|Miranda, C.H. -|
Submitted to: Brazilian Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 1, 2009
Publication Date: July 13, 2009
Repository URL: http://hdl.handle.net/10113/44736
Citation: Vogel, K.P., Miranda, C.B. 2009. Improving Grassland Profitability in the Mid-Continental USA by Breeding for Improved Forage Digestibility: Lessons Learned and Applications to South American Grasslands. Brazilian Journal of Animal Science (Revista Brazileria de Zootechnia) 38:160-169 (supl. especial). Interpretive Summary: Grassland profitability is dependent upon the stocking rate and live weight gains or milk produced by grazing animals. Livestock weight gains and milk production are highly dependent upon forage quality as well as the amount of forage available. USDA-ARS grass breeding research in the mid-continental USA has demonstrated that it is feasible to improve the forage quality of grasses adapted to the region. A series of grazing studies have demonstrated that a genetic improvement of 1% increase in forage digestibility generally leads to over a 3.2% increase in average daily gains of beef cattle. Because increased forage quality generally does not result in a decrease in forage yield, this results in a net increase in animal production per acre of hectare of land. In the Central Plains and Midwest of the USA, cultivars with improved IVDMD can increase net profit from $15 to $25 acre.
Technical Abstract: Grassland profitability is dependent upon the stocking rate and live weight gains or milk produced by grazing animals. Stocking rate is dependent upon forage availability while average daily gain also is dependent upon forage quality. In the early 1970’s research was initiated by the cooperative USDA-ARS and University of Nebraska grass breeding program to develop perennial grasses adapted to the mid-continental USA with improved forage quality. The initial breeding and animal evaluation work focused on switchgrass (Panicum virgatum) but has since expanded to several other warm- and cool-season perennial grasses. The in vitro dry matter digestibility (IVDMD) test was selected as the measure of forage quality that was used in the breeding work because of its previous successful application on improving bermudagrass (Cynodon dactylon). In all of the grass species that we have studied to date, there is genetic variability for IVDMD and forage yield. IVDMD is a heritable trait with narrow sense heritability’s ranging from 0.2 to 0.4 which are similar to heritability’s for forage yield. The genetic correlations between IVDMD and forage yield are usually slightly negative or neutral which makes it feasible to simultaneously breed for improved IVDMD and forage yield. A selection index is used which equally weights forage yield and IVDMD. Although it varies with species, it often takes two generations of breeding to detect significant improvements in IVDMD in small plot sward trials. If significant improvements or difference in IVDMD (> 1%) can be detected in small plot trials (r=6), differences in cattle gains among experimental strains or cultivars can be demonstrated in grazing trials. Averaged over both cool- and warm-season grasses, a 1% increase in in vitro dry matter digestibility (IVDMD) generally leads to a 3.2% increase in average daily gains of beef cattle. Because increased IVDMD generally does not result in a decrease in forage yield, this results in a net increase in animal production per hectare of land. In the Central Plains and Midwest of the USA, cultivars with improved IVDMD can increase net profit from $30 to $50 ha-1.