THE EFFECT OF WINTER FEEDING LEVEL ON SUBSEQUENT GRAZING BEHAVIOR ANDHERBAGE INTAKE OF CHAROLAIS HEIFERS

Two groups of eight Charolais heifers were used to examine the effect of feeding level during the post-weaning winter on the grazing behavio ur and herbage intake over three periods during the first 2 months of grazing. The winter diets (L and H) were given to achieve a mean diffe rence of 50 kg between groups at turn-out. The heifers were set-stocke d together on a hill pasture where sward height was maintained at 12 c m. The winter live-weight gains were 0.31 and 0.70 (s.e. 0.032) kg/day for L and H heifers respectively, and spring gains 1.94 and 1.66 (s.e . 0.082) kg/day respectively. Intakes increased throughout the spring grazing for both groups. Absolute intakes were lower for L than for H heifers only during the first period (P < 0.05). Intake pel kg live we ight was higher in L than in H heifers (23.0 v. 21.1 (s.e. 0.54) g org anic matter (OM) per kg live weight). Bite weights of H heifers were c onstant throughout (434, (s.e. 12.9) mg OM), while bite weights of L h eifers only reached those of H heifers in the last period. Bite weight was linearly related to live weight. Bite rates were not different be tween groups, bur L heifers compensated for lower bite weight by grazi ng longer and the?, increased their grazing time after turn-out faster than H heifers. Grazing time was mainly responsible for higher relati ve intakes in L heifers, and thus, partly, for compensatory gain obser ved.