The Relationship Between Coat Colour and Thermotolerance in Tropical Breeds of Sheep and Goats in Maiduguri, Nigeria
The escalating temperatures in Nigeria’s Sudano-Sahelian zone necessitate identification of morphological traits that enhance livestock resilience to thermal stress. This investigation examined how coat pigmentation influences thermoregulatory capacity in indigenous sheep and goats managed under semi-intensive systems in Maiduguri. One hundred and twenty adult animals comprising equal numbers of sheep and goats were stratified into four pigmentation categories: White, Black, Brown, and Spotted. Physiological assessments were conducted during the hottest diurnal period (1200-1500 hours) throughout the hot-dry season when environmental conditions reached 38.5 ± 1.2°C ambient temperature and 24 ± 5% relative humidity, yielding a Temperature-Humidity Index of 84.7, indicative of severe thermal challenge. Core body temperature and respiratory frequency served as primary thermotolerance metrics. Statistical analysis revealed highly significant associations between coat pigmentation and both physiological indicators across both species (p<0.01). Animals possessing black pigmentation consistently demonstrated elevated core temperatures and respiratory frequencies, whereas white-coated individuals maintained significantly lower values. Specifically, white-coated sheep maintained rectal temperatures at 39.1°C versus 39.8°C in black-coated counterparts, representing a 0.7°C differential. Similarly, respiratory frequency in white-coated goats averaged 48 breaths/min compared to 65 breaths/min in black-coated animals, reflecting a 35% reduction in thermoregulatory effort. Brown and spotted phenotypes exhibited intermediate values, suggesting a proportional relationship between melanin concentration and thermal load. These results provide empirical validation that lighter pigmentation confers substantial thermoregulatory advantages under extreme tropical conditions. Practical applications include prioritizing lighter-coated breeding stock, implementing targeted management interventions for dark-coated animals including enhanced shade provision and modified feeding schedules, and incorporating coat colour as a selection criterion in breed improvement programs to strengthen climate resilience of small ruminant production systems in tropical agroecological zones.
Running title: Coat colour effects on heat tolerance
Keywords: Heat stress, pigmentation, thermal regulation, small ruminants, climate adaptation, Sahel
