Silvopastoral systems as a strategy to attenuate the negative effects of heat stress on productivity of beef cows grazing natural grassland

Abstract

Heat stress affects cow-calf performance during the summer; thus, it is relevant to study attenuation strategies. The thermal environment, physiological response to heat stress, concentrations of metabolic hormones and productivity of cow-calf pairs grazing silvopastoral (SPS) and full sun (FS) systems, associated or not with temporary weaning (TW) were evaluated. Eighty-four Braford crosses cow-calf pairs were randomly assigned to four treatments in two years: (1) SPS + TW (n = 15), (2) SPS − TW (n = 28), (3) FS + TW (n = 18) and (4) FS − TW (n = 23). The black globe temperature humidity index was lower under the trees shade, thus SPS cows explored a larger area (P < 0.01) and grazed longer (P < 0.05). Live weight of cows and calves and body condition score of cows were greater in SPS than FS (P < 0.01). IGF-I concentrations were greater in SPS than FS (P = 0.001), but decreased in SPS + TW cow-calf pairs (P < 0.01). TW decreased insulin concentration in cows and increased its concentrations in calves (P = 0.01). Cows grazing SPS had less observations with vaginal temperature ≥ 39.1°C compared to FS cows (P < 0.001). SPS + TW cows tended to ovulate earlier postpartum (P ≤ 0.1), but days to conception and pregnancy were similar between groups. In conclusion, SPS provided a more comfortable thermal environment, associated to a decrease in the vaginal temperature of cows. This resulted in longer grazing sessions and hormone dynamics compatible with greater animal productivity and earlier reinitiation of cyclicity. TW decreased IGF-I concentrations in cows grazing SPS, thus the lack of its protective effect on the oocyte impeded the advancement of conception.