309. Nutrition, insulin, leptin and puberty in Merino ram lambs

Abstract

Merino sheep developed in Mediterranean regions so are well adapted to acute changes in food availability. However, restricted intake during pregnancy, especially in animals that are pregnant over the dry summer, could limit the positive effects of a winter rainy season on fetal development. In this study, we tested whether the level of nutrition during pregnancy and during pre-pubertal development affected blood concentrations of insulin and leptin, scrotal circumference and age of puberty in male Merino lambs fed with pasture. During dry weather, pregnant sheep were supplemented ad libitum with hay and lupin grain (Lupinus angustifolius) to compensate for decreases in pasture supply. Puberty was detected using a standardised behavioural test with oestrous ewes. Lambs were considered pubertal if they displayed mounting in two successive weekly tests. There were no differences in plasma concentrations of insulin or leptin. The values for both hormones simply displayed the same pattern, with a rise after feeding and a fall during non-feeding periods. There was no difference among treatments in either scrotal growth or age to puberty (Table 1). This might be because the dietary treatments, being administered by food restriction under field conditions, would not have the same effects as severe undernutrition that has been used in laboratory studies. Alternatively, Merino sheep may have a greater capacity to cope with mild nutritional stress.