The effects of natural light on measures of meat quality and adrenal responses to husbandry stressors in swine

Abstract

Two groups of pigs, born and housed under artificial and natural lighting, demonstrated increases in plasma and salivary cortisol levels at the time of weaning (day 24) and following handling and transport, indicating that these husbandry practices are stressful experiences for the animals. Piglets housed under natural light had a mean plasma cortisol response to weaning of 33.7%, compared with 47.9% for pigs in the artificial-lighting condition (P < 0.03). The relative percentage of eosinophils was reduced following weaning in both groups of pigs (P < 0.04). Salivary cortisol levels were significantly increased in response to handling and transport (P < 0.0001). Also, "basal" levels of salivary cortisol were lower in pigs exposed to natural lighting (P < 0.02) but no differences in the magnitude of the response to handling and transport were evident between different lighting conditions. Male pigs raised under artificial lighting had greater fat depth than those raised under natural light (P < 0.03) and a lower lean yield (P < 0.05). The longer photoperiod and full spectrum of natural light probably entrains the circadian rhythm of cortisol to an earlier clock time and are likely to be the major factors in differential cortisol concentrations between lighting conditions. Key words: Lighting, cortisol, saliva, pigs, stress, meat quality