The test for karyotype abnormalities (KA) indicates chromosomal defects that may not be detected by routine spermiograms, but cause fertility impairments in sows. The aims of this retrospective study were to (1) assess the incidence of de novo KA found in boar populations whose ascendants were negative, and (2) study the economic impact of the test for the farms. Since 2007 all maternal lines of Topigs Norsvin were analysed for KA. Defective boars were rejected as breeders. Terminal sires were also evaluated for KA before their first mating, meaning that all KA identified at this level were de novo produced. KA were detected by G-band staining of blood lymphocytes in metaphase in a private laboratory (Labocor, Spain).
Between March 2015 and February 2019, 777 evaluations were performed in all new Topigs Norsvin boars allocated in AIM Ibérica, Spain. Of these, it weas not possible to check 128 (16.47%) due to defective sampling. In the other 649 samples, 5 (0.77%) resulted in KA. The boar populations checked was Duroc (27.4%), Landrace (11.7%), Large White (18.0%), Pietrain (18.5%) and synthetic lines (24.3%). The positive boars were 2 Talents (synthetic), 1 Duroc, 1 Pietrain and 1 Large White. Breed was not associated with the occurrence of KA (p=0.876). The abnormalities detected were one inversion (Talent: 38,XY,inv(4)(p13;q23)), three translocations (Duroc: 38,XY,t(2;8)(p15;q21); Pietrain: 38,XY,t(3;10)(p16;q12); Talent: 38,XY,t(7;13)(q23;q34)) and one chimera (Large White: CHI 38,XX/38,XY). In the literature, including more than 180 reports of different chromosomic rearrangements in pigs , this is the first time that translocations affecting chromosomes 10-15, and 7-13 have been reported.
All boars affected by KA showed good sperm quality (>70% fresh sperm motility, <30% abnormalities, <10% reacted acrosomes) in control semen. On average, boars in AIM Ibérica produced 2200 doses/year for 18 months. This KA surveillance had a total direct cost of 54,516€ (84€ each successful sample), and an indirect cost of 5,226€ per positive boar (including feeding, quarantine, opportunity cost, handling and materials), meaning a final investment of 16,129.2€ per positive boar. However, 16,500 defective doses were prevented from use on farm. In Spain, sows receive 2.3 semen doses per heat, so 7,174 mating were prevented. Assuming a pregnancy rate of 88%, and a potential loss of 5 piglets per litter , we calculate a potential loss of 31,565 piglets because of mating with the five defective boars, and approximately 158,000€ saved at the farm per boar detected (a return of 9.8€ at the farm per euro invested at the Insemination Centre).
Investment by AI Centres in surveillance for karyotype abnormalities is a profitable routine control for farms, when prevalence of de novo defects is higher than 0.05%, when only lost piglets are considered.