Introduction Directory UMM :Data Elmu:jurnal:A:Animal Reproduction Science:Vol64.Issue1-2.Dec2000:

78 H. Quesnel et al. Animal Reproduction Science 64 2000 77–87

1. Introduction

In cyclic gilts which are chronically underfed, a transient increase in feed intake flush- ing increases ovulation rate Cox et al., 1987; Flowers et al., 1989; Beltranena et al., 1991. These effects are likely to be mediated by alterations in gonadotrophin secretions Cox et al., 1987; Flowers et al., 1989 andor alterations in ovarian responsiveness to gonadotrophin action, both related to nutritionally-induced changes in circulating metabolic hormones Cox et al., 1987; Beltranena et al., 1991. Indeed, exogenous insulin increases ovulation rate Cox et al., 1987 and decreases follicular atresia Matamoros et al., 1991, when ad- ministered during preovulatory follicular maturation, and stimulates follicular growth in nutritionally-restricted gilts Britt et al., 1988. Insulin also increases intrafollicular con- centrations of insulin-like growth factor I IGF-I in diabetic gilts Edwards et al., 1996 and in prepuberal gilts Matamoros et al., 1991. Therefore, the stimulatory action of insulin on final follicular maturation in gilts submitted to a nutritional flushing may be mediated by IGF-I stimulatory effects on folliculogenesis. In adult sows which are in energy deficit dur- ing lactation, supplementation with insulin either before or after weaning has no clear effect on ovulation rate, steroidogenesis or follicular IGF-I system review: Prunier and Quesnel, 2000. Mechanisms underlying the effects of nutrition on the ovaries may thus differ in young and adult sows or may depend on the pattern of feeding applied, feed restriction after high feed intake or flushing after feed restriction. The aim of the main experiment described here was to investigate the effect of insulin supplementation on final follicular development in gilts submitted to feed restriction. Because we previously observed that the luteal phase was not a critical period with respect to the influence of feed restriction on ovulation rate Quesnel et al., 1999, a preliminary experiment was carried out to determine whether a feed restriction starting at luteolysis is able to alter follicular growth.

2. Materials and methods