Effect of Steam Heating Alfalfa Hay on Utilization by Lactating Dairy Cows

Alfalfa hay was steam heated for an average of 47 min at 100 to 110C; net ruminal protein escape (total escape minus ADIN x 6.25), estimated in vitro, was 50% versus 29% for control hay. Heating increased ADIN content from 4.6 to 15.3% of total N and increased NDF from 43 to 53% of DM. In trial 1, 14 cows averaging 81 DIM and 30 kg/d of milk were fed, in a switchback design, diets containing 18% corn, .7% urea, and 81 % control or heated hay. Intake of OM, milk fat content, and fat yield were unaffected by hay source. However, feeding heated hay reduced production of milk; yields of protein, lactose, and SNF; digestibility of OM and N; and ruminal concentrations of ammonia and total VFA. In trial 2, 16 cows averaging 36 DIM and 38 kg/d of milk were fed, in balanced 4 x 4 Latin squares, diets containing 1) 76% alfalfa silage and 23% high moisture corn; 2) 76% alfalfa silage, 14% high moisture corn, and 9% soybean meal; 3) 52% alfalfa silage, 23% high moisture corn, and 24% control hay; and 4) 43% alfalfa silage, 32% high moisture corn, and 24% heated hay. High moisture corn content of the diet with heated hay was increased to equal-