Desempeño productivo y conducta de novillos a campo natural con suplementación proteica y sombra artificial en verano

Climatic and nutritional conditions can affect animal performance during summer. The objective of the study was to evaluate the effect of free access to shade and/or protein blocks on behavior and performance of yearling steers grazing natural pastures. Treatments were 1) control, 2) artificial shade (cloth), 3) protein block supplementation (28% crude protein), and 4) shade + protein blocks. According to the temperature-humidity index there were climatic conditions for mild and severe heat stress during 38 and 11% of the time, respectively. Crude protein of pasture was low (6.7%) and was associated with the high proportion of dry and dead fractions in forage species. Average daily gain (kg/a/day) was greater in animals with access to shade (0.779) or supplemented with protein blocks (0.650) than animals in the control group (0.537). When shade and protein blocks were offered together, daily gain was negatively affected (0.529 kg/a/day). Shade and protein blocks decreased diurnal grazing time in 20% (114 min) and increased 8% (47 min) compared to controls, respectively. Steers spent 237 min/day resting under the shade structure. Average intake of protein blocks was 0.047 and 0.218 kg/a/day in animals without and with shade, respectively. The greater intake of protein blocks of shaded animals did not reflect in greater average daily gain because they significantly reduced the grazing time. Based on these results shade availability was more important than protein block supplementation to increase animal productivity under rangeland conditions.