Response to different oestrous synchronisation protocols and fertility of ewes following artificial insemination

Abstract

The response of South African Mutton Merino (SAMM) ewes to synchronisation of oestrus and fertility following different protocols and artificial insemination (AI) were studied using data collected during the autumn breeding season. The study was aimed at comparing the effect of long and short-term progesterone (P4) treatment and their combination with either equine chorionic gonadotropin (eCG) or the ram effect (Ram) on oestrous response and fertility of ewes. Ewes (n = 78) were randomly allocated to four treatment groups in a 2×2 factorial design and primed with controlled internal drug release (CIDR) for a 9 (short) or 14 d (long) period. At CIDR withdrawal, ewes in each group received either a single intramascular injection of equine chorionic gonadotrophin (eCG; 300 IU) or exposure to the ram effect; eCGshort (n=19), Ramshort (n=21), eCGlong (n=19) and Ramlong (n=19). Oestrous behaviour was monitored from 12-84 h post CIDR withdrawal and ultrasound performed at 48 h post CIDR withdrawal to examine number and diameter of follicles. Artificial insemination (AI) was performed twice at 48 and 60 h post CIDR withdrawal with fresh undiluted semen using the cervical method. Non-return rate (NRR) was monitored 15-21 d post AI while pregnancy diagnosis was performed by transrectal ultrasound at 35 d post AI and confirmed by lambing data. Oestrous behaviour was observed in 98.7% of all synchronised ewes, with no significant difference between treatment groups. Overall, CR and the proportion of ewes lambing to synchronised oestrus were (74.4% and 52.6%, respectively). There was no significant difference between treatment groups in oestrus response, onset of oestrus, duration of oestrus, number of follicles, diameter of the largest follicle, NRR, conception rate (CR), AI to lambing interval, twinning rate and number of lambs born. When data were pooled, CIDR-14 d protocols showed a significantly shorter interval to onset of oestrus (24.9 ± 1.6 versus 30.8 ± 2.1, P < 0.05) than CIDR-9 d protocols but there was no difference (P > 0.05) between eCG and Ram protocols when data were pooled. CIDR-9 d protocols resulted in a significantly higher CR (85.0% versus 63.2%, P < 0.05 ) than CIDR-14 d protocols when data were pooled but there was no difference (P > 0.05) in CR between eCG and Ram protocols. Mean AI to lambing interval was 158.2 ± 1.2 d, ranging from 147-154 d and 166-186 d post AI. The proportion of ewes lambing to synchronised oestrus per treatment group were (eCGshort (52.6%), Ramshort (42.9%), eCGlong (63.2%), Ramlong (52.6%), P > 0.05). Therefore, it can be concluded that the 4 protocols investigated were effective in synchronising oestrus with similar response to synchronisation of oestrus and fertility between treatment groups. Of the 4 protocols, the Ramlong protocol offers the benefit of reduced cost, reduced hormonal use and adequate fertility compared to other protocols. In addition, the cost of labour involved is foregone and a safer product is disposed of to the environment compared to use of the eCGlong and Ramshort or eCGshort protocols respectively.