Kikuyu grass poisoning
Sporadic cases of kikuyu grass poisoning occur seasonally, but it remains unclear if the poisoning is caused directly by the grass, or in response to the presence of a pathogen, or directly by a pathogen. Several classes of plant toxins and mycotoxins can cause inflammation of the gastrointestinal mucosa and it is one of these, such as glycoproteins, triterpenoid saponins, glycosidic alkaloids, macrocyclic trichothecenes, and viridin-like furanosteroids, that could be the actual cause of toxicity (Bourke, 2007). Specific conditions appear to favour kikuyu poisoning, such as hot dry weather followed by rain and rapid grass regrowth. Infestations of armyworm caterpillars may also be involved. The majority of clinical signs of poisoning recorded have been consistent between outbreaks: ataxia, recumbency, loss of rumen motility, abdominal distension and excessive salivation. Histological analysis reveals severe damage to the mucosa of the rumen, and rumen epithelium necrosis in the omasum (Marais, 2001; Barnes et al., 2007; Bourke, 2007).
Oxalic acid toxicity
Kikuyu accumulates oxalic acid but not in amounts high enough to result in acute toxicity in cattle (3.9-24.4 g/kg DM < 69 g/kg). Ruminants readily adapt to oxalates due to a rumen bacterium, Oxalobacter formigenes, that converts oxalates to formate and carbon dioxide. However, as it binds with Ca, oxalic acid can result in hypocalcaemia in herbivores. Horses suffer from hyperparathyroidism (big head disease) and cattle may suffer from low calcium availability, resulting in possible low fertility and milk fever in dairy cows (Marais, 2001).
Nitrate poisoning
Lush growth associated with excessive applications of nitrogen can cause nitrate poisoning (Cook et al., 2005). Nitrates are non-toxic but their transformation into ammonia, within the rumen, produces toxic nitrites that bind with haemoglobin and prevent blood from binding with oxygen, resulting in oxygen starvation of the tissues and animal death in the most severe cases (Marais, 2001).