Bioscientifica Proceedings

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

During luteal regression episodic pulses of oxytocin secretion become coupled to the release of prostaglandin F2α (PGF2α) following synthesis of endometrial oxytocin receptors, but in early pregnancy the inhibition of oxytocin receptor formation by the conceptus prevents the development of the pulsatile pattern of PGF2α release needed to achieve luteolysis. Oxytocin receptors are present on the luminal epithelium in ovariectomize...

Summary. Milked dairy cows generally have a shorter post-partum interval to ovarian cyclicity than suckling dairy or beef cows. In milked and suckling cows, there is a strong seasonal influence with spring-calving cows remaining anoestrous longer. Increasing the suckling intensity further delays the onset of ovarian cyclicity, probably by increasing the frequency or strength of its inhibitory influence on hypothalamic activity. Plasma FSH levels rise in most c...

During early pregnancy the bovine embryo must produce a protein called interferon τ which inhibits the development of the luteolytic mechanism. Failure to inhibit luteolysis is the major cause of pregnancy loss in cows. The embryo must produce sufficient quantities of interferon τ by about day 16 to prevent luteolysis. Its ability to achieve this is largely dependent on the pattern of maternal progesterone production. A late rise in progesterone after ovulation or po...

Summary. Southern blotting of bovine genomic DNA indicated the presence of at least 3 bovine tIFN genes. The full DNA sequence of one of these genes, thought to be expressed in trophoblast, has been determined, including 193 bp of 5' non-coding region. The inferred amino acid sequence of bovine tIFN is more similar to ovine tIFN (80%) than to bovine IFN-αII (70%). The 5' flanking sequence has some similarity with bovine IFN-&#94...

Abstract unavailable© 2010 Society for Reproduction and Fertility...

Methods for sexing preimplantation embryos range from karyotyping to recording speed of development in vitro. The only method used routinely on a commercial scale is to biopsy embryos and amplify Y-chromosome-specific DNA using the polymerase chain reaction. This method is effective for more than 90% of embryos and is >95% accurate. Within males, spermatozoa are essentially identical phenotypically due to: (1) connection of spermatogenic cells by intercell...

The overall aim of this research was to improve fertility of cattle inseminated with sexed spermatozoa by improving sperm sorting procedures. Six field trials were conducted in which 4,264 heifers were inseminated into the uterine body with cryopreserved sexed or unsexed control spermatozoa. Pregnancy or calving rates with doses of 2 × 106 sexed spermatozoa ranged from 32 to 51%; these averaged 69% of the pregnancy rates with 20 × 106 un...

Summary. In the sheep both FSH and LH are necessary for development of large antral follicles. The secretion of FSH is controlled by the negative feedback effect of two ovarian hormones, oestradiol and inhibin, acting at the level of the anterior pituitary. Both are derived from the granulosa cells of large antral follicles which are present in sheep ovaries throughout the oestrous cycle. FSH stimulates growth and mitosis and so the fully differentiated granul...

This article reviews experiments performed to investigate the importance of thyroid hormones to the expression of the seasonal reproductive cycle of ewes. Thyroidectomy was found to block the transition from the breeding season to anoestrus and to cause ewes to exhibit oestrous cycles all year round. Mechanistically, thyroidectomy produced this effect by preventing the seasonal increase in responsiveness to the negative feedback action of oestradiol on episodic GnRH secretion,...