FEED-INTAKE AND DIGESTION BY HOLSTEIN STEERS CONSUMING LOW-PROTEIN FORAGE SUPPLEMENTED WITH DIFFERENT NITROGEN-SOURCES

Effects of moderate levels of supplements high in rumen undegradable p rotein and differing in protein quality on intake of low-protein forag e by growing steers were determined. Six Holstein steers (205+/-4.6 an d 272+/-17.6 kg initial and final body weight, respectively), in a 6 x 6 Latin square with 21-d periods, consumed prairie hay (4.8% crude pr otein, dry matter basis) ad libitum with 0.1% body weight (BW) ground corn (dry matter basis). Steers were not supplemented with additional crude protein (Control) or received (dry matter basis 0.19% BW soybean meal (S); 0.12% BW feather meal (F); 0.12% BW feather meal plus 0.017 % BW urea (F-U); a mixture of feather (0.39% BW), corn gluten (0.051% BW) and blood meals (0.39% BW; FGB); or the FGB supplement plus 0.017% BW urea (FGB-U). Total organic matter intake was increased (P<0.05) b y nitrogen supplementation and similar among supplement treatments (4. 69, 6.16, 5.82, 5.88, 5.89, and 6.18 kg/d for Control, S, F, F-U, FGB and FGB-U, respectively). Organic matter digestibility and digestible organic matter intake were increased (P<0.05) by supplementation and g reater (P<0.05) for S than for the mean of F and FGB, and tended (P<0. 09) to be increased by FGB and FGB-U compared with F and F-U (48.7, 56 .5, 50.9, 52.0, 53.0 and 54.4%, and 2.30, 3.48, 2.98, 3.07, 3.15 and 3 .39 kg/d for Control, S, F, F-U, FGB and FGB-U, respectively). In conc lusion, protein quality of feedstuffs high in rumen undegradable prote in and supplemented at moderate levels did not alter intake of low-pro tein forage by growing ruminants regardless of urea supplementation. H owever, digestible organic matter intake was lower for supplements hig h in rumen undegradable protein compared with a supplement high in rum en degradable protein.