Sheep adaptation management, and investigation of inherited resistance to prevent Brachiaria spp. poisoning

Brachiaria spp. is the most used forage in extensive cattle production in the Central-Western region of Brazil. However, livestock fed with these grasses can develop hepatogenous intoxication due to the presence of steroidal saponins that promote photosensitivity, inefficiency of production in the herds and death. Grass toxicity depends on factors related to animal susceptibility or resistance and intrinsic plant factors, providing significant differences in the clinical manifestation and mortality of livestock. Three experiments were conducted to investigate the adaptation management and inherited resistance to prevent Brachiaria spp. poisoning in sheep. In the first experiment, the adaptive management of lambs was performed, controlling the grazing time in Brachiaria spp. pastures. Groups of sheep grazing previously in Brachiaria decumbens paddocks for 2 h daily or on alternate days for 60 days presented low hepatotoxic changes and had reduced the number of intoxicated lambs when compared to the control group during the challenge. In experiment 2, ruminal transfaunation from adapted adult sheep to non-adapted lambs to grazing on the grass reduced the hepatotoxicity, which suggests that Brachiaria spp. poisoning resistance could be transferred by ruminal fluid to non-adapted animals. In the third experiment, lambs from flocks raised in Brachiaria pastures showed less susceptibility to poisoning than lambs from flocks raised in non-toxic pastures, suggesting inherited resistance to the toxicosis. These results suggest that the control of grazing time combined with transfaunation can be employed to decrease the frequency of poisoning in susceptible flocks. However, a definitive solution in the long-term would be the selection of resistant sheep herds.