The Effect of Group Composition and Mineral Supplementation during Rearing on Measures of Cartilage Condition and Bone Mineral Density in Replacement Gilts

SIMPLE SUMMARY: The lifetime performance of commercial sows relies on longevity, which is dependent on good health, particularly, limb health. In many countries, young female pigs (gilts) intended for breeding are often reared with male finisher pigs destined for meat production. However, finisher diets are not designed to meet the needs of developing gilts and may not supply the necessary minerals to support good limb health. Moreover, gilts reared with uncastrated (i.e., entire) male pigs are exposed to high levels of sexual mounting and aggression, which may cause physical damage. This experiment investigated the effect of female-only or mixed-sex rearing with and without supplementary minerals (Copper, Zinc and Manganese) on locomotory ability, cartilage condition and areal bone mineral density (aBMD) of breeding age gilts. The addition of the minerals to the diet resulted in increased aBMD in the humerus bone compared to gilts on the control diet. Rearing gilts in female-only groups reduced the number of cartilage lesions, and there were fewer incidences of elbow cartilage fractures. Overall, both strategies (mineral supplementation and female-only rearing) had benefits for limb health, which could help to improve sow longevity. ABSTRACT: Lameness is a major cause of poor longevity and poor welfare in replacement gilts. The problem is exacerbated by inappropriate housing and diet during the rearing period. Replacement gilts are often reared with male finisher pigs destined for slaughter. If they are not castrated, they perform high levels of potentially injurious sexual and aggressive behaviour. Furthermore, finisher pig diets are not designed to meet the needs of developing gilts and may not supply the necessary minerals to support good limb health. The objective of this study was to evaluate the effect of supplementing the diet of replacement gilts with copper, zinc and manganese and separating them from males during the rearing period on locomotory ability, bone mineral density and cartilage lesion scores. A 2 × 2 factorial design experiment investigated the effect of female-only or mixed-sex rearing, with or without supplementary minerals (Copper, Zinc and Manganese). In total, 384 maternal line gilts were assigned to 32 pens of 12 and were locomotion scored during the rearing period. A sub-sample (n = 102) of gilts were culled at breeding age and the front right limb was removed at slaughter. Areal bone mineral density (aBMD) was measured using dual energy X-ray absorptiometry, after which the limb was dissected to score the condition of the cartilage. The addition of trace minerals to the diet resulted in increased aBMD in the humerus (P < 0.05) compared to the control diet. Rearing gilts in female-only groups reduced the number of cartilage lesions overall (P < 0.05), and on the humeral condyle (P < 0.05). Rearing replacement gilts in female-only groups and with mineral supplementation had benefits for limb health.