Incidence and Inheritance of Splayleg in Nebraska Litter Size Selection Lines
University of Nebraska 2005 Swine Day Report. Incidence of abnormalities at birth is low in most populations, but accounts for a significant proportion of preweaning deaths. Splayleg pigs (SL) is the most common defect in newborn pigs and a high percentage of SL pigs die before weaning. In research at other institutions, SL incidence was associated with the Landrace breed and with large litters; however, a genetic association with litter size was not demonstrated. The University of Nebraska selection lines originated from a Landrace-Large White composite population and have been selected for 22 generations for increased litter size. These lines provided an excellent resource for the objectives of this study, which were 1) to identify traits associated with the SL condition, 2) to estimate genetic parameters for SL, and 3) to estimate the correlated response in incidence of SL to selection for increased litter size. Variables associated with the SL condition were sex, line, generation, line by generation interaction, birth weight, dams number of live pigs born, dams number of nipples, dams age at puberty, dams embryonic survival, and inbreeding of the dam. Boars were 234% more likely to display SL than gilts (P < 0.01). Decreased birth weight was associated with an increase in likelihood of SL (P < 0.01). The percentage of SL pigs increased as litter size increased (P < 0.01). Increased incidence of SL occurred in litters by gilts that reached puberty at younger ages (P < 0.01) and that had fewer nipples (P < 0.05). Decreased embryonic survival to d 50 of gestation also significantly increased the probability of SL pigs in the litter (P < 0.05). Inbreeding of the pig did not significantly affect the incidence of SL, but the likelihood of SL increased with dams inbreeding (P < 0.05). Estimates of 0.16 for maternal heritability and 0.32 for genetic correlation between number of pigs born alive and SL were obtained. Selection to increase litter size was not associated with genetic potential of individual pigs to be born with SL. However, selection for increased litter size indirectly increased the genetic potential for sows to create a uterine environment more likely to produce litters with SL pigs. The SL condition should be treated as a trait of the sow, rather than the individual piglet.