THE EFFECT OF HEAT STRESS ON THE COMPOSITION AND MICROBIOLOGICAL QUALITY OF BULK TANK MILK IN DAIRY CATTLE

In this study, the effects of heat stress on titratable acidity (degrees SH), fat, protein, dry matter, ash content and total aerobic mesophilic bacteria (TAMB), yeast and mold, micrococcus/staphylococcus, and coliform bacteria count of bulk tank milk in the milk collection center were investigated, and 156 cow's milk belonging to the Holstein breed was analyzed for three years (2011-2103), once a week. Temperature-humidity index (THI) was used to determine heat stress, and THI >= 70 was evaluated as heat stress. THI >= 70 is seen in June-September in 2011 and 2012, and in June-August in 2013. THI values of the day one day before sampling were taken into account when conducting the analysis. It was concluded that the effect of THI on the protein and ash content, the quantity of TAMB, yeast and mold, micrococcus/staphylococcus and coliform counts of milk was significant at the level of P <= 0.001; also its effect on the dry matter was significant at the level of P <= 0.05. It was found that when THI<50, the degrees SH, ash content of milk, TAMB, yeast and mold. micrococcus/staphylococcus and coliform counts were minimal, it reached maximum values when THI >= 70. The correlation between THI and SH, milk ash content, TAMB, yeast and mold, micrococcus/staphylococcus and coliform counts was positive and the correlation between THI and milk fat, protein, and dry content was negative. The importance of the correlation was found to be P <= 0.001 for degrees SH, protein and ash content of milk, and the quantity of TAMB, yeast and mold, micrococcus/staphylococcus and coliform found to be P>0.05 for the content of fat and dry matter. The number of positive samples for Listeria spp. and Salmonella spp. was determined as 31 (19.87%) and 28 (17.95%). respectively.