Microbial protein synthesis and flows of nitrogen fractions to the duodenum of dairy cows

Attempts have been made to increase nutrient availability for milk production by increasing feed intake, optimizing ruminal fermentation, and supplementing nutrients to the diet that will escape ruminal degradation. Energy and N are the nutritional factors that most often limit microbial growth and milk production. Ruminal fermentation and flow of microbial and dietary protein to the small intestine are affected by feed intake and by the amount and source of energy and protein in the diet. Feeding protein and carbohydrate that are not degraded in the rumen increases the quantity of dietary protein that passes to the small intestine but may decrease the quantity of microbial protein that is synthesized in the rumen. This often results in only small differences in the total NAN that passes to the small intestine. Because microbial protein supplies a large quantity of total AA that passes to the small intestine, differences in passage of individual AA often are only slight. Additional research with cows consuming large amounts of feed are needed to identify combinations of feed ingredients that synchronize availabilities of energy and N for optimizing ruminal digestion, microbial protein synthesis, nutrient flow to the small intestine, and milk production and composition.

Effects of source of protein and carbohydrate on ruminal fermentation and passage of nutrients to the small intestine of lactating cows

Four early lactation multiparous Holstein cows were used in a 4 x 4 Latin square to investigate the effects of source of protein (fish meal or soybean meal) and carbohydrate (corn or barley) on ruminal fermentation, flow of nutrients to the small intestine, and animal performance. The treatments, arranged in a 2 x 2 (protein x carbohydrate) factorial were: 1) corn plus soybean meal; 2) corn plus fish meal; 3) barley plus soybean meal; and 4) barley plus fish meal. Dry matter and starch intakes were greater when corn was fed than when barley was fed. Barley-based diets were more extensively degraded in the rumen than corn-based diets and therefore provided more energy for microbial growth. However, passage of amino acids and starch to the duodenum was greater for corn-based diets than barley-based diets, because of the greater intake and lower ruminal degradability of the corn-based diets. Microbial protein constituted a larger portion of the total N and had a greater influence on the pattern and quantity of amino acids that passed to the duodenum than did protein from fish meal or soybean meal, which escaped ruminal degradation. Feeding corn-based diets increased production of milk and milk protein compared with feeding barley-based diets.

Infusion of long-chain fatty acids varying in saturation and chain length into the abomasum of lactating dairy cows

Free long-chain fatty acids were infused into the abomasum of lactating dairy cows to determine postruminal effects on feed intake, production and composition of milk, nutrient digestibilities, and metabolites in blood. Four Holstein cows averaging 120 DIM and fitted with ruminal cannulas were used in a 4 x 4 Latin square design with 14-d periods. Treatments were abomasal infusions of 1) control, 168 g/d of meat solubles (carrier for fatty acids), 2) control plus 450 g/d of mostly saturated fatty acids (C16:C18 = .75), 3) control plus 450 g/d of a mixture of saturated and unsaturated fatty acids (C16:C18 = .40), and 4) control plus 450 g/d of mostly unsaturated fatty acids (C16:C18 = .11). Production of milk and milk components, DMI, and intake of digestible energy decreased linearly as unsaturation and chain length of infused fatty acids increased. Percentages of fat, CP, and SNF in milk and total tract apparent digestibilities of DM, OM, ADF, NDF, energy, and fatty acids were not affected significantly by treatments. Infusing fatty acids decreased proportions and yields of short- and medium-chain fatty acids and increased proportions and yields of unsaturated C18 fatty acids in milk fat. Increasing unsaturation and chain length of infused fatty acids linearly decreased proportion and yield of palmitic acid but increased proportions and yields of polyunsaturated C18 fatty acids in milk fat. Infusing fatty acids increased concentrations of NEFA and cholesterol in blood plasma. The profile of fatty acids reaching the intestine may be an important determinant of responses to supplemental fats fed to lactating dairy cows.

Effects of urea and starch on rumen fermentation, nutrient passage to the duodenum, and performance of cows

Four midlactation, multiparous Holstein cows fitted with ruminal and duodenal cannulas were used in a 4 x 4 Latin square design to determine the effects of supplementing urea or starch or both to diets containing fish meal on passage of nutrients to the small intestine and performance of lactating cows. The treatments (in a 2 x 2 factorial arrangement) were 1) control and control plus 2) urea, 3) starch, or 4) starch and urea. Supplementing diets with urea did not affect DMI; ruminal, postruminal, or total tract digestibilities of DM, starch, ADF, or NDF; ruminal fluid VFA concentrations or molar percentages; or ruminal fluid or particulate dilution rates. Feeding additional starch depressed DMI but did not alter ruminal or postruminal digestion of OM or VFA concentrations and molar percentages in ruminal fluid. Ruminal fluid ammonia concentration was increased by feeding urea and decreased by feeding additional starch. Passage of nonammonia N, nonammonia nonmicrobial N, or microbial N to the small intestine and efficiency of microbial CP synthesis were not affected significantly by supplying either urea or additional starch. Feeding urea increased passage of methionine to the small intestine, whereas feeding additional starch increased passage of methionine and arginine. Passage of other amino acids to the small intestine was not altered significantly by feeding urea or additional starch. Production of milk and milk protein was increased, but yields of fat and SNF were not altered by feeding diets supplemented with urea. Production of milk and milk fat was not affected, but yields of CP and SNF were decreased when additional starch was fed to cows.

Effects of dietary fat and protein on fatty acid flow to the duodenum and in milk produced by dairy cows

Four Holstein cows fitted with ruminal and duodenal cannulas were used in a 4 x 4 Latin square with treatments in a 2 x 2 factorial arrangement. Treatments were 1) soybean meal, no fat; 2) fish meal, no fat; 3) soybean meal, fat; and 4) fish meal, fat. Cows were fed for ad libitum intake a diet of alfalfa haylage, corn silage, and concentrate (30:20:50) on a DM basis. Intake of gross energy (105 Mcal/d) was not altered by treatment comparisons. However, feeding fat decreased energy digested in the rumen (15 vs. 24%) and increased energy digested postruminally (55 vs. 43%) but resulted in similar amounts of energy (72 Mcal/d) digested in the total tract. The flow of C14:0, C16:0, C18:0, C18:1, C18:2, C18:3, and total fatty acids to the duodenum was increased by feeding fat. The average flow of C14:0, total C18, and total fatty acids to the duodenum was greater than their intake for all treatments, suggesting de novo synthesis of fatty acids by ruminal microbes. Biohydrogenation of unsaturated C18 was decreased 70, 67, 59, and 51% for treatments 1 to 4, respectively, by feeding fat and fish meal. Digestibility of total fatty acids entering the small intestine (78%) was not altered by treatment comparisons; however, feeding fat altered digestibility of individual fatty acids. The proportion of C16:0 and C18:1 was increased, and the proportion of C6:0, C8:0, C10:0, C12:0, and C14:0 was decreased in milk fat produced by cows fed fat.

Effects of source and amount of protein on ruminal fermentation and passage of nutrients to the small intestine of lactating cows

Four Holstein cows fitted with ruminal and duodenal cannulas were used in a 4 x 4 Latin square to investigate the effects of source (corn gluten meal or soybean meal) and amount (14.5 or 11.0%) of CP on ruminal fermentation, passage of nutrients to the small intestine, and animal performance. Cows wee fed for ad libitum intake a diet of 60% corn silage and 40% concentrate on a DM basis. The treatments, arranged in a 2 x 2 (source x amount of CP) factorial, were 1) 14.5% CP, soybean meal; 2) 11.0% CP, soybean meal; 3) 14.5% CP, corn gluten meal; and 4) 11.0% CP, corn gluten meal. Digestion in the rumen of OM, starch, ADF, and NDF was not affected by source or amount of CP in the diet. Total VFA and NH3 concentrations in ruminal fluid were increased by feeding diets that contained 14.5% CP or soybean meal. FLows of non-NH3 N and amino acids to the duodenum were greater in cows fed the 14.5% CP diets because of a greater flow of non-NH3 nonmicrobial N to the duodenum. Larger amounts of lysine passed to the duodenum when cows were fed soybean meal compared with corn gluten meal. Microbial N flow to the duodenum and efficiency of microbial growth were not affected by treatments, suggesting that ruminal NH3 concentration was not limiting for maximal microbial protein synthesis. Feeding 14.5% CP diets increased the production of milk (29.5 vs. 26.8 kg/d) and milk protein compared with 11.0% CP diets, possibly because of greater passage of amino acids to the small intestine. Feeding soybean meal to cows increased production of milk protein compared with feeding corn gluten meal, possibly because more lysine passed to the small intestine.

Effects of calcium salts of fatty acids and proportion of forage in diet on ruminal fermentation and nutrient flow to duodenum of cows

Four Holstein cows fitted with ruminal and duodenal cannulas were used in a 4 x 4 Latin square to investigate the effects of calcium salts of long-chain fatty acids (fat) and proportion of forage in diet on ruminal fermentation, flow of nutrients to the small intestine, and animal performance. Treatments, arranged in a 2 x 2 (fat x forage) factorial, were 1) low (50%) forage, no fat; 2) low forage, fat; 3) high (67%) forage, no fat; and 4) high forage, fat. Feeding fat decreased OM intake and OM truly digested in the rumen. Feeding high forage diets decreased intakes of OM and starch and increased intakes of ADF and NDF. Ruminal pH and ratio of acetate to propionate were increased with high forage diets compared with low forage diets. Feeding fat and different amounts of forage to cows did not alter the flows of NAN and microbial N to the duodenum or efficiency of microbial growth. Production of milk and 4% FCM and percentage of fat in milk were increased by feeding fat. Feeding high forage diets decreased milk production, increased percentage of fat in milk, increased the yield of fat, and caused no change in 4% FCM production. The percentage of protein in milk was decreased by feeding high forage diets and fat, but yield of milk protein was decreased only by feeding high forage diets to cows.

Effects of calcium salts of fatty acids and protein source on ruminal fermentation and nutrient flow to duodenum of cows

Four Holstein cows fitted with ruminal and duodenal cannulas were used in a 4 x 4 Latin square to investigate the effects of calcium salts of long-chain fatty acids (fat) and source of protein (fish meal or soybean meal) on ruminal fermentation, flow of nutrients to the small intestine, and animal performance. Cows were fed for ad libitum intake a diet of 30% alfalfa haylage, 20% corn silage, and 50% concentrate on a DM basis. Treatments, arranged in a 2 x 2 (fat x protein) factorial, were 1) soybean meal, no fat; 2) soybean meal, fat; 3) fish meal, no fat; and 4) fish meal, fat. Intake of DM was not affected by fat or protein source, but feeding fat decreased the amount of OM truly digested in the rumen. Starch intake was decreased, but flow of starch to the duodenum was not altered by feeding fat. Nonammonia N and microbial N flows to the duodenum were not affected by treatment comparisons. However, efficiency of microbial growth was increased by feeding fat, but not by source of protein. Passage of amino acids to the duodenum was not affected by source of protein, probably because fish meal contributed only 17% of the total dietary CP, and microbial N constituted about 50% of the NAN passing to the duodenum; this had an equalizing effect on the pattern and quantity of amino acids that passed to the duodenum. Feeding fat or different sources of protein did not alter milk production. Milk fat percentage was increased, and protein percentage was decreased when fat was fed, but yields of milk fat and protein were not different.

Effect of recombinant bovine somatotropin and a shortened or no dry period on the performance of lactating dairy cows

The objective of this study was to determine the effects of altering dry period length in multiparous dairy cows (n = 341) on milk production for a full lactation (294 d). The study used 3 commercial herds in the western United States. Cows producing greater than 8,400 kg of mature-equivalent milk were assigned to treatments 60 d before their due dates. The 4 treatments were 1) 60-d dry period, label use of recombinant bovine somatotropin (rbST; 60d-L); 2) 32-d dry period, label use of rbST (32d-L); 3) 0-d dry period, label use of rbST (0d-L); and 4) 0-d dry period, continuous use of rbST (0d-C). Cows with shortened dry periods produced 625, 1,000, and 1,042 kg of milk during the prepartum period for treatments 2 to 4, respectively. During the postpartum period, cows on the 32d-L treatment produced similar amounts of milk compared with the 60d-L treatment (11,490 vs. 11,968 kg, respectively). However, cows on the 0d-L (10,316 kg) and 0d-C (10,195 kg) treatments produced significantly lower amounts of milk during the postpartum period compared with the 60d-L treatment. Total milk production from the prepartum and postpartum periods was not altered significantly and was 11,974, 12,112, 11,310, and 11,230 kg for treatments 1 to 4, respectively. The concentrations of beta-hydroxybutyrate and nonesterified fatty acids in serum after calving were decreased for cows on the 32d-L, 0d-L, and 0d-C treatments compared with cows on the 60d-L treatment, which may indicate improved metabolic status.

Supplemental fat and nicotinic acid for Holstein cows during an entire lactation

The objectives of this experiment were to determine long-term responses to supplemental fat (from whole soybeans and liquid animal fat) and to determine whether the supplementation of nicotinic acid would enhance milk protein content or yield. From wk 4 through 43 postpartum, 44 multiparous Holstein cows (10 to 12 per treatment) were assigned to one of four dietary treatments: 1) control, 2) control plus 12 g/d of nicotinic acid, 3) supplemental fat, and 4) supplemental fat plus 12 g/d of nicotinic acid. The dry matter intake of cows did not differ among dietary treatments. Yields of milk, solids-corrected milk, and 3.5% fat-corrected milk were increased by nicotinic acid; the yield of fat-corrected milk during wk 4 to 25 was increased by supplemental fat. Contents of crude protein (CP) and true protein in milk were less for cows fed diets supplemented with fat or nicotinic acid; casein content was decreased by nicotinic acid. Intake of net energy for lactation was greater for cows fed supplemental fat; energy balance was greater during wk 4 to 25 for cows fed diets supplemented with fat. Body condition score and body weight were less when nicotinic acid was added to the control diet than when it was added to the diet supplemented with fat. Supplemental fat increased the concentration of nonesterified fatty acids (NEFA) in plasma; nicotinic acid increased NEFA when it was added to the control diet but decreased NEFA when it was added to the diet supplemented with fat. Nicotinic acid did not prevent the decrease in milk CP content that was induced by dietary fat, but it did increase milk yield and tended to increase the yield of milk CP.

Influence of amount and degradability of dietary protein on nitrogen utilization by dairy cows

Four Holstein cows fitted with ruminal and T-type duodenal cannulas were utilized in a 4 x 4 Latin square design with a 2 x 2 factorial arrangement of treatments. The TMR contained 25% alfalfa haylage, 25% corn silage, and 50% concentrate and provided either 16.4 or 19.6% CP, with ruminal degradability calculated to be 30 or 45%. Intakes of DM, OM, ADF, NDF, and N were not altered by either amount or degradability of CP. Intake and ruminal and postruminal digestibility of starch were greater when cows were fed diets high in undegradable CP but was not altered by amount of CP. Apparent total tract digestibilities for DM, OM, starch, ADF, and NDF were similar among treatments. Apparent total tract digestibility of N was 4.7 percentage units greater for diets low in ruminally degradable CP. Apparent digestibility of OM, ADF, and NDF and true digestibility of OM in the rumen were not altered by amount of CP or undegradable CP. Increasing the CP content of the diet and the proportion of undegradable CP in the diet increased NAN flow to the duodenum. Except for Met, flows of all AA to the duodenum were increased when CP was increased. Flow of Met to the duodenum was not altered by undegradable CP content of the diet. Production of milk, 4% FCM, and milk CP was not altered by amount of CP or undegradable CP. Milk fat content and yield were increased when diets high in undegradable CP were fed. Results suggest that all diets supplied adequate amounts of AA for these cows or that Met was deficient for all cows.

Effects of feeding or infusing ammonium salts of volatile fatty acids on ruminal fermentation, plasma characteristics, and milk production of cows

Eight rumen-fistulated Holstein cows, averaging 77 d postpartum, were used in a replicated 4 X 4 Latin square design with 28-d periods to investigate the effect of ammonium salts of isobutyrate, 2-methylbutyrate, isovalerate, and n-valerate on animal performance and their possible mechanism(s) and site(s) of action. Each cow was fed ad libitum a complete mixed diet of 55% corn silage and 45% concentrate on a dry basis that was supplemented with 1.8 kg of premix daily. Treatments were 1) control, 2) ammonium salts of volatile fatty acids in premix, 3) ammonium salts of volatile fatty acids ruminally infused, or 4) ammonium salts of volatile fatty acids abomasally infused. Mean ruminal fluid pH and concentrations of ammonia and volatile fatty acids for treatment comparisons were not different. Plasma concentrations of isobutyrate, 2-methylbutyrate, and valerate differed among treatments, but there was no significant effect on dry matter intake, milk production, milk composition, or efficiency of feed utilization. Apparent nutrient digestibility; disappearance of dry matter, cellulose, and nitrogen from polyester bags suspended in the rumen; and plasma concentrations of glucose, free fatty acids, and growth hormone also were not significantly affected by treatment.

Effects of somatotropin and duodenal infusion of amino acids on nutrient passage to duodenum and performance of dairy cows

Four multiparous Holstein cows were used in a 4 x 4 Latin square to investigate the effects of bST and postruminal infusion of lysine and methionine on ruminal fermentation, flow of nutrients to the small intestine, and animal performance. The treatments were 1) control; 2) control plus 24 g of lysine and 8 g of methionine/d; 3) control plus 25 mg of bST/d; and 4) control plus 25 mg of bST/d plus 24 g of lysine and 8 g of methionine/d. Intakes of DM, OM, CP, starch, NDF, and ADF were similar among treatments. Ruminal characteristics, flow of nutrients to the small intestine, and total tract apparent digestibilities of nutrients were not affected by injection of bST or postruminal infusion of lysine and methionine in this short-term experiment. Milk production, 4% FCM, milk fat percentage and yield, and production of milk CP were increased by administering bST. Postruminal infusion of lysine and methionine did not affect milk production or composition.

Effects of feed processing and frequency of feeding on ruminal fermentation, milk production, and milk composition

Twenty Holstein cows, averaging 108 d postpartum, were used in five replicated 4 x 4 Latin squares to investigate the effects of feed processing and frequency of feeding on ruminal fermentation, milk production, and milk composition. Four rumen-fistulated cows were used in one of the replicates to monitor ruminal fermentation. Each cow was fed for ad libitum intake a diet of 55% alfalfa and 45% concentrate on a DM basis. Treatments were 1) noncubed diet fed two times daily, 2) noncubed diet fed four times daily, 3) cubed diet fed two times daily, and 4) cubed diet fed four times daily. Alfalfa was fed as long hay in the noncubed diet and chopped and pressed into a cube in the cubed diet. Dry matter intake by cows was not different between treatment comparisons. However, cows fed the noncubed diet consumed 5% more concentrate and 5% less alfalfa than did cows fed the cubed diet. Milk production was greater (1.4 kg/d) when the cubed diet was fed to cows, but the percentage and yield of milk fat were depressed (.43 percentage units and .09 kg/d), causing a decreased production of 4% FCM (.9 kg/d). The depression in milk fat percentage and yield may have been attributed to lowered ruminal fluid pH and a decreased ratio of acetate to propionate in cows consuming the cubed diet. Even though ruminal fluid pH and the ratio of ratio of acetate to propionate tended to be lower when cows were fed four times rather than two times per day, production and composition of milk were not affected by frequency of feeding the diets.

Comparison of three methods for incorporation of liquid fat into diets for lactating dairy cows

Two experiments were conducted to determine whether method of incorporation of tallow (iodine value = 57.7) into a TMR for lactating dairy cows affected DMI, milk production or composition, ruminal characteristics, or nutrient digestibilities. In Experiment 1, 8 Holstein and 8 Jersey cows were fed diets containing 1) control, no fat; 2) fat (5% of DM) added first to the concentrate; 3) fat added first to the haylage; and 4) fat added as the last ingredient in the TMR. The DMI was lower when fat was added last to the TMR; DMI was decreased for Jerseys, but not Holsteins, when fat was added first to the concentrate. Milk production was increased, and milk fat percentage decreased, by fat supplementation, but neither differed among application methods. Milk protein percentage was decreased by fat supplementation but was decreased less when fat was added last to the TMR. Production of milk CP, true protein, and casein protein was greater when fat was first mixed with haylage or added last to the TMR. In Experiment 2, four Holstein cows with ruminal cannulas were fed the same diets. Ruminal fermentation characteristics and apparent total tract digestibilities of DM, OM, CP, NDF, ADF, and ash were not different among diets. Digestibility of total fatty acids was decreased when fat was added first to haylage or last to the TMR. Incorporation method had relatively minor effects on variables.