Effect of temperature-humidity index on productive and reproductive performances of Iranian Holstein cows

Abstract

Calving records from April 1996 to December 2005 comprising 31863 calving events of 1173 dairy cows in a large commercial dairy herd were used to evaluate the effects of heat stress, using temperature-humidity index (THI) on milk yield and composition and reproductive performance of Holstein dairy cows under humid climatic conditions of Rasht in Iran. THI values were grouped into six groups: 30-40 (THI1), 41-50 (THI2), 51-60 (THI3), 61-70 (THI4), 71-80 (THI5) and 81-90 (THI6). Dairy cows in THI6 had lower milk and fat yields than other groups of THI, but cows in THI1 and THI2 had the greatest amounts of milk and fat yields, respectively (P