Abstract
SummaryBalanced chromosomal aberrations have been shown to affect fertility in most species studied, often leading to hypoprolificacy (reduced litter size) in domestic animals such as pigs. With an increasing emphasis in modern food production on the use of a small population of high quality males for artificial insemination, the potential economic and environmental costs of hypoprolific boars, bulls, rams etc. are considerable. There is therefore a need for novel tools to facilitate rapid, cost‐effective chromosome translocation screening. This has previously been achieved by standard karyotype analysis; however, this approach relies on a significant level of expertise and is limited in its ability to identify subtle, cryptic translocations. To address this problem, we developed a novel device and protocol for translocation screening using subtelomeric probes and fluorescence in situ hybridisation. Probes were designed using BACs (bacterial artificial chromosomes) from the subtelomeric region of the short (p‐arm) and long (q‐arm) of each porcine chromosome. They were directly labelled with FITC or Texas Red (p‐arm and q‐arm respectively) prior to application of a ‘Multiprobe’ device, thereby enabling simultaneous detection of each individual porcine chromosome on a single slide. Initial experiments designed to isolate BACs in subtelomeric regions led to the discovery of a series of incorrectly mapped regions in the porcine genome assembly (from a total of 82 BACs, only 45 BACs mapped correctly). Our work therefore highlights the importance of accurate physical mapping of newly sequenced genomes. The system herein described allows for robust and comprehensive analysis of the porcine karyotype, an adjunct to classical cytogenetics that provides a valuable tool to expedite efficient, cost effective food production.
Highlights
The domestic pig (Sus scrofa domesticus) provides 43% of meat consumed worldwide, making it the leading source of meat protein globally (US Department of Agriculture 2015)
The primary identification of boars that exhibit hypoprolificacy is deduced from both litter sizes and ‘non-return rates’, i.e. the proportion of sows/gilts served by that boar that return to heat after 21 days
Four translocation carriers were identified by classical cytogenetics with no abnormalities identified in the remainder
Summary
Purebred boars selected for their genetic merit are used at the top (nucleus) level of the breeding pyramid, meaning that any fertility problems in these animals could significantly reduce litter sizes throughout the breeding population. This leads to a reduction in food production. Semen used in AI preparations is routinely assessed for parameters that are considered to be indicative of fertility such as sperm concentration, morphology and motility. Evidence suggests that these parameters are, not reliable indicators of prolificacy (Gadea 2005).
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