干旱区生态环境知识资源中心

In recent years livestock death losses from poisonous plants in the western United States have averaged about 2-3% annually. A review of 36 grazing studies in North America shows poisonous plant availability and death losses of livestock from poisonous plants are closely associated with grazing intensity. Across studies, livestock death losses to poisonous plants average about 2.0% under moderate grazing compared with 4.8% under heavy grazing intensities. Sheep and goat losses from poisonous plants appear to be increased more by heavy stocking than those from cattle. Impacts of poisonous plants on livestock reproductive success are difficult to quantify, but probably reduce calf and lamb crops, even when grazing intensities are conservative. Increased poisonous plant consumption may explain in part why calf and lamb crops average about 7% lower under heavy compared to moderate grazing. With the exception of 1 Texas study. rotation and continuous/season long grazing systems show little differences in livestock death losses under comparable stocking rates. Certain plants, such as locoweeds (Astragalus sp.) and larkspur (Delphinium sp.), can elevate livestock death losses, even when grazing intensities are moderate or conservative. Special management programs that involve careful timing of grazing, aversive conditioning, and creation of locoweed (or larkspur)-free pastures can reduce problems with these plants. Use of adapted livestock is a critical part of minimizing poisonous plant problems. However, on some rangelands, such as those with infestations of locoweed and larkspurs, naive livestock may be less affected by poisonous plants than familiar livestock. Knowledge of poisonous plant identification, conditions of toxicity, and affects on the animal, in conjunction with conservative grazing, will in most cases avoid excessive death and productivity losses from poisonous plants. In some cases livestock can be conditioned or trained to not consume poisonous plants. It can be concluded that most livestock losses from poisonous plants are caused by poor management.