Abstract

Early embryo survival was examined in recipient heifers following the transfer of either 5 or 15 (Expt 1, N=19), or either 2 or 10 (Expt 2, N=46) in vitro produced embryos transferred into the same uterine horn. In Expt 1, the mean ± s.e. number of conceptuses per pregnant recipient was 2.5 ± 0.6 and 10.8 ± 0.8 (P<0.001) in recipients receiving either 5 or 15 embryos. Overall, 63 ± 4% of embryos survived (mean ± s.d.), with no difference among recipients receiving 5 embryos and examined on Day 15, or receiving 15 embryos and slaughtered on either Day 15 or Day 22 (56 ± 10%, 77 ± 5% and 68 ± 5%, respectively, X² = 3.67, NS). Survival was inexplicably lower on Day 22 in recipients receiving 5 embryos (24 ± 9% vs. 69 ± 4%, X² = 19.15, P<0.001). Pregnancy rate was similar in heifers receiving either 5 or 15 embryos (9/9 vs. 8/10, X² = 2.01, NS), and the mean ± se number of conceptuses per pregnant recipient was 2.5 ± 0.6 vs. 10.8 ± 0.8, (P<0.001). In Expt 2, embryo survival was 80 ± 5% and 73 ± 2% (NS), and the mean ± s.e. number of conceptuses per pregnant recipient 1.6 ± 0.2 and 7.3 ± 0.3 (P<0.001) in recipients receiving either 2 or 10 embryos. These preliminary results demonstrate that recipient cattle are apparently capable of supporting large numbers of viable conceptuses (5-15) up until at least the fourth week of pregnancy. Whether these can be maintained to term is yet to be demonstrated, although published evidence suggests that the biological limit may be 5 calves per cow at term.

WH, McMillan, J Peterson, J Thompson, and PA Pugh

Proceedings of the New Zealand Society of Animal Production, Volume 59, , 216-218, 1999