An attempt to advance the breeding season of red deer (Cervus elaphus) hinds

Abstract

An attempt was made to advance the calving date of red deer (Cervus elaphus) hinds by inducing them to ovulate prior to the normal breeding season with a GnRH analogue, buserelin. Recent work in this area has shown that buserelin will induce ovulation, but not overt oestrus or conception, in anoestrous red deer hinds. This study attempted to improve the fertility of hinds prior to the breeding season by (a) introducing the stag after the hinds had already cycled once, and (b) lowering the buserelin dosage used in previous trials. Twelve lactating hinds (Group HH) were each treated with 2 CIDRs (Type G) from 23 January to 4 February. Between 2 and 6 February these hinds received 4 injections of buserelin at a high (4,3,2 and 10 µg respectively) dosage regime. Group H and L hinds (n = 12) received CIDR treatment from 5 February to 17 February. Ovulation was synchronised in Group HH hinds on 17 February with a prostaglandin analogue. All treated hinds received 4 i.m. injections of buserelin between 15 and 19 February at either the high (Groups HH and H) or low (2, 1, 1, and 4 µg respectively; Group L) dosage regimes. Control hinds (n = 12) received no treatment throughout the experiment. All groups were run with a stag (in which rutting had been advanced with melatonin implants) from 18 February, and hinds were observed for 45 hours from this time for oestrus and mating. These events failed to occur and ovulation was again synchronised in all treated hinds on 29 February with prostaglandin analogue. Half (i.e. 6) of the hinds in each of the treated groups received buserelin injections between 27 February and 2 March at the high (Subgroup H(h)) or low (Subgroups HH(l) and L(l)) dosage regimes. All hinds were observed for oestrus and mating as previously. None of the hinds showed oestrus behaviour, and hence were not mated, throughout the experiment. Examination of all hinds by rectal ultrasonography suggested that the mean date of conception in all treated groups was not significantly different from that of controls, although because foetal ageing was based primarily on measurements of placentomes rather than on the foetus itself it was probably not accurate. Following synchronisation on 17 February, plasma progesterone concentrations indicated that 1/12, 6/12,4/12 and 3/11 of Groups C, HH, H and L hinds had ovulated. Hinds were more likely to ovulate if they had already been exposed to natural hormones from 1 or 2 previous cycles. The hinds appeared to revert to anoestrus following the induced cycles. In this study, lowering the dosage of buserelin did not overcome the lack of conceptions observed in previous experiments. It is still not known why GnRH administration fails to induce overt oestrus or conception in anoestrus deer hinds, as it does for other species of domestic animals, even after 2 or 3 induced cycles in succession. It is suggested that future research is targeted to investigate the contribution of post partum or lactational anoestrus to infertility prior to the breeding season.