Prevalence of congenital defects in Swedish Hampshire, Landrace and Yorkshire pig breeds and opinions on their prevalence in Swedish commercial herds
This study concerns congenital defects in pigs; umbilical and scrotal hernia, cryptorchidism, kyphosis, splay legs, anal atresia, intersexuality and congenital tremor. The aim was to describe and estimate the prevalence of these defects and estimate the heritability for the most frequent defects, scrotal hernia and cryptorchidism in purebred Swedish Hampshire, Landrace and Yorkshire populations. Furthermore, information and opinions from herdsmen in commercial herds was collected and analysed. A low proportion of congenital defect pigs is of importance both from animal welfare and economic point of view. The accuracy of registration of the presence of defects in the litters has a decisive role for the ability to select against these defects. Linked with that is also the question to what degree these defects have a hereditary background. During summer and autumn 2008, data from Nordic Genetics? database of recorded defects for purebred litters born in the period January 2000 to October 2007 was analysed. Data from 15 purebred herds, 5 from each breed, with at least 400 purebred litters, with in total 19 308 litters were included in the analysis. Two statistical models were applied to the data. One included fixed effects of breed, herd, season and parity number and the other was expanded with the effect of litter size. The effect of the boars on the prevalence of scrotal hernia and cryptorchidism, as fathers or maternal grandfathers of the litters, was analysed. The results show a variation of mean prevalence of congenital defects in purebred litters. The mean prevalence of any defect in litters was 7.0% in Hampshire, 12.0% in Landrace and 16.8% in Yorkshire. Cryptorchidism was the most common defect in Hampshire (4.3%) and Yorkshire (8.3%), and in Landrace (6.5%) scrotal hernia was most common. Significant effects of breed and herd and significant interactions between breed and year was found for scrotal hernia and cryptorchidism. Prevalence of scrotal hernia and cryptorchidism varied with parity number and month of birth. Prevalence increased with increasing litter size. For Landrace and Yorkshire boars, positive correlations were found between the prevalence of cryptorchidism in the litters when the boar was used as father and maternal grandfather, 0.4 for Landrace and 0.3 for Yorkshire. For Yorkshire there were positive correlations also for scrotal hernia, 0.3. Estimated heritabilities were generally low (