Determination of the Effect of Daily Production Level of Primiparous Holstein Cows on Response to Heat Stress Conditions (THI Threshold) in Eastern Croatia

Abstract

The goal of this paper was to determine the effect of daily production level of primiparous Holstein cows kept on dairy cattle farms in Eastern Croatia on response to heat stress conditions (THI threshold). With that purpose, individual test-day records with data on ambient temperature and relative humidity in the barns were analysed. Data were collected in regular milk recording from 2006-2012. The THI threshold values for daily milk yield were determined by least square analyses of variance for each given THI value (from 68 to 72) using the PROC MIXED (SAS). Low producing cows experienced significant drop at THI=68, while in high producing primiparous Holsteins first significant drop in daily milk yield was observed when THI=69. Also, the amount of daily production drop depended on cow’s production level (0.155-0.256 kg/day in high producing; 0.319-0.460 kg/day in low producing). It could be concluded that the response of primiparous Holstein cows kept in Eastern Croatia to heat stress conditions depends on daily production level.