The growth of hill lambs on herbage diets

Abstract

SUMMARYEarly-weaned lambs were penned indoors for 6 weeks and individually fed to appetite on cold-stored ryegrass (Lolium perenne) or indigenous Agrostis-Festuca herbage of differing maturity. In another experiment similar lambs grazed for 12 weeks on swards of perennial ryegrass or Agrostis-Festuca. Live-weight gain (LWG), herbage organic-matter intake (OMI) and digestibility (OMD) were measured. In the indoor experiment ryegrass was 4–6 percentage units higher in OMD than was Agrostis-Festuca;first harvests were superior to later harvests by the same amount. The intake of ryegrass was 22% greater than that of Agrostis-Festuca. The correlation between OMI/W'73 and herbage cell-wall constituents was —0·80, and that between OMI/W'3 and OMD was 0·78. OMI/W0·73 increased progressively up to about 13 weeks of age.LWG was higher on ryegrass than on Agrostis-Festuca; and LWG on the early harvests of each herbage type exceeded those on the later harvests. LWG was significantly correlated with the intake of digested organic matter (DOMI) (r = 0·85).In the grazing experiment, OMD, OMI and LWG were all lower than in the indoor experiment. LWG on ryegrass was again superior to that on Agrostis-Festuca, and the difference was partly explained by the relationship between DOMI and LWG which had been established indoors.These results suggest that the increase in the growth rates of hill lambs consequent on the improvement of indigenous Agrostis-Festucaswards would be less than that due to the provision of sown pastures of perennial ryegrass.