Abstract
This study was conducted to determine in situ ruminal protein degradation and animal responses to ruminally degraded and escape protein supplementation of warm-season grass. Cattle grazed a mixed stand of primarily big bluestem (Andropogon gerardii Vitman) and switchgrass (Panicum virgatum L.) with some indiangrass (Sorghastrum nutans [L.] Nash) from the 1st wk of June to the 3rd wk of August. In 1987, 72 yearling steers (286 kg) were allotted randomly to three treatments: energy control (cornstarch-molasses mixture) or energy control plus .1 or .2 kg.animal-1.d-1 of escape protein. The total amount of a supplement fed per day was 1 kg. In 1988, 90 yearling heifers (240 kg) were allotted to five treatments: negative control (no supplement), energy control, energy control plus .14 kg.animal-1.d-1 of escape protein, energy control plus .18 kg.animal-1.d-1 of ruminally degraded protein, or .36 kg.animal-1.d-1 of protein supplied by a combination of the two protein sources. The total amount of a supplement fed per day was 1.7 kg. During 1987, the .2-kg level of escape protein produced the greatest gains (P < .10). In 1988, gains did not differ between the control and escape protein treatments. Ruminally degraded protein tended (P = .12) to increase gains (.09 kg/d) compared with the energy control. The combination treatment supported .13 kg/d more ADG (P < .10) than the negative and energy controls and the escape protein treatment. Ruminal ammonia concentrations in unsupplemented steers were low, with few values > 5 mg/dL. Based on in situ measurements, 42 to 54% of the forage protein escaped ruminal degradation.(ABSTRACT TRUNCATED AT 250 WORDS)
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