Influence of the daily milk yield level on some physiological parameters of dairy cows reared under the same temperature and humidity conditions

Hristo Hristev, Zhivka Gerovska and Rumyana Ivanova

Abstract: The present study examines the relationship between the level of daily milk yield and some physiological parameters of dairy cows of the Holstein cattle breed under the same temperature and humidity conditions. The tests were carried out in the course of one year in three cattle-breeding farms with a different capacity. The farms are located in the central part of Southern Bulgaria in the region around Plovdiv. The conditions in the rearing premises in the farms examined range from mild to moderate heat stress during the summer and partially- during the spring. When they are compared to the cows with low milk yield of up to 30 kg, the cows with high daily milk yield – over 40 kg show higher values in all physiological indicators even under conditions of temperature comfort (THI up to 72). The cows with lower milk yield – up to 40 kg react with an increased rectal temperature upon THI values above 72. The cows with low milk yield (up to 30 kg) react with an increase in the skin temperature at higher THI values – over 80. All milk-yield groups indicate quickened pulse rate upon increase of the THI values. The pulse rate quickening upon THI of up to 72 and over 80 is by 26, 23.2 and 29.8% respectively for the three cow groups based on their milk yield group. The pulse rate of the cows with daily milk yield of up to 30 kg is considerably quickened upon THI increase over 80, while the pulse rate of the cows with a milk yield between 30 and 40 kg quickens by 19% upon THI values from 72 to 80. The breathing intensity significantly increases (from 26 to 30%) in all three milk – yield groups upon increase of the THI values: from conditions of comfort (up to 72) to reaching the conditions of a moderate stress (above 80).

Keywords: daily milk yield; dairy cows; physiological parameters; THI

Date published: 2022-11-01