Sleepy Sickness and Milk Fever in Ewes

New Zealand Journal of Agriculture, Volume 85, Issue 2, 15 August 1952, Page 115

Sleepy Sickness and Milk Fever in Ewes

SOME of the facts about sleepy sickness of ewes and how knowledge of them can be applied are dealt with in this article, which is based on a paper given at the Ruakura Farmers' Conference week by J. C. Gerring, Animal Research Extension Officer, Department of Agriculture Animal Research Station, Ruakura. A section on milk fever in ewes, a condition which is sometimes confused with sleepy sickness, is also given.

SLEEPY sickness is a disease of sheep which occurs toward the end of pregnancy, usually during the last 3 weeks before lambing. Older ewes in good condition are, more readily affected than young sheep or ewes in poor condition. Despite the enormous amount of detailed research work which has been carried out in many countries, including U.S.A., South Africa, Britain, Australia, and New Zealand, the cause is still unknown; that is, it cannot be explained why the affected animal shows the symptoms typical of the disease, nor is there any effective treatment once these symptoms have developed fully. Though odd cases occur without any obvious precipitating cause, where a number of cases develop in a flock these are always associated with a fall in the level of feed intake during the last few weeks of pregnancy. Though this reduction in feed intake may be due to a fall in the amount of feed available, it may also be due to conditions 1 ■ which adversely affect the appetite of the sheep; for example, a sudden change to a different kind of feed, a spell of cold weather, or the development of some other disease, such as foot-rot, worms, etc. Some farmers have associated the feeding of swedes to in-lamb ewes with the occurrence of sleepy sickness. Many farmers feed ewes on swedes without sleepy sickness occurring. Providing the change to swedes is not too sudden and not too close to lambing, and providing plenty of swedes are available, there is no reason why the disease should occur on this crop. Disease Produced Experimentally Hopkirk, working at the Department of Agriculture Animal Research Station, Wallaceville, was one of the first to produce the disease experimentally, and this has since been done by many workers in other countries. In each of these experiments reduction in the level of feed intake was the method used. . Other methods tried included restricting exercise, feeding a maintenance ration followed by liberal feeding, and feeding rations both low and high in protein. These did not produce the disease. Symptoms of sleepy sickness were produced in ewes which were within a few weeks of lambing in 3 to 7 days after a severe reduction in feed intake. A group' of non-pregnant ewes whose feed intake was similarly reduced also developed symptoms of the disease, but they were much less severe and took 24 to 48 days to develop. For many years the opinion was held that the disease was due to poisonous waste products produced by the developing foetus which the ewe, owing - presumably to some abnormality in her excretory system, was unable to eliminate. For this reason the disease got the name of pregnancy toxaemia. There is no

evidence for this theory, and the fact that the disease can be produced in non-pregnant animals would seem to disprove it. t The importance of pregnancy in causing the disease is due to the increased demand it makes on the maternal system, and this is still further increased when two or more lambs are present. Of even greater significance is ■ that this demand increases very rapidly during the last month of pregnancy. Wallace, while working at the School of Agriculture, Cambridge, England, made some interesting investigations on the development of the young lamb during pregnancy. Fig 1, showing

development of twin foetuses, illustrates his findings. At the end of the first month of pregnancy each developing foetus weighs only V6OOZ. One month later it weighs only 2oz. Three months after conception it weighs only

between 1 and 21b. By the end of the fourth month its weight increases to between 4 and 51b., and at birth, 5 months from conception, the new-born lamb weighs about 101 b. Over 50 per cent, of its weight increase takes place during the last month of pregnancy; that is, at the most critical time for the development of sleepy sickness.

Another important aspect of this demand which the developing lamb makes on the ewe is illustrated in Fig. 2.

This is Hammond’s theoretical conception of the order of priority in demand which different tissues have on available nutrients. This emphasises how tissues of high metabolic activity, such as the foetal membranes, foetus, and brain, can draw from depleted nutrients at the expense of other maternal tissues of low metabolic rate. In other words, unless the feed intake is very low, the foetus can go on developing at the expense of . the mother’s own requirements for available nutrients. Influence of Nutrition Ewes in good condition are more readily affected with sleepy sickness than poor-conditioned animals, though over-fatness is by no means essential for development of sleepy sickness. This is probably due to the effect of the level of feeding on the development of the lamb during pregnancy. The design of an experiment in further studies by Wallace supporting this contention is illustrated diagrammatically in Fig. 3. One of the points Wallace-was interested in determining was the influence of nutrition on the growth of the developing lamb during pregnancy. He started with two groups of ewes similar in condition which had just been mated to the same ram. For the first month both groups were fed on the same level, so that they were ■ kept at a constant body weight. At this stage one group was fed at a high level to obtain the maximum gain in liveweight and the other group was fed on a low level so that it lost weight. This difference was continued to the end of the third month of pregnancy, when a representative sample of ewes from each group was killed and their lambs weighed. Half of the ewes remaining in the well-fed group were then switched to a low level of feeding and half of those in the poorly fed group were well fed. These treatments were continued until within a few days before the ewes were due to lamb, when each was killed and the lambs weighed.

In considering the results Wallace emphasises that they apply only to twin lambs and that the differences in feeding treatments were very severe.

Foetuses obtained from the ewes killed when 3 months in lamb were approximately the same weight, 1.71 b., from both the.well fed and poorly fed groupsthe level of feeding during the first 3 months of pregnancy had little if any effect on the growth of the developing lamb. Lambs from these ewes which were ell fed throughout pregnancy weighed 11.31 b.; those from the ewes poorly fed throughout pregnancy weighed only 5.81 b. The most interesting feature, however, was that lambs from the ewes well fed early in pregnancy and poorly fed later averaged 6.51 b., and the . lambs from the ewes fed poorly at first and then well fed during the last 2 months had an average weight of 11.11 b. and were almost as well developed as the lambs from ewes fed on a high plane throughout pregnancy. The level of feeding during the last 2 months of pregnancythe time when most of the increase in weight of the developing lamb takes placehas a marked effect on the size of the lamb at birth. The fatter sheep carrying twin lambs get toward the end of pregnancy the bigger their lambs are likely to be, and the increased demand 1 on the maternal system made by these heavy lambs renders such ewes more susceptible to sleepy sickness.

The severity of an outbreak of sleepy sickness in a flock will depend on:—

1. The level of feeding during the previous months.

2. The extent to which the level of feed intake is reduced.

3. The suddenness with which the intake is reduced.

4. The length of time sheep are kept at this level. 5. Whether, in individual cases, there is single or multiple pregnancy. If the reduction in feed intake is sudden, severe, and prolonged, even thin ewes carrying single lambs are liable to develop the disease. On this basis, and because of the fluctuating nature of available feed in grassland farming, the time to institute preventive • measures against sleepy sickness is as early in pregnancy as possible. Wallace has emphasised the importance of flushing ewes, beginning 2 to 3 weeks before the rams are put out and continuing for from ’3 to 4 weeks after that. If the ewes’ level of feeding is then tightened up, some of the autumn growth can be saved for use during the 5 to 6 weeks before lambing is due to begin. In very adverse seasons when feed is short it is better to delay this lift in the level of feeding until the last 3 weeks of pregnancy than to run short of feed at the critical time. When to begin this rise in feed intake requires careful judgment, based on the condition of the ewes and the availability or likely availability of feed.

Remedial Measures

It is important to be able to recognise sleepy sickness in its early stages, not because affected ewes can be saved by any particular treatment,' but so that immediate remedial measures can be taken with the rest of the flock to prevent further, cases developing. The chances of saving a ewe noticed with symptoms of sleepy sickness by giving extra feed depend entirely on how far the disease has developed before it is noticed. In the very early stage a dose of molasses, | to lib., and a. shift to green feed may prevent death; There is no special substance in molasses which is beneficial in the prevention of any particular type of disease; molasses is merely a readily available form of energy. It is much more practical to have other and cheaper food available. If nothing else is available, molasses can be a useful, but expensive, source of food.

Symptoms usually develop gradually. Symptoms in the very early stages of the disease can be seen if a mob of sheep is driven quietly round the paddock; an affected sheep lags behind, and if forced to move, shows an unsteady gait. As the disease progresses the ewe appears to become increasingly unaware of her surroundings. She may stand for several hours in the same position, with the head held high and often moved to one side, as illustrated in Fig. 4, or she may assume a dopy attitude with her head hung down (Fig. 5). At this stage it is possible to walk right up to the ewe without her making any real attempt to move away. Blindness, usually in both eyes, is a very common symptom and in many cases is the first abnormality noted by the farmer. Probably the most striking feature is the unusual postures which an affected ewe will adopt. Later the ewe goes down, becomes semi-comatose, and may remain in this condition for several days. Death may occur from 36 hours to about 8 days after the first symptoms develop. When the carcass is opened up the liver is generally found to be much paler than normal owing to an excessive accumulation of fat. Examination of the blood ' and urine from affected ewes taken before death usually reveals a condition known as ketosis. This is an indication that the animal is drawing excessively on her own body reserves. However, ketosis commonly occurs without any symptoms developing, and some animals affected with sleepy sickness show very little evidence of ketosis. Possible Cause of Disease It may well be that the important factor determining whether an animal is affected or not is. her ability to switch over quickly enough from a state where the feed intake is sufficient for her requirements to one where she must draw on her own body reserves to meet her needs. If this change in the source of supply of nutrients is gradual, she is able to cope with the situation, at least for a time. If, however, the demands on her body reserves go beyond a certain level, she is again unable to meet them. This, however, is merely a hypothesis, and it would need

to be supported by a better understanding than exists at present of the physiological mechanism controlling the animal’s ability to mobilise her body reserves quickly. What is certain is that sleepy sickness can be prevented by gradually increasing the level of feed intake throughout the last month of pregnancy. MILK FEVER Milk fever in ewes, or lambing sickness, bears some resemblance in its clinical symptoms to sleepy sickness, and' the two conditions'are often confused when first encountered. As with sleepy sickness, older ewes are more susceptible to milk fever. It is important, however, to be able to differentiate between the two conditions, . because milk fever, unlike sleepy sickness, is readily amenable to treatment. Milk fever in the ewe is associated, as it is in the cow, with a sudden fall in the calcium content of the blood, and both in-lamb and lactating ewes may contract the disease. Under certain circumstances the disease may occur in any type of sheep. It is more

common before and just on lambing. In the South Island it has occurred at shearing time after the mustering and yarding of sheep. ' Outbreaks in Waikato Though milk fever, occurs less frequently than sleepy sickness and is therefore of less importance, in several outbreaks in the Waikato up to 30 per cent, in the mob were affected. In one outbreak a mob of stud Southdown ewes in good condition were brought into the yards for crutching just before lambing. They were left in the yards overnight, and the next morning the owner found 15 ewes in various stages of the disease, some of them lying fiat on their sides and unconscious. A further 40-odd cases occurred during that same day after the ewes had returned to their paddock. All but two, which were the first cases to occur, recovered promptly after treatment. Yarding of ewes which are close to lambing is the commonest cause of milk fever in the Waikato. Franklin’s work on calcium metabolism in sheep in Australia has shown that quite short

periods of fasting may be followed by a sudden drop in blood calcium.

Milk fever may also be associated with droving in-lamb or lactating ewes, though in experiments carried out by Franklin only those ewes in which the blood calcium was already below normal developed symptoms of milk fever after exercise. Another common predisposing cause is a sudden change to lush feed. Features which distinguish milk fever from sleepy sickness are: Milk fever is . more likely to occur after a mild winter with ample lush feed available than is sleepy sickness. It is also much more dramatic in its onset in that often several ewes are suddenly affected within a few hours and symptoms develop rapidly. In the early stages an affected ewe walks with a staggering gait, due to a stiffness of the hind legs. She Often appears nervous and distressed, and when disturbed may shiver or tremble. Such symptoms are often transient and are' frequently missed. She soon becomes drowsy and goes down (Fig. 6), often lying with her head turned to the flank; or the ewe may lie on her chest with hind legs straddled out behind and the head stretched out in front. Consciousness is soon lost (Fig. 7) and death may occur within 4 to 6 hours or up to 48 hours. Because of this rapid onset, sheep are often found in varying stages of the disease. Treatment Injection under the skin with 40 to 80 c.c. of a 20 per cent, solution of calcium borogluconate is extremely effective—the response, even in advanced cases, is usually spectacular • —and should always be attempted where there is any doubt whether the animal is affected with sleepy sickness or milk fever.

Ewes treated for milk fever have sometimes borne dead lambs. Veterinarians sometimes consider it necessary to give magnesium as well as calcium to avoid causing the ewe’s death through, heart failure, and this may have some bearing on the death of the lamb. A veterinarian who had treated a number of ewes for milk fever used to give the injection into the vein and the lambs were usually born dead. He started giving it under the skin in small doses and there was a marked reduction in the number of dead lambs. Giving a small dose and repeating this dose several times seems to reduce the number of dead lambs.

Dr. C. S. M. Hopkirk Appointed to FAO Position

F\R. C.-S. M. HOPKIRK, veterinary adviser io the New Zealand High Commissioner in London since 1948, who has completed 40 years’ service with the Department of Agriculture, has accepted an appointment as Mission Chief in Ethiopia for the Food and Agriculture Organization of United Nations. Dr. Hopkirk left London to spend a month in Rome before beginning his new duties in Ethiopia on I August. DURING a distinguished career with the Department of Agriculture Dr. Hopkirk made many valuable contributions to knowledge of stock diseases in New Zealand. He has-been closely connected with research into mastitis, facial eczema, black disease of sheep, and sterility problems. In 1945 Dr. Hopkirk was appointed senior veterinary ■ officer for UNRRA in Europe and China, a position he occupied for 2 J years. His duties involved the procuring of veterinary supplies and the rehabilitation of production laboratories, research ' and diagnostic .stations, and veterinary schools in many war-ravaged countries. One of Dr. Hopkirk’s most important tasks was to plan the establishment of a veterinary division in Ethiopia—an innovation in a country where stock

disease is very high. He was invited to implement his plan, but declined the position offered him. After graduating Bachelor of Veterinary Science with first-class honours at Melbourne University in 1923, Dr. Hopkirk returned to New Zealand as Officer-in-Charge of the Department’s Wallaceville Veterinary Laboratory, as it was then known. He continued his close association with research at Wallaceville, which in 1939 was incorporated in the Department’s newly formed Animal Research Division and was named. the Wallaceville Animal Research Station. A thesis on mastitis in dairy cows gained Dr. Hopkirk the degree Of Doctor of Veterinary Science from the University of Melbourne in 1934. In 1938 he made a world tour on behalf of the Department of Agriculture, ; visiting all the important veterinary research stations abroad . and representing New Zealand at the first Imperial Veterinary Congress in London and the International Veterinary Conference in Switzerland. Dr. Hopkirk’s new appointment in Ethiopia is for 1 year, with the option of renewing it for a further term.