Poisoning
Young calves can get lead poisoning if they lick lead paint or batteries. A number of plants are poisonous to cattle, including yew leaves, and acorns. On North Island hill country in particular, cows can be poisoned after eating bracken fern and tutu plants.
Feed-related diseases
Bloat in dairy cows is a major concern to farmers. A cow’s abdomen becomes distended when gases accumulate in the rumen (first compartment of the stomach) after eating clover-rich pasture, and if untreated the cow collapses and may die. Treatment is by oral drench to stabilise the foam, inserting a tube down the cow’s throat to release the gas, or as in earlier days, stabbing the cow in the rumen to release the gas.
Nitrate or nitrite poisoning
Cattle suffer nitrate poisoning when there are high nitrate levels in pasture and brassica crops, especially after dry weather or where a lot of nitrogen fertiliser has been applied in winter or spring. Poisoning occurs because nitrate accumulates at a faster than normal rate in the rumen. Nitrate gets converted to nitrite in the rumen, and is then absorbed into red blood cells, discolouring them and blocking the transport of oxygen. In extreme cases the animal dies from lack of oxygen.
Red water (haemoglobinuria)
When red blood cells are destroyed they release haemoglobin, which is filtered by the kidneys and released into the urine, turning it red. In grazing animals, this can be caused by a chemical (S-methyl cysteine sulphoxide) in brassica crops.