The effect of embryo donor age and parity on the superovulatory response in Boer goat does
This study was conducted to evaluate the effect of the age and parity of the embryo donor on the superovulatory response and embryo recovery rate in Boer goat does. The oestrous cycles of seven maiden does (young, 1 - 2 years) and nine multiparous does (adult, 3 - 4 years) were synchronised using controlled internal drug release dispensers (CIDR’s) for a period of 17 days, and superovulated with pFSH during the natural breeding season. The superovulation treatment was administered as a total dose of 200 mg pFSH/doe given i.m. in seven dosages (at 12 h intervals) - starting 48 h prior to CIDR removal. Does were observed for oestrous behaviour three times daily, at 8 h intervals following CIDR withdrawal. Cervical inseminations (0.01 mL fresh undiluted semen) were performed 36 h and 48 h following CIDR removal and the embryos surgically flushed six days following the second artificial insemination. All does showed overt signs of oestrus. The time interval from CIDR removal to the onset of oestrus in the adult multiparous does (24.0 ± 4.0 h) was significantly shorter than that recorded in the younger does (32.0 ± 4.6 h). The age and parity of the embryo donors did not have any effect on the duration of the induced oestrous period. The mean number of CL’s, structures and embryos recovered were significantly higher in the adult multiparous does (19.8 ± 4.8, 21.3 ± 3.9 and 20.9 ± 4.5, respectively), compared to the young maiden does (13.7 ± 3.8, 11.7 ± 5.0 and 11.7 ± 5.0, respectively). The fertilisation rate, the mean number of unfertilised ova and degenerate embryos recorded did not differ between the young and adult multiparous does. The mean number of transferable embryos in the adult does (15.8 ± 6.4) was, however, significantly higher than in the young does (9.5 ± 3.7). The longer response time taken to the onset of oestrus had no influence on the fertilisation rate in young does. Although the young does recorded an acceptable fertilisation rate, the number of transferable embryos was, however, lower due to the lower total number of embryos produced by the young donor does and this may favour the use of older multiparous does as embryo donors in a multiple ovulation and embryo transfer programme.
Keywords: Maiden, multiparous, ovulation rate, embryo recovery