Effect of Abrupt Ration Changes on Milk and Blood Components

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-cousnming metabolic adaptations by the host, rather than by immediate availability or supply of acetate, propionate, or butyrate from the tureen. Arterial levels of blood glucose, ketones, acetate, and triglycerides with the normal ration were