Incidence, Reproductive Outcome, and Economic Impact of Reciprocal Translocations in the Domestic Pig

Abstract

Pigs (Sus scrofa) have vast economic importance, with pork accounting for over 30% of the global meat consumption. Chromosomal abnormalities, and in particular reciprocal translocations (RTs), are an important cause of hypoprolificacy (litter size reduction) in pigs. However, these do not necessarily present with a recognizable phenotype and may cause significant economic losses for breeders when undetected. Here, we present a reappraisal of the incidence of RTs across several European pig herds, using contemporary methodology, as well as an analysis modelling the economic impact of these abnormalities. Molecular cytogenetic investigation was completed by karyotyping and/or multiprobe FISH (fluorescence in situ hybridisation) between 2016–2021, testing 2673 animals. We identified 19 types of chromosome abnormalities, the prevalence of these errors in the database was 9.1%, and the estimated incidence of de novo errors was 0.90%. Financial modelling across different scenarios revealed the potential economic impact of an undetected RT, ranging from £69,802 for an individual affected terminal boar in a commercial farm selling weaned pigs, to £51,215,378 for a genetics company with an undetected RT in a dam line boar used in a nucleus farm. Moreover, the added benefits of screening by FISH instead of karyotyping were estimated, providing a strong case for proactive screening by this approach.

The Economic Burden of Chromosome Translocations and the Benefits of Enhanced Screening for Cattle Breeding

“…To then understand the nature of the cattle breeding industry and, in particular, how an improved chromosomal screening approach might be a substantial improvement on Giemsa chromosome staining, an approach mirroring that of our previous study [ 8 ] was used. Specifically, we examined the UK industry, focusing on the effects relating to genetics companies, bull stud businesses, pure dairy farms, dairy and beef combined, as well as pure beef businesses.…”

“…Because cattle are not litter-bearing animals, unlike our previous work in pigs [ 8 ], we focussed our model on the effects of a chromosome on the herd. Moreover, in the pig breeding industry, a relatively rigid pyramid structure exists, including dam line and nucleus great grandparents (GGP), multiplier grandparents (GP), and commercial parents (P) of the slaughter generation.…”

“…In order to demonstrate such benefits, it is necessary to establish the potential economic hazards of a bull with an RT to the herd. It has been previously reported that a calving rate of 50–60% is reduced by 5–10% by each Rob1:29 translocation [ 3 , 8 , 13 , 15 ] and, thus, a conservative estimate of a reduction in calving rate from 55% to 50% was first used in our calculations. Through this model, we expressed results as the number of cows not impregnated and thus likely not lactating (see results and Table 2 ).…”

“…Balanced chromosomal rearrangements are the leading genetic cause of fertility issues in livestock, recently reassessed in the pig breeding industry as being present in around 1% of breeding boars when enhanced screening approaches are used [ 7 , 8 ]. We recently calculated the financial impact on the industry of a translocation-carrying boar as between GBP 69,802 and GBP 51,215,378 per animal, depending on its position in the breeding pyramid [ 8 ]. In pigs, most chromosomes in the karyotype are found translocated; however, among bulls, the distribution is non-random.…”

“…This, in turn, is based on our current pig-based screening approach [ 7 ] which has, to date, been used to screen over 2500 boars in our laboratory. While we have calculated the potential financial impact of a pig chromosome translocation entering the breeding herd [ 8 ], we have yet to do the same for the (dairy) cattle breeding industry. The purpose of this study is to achieve this.…”