Effect of stocking rate on dry matter production, sward structure, sward morphology and tiller density throughout a whole grazing season.

Stocking rate (SR) influences the sward through grazing intensity. A 4 ha grazing area, within a large grazing system experiment, was rotationally grazed by dairy cows from 10 February to 18 November (early spring to late autumn in the northern hemisphere) comparing the effects of three SR treatments: Low (L; 2.51 cows ha -1 ), Medium (M; 2.92 cows ha -1 ) and High (H; 3.28 cows ha -1 ). There was no significant difference in herbage accumulated or harvested among treatments. High SR swards were grazed 0.5 cm shorter than M and 1.1 cm shorter than L. Leaf proportions increased from 60.7 to 66.0 and 70.5%, and stem proportions decreased from 24.8 to 20.0 and 17.7% for L, M and H paddocks, respectively. Tiller densities of weed grass tillers for L, M and H paddocks decreased from 3,350 to 2,780 and 1,771 tillers m -2 , respectively. Rejected areas significantly increased for L (27%) treatment compared to the M (20%) and H (10%) treatments. The findings confirm, over a full grazing season with a dairy herd, what has often only been demonstrated in short term studies or with sheep.