Follicle development, endocrine profiles and ovulation rate in adult Merino ewes: effects of early nutrition (pre- and post-natal) and supplementation with lupin grain.

In adult ewes, we tested whether ovarian function, including the response to short-term supplementation, was affected by the nutrition of their mothers during the pre-/post-natal period. A 2×2 factorial design was used with nutrition in early life (low or high) and a 6-day supplement (with or without) as factors. All ewes received three prostaglandin (PG) injections 7 days apart, and the supplement (lupin grain) was fed for 6 days from 2 days after the second until the third PG injection. We measured reproductive and metabolic hormones, studied follicle dynamics (ultrasonography), and evaluated granulosa cell numbers, aromatase activity and oestradiol (E2) concentrations in follicular fluid in healthy follicles at days 3 and 7 of supplementation. Ovulation rate was increased by 25% by exposure to high pre-/post-natal nutrition (1.5 vs 1.2; P<0.05), in association with a small decrease in FSH concentrations (P=0.06) and a small increase in insulin concentrations (P=0.07). The number of healthy antral follicles was not affected. Acute supplementation increased the number of granulosa cells (3.7±0.2 vs 3.0±0.2 million; P<0.05) in the largest follicle, and the circulating concentrations of E2 (4.6±0.3 vs 3.9±0.3 pmol/l; P<0.05) and glucose (3.4±0.03 vs 3.3±0.03 mmol/l; P<0.01). Both early life nutrition and acute supplementation appear to affect ovulation rate through changes in glucose-insulin homoeostasis that alter follicular responsiveness to FSH and therefore E2-FSH balance.

Embryo losses in sheep during short-term nutritional supplementation.

To test whether a nutritional supplement fed from 6 days before until 15 days after insemination reduces progesterone concentrations and increases embryo losses, Merino ewes were artificially inseminated (Day 0). Control ewes (n = 116) were not supplemented whereas Lupin6 ewes (n = 112) were supplemented with 500 g lupin grain daily for 6 days before insemination, and Lupin6+15 ewes (n = 122) from 6 days before until 15 days after insemination. There were no major differences between treatment groups in progesterone concentrations over the first 17 days of pregnancy. Embryo losses over Days 10-17 were lower in the Lupin6+15 than in the Control and Lupin6 groups, but the opposite occurred from Day 17-30. The concentrations of insulin and IGF-I were higher in Lupin6+15 ewes on Days 5, 12 and 17, compared with Lupin6 and Control ewes, while leptin concentrations decreased by Day 17 in the Lupin6+15 group. We conclude that feeding ewes for 15 days after mating improved embryo survival, which was associated with an increase in the concentrations of metabolic hormones and lower progesterone concentrations. However, the decrease in leptin concentrations promoted by the interruption of supplementation seems be linked to increased embryo mortality up to Day 30.

The use of a 'first-wave' model to study the effect of nutrition on ovarian follicular dynamics and ovulation rate in the sheep.

We have developed an experimental model in which groups of ewes are simultaneously experiencing the first ovarian follicular wave of their oestrous cycle. We used this 'first-wave model' in a 2 × 2 factorial experiment (ten ewes per group) to study the effect of body condition (BC) and a short-term supplement on follicular dynamics and ovulation rate. The 'first-wave' was established by giving ewes three injections of prostaglandin (PG), 7 days apart. The 6-day supplement (lupin grain) began 2 days after the second PG injection and continued until the third. Follicles were studied by ultrasound, and blood was sampled to measure glucose and hormones. The supplement increased (P<0.01) the concentrations of glucose, insulin and leptin, decreased FSH concentrations (P<0.01) and tended to increase oestradiol concentrations (P=0.06). The supplement tended to increase the number of 3 mm follicles (P=0.06). Compared with low-BC ewes, high-BC ewes had more follicular waves (P<0.05), higher concentrations of insulin, leptin and IGF1 (P<0.05) and tended to have higher FSH concentrations (P=0.09). Leptin and insulin concentrations remained high until the end of supplementation in high-BC ewes, whereas they decreased after the third day of supplementation in low-BC ewes. In conclusion, high concentrations of metabolic hormones in fat ewes are associated with the development of more follicular waves. When a supplement is superimposed on this situation, changes in glucose and metabolic hormones allow more follicles to be selected to ovulate.