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Physiol Behav. 2018 Oct 1;194:362-370. doi: 10.1016/j.physbeh.2018.06.001. Epub 2018 Jun 15.

Circadian rhythms of melatonin and behaviour in juvenile sheep in field conditions: Effects of photoperiod, environment and weaning.

Author information

1
Institute of Biodiversity, Animal Health and Comparative Medicine, University of Glasgow, Glasgow G61 1QH, United Kingdom; Department of Molecular and Cellular Therapeutics, Royal College of Surgeons in, Ireland, 123, St Stephens Green, Dublin. Electronic address: cathywyse@rcsi.com.
2
Institute of Biodiversity, Animal Health and Comparative Medicine, University of Glasgow, Glasgow G61 1QH, United Kingdom.
3
School of Veterinary Medicine, University of Glasgow, G61 1QH, United Kingdom.
4
School of Psychology, 58 Hillhead Street, Glasgow G12 8QB, United Kingdom.
5
Department of Molecular and Cellular Therapeutics, Royal College of Surgeons in, Ireland, 123, St Stephens Green, Dublin.

Abstract

Entrainment of circadian rhythms (CR) to the light dark cycle has been well described under controlled, experimental conditions. However, studies in rodents have reported that rhythms in the laboratory are not always reproduced under field conditions. The aim of this study was to characterise the CR of sheep maintained under conditions of standard UK farm animal husbandry and to investigate the effects of environmental challenges presented by season, weaning and changes in housing on CR. Male sheep (n = 9) were kept at pasture, or group housed in barns, under natural photoperiod for one year. CR in locomotor activity were monitored using accelerometry, and 24 h patterns in plasma cortisol and melatonin were measured every 4 h by ELISA. CR was measured before and after weaning, in summer and winter, and at pasture and by barn housing. Cosinor analysis revealed high amplitude, diurnal rhythms in locomotor activity that were disrupted by weaning and by barn housing. Rhythms in winter showed an interrupted night time activity pattern, but only when the sheep were kept at pasture. Cortisol and melatonin secretion followed typical circadian patterns in winter and summer. The CR of the sheep under the field conditions of this study were strikingly robust under basal conditions, but easily disrupted by environmental challenges. Interrupted patterns of activity during the long nights of wintertime, not previously reported for sheep kept in experimental conditions were recorded. Based on these findings, we propose that animals require exposure to more complex environments than the laboratory in order to exhibit their true circadian phenotype.

KEYWORDS:

Chronobiology; Circadian; Ovine; Rhythms; Seasonal; Sheep

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