Effects of protein supplementation on steers grazing dormant tobosagrass

Studies were conducted through the 1989-90, 1990-91, and 1991-92 winter seasons at the Texas Tech Experimental Ranch, close to Justiceburg, Texas. The objective was to evaluate the effects of feeding various levels of cottonseed meal pellets (CSM) (0.00, 0.68 and 1.36 kg/hd/d) to steers on a tobosagrass range to determine weight gain. In addition, the effects of feeding those supplementation levels on forage intake and in vitro organic matter disappearance were evaluated during the winter seasons of 1989-90 and 1990-91. Furthermore, additional studies were done regarding in situ protein and organic matter disappearance from the forage and from the supplement, and the rumen degraded nitrogen:rumen degraded organic matter (RDNrRDOM, g/kg^-1) ratio of the complete diet on steers grazing dormant tobosagrass.

I concluded that protein supplementation had a positive effect {P<0.05) on stocker cattle grazing dormant tobosagrass. Protein supplementation was most effective (P<0.05) during the second grazing period (mid-winter) and on colder winters rather than in mild ones. Average daily gain was 73.0 and 82.0% higher for the low and high levels of supplementation than for the control steers during the 3 years of this study.

In conclusion, this study illustrated that protein levels did not affect (P>0.05) forage intake nor fecal output. Rate and extent of in situ digestion of protein and organic matter from the forage were modified (P<0.05) by the level of supplementation. Total protein degradation as well as the protein fractions decreased (P<0.05) along with the grazing periods, having the lowest values in the second grazing period.

The level of protein supplementation slightly affected protein disappearance and organic matter from the supplement. The soluble protein or fraction A from the cottonseed meal (CSM) remained uniform during the 2 years of study. In contrast, the slowly degradable and undegradable fractions showed different patterns. Ruminal escape protein from CSM was similar between the 2 levels of protein supplementation, but different (P<0.05) across sampling periods. Results from RDN/RDOM ratios also suggested to feed the low rate of supplementation at the beginning and towards the end of the winter and to go to the high level at midwinter.

Protein supplementation was most effective during the second period in which the lowest forage protein contents were found. These data indicated that feed protein escape values may differ on different range types, even within one winter. These results illustrated that no single estimate of protein escape can be applied to these feeding conditions. Consequently, there should be a combination of feeding a rumen degradable (CSC) with an escape protein to have better animal performance.