Effects of High Concentrate Feeding and Fasting on Plasma Glucocorticoids in Dairy Heifers

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Abstract
A feeding trial was conducted to compare effects of a high concentrate diet on plasma glucocorticoids and observe postprandial relations between glucocorticoids, insulin, glucose and free fatty acids. Twelve Holstein heifers were randomly alloted to one of two treatments. Six heifers received a control ration of corn silage and concentrate (16% crude protein) in an approximate ratio of 80:20 on a dry matter basis and the remaining six heifers were adjusted to corn silage and concentrate in a 30:70 dry matter ratio. After a 30-day adjustment period, rumen fluid was sampled and analyzed for volatile fatty acids. Blood samples were drawn just prior to the morning feeding and at 2. 4, 8, 12, 24, 48 and 72 hr postfeeding. High concentrate feeding resulted in a decrease in the molar proportion of rumen acetate and an increase in the molar proportion of propionate. Treatment means through the first 12 hr postfeeding (feeding period) for high concentrate or control heifers were 87.4 and 79.9 mg/ 100ml for glucose; 27.7 and 13.4 μU/ml for insulin; .05 and .05 meq/1 for free fatty acids; and 14.8 and 7.9 ng/ml for total glucocorticoids. Fasting caused decreases in plasma glucose and insulin and increases in plasma free fatty acids and glucocorticoids with a loss of treatment differences in all cases. Copyright © 1979. American Society of Animal Science . Copyright 1979 by American Society of Animal Science.