Avoiding salmonella epidemics in dairy herds

With spring calving herds into their final weeks of lactation, vaccinations of herds for lepto and with Rotavec Corona or Scourguard are underway or planned.

If you are not already doing so, please add salmonella vaccinations to this list. Salvexin+B is a New Zealand (NZ) manufactured vaccine and is produced by MSD Animal Health at their Upper Hutt plant. This is the same company that produces Multine and Covexin 10 for the prevention of clostridial diseases.

Initially, each heifer entering the herd and each cow will require a sensitising dose of Salvexin+B followed by a booster four to six weeks later. Thereafter it is just an annual booster. Vaccination will cause a drop in milk production in some animals; this is associated with a temperature rise so it is a vaccine to be given by itself. No other treatments are to be given for two to three days after each Salvexin+B jab.

In a dairy situation Salmonella is ubiquitous; if you go looking, it will be on every dairy herd but certainly not in every cow or heifer. So often when we work with a herd owner during an on-farm epidemic the question is asked, “where has this Salmonella come from?” While people look accusingly at wildlife, possums, birds, and cats etc., the truth is, the bacteria will have been sitting in the herd.

Salmonella is just waiting for the correct conditions and then it becomes obvious as sick and dying cows plus or minus abortions or still-births.

Within the rumen, the production of volatile fatty acids (VFAs) by bacteria and protozoa controls Salmonella when these are in the gut. Any situation which upsets the rumen and lowers VFAs, increases the probability of disease. Lower VFAs, and Salmonella flourishes.

What can upset the rumen? These can be anything like changes in the cow’s diet, sickness from another cause, irritants such as roughly milled Mag Oxide. What happens next is damage to the gut lining which we see as severe diarrhoea.

The diarrhoea contains millions of Salmonella bacteria, a potent way of spreading the disease from cow to cow and cow to human. Salmonella is a zoonosis with over 50% of NZ’s human cases associated with people working on farm. If the gut wall is breached, the powerful toxins produced by these bacteria enter the bloodstream and cause septic shock. The major organs shutdown and the cow or heifer dies.

Salmonella cases in dairy herds occur throughout the year – we have recently been involved in one severe epidemic – but cases of this disease do spike around calving.

It is a hobbyhorse but please vaccinate. The loss of cows is one thing but also consider the protection of your health and that of your family and workers as well as the time and money you will invest when treating animals during an outbreak.

Vaccinating dairy herds to prevent Salmonella epidemics is a no-brainer.

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