One of the main factors affecting cattle fertility is pre-implantation development of the bovine embryo, which is a complex process regulated by various signal-transduction pathways. The transforming growth factor-β (TGF-β) signalling system, which is responsible for many biological processes including cell proliferation, differentiation and apoptosis, also is involved in embryo development. We hypothesized that altered expression of TGF-β genes in pre-implantation bovine embryos is associated with morphological abnormalities of these embryos. To test this hypothesis, we produced embryos in vitro and classified them at the blastocyst stage as either normally developed blastocysts or degenerates (growth-arrested embryos). The expression patterns of 25 genes from the TGF-β pathway were assessed using quantitative real time PCR. Ten genes showed differential expression between the two embryo groups, four genes displayed similar expressional profiles, and 11 genes had no detectable expression. An altered expression profile was statistically significant for 10 of the 14 expressed genes, and all were up-regulated in degenerate embryos vs. blastocysts. Furthermore, genomic association analysis of the cows from which embryos were produced revealed a significant association of ID3 and BMP4 polymorphisms—two of the most significant differentially expressed genes—with fertilization rate and blastocyst rate, respectively. Taken together, we conclude that TGF-β pathway genes, especially BMP4 and ID3 play a vital function in the regulation of pre-implantation embryo development at both embryo and maternal levels. Hence, these genes may be suitable as genetic markers for embryo development and fertility in cattle.

It is proposed that desiccation tolerance in the embryo of seeds depends upon the capacity to repair damage to genomic DNA when the desiccated embryo is rehydrated. From a study of imbibed and hydrated embryos of rye (Secale cereale) and wild oat (Avena fatua) evidence is provided that it is neither the extent of water uptake by the cells, the ensuing stability of the DNA to desiccation, nor the onset of S-phase DNA synthesis in the first cell cycle of germination that determines whether the desiccated embryo will survive. It is shown that when α- and β-polymerases of DNA repair are inhibited by aphidicolin and dideoxythymidine-5'-triphosphate, respectively, a γ-irradiation-induced DNA fragmentation cannot be fully repaired. It is shown that in hydrated embryos, at a stage when desiccation tolerance is lost, embryo cells still repair irradiation-induced damage, but this repaired DNA is unstable to desiccation and cannot be rerepaired when water is again made available. The failure to re-repair on rehydration appears to be critical to embryo survival and successful germination.

An investigation was conducted to determine the effects of treatment with the GnRH agonist buserelin on day 12 post mating on the reproductive performance of ewes. There was a non-significant (P > 0·05) increase in nonreturn rate (control 0·76 v. buserelin 0·83) and litter size (control 1·51 v. buserelin 1·77) in three flocks. However, there was a significant (P < 0·05) increase in the number of twin lambs born (control 20 v. buserelin 40) and litter size (control 1·44 v. buserelin 1·68) in the yearling flock. There was no effect of buserelin on oestrous cycle length, although there was a tendency for treated animals to have a longer gestation length and heavier lambs. In a ewe lamb flock there was no effect of buserelin on non-return rate or litter size assessed post slaughter on day 31 of pregnancy. However, ovulation rate tended to be greater in the treated animals, which suggests that buserelin may have induced the formation of accessory corpora lutea. These results indicate that buserelin treatment improves embryo survival and that this effect is particularly evident in yearling ewes.