Performance and digestion by steers grazing tall fescue and supplemented with energy and protein.

We studied the effects of different levels of protein and energy supplementation on BW gains and sites of nutrient digestion in steers grazing the primary growth of endophyte-infected tall fescue (Festuca arundinacea Schreb cv. Kentucky 31). Angus steers (n = 168; mean BW = 246.8 +/- 15.0 kg) grazed tall fescue without supplementation (C) or were supplemented with 1.4 kg/d of cracked corn (CC1), 1.4 kg/d of corn gluten feed (CGF1), 2.8 kg/d of CC (CC2), 2.8 kg/d of CGF (CGF2), or .7 kg/d of cornstarch and .7 kg/d of corn gluten meal (CS-CGM) during an 85-d period in a randomized complete block design. Supplemented steers (S) had a higher (P = .03) ADG than the control steers (.64 vs .74 kg/d). There was an interaction (P = .02) between supplement type and level. Supplementation during the grazing period had no effect on subsequent feedlot ADG (average 1.3 kg/d). In a digestion study, Angus x Simmental steers (n = 4; 412 +/- 20.4 kg) fitted with cannulas in the esophagus, rumen, and duodenum grazed tall fescue (C), C + 3.1 kg/d CGF, C + 3.1 kg/d of cracked corn (CC), or C + 1.4 kg/d CS-CGM over four experimental periods in a Latin square design. The ruminal ammonia nitrogen concentration tended to be higher (P < .09) in C than in CGF and in CC (21.9 vs 19.2 mg/dL), but ruminal pH and total VFA concentration did not differ among treatments. Forage OM intakes were lower (P < .05) in steers supplemented with CC or CGF (an average of 7,570 g/d) than in C (9,658 g/d). Total OM intakes and digestibilities did not differ (P > .10) among treatments. Duodenal N flows and efficiencies of net ruminal microbial protein synthesis were not different (P > .10) among treatments. Supplementation of steers grazing primary growth of tall fescue improved animal gain but did not have a great effect on ruminal fermentation, OM digestion, or net ruminal microbial protein synthesis.