Leptospirosis is the cause of a significant disease of cattle (and to a lesser extent, sheep) resulting in abortion, infertility and milk drop. Leptospira hardjobovis and L.pomona are the most common types found to infect cattle in New Zealand. Leptospirosis is also a zoonotic agent and therefore an important risk to human health.
The infection starts when the bacteria gains access through the skin and mucous membranes resulting in fever and ‘flu-like’ symptoms. Eventually, bacteria from infected animals are passed on in urine, causing more infected animals - especially if the urine contaminates water sources frequented by susceptible animals. Cattle and other animal species can also acquire infection with L. Icterohaemorrhagiae mainly from rodents (also zoonotic) resulting in systemic illness, including abortions and the birth of weak and unviable calves.
The disease can be severe and occasionally fatal. Due to the human health risks of Leptospirosis, herd vaccination should be seriously considered if infection due to Leptospira Hardjo is demonstrated.
Sources of infection
The major sources of infection for cattle are:
- Infected urine (main source of infection)
- Semen, uterine discharges and the products of abortion.
- Contaminated/shared drinking watercourses
- Purchased infected cattle or hired/shared bulls
Disease syndromes associated with Leptospirosis infection
- Abortion: This usually occurs in the second half of pregnancy. Infection in late gestation may result in the birth of weak or unviable calves. When infection is endemic in a herd, the only sign of disease may be abortion in newly introduced unvaccinated or naïve heifers.
- Infertility: can be significant in the first year following infection and is characterised by a low conception rate to first service, an increased calving to first service interval and an increase in the number of services for each successful pregnancy. It may also typically be seen in heifers in infected herds that stop vaccinating
- Milk drop: may affect a large proportion of the herd simultaneously. Some affected cows will have a fever and some may show a ‘flabby’ udder affecting all four quarters. There can be an associated high somatic milk cell count. The classical acute milk drop syndrome is now uncommon in New Zealand. However, reduced herd milk yield may occur as a result of sub-clinical cases in naïve animals in endemically infected herds.
Control of Leptospirosis
As stated earlier whole-herd vaccination is the main control and preventative measure for L. Hardjo in cattle.
The key to control is the vaccination of young calves and heifers. Vaccination will prevent reproductive tract colonisation and later infertility while vaccinating heifers before first calving prevents abortion. It is important to remember that vaccination of infected cattle does not prevent the shedding of L. Hardjo. Antibiotics can be used to clear infection from sero–positive animals.
What is the best time to vaccinate?
February - April is the time to vaccinate for Leptospirosis. Do not leave it until late May or June – this is heading into the danger season (autumn is the high risk season for Leptospirosis). That’s why it is best practice to give your animals their annual booster early in gestation.
- Unvaccinated calves can be vaccinated from 4 weeks of age with Ultravac 7 in 1: They require 2 vaccinations (4-6 weeks apart). Please note that 5 in 1 vaccine does not vaccinate against Leptospirosis.
- Previously vaccinated calves with 7 in 1: require a booster jab of Leptoshield at the same time as the rest of your herd to get them in line with your yearly vaccination scheme.
- Rising 2 year olds and cows will only need a booster dose with Leptoshield (no more than 12 months since their last shot).
As with any infectious disease, strict adherence to biosecurity measures and monitoring of infection status must be undertaken to ensure infection does not re-enter the herd.
At Selwyn Rakaia Veterinary Services we will confirm that the appropriate biosecurity and management measures have been implemented on your farm.