Utilization of oaten hay by cattle: effects of milling and urea supplementation

Abstract

Oaten hay in either long or milled form, with or without a continuous intra-ruminal infusion of urea at the rate of 160 g/d, was offered ad libitum to four rumen fistulated steers in a 4 x 4 Latin square design experiment. Milling increased dry matter intake from 49.2 to 65.4 g/kg LW0 75.d (P< 0.001) and decreased mean retention time from 66.7 to 54.2 h (P< 0.001). Rates of cellulose digestion and dry matter digestibilities were similar for long and milled hay. Urea increased dry matter intake (from 49.0 to 65.6 g/kg LW0 75.d; P< 0.001), dry matter digestibility (from 58.1 to 65.3%; P< 0.01) cellulose digestibility (from 48.5 to 63.1%; P< 0.01) and the rate of cellulose digestion (P< 0.001), and decreased mean retention time from 65.3 to 55.6 h ( P < 0.01). Digestible dry matter intakes increased 29% with milling and 52% with urea and the effects were additive. Urea increased digestible cellulose intake to a greater extent with milled hay (91 %) than with long hay (64%). Digestible dry matter intake was closely related to liveweight change. When urea was given liveweight gain was higher for milled hay than for long hay (0.69 vs 0.11 kg/head.d) and without urea liveweight loss was less for milled hay than for long hay (-0.07 vs -0.45 kg/head.d). Nitrogen digestibility and balance were significantly higher when urea was given. Total volatile fatty acid concentrations were significantly higher and rumen pH significantly lower with urea compared with no urea and with milled hay compared with long hay. Urea increased rumen-ammonia concentration from 1.65 to 19.68 mg1100 ml (P< 0.001) and total free bacterial concentration (P < 0.05). The results demonstrate significant and additive benefits from the administration of urea to hay containing 0.8% nitrogen and from milling through a screen size of 7.6 mm.