Bioscientifica Proceedings

Summary. Since one bull may be responsible for impregnating numerous cows, testicular function and fertility are of critical importance. Within this broad context, this review will focus on: the effects of nutrition on reproductive development; scrotal/testicular thermoregulation; breeding soundness; and sperm function/fertility. Bulls fed above-maintenance levels of energy and protein before 30 wk of age had increased luteinizing hormone pulse frequency, hast...

Summary. Single genes can now be added routinely to the genome of mice by molecular manipulation as simple Mendelian dominants; this complements the normal process of reproduction to give ‘transgenic’ animals. Success in ruminants is limited to a few examples in sheep and although gene expression has yet to be documented, there is every reason to expect that it will be achieved. The application of this technology to livestock improvement depends on...

Summary. Exposure of male and female pigs to elevated ambient temperatures can result in reduced reproductive efficiency. When boars and gilts are exposed to heat stress, respiratory rates increase to enhance evaporative cooling because minimal sweating occurs.During early pregnancy, gilts are especially susceptible to heat stress. Decreased conception rates and reduced litter size occur when gilts are exposed to elevated ambient te...

The occurrence of puberty in the female is due to the interplay of central and peripheral mechanisms in which the hypothalamic-pituitary-ovarian axis regulates growth and gonadal function, as well as adipocyte hormone secretion. Hypothalamic GnRH mRNA expression increased at 3.5 months of age and declined by 6 months of age. Concomitant with the age related reduction in the oestrogen negative feedback on LH secretion was a decline in hypothalamic oestrogen receptor-&alph...

The ancestral wild pig is a short day length seasonal breeder. The domestic pig appears to have retained some of this seasonality as evidenced by a reduction in fertility during the summer—autumn period. The most important aspect of this seasonality is a reduction in the number of mated sows that farrow. Many of these sows conceive and embryos develop normally for 20 - 25 days before pregnancy is terminated and the sow returns to oestrus (25 - 35 days after mating). In ot...

Abstract unavailable© 1995 Journals of Reproduction and Fertility Ltd...

The field of livestock genomics has made considerable advances in the past decade. In the area of pig reproduction, a number of genome scans have identified several genomic regions associated with variation in reproductive measures ranging from ovulation rate, litter size and testis size. Additionally, several candidate genes have been associated with variation in litter size. These studies primarily focused on developing genetic markers to facilitate selection decisions...

Functional genomics is an experimental approach that incorporates genomewide or system-wide experimentation, expanding the scope of biological investigation from studying single genes to studying potentially all genes at once in a systematic manner. This technology is highly appealing because of its high throughput and relatively low cost. Furthermore, analysis of gene expression using microarrays is likely to be more biologically relevant than the conventional paradigm ...

Summary. Nuclear transfer for the study of differentiation in amphibians has been used since the 1950s, but not until recently have the same procedures been applied successfully to some mammals. Nuclear transfer, as developed for the amphibian, is successful in sheep, cattle, rabbit, and pig, but not mouse embryos. This fact is discussed in relation to the species-specific timing of the activation of the zygotic genome. Nuclear transfer to an oocyte presu...

Research in France and in the UK confirms the prolificacy of the Chinese Meishan breed to be about three to four piglets greater than that of control Large White females. Crossbreeding studies clearly indicate that this breed difference is due to genes acting in the dam and not in the litter itself. There is high heterosis for litter size in F1 Meishan x Large White crossbred females, such that their litter size is similar to or greater than that of purebred Me...