A shortage of calcium in ewes, but more commonly in breeding cows, and especially older, high-producing cows, causes milk fever or parturient paresis (hypocalcaemia). It can be triggered by stress or a sudden change of feed. Animals with milk fever become restless, suffer lost appetite, muscle tremors and staggers, and usually die if left untreated. Most pastures in New Zealand provide animals with enough calcium, but the sharp increase in demand for this mineral by cows at the start of lactation in early spring can lead to deficiency. Cows with milk fever should be injected under the skin with calcium borogluconate and kept warm.
Animal disease research
In March 2007 the Hopkirk Research Institute was opened at Massey University to accommodate up to 400 scientists working on animal diseases. Bovine TB, Johne’s disease, and the development of parasite-resistant drenches were highlighted as priorities for the AgResearch and Massey University Veterinary School staff who will work there.
Grass staggers or grass tetany (hypomagnesaemia) is caused by a shortage of magnesium in the diet and an impaired ability to absorb magnesium by lactating sheep and cows. Animals with grass staggers have body tremors, walk with a stiff-legged gait, and are liable to collapse on their side kicking their legs in a paddling motion. Affected cows are injected under the skin with magnesium chloride. To limit grass staggers in a herd their diet should be supplemented with magnesium three to four weeks before calving, and up to 12 weeks afterwards, by dusting pasture or hay with magnesium oxide, or adding magnesium to drinking water. The absorption of magnesium and calcium is affected by too much potassium in the diet, so farmers avoid using large amounts of potassic fertilisers in spring.
Sleepy sickness or twin lamb disease (acetonaemia or ketosis) is the most common metabolic disease of sheep in New Zealand. It occurs in the weeks before lambing, and ewes carrying two or more lambs are particularly at risk. Signs include lethargy, staggering and not eating. The main cause is underfeeding in late pregnancy. The best prevention is to scan pregnant ewes and give those carrying multiples more feed near lambing.