Effect of Abrupt Ration Changes on Milk and Blood Components

Abstract

The effect of abrupt change between a normal and a fat-depressing ration on milk composition and several blood components was examined. An abrupt ration change was accomplished by simultaneously switching rumen contents and rations between two cows, one fed a ration having a grainto-roughage ratio of approximately 1:2 and the other a fat-depressing ration with a 3:1 ratio. Feed intake was not altered when the cows were abruptly switched from one ration to the other. Five to six days were necessary to affect complete transition in the level of milk fat following a ration change. This was interpreted to mean that the ration effect on milk fat content was eventually mediated through time-consuming metabolic adaptations by the host, rather than by immediate availability or supply of acetate, propionate, or butyrate from the rumen. Arterial levels of blood glucose, ketones, acetate, and triglycerides with the normal ration were 50.2, 2.13, 12.6, and 11.1 mg/100ml, respectively. Corresponding values with the fat-depressing ration were 56.3, 2.44, 7.9, and 11.5 mg/100ml. Values for blood glucose and acetate were significantly different (P<0.05), whereas those for ketones and triglycerides were not. The only arterial-venous difference across the mammary gland that approached significance was that for acetate.