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Preparing Your Flock: Vaccinations Before Breeding Season

10 September 2015

GLOBAL - Several preparations should be made for breeding season, such as flushing ewes and conducting breeding soundness tests in rams, writes Elise Brown for TheSheepSite.

One of the most important preparations is to vaccinate animals against diseases that cause abortion, deformed lambs and infertility.

Abortion, which includes both lamb losses during pregnancy and weak or deformed lambs at birth, can be caused by several diseases, including Vibriosis (Campylobacter), Chlamydia (also known as Enzootic Abortion of Ewes [EAE]), Toxoplasmosis and Leptospirosis. In some regions of the United States, the list also includes Border disease virus, Cache Valley virus, Listeria and Salmonella. Vaccinations are available for Vibriosis, EAE and toxoplasmosis (although the toxoplasmosis vaccine is not available in the United States).

Vibriosis results in late pregnancy abortions or stillbirths. If a ewe is affected, tetracycline or sulfa drugs can be given to prevent further abortions.

Ensuring fit and healthy lambs in the spring means diligence in  summer and autumn

EAE causes abortions during the last two to three weeks of gestation. While infected ewes rarely abort more than once due to EAE, they can shed the bacteria and infect fellow sheep. Treatment includes giving ewes tetracycline in feed or through injections.

However, as with many other diseases and threats to the health and wellbeing of sheep flocks, prevention rather than treatment is the best management practice. Vaccination against these two diseases can be given together as a combined vaccine or individually. According to University of Minnesota Extension, the vaccines should be given two weeks prior to breeding, and ewes that are vaccinated for the first time should receive a booster mid-gestation.

When a ewe is infected with toxoplasmosis, a diagnosis can be difficult, as blood sampling alone is not sufficient for confirming that an abortion was due to toxoplasmosis. Specific changes in the placenta and high levels of antibodies also are present. An infection during mid pregnancy leads to abortion or weak live lambs with a dark brown, leathery mummified fetus.

Toxoplasmosis vaccinations need to be given three weeks or more before the breeding season. While the vaccine is not available in the United States, the disease can be prevented by keeping cats and vermin out of sheep feed.

Vaccinations also are important because pathogens that cause abortions can be passed to humans. Pregnant women should especially take care during lambing season and should not handle the vaccines.

However, University of Minnesota Extension noted, even in vaccinated flocks, abortions can still occur. The pathogen that caused the abortion may be one that does not have a vaccine against it, and no vaccine is 100 percent effective at preventing abortions.

Toxoplasma gondii abortion. Picture courtesy of NADIS. 

Vaccinating Rams

Reduced fertility in rams in the western United States can be caused by epididymitis. This disease causes the epididymis to become hardened and swollen and causes lower quality semen production.

Vaccines are available, but their effectiveness can be questionable. Use is recommended only when the risk for epididymitis is high.

Schmallenberg virus vaccines

Shmallenberg virus (SBV) was discovered within the last four years in Germany and the Netherlands but today has been noticed in many other European countries, including the United Kingdom. SBV affects sheep, cattle and goats and is spread by infected midges. The adults do not show symptoms, and the disease is only recognized when a deformed lamb, calf or kid is born. SBV damages the brain and spinal cord and causes deformity of the legs, spine and head.

"Most of the time, similar viruses do not cause disease in non-pregnant animals, so Schmallenberg virus may be slightly different; careful surveillance will be needed in affected areas to determine how important this is," said Kim Willoughby, head of the Virus Surveillance Unit at the Moredun Research Institute in the United Kingdom.

Farmers should vaccinate against the disease three weeks before the breeding season and be on the lookout for and report milk drop, diarrhea, fever and lack of appetite in adult animals and congenital deformities in newborns. It is unlikely that SBV affects people, but at-risk groups such as pregnant women and immunosuppressed people should be cautious.

The Economics

According to the National Animal Disease Information Service, over 70 percent of the United Kingdom's abortion outbreaks are caused by enzootic abortion, toxoplasma gondii and Campylobacter species. The cost of abortion ranges from £20 to £65 per ewe that aborts.

The cost of vaccination is much lower. A toxoplasmosis vaccine costs £3 per dose, but because it provides immunity for a ewe's entire life, the cost ends up being 50-60 pence per pregnancy. The case is similar for C. abortus, which costs £2-3. This cost must be divided over three pregnancies or more.

Vaccinations that are given are not limited to the challenges described above. Vaccinations may also be given for issues specific to a given flock or sheep, said Mike Neary, Purdue University Extension Sheep Specialist.

TheSheepSite News Desk