Abstract
Abstract. Suffolk rams were fed melatonin pellets in 2 experiments to control their reproductive seasonality. In Exp. 1, 6 rams were randomly divided into 2 groups: Group 1M rams (n=3) were fed 4 mg of melatonin daily for 100 days from February 17 (Day 0), and Group 1C rams were untreated. Scrotal circumference in Group 1M was significantly larger than that in Group 1C on Day 45 and 75 (P<0.05). Libido tests, performed on Day 104, indicated that mating behaviour in the Group 1M rams was more active compared to Group 1C rams. Group 1M rams had more sperm per ejaculation than control rams. In Exp. 2, 4 rams were divided into 2 groups: Group 2M rams (n=2) were fed 4 mg of melatonin daily for 45 days from May 16 (Day 0), and Group 2C rams were untreated. The timing of seasonal development in scrotal circumference was advanced in Group 2M rams; the circumference reached maximum on Day 45. However, an abrupt decrease in scrotal size was seen in Group 2M 45 days after cessation of melatonin feeding. These results suggest that melatonin feeding either from February or May can increase the reproductive activity of Suffolk rams during periods of seasonal regression.
