Effects of tallow in diets based on corn silage or alfalfa silage on digestion and nutrient use by lactating dairy cows.

Six multiparous Holstein cows (average 31 days in milk; 36.3 kg/d of milk) fitted with ruminal cannulas were used in a 6 x 6 Latin square with 21-d periods to investigate the effects of diets that varied in forage source and amount of supplemental tallow. Isonitrogenous diets in a 2 x 3 factorial arrangement were based on either high corn silage (40:10 corn silage to alfalfa silage, % of dry matter) or high alfalfa silage (10:40 corn silage to alfalfa silage, % of dry matter) and contained 0, 2, or 4% tallow. Intakes of dry matter and total fatty acids were lower when cows were fed the high corn silage diet. Tallow supplementation linearly decreased dry matter intake. Milk yield was unaffected by diet; yields of milk fat and 3.5% fat-corrected milk were higher for the high alfalfa silage diet but were unaffected by tallow. Milk fat percentage was higher for the high alfalfa silage and tended to decrease when tallow was added to the high corn silage diet. Contents of trans-C18:1 isomers in milk fat were increased by high corn silage and tallow, and tended to be increased more when tallow was fed in the high corn silage diet. Ruminal pH and acetate:propionate were lower when high corn silage was fed. Ruminal acetate:propionate decreased linearly as tallow increased; the molar proportion of acetate was decreased more when tallow was added to the high corn silage diet. Ruminal liquid dilution rates were higher for the alfalfa silage diet; ruminal volume and solid passage rates were similar among diets. Total tract apparent digestibilities of dry matter, organic matter, crude protein, starch, energy, and total fatty acids were unaffected by diet. Digestibilities of neutral detergent fiber, acid detergent fiber, hemicellulose, and cellulose were lower when high corn silage was fed. The high alfalfa silage diet increased intakes of metabolizable energy and N, and increased milk energy and productive N. Tallow decreased the amount of N absorbed but had few other effects on utilization of energy or N. Tallow linearly increased concentrations of nonesterified fatty acids and cholesterol in plasma; cholesterol was increased by high alfalfa silage. Overall, forage source had more pronounced effects on production and metabolism than did tallow supplementation. Few interactions between forage source and tallow supplementation were detected except that ruminal fermentation and milk fat content were affected more negatively when tallow was fed in the high corn silage diet.

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.

Ruminal degradation and dose response of dairy cows to dietary L-carnitine.

In Experiment 1, in vitro degradation of L-carnitine was measured in ruminal fluid obtained either from a cow that was fed a 75% concentrate diet or from a cow fed a control (50% forage and 3% fat) diet. Carnitine degradation was greater in ruminal fluid from the cow fed the control diet than in ruminal fluid from the cow fed the 75% concentrate diet and was more rapid in ruminal fluid obtained after 2 wk of adaptation to dietary carnitine supplementation (7 g/d). In Experiment 2, 20 multiparous Holstein cows were used in a replicated 5 x 5 Latin square design to determine the effects of increasing the amount of dietary L-carnitine (0, 0.875, 1.75, 3.5, or 7.0 g/d) that was fed to lactating dairy cows. All cows received the same diet, which contained 3% added fat. Carnitine concentration in milk and plasma increased linearly with carnitine supplementation. The DMI, milk yield, and milk composition were unaffected by carnitine. Apparent total tract digestibilities of NDF and fatty acids decreased quadratically as the amount of supplemented carnitine increased; generally, means were lowest when cows were fed 1.75 g/d of carnitine. The concentration of total VFA and molar percentages of individual VFA in ruminal fluid were unaffected by the amount of carnitine fed. Concentrations of glucose, NEFA, and urea N in plasma were unaffected by the amount of dietary carnitine; however, plasma cholesterol concentration decreased linearly as carnitine increased. Supplementation of < or = 7.0 g/d of dietary carnitine did not benefit DMI, milk yield, milk composition, or digestive measurements in this experiment.