Bioscientifica Proceedings

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...

In boars, the primary determinant of daily sperm production is the number of Sertoli cells, which establishes testicular weight. The only breed comparison of foetal testicular development in boars contrasted two diverse breeds, White composite (WC, Landrace-Yorkshire) with Meishan, a Chinese breed that undergoes pubertal development at a young age and has small testicular size. During the prenatal period, the pattern of change in testicular development is similar in thes...

Circannual clocks drive rhythms in reproduction and many other seasonal characteristics but the underlying control of these long-term oscillators remains a mystery. Now, we propose that circannual timing involves mechanisms that are integral to the ontogenetic life-history programme where annual transitions are generated by cell birth, death and tissue regeneration throughout the life cycle ߝ the histogenesis hypothesis. The intrinsic cycle is then timed by cues...

The New Zealand (NZ) economy and its dairy industry are sensitive to global consumer perception of farming practices used to generate milk products because milk exports account for >25% of national export earnings and >90% of milk produced is exported as products. Astute management of product image and market risk is, therefore, important for the viability of the industry and country. More than 95% of milk produced in NZ comes from strictly seasonal, pastur...

Summary. In the ram, changes in daylength influence testicular activity by modifying the release of luteinizing hormone-releasing hormone (LH-RH) and thus the gonadotrophins. To investigate the nature of this response the hourly fluctuations in the circulating levels of prolactin, luteinizing hormone (LH) and melatonin were measured in rams kept under various artificial lighting conditions.In Exp. 1, 8 Soay rams (4 control and 4 from whi...

Estrous synchronization and timed ovulation programs that permit AI at a predetermined time (timed AI) rather than as determined by detection of spontaneous estrus are requisite for increased adoption of AI in the beef cattle industry. In the past two decades, significant progress has been achieved in developing programs that synchronize ovulation to address this need. While this progress has been driven by a multitude of fundamental discoveries in reproductive biology, the gr...

This review integrates established information with new insights into molecular and physiological mechanisms responsible for events leading to pregnancy recognition, endometrial receptivity, and implantation with emphasis on sheep. After formation of the corpus luteum, progesterone acts on the endometrium and stimulates blastocyst growth and elongation to form a filamentous conceptus (embryo/fetus and associated extraembryonic membranes). Recurrent early pregnancy loss in the ...

Early pregnancy is maintained in ruminants through the actions of conceptus-derived interferon (IFN)-tau on the endometrium. IFN-tau alters uterine release of PGF2α, which results in rescue of the corpus luteum and continued release of progesterone. The mechanism of action of IFN-tau includes inhibition of oestradiol receptors, consequent reduction in oxytocin receptors, activation of a cyclooxygenase inhibitor, and a shift in the PGs to favour PGE2 ...

The adaptation of Bos indicus cattle to tropical and subtropical environments has led to their widespread distribution around the world. Although artificial insemination (AI) is one of the best alternatives to introduce new genetics into Bos indicus herds, the peculiarity of their temperament and the tendency to show short oestrus (many of them during the night) greatly affects the effectiveness of genetic improvement programs. Therefore, the most useful alte...

Timing of conceptus growth and attachment to the uterine luminal epithelium is regulated by progesterone secretion from the corpus luteum and by expression of progesterone receptor in the uterine epithelia and stroma. Conceptus growth and uterine attachment are temporally associated with the disappearance of progesterone receptors from uterine epithelia. While the loss of progesterone receptor from the endometrial epithelia on day 10 of the oestrous cycle and pregnancy h...