Genetic variation in red clover for rumen protein degradability

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 saliva 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. (C) 2003 Elsevier B.V. All rights reserved.