Herbage intake and performance of grazing lambs in tropical erect grass pastures maintained at different heights

One of the main constraints for sheep production in tropical and subtropical areas is the lack of knowledge of how to manage erect tropical grasses for lambs. The objective of this study was to assess the effect of pasture height and structure of an erect tropical grass, Aruana Guinea grass (Megathyrsus maximus cv. IZ-5) on the intake and performance of young weaned lambs. The experiment was repeated in two consecutive years. Thirty young weaned lambs were equally assigned, each year, to three pasture heights: (1) Tall 75 cm; (2) Medium 50 cm and (3) Short 25 cm. Herbage mass (HM), pasture height, plant morphological composition, pasture nutritional quality, lambs' average daily gain, gain per hectare and herbage intake were measured. The Short treatment had higher (p < 0.05) leaf:stem ratio (L:S; 2.6 & PLUSMN; 0.27) and average daily gain (ADG; 92 & PLUSMN; 10 g day(-1)) than the Tall treatment (0.9 & PLUSMN; 0.11 and 40 & PLUSMN; 13 g, respectively). The Medium treatment showed intermediate ADG (69 & PLUSMN; 11 g) and L:S ratio (1.4 & PLUSMN; 0.09). The height of the pasture affects the rate at which the number of stems increases relative to the number of leaves. There was a significant interaction between treatment and period (summer and early autumn) for herbage intake. Intake decreased markedly on the Tall treatment from the first to the second period. This study showed that for a better performance of weaned young lambs during summer-autumn, it is important to maintain tropical swards at a short height (25 cm). However, if the grass height exceeds this condition, the use of cattle or a mower are good options to maintain the sward height.