Sex and season are major determinants of voluntary food intake in sheep

Abstract

Seasonal changes in voluntary food intake (VFI) are seen in various species, including sheep. This paper reviews recent work in this area, especially in relation to alterations in the expression of appetite-regulating peptides in the brain of the sheep. Work in the hamster is also reviewed because this is another species in which VFI is regulated by photoperiod. In normally grazing sheep, appetite is maximal in the late summer/early autumn and minimal in spring. This appears to be owing to increased expression of the orexigenic peptide, neuropeptide Y. Similar results are obtained in sheep that are subjected to controlled photoperiod. The same does not appear to be true for hamsters. Further work in sheep has shown that there is a seasonal pattern of responsiveness to leptin that is more pronounced in females than in males. In particular, the effect of leptin to reduce food intake is maximal in female sheep in the spring; reasons for the sex difference are discussed.