Effect of amount and source of dietary nitrogen on milk fat depression in early lactation dairy cows

Response of lactating dairy cows to dietary protein from canola meal or distillers’ grains on dry matter intake, milk production, milk composition, and amino acid status

Acharya I. P., Schingoethe D. J., Kalscheur K. F. and Casper D. P. 2015. Response of lactating dairy cows to dietary protein from canola meal or distillers’ grains on dry matter intake, milk production, milk composition, and amino acid status. Can. J. Anim. Sci. 95: 267–279. A study was conducted to determine the response of feeding two different crude protein (CP) concentrations [low protein (LP, 14.3% CP) and high protein (HP, 16.3% CP)] and sources of protein [canola meal (CM) and high-protein dried distillers’ grains (HPDDG)] on dry matter intake, milk production and composition, and amino acid (AA) status of high producing dairy cows. Sixteen Holstein cows were used in a replicated 4×4 Latin square having a 2×2 factorial arrangement of treatments. All diets contained 55% forage (50% alfalfa hay and 50% corn silage) and 45% concentrate. Diets were formulated to contain LP with CM, LP with HPDDG, HP with CM and HP with HPDDG. Experimental feeding periods were 4 wk with data collected during weeks 3 and 4 of each period. Dry matter intake (24.6 vs. 25.9 kg d−1 for LP and HP, respectively) was increased for cows fed the higher CP diets, milk yield was greater for cows fed HP diets (34.0 vs. 36.4 kg d−1), and milk fat percentage was greater for cows fed HP compared with LP, but were similar between dietary protein sources. Feed efficiency calculated as fat-corrected milk and energy-corrected milk was greater for cows fed HP than LP, but was similar between sources. Dietary metabolizable protein of CM diets was utilized more efficiently than from HPDDG diets for milk protein production. Mammary gland extraction efficiency of essential AA indicated that Met was the first limiting AA for CM-based diets while Lys was first limiting for HPDDG-based diets. In summary, canola meal and distillers’ grains are both good quality protein supplements for lactating cows.

Impacts of the source and amount of crude protein on the intestinal supply of nitrogen fractions and performance of dairy cows

The objective of this article was to review and summarize the significance of the amount and source of dietary crude protein supplements on the supply of nitrogen fractions passing to the small intestine and the performance of lactating dairy cows. A meta-analysis was used to evaluate 2 data sets, one for nitrogen flow to the small intestine and one for performance of cows. The response of dairy cows to rumen-undegradable protein supplements is variable. A portion of this variable response from research trials is explained by the source of crude protein in the control diet, the proportion and source of rumen-undegradable protein in the experimental diet, the effect of rumen-undegradable protein on microbial protein outflow from the rumen, the degradability and amino acid content of the rumen-undegradable protein, and the crude protein percentage of the diet. Compared with soybean meal, the mean milk production responses to feeding rumen-undegradable protein supplements ranged from -2.5 to +2.75%. Because of the large variation and small magnitude of response when rumen-undegradable protein supplements are fed compared with soybean meal, efficiency of nitrogen utilization and the cost to benefit ratio for these crude protein supplements may determine the source and amount of crude protein to feed to dairy cows in the future.

Effect of Two Levels of Crude Protein and Methionine Supplementation on Performance of Dairy Cows

Sixteen Holstein cows in midlactation were randomly assigned to treatments in a replicated 4 x 4 Latin square. Two levels of CP (16.1 vs. 18.8%) with or without supplemental methionine (0.07 g/100 g of DM) were tested in a 2 x 2 factorial arrangement of treatments. Dry matter intake, milk production, milk composition, and N excretion were determined. No interactions between CP level and methionine supplementation were observed. Milk production and dry matter intake were not different among treatments. Milk protein concentration increased from 3.17 to 3.26% with the addition of methionine and decreased from 3.24 to 3.17% with increased CP. No differences were observed among treatments in milk protein yield. Milk fat concentration was low across all diets, but was increased from 2.33% with 16.1% CP diets to 2.68% with 18.8% CP diets. No significant treatment effects were observed for SNF, lactose concentration in milk, or casein N as a fraction of skim milk N. Increased dietary CP increased milk urea N by 3.9 mg/dl. Methionine supplementation did not affect N excretion in urine or feces. The higher protein diets increased estimated urine volume by 2.9 L/d and increased N concentration by 1.7 percentage units in both urine and feces. Feeding higher protein increased milk urea and urine N excretion as expressed as a percentage of total N excreted (44 vs. 38% for 18.8 and 16.1% CP, respectively). Overall, feeding 16.1% CP produced milk and milk protein yields similar to feeding 18.8% CP, but reduced the N losses in urine and milk urea.

Nitrogen supplementation of corn silages. 1. Effects on feed intake and milk production of dairy cows

Feed intake and milk production responses to N supplementation of corn silage-based diets were measured in three 3 x 3 Latin square experiments. In each experiment, 9 Holstein cows received total mixed rations (TMR), based on corn silage. In Exp. 1, midlactation cows were used to study effects of diets with different ratios of effective rumen-degradable protein (ERDP; g) to fermentable metabolizable energy (FME; MJ), providing a large deficiency (RL), a slight deficiency (RM), and a slight excess (RH) in relation to the target level of 11 g of ERDP/MJ of FME, respectively, for lactating cows. Diets were formulated to be isoenergetic, and to satisfy the metabolizable protein requirements. In Exp. 2, early-lactation cows were used to evaluate effects of different proportions of quickly and slowly rumen-degradable protein (RDP), achieved by replacing soybean meal with urea in the concentrates (0, 0.5, and 1% urea). Experiment 3 investigated effects of synchronizing the availability of FME and ERDP in the rumen. Midlactation cows received a diet containing, on a dry matter (DM) basis, 45% corn silage, 5% ryegrass hay, 35% energy-rich concentrate, and 15% protein-rich concentrate (crude protein: 38% of DM; urea: 2% of DM). The protein-rich concentrate was fed either once (D1) or twice (D2) per day before the meal, or included in the TMR (DU). Treatment RL led to lower DM intake and milk yield, but higher milk production efficiency; there were no significant differences between treatments RM and RH. There were no significant treatment effects on DM intake, milk yield, or milk composition in Exp. 2. Manipulating rumen synchrony by altering the timing of feeding affected milk yields, with D1 cows producing significantly less than D2 and DU cows, which were similar. The amount of ERDP in the diet should be matched to the amount of fermentable energy available to maximize intake, milk yields, and the conversion of feed N into milk protein. However, this study showed only small benefits to altering the diurnal pattern of supply of RDP and FME, and only with extreme feeding strategies that would not be used in practice. Urine volume increased in response to increased or unbalanced protein supply. Analysis of the allantoin:creatinine ratio in spot samples of urine was not useful in identifying predicted differences in microbial protein yield from the rumen.

Evaluation of ruminally protected methionine and lysine or blood meal and fish meal as protein sources for lactating Holsteins

Forty lactating Holstein cows averaging 55 days in milk were used in a randomized block designed experiment to evaluate the effectiveness of ruminally protected Met and Lys compared with that of ruminally undegradable protein for supporting lactation. Cows were fed total mixed diets for 15 wk. Diets were formulated to be isonitrogenous with the same base ingredients resulting in base crude protein percentage of 15.5. Supplemental crude protein supplied by urea, soybean meal, or a 50:50 (wt/wt) mixture of fish and blood meal increased total dietary nitrogen to 18.0% of diet DM. Two additional diets consisted of the basal diets soybean meal and urea, which were supplemented with ruminally protected DL-Met and Lys-HCL at 10 and 25 g/d, respectively (soybean meal + amino acids (AA), urea + AA). Mean measures of dry matter intake, milk yield, milk protein percentage, and milk fat percentage were not affected by protein supplement. Milk protein yield, milk fat yield, casein yield, and casein percentage also were not affected by source of supplemental protein. Results indicate that at the level of crude protein intake relative to milk production in this experiment, the source of protein did not affect lactational performance.

Effects of postruminal protein on fatty acid digestibility in dairy cows

Eight ruminally cannulated Holstein cows (four multiparous and four primiparous) were used in a replicated 4 x 4 Latin square with an extra period to determine the effects of postruminal protein on fatty acid digestibility. Samples were collected during the last 4 d of each 14-d period. Total mixed rations were composed of 41% alfalfa haylage, 42% corn silage, 12% concentrate based on corn, and 5% tallow. Cows were fed at 90% of ad libitum intake. Treatments were abomasal infusion of guar gum or guar gum plus urea, corn gluten meal, or blood meal in 12 L of water. The basal ration contained 12% crude protein (CP), and infusion of N sources increased CP to approximately 14%. Dry matter intake was similar for cows on all treatments. Milk, 3.5% fat-corrected milk, milk protein, and milk fat yields increased for cows receiving postruminal CP. Postruminal CP did not affect milk fat and protein percentages. Dry matter, organic matter, and CP digestibilities were greater in cows receiving postruminal CP. Total fatty acid and total C18 fatty acid digestibilities were not affected by treatment. Total C16 fatty acid and C18:0 fatty acid digestibilities were greater for cows receiving nonprotein N than for those receiving true protein.

Influence of dietary protein and supplemental niacin on lactational performance of cows fed normal and low fiber diets

Forty-seven cows (24 primiparous) were assigned to one of four normal (20.5%) ADF diets for wk 2 to 5 postpartum. Dietary treatments in a 2 x 2 factorial design were diets of 13.8 versus 18.8% CP and 0 versus 12 g/d of niacin per cow. During wk 6 to 13 postpartum, cows were fed low (11.8%) ADF diets while maintaining CP and niacin treatments. Low CP diets contained solvent-extracted soybean meal; rumen soybean meal with enhanced undegradable protein was used in high CP diets. High CP diets increased milk protein percentage in multiparous cows and yields of milk, 4% FCM, fat, protein, and SNF in primiparous cows during the normal fiber period. High dietary CP also increased yields of 4% FCM, fat, protein, and SNF in primiparous cows fed normal fiber diets. When switched to low fiber diets, primiparous cows fed high CP diets decreased more in 4% FCM and fat yields than those fed low CP. Primiparous cows fed niacin decreased more in 4% FCM than controls. High dietary CP increased DMI in primiparous cows fed normal fiber diets, but those fed low CP diets increased more in DMI when switched to low fiber diets. Supplemental niacin appeared to interact with dietary CP in multiparous cows, increasing blood glucose and decreasing blood beta-hydroxybutyrate and NEFA concentrations with the high CP, normal fiber diet. Increased dietary CP improved yields of milk and milk components in primiparous cows.

Effect of total and rumen undegradable protein on the performance of cows fed low fiber diets

Twelve multiparous and 18 primiparous Holstein cows were fed a 17.3% CP, 21.0% ADF diet during wk 2 through 6 postpartum. Cows then were assigned from wk 7 through 14 to one of three low fiber (10.7% ADF) dietary treatments containing either 14.4 or 18.7% CP, the latter with or without a soybean meal enhanced with rumen undegradable protein. Treatments had no effect on milk yield or composition in multiparous cows, although milk fat percentage was not depressed in multiparous cows receiving the low fiber diets. The soybean meal diet enhanced with rumen undegradable protein increased yields of milk, 4% FCM, fat, protein, and DMI compared with the 14.4% CP diet in primiparous cows; it also increased yields of 4% FCM and fat versus the 18.7% CP, untreated diet in primiparous cows. Blood urea N concentrations were greater for high CP diets than for the low CP diet in both parity groups. Rumen acetate: propionate ratios were higher for both high CP diets than for the low CP diet in multiparous cows. Soybean meal enhanced with rumen undegradable protein improved yields of milk and its components in primiparous cows fed low fiber diets, even when high protein diets were fed.

Effects of protein level and forage source on milk production and composition in early lactation dairy cows

Twenty multiparous and 12 primiparous Holstein cows were assigned at calving to one of three grass hay-based diets containing either 14, 18, or 22% CP or an alfalfa hay-based diet containing 22% CP to examine the effect of protein level and forage source on milk yield and composition. The diets contained 23% ADF during wk 1 to 4 postpartum, which was lowered to 11% for wk 5 to 12 postpartum. Cows fed the 18 and 22% CP grass-based diets produced higher yields of milk, 4% FCM, fat, protein, and SNF than those fed the 14% CP diet during the high fiber period. In addition, cows fed the 22% CP grass-based diet had higher milk fat tests than those fed the 14% CP diet during the high fiber period, due primarily to an increase in short-chain fatty acid synthesis. Milk fat depression was more severe when cows were changed to low fiber diets while fed the 22% CP alfalfa-based diet than when fed the 22% CP grass-based diet. Depression in milk fat content was 15.0, 17.0, 15.6, and 27.0% for 14, 18, and 22% CP grass-based and 22% CP alfalfa-based diets, respectively. Cows receiving the 18 and 22% CP grass-based diets exhibited higher blood NEFA during the high fiber feeding period than those fed the 14% CP diet. After fiber was lowered, changes in rumen acetate:propionate ratios were unaffected by treatment. Lowering fiber level resulted in an increased milk CP percentage regardless of treatment. Grass hay appeared to be more effective than alfalfa hay in preventing depression in milk fat test upon the change to a low fiber diet.

Milk fat depression and the influence of diet on milk composition

Milk composition depends on inheritance, stage of lactation, age, infection, and diet. Fat is the most variable component of milk, and its concentration depends on the supply of acetate, butyrate, and performed fatty acids to the mammary gland. This supply depends on diet and competition among organs. Adequate, effective fiber is the critical dietary consideration.