An evaluation of the success of MOET in two breeds of hill sheep maintained under normal systems of hill flock management

Abstract

AbstractThis study was undertaken to investigate factors affecting the success of multiple ovulation and embryo transfer (MOET) in Scottish Blackface (no. = 120) and Welsh Mountain (no. = 120) ewes, over a period of 2 years using a laparoscopic procedure for both embryo recovery and transfer. Superovulation was induced with ovine FSH, with 98 to 100% of ewes of both the breeds responding to the treatment. The overall mean superovulatory responses were 15⋅0 (s.e. 0⋅8) and 12⋅5 (s.e. 0⋅7) for Scottish Blackface and 15⋅3 (s.e. 0⋅9) and 12·8 (s.e. 0⋅8) for Welsh Mountain ewes in years 1 and 2, respectively. However, there was a wide degree of variation in superovulatory responses within each breed, with a range of 3 to 29 in Scottish Blackface and 1 to 40 in Welsh Mountain ewes. The mean embryo recovery rate was 71⋅9 (s.e. 3⋅5) % and 69⋅6 (s.e. 3⋅4) % for Scottish Blackface and 57⋅5 (s.e. 4⋅1) % and 60⋅6 (s.e. 3⋅6) % for Welsh Mountain ewes in years 1 and 2, respectively. The mean number of embryos recovered from Welsh Mountain ewes was significantly (P < 0⋅05) lower than that from Scottish Blackface ewes in both years. The lower mean number of embryos recovered in year 2 for both breeds was entirely a reflexion of the lower superovulatory responses in year 2. A significant (P < 0⋅001) relationship was observed between superovulatory response and the number of embryos recovered for both breeds. Some 77% and 72% of Scottish Blackface ewes and 65% and 73% of Welsh Mountain ewes yielded four or more transferable embryos in years 1 and 2, respectively. Neither the mean number nor the mean percentage of transferable embryos per donor ewe differed between breeds or years. A significant (P < 0⋅001) negative relationship was observed between the time of onset of oestrus and both superovulatory response and number of embryos recovered in Scottish Blackface ewes only. Embryo quality was affected by the time of onset of oestrus. In both breeds, the highest proportion of grade 1+2 embryos and the lowest proportion of unfertilized/degenerate embryos occurred in the middle range time, with a reduction in the proportion of grade 1+2 embryos in ewes that came into oestrus either early <19 h) or late (>30 h) after sponge removal. Only one embryo was transferred to each recipient and the embryo survival rates were 76⋅8% and 74⋅6% (Scottish Blackface), and 69⋅6% and 87⋅3% (Welsh Mountain) for years 1 and 2, respectively. Overall the results of this study suggest that MOET is as successful in hill ewes as has been reported for lowland breeds, even without making any major concessions to their hill status.