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Relationship of Various Blood Metabolites to Voluntary Feed Intake in Lactating Ewes^{1, 2,}

Department of Animal Science, Cornell University, Ithaca, New York 14850

Two-day trials were conducted with ewes in early lactation. A pelleted ration (45% conc-55% roughage) was fed for a period of three hours at 8 AM and 3:30 PM. On day 1 sufficient feed was offered to insure ad libitum consumption at both periods. On day 2 the AM feed was limited to one-half the amount consumed during the pre-experimental AM period, and the PM feed was ad libitum. Carotid and jugular blood samples were taken at 0, 0.5, 1.5, 3 and 7 hours after the AM meal. Correlations were calculated between AM and PM feeding periods on days 1 and 2. Interval feed consumption was measured after 0.5, 1.5 and 3 hours in the AM and 0.5 and 3 hours in the PM. Seventy percent of the feed was consumed in the first 20 to 30 minutes. Blood volatile fatty acids (VFA) and ketones increased markedly and peaked at 3 hours (day 1) and 1.5 hours (day 2). Blood glucose levels dropped sharply by 0.5 hour but increased significantly by 1.5 hours on both days. Plasma free fatty acids (FFA) decreased on both days, but rose markedly on day 2 by 7 hours. Acetate, propionate and glucose levels were poorly correlated to feed intake patterns. Ketone correlations, although low, had a pattern similar to butyrate correlations. Butyrate and FFA levels were the most highly correlated to subsequent VFI. FFA concentration at 7 hours was the best single predictor of subsequent feed intake, accounting for 50% of the variation (R² = 0.496).

² Supported in part by U. S. Department of Agriculture Grant no. CSRS 427-15-17. The senior author was supported by a National Institutes of Health Traineeship, No. 5 TOI GM 01221-05.

³ Present address: Department of Human Nutrition and Foods, Virginia Polytechnic Institute, Blacksburg, Virginia.

Manuscript received 22 July 1969.