SummaryThe objectives of this study were to determine the microclimatic conditions in stables in threeclimactic regions (East, Mediterranean, and Central) of Croatia as well as to evaluate the effect oftemperature-humidity index (THI) values on the daily production of dairy cattle. With that purpose,1675686 test-day records collected from January 2005 until April 2010 were extracted from HPA(Croatian Agricultural Agency) database. For estimation of the effect of THI on daily productionof dairy cows fixed-effect model that took into account the effects of lactation stage, breed, calvingseason, measuring season, and THI group (T1 - THI≤72; T2 - THI>72) was used. Model was appliedto each class of parity (P1, P2, P3, P4 and P5) and region. During the analysed period, the highestmonthly averages of ambient temperature were determined in Mediterranean region, the highestmonthly averages of relative humidity were observed in Central region, while the highest monthlymean values of temperature-humidity index (THI) were determined in Mediterranean region. Heatstress conditions indicated with mean daily values of THI>72 were determined during spring andsummer season in all analysed regions. Absence of heat stress conditions during autumn and winterseason also characterised all three regions. Highly significant (P<0.01) decrease of daily milk yield aswell as of daily fat and protein content due to enhanced THI was observed in all cows regardless theparity class and in all three climatic regions. Furthermore, the most deteriorate effect of heat stresswas observed in East region. During heat stress period, with the aim of minimization of the effects ofheat stress, it is necessary to regulate management strategies in the dairy herd.
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