Effect of topping pastures 2. Lamb growth during summer

Lamb growth was measured in three trials during summer on ryegrass ( Lolium perenne L.)—white clover ( Trifolium repens L.) pastures topped when ryegrasses were at various stages of flowering. On a pasture estimated to contain 2000 seed heads/m 2 , lamb growth over eight weeks was higher on a sward topped in early December when seed heads were emerging (135 g/d) than on nontopped pasture (121 g/d). When seed head density was 1200/m 2 , treatments topped in late November (ear emergence) and topped twice (late November and early January) had similar live weight gains (mean = 120 g/d), which were higher than those on treatments topped in early January (seed watery ripe) and non‐topped treatments (mean = 102 g/d). Green dry matter allowances (kg/head per day) were also higher on the late November and twice topped pastures (mean = 3.8) than on the early January topping and non‐topped swards (mean = 3.2). In a third trial where there were < 600 seed heads/m 2 because of a hard spring grazing, topping had no effect on lamb growth (mean = 126 g/d). Lambs in this trial tended to grow better during summer on pastures set stocked during spring (132 g/d) rather than on rotationally grazed pastures (112 g/d). When seed heads were dense (1200–2000/m 2 ), growth responses on early topped pasture lasted 8– 10 weeks and were greater in lambs set stocked at 40/ha (16–26%) than at 56–60/ha (7–11%).