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10 August 1998
Every year around lambing and calving, sleepy sickness, grass staggers and milk fever take their toll of valuable breeding animals and their offspring.
The Ministry of Agriculture and Forestry says this year, in the wake of the drought, the risk may be particularly high because predisposing factors include poor body condition, a check in feed supply, cold wet windy weather, the stress of yarding or transportation and some types of top-dressing.
To help farmers keep losses to a minimum, MAF offers the following advice which describes factors which might predispose stock to these problems, how blood tests can be used to predict them, how to recognise the signs early and how to deal with the diseases when they occur.
Sleepy sickness (pregnancy toxaemia) is the most common metabolic disease in sheep. It occurs in the weeks before lambing. Very thin (or very fat) ewes are particularly at risk, especially when carrying two or more lambs. The main cause is a check in feed supply in the last few weeks of pregnancy due to a reduction in the quantity or quality of feed eaten. The signs include dullness, not eating, staggering or aimless wandering, twitching of the face and ears, blindness leading to recumbency, coma and death in 2 to 7 days.
Acetonaemia in cows (also known as ketosis) is fairly common. It occurs most often in high-producing cows in early lactation so the best cows are most at risk. The disease develops when milk production demands more of the cows energy resources than can be met by her intake. The signs may be the same as in sheep, but often the only signs are a drop in milk production and weight loss.
Ketones are excreted in the urine and in the breath. These have a characteristic sweet smell (nail varnish remover!) which those with a keen nose may detect around affected animals.
Acetonaemia in animals that have been underfed for some time is generally very difficult to treat because of liver damage. However, there are various energy supplements, some with electrolytes added, which can be given by mouth and which may be helpful if treatment is begun early.
Milk fever in cows (hypocalcaemia) occurs most often in high producing older cows within 48 hours of calving, but it can occur several weeks before or after calving. Ironically predisposing factors include high calcium or phosphorus in the diet in late pregnancy. High dietary sulphur can reduce the risk of the disease.
Affected cows are often just found down, characteristically with the head swung round beside the body. Early signs can include reduction of appetite with a preference for roughage, a drop in milk production, reluctance to move and after a few days "drunken behaviour", walking in circles aimlessly, with vigorous licking, great anxiety and trembling. Commonly cows develop a mild form of the disease, in which the only signs are a drop in milk production and infertility problems. This may well go unnoticed.
In ewes, milk fever (lambing sickness, hypocalcaemia) occurs most often in older ewes near lambing. The disease is often brought on by a very sudden stress. This might be yarding, transportation, forced exercise, very bad weather or insufficient feed. Sometimes a sudden change of feed, eg a move to lush pasture, will trigger outbreaks. The signs are restlessness, trembling, staggering, depression and recumbency. It is characteristic to find ewes down on their chest rather than on their side with hind limbs extended backwards or head down and extended forwards. There may be a discharge from the nose, they may become bloated and they usually abort dead lambs. Affected ewes may just be found dead.
Blood calcium concentrations do not usually fall until signs develop, so monitoring using blood tests is not useful. Veterinarians can arrange for measurement of the dietary anion-cation difference in feed samples for dairy cows, and this can warn when cows are at risk.
Hypomagnesaemia (grass tetany) is most common in cows and ewes in heavy lactation and on lush pasture. It also occurs in cattle of any age that are undernourished or on a falling plane of nutrition. Basically the cause is a low magnesium intake, and changeable bad weather, yarding and transportation all predispose. Another contributing factor is the autumn/late winter application of nitrogen and potassium, which can interfere with the absorption of magnesium in the animal’s digestive system.
In cows the condition tends to occur soon after calving when they are moved to lush pasture (inadequate energy intake and low magnesium content) and when the weather suddenly turns cold wet and windy. Wind chill is known to be a particularly important contributing factor. Hypomagnesaemia in cows usually causes sudden death but sometimes obvious signs develop before death such as increased nervousness, body tremor, walking with stiff legs, collapse with paddling and the head held back. It’s not unusual for affected cows to be extremely aggressive. This can make treatment very difficult! Affected cows soon develop fits and die. It’s very common for a mild form of the condition to develop with the only signs being lowered milk production, weight loss and increased nervousness, which may make the cow seem "difficult" in the shed.
Hypomagnesaemia in ewes sometimes causes dramatic signs such as body tremor, walking with stiff legs, collapse with paddling and the head held back. Sometimes they are just found dead, but more often the signs are rather subtle, with an increase in nervousness and anxiety that can be easily overlooked or misinterpreted. The ewes are flighty and easily upset by dogs etc, but the real crunch comes soon after lambing when their nervousness leads to mismothering.
Prevention includes providing a high energy diet in the form of concentrate pellets or grain, or dusting pasture or hay with magnesium oxide powder or calcined magnesite. However dusted pasture may not be very palatable, and if the powder is applied too liberally the stock may go hungry to avoid it. This can precipitate sleepy sickness/acetonaemia.
In both acetonaemia and hypomagnesaemia, blood concentrations fall before signs develop, so blood tests can be used to predict problems. Testing can be arranged by a veterinarian.
Treatment of both milk fever and hypomagnesaemia is by injection of calcium and/or magnesium solutions by a veterinarian, or by the farmer with veterinary help and guidance. It is wise for the farmer to discuss treatment options with a veterinarian before cases develop.
Marjorie Orr, MQM Animal Welfare Services Group,
Invermay Animal Health Laboratory, Private Bag 50035, Mosgiel.
Phone 03 489 3809, fax 03 489 7988