on alfalfa and corn silage; H50 = 175 g CP/kg DM with 50:50 alfalfa to corn silage, L50 = 150 g CP/kg DM with 50:50 alfalfa to corn silage, and L60 = 150 g CP/kg DM with 60:40 alfalfa to corn silage.
The DMI of cows receiving L50 was 2 kg/d lower (P = 0.019) than when receiving H50 (Table 5). Milk yield was 2 kg/d lower (P = 0.010) in cows receiving L60 compared with H50, but we found no difference (P > 0.05) in ECM or FCM yield between treatments. Diet also had no effect (P > 0.05) on milk fat or lactose contents. In contrast, milk protein concentration was 0.6 g/kg lower (P = 0.024) in cows receiving L60 than H50. We also observed that cows fed L60 had lower (P < 0.05) milk protein and lactose yields compared with those fed H50. The concentration of milk urea was 7.2 mg/dL higher (P < 0.001) in cows fed H50 compared with those fed L50 or L60. Feed efficiency was comparable across all 3 treatments. We found no effect (P > 0.05) of diet on mean BW or BCS, but we found a tendency (P = 0.070) for BW gain to be higher in cows receiving H50 than L50.
Nutrient Intake and Apparent Total-Tract Digestibility
Study 1
We observed that DM, OM, N, and NDF intakes were lower (P < 0.05) in cows receiving L compared with H or M (Table 6). In contrast, the fecal outputs of DM, OM, and ADF were higher (P < 0.05) in cows fed L compared with those receiving H, whereas cows receiving L had a lower (P < 0.05) amount digested and a lower digestibility of DM, OM, N, NDF, and ADF compared with those fed either of the other 2 diets. In general, we found that the total-tract digestibility in cows receiving H or M was comparable, although total N digested was lower (P < 0.001) in animals when fed diet M compared with H. As a proportion of total N intake, N output in feces was 11 percentage units higher (P = 0.001) in cows fed L at 45.1% than those fed H or M. The NUE was approximately 5 percentage units higher in cows fed L than H or M.
Table 6Intake, output, and apparent total-tract digestibility (kg/d) of nutrients and nitrogen partitioning (%) in dairy cows fed diets based on red clover and grass silage or alfalfa and corn silage in studies 1 and 2
Study 1 based on red clover and grass silage; H = high- (175 g CP/kg DM), M = medium- (165 g CP/kg DM), and L = low-CP diets (150 g CP/kg DM). Study 2 based on alfalfa and corn silage; H50 = 175 g CP/kg DM with 50:50 alfalfa to corn silage, L50 = 150 g CP/kg DM with 50:50 alfalfa to corn silage, and L60 = 150 g CP/kg DM with 60:40 alfalfa to corn silage. Measured using 12 cows for each study (4 cows for each treatment group).
Means within a row within a study with different superscripts differ (P < 0.05).
0.77
<0.001
a,b Means within a row within a study with different superscripts differ (P < 0.05).
1 Study 1 based on red clover and grass silage; H = high- (175 g CP/kg DM), M = medium- (165 g CP/kg DM), and L = low-CP diets (150 g CP/kg DM). Study 2 based on alfalfa and corn silage; H50 = 175 g CP/kg DM with 50:50 alfalfa to corn silage, L50 = 150 g CP/kg DM with 50:50 alfalfa to corn silage, and L60 = 150 g CP/kg DM with 60:40 alfalfa to corn silage. Measured using 12 cows for each study (4 cows for each treatment group).
2 NUE = apparent nitrogen use efficiency (milk N/N intake).
The intakes of DM, OM, N, and NDF were lower (P < 0.05) in cows fed L50 compared with H50, with those fed L60 being intermediate, except for total N intake, which was similar in cows fed L50 or L60 at 0.59 kg/d (Table 6). We observed that the amounts of DM and OM digested were higher (P < 0.05) in cows fed H50 compared with L50, with those receiving L60 having intermediate values. Similarly, the amount of N digested was 0.14 kg/d higher (P < 0.001) in cows receiving H50 than L50 or L60. However, we found that dietary treatment had no effect (P > 0.05) on apparent whole-tract digestibility of DM, OM, N, NDF, or ADF.
Milk N output was higher (P = 0.011) in cows receiving H50 compared with L60, but, as a proportion of total N intake, we found no effect (P > 0.05) of diet on fecal N output. In contrast, the apparent NUE was approximately 5 percentage units higher (P < 0.001) in cows receiving L50 or L60 compared with H50.
Blood Plasma Metabolites
Study 1
Dietary treatment had no effect (P > 0.05) on the concentrations of plasma ammonia, glucose, or BHB (Table 7). In contrast, mean plasma urea concentration was lower (P = 0.011) in cows receiving L, but similar in those receiving H or M, and increased with time after feeding (Figure 1a).
Table 7Plasma ammonia, BHB, and glucose concentrations in dairy cows fed diets based on red clover and grass silage or alfalfa and corn silage in studies 1 and 2
Study 1 based on red clover and grass silage; H = high- (175 g CP/kg DM), M = medium- (165 g CP/kg DM), and L = low-CP diets (150 g CP/kg DM). Study 2 based on alfalfa and corn silage; H50 = 175 g CP/kg DM with 50:50 alfalfa to corn silage, L50 = 150 g CP/kg DM with 50:50 alfalfa to corn silage, and L60 = 150 g CP/kg DM with 60:40 alfalfa to corn silage. D = main effect of diet; T = main effect of time; Int. = interaction between diet and time.
Item
Study 1
Study 2
H
M
L
SEM
P-value
H50
L50
L60
SEM
P-value
D
T
Int
D
T
Int
Ammonia (μmol/L)
35.2
35.6
34.4
2.36
0.690
<0.001
0.768
40.2
41.4
41.7
4.75
0.720
0.004
0.972
BHB (mmol/L)
0.76
0.73
0.79
0.065
0.630
<0.001
0.856
0.49
0.49
0.53
0.046
0.640
<0.001
0.087
Glucose (mmol/L)
3.72
3.67
3.68
0.108
0.832
<0.001
0.492
3.63
3.61
3.61
0.068
0.952
<0.001
0.505
1 Study 1 based on red clover and grass silage; H = high- (175 g CP/kg DM), M = medium- (165 g CP/kg DM), and L = low-CP diets (150 g CP/kg DM). Study 2 based on alfalfa and corn silage; H50 = 175 g CP/kg DM with 50:50 alfalfa to corn silage, L50 = 150 g CP/kg DM with 50:50 alfalfa to corn silage, and L60 = 150 g CP/kg DM with 60:40 alfalfa to corn silage. D = main effect of diet; T = main effect of time; Int. = interaction between diet and time.
Figure 1Plasma urea concentration in dairy cows fed a high- (H, ♦), medium- (M, ▪), or low-CP (L, ▴) diet based on red clover and grass silage (study 1, a), a high-CP diet with 50:50 ratio of alfalfa to corn silage (H50, ♦), or a low-CP diet with either a 50:50 (L50, ▪) or 60:40 (L60, ▴) ratio of alfalfa to corn silage (study 2, b). For study 1: pooled SEM = 0.276; diet, P = 0.011; time, P = 0.006; and diet × time, P = 0.598. For study 2; pooled SEM = 0.326; diet, P < 0.001; time, P < 0.001; and diet × time, P = 0.781. The arrow indicates the time of feeding. Error bars indicate SEM.
Dietary treatment did not affect (P > 0.05) plasma ammonia, glucose, or BHB concentrations (Table 7). In contrast, plasma urea concentration was higher (P < 0.001) in cows fed H50 compared with L50 or L60, and increased immediately after feeding (Figure 1b).
Milk Fatty Acid Profile
Study 1
The highest milk fat proportions of C8:0, C11:0, C12:0, C15:0, C15:1 cis-10, and C16:1 were observed in cows fed H, and lowest among those fed M (P < 0.05), except for C15:0 and C15:1 cis-10, which were lowest in milk from cows fed L (Table 8). In contrast, the milk fat proportion of C18:2 cis-9,cis-12 was higher (P = 0.002) in cows receiving L or M than H. Milk fat proportion of C18:1 trans-9 was higher (P < 0.05) in cows when fed M than L, whereas C18:1 trans-12 was higher in those fed L than H. We found that diet had no effect (P > 0.05) of diet on milk FA of chain length >C16:0 or C16:0 + 16:1, but those <C16:0 were higher (P = 0.040) in cows fed H compared with M. Also, dietary treatment did not affect the total milk fat proportions of SFA or MUFA, but the PUFA proportion was higher (P = 0.017) in cows receiving L than H. The total proportions of milk fat linear odd-chain FA or odd- and branched-chain FA (OBCFA) were higher (P < 0.05) in cows fed H compared with L.
Table 8Milk fatty acid composition of dairy cows fed diets based on red clover and grass silage or alfalfa and corn silage in studies 1 and 2
Study 1 based on red clover and grass silage; H = high- (175 g CP/kg DM), M = medium- (165 g CP/kg DM), and L = low-CP diets (150 g CP/kg DM). Study 2 based on alfalfa and corn silage; H50 = 175 g CP/kg DM with 50:50 alfalfa to corn silage, L50 = 150 g CP/kg DM with 50:50 alfalfa to corn silage, and L60 = 150 g CP/kg DM with 60:40 alfalfa to corn silage.
Means within a row within a study with different superscripts differ (P < 0.05).
0.023
0.001
2.44
2.27
2.43
0.081
0.259
a,b Means within a row within a study with different superscripts differ (P < 0.05).
1 Study 1 based on red clover and grass silage; H = high- (175 g CP/kg DM), M = medium- (165 g CP/kg DM), and L = low-CP diets (150 g CP/kg DM). Study 2 based on alfalfa and corn silage; H50 = 175 g CP/kg DM with 50:50 alfalfa to corn silage, L50 = 150 g CP/kg DM with 50:50 alfalfa to corn silage, and L60 = 150 g CP/kg DM with 60:40 alfalfa to corn silage.
Diet had no effect on the milk FA profile except for CLA cis-9,trans-11, which was higher (P = 0.019) in cows when receiving L60 compared with H50, and intermediate in those fed L50 (Table 8). Similarly, we found that CLA trans-10,cis-12 tended (P = 0.071) to be higher in cows receiving L60 compared with those fed H50. Diet had no effect on the milk FA proportion of chain length higher or lower than C16:0, and C16:0 + 16:1. Similarly, we found no effect of dietary treatment on the total milk fat proportions of SFA, MUFA, PUFA, linear odd-chain FA, or OBCFA.
DISCUSSION
Feed Characteristics and Particle Size Distribution
The chemical compositions of the forages used in both of our studies were comparable to previous work by
Replacement of grass and maize silages with lucerne silage: Effects on performance, milk fatty acid profile and digestibility in Holstein-Friesian dairy cows.
, the grass silage had the highest concentration of NDF, although the content of CP was marginally lower than that of the red clover or alfalfa silage.
also reported that grass silage usually contains less CP but more fiber than legume forages, although factors such as variety, fertilizer application rate, and stage of maturity at harvest can all influence the content. According to
, red clover silage contains 20 g/kg of DM less CP than alfalfa silage when harvested at a similar growth stage or NDF content. However, in our studies the CP content of red clover silage was only 10 g/kg of DM lower than the alfalfa silage. The higher pH of red clover and alfalfa silages compared with grass or corn silage is a common feature for legume forages due to their higher CP and ash content, and reflects a high buffering capacity with a low concentration of soluble CP (
Replacement of grass and maize silages with lucerne silage: Effects on performance, milk fatty acid profile and digestibility in Holstein-Friesian dairy cows.
also noted a higher concentration of lactate and acetate in red clover than grass or corn silage. The PS distributions of our grass and corn silages were similar to that reported by
except for the long PS (mainly >44 mm), which was not found in our current study. The mean Xm and peNDF were highest in our alfalfa and grass silages, respectively, primarily due to the greater content of the long-PS (19 to 32.9 mm) fraction of our alfalfa silage and the higher NDF content of our grass silage.
The nutrient composition of the TMR was similar in both of our studies except for CP, as we predicted, although we found a tendency for an interaction for pef>8mm in our study 1, which indicated that eating behavior differed between the dietary treatments (
). The observation that the mean pef>8mm was lowest at 4 h and highest at 24 h after the morning feed for diet H in study 1 could be attributable to an increase in the consumption of large PS (>8 mm) during the first 4 h and short PS (<8 mm) between 4 and 24 h after feeding. In study 2, a numerically higher proportion of small-PS (<4 mm) and lower content of medium-PS (8–19 mm) fractions was the major factor causing the higher Xm, pef, and peNDF in H50 than the other 2 diets. Moreover, the consumption of medium (8–19 mm) fractions by our cows was lower during the first 8 h following the morning feeding in study 2, mainly due to the preference for a short PS (
The effect of bale density and addition of formic acid on the in situ dry matter and crude protein degradation of lucerne, red clover and red fescue silages.
, who examined the soluble fractions of different legumes and grass silages. Red clover silage has a higher concentration of potentially degradable CP compared with grass or other non-legume silages, as reported in a series of other studies (
The effect of bale density and addition of formic acid on the in situ dry matter and crude protein degradation of lucerne, red clover and red fescue silages.
) have shown that red clover silage has a greater content of ED of CP than grass silage, with the higher content of NPN relative to neutral detergent insoluble CP being responsible for a rapid ruminal degradation of legume forage proteins. In contrast, red clover had a slightly higher ED of the DM compared with grass silage and therefore would be predicted to supply more rumen available energy for microbial growth (
The contents of the immediately soluble fractions of DM and CP were lower in our alfalfa silage, but the potentially degradable fractions and the rates of degradation for DM and CP were higher than corn silage, a finding in accordance with
. In comparison to alfalfa silage, red clover silage had a lower ruminal degradability of CP in our studies. This may be attributable to the presence of o-quinones that are synthesized by the enzyme PPO present in red clover, reducing protein degradation by creating a cross-linked complex with soluble and other dietary proteins inhibiting the function of proteases (
Our cows had a reduced DMI in both studies when the dietary CP concentration was decreased from 175 to 150 g/kg of DM, a finding consistent with other studies (
reported that the DMI responds negatively when the concentration of dietary CP decreased between 220 to 140 g/kg of DM. The reduced DMI in cows fed diet L (study 1) or L50 (study 2) could be related to a lower supply of available N in the rumen, which depressed the activity of fiber-degrading bacteria, resulting in a lower intake. However, plasma urea concentrations in both of our studies were within the range generally considered to indicate that ruminal N supply was not limiting (
noted that dietary CP concentration ranging from 135 to 194 g of CP/kg of DM had no effect on DMI in Holstein dairy cows fed alfalfa and corn silage-based rations. Increasing the inclusion rate of alfalfa silage from 50 to 60% in our study 2 did not affect the DMI of the cows (L60), supporting the findings of
Performance, digestion, nitrogen balance, and emission of manure ammonia, enteric methane, and carbon dioxide in lactating cows fed diets with varying alfalfa silage-to-corn silage ratios.
Replacement of grass and maize silages with lucerne silage: Effects on performance, milk fatty acid profile and digestibility in Holstein-Friesian dairy cows.
reported that decreasing the concentration of dietary CP from 165 to 145 g/kg of DM (resulting in a 5 to 10% deficiency in MP supply) reduced milk yield by approximately 4.3 kg/d when cows were fed a 1:2 (DM basis) alfalfa haylage and corn silage-based ration. In contrast, feeding a low-CP diet had no effect on milk yield or composition in our studies, supporting the findings of
, who also reported that feeding a low-CP (144 g of CP/kg of DM) alfalfa and corn silage-based diet (48:52 ratio, DM basis) had no effect on milk performance. We predicted that the supply of MP was similar across all the diets, which would be anticipated to result in a similar level of performance, irrespective of dietary CP content (
). The exception was diet L in study 1, which was predicted to supply 95% of MP requirements, principally due to the high CP content of the grass silage and the subsequent difficulty in formulating a low-CP diet while providing sufficient supplementary RUP to meet the MP requirements. Despite this, performance was similar to animals fed H or M, which may possibly be attributable to inaccuracies in the prediction of MP requirements or to a greater mobilization of body tissues to meet nutrient demand. Body weight change did not, however, differ between treatments in our study 1, although the short-term changeover study design that we used may not have permitted an accurate assessment, and longer-term studies are required.
Milk yield and milk protein concentration have been found to be reduced when dairy cows were fed a high compared with a low proportion of alfalfa-based diet (75:25 vs. 25:75 alfalfa to corn silage ratio;
The effect of varying proportion and chop length of lucerne silage in a maize silage-based total mixed ration on diet digestibility and milk yield in dairy cattle.
), which supports our findings in study 2. The decrease in milk yield and milk protein content with increasing alfalfa proportion might have been due to the ME density of the alfalfa silage, which may have led to a lower supply of rumen available energy and subsequent MCP flow to the duodenum. However, several studies have reported that the replacement of corn with alfalfa silage has little consistent effect on milk yield or composition (
Replacing alfalfa silage with corn silage in dairy cow diets: Effects on enteric methane production, ruminal fermentation, digestion, N balance, and milk production.
Performance, digestion, nitrogen balance, and emission of manure ammonia, enteric methane, and carbon dioxide in lactating cows fed diets with varying alfalfa silage-to-corn silage ratios.
Replacement of grass and maize silages with lucerne silage: Effects on performance, milk fatty acid profile and digestibility in Holstein-Friesian dairy cows.
). It has also been suggested that milk and milk protein yield could be improved by improving the AA profile of the MP, particularly the limiting essential AA such as lysine, methionine, or histidine (
Effects of metabolizable protein supply and amino acid supplementation on nitrogen utilization, milk production, and ammonia emissions from manure in dairy cows.
The apparent whole-tract digestibilities of DM, OM, N, NDF, and ADF in both of our studies were similar to previous reports that have examined the effects of dietary CP concentration in red clover or alfalfa silage-based diets (
), the apparent digestibilities of DM, OM, N, NDF, and ADF were decreased when a low-CP diet (L) was fed to our dairy cows in study 1, but this was not observed for the low-protein diets (L50 and L60) in study 2, although we acknowledge that the low frequency of fecal sampling in our study could have influenced the results (
reported no change in the apparent digestibility of alfalfa and corn silage-based rations, except for OM and CP, which were decreased when the dietary concentration of CP was reduced from 185 to 152 and from 155 to 137 g/kg of DM, respectively.
Replacement of grass and maize silages with lucerne silage: Effects on performance, milk fatty acid profile and digestibility in Holstein-Friesian dairy cows.
Performance, digestion, nitrogen balance, and emission of manure ammonia, enteric methane, and carbon dioxide in lactating cows fed diets with varying alfalfa silage-to-corn silage ratios.
reported that the replacement of corn with alfalfa silage did not affect apparent nutrient digestibility, except for fiber digestibility, which was increased by the inclusion rate of alfalfa silage (
Performance, digestion, nitrogen balance, and emission of manure ammonia, enteric methane, and carbon dioxide in lactating cows fed diets with varying alfalfa silage-to-corn silage ratios.
). Alternatively, feeding alfalfa-based diets may enhance the duodenal flow of indigestible fiber, resulting in an increased sloughing of endogenous cells from the intestinal wall, with a resultant reduction in the apparent digestibility of CP (
Several studies have reported that reducing dietary N intake can increase apparent NUE in lactating dairy cows when fed either alfalfa or alfalfa and corn silage-based rations (
), a finding in agreement with our results, where reducing dietary CP from 175 to 150 g/kg of DM while maintaining the MP supply increased NUE by approximately 25%. We found no difference in N output in milk or NUE when alfalfa replaced corn silage (L50 vs. L60) in our study 2, although numerically NUE was lower in cows fed L60 than L50. Increasing the rate of inclusion of alfalfa silage in corn silage-based diets up to 75 or 80%, has been shown to decrease NUE, which may be associated with a lower milk yield, oversupply of RDP, or limitation of rumen available energy in high alfalfa silage-based rations (
Performance, digestion, nitrogen balance, and emission of manure ammonia, enteric methane, and carbon dioxide in lactating cows fed diets with varying alfalfa silage-to-corn silage ratios.
The effect of varying proportion and chop length of lucerne silage in a maize silage-based total mixed ration on diet digestibility and milk yield in dairy cattle.
We detected a reduction in plasma urea in cows receiving the low-CP diets (L, L50, or L60) compared with the high-CP diets (H or H50), which could be attributable to a lower content of degradable N in the rumen with these diets (
The partial replacement of soyabean meal and rapeseed meal with feed grade urea or a slow-release urea and its effect on the performance, metabolism and digestibility in dairy cows.
). Moreover, the lower concentration of milk urea in cows receiving the low-CP diets in our studies was associated with a reduction in plasma urea content, which is supported by
reported no difference in plasma glucose or BHB concentrations in cows when fed a corn and grass silage-based low-CP diet (139 g/kg of DM) compared with a higher-CP diet (157 g CP/kg of DM), whereas plasma urea was reduced by 1.17 mmol/L. When we increased the proportion of alfalfa silage in the diet in study 2 (L50 vs. L60), this did not affect the concentration of plasma metabolites, although plasma BHB was numerically higher in cows when fed the high-alfalfa diet (L60). The highest concentration of plasma BHB was also associated with a high inclusion rate of alfalfa in the study of
Replacement of grass and maize silages with lucerne silage: Effects on performance, milk fatty acid profile and digestibility in Holstein-Friesian dairy cows.
Replacing alfalfa silage with corn silage in dairy cow diets: Effects on enteric methane production, ruminal fermentation, digestion, N balance, and milk production.
). In our current studies the milk FA proportion of CLA cis-9,trans-11 was not affected by dietary CP concentration, but CLA cis-9,trans-11 increased with alfalfa inclusion rate (L60 vs. H50) in study 2. Increased milk FA proportion of CLA cis-9,trans-11 can be associated with a greater dietary supply of C18:2 cis-9,cis-12 or C18:3 cis-9,cis-12,cis-15, although the dietary concentrations of these fatty acids were similar in L50 and L60. The lower proportion of CLA in the milk fat of cows fed H50 may also partly be due to a higher DM and fiber intake, which increased the passage rate and reduced the time available for ruminal biohydrogenation.
The highest proportion of total milk PUFA (mainly C18:2 cis-9,cis-12) and C18:1 trans-12 in the milk from cows fed the low-CP diet (L) in our study 1 could be related to a lower dietary supply of RDP that might have reduced rumen microbial metabolism and subsequent biohydrogenation of long-chain FA in the rumen (
). For example, milk from cows fed red clover and grass silage-based diets in our study 1 had higher total PUFA than milk from cows fed the alfalfa and corn silage-based rations in study 2. The higher proportion of milk PUFA in lactating cows fed red clover-based diets could be due to the action of PPO reducing the ruminal biohydrogenation of long-chain FA (
), but it has been suggested that encapsulation of plant lipids in a phenol-protein complex reduces the accessibility of lipids to microbial lipolysis, lowering biohydrogenation (
reported a lower concentration of PUFA in milk fat when an alfalfa and corn silage-based low-CP diet (145 to 148 g/kg of DM) was fed to dairy cows, an effect that was attributed to the inclusion of dietary heat-treated or expeller soybean meal, which contained more saturated fat. The low-CP diets in our current studies also contained more RUP sources, which may have altered the milk FA profile.
Milk OBCFA and <C16 FA in ruminants have been suggested to be markers that could be used to predict MCP synthesis (
). In our study 1, the yields of milk <C16 (mainly C8:0, C11:0, and C12:0) and OBCFA (mainly C15:0 and C15:1) were lower when fed L or M compared with H, a finding in agreement with previous work (
), where the microbial synthesis of OBCFA was decreased when diets low in RDP were fed. Indeed, a positive relationship has been found between dietary N supply and MCP synthesis in ruminants (
Effects of synchronizing the rate of dietary energy and nitrogen release in diets with a similar carbohydrate composition on rumen fermentation and microbial protein synthesis in sheep.
Reducing the dietary CP concentration from 175 to 150 g/kg of DM in a red clover and grass silage or alfalfa and corn silage-based diet that were predicted to meet or be marginally deficient in MP supply decreased DMI but had no effect on milk yield or composition, whereas increasing the proportion of alfalfa in a low-CP diet from 50 to 60% of the forage DM reduced milk yield and milk protein content but not DMI or ECM yield. The apparent whole-tract nutrient digestibility was decreased by reducing dietary CP in a red clover and grass silage-based diet but not in an alfalfa and corn silage-based diet. Importantly, feeding a low-CP diet based on either red clover and grass silage or alfalfa and corn silage improved the apparent nitrogen use efficiency in dairy cows by approximately 25%.
ACKNOWLEDGMENTS
The authors are grateful to S. J. Williams, J. Clarke, J. Helen, and T. Almekinders (Harper Adams University, Newport, Shropshire, UK) for technical assistance during the sampling periods. The Agricultural and Horticulture Development Board (Warwickshire, UK) is also gratefully acknowledged for funding the study. The authors have not stated any conflicts of interest.
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Lund P.
Nielsen M.O.
Milk production response to varying protein supply is independent of forage digestibility in dairy cows.
Performance, digestion, nitrogen balance, and emission of manure ammonia, enteric methane, and carbon dioxide in lactating cows fed diets with varying alfalfa silage-to-corn silage ratios.
Replacing alfalfa silage with corn silage in dairy cow diets: Effects on enteric methane production, ruminal fermentation, digestion, N balance, and milk production.
Performance and nutrient utilisation of dairy cows offered silages produced from three successive harvests of either a red clover–perennial ryegrass sward or a perennial ryegrass sward.
Effects of metabolizable protein supply and amino acid supplementation on nitrogen utilization, milk production, and ammonia emissions from manure in dairy cows.
The effect of bale density and addition of formic acid on the in situ dry matter and crude protein degradation of lucerne, red clover and red fescue silages.
The partial replacement of soyabean meal and rapeseed meal with feed grade urea or a slow-release urea and its effect on the performance, metabolism and digestibility in dairy cows.
Replacement of grass and maize silages with lucerne silage: Effects on performance, milk fatty acid profile and digestibility in Holstein-Friesian dairy cows.
Effects of synchronizing the rate of dietary energy and nitrogen release in diets with a similar carbohydrate composition on rumen fermentation and microbial protein synthesis in sheep.
Effects of inclusion of whole-crop pea silages differing in their tannin content on the performance of dairy cows fed high or low protein concentrates.
Gaillon P. Chabert Y. A Nordic Proposal for an Energy Corrected Milk (ECM) Formula. Paris, France. EAAP publication 50. Centre for Agricultural Publishing and Documentation (PUDOC),
1991
The effect of varying proportion and chop length of lucerne silage in a maize silage-based total mixed ration on diet digestibility and milk yield in dairy cattle.
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