Interpretive Summary: Genetic correlation between scapula shape and shoulder lesions in sows.
By: Dr. Caitlin Vonderohe
Sows can develop shoulder lesions during lactation because the pressure of the sow laying on a solid surface places pressure on the prominences of the scapula which can result in necrosis and open sores. These open sores may create an entrance for pathogens that results in systemic disease. Shoulder lesions represent a significant challenge in modern swine production because they can result in excessive antibiotic use, death loss or premature culling of sows. Nordbo et. al., recently published, “The genetic correlation between scapula shape and shoulder lesions in sows” in the Journal of Animal Science, quantifying the effect of scapula shape on the incidence and prevalence of shoulder lesions, and body condition score by weaning.
The severity and prevalence of shoulder lesions are affected by environmental factors such as feed, ambient temperature, and genetics. The selection for traits such as litter size and genetic leanness has resulted in a reduction in body fat reserves in lactating sows, resulting in less fat cover over the scapula and increased risk of shoulder lesions.
Nordbo et al. (2018) used sows and boars from Norsvin genetic nucleus and multiplier herds. Boars were CT scanned and evaluated for conformation. CT scans of boar scapula’s were evaluated for the volume, width, surface area and thickness. Sows were body condition scored and shoulder lesions were evaluated on a scale of 0 (no ulceration) to 4 (spine of scapula protruding through skin). The traits of the boar scapulae derived from CT scans were genetically correlated with shoulder lesions and body condition scores observed during the first parity of their descendent sows.
The final model included shoulder lesions, body condition score, age of sow and boar, season, number of piglets weaned. The heritability of CT-derived scapula traits ranges from moderate to highly heritable, but the correlation between scapula traits and the observation of shoulder lesions and body condition score was lower. The high heritability of the scapula shape was expected because traits related to skeletal size and shape have been shown to be highly heritable in humans and other livestock. These results also showed that sows with wider scapulae are more likely to have shoulder lesions. The authors believe that a wider scapula may place greater mechanical stress on soft tissue between the spine of the scapula and subcutaneous soft tissues of the shoulder.
There is also a significant genetic correlation between scapula shape and low body condition score at weaning. Previous work has shown that there is an increased risk of shoulder lesions when sows have a low body condition score. Norsvin et al. believe that these traits are related; scapula shape may initially result in a shoulder lesion, the pain and inflammation increase resting energy requirements and make sows less likely to stand to eat, which further reduces body condition score. Therefore, although shoulder lesions are correlated to both scapula shape and body condition score, the primary correlation is likely between scapula shape and shoulder lesion incidence.
Overall, this study established means to better select boars to improve body condition scores and reduce the risk of shoulder lesions in lactating sows that descend from Norsvin Landrace boars.
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