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Control of Feed Intake in Sheep^{1, 2,}

Monsanto Company³ and Washington University^,3, St. Louis, MO 63167

Abstract

The control of feed intake is highly complex, involving many peripheral, as well as central nervous system (CNS) factors. The various signals involved in the control of feeding behavior are integrated in the hypothalamus and appropriate responses, i.e., feeding or cessation of feeding, are generated. The actual neurochemical events subserving this function are not well understood, although specific roles for each of the neurotransmitter systems have been proposed. More recently, certain neuropeptides have been shown to affect feeding behavior in sheep, as well as many other species. Most of the evidence points to the involvement of two families of neuropeptides in the control of feed intake in sheep: the opioid peptides, which include enkephalins, endorphins and dynorphins, and cholecystokinin (CCK) peptides, of which CCK-8 is the primary brain form. Certain opioid peptides, such as metenkephalins, β-endorphin and dynorphin A peptides, have been shown to stimulate feeding after CNS administration in sheep, while CCK peptides suppress feeding. Thus it has been proposed that opioid peptides are involved in the initiation of feeding, or hunger, and CCK peptides, in the inhibition of feeding, or satiety. Although much more is known about the effects of CCK peptides than opioid peptides on feeding behavior of sheep, evidence is accumulating for direct interaction between CCK- and opioid-containing neurons that could lead to better understanding of hunger and satiety in sheep.

¹ Research from the authors' laboratory was supported in part by Grants NS17670, GMO2O51, MH35746 and NIH Postdoctoral Fellowship NSO6595 and Sloan Foundation Fellowship BR2190 awarded to M. A. Della-Fera.

² Presented at a symposium on "Controls of Feeding in Farm Animals" held July 27, 1983 at the 75th Annu. Meet. Amer. Soc. Anim. Sci., Washington State Univ., Pullman.

³ Nutrition Chemicals Division, Monsanto Agriculture Co. and Dept. of Preventive Med., School of Med., Washington Univ.