Determination of starting level of heat stress on daily milk yield in Holstein cows in Bursa city of Turkey

Abstract

The aim of this study was to investigate the starting levels of heat stress on daily milk yield (DMY) in Holstein cows reared in Marmara region in Turkey. For this purpose, a total of 68113 daily milk records of 212 Holstein Friesian cows raised in Bursa, a city in Marmara region, during 2010-2012 were evaluated. The temperature humidity index (THI) was used to investigate the effect of heat stress. The effects of year, lactation number, days in milk (DIM) and THI on milk yield were found significant (P<0.01). DMY's smallest, largest, average values were 3.0, 72.1, 28.9±0.04, respectively, and the 305-day average milk yield was 9435±156.12 kg. DMY smallest adjusted average occurred in August (24.0 kg), while the highest occurred in April (31.5 kg). THI ranged between 26 and 79, the first THI value having adverse effect on milk yield was 65, and THI threshold value irreversibly affecting the milk yield is 70. THI value of 70 and above were detected more than 268 days from May to September in three years. The correlation coefficient between THI and the daily milk yield was calculated as -0.771. Also on farms in similar climatic conditions, precautions must be taken against heat stress. Continuous recording of temperature and humidity and the operation of the cooling system in the barns according to the THI can be more effective against heat stress.