Reproductive performance of Karakul ewes following different oestrous synchronisation treatments outside the natural breeding season

Abstract

This study was designed to evaluate the efficiency of five different hormonal treatments of oestrous synchronization in Karakul ewes reared in southern Iran. During mid- to late spring, (outside the natural breeding season), 180 Karakul ewes were stratified based on age and body weight and then randomly allocated to six groups (n = 30/group). The oestrous cycles of the ewes in each group were synchronized using one of the following hormonal treatments: T1 - intramuscular (im) administration of 20 mg progesterone acetate in oil every second day for a 12-day period and an im administration of 500 IU equine chorionic gonadotrophin (eCG) on day 12; T2 - insertion of a controlled intravaginal drug releasing device (CIDR) containing 0.3 g progesterone for 12 days; T3 - administrating an intravaginal sponge containing 60 mg medroxyprogesterone acetate (MAP) for 12 days; T4 - a double injection (im) of 10 mg prostaglandin F2α nine days apart; T5 - a double injection (im) of 10 mg prostaglandin F2α nine days apart plus an im injection of 500 IU eCG on the day of the second prostaglandin F2α administration; T6 - control group. The ewes in Treatments 2 and 3 were intramuscularly injected with a 500 IU eCG at CIDR or sponge withdraw. Twenty-four hours after the last hormonal treatment, three fertile Karakul rams were introduced to the ewes in each experimental group and remained there for five days for oestrous detection and mating. Significant differences in oestrous response, number of ewes that lambed within the 152 ± 7 day period, fecundity and fertility rate were recorded between treatment groups. The oestrous response was comparable in Treatments 2 (93%) and 3 (100%), and significantly higher than the other treatments (T1 = 80; T4 = 37; T5 = 30 and T6 = 20%). The highest and the lowest number of ewes that lambed within 152 ± 7 days were 27 (90%) in Treatments 3 and 4 and 13% in Treatments 4 and 5, respectively. The highest recorded fecundity rate was 133% in Treatment 3 and the lowest, 75% in Treatment 4. Furthermore, the fertility rate was 90% in Treatment 3 that was significantly higher than in Treatments 4 (36%) and 5 (44%). The results of the present study indicated that oestrous synchronisation with progestagens plus eCG induced a synchronized oestrus in a higher percentage of Iranian fat-tailed Karakul ewes than prostaglandin F2α (with or without eCG) outside the breeding season. Furthermore, the administration of an impregnated intravaginal sponge for a 12-day period plus a dose of 500 IU eCG resulted in higher fertility, fecundity and lambing rates compared to the other hormonal treatments considered.

Keywords: Karakul ewes, oestrous synchronization, reproductive performance

South African Journal of Animal Science Vol. 36 (4) 2006: pp. 229-234