Adaptive performance of hairy thin-tailed (Yankasa) and wooly fat-tailed (Ossimi) sheep in tropical hot-dry season

•A marked increase in heart rate during the afternoon hours was observed only in wooly fat-tailed sheep.•The hairy thin-tailed sheep had significantly lower heart rate and eye temperature during the afternoon hours.•The skin temperature in the morning hours was significantly lower in wooly fat-tailed than hairy thin-tailed sheep.•Erythrocytes of the hairy thin-tailed sheep were osmotically more fragile than those of the wooly fat-tailed sheep.•All haemato-biochemical parameters showed relative similarity in heat-stress response between the two sheep types. The aim of the study was to comparatively evaluate the thermoregulatory, haematological, oxidative stress and serum electrolyte variations in an indigenous, hairy thin-tailed Yankasa (n = 10) and a recently introduced, wooly fat-tailed Ossimi (n = 10) sheep in the Northern Guinea Savannah zone during the peak of the hot-dry season. Thermoregulatory variables were recorded in the morning and afternoon hours, while samples were collected to evaluate variations in blood parameters. The results revealed that the rectal, skin, eye and fibre surface temperatures, as well as respiratory rate significantly (P < 0.05) increased from morning to afternoon hours in both sheep types. The heart rate significantly increased from morning to afternoon hours in wooly fat-tailed sheep, but no significant increase was observed in the hairy thin-tailed sheep. The wooly fat-tailed sheep exhibited higher (P < 0.05) heart rate and eye temperature than the hairy thin-tailed sheep in the afternoon hours. In the morning hours, the skin temperature was higher (P < 0.05) in the hairy thin-tailed sheep than the wooly fat-tailed sheep. Erythrocyte osmotic fragility was higher (P < 0.05) in hairy thin-tailed than wooly fat-tailed sheep. No significant difference (P> 0.05) was observed between sheep types in respiratory rate, sweating rate, rectal temperature, haematological parameters, serum malondialdehyde, potassium and sodium ion concentrations. It is concluded that the wooly fat-tailed sheep showed greater sensitivity, but higher erythrocyte membrane integrity during the hot-dry season. The non-significant difference between sheep types in most evaluated parameters suggests a relative similarity in their responses to heat stress, affirming the prime influence of adaptation to heat, and not fibre type, in the development of heat tolerance in the sheep.