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 110°C; 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 DM, 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 DM 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 equalReceived May 18, 1992. Accepted September 17, 1992. 'Mention of a trademark or proprietary product in this paper does not constitute a guarantee or warranty of the product by the USDA or the Agricultural Research Service and does not imply its approval to the exclusion of other products that also may be suitable. 2Corresponding author. 3Present address: Guangxi Animal Husbandry Research Institute, Nanning, Guangxi, People's Republic of China. 0. A. BRODERICK,2 J. H. YANG,J and R. G. KOEGEL Agricultural Research Service, USDA US Dairy Forage Research Center 1925 Linden Drive West Madison. WI 53706 ize NEL. Reduced ruminal ammonia and branched-chain VFA indicated decreased ruminal protein degradation on heated hay. Intake of DM, production of milk, and yields of protein, lactose, and SNF were greatest on heated hay, intermediate on soybean meal, and lowest on alfalfa silage and unheated hay. Digestibility of DM and ruminal pH were slightly lower on heated hay. Results indicated that steam heating alfalfa hay improved protein utilization but reduced energy digestibility. (