Studies on superovulation and embryo sexing in dairy cattle

• Main Author: Calder, Michele D.
• Format: Others
• Language: English
• Published: 2008
• Online Access: http://hdl.handle.net/2429/3256

The presence of a dominant follicle has been shown to reduce response to superovulatory treatment. Studies were carried out to assess the superovulatory response to FSH/PGF2atreatment using ultrasound scanning and progesterone profiles in the absence of a dominant follicle. The first experiment examined the effect of initiating superovulatory treatment at Day 2 of the estrous cycle, before a dominant follicle was identifiable. Although adequate follicular development occurred after administration of superovulatory hormones, few animals demonstrated estrus and ovulation rates and the number of embryos recovered was low. In the second experiment, humanchorionic gonadotrophin (hCG) was used to remove the dominant follicle present at Day 7 of the estrous cycle prior to induction of superovulation on Day 9. Cows treated with hCG tended to have higher numbers of follicles, corpora lutea and embryos recovered after treatment, however values were not significantly different from control cows superovulated at mid-cycle. Because the cost of superovulation and embryo transfer is high, economically it may be necessary to produce only calves of the desired sex. Several methods have been used to select for calves of the desired sex, including: production of sexed semen; determination of fetal sex in early pregnancy; and detection and selection of the sex of preimplantation bovine embryos prior to embryo transfer. Two methods of selection of embryonic sex were investigated. Karyotyping was done to directly visualize the sex chromosomes of bovine preimplantation embryos. Previously, anti-H-Y antisera has been used in vitro and in vivo to select against male cells. Antibodies to H-Yantigen were produced in female mice after several weeks of immunization against male cells. Anti-H-Y antibody titre was assessed in enzyme-linked immunosorbent assays (ELISAs).Immunized females were then bred to study the effect of H-Y antibodies on litter size and sex ratio. Unexpectedly, increases in the male offspring were noted in the first litters of immunized females. === Land and Food Systems, Faculty of === Graduate