Journal of Animal Science, Vol 71, Issue 2 522-529, Copyright © 1993 by American Society of Animal Science

JOURNAL ARTICLE

Supplementation of growing cattle grazing warm-season grass with proteins of various ruminal degradabilities

J. L. Hafley, B. E. Anderson and T. J. Klopfenstein
Department of Agronomy, University of Nebraska, Lincoln 68588.

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)