Salmonella on dairy farms - What is it and what can be done?

During the Winter and Spring last year Southland had a massive number of salmonella outbreaks on farm. It was unexpected and was just the cherry on top of an extremely rough season.

Salmonella is also zoonotic which means humans can get it too. Young old, pregnant, and sick people are more prone to a more severe form of salmonella infection therefore, they should not handle stock during an outbreak.

What is it?

Salmonella is a bacteria that infects the gut, it specifically designed to enter gut cells, then enter the white blood cells and hide from the immune system of the cow. This make is hard to be killed by the cow’s own immune system and hard to be killed by antibiotics. While in the white blood cell it takes a ride in the blood stream and can infect other organs like the brain and uterus which can cause death and abortions.

What does salmonella look like?

Salmonella can cause a drop in body condition, drop in milk production, loose faeces (or a nasty, watery, blood tinged, diarrhoea), sepsis, abortion and death.  Most of the cases we saw last year were cows that had a; drop in body condition, drop in milk production, and develop loose faeces they looked very similar to Johnes cows.

Some farms had special cow technology like collars or ear tags that was able to alert them to a problem earlier on. Cows infected with salmonella had an alert of reduced rumination prior to them losing condition or dropping in milk production.

There are different types of salmonella, some are more likely to kill cows than others. Salmonella Brandenburg is more likely to abort cows than the rest.

Calves can also get salmonella, an outbreak in the cow shed can look like a severe scour issue or calves found dead suddenly the next day.

What causes an outbreak?

Outbreaks occur in times of stress (nutritional or weather). In any herd of cows 0.3-15% of cows in any herd can be carriers of salmonella. This means they have the salmonella bacteria in their gut but aren’t sick. As long the rumen and gut of these carrier animals are healthy they only shed small amounts of salmonella, so no outbreak occurs. In times of stress, or sudden food change, the gut shed more salmonella increasing the risk of other cows getting infected.

Farms that have had outbreaks will have more carrier cows in the next season increasing the risk of an outbreak in seasons to come.

Birds may play a small part, carrying infected aborted material around the farm, and contaminating feed, but more research is needed to see how much of an impact they have.

How bad can it get?

Based on information collected from Farmers in Southland the percentage of cows in a herd that were affected by salmonella ranged from 2% to 14%. The number of cows that died ranged from     0-5%. If salmonella Brandenburg is the cause, cows can abort. Up to 35% of heifers can abort in an outbreak, some farmers experienced abortions of around 25% in their heifers last year.

What can you do?

The best thing you can do is prevent your cows from getting salmonella in the first place. There is a vaccine available it is not too expensive, and it reduces the amount of salmonella shed reduces the severity of the disease. Farms that had vaccinated had significantly less cows affected by the bacteria no deaths. Vaccines are like insurance policies you don’t know you need them until disaster strikes. To vaccinate your herd, cows will need a sensitiser, and a booster shot 4- 8weeks later, then a yearly booster after that. The vaccine can’t be given within 1 week of dry off, or the last 4 weeks of pregnancy unless advised by a veterinarian.

Calves can also be vaccinated if needed.

If you think you may be experiencing an outbreak, contact the clinic for next steps. While waiting for a vet isolate the suspect cows until a vet can examine them. Ensure you wear gloves, overalls and gumboots when handling the suspect cows and wash your hands and gumboots with disinfectant afterwards.