Rotational grazing system "First and last grazers" for beef heifers. 1. Body development

The objective of this work was to evaluate the development or beef heifers in a rotational grazing system as "first grazers" and "last grazers" during the first (Year-l) and second (Year-2) winter/spring seasons post weaning until the end of the first mating at 22-24 months of age. Seventy-six crossbred female calves were maintained during Year-1 and Year-2 on improved natural pasture of ryegrass (Lolium multiflorum L.) and arrowleaf clover (Trifolium vesiculosum cv. Yuchi). During the summer/autumn period and mating season, the heifers were maintained on natural pasture as a unique mob. The First grazers (FC) treatments: group eating the superior half of the available pasture, Last grazers (LG): group eating the inferior half of the available pasture, were tested: The live weight evolution (LW) in each phase of the experiment and average daily weight gain (ADG) per period were analyzed. The live weight of FC differed from LG at the end of the Year-1 (195.6 vs. 168.1 kg), at the end of the Year-2 (316.3 vs. 274.1 kg), at the beginning (318.5 vs. 275.7 kg) and at the end (341.5 vs. 304.4 kg) of the mating period, respectively. The higher LW was due to the higher ADC obtained by FG over LC during the use of the improved pastures, with ADG of .790 vs. .563 kg/day and .753 vs. .522 kg/day, at Year-1 and Year-2, respectively. There was an inversion in the ADG with a better performance of LG in relation to FC (.377 vs. .303 kg/day, respectively), in the mating period. The raising systems for replacement heifers that favored a determined animal group (FG) is one of the alternatives to obtain a satisfactory live weights, making them able to conceive at 22-24 months of age.