Prevalence of congenital defects in Swedish Hampshire, Landrace and Yorkshire pig breeds and opinions on their prevalence in Swedish commercial herds
Abstract: 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 (<0.1). 17 commercial herds with known high level of skill were visited and the herdsmen were interviewed during August and September 2008. The data were summarized and estimations of prevalence of defects among live born piglets were done. The commercial herds did all report that they see most of the defect piglets during farrowing, at teeth grinding and castration. Umbilical hernias and pigs with kyphosis were found later in life. Most common defect was splay legs, with a prevalence of 4% of all piglets born alive. Umbilical hernia was found in about 2% of all growers. Umbilical hernias were pointed out to be a troublesome defect due to decreased growth, problems to deliver pigs with the defect and reduced animal welfare. An increase of umbilical hernias had been seen during the last two years. Defects in the umbilical region are complex and need to be investigated more. In Norway defects have been included as health traits in the breeding program for Norwegian Landrace and Duroc. The large variation of prevalence of defects in the analysed Swedish purebred herds, within breeds, indicate a variation in accuracy of recording the defects. If more herds did record the prevalence of defects, the most important defects could be included in the breeding program. For the future, it might be possible to select against defects using genetic markers.
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