Effect of hormone therapy on lambing performance of Zandi ewes at different ages under 3 lambing in 2 years schedule

To investigate the effect of hormone therapy and 3 lambing in 2 years schedule on lambing performance of Zandi ewes in different ages, 149 ewes were randomly assigned to 7 groups as their ages (1 year old to 7 year old). In all group ewes were exposed to hormone therapy for 3 lambing periods by 8 months intervals. Hormone therapy comprised that all ewes were inserted progesterone sponges for 12 to 14 days before their own mating dates and administrated with 400 IU PMSG at sponge removal. All ewes were mated with rams naturally. There were significant differences among age groups as parturition mean, lambing rate, litter size, weaning rate, lamb born crop and lamb weaned crop (P<0.01), while the bareness of ewes and lamb mortality rate before weaning, were statistically equal in all groups. The results revealed that 5 year old and 6 year old ewes had the highest response to hormone therapy under a 3 times lambing in two years schedule and have a highest lamb production, whereas 1 year old and 7 year old ewes had a lowest performance.