Effect of ammoniation and urea addition on chemical composition and digestibility of mature timothy hay, and rumen fluid characteristics of growing steers

Feed quality of timothy (Phleum pratense L.) harvested at the beginning of heading (H), with a crude protein (CP) content of 13.3%, was compared to timothy harvested at a late stage of growth either untreated (M) or treated with anhydrous ammonia (30 g kg−1 dry weight) (MA); or with urea added at feeding (MU) making it isonitrogenous with MA. These diets were fed to eight ruminally fistulated steers (220 ± 12 kg) in a 4 × 4 double Latin square. Treatments MA and MU increased the crude protein (CP) content of timothy from 8.3 (M) to 19.8 and 21.8%, respectively. Ammoniation improved the apparent digestibility of dry matter (DM) (68 vs. 62%), CP (66 vs. 47%), hemicellulose (HC) (85 vs. 67%), and cellulose (C) (79 vs. 65%), compared to M. In support, in sacco DM disappearance was about 18% units greater (P < 0.01) for ammoniated hay (MA) as compared with M. Ammoniated timothy hay had apparent digestibility of DM, CP and C (68, 66 and 79%, respectively) similar to that of timothy hay from early harvest (67, 6...