Effect of heat stress on some reproductive traits in Holstein-Friesian cows under temperate continental climate

Toncho Penev, Dimo Dimov, Nasko Vasilev, Jurii Mitev and Chonka Miteva

Abstract: The aim of the present study was to determine the effect of heat stress (HS) on some reproductive traits in Holstein-Friesian cows in the central part of southern Bulgaria. The survey was conducted in a dairy cattle farm for the period 2015 - 2018 inclusive, on 155 lactations of cows on first to sixth parity. HS was determined by a modified Kelly and Bond (1971) equation using the maximum temperature (°C) and the average values of relative humidity (%) for each month of the study. Temperature and humidity data were taken from the nearest meteorological station in the area. It was found that Tempera-ture-humidity index (THI) at first insemination had a significant (P <0.05) effect on the length of the Days open interval (DO) and on the number of inseminations for conception (NIC) (P <0.01). Depending on the different levels of THI at first insemination, the DO varied from 130.43 to 206.7 days, respectively for THI below 72 and over 90. The NIC varied from 2.43 to 4.24, respectively, at THI values within of 73-78 and over 90 reported during the month of the first insemination. The highest conception rate (CR) of inseminated cows and the highest conception rate at first insemination (CRFI) were found during the period of mild HS (THI 73-78) 41.7% and 32.5% respectively. With the onset of severe HS months (over 90), these trait values fall to 25% and 26.1%, respectively. In July and August the highest values of THI and the lowest CR 19.4% and CRFI 16.7% were reported. With an increase in THI an increase in the interval between inseminations (IBI) was observed from 35 days at THI below 72 to 45.6 days at THI over 90.

Keywords: heat stress; Holstein-Friesian cows; reproductive traits

Date published: 2020-12-15