Veterinary advice: If free of salmonella, maintain a closed herd

Last week I received a call from a client anxious about the impact Bovine Salmonellosis would have on his herd of spring-calving cows, and wanting to prevent the nightmare his neighbour endured last winter.

I explained that Bovine Salmonellosis is caused by a bacterium which is commonly involved in clinical disease in Ireland.

Clinical signs

Salmonella dublin and Salmonella typhimurium cause clinical signs of disease in adult cattle, including fever, dullness, inappetence, abortions, and profuse, watery, foul-smelling diarrhoea.

Up to 75% of clinically sick animals will die if left untreated.

In an abortion storm, up to 25% of the herd will abort. However, not all cases that are clinically sick will abort, and many cases who do abort have no clinical signs.

In calves, the disease signs include scour, meningitis, pneumonia, joint-ill, septicaemia, and gangrene of the distal extremities.

Salmonella is a zoonotic disease (spreads from animals to man).

Humans can be infected by working with infected animals and their environment; by eating animal products that have come from infected animals (including unpasteurised milk, and meat contaminated by faecal matter during slaughter).

Transmission

The most common route Salmonella enters a farm is through an infected, bought-in animal showing no signs of illness.

Salmonella can also be carried by wildlife, dogs, cats, equipment, vehicles, clothing, and in water and purchased feeds.

Salmonella can survive for months in slurry and soil, and for years in dried faecal matter. Ideally, slurry should only be spread on land used for tillage, but resting pasture for 4-5 weeks after spreading is a good compromise.

When a susceptible animal encounters Salmonella, the most common outcome is clinical disease (such as abortion, scour) followed by a 2-3 week period of shedding of the infection.

Most of these animals in turn become “latent carriers”, who, in times of stress (drying-off, calving, changes in the weather) will start to shed the Salmonella bacteria, infecting those around them.

Control

If free of Salmonella, you need to maintain a closed herd with strict biosecurity.

If it becomes necessary to buy in (a stock bull, for example), buy directly from disease-free herds; quarantine the animal in a proper isolation facility; and test using serology (blood test) and faecal culture before joining the main herd.

Control and elimination of bovine Salmonella from an infected herd (as with all other diseases) involves testing to identify and remove positive animals, and management practices to prevent spread of the bacteria.

Any animal that aborts or displays symptoms of illness should be isolated from other animals. Investigation by your vet, in conjunction with the Regional Veterinary Laboratory, is highly recommended.

To reduce the potential for disease spread:

* Improve general hygiene in sheds.

* Avoid faecal contamination of feed.

* Clean out water troughs regularly.

Vaccination

Vaccination will rapidly stop shedding of Salmonella in infected herds, and will help prevent the disease entering uninfected herds.

The peak time for Salmonella abortions is around drying-off; it is vital to vaccinate before the risk period, to give maximum herd protection.

If there is a particular problem with Salmonella scour in calves, it may be necessary to re-vaccinate cows/heifers closer to calving.

There is evidence that fluke damaged livers can lead to an increase in Salmonellosis. Therefore, dosing pregnant animals properly with a quality flukicide is vital.

As preventative medicines and anthelminthics are becoming significant cost areas on farms, consulting your vet on the optimum vaccination and parasite/fluke control programmes is time well spent.

As all “Game of Thrones” fans are well aware, winter is coming!