Rumen Bypass of Protein Through Suckling of Liquids by Lactating Heifers

Abstract

Holstein heifers (22 mo) were trained to suckle from a nipple pail through prolonged withdrawal of water from their rations. After 2 to 3 wk the suckling habit was firmly established, and most of the heifers would accept readily the nipple. Bypass of liquid was confirmed by rapid and large increases in blood glucose in trained heifers after suckling a test solution of 500g glucose, whereas there was little rise in heifers with glucose placed directly into the rumen. When heifers suckled slowly, bypass was less efficient as evidenced by flat tolerance curves for glucose. In heifers that suckled readily, mean blood glucose was over 30 mg/100ml higher at 2 than at 0h after suckling.In a reversal trial, six heifers in early lactation suckled 17% (or 321g) of their protein intake as whole milk or received a like quantity of casein mixed in their concentrate. Milk yields and protein content of milk were raised slightly by suckling, but milk protein production was increased significantly. Efficiency of conversion of suckled protein to milk protein was estimated between 35 and 63%.