Estimation of genetic parameters for lesion scores and growth traits in group-housed pigs1

Abstract

Pigs housed in groups are remixed with unfamiliar individuals, which can trigger aggressive interactions, potentially compromising animal welfare. Skin lesions are a reliable indicator trait of aggression and are moderately heritable, suggesting that aggression may be reduced through selection. This study estimated genetic parameters of skin lesions of pigs at multiple life stages, explored genetic correlations of skin lesions between age groups and body location, and studied the relationship between skin lesions and production traits of commercial importance. A population of 1,079 Yorkshire pigs was strategically remixed into new groups of familiar and unfamiliar animals at 3 life stages (weaning, grow-finish, and mature gilts). Skin lesions (fresh, bright red cuts) were counted immediately prior to mixing and 24 h and 3 wk after mixing across 3 body regions: anterior, central, and caudal. Weights were recorded prior to each mixing event. Prior to slaughter, backfat thickness and loin muscle area were determined using ultrasound. Univariate analyses were performed to obtain heritability estimates of lesion scores. Bivariate analyses were performed with response variables being skin lesions, weight gain per life stage, backfat thickness, or loin muscle area, depending on the relationship of interest, to obtain correlations. Lesion score heritabilities ranged from 0.10 to 0.40 and were significant (< 0.05). Heritability was highest for lesions on the anterior region of the body for 24 h and 3 wk after mixing. Lesions to the central and caudal areas showed the highest genetic correlation at each stage of production, whereas those to the anterior and caudal regions had the lowest correlation. The highest genetic correlation was found between the mature gilt and grow-finish stages, whereas the weaning and mature gilt stages had the lowest correlations. Genetic correlations between lesions and production traits were not significantly different from 0 for weight gain and backfat thickness, but loin muscle area was negatively correlated with lesions ( = 1.17 × 10, = 2.30 × 10, and = 6.08 × 10 for anterior, central, and caudal lesions, respectively). These results are promising for the industry because they suggest that pigs selected for reduced lesions will show increased loin muscle area without negative effects on growth. Alternatively, selection for these production traits would not increase lesions.

A Short Period of Darkness after Mixing of Growing Pigs Intended for PDO Hams Production Reduces Skin Lesions

“…Turner and collaborators [ 5 ] observed an increase of SL 24 h post-mixing in the vast majority of pigs evaluated, with a greater increase for front SL compared to the rear body part. Similarly, Wurtz and collaborators [ 22 ] reported a steep increase of SL in all body locations 24 h following regrouping, whereas three weeks after regrouping SL decreased and accumulation was generally lower than that scored at regrouping. Stukenborg and collaborators [ 24 ] observed an increase in SL evaluated 48 h after regrouping on the front part of the body on the majority of pigs considered; conversely, no positive difference was found for over 60% and 70% of pigs in LS observed in the middle and rear regions, respectively, concluding that their contribution in the prediction of agonistic behavior seemed to be rather insignificant.…”

“…Skin lesions are a useful and practical indicator of aggressive behavior and poor welfare, as their assessment requires little time, no specific equipment, and limited training [ 22 ]. Moreover, SL are a direct outcome of physical damages due to agonistic interactions, and their frequency and intensity can be related to the level of welfare impairment following regrouping.…”

“…Lesions were recorded by direct observation of each pig, and it was performed independently by two trained observers who counted the total number of fresh lesions. A lesion was defined as a single and continuous scratch, regardless of severity, whereas freshness was judged on the basis of lesion color, usually red-pink, and development of scabbing [ 21 , 22 ]. Lesions were recorded independently on three different locations of the body: front (head, neck, shoulders, and front legs), middle (flanks and back), and the rear part of the animal (rump, hind legs, and tail), because the accumulation of skin lesions in different locations has been associated with different types of agonistic behavior [ 5 , 22 ].…”

Genome‐wide association analyses of lesion counts in group‐housed pigs

“…, ; Wurtz et al . ). Skin lesions are a reliable proxy measure of levels of aggression and have been shown to be moderately heritable as well (Turner et al .…”

“…, ; Wurtz et al . ). The location of the lesions on the body is associated with different types of aggressive encounters, with lesions on the anterior of the body associated with pigs engaging in reciprocal aggression and lesions on the caudal region associated with retreat from bullying or the receipt of one‐sided attacks (Turner et al .…”