Variation of somatic cell count (SCC) of dairy cattle in conditions of Mediterranean region in Croatia

Abstract

With the aim of analysing the variability of somatic cell count (SCC) of dairy cattle in conditions of Mediterranean region in Croatia, 217,509 test-day records, collected from January 2005 until April 2010, were extracted from HPA (Croatian Agricultural Agency) database. Milk recording in Croatia occurs according to the AT4 milk recording method. SCC in milk samples taken from each lactating cow was analyzed and determined values natural log-transformed (LSCC). The test-day records with SCC value above 200,000 cells/ml (LSCC >2.301) as well as the test-day records recorded after the 500^th lactation day were deleted from the dataset. According to the parity, cows were divided into three classes, that is first calvers, cows in second lactation and cows in third and higher lactations. From the total number of cows 64.76% belonged to the Simmental breed, while 35.24% were Holsteins. According to the test date, four measuring season subgroups were created. Cows were also divided in two calving season subgroups regarding the calving date. The temperature and the relative humidity in stable were also recorded at each milk recording. Significant rise of average daily temperature, as expected, was observed from January till July. During summer season besides high temperatures, increased relative humidity produce stress microclimatic condition for dairy cows. For estimation of LSCC variability due to measuring season effect with particular regard to parity and breed a fixed-effect model that take into account the effects of lactation stage, calving and measuring season was used. The significance of differences between the means of the LSCC within the measuring season classes in regard to parity classes and animals' breed was tested with Scheffe test. An increasing trend of LSCC in summer and autumn season was noticed in both analysed breeds regardless the parity class. Regarding the measuring months, in both Simmental and Holstein first calvers, the highest value of LSCC was measured in October and November, while in cows in second as well as in third and higher lactations, the highest values of LSCC were noticed during September, October and November. Regarding the parity class the highest values of LSCC were obtained in both breeds in third and higher lactations. In all cows, regardless the breed and parity, the highest value of LSCC was determined during autumn period, while the lowest value occurred in spring season. In order to control and reduce the level of mastitis in a herd, udder health must be monitored. Somatic cell count measurements provide to breeders the opportunity to monitor and evaluate udder health.