Plants Poisonous to Livestock in Botswana

Abstract

Livestock plant poisoning is very common in Botswana. Two plants, Dichapetalum cymosum and Pavetta harborii, are especially notorious for causing large-scale mortality in some areas of the country. In 1975, for instance, a D. cymosurn poisoning outbreak killed 210 cattle in east central Botswana. In the same year P. harborii caused large-scale deaths of cattle in the Mochudi area. The losses caused alarm among livestock farmers and the problem was among the issues discussed in the 1975 session of the Botswana Parliament. Because of their potency, farmers in South Africa refer to these species as "sudden death 11 plants. Unlike D. cymosum and P. harborii, most poisonous plants do not kill immediately after ingestion. Some poisonous plants may not produce symptoms until months later after ingestion. Other toxic plants will cause death only after the plant has been eaten over prolonged periods of time. Still other poisonous plants do not cause death, but simply produce illness in the livestock animals. Livestock animals are generally selective eaters and eat poisonous plants accidentally or when nothing else is available for them. Thus drought, overgrazing, overstocking and fire are major factors that can create an ideal environment for poisonous plants to flourish. Hence the chances of livestock poisoning are greatest during certain times of the year and when environmental conditions favor their growth and their ingestion by animals. The poisonous plants affect different animal species differently, with some plant species producing toxic reactions in certain types of livestock but not in others. Also, some of the plants are poisonous only during certain developmental stages of their life cycles, and even then, only certain parts of the plants may be poisonous. Knowledge of the toxic plants and the conditions that favor poisoning will aid livestock farmers in protecting their livestock from plant poisoning. Although Dichapetalum cymosurn and Pavetta harborii are readily recognized as poisonous plants by livestock growers and agricultural personnel, many other poisonous plants are not generally known. A greater knowledge of potentially poisonous plants is needed in order to reliably determine the causes of unexplained livestock deaths and illnesses. The objectives of this study are to index and describe the common livestock poisonous plants of Botswana and to note their distributions in the country. Their toxic principles, and where these occur in the plant body are also described as well as the conditions that promote the growth and toxigenicity of poisonous plants. This study considers only those poisonous plants that have been reported to have actually caused death or illness in livestock in southern Africa. The geographical scope of this study is necessarily limited to accessible portions of the major grazing areas of eastern and northern Botswana.