Conception rate after uterine transfer of cow eggs, in relation to synchronization of oestrus and age of eggs.

Abstract

In sheep, the transfer of twoto four-cell eggs from the oviduct of donors to the uterus of recipients results in a poor conception rate, while uterine transfers of Day-3 (eight-cell) eggs (Day 0 = day ofoestrus) give a satisfactory conception rate (Averill & Rowson, 1958). Moore & Shelton (1964) found that transfers to the oviduct were more successful than those to the uterus, but Trounson & Moore (1974) found that the site of transfer of Day-3 eggs had no effect upon their subsequent survival. In sheep, most eggs are present in the uterus 66 hr after ovulation (Holst, 1974), whereas in the cow, which ovulates about 12 hr after the end of standing oestrus, Hamilton & Laing (1946) could find no eggs in the uterus before 96 hr after the end of oestrus. Thus, although the cleavage rates of eggs are approximately similar in relation to oestrus in both sheep and cow, sheep eggs are entering or are already present in the uterus on Day 3, but cow eggs of a comparable age remain in the oviduct for a further 24 hr. In the present study, the conception rate after uterine transfer of cow eggs of different ages has been examined in relation to the degree of synchronization of the donor and recipient. Conception was assessed by rectal palpation 35 to 42 days after the oestrus before transfer. The eggs used for this purpose were collected and transferred as described by Rowson, Moor & Lawson (1969) or with minor modifications. The flushing and transfer medium was either TCM 199 or Dulbecco phosphate-buffered saline. No pregnancies resulted from the transfer of twenty-two 2-day eggs to the uterus of recipients and these results were therefore excluded from the statistical analysis. The number of uterine transfers carried out on Days 3 to 7 to animals with synchronous oestrus or to recipients in which oestrus differed from the donors by +1 or