Submitted to: Animal Feed Science And Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/1/2003
Publication Date: 1/1/2004
Citation: Broderick, G.A., Albrecht, K.A., Owens, V.N., Smith, R.R. 2004. Genetic variation in red clover for rumen protein degradability. Animal Feed Science And Technology. 113:157-167. Interpretive Summary: Partly because it is very high in total protein, alfalfa is the principal legume forage fed to U.S. dairy cattle. However, extensive breakdown of alfalfa protein by the microbes living in the rumen, the first compartment of the cow's stomach, leads to inefficient utilization and depressed production of milk and milk protein. Red clover, another forage legume, has nearly as much protein as alfalfa but its protein is less extensively degraded by the rumen microbes. A study was done to see if there were genetic differences in red clover that could be used to produce forages with protein that was better utilized by dairy cows and other ruminants. One hundred thirty-three samples of genetically different red clover were grown and harvested from small field plots. The forage produced was incubated in vitro (that is, outside the live animal) with microbes collected from the cow's rumen to see how rapidly the protein was broken down. The rumen microbes degraded the protein in all 133 red clovers protein more slowly than they degraded the protein in a standard alfalfa tested along with the clovers. There was a wide range of differences among the red clovers in the speed with which the protein was degraded by the rumen microbes. This research indicates that there are genetic differences in red clover that could be used by plant breeders to develop new red clover varieties with improved protein value when fed to dairy cows. Feeding cows forage from improved red clover varieties also would reduce costs to dairy farmers for buying protein supplements for their cows and could reduce nitrogen levels in manure and nitrogen pollution of the environment.
Technical Abstract: Protein in red clover (Trifolium pratense L.), a forage that does not contain condensed tannins, has been found to be degraded less extensively in the rumen than the protein in other non-tannin legumes. The objective of this study was to determine if there are genetic differences in rumen degradability of the protein in red clover forage. Field grown forage was harvested from 133 red clover entries (117 plant introductions and 16 cultivars or experimental lines) plus one cultivar of lucerne (Medicago sativa L.). Forages were analyzed for total N and for crude protein (CP; N x 6.25) that was undegraded at 0 h, as well as for rate of protein degradation and rumen protein escape estimated using a rumen in vitro system. There were small but significant (P = 0.007) differences in total N among the 133 red clover entries but no differences in proportion of CP that was undegraded at 0 h. Protein degradation rate was more rapid for the lucerne cultivar than for any of the red clover entries; this difference was significant (P < 0.05) for 132 of the red clovers. Protein degradation rate ranged from 0.088 to 0.146/h and rumen protein escape ranged from 287 to 409 g CP/kg CP among red clover entries; effect of accession was highly significant (P < 0.001) for both traits. The frequency distributions for the red clover entries for protein degradation rate and rumen protein escape were normal, showing relatively little skewness. The consistency and distribution of these results suggested that conventional plant breeding techniques could be used to develop lines of red clover forage with improved protein utilization in ruminants.