Losses in milk production and quality due to milk somatic cell count and heat stress of Holsteins cows in temperate climate Perdas na produção e qualidade do leite devido contagem de células somáticas no leite e estresse térmico de vacas da raça Holandesa em clima temperado

The aims of present study were to evaluate the effects of milk somatic cell count (SCC) and heat stress on yield and milk composition of cows in a herd for commercial production in a temperate region during the period 2008-2012. Data from the monthly milk test-day records of 161±9 Holstein, totaling 9,650 milkings, were provided by the Association of Holstein Cattle Breeders of Parana State, and analyzed by descriptive analysis, correlation, analysis of variance, and regression analysis. The average daily milk yield was 31.78 kg/cow, which decreased to 29.31% when the somatic cell score (SCS) was 9, and to 11% when the Equivalent Temperature Index (ETI) was 32 or above. Lactose content decreased from SCS 0 until 9 and fat content decreased from SCS 1 until 9, totaling decrease 7.88 and 9.23%, respectively, when the SCS was 9. An opposite effect was observed for the protein content, which increased by 3.6% at SCS 8, when compared to SCS 0. Losses were observed in the daily total solids production from the SCS 0, totaling 30.64% at SCS 9.The increase in ETI to 32 or above reduced all milk constituents as much as 3.42%, except protein. These results, combined with the losses in milk yield at that ETI level, led to a decrease of up to 12.74% of milk solids. It is concluded that since losses in milk quality and yield resulting from SCC and ETI are significant, actions to prevent infection in the mammary gland and to provide a comfortable environment for dairy cattle are needed even in temperate regions.