The effect of response to heat stress, parity, breed and breeding region on somatic cell count in dairy cattle

Abstract

With the aim of determining the effect of response to heat stress, parity, breed and breeding region on somatic cell count (SCC) in dairy cattle, the individual test-day records of dairy cows collected from 2005 to 2012 in regular milk recording (AT4 / BT4 method) in Croatia were used. The proportional differences in log somatic cell count, and logSCC (in %) in subsequent milk recordings (1st, and 2nd) were determined in cows with a significant decrease in daily milk yield at a set temperature-humidity index, THI threshold (68, 72, and 76). The results indicate high variability in somatic cell count due to the animal’s response to heat stress (heat stressed at THI in 68, 72, and 76), parity (1, 2, and 3+), breed (Holstein, and Simmental) and breeding region (Central, and Eastern Croatia). Also, it could be pointed out that Holsteins, especially cows in higher parities (2, 3+) reared in Eastern Croatia were shown to be more sensitive to environmental stress, even in the period after heat stress (1st, and 2nd subsequent milk recording). Since SCC is not only an indicator for mastitis, but also reflects a cow’s immune response to general stress situations, the high variability determined may be explained by the individual adaptation capabilities of these two breeds to breeding conditions in the analysed regions.