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

Two groups of pigs, born and housed under artificial and natural lighting, demonstrated increases in plasma and salivary cortisol levels at the time o f weaning (day 24) and following handling and transport, indicating that th ese husbandry practices are stressful experiences for the animals. Piglets housed under natural light had a mean plasma cortisol response to weaning o f 33.7%, compared with 47.9% for pigs in the artificial-lighting condition (P < 0.03). The relative percentage of eosinophils was reduced following we aning in both groups of pigs (P < 0.04). Salivary cortisol levels were sign ificantly increased in response to handling and transport (P < 0.0001). Als o, "basal" levels of salivary cortisol were lower in pigs exposed to natura l lighting (P < 0.02) but no differences in the magnitude of the response t o handling and transport were evident between different lighting conditions . Male pigs raised under artificial lighting had greater fat depth than tho se 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 entrain s the circadian rhythm of cortisol to an earlier clock time and are likely to be the major factors in differential cortisol concentrations between lig hting conditions.