Grazing behavior and productive response of steers in a Lotus tenuis pasture

This investigation, conducted at the INTA experimental farm in Chascomus, Buenos Aires, Argentina (35o 56’ S, 57o 83’ W), studied the effect of two different time of day (am and pm) to initiate grazing of a legume summer pasture on animal production. Two groups of 10 Angus steers each (311 ± 3.9 kg liveweight), allocated at random to treatments, grazed daily a new strip of herbage, the main component of which was birdsfoot trefoil (Lotus tenuis), starting at 09:00 (morning) or 13:00 (afternoon). There were three experimental periods: during the summer of 2012/2013: PI (10/12–02/01), PII (03/01-25/01), and PIII (26/01–20/02); in the last three days of each period herbage quality, grazing behavior, dry matter (DM) intake, and liveweight gain were measured. Data were analyzed per period by ANOVA using a completely randomized design in a general linear model. Grazing time in PII was longer in the afternoon than in the morning (P< 0.05) and the same trend was observed in PIII (P< 0.07). A similar result was recorded for rumination time. Afternoon grazing tended to result in higher intake in and liveweight gain in all periods, but the differences between treatments were (P<0.05) only in PIII (1102 vs. 1565 kg MS ha-1 and 0.022 vs. 0.456 kg d-1). It is concluded that the hour of grazing initiation of a Lotus summer pasture affected the grazing behavior of finishing steers; afternoon grazing promoted greater herbage intake and more rapid liveweight gain.