Effects of Cold-Dry (Harmattan) and Hot-Dry Seasons on Daily Rhythms of Rectal and Body Surface Temperatures in Sheep and Goats in a Natural Tropical Environment.

Ndazo S Minka,Joseph O Ayo

doi:10.5334/jcr.143

Abstract

Studies on daily rhythmicity in livestock under natural conditions are limited, and there is mounting evidence that rhythm patterns differ between chronobiological studies conducted in the laboratory and studies conducted under pronounced natural seasonality. Here, we investigated the influence of cold-dry (harmattan) and hot-dry seasons on daily rhythmicity of rectal (RT) and body surface temperatures (BST) in indigenous sheep and goats under natural light-dark cycles. The RT and BST of the animals, and the ambient temperature (AT) and relative humidity (RH) inside the pen, were measured every three hours for a period of two days, twice on separate days during the hot-dry and the harmattan seasons, respectively. The AT and RH had minimum values of 16°C and 15% recorded during the harmattan and maximum values of 32°C and 46% recorded during the hot-dry season, respectively. A trigonometric statistical model was applied to characterize the main rhythmic parameters according to the single cosinor procedure. The result showed that RT and BST exhibited different degrees of daily rhythmicity, and their oscillatory patterns differed with the seasons (larger amplitude during the harmattan season than during the hot-dry season). The goats displayed greater (p < 0.05) amplitude of BST than the sheep in all seasons. The acrophases were restricted to the light phase of the light-dark cycle. The mesor of RT in goats was not affected by the season, but mesors of BST in both species were significantly higher (p < 0.05) during the hot-dry than the harmattan season. The goats had a more robust RT rhythm (70%) as compared to the sheep (56%). Overall, the results demonstrated that seasonal changes influenced considerably the daily rhythmicity of RT and BST in sheep and goats under natural light-dark cycle. Awareness of these changes may be useful in the improvement of diagnosis, treatment and prevention of diseases, and welfare and productivity of sheep and goats under cold-dry and hot-dry conditions.

Highlights

The rhythmicity of body temperature is an important process to be studied, to advance knowledge of the temporal variability of thermal homeostasis, and as a means to facilitate the study of biological rhythmicity in general
The result showed that RT and body surface temperature (BST) exhibited different degrees of daily rhythmicity, and their oscillatory patterns differed with the seasons
The mean ambient temperature (AT) and relative humidity (RH) recorded in the present study in both seasons were within the thermoneutral zone of 22 – 35°C and 28 – 60%, respectively, established for sheep and goats [5, 23, 24]

Summary

Introduction

The rhythmicity of body temperature is an important process to be studied, to advance knowledge of the temporal variability of thermal homeostasis, and as a means to facilitate the study of biological rhythmicity in general. Studies on daily rhythmicity of physiological variables have been conducted mostly on humans and laboratory animals, while the subjects were maintained in a thermoneutral environment or controlled experimental photoperiod [3, 10]. While such studies remain relevant in understanding the endogenous and exogenous roles in producing circadian rhythms, there is mounting

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