Lactational, metabolic, and physiological effects of dietary fats and isoacids on early lactating first-calf Holstein heifers
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Forty four first-calf heifers were randomly selected to determine lactational and metabolic responses to high fat diets and isoacids. All heifers were allowed ad libitum consumption of a control diet for the first 2 weeks of lactation and then offered experimental diets Eor the next 4 weeks. Each 6 cows of twenty four were randomly assigned to 1) a control diet (C) with 35.2% corn silage, 14.4% alfalfa haylage and 50.4% concentrate (dry matter basis), 2) C with 2% calcium stearate (S) substituted for corn grain, 3) C with 2% tallow (T) for corn grain, and 4) C with 10% whole cottonseed (W) for corn grain, cottonseed meal and cottonseed hulls. The remaining 20 heifers were randomly assigned to diets C, S, T, and W, each with 4g/kg isoacids added (CI, SI, TI, and WI). Fat supplementation or isoacid addition did not affect milk production. Addition cf isoacid increased milk fat percentage, 4% fat-corrected milk, milk fat production (kg/day) and dry matter intake. Differences due tc isoacid were greatest when added to W. Increased milk lactose percentage and weight gain were evident in animal receiving WI compared to W ration. Fat supplementation depressed percentages cf milk fat, milk lactose and milk solids-not-fat. Milk protein percentage and somatic cell count were not affected by treatments. Plasma glucose,and glucose and epinephrine challenge parameters were not affected by diet. Peak plasma non-esterified fatty acid response to epinephrine injection, detected at 10 to 12 minites, was similar for C, S, T, and W. Concentrations of individual volatile fatty acids (VFA) and total VFA in rumen fluid were increased by fat supplements. Isoacid addition increased the amounts of isobutyrate and isovalerate; however, acetate and total VFA concentrations were decreased compared to CI when isoacids were added to high fat diets. The ratio of acetate to propionate was similar for all diets. Digestibilities cf dry matter, crude protein, and acid detergent fiber were not influenced by diet. The efficiency of energy utilization was highest for control diet. In conclusion, lactational, metabolic, and physiological responses to S, CI, and WI were favorable. Responses to W were lowest.
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