Destete precoz a corral: efecto de la forma de transición corral-pasto sobre la digestión del forraje y la posterior performance de los terneros en pastoreo

The present work was carried out between April 20 and August 18, 2021, at the Mario A. Cassinoni Experimental Station (EEMAC), located in the department of Paysandú.  The objective was to evaluate in early weaned calves, the effect of the post-weaning feeding system (DPC or DP + grazing supplementation) and the form of concentrate removal (abrupt or gradual) in the DPC at the exit of the pen, on subsequent grazing performance, and its relationship with variables such as apparent digestibility of the pasture and changes in the composition of live weight gain. Fifty-four Hereford calves were used, which had been early weaned at 60 days of age, and managed after weaning in two different feeding systems: pen (early weaning to pen: DPC) and pasture plus supplement (PAS). Of the total number of animals, 18 corresponded to PAS, and grazed a perennial pasture with a forage allowance of 8 kg DM/100 kg live weight, supplemented with an energy-protein ration for early weaning (EM, % CP), offered at a rate of 1% of live weight. The remaining 36 animals were fed four totally mixed rations (RTM; 20% alfalfa hay/ 80% concentrate) that differed in the level of lupine in the concentrate (0, 15, 30 or 45%) with an average concentration of ME and CP of the diets. Animals corresponding to the DPC feeding system were randomly distributed (balanced by diet type) into two groups, and these drawn to one of two forms of transition between diets at the time of leaving the pen and moving to grazing: 1) gradual transition (DPC-G), during the last 5 days prior to exit to pasture (-5 days relative to experimental day 1), concentrate began to be gradually substituted for bulking in the calves' diet until full substitution; and 2) abrupt transition (DPC-A), calves abruptly transitioned (without transition) from pen to pasture on experimental day 1 (4/27/21). The animals in the PAS feeding system were kept supplemented until 4/27/21, and the supplement was abruptly withdrawn. Thus giving rise to 3 treatments. From day 1, all animals, both from the pen and from the pasture, grazed together the same pasture, with a forage DM supply of 5 kg/100 live weight. Animal performance, measured as daily liveweight gain, was not affected by either the feeding system or the post-weaning transition system for the entire experiment, but was affected by the feeding system in the first 0-21 day period, and then by both systems in the 21-65 day and 65-107 day periods. For the animals that were managed in the pen, lower gains were determined during the first 65 days of evaluation, reversing this result from day 65 onwards. Likewise, in the first half of the experimental period, the depressive effect of DPC on GMD could not be attenuated by the gradual removal of the concentrate and its replacement by bulking. As for GMD, it was not affected by either SA or ST. Regarding the composition of the average daily gain, the AOB for the three treatments was not higher at the end than at the beginning; the EGD was increased by the animals that were always grazing, but the opposite happened with the animals coming from the pen that had a reduction.