This disease is known by a number of other names, including Ante-partum Paralysis, Acidosis or Ketosis of pregnant ewes, Pregnancy Disease, twin-lamb Disease. It is a nutritional disease associated with pregnancy, and is not contagious. It occurs in pregnant ewes shortly before lambing, and those ewes carrying twin lambs are most likely to be affected. Ewes carrying single lambs are also subject to the condition.
Differential Diagnosis—The hypothesis that Toxaemia of Pregnancy is analagous to milk fever in the cow, and therefore a hypocalcaemia, is founded on a confusion with another disease commonly called Lambing Sickness or Milk Fever in ewes. In the case of the latter disease, the clinical symptoms and method of treatment are similar to those of milk fever in the cow, and sheep respond to udder inflation and injections of calcium gluconate. With Toxaemia of Pregnancy, the symptoms are different, and affected ewes do not respond to treatment with calcium gluconate.
In Lambing Sickness, there is an acute lowering of blood calcium, but the urine tests normal. In Toxaemia of Pregnancy, on the other hand, although the blood calcium may at times be somewhat lowered, it is frequently within the normal range. The urine, however, contains ketone bodies and gives an acid reaction—hence the name Acidosis of pregnant ewes.
The disease occurs all over the world wherever sheep are raised and has and is still receiving much attention by research workers.
Cause—The etiology of the disease has not yet been completely worked out. There is much experimental evidence to support the contention that Toxaemia of Pregnancy is essentially a ketosis (acidosis) associated with a marked lowering of the glycogen reserves of the body, disturbed metabolism leading to breakdown toxic ketones being set free, which, on absorption, lead to an auto-intoxication and death of the animal.
The disease occurs on all classes of pasture from a week to a month off lambing. The quality of the feed, methods of feeding and general animal husbandry are important factors in causing the disease.
Although many of the experimental results have been contradictory, there is a possibility that this condition in ewes is related to carbohydrate metabolism. It is suggested by American workers that with an inadequate carbohydrate intake the glycogen is withdrawn from the liver to maintain the blood sugar level in metabolism, and fat takes its place. The fetal lamb contains a high percentage of glycogen in its liver, and there is a considerable drain on the mother, which is increased in a twin pregnancy.
Other workers suggest that the disease develops from an overloaded maternal mechanism and an excessive excretory burden, which overwhelms the detoxicating function of the liver, and when the damage occurs in that organ the symptoms of intoxication from acidosis occur.
Conditions under which the disease occurs—The disease develops mainly in forward in-lamb ewes that are falling away in condition as a result of an inadequate food supply for the needs of the ewe and rapidly developing lamb or lambs.
The disease is not uncommonly seen in pregnant ewes following a rail Journey or confinement for any length of time in sheds or yards. It occurs when dry seasonal conditions occur during the last two months of pregnancy, and especially if hand-feeding of the ewes is not commenced early enough. In New Zealand, heavy root feeding of breeding ewes and the wintering of ewes on low grade pasture are held to be common causes. Leslie (New Zealand) postulates that the development of the disease in root-fed ewes is associated with a low intake of protein and minerals and a high intake of water. New Zealand conditions, however, are not strictly applicable to this country, especially in those parts where there is winter herbage.
The disease is also seen in this State in fat ewes that are well fed on rich pastures. When it occurs under these conditions, it is usually associated with lack of exercise. Certainly, it would appear that the predisposing cause of the disease is associated with the feeding and management of the pregnant ewe.
Symptoms—The early symptoms of Toxaemia of Pregnancy are seldom noticed by the average observer. Usually from a month to a week before lambing is due to commence, sometimes earlier, one or more ewes heavy in lamb may be seen to separate from the rest of the flock and to be dull and "off food." If approached, little or no notice is taken, and when actively disturbed the affected animal will only move off very slowly in an aimless manner. It appears to be blind. There will usually be exhibited a staggering gait, with partial paralysis of the hindquarters, and stupor. Later, the animal goes down and will probably not rise again unless assisted. When lifted on to its feet, it will stand listlessly, and if forced to move will stagger a few paces with swaying of the hindquarters, and then probably fall. There may be grinding of the teeth and clamminess of the mouth, and the wool is probably already beginning to lift. Sometimes there is a dark discharge from the vagina. Such a case, which is the common form of the disease, will last four or five days or longer from the onset of the symptoms. Finally, the animal goes down and lies in a semi-conscious state until death occurs. In the maiority of cases, the trouble is only observed when the animal is in the latter stages, and so the course of the disease appears much shorter than is really the case. Sometimes lambing may take place, and the animal will recover. This is, however, usually followed by shedding of the wool.
In the more violent cases the ewe, without showing any earlier symptoms, falls insensible to the ground and dies in a short time, with or without convulsions. A post-mortem examination shows the liver to be the most abnormal organ, and its appearance is the most characteristic feature of the disease. Almost without exception, the liver is somewhat enlarged and pale yellow or greyish in colour. This is called fatty degeneration of the liver, which seriously interferes with its functioning. It is probably mainly toxic in origin.
The kidneys may also appear abnormal and paler in colour, but this is not a constant feature, as in the abnormality of the liver. The intestines are frequently found to be almost empty. but evidence of constipation, as exhibited by the contents of the lower bowel and rectum being distinctly hard and dry, is often observed. In the majority of cases, twin lambs, usually within two or three weeks or less of full time, will be found. The womb and the lambs are, as a rule, healthy.
Treatment—Medicinal treatment of affected animals, unless undertaken in the very early stages, is not very satisfactory. The administration of calcium gluconate subcutaneously has given mixed results, and it is considered that where success was obtained the animals were actually suffering from lambing sickness (milk fever).
The best results in the treatment of Toxaemia of Pregnancy have been obtained by the administration, by the mouth, of large doses of sugar and water or molasses and water: ½ to 1 lb. sugar and 1 pint of water may be given as a drench, or an equal quantity of molasses and water. Care must be taken in administering the drench, as in many instances affected sheep can swallow only with difficulty.
Intravenous injections of 10% glucose in saline solution (10 to 30 c.c.) have also given good results in the early stages of the disease. This treatment needs to be repeated.
The administration of Epsom salts as a laxative drench has not given good results, and it is suggested that the best laxative is treacle in large doses.
It is not difficult to understand why treatment generally is unsatisfactory when consideration is given to the extent of the liver damage. More satisfaction will be secured by prompt attention to preventive measures directed to the flock itself and to those ewes which are still apparently normal than attempting to treat those which are obviously sick.
Prevention—The essentials in prevention are closely wrapped up in good breeding ewe husbandry. The indications are that rational management should be practised throughout the whole of the in-lamb period. The ewes should be kept in good condition by judicious feeding, but not allowed to become over-fat, and should not suffer as a result of malnutrition. Allowing the ewes to run on comparatively poor pasturage, and then placing them on extra good feed just prior to lambing is equally bad practice as the converse. Cases are on record where ewes closely confined on rich pasture throughout the whole of the gestation period have succumbed to this disease. Conversely, many cases are recorded where under-feeding and unbalanced feeding, as occurs in drought time, have apparently been responsible for the condition.
There is much evidence to show that prolonged improper feeding may produce the condition. The question of the hand-feeding of ewes in lamb should receive greater consideration than the feeding of dry sheep, not from the point of view of an additional allowance of concentrate but with the idea of a better balanced ration and the avoidance of constipation.
Breeding ewes, particularly Merinos, should not be confined to small areas of good pasturage, but should be allowed a large enough area for exercise in obtaining their food. If this is impossible, as it may be sometimes on small farms, judicious daily exercise of the ewes by driving, if they are very fat, is justifiable, and likely to be attended with good results.
Frequently the feed is good but rather dry, and as the ewes appear to be in good condition they are not moved from the pasture. The removal of these ewes to green feed prior to the commencement of lambing will frequently prevent the development of Toxaemia of Pregnancy, provided the sheep are not confined to a small area for any length of time.
If the eves are being hand-fed, consideration should be given to balancing the ration, and the sheep should be fed in a different place each day to prevent them standing about in the one place waiting for the feed to be put out. A drought is seldom so bad that the sheep are unable to pick up something in the way of roughage about the paddock. Such roughage assists in balancing the ration. In addition, also, the sheep obtain natural exercise, which is very desirable in all animals forward in pregnancy. The prolonged feeding of such ewes on the one class of feed, be it hay, silage, Kurrajong or other scrub, or concentrates, should be avoided. Such feeding might carry dry sheep through quite safely, but is likely to be followed by an appearance of the subject disease in the case of pregnant ewes. A change of food is very desirable, and an attempt should always be made to balance the feed if possible by feeding hay with grain or other concentrates, a small quantity of bran with chaff, grain with scrub, and so on. Sterilised bone-meal or di-calcic phosphate and coarse salt should be made available to the sheep in covered troughs. The bone-meal and salt may be kept separate by means of a partition in the trough, but in the case of the dicalcic phosphate, owing to its finely powdered state, it is advisable to mix it with salt in the proportion of fifty-fifty.
Molasses is useful during dry periods on account both of its feed value and laxative action. It should not, however, be added in any great quantity to a salt lick, otherwise the sheep may eat too much salt. If added to a lick, 5 parts to 100 parts of lick is sufficient. It should be broken down with water, poured over the lick, and thoroughly mixed.