Effect of High Potency Growth Implants on Average Daily Gain of Grass-Fattened Steers.

High potency growth promoter implants (HGPs) are widely used under feedlot conditions but there are few reports under grazing conditions. The study's goal was to assess the effect of HGPs on the average daily gain of steers fattened in pastures. A total of 57 crossbreed steers (Hereford × Angus)-initial body weight = 356.65 kg ± 5.04 (SEM)-were randomly allocated to one of three groups: Control without HGP (n = 19), Synovex group (n = 17), and Revalor group (n = 21). The fattening period was 67 days using paddocks of Lolium perenne L. and Trifolium repens L. Body weight was recorded three times in the period. The data were analyzed using an analysis of covariance with a level of significance of 5%. The average daily gain (ADG) (1.55 ± 0.07 and 1.48 ± 0.09 kg/d) and the total weight gain (103.4 ± 4.9 and 99.2 ± 5.8 kg) were similar for Revalor and Synovex, respectively (p > 0.05). Moreover, HGP groups showed higher ADG and total weight gain (p < 0.01) than the control group (ADG = 0.93 ± 0.08 kg/d and a total weight gain of 62.2 ± 5.2 kg). Final body weights were 527.8 ± 8.5 kg and 512.2 ± 9.9 kg for Revalor and Synovex, respectively; and 479.9 ± 10.1 kg for Control. In conclusion, grazing-finished steers showed better performance when high potency HGPs were used, improving the ADG and final live body weight, generating a marginal income that justifies the use of the technology under grazing conditions.