Inter-breed ovum transfer in sheep

Abstract

Fertilized ova have been transferred from Border Leicester to Welsh Mountain ewes, and vice versa. The oestrous cycles of the ewes were synchronized by progesterone treatment, and donor ewes were super-ovulated with PMS. 68–90 hr. after the onset of oestrus in the donors, thirty-seven ova, representing 58% of the ovulations, were recovered in vivo from thirteen ewes. Nineteen ova were transferred to eighteen recipient ewes and a total of eight pure-bred lambs were born to ewes of the opposite breed.Transfers resulted in pregnancy when oestrus in the recipients commenced from 16 hr. before to 20 hr. after that in the donors; two of the ova which developed to term were 4-cell, five were 8-cell and one was a 16-cell ovum at the time of transfer. Four out of seven and four out of eleven transfers, using blood serum and Ringer's solution respectively, resulted in the birth of lambs. Prior to transfer to the recipients seven of the ova which developed to term were exposed for 30–45 min. at room temperature, whilst one developed after exposure for 70 min.

Transfer of Sheep Ova

“…The results of our observations confirm the value of the technique described by Hunter et al (1955) for the transfer of ova between sheep but it seems worth¬ while to re-examine at this stage some of the factors that have a bearing on the success of the operation. Leaving aside for the moment the surgical problems of transfer, it was believed when these investigations were begun that two main experimental needs had to be met.…”

“…The onset of heat after pms tends to be more erratic and failure of injected ewes to show heat was a source of some loss. Although there is some evidence (Averill & Rowson, 1958) that precise synchronization of recipients and donors is unnecessary for the successful transfer of sheep ova beyond the 6-cell stage, there is other evidence (Hunter et al, 1955;McLaren & Michie, 1956;Noyes & Dickmann, 1960) that the transfer of'older' ova into 'younger' uteri is generally more favourable to success than the transfer of younger ova into older uteri and on these grounds it seems a wise precaution to minimize the possibility that heat will occur in the recipients before it occurs in the donor. Accordingly, where it is intended to transfer ova to progesteronetreated ewes, the last dose of progesterone should be injected on the day after injection of the donor with pms.…”

“…296 J. L. Hancock and G. J. R. Hovell Management of the flocks and experimental procedures followed were based on the methods developed in the A.R.C. Unit of Reproductive Physiology and Biochemistry at Cambridge (Hunter, 1954;Hunter, Adams & Rowson, 1955;Averill & Rowson, 1958;Averill, 1958 Vasectomized ('teaser') rams marked with coloured raddle were used to detect the onset of oestrus ; the ewes were inspected twice daily for evidence of heat until the rams were removed about the end of January.…”

The viability of early cleavage stages containing half the normal number of blastomeres in the sheep

“…The slightly reduced viability compared to that normally observed after embryo transplantation in the sheep (Moore & Shelton, 1964;Rowson & Moor, 1966) (Willadsen, 1980. ; see also Hunter, Adams & Rowson, 1955). A phosphate-buffered saline medium (PBS: Whittingham, 1971) was used for recovery, storage and transfer of embryos and also for holding embryos during the various manipulations except as otherwise noted.…”

Abnormalities and dimensions of ova from New Zealand Romney ewes

“…Laparotomies were conducted on the ewes 36-101 hours after the onset of oestrus, and ova were recovered from the reproductive tract using the technique of Hunter, Adams, and Rowson (1955). Seitz-filtered sheep serum was used as the medium for the recovery of ova.…”