If animals have to be brought into a herd they should come from a known source with a good record of disease control, ideally with certification of disease status.
However, each farmer needs to take responsibility on his own farm, so animals coming onto it should be suitably quarantined, tested and vaccinated to ensure that they are not introducing disease.
To get the all clear may take 3-6 weeks depending on what diseases need to be assessed.
Control Plans -- is there a blueprint?
The short answer to this is no. It is not possible to give a blueprint for all farms, but in figure 1 (far right) there is a guide to when peak risk periods are likely for a spring calving herd and when vaccinations could take place.
Each herd should have an individual control plan developed that will take into consideration the individual risks and unique situations that exist on different farms.
This will involve the farmer sitting down with his vet and farm adviser and reviewing the previous year's herd health events, production records and any lab results that have been received.
This is a highly infectious virus that is found in herds throughout Ireland. It is principally maintained in herds by Persistently Infected (PIs) animals.
Rather than evolving into such, these are born infected due to events that happen early in pregnancy.
They cannot be cured and will eventually succumb to the disease. However, they can live for a number of years and during this time they will excrete large quantities of virus, which can both infect other animals and cause immuno-suppression, whereby the ability to fight all infections is compromised.
If a PI female goes in calf, the calf will be born persistently infected and so the cycle continues. So having a PI in the herd will have serious consequences for the general health of the herd and will impact on the fertility performance.
Animal Health Ireland and other bodies now recommend that PIs should be identified and slaughtered. They should never be offered for sale. Once a herd has identified and removed any PIs, measures should be put in place to ensure that they are not reintroduced and a vaccination programme instigated.
It is generally accepted that a combination of ongoing PI screening and vaccination is the only way to control the disease in Ireland at present.
Leptospirosis causes abortion, infertility, birth of weak calves and milk drop in cattle. The infection is generally transmitted in the urine of infected animals and it can also cause disease in man.
It is endemic in many herds in Ireland and vaccination is the main way to control it. Animals can become infected during their first grazing season, although they will not show any signs of disease at this time.
Depending on which Leptospirosis vaccine you choose, calves can be vaccinated with two injections from four weeks of age to prevent them from becoming carriers. They receive an annual booster vaccination after this.
IBR is caused by a herpes virus (Bovine Herpes Virus, BHV1) and, like most herpes infections, once an animal becomes infected they are carriers for life, although they will frequently not display any clinical signs, nor shed the virus, except at times when they are stressed.
Clinical signs include respiratory signs (nasal discharge, cough and a high temperature), milk drop and abortion. Although contagious, there are herds in Ireland that have no evidence of having been infected. Unfortunately, they are the minority and approximately 70-75pc of farms now have the virus in their herd.
There are two types of vaccine, live and inactivated. If the disease is first identified in the herd because animals are sick with the virus, the live vaccine would be recommended as it produces a quicker immune response. However, once the clinical signs have been controlled, or if the virus is detected in the bulk tank without clinical signs of disease, then the inactivated vaccine should be used. The inactivated vaccine has been shown to give robust protection and be more effective at reducing the amount of virus that is shed by carrier animals.
It also prevents mid-pregnancy abortions caused by IBR/BHV1. It is possible to eradicate IBR from a herd using biosecurity and vaccination.
Salmonella can cause a severe scour in calves and it can cause abortion and disease in adult cows. Like Lepto, it can also cause disease in man. It is commonly introduced into a herd by buying in apparently healthy carrier animals, but it can also enter the farm in contaminated slurry, equipment or water that has been in contact with dung infected with Salmonella.
If the problem in the herd is Salmonella scour in calves, it has been shown that vaccinating cows during the last two months of pregnancy increases the protective value of the colostrum that they produce. Alternatively, if Salmonella abortions are encountered vaccination should be carried out a month before the period of risk.
Johne's Disease is caused by a bacterial infection that eventually leads to chronic wasting and scouring in cows.
Generally, animals will not show signs until they are at least three years old, but they are most susceptible to picking up the infection when they are calves. The infection is commonly passed on from infected cows that may not be showing any obvious signs of disease in their colostrum and milk. There is no treatment or vaccine available. It is essential to prevent its introduction into herds. It may be introduced by buying in an animal that is carrying the bacteria or through importing colostrum from a herd.
Unfortunately, screening for the disease is not straightforward and a negative result does not mean that an animal is free of the infection. A negative bulk milk tank can also be misleading, as early in the course of the infection there may not be enough cows in the herd with antibodies to give a positive result. By the time the bulk tank is positive the infection will be well established. Screening requires regular sampling of individual milk or blood samples and drawing up control measures for the individual farm.
Charles Chavasse is a vet with Pfizer Animal Health