Functional properties of cream from dairy cows with experimentally altered milk fat composition.

Modification of milk fat composition might be a desirable method to alter manufacturing characteristics or produce dairy products low in saturated fat that more closely meet consumer dietary preferences. The aim of this research was to evaluate functional properties of cream obtained from milks with fat composition modified by altering the profile of long-chain fatty acids (FA) absorbed from the intestine. A control and 5 mixtures of long-chain free FA were infused into the abomasum of lactating dairy cows in a 6 × 6 Latin square design with 21-d periods. Treatments were as follows: (1) control (no FA infused), (2) mostly saturated FA (C16:C18 = 0.74), (3) low linoleic palm FA (C16:C18 = 0.73), (4) palm FA (C16:C18 = 0.73), (5) soy FA (C16:C18 = 0.10), and (6) high palmitic soy FA (C16:C18 = 0.73). All treatments included meat solubles and Tween 80 as emulsifiers. Viscosity, overrun, whipping time, foam firmness, and foam stability were evaluated in creams (33% fat). Cream from cows infused with soy FA (treatment 5) had the longest whipping time and lowest overrun, foam stability, viscosity, melting point, firmness, and solid fat content at 5 and 20°C because the fat had the highest unsaturated FA content. Increasing palmitic acid content of soy FA (treatment 6) improved functional variables in cream relative to soy FA alone. Differences among treatments 1 to 4 were less pronounced because of the effect of C18:1 trans in treatments 3 and 4 on milk fat yield and composition. Milk fat from cows infused with palm FA (treatment 4) exhibited comparable or better functionality than control cream. Increased polyunsaturated FA in milk fat resulted in increased amounts of triglyceride (TG) fractions with 28, 30, 38, and 40 carbon numbers, increased oleic acid resulted in increased 50-carbon TG, and higher palmitic and myristic acids resulted in greater 44, 46, and 48 carbon number TG. These TG groups consistently correlated with functional properties of creams from different treatments. Our results indicated that optimal functionality of cream is dependent more on its content of palmitic acid than on unsaturated FA. However, an optimal composition of milk fat for cream functional characteristics might be obtained through nutritional manipulation of diets for dairy cows to deliver an optimal profile of FA.

Heavy metals in the soils of Bloemfontein, South Africa: concentration levels and possible sources.

The possible heavy metal and metalloid contamination in the soils around a coal-generated power station, situated on the eastern end of the central business district of Bloemfontein, central South Africa, was investigated. One-hundred and thirty-three samples (22 dust samples collected inside buildings and 111 soil samples) were collected for the study and analysed for As, Se, Cd, Sb and Hg. The results indicated generally elevated levels for Cd, Sb and Hg, and some localised contamination of As, but no significant increases in the non-metal Se. In fact, Se levels indicated a deficiency of the element in the study area. In general, the dust samples showed elevated levels of all elements (except Se) relative to the soils. A possible source for the enrichment might have been the release of ash, containing trace amounts of these elements, from the local power station; however, because the highest concentration in soils was found in the industrial areas, other processes could have contributed or even have been the sole cause of the elevated levels. High levels of As occur at an abandoned horse race course and were probably caused by the questionable practice of administering As-containing tonics to the horses shortly before they run a race.

Effects of sodium sesquicarbonate on dry matter intake and production of milk and milk components by Holstein cows.

Forty-six multiparous Holstein cows were used to investigate the effects of sodium sesquicarbonate on dry matter intake, body weight, and production and composition of milk during a 308-d lactation. Diets contained alfalfa silage, corn silage, and concentrate. Composition of diets was changed twice during the 308-d lactation experiment. Diets fed during d 1 to 175 and d 176 to 245 were formulated to contain more rumen-undegradable protein and fat, and less forage than that fed during d 246 to 308. Sodium sesquicarbonate did not affect yields of milk, 4% fat-corrected milk, and components in milk, or percentages of components in milk during the complete 308-d lactation or during d 1 to 175 or d 176 to 245. However, from d 246 to 308, cows fed sodium sesquicarbonate produced more milk, 4% fat-corrected milk, fat, protein, and solids-not-fat than did control cows. Milk composition was not altered. These data suggest that composition of the diet has a significant effect on the response to dietary buffers by lactating dairy cows.

Functional properties of butter oil made from bovine milk with experimentally altered fat composition.

Modification of milk fat composition might be desirable to alter manufacturing characteristics or produce low saturated fat dairy products that more closely meet consumer dietary preferences. The aim of this research was to evaluate functional properties of butter oil obtained from milks with fat composition modified by altering the profile of long-chain fatty acids (FA) absorbed from the small intestine of cows. A control and 5 mixtures of long-chain free FA were infused into the abomasum of lactating dairy cows in a 6 x 6 Latin square design with 21-d periods. Treatments were 1) control (no FA infused), 2) mostly saturated FA (C16:C18 = 0.72), 3) low-linoleic palm FA (C16:C18 = 0.85), 4) palm FA (C16:C18 = 0.72), 5) soy FA (C16:C18 = 0.10), and 6) high-palmitic soy FA (C16:C18 = 0.68). All treatments included meat solubles and Tween 80 as emulsifiers. Solid fat content (from 0 to 40 degrees C), melting point, and force at fracture were determined in butter oil. Milk fat from cows infused with palm FA (treatment 4) exhibited functionality equal to or better than control butter oil. Infusion with palm FA increased amounts of triglyceride (TG) fractions with 48, 52, and 54 carbon numbers but decreased TG with 32, 34, 36, and 42 carbon numbers. Infusion with soy FA increased TG with 26, 38, 40, 52, and 54 carbon numbers but decreased TG with 34, 42, and 46 carbons. Infusion of the mostly saturated FA increased TG with 38, 50, 52, and 54 carbon numbers but decreased TG with 32, 34, and 42 carbon numbers. These TG groups were consistently correlated with functional properties of butter oils from different treatments. The content of palmitic acid is important for maintaining functionality in the presence of increased polyunsaturated FA. The composition of milk fat may be able to be optimized through nutritional manipulation of diets for dairy cows if the optimal composition of FA and TG is defined for a particular dairy product.

Effects of dry matter intake restriction on diet digestion, energy partitioning, phosphorus retention, and ruminal fermentation by beef steers.

Two experiments were conducted to determine the effects of DMI restriction on diet digestion, ruminal fermentation, ME intake, and P retention by beef steers. In Exp. 1, twelve Angus x steers (average initial BW = 450 +/- 18 kg) were assigned randomly to 1 of 3 diets that were formulated to promote a 1.6-kg ADG at intake levels corresponding approximately to 100% (ad libitum, AL), 90% (IR90), or 80% (IR80) of ad libitum DMI. In Exp. 2, twelve crossbred steers (average initial BW = 445 +/- 56 kg) fitted with ruminal cannulae were randomly assigned to 1 of 2 diets that were formulated to promote a 1.6-kg ADG at AL or IR80. All diets delivered similar total NE, MP, Ca, and P per day. During both experiments, fecal DM output by IR80 was less (P /= 0.20) among treatments during both experiments, whereas P retention was similar (P >/= 0.46) among treatments during Exp. 1. Total VFA and the molar proportion of acetate of AL were greater (P

Omasal flow of soluble proteins, peptides, and free amino acids in dairy cows fed diets supplemented with proteins of varying ruminal degradabilities.

Three ruminally and duodenally cannulated cows were assigned to an incomplete 4 x 4 Latin square with four 14-d periods and were fed diets supplemented with urea, solvent soybean meal, xylose-treated soybean meal (XSBM), or corn gluten meal to study the effects of crude protein source on omasal canal flows of soluble AA. Soluble AA in omasal digesta were fractionated by ultrafiltration into soluble proteins greater than 10 kDa (10K), oligopeptides between 3 and 10 kDa (3-10K), peptides smaller than 3 kDa (small peptides), and free AA (FAA). Omasal flow of total soluble AA ranged from 254 to 377 g/d and accounted for 9.2 to 15.9% of total AA flow. Averaged across diets, flows of AA in 10K, 3-10K, small peptides, and FAA were 29, 217, 50, and 5 g/d, respectively, and accounted for 10.3, 71.0, 17.5, and 1.6% of the total soluble AA flow. Cows with diets supplemented with solvent soybean meal had higher flows of Met, Val, and total AA associated with small peptides than those whose diets were supplemented with XSBM, whereas supplementation with corn gluten meal resulted in higher total small peptide-AA flows than did XSBM. Averaged across diets, 27, 75, and 93% of soluble AA in 10K, 3-10K, and peptides plus FAA flowing out of the rumen were of dietary origin. On average, 10% of the total AA flow from the rumen was soluble AA from dietary origin, indicating a substantial escape of dietary soluble N from ruminal degradation. Omasal concentrations and flows of soluble small peptides isolated by ultrafiltration were substantially smaller than most published ruminal small peptide concentrations and outflows measured in acid-deproteinized supernatants of digesta.

Rumen fermentation and intestinal supply of nutrients in dairy cows fed rumen-protected soy products.

Four multiparous lactating Holstein cows that were fistulated in the rumen and duodenum and that averaged 205 d in milk were used in a 4 x 4 Latin square design to evaluate the practical replacement of solvent-extracted soybean meal (SSBM) with soy protein products of reduced ruminal degradability. On a dry matter (DM) basis, diets contained 15% alfalfa silage, 25% corn silage, 34.3 to 36.9% corn grain, 19.4% soy products, 18.2% crude protein, 25.5% neutral detergent fiber, and 35.3% starch. In the experimental diets, SSBM was replaced with expeller soybean meal (ESBM); heated, xylose-treated soybean meal (NSBM); or whole roasted soybeans (WRSB) to supply 10.2% of the dietary DM. Intakes of DM (mean = 20.4 kg/d), organic matter, and starch were unaffected by the source of soy protein. Similarly, true ruminal fermentation of organic matter and apparent digestion of starch in the rumen and total tract were not altered by treatments. Intake of N ranged from 567 (WRSB) to 622 g/d (ESBM), but differences among soy protein supplements were not significant. Compared with SSBM, the ruminal outflow of nonammonia N was higher for NSBM, tended to be higher for ESBM, and was similar for WRSB. The intestinal supply of nonammonia nonmicrobial N was higher for NSBM and WRSB and tended to be higher for ESBM than for SSBM. However, no differences were detected among treatments when the flow to the duodenum of nonammonia nonmicrobial N was expressed as a percentage of N intake or nonammonia N flow. The ruminal outflow of microbial N, Met, and Lys was not altered by the source of soy protein. Data suggest that partially replacing SSBM with ESBM, NSBM, or WRSB may increase the quantity of feed protein that reaches the small intestines of dairy cows. However, significant improvements in the supply of previously reported limiting amino acids for milk production, particularly of Met, should not be expected.

Varying protein and starch in the diet of dairy cows. I. Effects on ruminal fermentation and intestinal supply of nutrients.

The main objective of this experiment was to examine the effects of the percentage and source of crude protein (CP) and the amount of starch in the diet of dairy cows on ruminal fermentation, nutrient passage to the small intestine, and nutrient digestibility. For this purpose, 6 multiparous Holstein cows fistulated in the rumen and duodenum that averaged 73 d in milk were used in a 6 x 6 Latin square design with a 2 x 3 factorial arrangement of treatments. Two sources of CP [solvent-extracted soybean meal (SBM) and a mixture of SBM and a blend of animal-marine protein supplements plus ruminally protected Met (AMB)] and 3 levels of dietary protein (about 14, 16, and 18%) were combined into 6 treatments. On a dry matter (DM) basis, diets contained 25% corn silage, 20% alfalfa silage, 10% cottonseed, 26.7 to 37% corn grain, and 4 to 13.5% protein supplement. Intakes and digestibilities in the rumen and total tract of DM, organic matter, acid and neutral detergent fiber were unaffected by treatments. Increasing dietary CP from 14 to 18% decreased the intake and apparent ruminal and total tract digestion of starch, but increased the proportion of starch consumed by the cows that was apparently digested in the small intestine. At 14% CP, starch intake and total tract digestion were higher for the AMB diet than for the SBM diet, but the opposite occurred at 16% CP. Across CP sources, increasing CP in the diet from 14 to 18% increased the intakes of N and amino acids (AA), and ruminal outflows of nonammonia N, nonammonia nonmicrobial N, each individual AA except Met, total essential AA, and total AA. Across CP percentages, replacing a portion of SBM with AMB increased the intake of Met and Val and decreased the concentration of ammonia N in the rumen, but did not affect the intake of other essential AA or the intestinal supply of any essential AA and starch. The ruminal outflow of microbial N, the proportional contribution of Lys and Met to total AA delivered to the duodenum, and milk yield were unaffected by treatments. Data suggest that the intake of N by high-producing dairy cows that consume sufficient energy and other nutrients to meet their requirements can be decreased to about 600 to 650 g daily without compromising the supply of metabolizable protein if the source and amount of dietary CP and carbohydrate are properly matched.

Varying protein and starch in the diet of dairy cows. II. Effects on performance and nitrogen utilization for milk production.

The main objective of this experiment was to examine the effects of the percentage and source of crude protein (CP) and the amount of starch in the diet of dairy cows on the lactational performance and use of N for milk production. Sixty multiparous Holstein cows were used in a 210-d lactational trial with a completely randomized design with a 2 x 3 factorial arrangement of treatments. Two sources of CP [solvent-extracted soybean meal (SBM) and a mixture of SBM and a blend of animal-marine protein supplements plus ruminally protected Met (AMB)] and 3 levels of dietary CP (means = 14.8, 16.8, and 18.7%) were combined into 6 treatments. On a dry matter (DM) basis, diets contained 25.0% corn silage, 20.0% alfalfa silage, 10.0% cottonseed, 26.7 to 37.0% corn grain, and 4.8 to 13.5% protein supplement, plus minerals and vitamins. Across the 210 d of lactation, the productive response of dairy cows to the source of supplemental CP depended on the concentration of CP in the diet. At 18.7% CP, cows fed SBM consumed more DM and produced more milk, 3.5% fat-corrected milk, fat, and true protein, but had lower efficiency of feed use and body condition score than cows fed AMB. At 16.8% CP, cows fed AMB produced more 3.5% fat-corrected milk, fat, and true protein than cows fed SBM. At 14.8% CP, cows fed SBM consumed more DM but produced less true protein and had lower feed efficiency than cows fed AMB. Across CP sources, cows fed 14.8% CP produced less fat-corrected milk and true protein than cows fed 16.8 and 18.7% CP. Across CP percentages, cows fed AMB produced more fat-corrected milk per kilogram of DM consumed than cows fed SBM. Despite these interactions, improvements in the gross efficiency of N use for milk production were achieved through reductions in the intake of N independently of the source of CP. Data suggest that the intake of N by high-producing dairy cows that consume sufficient energy and other nutrients to meet their requirements can be decreased to about 600 to 650 g daily if the source of RDP and RUP are properly matched with the source and amount of carbohydrate in the diet.

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 feeding supplemental fibrolytic enzymes or soluble sugars with malic acid on milk production.

Two trials were conducted to evaluate effects of feeding supplemental fibrolytic enzymes or soluble sugars and malic acid on milk production. In trial 1, 257 cows at four sites were fed a basal diet consisting of no more than 60% of forage DM as corn silage and less than 40% as alfalfa hay. Cows were assigned randomly within site, parity, and two stages of lactation to: 1) control; 2) enzyme A; 3) enzyme B; and 4) soluble sugars and malic acid. There was a 14-d pretreatment and an 84-d treatment period. Enzyme solutions were sprayed on either the forage component or the TMR each day while mixing feed. Trial 2 was similar, except 122 cows at one site in the United Kingdom were fed diets containing forage that was 75% corn silage and 25% grass silage, and all cows began the study between 25 to 31 DIM. Mean milk productions for 233 cows that completed trial 1 were 32.9, 32.5, 32.4, and 32.9 kg/d for control, enzyme A, enzyme B, and soluble sugars and malic acid, respectively. Mean milk productions for 116 cows that completed trial 2 were 28.2, 27.9, 28.8, and 28.4 kg/d, respectively. In vitro analyses of the activities of enzyme solutions indicated that all major cellulose and hemicellulose degrading activities were present; however, the pH optima (approximate pH = 4 to 5) were more acidic, and the temperature optimum (approximately 50 degrees C) was greater than normal pH and temperature in the rumen. If fibrolytic activity in the rumen is a major mechanism of action of supplemental fibrolytic enzymes, it appears that considerable activity of these preparations was lost due to conditions in the rumen. In conclusion, feeding supplemental fibrolytic enzymes or malic acid with soluble sugars had no effect on milk production under the conditions used in this study.

Fatty acid metabolism in liver of dairy cows fed supplemental fat and nicotinic acid during an entire lactation.

Liver biopsies from 38 multiparous Holstein cows were used to determine rates of peroxisomal beta-oxidation and total beta-oxidation of palmitate in liver homogenates and contents of total lipid, triglyceride, and glycogen during the lactation cycle. Cows were assigned to one of four diets from wk 4 through wk 42 of lactation: control, control plus nicotinic acid (12 g/d), supplemental fat, or supplemental fat plus nicotinic acid. Liver biopsies were obtained at wk 3 (covariate), 6, 12, 24, and 42 of lactation. Neither supplemental fat nor nicotinic acid affected palmitate oxidation in liver homogenates or liver composition. Peroxisomal beta-oxidation capacity and the ratio of peroxisomal to total beta-oxidation decreased from wk 3 to 12 and then increased at wk 42. Contents of total lipid and triglyceride decreased, and content of glycogen increased, from wk 3 to 12. Total oxidation capacity in liver homogenates was correlated negatively with total lipid and triglyceride in liver, yields of milk and solids-corrected milk (SCM), and plasma nonesterified fatty acids (NEFA), and was correlated positively with liver glycogen, dry matter intake (DMI), energy balance, and plasma glucose. Peroxisomal beta-oxidation was correlated negatively with yields of milk and SCM. The ratio of peroxisomal to total beta-oxidation was correlated positively with liver total lipid, liver TG, and plasma NEFA and negatively with DMI and energy balance. When only data from wk 3 postpartum were considered, both total and peroxisomal beta-oxidation were correlated negatively with hepatic concentrations of total lipid and TG. Peroxisomal beta-oxidation in liver of dairy cows is not affected by feeding supplemental fat or nicotinic acid during wk 4 to 42 of lactation but may be a part of the hepatic adaptations to negative energy balance.

Effects of Yucca shidigera extract and soluble protein on performance of cows and concentrations of urea nitrogen in plasma and milk.

Twelve multiparous Holstein cows averaging 122 d postpartum were used in a replicated Latin square design with 21-d periods. Cows were fed diets containing either low or high soluble protein supplemented with 0 or 9 g/d of Yucca shidigera extract per cow. Dry matter intake and yields of milk, fat, 3.5% fat-corrected milk, and total solids were not affected by treatment. High soluble protein increased percentages of fat and total solids in milk but decreased percentages of crude protein and true protein in milk. Yucca shidigera extract did not affect percentages or yields of milk components, ruminal NH3 N, or urea N in milk or plasma. High soluble protein tended to increase both ruminal pH and concentrations of ruminal NH3 N. Yucca shidigera extract did not affect ruminal pH or NH3 N. High soluble protein increased concentrations of urea N in plasma and milk when both were measured by enzymatic assay, but differences in milk urea N measured by mid infrared reflectance spectroscopy were not significant. Neither Yucca shidigera extract nor increased ruminally undegradable protein was beneficial in this trial when fed to cows milking 30 to 35 kg/d. Concentrations of urea N in milk as measured by mid infrared reflectance spectroscopy were higher than those measured by enzymatic assay, but measurements by mid infrared reflectance spectroscopy were not as sensitive to treatment differences as were measurements by enzymatic assay.

Effects of chain length and unsaturation of fatty acid mixtures infused into the abomasum of lactating dairy cows.

Six cows were utilized in a 6 x 6 Latin square design with 21-d periods to determine effects of the postruminal profile of fatty acids on dry matter (DM) intake, milk yield and composition, nutrient digestibilities, and plasma metabolites. Treatments were abomasal infusions of 1) control [168 g/d of meat solubles (carrier for fatty acids) plus 10.6 g/d of Tween 80 (emulsifier)], 2) control plus 450 g/d of mostly saturated fatty acids, 3) control plus 450 g/d of palm oil fatty acids low in linoleic acid, 4) control plus 450 g/d of palm oil fatty acids, 5) control plus 450 g/d of soybean oil fatty acids, and 6) control plus 450 g/d of soybean oil fatty acids high in palmitic acid. Treatments 2, 3, 4, and 6 contained similar ratios of C16 to C18 fatty acids. Infusion of soybean oil fatty acids or soybean oil fatty acids high in palmitic acid decreased intakes of DM, organic matter, crude protein, acid detergent fiber, neutral detergent fiber, gross energy, and total fatty acids and tended to decrease yields of milk and fat-corrected milk compared with the infusion of mostly saturated fatty acids. Infusion of palm oil fatty acids low in linoleic acid or palm oil fatty acids decreased milk fat percentage compared with other treatments. Ruminal characteristics and apparent digestibilities of DM, organic matter, crude protein, acid detergent fiber, neutral detergent fiber, energy, total fatty acids, and total C18 fatty acids were not different. Infusion of fatty acids increased concentrations of cholesterol in plasma. The amount of unsaturated fatty acids passing into the small intestine may influence responses of dairy cows to supplemental fat.

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.

Effects of source of carbohydrate and protein and rumen-protected methionine on performance of cows.

Multiparous Holstein cows were fed diets consisting of alfalfa silage, corn silage, and a concentrate mixture containing primarily ground shelled corn or corn gluten feed; the diets were supplemented with 0 or 20 g/d of rumen-protected Met. The 183-d experimental period followed a 21-d covariate period beginning at calving. Data from early lactation (d 22 to 105) and the entire experiment were analyzed. Yields of milk and milk crude protein were not affected by treatment. Corn gluten feed increased the percentages of milk fat and total solids. The rumen-protected Met tended to increase both the crude protein and casein N content of milk. Body weight, milk fat percentage, and yields of milk fat, 3.5% fat-corrected milk, and total solids were greater when ground shelled corn and 20 g/d of rumen-protected Met or corn gluten feed and 0 g/d of rumen-protected Met were fed than when ground shelled corn and 0 g/d of rumen-protected Met or corn gluten feed and 20 g/d of rumen-protected Met were fed. A similar interaction for dry matter intake was significant only during d 22 to 204. Corn gluten feed increased plasma concentrations of His, Ile, Leu, and Val. Rumen-protected Met increased plasma concentrations of Met, decreased His, and tended to decrease Arg, Lys, and Orn. These data suggest that the dietary source of carbohydrate and protein can modulate the response of cows to rumen-protected Met.

Production and composition of milk from Jersey cows administered bovine somatotropin and fed ruminally protected amino acids.

Eight multiparous and 4 primiparous Jersey cows averaging 92 d of lactation were utilized in a replicated 4 x 4 Latin square design with 28-d periods to determine responses to bovine somatotropin (bST) and ruminally protected Met and Lys when diets were fed that contained supplemental fat. Treatments were 1) control [no bST or ruminally protected amino acids (AA)], 2) control plus bST, 3) control plus ruminally protected AA, and 4) control plus bST plus ruminally protected AA. Dry matter intake was increased by bST but was unaffected by ruminally protected AA. Milk yield was increased by bST but was not altered by ruminally protected AA compared with the control diet. The bST tended to increase percentages of fat and total solids in milk and increased yields of fat, protein, 3.5% fat-corrected milk, and total solids. Ruminally protected AA increased percentages of fat, protein, and total solids in milk; however, yields of milk components were unaffected by ruminally protected AA. Body weight and body condition scores were unaffected by treatment. Concentrations of essential AA in plasma were unaffected by bST administration. Ruminally protected Met and Lys increased the concentration of Met and tended to increase the concentration of Lys in plasma. The lack of an increase in yields of milk and milk protein when ruminally protected AA were fed suggests that adequate amounts of Met and Lys were supplied by the control diet and protein reserves of the cows to meet the AA requirements for synthesis of milk and milk components.

Response of cows fed a low crude protein diet to ruminally protected methionine and lysine.

Ten cows (mean = 128 DIM) were utilized in a replicated 5 x 5 Latin square design and fed diets formulated to supply adequate (18% CP) or inadequate (14% CP) Met and Lys. A prototype supplement of ruminally protected Met and Lys was added to the 14% CP diet to provide 0, 50, 100, and 150% of the predicted deficiency of Met and Lys. The DMI; yields of milk, 3.5% FCM, total N, protein N, and whey N; plasma concentrations of Arg, Cit, His, Ile, Leu, Orn, Phe, Pro, Tyr, Val, and urea N were greater for cows fed the 18% CP diet. Supplementing ruminally protected Met and Lys to the 14% CP diet did not affect DMI or yields of milk, 3.5% FCM, milk CP, and milk SNF. Milk fat yield was affected quadratically because it was greater when 0 or 150% of the deficiency of Met and Lys was supplied. Percentages of CP and casein N in milk increased linearly as cows were fed increasing amounts of ruminally protected Met and Lys. Plasma concentrations of urea N, Met, and Lys increased when ruminally protected Met and Lys were fed; however, other nutrients probably were limiting for synthesis of milk and milk protein when cows were fed a 14% CP diet because yields of each were not increased by ruminally protected Met and Lys.

Effects of dietary fat with or without nicotinic acid on nutrient flow to the duodenum of dairy cows.

Four Holstein cows, fitted with ruminal and duodenal cannulas, were utilized in a 4 x 4 Latin square design to investigate the effects of supplementing nicotinic acid to diets that contained 35% alfalfa haylage, 15% corn silage, and either 50% of a low fat concentrate or 10% whole raw soybeans and 40% of a high fat concentrate containing tallow. Treatments in a 2 x 2 arrangement were 1) low fat, no supplemental nicotinic acid; 2) low fat, 12 g/d of nicotinic acid; 3) high fat, no supplemental nicotinic acid; and 4) high fat, 12 g/d of nicotinic acid. The DMI and OM apparently and truly digested in the rumen and apparently digested postruminally were not different among treatments. Addition of fat to the diet decreased the concentration of total VFA in ruminal fluid but did not alter the molar proportions of any of the VFA; supplementation of nicotinic acid tended to decrease the molar proportion of acetate. Amounts of NAN, microbial N, nonammonia nonmicrobial N, and AA that flowed to the duodenum were similar among diets. The concentration of urea N in plasma decreased, and concentrations of cholesterol and triglycerides increased, when cows were fed supplemental fat. Milk composition and production of milk, 4% FCM, and milk components were not altered by addition of fat or nicotinic acid to the diet. Supplementation of fat or nicotinic acid to diets of dairy cows was not beneficial in this experiment.

High oil corn as silage or grain for dairy cows during an entire lactation.

Forty-five multiparous Holstein cows were used to compare the effects of diets that contained high oil corn grain, high oil corn silage, or a combination of both. At wk 4 after calving, cows were assigned to one of four treatment in a 2 (silage type) x 2 (grain type) factorial arrangement: 1) control silage and control grain, 2) high oil silage and control grain, 3) control silage and high oil grain, or 4) high oil silage and high oil grain. Diets contained haylage, corn silage, and concentrate (25:25:50, DM basis); corn grain was 27% of dietary DM. Data were analyzed for wk 4 to 17 and wk 4 to 43 of lactation and adjusted for covariate measurements made during wk 3. During wk 4 to 43, DMI increased when high oil grain was included in the diet, but was unaffected by type of silage. During wk 4 to 43 of lactation, yields of milk, CP, and fat; percentages and yields of N components in milk; body condition score; BW; and concentrations of NEFA, glucose, BHBA, and urea N in plasma were not affected by type of silage or corn grain fed. Results were similar for wk 4 to 17, except that milk yield tended to be higher for cows fed the high oil grain, and CP content of milk was lower when high oil corn silage was in the diet. Compared with corn grain from typical hybrids, high oil grain may improve DMI and milk yield of dairy cows during early lactation.