Submitted to: Journal of Dairy Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/7/1997
Publication Date: N/A
Interpretive Summary: Osteoporosis, a significant health problem caused by loss of calcium from the bone of the elderly, costs our health care system several billion dollars annually. Increasing the calcium content of milk could benefit individuals at risk and markedly reduce health care costs associated with osteoporosis. Also, increasing the protein content of milk could have additional health benefits, particularly in growing children. The present study with dairy cows examined the effect of insulin in the blood and the addition of a protein, casein, into the stomach on milk protein synthesis and milk calcium content. Milk protein yield and milk calcium content increased significantly when casein was added directly to the stomach of cows with elevated concentrations of insulin in blood. This study indicates that the mammary gland of dairy cows generally is not functioning to maximum capacity and that there is a previously unrecognized potential to enhance the quality of milk. Increasing the amount of calcium available for consumption in milk will lead to improved nutritional health.
Technical Abstract: We utilized the hyperinsulinemic-euglycemic clamp approach in combination with abomasal infusion of casein to examine the role of insulin in milk protein synthesis. The two experimental periods consisted of abomasal infusion (water or 0.5 kg/d casein) with the insulin clamp conducted over the last 4 days of each period. During the insulin clamp, circulating insulin was elevated by 4-fold and euglycemia was maintained by infusion of exogenous glucose. Casein infusion increased milk yield so that milk protein yield was 10% above baseline. Combining the insulin clamp with casein infusion increased milk protein yield by 230 g/d (28% over the baseline). Milk protein composition was not altered but content was increased from 3.13% during the baseline period to 3.44% y day 4 of the clamp; milk calcium concentration increased about 10\% to 1.2 g/kg. During the clamp, circulating concentrations of essential amino acids were dramatically reduced with the most pronounced effects on branched chain amino acids (64% reduction from baseline values). The insulin clamp resulted in alterations in circulating IGF-I (increase) as well as IGF-11 and IGFBP-2 (decreases). Overall, results indicate that the biochemical machinery for milk protein synthesis is not functioning to maximum capacity and that there is a previously unrecognized potential to enhance milk protein percent and yield.