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Title: Variation in Crude Protein and Initial in Vitro Dry Matter Digestibility of Wheat Forage.

Author
item MACKOWN, CHARLES
item CARVER, BRETT - OKLAHOMA STATE UNIVERSITY
item EDWARDS, JEFFREY - OKLAHOMA STATE UNIVERSITY

Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/8/2010
Publication Date: 4/26/2011
Citation: Mackown, C.T., Carver, B.F., Edwards, J.T. 2011. Variation in crude protein and initial in vitro dry matter digestibility of wheat forage. Crop Science. 51:878-891.

Interpretive Summary: Cattle producers in the southern Great Plains rely heavily on winter wheat for their cool-season forage base. Even though winter wheat pasture is considered excellent forage, devastating losses of stocker cattle can occur due to pasture bloat. The development of wheat varieties that decrease losses of average daily weight gain to non-lethal bloat episodes, death losses due to bloat, and the cost and uncertainties of active bloat intervention strategies would be useful to cattle producers. Elevated levels of forage crude protein (CP) and a rapid rate of forage digestibility contribute to pasture bloat. We examined adapted wheat varieties that are commonly grazed and a set of 221 diverse breeding lines to characterize the variation in CP and digestibility that might be exploited through wheat breeding to deliver wheat that could offer a decreased frequency and severity of bloat. Substantial differences in the CP concentration and rate of digestibility were observed among adapted varieties and breeding lines. This variation may be useful to breeders wishing to develop lines intended for grazing by stocker cattle. The CP and digestibility traits, however, were poorly correlated, indicating that it will be necessary to select for both traits simultaneously if one seeks to reduce both CP concentration and forage digestibility. These results will be useful to wheat breeders seeking to develop varieties better suited for use in the southern Great Plains.

Technical Abstract: Annually 6 to 7 million spring-born calves (Bos taurus L.) are received in the southern Great Plains and pastured on winter wheat (Triticum aestivum L.) before feedlot finishing. Frothy bloat can be a serious problem for ruminant livestock grazing pastures of winter wheat. Wheat pastures have high digestibility, crude protein (CP), and soluble N fractions; all traits associated with bloat-provoking forages. We assessed the variation in CP concentration and initial in vitro dry matter digestibility (IVDMD) of released wheat varieties and experimental lines to provide information needed to characterize varieties and evaluate the feasibility of developing genotypes that could offer a decreased frequency and severity of bloat. Late fall forage from seven variety trials (34 varieties, 15 to 23 varieties per trial) and late fall and late winter forage samples from 221 diverse experimental breeding lines were analyzed. Significant (P < 0.05) differences among varieties and breeding lines were found for CP and IVDMD traits; trait variation among breeding lines was often substantially greater than among varieties. Differences in CP levels among breeding lines were as great as 47% and averaged 15% for the seven variety trials. Differences in the percent IVDMD occurring in the first 8 h of incubation among breeding lines were as great as 97% and averaged 24% for the seven variety trials. Correlations between CP and initial IVDMD traits were not significant or at best very weakly correlated (breeding line trial r=0.11, P=0.01, n=448), thus the development of wheat varieties with both reduced CP and low initial rates of IVDMD will require simultaneous selection for both traits.