Abstract
Effects of heat stress on blood profiles, feed intake and lactation performance during the hot season were examined in 45 dairy cows, which were either on separate feeding or on total mixed rations (TMR). Feed intake, lactation performance and blood profiles were examined once a month over a year. Accumulated 277 data sets were analyzed separately for separate feeding and TMR feeding and compared between the hot season (June to September)and optimum temperature period. In the separate feeding group, 43 data sets were obtained during the hot season, and 81 during the optimum period. During the hot season, dry matter intake(DMI, p<0.05), metabolizable energy intake (p<0.01), milk yield (p<0.01), % milk fat (p<0.05), % milk protein (p<0.001), blood glucose (p<0.001), total cholesterol (p<0.01), phospholipids (p<0.001), hematocrit (Ht, p<0.001), total protein (p<0.05), calcium (p<0.01) and aspartate aminotransferase(AST, p<0.05)were significantly lower, and betalipoprotein (BL, p<0.001)was significantly higher compared to those during the optimum period. In the TMR group, 43 data sets were obtained during the hot season, and 110 during the optimum period. Although DMI and milk yield did not differ between the two seasons, % milk fat(p<0.05), % milk protein (p<0.01), Ht (p<0.001)and AST (p<0.01)were significantly lower, and BL (p<0.001) and albumin (p<0.01)were significantly higher during the hot season compared to those during the optimum period. Thus, changes in blood profiles were more frequently observed in cows on separate feeding than in those on TMR feeding. As the separate feeding system resulted in decreased DMI and milk yield during the hot season and TMR feeding did not, the effects of heat stress observed in blood profiles seem to be the results of altered feed intake and lactation performance.
