THE EFFECT OF SWARD HEIGHT ON GRAZING BEHAVIOR AND HERBAGE INTAKE OF 3 SIZES OF CHAROLAIS CATTLE GRAZING COCKSFOOT (DACTYLIS-GLOMERATA) SWARDS

Mature non-lactating cows, 18-month-old heifers and 7-month-old female calves of the Charolais breed (eight animals of each age) were strip- grazed on short (S, sward surface height: 7.5 cm), medium (M, 10.2 cm) and;all (T, 21.2 cm) cocksfoot (Dactylis glomerata) swards at a daily herbage allowance of 40 g dry matter per kg live weight over three 15 -day experimental periods. The swards were leafy regrowths of 1 (S), 2 (M) and 3.5 (T) weeks of age. Herbage intake was estimated by the n-a lkane method, and grazing behaviour was recorded visually. Intakes per kg live weight of calves and heifers were higher than those of cows o n all swards (P < 0.01). Calves tended to maintain intake, whereas cot es and heifers reduced their intake as sward height decreased. Bite we ight decreased linearly with sward height, this decrease being greater for larger animals (P < 0.001). As sward height decreased, the scalin g factor of bite weight to live weight decreased. Biting rates increas ed as sward height decreased (P < 0.001) and were lower in calves than in older cattle (P < 0.01). Calves had lower intake rates per kg live weight than cows in T swards, and the reverse was true in S swards (P < 0.001). Younger cattle always grazed longer than cows, but differen ces were reduced as sward height decreased (P < 0.01). Co ius and heif ers were unable to increase their grazing lime sufficiently to compens ate for lower intake rates in S and M swards, resulting in reduced her bage intakes. Faecal markers and grazing behaviour suggested a greater selectivity by calves compared with older cattle.