Identifying reciprocal chromosomal translocations to reduce early embryo mortality

This proposal addresses the Program 3  Return on Assets priority Investigate and review new reproductive technologies and nutrient requirements that optimize piglets weaned/sow and reduce litter weight variability.
Semen that is used in artificial insemination is routinely checked for usual quality assessment for fertility assessment, such as sperm concentration, morphology and motility. However, these assessments are not enough to detect small scale chromosome rearrangements, such as reciprocal translocation, which are known cause of infertility leading to hypoprolificacy (reduced litter size) in domestic animals including pig. The mating with hypoprolific boars can have a significant effect on litter sizes and non-return and, in some cases the number of piglets in a litter can be reduced to up to 50% (O’Connor et al. 2017). Australian herds which have been
Balanced chromosome translocations (reciprocal chromosome translocations) are reported to occur frequently in pigs and accounting upto 0.47% of AI boars (Ducos et al. 2007). In pigs, more than 130 reciprocal translocations have been identified genome wide which cause reduction in litter size due to high mortality among early embryos (Rothschild & Ruvinsky 2011). Published data showed that approximately 50% of boars have hypoprolificacy due to reciprocal translocation with normal semen parameters (Rodríguez et al. 2010). The primary reason for hypoprolificacy in pigs is due to balanced translocations, which leads to early loss of zygotes, resulting in 25–50% smaller litter sizes (Gustavsson 1990; Pinton et al. 2000). Australian herds have been a closed genetic group since the 80s largely as a consequence of Australian quarantine and biosecurity reasons. A higher than global average incidence of chromosomal translocations contributing to hypoprolificacy in Australian boars is possible given our closed genetic herds of boars over decades and there is some anecdotal evidence to this effect in the local industry.
The traditional chromosome analysis which is routinely performed (e.g. karyotyping and Giemsa staining) is unable to detected small-scale chromosome rearrangements if the translocated region is less than 3MB. This traditional chromosome screening requires high quality chromosome preparations, which is often challenging even for the best cytogenetics laboratory, and costly. Recent advances in molecular cytogenetics which uses genomic bacterial artificial chromosomes clones (BAC clones) can detect small scale rearrangements with 100% efficiency. The recent development of molecular cytogenetic approaches using BAC clones therefore provide high efficiency with precision to detect all balanced translocations (>140) known to cause hypoprolificacy in pigs (O’Connor et al. 2017).
This project will validate a methodology involving recently developed molecular cytogenetic tools to screen boars for reciprocal translocations affecting early embryo survival. The second part of this project will determine the incidence of hypoprolific boars in a commercial boar stud.
This study will enable Australian pig genetics companies to screen and implement viable strategies to reduce the incidence of hypoprolific boars to improve the performance of the Australian breeding herd.