Assessment of the age of lesions on the pig carcass at the abattoir through spectrophotometric color assessment and gene expression analysis

The presence of skin lesions downgrades carcass value and indicates poor animal welfare preslaughter. The aim of this study was to assess the age of lesions on the carcass at slaughter through spectrophotometric color assessment and gene expression of the following genes involved in tissue inflammation and repair: CCL2, IL6, ITGA3, MMP1, and SERPINE1. A total of 96 barrows (100 ± 10kg), allotted into 8 pens of 12 pigs each, were used. Over a three day period, each pig was mixed four times: in the finishing pen 2 d before slaughter, at loading, and in the lairage pen at the abattoir. Fighting- and mounting-type lesions were selected through visual assessment and video validation. Twenty lesions and control skins (with no lesions) per age group (total of 80 lesions and control skins) were selected, with each group consisting of 1, 4, 24, and 48 h old lesions. Data and skin samples were collected at the abattoir. For gene expression analysis, a skin biopsy of 4 mm was taken on each lesion and control skin at bleeding. After extraction, RNA was analyzed by qPCR to evaluate gene expression involved in tissue inflammation and repair. In the cooler, the color of each lesions and control skin was assessed through Minolta spectrophotometer. Delta values for each lesion were calculated between color and gene expression values obtained from the lesioned and control skin. Statistical analyses were performed using the mixing procedure of SAS, with log transformation applied to gene expression data. The time of infliction had an effect on Minolta L* and a* values (P < 0.01 for both), with 1 h old lesions being darker (higher-∆L* value) than 4 and 24–48 h old ones (P < 0.05) and redder (higher ∆a* value; P < 0.01) than 24–48 h old lesions. The different lesions age resulted in a different expression of CCL2 and IL6 cytokines (P < 0.001), and other genes involved in tissue repair and remodeling (MMP1, ITGA3, SERPINE1) whose genetic expression was greater (P < 0.01) in 1 h old lesions compared with 24–48 h old ones. Furthermore, when compared with 4 h old lesions, 1 h old lesions presented a greater expression of CCL2 and ITGA3 (P < 0.01), and MMP1 (P < 0.05). To conclude, the spectrophotometric color assessment and the analysis of inflammatory and tissue repair gene expression in the carcass lesions at slaughter may be reliable methods to discriminate between fresh and older lesions at the abattoir.