Liveweight gain and apparent diet selection by bulls grazing a perennial ryegrass-white clover pasture with and without sorghum-sudangrass hybrid (Sudax ST-6)

Abstract

Abstract Forage production from perennial ryegrass-white cloverpastures during summer in the Manawatu is often insufficient for optimal animal production. A system consisting of 25% sudax and 75% pasture was compared with 100% pasture. Sudax was sown on 24 November. Grazing of both systems started on 14 January with sudax grazing starting on 12 February; grazed areas were back-fenced to allow regrowth. Sudax yield increased from 4.11 dry matter (DM)/ha on 29 January to 18.3 t DM/ha on 30 March. Regrowth (12 February–6 April) was higher on sudax (6.0 t DM/ha) than on pasture (2.8 t DM/ha). In the pasture and sudax system, sudax contributed 55–59% of the diet. The apparent composition of consumed sudax was 40% leaf, 18% sheath, 38% stem, and 4% inflorescence. On the pasture system, apparent composition of the diet was 28% grass, 38% white clover, and 34% dead matter. The in vitro DM digestibility of the total sudax plant was 66.8% and of pasture was 65.6–66.1%. Liveweight gain over the 82-day experiment was 0.89 and 0.85 kg/day for the pasture and sudax, and pasture only systems respectively. All components of sudax were acceptable to bulls and there was no evidence of ill-health. Sudax has the potential to contribute large quantities of medium-quality forage during late summer-early autumn.