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Heat stress and milk production in the first parity Holsteins – threshold determination in Eastern Croatia

In the light of increasingly rapid climate change worldwide, one of the primary goals is to reduce financial losses of dairy farmers and to enable the sustainable farming. In order to realize those goals, the necessity of implementation of breeding values for heat resistance in breeding strategies, have become more and more pronounced. Estimation of breeding values requires determination of temperaturehumidity index (THI) threshold value. Therefore, the objective of this research was to determine the THI threshold value for the first parity Holsteins in environmental conditions in Eastern Croatia. With that purpose individual test-day records of the first parity Holsteins with records of ambient temperature and relative humidity in the barns were analysed. Data were collected in regular milk recording from January 2006 to December 2012. The THI threshold values for daily milk yield were determined by least square analyses of variance for each given THI value (from 65 to 76) using the PROC MIXED (SAS). The THI< 68 did not cause significant change in daily milk production of the first parity Holsteins. Significant decrease of daily milk yield was observed at THI ≥ 68 with estimated drop from 0.240 to 0.716 kg milk/day (THI from 68 to 76). The THI=68, as the lowest value at which significant decrease in daily milk yield was determined, was taken as the threshold value for the first parity Holsteins in Eastern Croatia.

first parity Holsteins ; heat stress ; temperature-humidity index ; threshold ; Eastern Croatia

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