Influence of Nutritional Management on Folliculogenesis in Ewes

In sheep, follicle populations are very responsive to dietary intake. Definitions of effect of nutrition on ovulation rate have been identified 1) static effect, 2) dynamic effect and 3) immediate effect. An example of the immediate effect is short-term lupin grain supplementation for 4-6 days during the end of luteal phase prior to ovulation. This treatment increases the number of follicles and ovulation rate without altering body weight. The mechanisms of nutritional effects on folliculogenesis are not effects associated with the amount of nutrient supplies. It is much more prone that they are specific nutrient signaling effects. Nutrition modulates reproductive function at multiple levels through the circulating metabolic hormones such as insulin, insulin-like growth factor-I and growth hormone. These hormones have important roles in the control of follicle growth and are likely to be mediators of the effects of nutritional intake on ovulation rate, by acting to regulate the action of key reproductive hormones such as gonadotrophins and steroids in follicles. Insulin is an important regulator of folliculogenesis because the uptake of glucose is regulated by insulin, suggesting a role for insulin as a mediator in the mechanism of nutritional effects on ovulation. FSH and negative feedback mechanisms of the hypothalamus-pituitary-ovarian axis are important in regulating follicular response to nutritional stimulation. Ovarian steroids can also modulate the action of metabolic hormones, resulting in interactive positive and negative feedback loops. Nutritional supplementation with high energy diets stimulates folliculogenesis by decreasing negative feedback to induce compensatory increases in folliculogenesis. We suggest that nutritional suppression of oestradiol leads to the increases in FSH that stimulate folliculogenesis.