Evaluating the impact of heat stress as measured by temperature-humidity index (THI) on test-day milk yield of small holder dairy cattle in a sub-Sahara African climate

•This study evaluates the effect of heat stress on milk production and describes the pattern of response of milk yield to increasing heat load, in small holder dairy farms in sub-Saharan Africa.•Milk yield showed a W-shaped pattern of response across the THI scale.•Cows experienced heat stress in the THI window between THI values of 67 and 76.•Milk loss plateaued beyond THI value of 76 suggesting that the animals acclimatized to the heat stress conditions despite the initial heat load shock.