Effect of progestagen/PMSG treatment for oestrus synchronization of Tuj ewes to be bred after the natural breeding season

Abstract

The aim of this study was to investigate the effect of pregnant mare serum gonadotrophin (PMSG) and progestagen sponge on oestrus synchronization of Tuj ewes mated after breeding season. Body weights (b.w.) and condition scores (BCS) of seventeen mature fat-tailed Tuj ewes were recorded prior to the experiment and they were divided into two compared groups. All the ewes were treated by 30 mg Chronolone-impregnated intravaginal sponges for 14 days. Ewes in the first group (Group I, n = 9) were then injected with i.m. 600 I.U. PMSG upon sponge withdrawal while others, as control (Group II, n = 8) received placebo injection only. Ewes were monitored (at 2 h intervals) for both the signs of oestrus behaviour (classified as attractivity and receptivity) and their durations over the 102 h. Non-return rates were monitored (twice daily) during day 14-21 with the aid of a fertile ram. Lambing rates and litter sizes were recorded following the 150 ± 5 days of inseminations (hand-mating). Results showed that oestrus period was significantly prolonged (P < 0.05) in Group I. Additionally, a positive significant correlation (P = 0.021, R2 = 0.345) was found between BCS in situ and the litter size, regardless of PMSG administration. Furthermore, regardless of the nature of oestrus (induced or natural) in all the ewes, there was a profound effect of BCS per se on the overall litter size (P = 0.000, R2 = 0.633). It was significantly higher in ewes that had BCS higher than both 2.0 (P = 0.001, R2 = 0.633) and 2.5 units (P = 0.001, R2 = 0.654). In conclusion, PMSG combined with progestagen sponge administration for oestrus synchronization prolonged the duration of oestrus period but with no marked effects on the nonreturn rate, lambing rate or the litter size in Tuj ewes mated after breeding season. During this period, however, body energy reserves appeared to be the major effector of the litter size.