This chapter will mention only the specific problems and diseases directly affecting the establishment and maintenance of pregnancy, and the health of the pregnant ewe. Common problems such as internal and external parasites, which can adversely affect sheep at any time, have been dealt with in Chapter 7. Gestation length is usually 145–7 days, although there are breed and individual variations. In the flock of one of the author’s, careful records were kept by noting raddle mark dates, and the shortest gestation to produce live lambs was 142 days and the longest was 153 days.

Pregnancy can be considered in three main stages:

Early Pregnancy – the First Month

After fertilization, the early embryos spend the first two weeks of their development lying free in the interior of the uterine horns, after which implantation starts to occur, this being completed by the fourth week. During this early stage some embryos do not survive, mortality rate being increased by stressful situations such as a significantly reduced food supply and loss of body condition, gathering and handling, or adverse weather conditions.

If more than one viable embryo is present during these first weeks, they distribute themselves throughout the two uterine horns, each ‘claiming’ a share of the caruncles (‘buttons’) on the inner surface of the uterus, the locations where the placentas attach. If an embryo dies after this stage the remaining ones cannot utilize the vacated caruncles. This sometimes explains the birth of, for example, twins of very differing size, in that the pregnancy may well have started with three embryos, one of which died after implantation. To maximize the success of implantation, ewes should be subjected to as little disturbance as possible during this crucial stage, and should certainly maintain body condition.  

Fig. 310 The contents of a uterus in the fourth month of pregnancy. You can see the cotyledons (‘buttons’) which are the sites at which the placenta is attached to the inside of the uterus. You can also see how much growth of the foetus is still to take place during the last weeks of pregnancy.

Fig. 311 Make sure ewes are disturbed as little as possible in the first month of pregnancy to avoid loss of early embryos.

Diseases such as toxoplasmosis and border disease (see later in this chapter for details), and anything causing a rise in body temperature at this stage, also lead to embryo death and resorption. The affected ewes may return to service after a prolonged interval, so if the ram is still with the flock some very delayed pregnancies can be the outcome. If the rams have been removed, the first sign that anything is wrong will be picked up at scanning when an abnormally high number of barren ewes will be identified. If scanning is not carried out it will be the next lambing time when the problem comes to light, resulting in a sometimes disastrously high barren rate.

Mid-Pregnancy – the Second and Third Months

After implantation is complete the pregnancy is more secure and unlikely to be affected by normal gathering and handling or gradual changes in nutrition. Rough handling or chasing by dogs, for example, may upset matters, and diseases such as toxoplasmosis in particular can lead to foetal death. Mid-pregnancy is the stage during which the placenta develops and grows, reaching more or less its maximum size by the end of the third month. By contrast, foetal growth is slow.

Providing the ewes were in good condition at tupping time, a slight loss of body condition (0.5 score) is not harmful; in fact it may even be beneficial, stimulating maximum placental development so that foetuses benefit in late pregnancy, bringing about improved birth weight of lambs. Excessive or rapid loss of condition or gaining condition should all be avoided. Gaining condition during this stage can lead to poor placental development and the birth of underweight lambs. Excessive loss of condition will mean ewes enter late pregnancy in too lean a state, and it is difficult or impossible to correct at this stage.

Disease Problems of Mid-Pregnancy

The main diseases that can affect the developing foetuses are again toxoplasmosis and border disease, resulting in later abortions or the birth of abnormal lambs. With toxoplasmosis the most common outcome is foetal death and mummification, the dead lambs being born at a slightly shortened gestation length. Sometimes the infected foetuses survive, but are born underweight and weak. With border disease, the outcome of infection at this stage is sometimes foetal death and mummification, but more commonly it is the birth of typical persistently infected live lambs called ‘hairy shakers’ because of their characteristic appearance – this is the result of the effect of the virus on the developing brain and wool-producing follicles. These lambs will not thrive. Sometimes persistently infected but normal-looking lambs are born, but these are ‘poor doers’ that will not fatten and often die eventually. (See later for more details of both diseases.)

Late Pregnancy, the Fourth and Fifth Months

This is the stage during which the majority of foetal growth occurs and the requirements of the developing lambs take priority over those of the ewe. It therefore becomes increasingly difficult, and impossible in the last four to six weeks, to get a thin ewe to gain any body condition. Thinness in ewes at this stage often leads to below normal lamb birth weights, reduced udder development, and poor colostrum and milk production, all combining to result in increased lamb mortality. Grouping ewes between six and eight weeks before lambing is due to begin according to body condition and scanning results allows the best quality forage and appropriate concentrates to be allocated to those ewes that most need it. When grouping, rely on what the ewe tells you by her body condition as well as on scanning results, so put lean single-bearing ewes in with those expecting twins, and similarly, lean twin-bearing ewes with those carrying triplets or more. (For more details on feeding, see Chapter 5.)

Booster vaccinations for clostridial diseases should be given at the four to six-week pre-lambing stage. (For schedules for these and other vaccines, see Chapter 4.)

This is also the stage at which ewes become increasingly susceptible to pregnancy-related diseases, the most important of which are:

Abortion

Several of the important types of abortion can cause disease in people (they are zoonoses), so good hygiene precautions should be taken, and pregnant women or people with a compromised immune system should not have either direct or indirect contact with pregnant sheep (for example, by handling clothing worn when looking after the sheep).

Where an abortion has taken place, try to isolate the ewe(s), clean up and disinfect the area where it happened as well as possible, consult your vet (particularly if several ewes have aborted), and select appropriate samples for laboratory examination. Safely dispose of any other foetuses and placentas through the Fallen Stock Scheme (see Chapter 16). Once a diagnosis has been made, a decision can be taken about what to do with affected ewes and the rest of the group.

In most flocks there is the occasional abortion in most years, but when several sheep in a group or flock abort, veterinary help is needed to try to find the cause. Then decisions can be made about possible treatment and future prevention. At the moment a specific diagnosis is made for only about 50 per cent of samples submitted to a laboratory – this may be because the samples are poor, the cause is not an infectious agent, the agent is not being looked for, or even has not yet been identified (the most common cause of abortion in cattle, Neospora, was only identified about twenty-five years ago). Your vet will want a good history of the flock – origins, what happened in the previous year, management, vaccinations and other details. The chances of making a diagnosis are increased by selecting the best specimens to send – whole fresh foetuses and, importantly, the fresh placentas. Most abortions caused by infectious agents occur because of damage to the placenta, which is then unable to sustain the foetus, which then dies. Examining the placenta may give an answer, whereas it might be more difficult to get an answer from the foetus alone, but supplying both types of specimen gives the best chance of a diagnosis.

The most common infectious causes of abortion are given below, with brief information on each. Laboratory tests are likely to be required to confirm a diagnosis. Toxoplasmosis and enzootic abortion are the most common causes in this country, and can be on-going problems from year to year; most other types occur sporadically.

Toxoplasmosis

Toxoplasmosis is caused by the protozoon Toxoplasma gondii and is a common and important cause of abortion. Take care, because this is a zoonosis – although cat faeces are a more usual source of human infection, and play an important role in the disease in both humans and sheep. Cats pick up the organism from eating infected birds and mice, the end result being the production of many Toxoplasma oocysts (eggs) in their faeces. Sheep then become infected by eating food contaminated with these (concentrates, grass, hay).

The outcome depends on the stage of production of the sheep at the time of infection. Non-pregnant animals develop a strong protective immunity. The results of infection in early pregnancy (embryo death and barrenness) have already been highlighted. Infection in mid- and late pregnancy produces a mixed picture of foetal death and mummification, the abortion of freshly dead lambs, and the birth of weak lambs. The cotyledons on the placenta often show typical pale pinhead-sized spots pointing to this as a likely cause. Ewes that abort as a result of this disease are not usually ill.

There is no treatment that will have a beneficial effect on other sheep in the group at this late stage, since most of the damage has already been done, but ewes that abort should be kept, as they are now immune. There is an effective vaccine for future use (see Chapter 4). Don’t, however, get rid of the cats! Keep kitten numbers to a minimum, since it is these that produce most of the oocysts, so have the resident cats neutered.

Fig. 320 Young cats play a central role in the transmission of toxoplasmosis to sheep, but a healthy, stable population of neutered adult cats is not a risk, and can safely carry on keeping the mouse population under control. Make sure that sheep food is kept in closed bins or sacks so cats cannot contaminate it.

Enzootic Abortion (EAE, Chlamydial Abortion)

Enzootic abortion is caused by the bacterium Chlamydophila abortus and is of equal importance to toxoplasmosis as a cause of loss. This is an important zoonosis, particularly for pregnant women and anyone who is immunocompromised. However, the way in which sheep become infected, and how the disease spreads, is very different from toxoplasmosis.

The disease usually gets into a flock with ewes that are already infected but show no signs of it (latently infected), and cannot be identified by blood sampling. These ewes then abort or produce weak, premature lambs at the end of their next pregnancy. The placenta and birth fluids are heavily infected with the bacteria, which contaminate the surroundings and are inevitably accidentally ingested by other ewes while eating or foraging in the surroundings. If these ewes are themselves heavily pregnant they lamb normally, but then become latently infected, and so the cycle continues in successive years. If the flock has a very spread out lambing period, it is possible for ewes to become infected and to abort in the same season. Ewes are generally not ill at the time of abortion and become immune, although some people think they may occasionally shed bacteria at a subsequent lambing.

Once a positive diagnosis has been made, injection of all ewes at risk with antibiotic (oxytetracycline) will reduce further losses, though will not eliminate the infection. Future control is by vaccination (see Chapter 4). There is a scheme run by SAC to identify uninfected flocks, which are then a good source for buying replacements.

Fig. 323 If enzootic abortion is present in a flock the infection spreads to previously uninfected ewes in the lambing pens, but they do not abort until the following year.

Fig. 324 A placenta from a ewe that aborted as a result of enzootic abortion. The main diagnostic features are thickening of the areas between the cotyledons, and a greyish discharge on some parts, although laboratory tests are needed to confirm the diagnosis.

Campylobacteriosis

Campylobacteriosis is caused by the bacterium Campylobacter foetus foetus and is a sporadic cause of abortion storms, usually during just one season because animals become immune after infection. This disease is also a zoonosis, so good personal hygiene should be observed. Infection is introduced either by carrier sheep (these cannot be identified, so buying in is always a risk), or as a result of contamination of troughs or feedstuffs by scavenging birds such as crows and seagulls. Abortions are seen from about a month before lambing is due to start, and affected ewes are usually not particularly ill. Lambs are fresh, but the placenta looks red and inflamed, and laboratory examination will be needed to confirm the diagnosis.

Aborting ewes should be isolated from those yet to lamb, but can be mixed with those that have already lambed – although only once this particular disease has been diagnosed: do not mix unless this is the case – since this will ensure that they encounter the infection and become immune.

The treatment of ewes yet to lamb with antibiotic in the hope of preventing further losses may be indicated, but your vet will advise. There is no vaccine available in this country, but the problem is unlikely to recur in the next lambing season.

Salmonellosis

Salmonellosis is caused by a number of species in this group of bacteria, including Salmonella Montevideo, Salmonella Dublin and Salmonella typhimurium. Salmonellosis can cause serious disease in people, so great care should be taken, as already highlighted above. Outbreaks occur sporadically, and rarely in more than one season in the same flock. These diseases may be introduced by carrier sheep or cattle, or wildlife, or the route may never be identified. Some of these bacteria cause illness or even death in affected ewes, so if ewes have diarrhoea, or are sick or dying, salmonellosis is a distinct possibility.

Antibiotic treatment of contact ewes may be advised, but it is unclear how helpful this actually is. There is no vaccine for sheep.

Border Disease

This disease is caused by a pestivirus that gets into flocks with what are referred to as persistently infected animals. These are sheep that were infected as foetuses in about the third month of pregnancy and survived, but live with permanent infection with the virus, able to infect other non-immune sheep with which they come into contact. They are referred to as ‘virus positive, antibody negative’, and can be identified by testing blood samples in the laboratory, although it may be expensive to do so. As has already been mentioned, the disease is a cause of early embryo death, the abortion of deformed lambs, and the birth of characteristically ‘hairy shaker’ lambs. Obviously infected lambs are best culled as they will never thrive, and are a constant source of infection for others.

There is no treatment or vaccine, so it is best to buy replacements from flocks that have never had this problem. If this is not possible, mixing replacements with sheep already on the farm well before tupping may allow uninfected animals to meet the infection and become immune – although mixing at this stage risks introducing other diseases, too.

Other Sporadic Causes of Abortion

Other causes of abortion include E. coli, listeriosis, fungal abortion and Q fever, and will all be diagnosed as a result of laboratory testing, following which your vet will give advice based on the specific pathogen identified.

Prolapse of the Vagina and Cervix

Prolapses are extremely common in some flocks, particularly in prolific lowland flocks, though less commonly in hill ewe flocks. There have been many suggestions as to the possible cause but no single factor has been identified – lack of exercise and multiple births are certainly important, but a variety of other factors are likely to be involved. What is clear is that once a ewe has had a prolapse she is extremely likely to do so at the next pregnancy, so it is usually recommended that affected animals are culled after they have reared their lambs (if indeed they lamb successfully). If a prolapse is dealt with effectively at an early stage, the ewe is likely to go on to lamb successfully. Delay in treating or inappropriate treatment causes pain and distress to the ewe, and threatens the life of both her and her lambs.

Early cases where the ewe is not straining severely can usually be dealt with on the farm. First make sure that there is no sign of imminent lambing, such as membranes or a waterbag visible – if so, the ewe needs to lamb soon, but may also be suffering from ringwomb (failure of the cervix to fully dilate). If there is no sign of imminent lambing, clean up the prolapse with warm water and a mild disinfectant, apply lubricating jelly and gently push it back into place. Often the urethra, the tube from the bladder, has become kinked and blocked as the ewe has been straining, so the first thing that happens on replacing the prolapse is that the ewe urinates, and then feels less uncomfortable.

Once the prolapse has been replaced, some method must be put in place to prevent it happening again. We favour the use of a prolapse harness, which usually works well if correctly fitted; however, its main disadvantage is that the ewe cannot lamb through the harness, and must therefore be closely observed for when she starts lambing. More serious prolapses, where there is delay, damage and constant straining, need veterinary attention. Your vet can give an epidural injection to make the ewe more comfortable and to reduce or abolish straining. It is common to stitch the vulva at this stage, though a well fitted harness may be equally effective. Anti-inflammatory and antibiotic injections are also indicated.

There is no evidence that this is an inherited condition, so although culling is usually recommended, it is possible to manage a valuable pedigree ewe through future pregnancies by putting on a harness about a month before lambing is due, to pre-empt her prolapsing. The harness must fit comfortably, and its adjustment should be checked every few days.

Other Disasters in Late Pregnancy

Ruptured Abdominal Muscles

Quite often, the burden of a large uterus in prolific ewes stretches the abdominal muscles, causing the abdomen to become distended and lopsided, usually on the left side where there is the added weight of the rumen. Occasionally the ventral abdominal muscle on one or both sides may rupture so that the abdomen drops abnormally. Depending on the extent of the rupture the ewe may be able, with extra care, to manage through to lambing (when she will almost certainly need assistance). However, the ewe’s welfare needs must be assessed, to decide whether slaughter on humane grounds is necessary.

Prolapse of the Intestines

Prolapse of the intestines through the wall of the vagina is another spontaneous, unpreventable disaster that occasionally occurs in late pregnancy. It is inevitably fatal. If the ewe is found alive she should be humanely destroyed as soon as possible. It may be possible to get the lambs out immediately after slaughter, but the chances of them surviving are generally low.

Metabolic Diseases and Listeriosis

Metabolic diseases – pregnancy toxaemia and hypocalcaemia – and listeriosis are the other most common and important diseases associated with late pregnancy. The end stage of each is recumbency and death, so it can at times be difficult to distinguish them from each other without the help of your vet, who will do a clinical examination and further tests if necessary.

Hypocalcaemia (‘Trembling’)

Hypocalcaemia occurs most commonly in the last month of pregnancy, although it can occur occasionally in early lactation, too. It is mainly brought about by the demand of the rapidly growing foetuses for calcium which cannot be obtained from the daily diet, so relies on breakdown of stored calcium from the bones. Any stressful situation such as gathering, vaccinating, housing or bad weather can trigger hypocalcaemia, often, but not necessarily, in several animals.

Affected sheep become unsteady on their feet, and after a few hours go down and are unable to rise. Gradually they become comatose, drooling saliva, or with saliva and rumen fluid coming down the nose. This can be mistaken for nasal discharge and misdiagnosed as pneumonia. If not treated, affected animals will die after about twenty-four hours.

Treatment with a proprietary calcium injection (50–80ml) is very effective in straightforward cases – injecting into the vein gives a response within a few minutes, but as the sheep are often treated by farmers, the solution is usually given under the skin, when response is within half to one hour. If there is no response it is likely that the diagnosis is incorrect. If a number of sheep are affected, your vet will want to check the diet, as this might indicate a mineral imbalance that needs correcting.

Pregnancy Toxaemia (Twin Lamb Disease, Snow Blindness)

Pregnancy toxaemia also occurs in the last month of pregnancy, but takes a slower course than hypocalcaemia. It mostly affects excessively thin ewes carrying multiple foetuses, and is caused by a deficit of energy in the diet. This results in internal body fat being metabolized, fatty infiltration of the liver, which then cannot function properly, and raises levels of betahydroxybutyrate (BOHB) in the blood. It occasionally affects very fat ewes because of excessive fat deposition in the liver.

The first sign that a ewe may be affected is that she is dull and does not eat her concentrates. If not treated immediately there is then a downhill spiral over several days, with blindness and recumbency developing, and eventually death. If the lambs die and the ewe manages to lamb them, she may recover, but more often the lambs putrify and the ewe dies. It is essential therefore to give treatment as soon as a ewe goes off her food.

There are several types of drench that are commonly used with varying success, and the ewe should be offered palatable concentrates such as sugarbeet pulp and flaked maize, and the best hay available. If there is any grass and the weather is suitable, turning her out for a few hours may stimulate her appetite. If the ewe is particularly valuable, intensive veterinary treatment may be successful, but must be sought earlier rather than later. Options include intravenous injection of glucose, inducing lambing, or removing the lambs by means of a caesarean operation.

The risk of pregnancy toxaemia affecting a group or flock can be assessed by blood sampling for BOHB levels, but if the group is thin they should immediately be given more energy by feeding a better quality concentrate, better forage, and supplying molasses as a readily available energy source. The key factor is to prevent it occurring in the first place by monitoring body condition and feeding adequate amounts of good quality forage and concentrates in the last six to eight weeks of pregnancy. This may appear expensive, but it is more expensive to lose ewes and lambs after all the investment that has already been put into them.

Listeriosis

Listeriosis can occur at any time of the year, but is seen most commonly when sheep are being fed silage, so is one of the conditions that must be considered when sheep become ill in late pregnancy; also ewes in late pregnancy are generally more susceptible to disease because their immune systems are less effective than normal.

The bacteria that cause listeriosis are called Listeria monocytogenes, and are found in soil. If grass which is being made into silage is cut too low, or there are molehills in the field, soil is incorporated into the silage. The bacteria multiply, particularly if fermentation is not very good or air gets in during storage, if, for example, the wrapping of big bales is damaged. Another management factor increasing the risk is feeding more silage than the sheep can eat within a maximum of two days, since this practice also creates the right conditions for the bacteria to multiply.

The classic signs of the disease are dullness and one-sided paralysis of the muscles of the face, producing a drooping ear, eyelid and nostril, with a flaccid cheek and drooling of saliva on the affected side. Sometimes the sheep circles to one side, but fairly quickly becomes recumbent on one side, and it can be difficult to get it to lie on the other side. It is easy to mistake this disease for hypocalcaemia, but of course there is no response to injection of calcium, and a careful look at the face should reveal the classic signs of facial paralysis.

Treatment at this stage is usually hopeless. If cases are spotted early it might be worth treating with high doses of antibiotic – your vet will advise – but this is not a rewarding disease to treat. Good management in making, storing and feeding silage will reduce the risk of this disease.