The effect of herbage allowance of Lotus pedunculatus cv. Grasslands Maku on winter and spring beef heifer performance

Abstract

Beef cattle production in Uruguay is limited by heifer mating age when grazing natural pastures. Lotus pedunculatus cv. Grasslands Maku is a forage species that was recently introduced to Uruguayan farming systems, with high potential to improve herbage production in acid and low fertility soils. This paper provides information about winter and spring performance of Hereford x Angus heifers grazing an improved Lotus pedunculatus cv. Grasslands Maku pasture when fed at different pasture allowances. Four pasture allowances (3, 5, 10 and 16 kg DM/100 kg animal liveweight/day) from June 30 to October 9 (P1) followed by one pasture allowance of 9 kg DM/100 kg animal liveweight/day from October 9 to November 28 (P2), were assigned to 9 months old Hereford x Angus heifers weighing 129 kg. Measurements included herbage mass, botanical composition, pasture growth rate, sward height and animal liveweight. Liveweight gains were evaluated using a repeated measurement model in time. Pasture mass decreased from 4000 kg DM/ha to 1100, 1050, 1350 and 2000 kg DM/ha for the herbage allowances of 3, 5, 10 and 16% respectively during P1. Legume content at the end of P1 was 550, 400, 700 and 700 kg DM/ha for 3, 5, 10 and 16% of total pasture mass respectively. Herbage mass increased by 328 kg DM/ha per cm sward height (P<0.01, r2= 0.69, n=240). Mean pasture growth rate in P1 was 21 kg DM/ha/day, being promoted by intensive grazing. In P2, mean pasture growth rate was 58 kg DM/day, increasing when laxly grazed in the previous period (P1). During P1, herbage allowance explained 77% (P<0.001) of liveweight gain, with significant differences (P<0.05) between all treatments (0.20, 0.36, 0.57 and 0.70 kg/heifer/day for allowances of 3, 5, 10 and 16 kg DM/100 kg liveweight/day respectively). In P2, liveweight gains were inversely correlated to the liveweight gains achieved in P1 (1.03, 0.96, 0.85 and 0.76 kg/heifer/day for P1 allowances of 3, 5, 10 and 16 kg DM/100 kg liveweight/day respectively). Feed planning in P1 produced a range of differences of liveweight of 51 kg/heifer and that reduced to 38 kg/heifer in P2. During P1, daily liveweight gains and production/ha were maximized at 16 and 3% of herbage allowance respectively. Keywords: beef heifer growth, herbage allowance, Lotus pedunculatus cv. Grasslands Maku