Nutrition and reproduction in the ram in a Mediterranean environment.

The stimulation of gonadotrophin secretion and testicular growth in lupin grain-supplemented rams is presented as a working model. This effect is characterised by three types of responses, the first of which is the stimulation of pulsatile secretion of LH. This response is expressed as a 2 to 3 fold increase in pulse frequency and is obtained after a period as short as 2-3 days, but thereafter it declines and becomes undetectable after 3-4 weeks. The second response is that of FSH which usually starts to be detectable 1 week to 10 days after supplementation has started and is maintained for several weeks. The third response, an increase in testicular size, is rarely detectable before 2 weeks but continues for at least 5 weeks. Nutritional cues seem to control testicular growth through changing the secretion of gonadotrophins. These changes do not fully explain the effects of supplementary feeding on reproduction in the ram. It is thus suggested that gonadotrophin-dependent mechanisms play a permissive role for testicular growth, but gonadotrophin-independent mechanisms are also involved in transducing the effects of nutrition on reproduction in the ram.