Caracterización productiva de terneros destetados precozmente con énfasis en el periodo de acostumbramiento

This research was conducted at the Experimental Station Mario A. Cassinoni, at the beef cattle production unit (UPIC) from January 4th to March 16th, 2024. The objective was to identify and analyze the main factors affecting average daily gain (ADG) in early-weaned calves, with emphasis on the adaptation period. A total of 181 spring-born Hereford calves were evaluated and divided into two groups based on age and weight. The first group was managed under a feedlot early weaning protocol (DPC), while the second group followed a pasture-based early weaning protocol (DPP). Variables such as age, weight, health status, dam age, sex, dry matter intake (DMI), and feed to gain ratio (FG) were assessed using the Stepwise method. During the adaptation period (12 days), the DPC group showed an average ADG of 0.479 ± 0.33 kg/day. Health status had a significant effect (p = 0.0775), with a 17.8% reduction in ADG in the sick calves group compared to the healthy ones (0.473 vs. 0.576 kg/day). Age of the dam was also significant (p < 0.0001), showing an effect linked to calving season and calf age (p = 0.0002). Initial weight also had a significant but marginal effect on ADG (p = 0.0948), while sex showed no significant influence. Average DMI was 1.49 kg DM/animal/day, with a FG of 3.11. By day 8, 95% of the calves had adapted to the feeding system. After the adaptation period, DPC calves achieved an ADG of 1.45 kg/day with an average intake of 2.97 kg DM/day and a FG of 2.64. In the DPP group, the adaptation phase achieved an ADG of 0.453 ± 0.25 kg/day, with 1.23 kg DM/day of DMI and a FG of 2.7. No significant influencing factors were identified in this group, likely due to the lower incidence of illness and a less stressful environment. Calves' adaptation to the feeders occurred earlier in time (days 4–5). After the adaptation period, DPP calves grazed a pasture with an 8% BW forage allowance (2984.7 kg DM/ha and a stocking rate of 13 calves/ha) and received a ration supplementation (1% BW), achieving an ADG of 0.71 kg/day with 1.08 kg DM/day ration intake, resulting in a supplement FG of 2.32. The technical coefficients obtained were consistent with those reported in similar feeding systems, confirming their reliability. In the bioeconomic analysis, assuming a calf price of 2.23 USD/kg and a feed cost of 0.38 USD/kg as-fed, the DPC system yielded a gross margin 35.57 USD higher than the DPP system. Results indicate that calf health status and age significantly influenced ADG during the adaptation period. Both systems proved viable, with DPC standing out for its higher economic margin under the evaluated conditions.