The effects of grazing forage legumes on the performance of finishing lambs

Abstract

An experiment was conducted to investigate the effect of grazing legumes and ryegrass on the performance of Suffolk×Mule finishing lambs in terms of growth rate, days to finish and carcass characteristics. Replicate plots (n=2) of red clover (Trifolium pratense), lucerne (Medicago sativa), lotus (Lotus corniculatus) and perennial ryegrass (Lolium perenne) were established in May 1999 at the Institute of Grassland and Environmental Research (IGER), Aberystwyth, and maintained at a similar vegetative growth stage. From the beginning of September 1999 each forage was grazed by 10 wether lambs and 10 ewe lambs. The lambs grazed the experimental plots from weaning until they reached fat-class 3L. There was a significant decline in crude protein (CP) concentration in lucerne (−2·6 g/kg DM/day, P<0·05) and lotus (−2·5 g/kg DM/day, P<0·001) over the grazing period, while the CP concentration in red clover and ryegrass remained comparatively constant. Growth rates were highest for lambs grazing lotus compared with lambs grazing the other forages, and growth rates were significantly higher for lambs grazing red clover than for lambs grazing ryegrass. Growth rates of lambs grazing lucerne were significantly lower than lambs grazing lotus but similar to that of lambs grazing red clover and ryegrass. Lambs grazing the legume forages required significantly fewer days to finish compared with lambs grazing ryegrass. Cold carcass weight and killing out percentage were significantly higher for lambs grazing red clover compared with that for lambs grazing the other forages. Lambs grazing red clover and lucerne had significantly higher voluntary intakes, estimated using n-alkanes, than lambs grazing ryegrass, with intakes for lambs grazing lotus not significantly different. There were no treatment effects on in vivo digestibility. Levels of total protein and β-hydroxybutyrate in blood were unaffected by dietary treatment, although lambs grazing the forage legumes had significantly higher blood glucose and urea concentrations compared with lambs grazing ryegrass. Lambs grazing lotus had the highest plasma albumin. The results indicate that by grazing finishing lambs on forage legumes it is possible to increase growth rates and reduce time to finish without compromising carcass quality.