Study purpose: In domestic swine populations lacking proactive screening for chromosomal defects, approximately 50% of hypoprolific boars responsible for reduced litter sizes are afflicted by a reciprocal translocation . Pre-screening of young boars can identify the carriers of these abnormalities before sows are inseminated and economic losses incurred. Chromosomal screening of boar populations by karyotyping is well established in multiple European countries. The cytogenetics lab in Toulouse, France has karyotyped over 35,000 boars and characterized over 180 unique reciprocal translocations (RTLs) since 1992. In contrast, North America had been slower to adopt karyotype screening since first using it to explain low litter size boars in the early 1990s. However, awareness of the importance of screening is growing and access to this service is no longer an issue. The purpose of this study was to present the prevalence and economic consequences of chromosomal defects in the North American boar population.
Methods: Karyotyping identifies abnormalities in chromosome number and appearance with structural rearrangements most relevant to swine reproduction, particularly RTLs. Using a classical cytogenetics GTG-banding technique and Smart Type software our lab has karyotyped approximately 2,000 blood samples from US and Canadian boars since 2013.
Results: The screening of 1,877 boars with no specific reproductive records identified 13 RTL carriers (0.69%), while an analysis of 62 suspected hypoprolific boars submitted for karyotyping identified 30 RTLs with a frequency of 48.4%. Economic modelling highlights the consequences of RTLs, with a single carrier boar resulting in $180,821 USD in lost revenue over his lifetime when processed at 2.5 billion sperm per dose at a weaned pig value of $35 USD.
Conclusions: Karyotyping is a valuable tool for enhancing reproductive performance and minimizing economic losses, due to the unique ability of a single test to identify a high proportion of hypoprolific boars. Data from our lab demonstrates that the frequency of RTLs in North American is similar to the European boar population, providing compelling evidence for including karyotyping in the comprehensive quality control of boar studs everywhere. Also, due to the high proportion of hypoprolific boars explained by chromosomal translocations, it is advisable for researchers investigating other types of andrology assays related to boar fertility to have their subjects screened for RTL’s to avoid interference with their conclusions.