Performance and digestion by steers grazing tall fescue and supplemented with energy and protein
1998
Elizalde, J.C. | Cremin, J.D. Jr | Faulkner, D.B. | Merchen, N.R.
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.
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