Variation in back conformation and prevalence of ulcers on the shoulders : a cohort study of related Swedish Landrace and Landrace ' Yorkshire sows

Abstract: This study deals with two characters in pig conformation: status and health of the back and ulcers of the shoulder. The aim was to estimate prevalence and causes of variation for the characters focused. The effect of parity number, body condition score and reproductive stage was analysed. A high prevalence of piglets with defect backs (kyphosis) has been noted in a few piglet-producing herds in the south of Sweden. These herds are all buying their crossbred Landrace-Yorkshire females from the same line of Landrace sows. At the same time, another back defect has been seen within the pure-bred Landrace population: "hanging" backs. A nickname for the symptom is "hammock". The breeding company Quality Genetics is today culling many prospective AI-boars because of remarks on the back and asked for an investigation on this problem. In April 2004, in total 10 swine herds were visited: 8 piglet producers, one nucleus herd with breeding stock of Landrace and one producer of LY-females, who is buying their Landrace females from the above mentioned nucleus herd. In total, about 1000 sows where judged and scored on a scale from 1-5: exterior of the back; both kyphosis and hanging backs, body condition score and prevalence of ulcers on the shoulders. The sows' parity number was also noted. Analysis of the collected data was performed at the Department of Animal Breeding and genetics, SLU, Uppsala during autumn 2004. The collected data was analyzed in two groups: Landrace sows and crossbred hybrids with Landrace as mother and Yorkshire as sire. The result shows that about 75 % of the sows studied had no tendencies of kyphosis. 22 % was scored as a "4" which maybe should be seen more as a natural variation than a defect. In analysis of variance, herd and parity number influenced kyphosis score in both groups of sows. Estimated heritability for kyphos is 0.2. Concerning line of the back, a higher proportion of the Landrace sows had a lowered back (11.4 %) compared with the hybrid sows (6.3 %). For the hybrid sows an effect of parity number on the line of the back was found. No clear trend was seen, but the back score was highest for sows in parity number 2, and lowest for gilts (parity number 0). In analysis of variance, significant influence could be found of herd and parity number for the hybrid sows, but not for Landrace. Estimated heritability for line of the back was 0.1. Of the sows examined, 6.4 % had some remarks concerning ulcers on the shoulder. A significant correlation between ulcer score and body condition score was found, and also a significant association between parity number and ulcer score for both groups. A low heritability (0.04) was estimated, which indicates that ulcers of the shoulder are most of all environmentally induced. The fact that prevalence of ulcers differed between herds also support this theory. In one herd no sows with ulcers was found, and the worst had 15 % of sows with remarks. Overall the back status and health seems to be good in the production herds. The culling of prospective sires with remarks on the back seems to be paying. Back problems are today not any of the foremost reasons for culling LY-hybrid sows in piglet producing herds.