Appetite and Insulin-Metabolite Harmony in Portal Blood of Sheep Fed High or Low Roughage Diet with or without Intraruminal Infusion of VFA

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Abstract
Two experiments were conducted with mature Awasi wethers to study feed intake behavior and the effect of intraruminal infusion of physiological solutions of saline, acetate, propionate or butyrate at pH 6.5 on the plasma levels of insulin, glucose, ketone bodies and free fatty acids in portal and jugular blood of sheep fed ground rations containing hay and grain in the proportion of 75:25 or 25:75. The digestible energy content of high- and low-roughage diets were 2.9 and 3.5 kcal/g, respectively. Experiment 1 involved eight sheep to study the digestible energy intake patterns of rations at 1/2, 1, 2, and 3 hr (am and pm) post-feeding, while in experiment 2 changes in the blood components also were studied in six catheterized sheep at 0, ½, 1, 2, 3, and 7 hr post-feeding. Fifty-two and 48% of their digestible energy intake from high grain and high roughage diets, respectively, were consumed by ½ hr; the value was 70% for both rations by 1 hour. The digestible energy intakes of both rations were decreased (P<.05) following intraruminal infusion of each VFA and the severity of depression decreased with an increase in VFA chain length. Plasma level of insulin and ketones increased in both portal and jugular veins following feeding or intraruminal infusion of acetate, propionate or butyrate. Plasma free fatty acid levels, on the other hand, decreased significantly following the same treatments while portal blood glucose tended to decrease at 30 min after initiation of eating. Plasma insulin concentrations showed the highest and most sustained peaks with propionate infusion. The results indicate the possibility that insulin could regulate a primary satiation by increasing the uptake of already existing propionate in the portal circulation by the liver tissue in the early hours of eating. Copyright © 1975. American Society of Animal Science. Copyright 1975 by American Society of Animal Science.

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