The Development of Methods to Improve In Vitro Embryo Production in Pigs and Cattle

The global livestock industry is continually tasked with developing innovative solutions to meet rising food demand. In both economically developed and developing countries, sustainable supplies are essential for the continuous advances in productivity through genetic selection to improve feed conversion efficiency, disease resistance, and fertility. The interval between conception and birth, however, limits the rate at which these enhancements can be implemented. Furthermore, companies often export breeding animals to developing countries to boost genetic quality, but this comes with production, environmental, and logistical costs, as well as ethical issues.

In vitro embryo production (IVP) is an emergent technology that is progressively being applied to livestock breeding. IVP could bring incredible economic and environmental benefits, serving to increase selection intensity and facilitate the transport of genetically favourable livestock in a highly assistive, inexpensive, and bio-secure manner. Therefore, the main purpose of this thesis was to improve the efficiency of IVP procedures. IVP offers attractive benefits to breeders, such as increasing the offspring numbers derived from high genetic value animals, in less time, and at a cheaper cost than those produced in vivo. Moreover, it facilitates the study of the genetic constitution of the embryos to transfer only those carrying commercially desirable traits to improve genetic selection. IVP is key to reducing the transportation of live animals as the transport of embryos decreases the costs and reduces the risk of pathogen or disease transmission, favouring biosecurity. With this in mind, this thesis had five specific aims:

The first was to improve embryo quality with the addition of cytokines to porcine IVM media. This was successfully achieved as improvements were observed in oocyte maturation and developmental competence to produce higher quality embryos than those produced without cytokine supplementation. The second aim was to assess the effect of different sperm selection methods on basic boar sperm parameters and in vitro fertilisation (IVF) outcomes. This aim was partly successful in that it identified a microfluidic chip-based system as a selection method that produces similar parameters and IVF outcomes to density gradient selection, but with less morphological abnormalities. The third was to compare the slow freezing of boar sperm against modified vitrification protocols. The development of a suitable vitrification protocol was successful in preserving basic sperm parameters, but further work is needed to improve the efficiency compared to slow freezing, the "gold standard" in the breeding industry. The fourth aim was to use preimplantation genetic testing for aneuploidies (PGT A) and SNP chip data from genomic estimated breeding values to screen in vitro produced bovine embryos. This allowed for the identification of chromosomal abnormalities and their origin, which when applied to embryo selection can yield improved pregnancy and live birth rates. The final aim was to use PGT-A to screen the inner-cell mass and trophectoderm of in vivo and IVP bovine embryos to identify and analyse chromosomal abnormalities. A comparison of the data between the inner-cell mass and trophectoderm revealed that trophectoderm biopsies reflect the true ploidy status of the embryo and demonstrate a reliable mean for screening embryos. Taken together, these results have improved the efficiency of porcine and cattle IVP procedures, furthering the development of techniques used for livestock animals.