Search

Four multiparous, ruminally and duodenally cannulated Holstein cows in midlactation were utilized in a 4 x 4 Latin square to evaluate the effects of supplemental fat from sources varying in proportions of unsaturated and saturated fatty acids on nutrient digestion and lactation performance. All diets (45% alfalfa hay) contained 12% whole cottonseed (as-fed); treatments were no supplemental fat (control, 3% total fatty acids, dry matter basis) or additional 2% tallow, 2% yellow grease, or 2% blend (60% tallow: 40% yellow grease). The unsaturated to saturated fatty acid ratios were 1:1 for tallow and 2.5:1 for yellow grease. Dry matter intake, apparent ruminal and total tract digestibilities of organic matter, neutral detergent fiber, acid detergent fiber, N, and fatty acids, and microbial efficiency were similar across treatments. Microbial N flow to the duodenum was increased by yellow grease. Supplemental fat reduced the postruminal digestibility of fatty acids, primarily the saturated fatty acids; increasing saturation of the fat source magnified the reduction. Total volatile fatty acid concentrations and ruminal fluid pH were unaffected by fat supplementation or saturation level. Blend decreased ruminal pH and acetate to propionate ratio. Yields of milk and milk fat increased with fat supplementation. Concentrations and yields of trans vaccenic acid in milk increased linearly with the unsaturated fatty acid content of the fat supplement. Modest supplementation using highly unsaturated fats to diets containing whole cottonseed can increase milk production without disturbing rumen function, evident by the similar VFA concentrations, nutrient digestibilities, and milk composition.

Five primiparous Holstein cows (55 d in milk) that were fitted with ruminal and duodenal cannulas were used in a 4 x 5 incomplete Latin square to determine the effects of blends of steam-flaked and dry-rolled corn on site and extent of nutrient digestion and milk yield and composition. Diets were fed as total mixed rations and consisted of 45% forage and 55% concentrate; each diet contained 27% corn grain. Dietary treatments were composed of blends of dry-rolled and steam-flaked corn in ratios of 100:0, 67:33, 33:67, and 0:100. Intake of dry matter; digestibilities of dry matter, organic matter, acid detergent fiber, cellulose, neutral detergent fiber, fatty acids, and N; and microbial efficiency were unaffected by diet. Ruminal, postruminal, and total tract digestion of starch increased linearly, and starch passage to the duodenum decreased linearly, as the proportion of dry-rolled corn in the diet decreased. Ruminal propionate and valerate increased linearly, and acetate, butyrate, isovalerate, and the acetate to propionate ratio decreased linearly, as proportions of dry-rolled corn in the diet decreased; however, no changes in total volatile fatty acid concentrations in ruminal fluid were observed. Ruminal fluid pH was similar across diets. A decrease in dry-rolled corn decreased ruminal ammonia N and plasma urea N linearly. Milk yield and composition, as well as milk N fractions, were similar across diets. Although changes in fatty acid composition of milk fat were small, linear decreases in percentages of trans-C16:1 and cis-9- and cis-10-C18:1, as well as a linear increase in the percentage of C18:2 occurred as the proportion of dry-rolled corn in the diet decreased. An increased proportion of dry-rolled corn in the diet decreased digestion of starch in the rumen, and patterns of volatile fatty acid concentrations shifted accordingly. However, no effects on lactational parameters were observed.

Three multiparous Holstein cows in midlactation were fitted with ruminal and duodenal cannulas. Cows were used in an experiment with a 3 x 3 Latin square design to study the effect of corn processing on nutrient flow from the rumen to the duodenum and on ruminal fermentation in lactating cows. Cows were fed diets consisting of 40% forage and 60% concentrate. The only difference in dietary ingredients was the type of processed corn included at 24% of the total diet (as-fed basis). Treatments were dry-rolled corn with a bulk density of 0.54 kg/L and steam-flaked corn with a bulk density of either 0.39 kg/L or 0.31 kg/L. Ruminal fluid pH was not affected by corn processing, but steam-flaking decreased the molar percentage of acetate and increased the molar percentage of propionate. Digestibility of starch in the rumen was not affected by processing. Digestibility of starch entering the duodenum as well as apparent digestibility of starch in the total tract were increased by steam-flaking. Flow of feed and microbial N from the rumen and microbial N efficiency were not affected by grain processing. Yields of milk and milk components as well as composition of milk were not affected by grain processing.

Five multiparous Holstein cows in midlactation that were fitted with ruminal and duodenal cannulas were used in a 3 x 5 incomplete Latin square. The objective of this study was to examine the effects on nutrient digestion of wheat processing and method of tallow addition to the diets of lactating dairy cows. Diets consisted of 45% forage and 55% concentrate, and each diet contained 20% wheat and 2% tallow (as-fed basis). Treatments were dry-rolled wheat with tallow added to the concentrate, steam-rolled wheat with tallow added to the concentrate, and steam-rolled wheat with tallow added first to the wheat. The dry matter intake; digestion of starch, fiber, and fatty acids; ammonia N concentration; and molar proportions of volatile fatty acids in ruminal fluid were not affected by treatments. The apparent digestibility in the total tract of organic matter and nitrogenous compounds was significantly higher for the steam-rolled treatment with tallow added first to the wheat. Mean ruminal fluid pH was similar across treatments; however, cows fed the diet containing steam-rolled wheat with tallow added first to the wheat had the smallest pH change from 0 to 2 h postfeeding. Milk yield did not differ, regardless of cow diet. Method of tallow addition had marked effects on the apparent digestibility of organic matter and N in the total tract of lactating dairy cows.