Peter Green MRCVS finds out why you need to exercise caution when using manure in your garden

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Significant numbers of horses carry salmonella bacteria in their gut. Most are simply carriers and remain healthy with no sign of illness. But occasionally the salmonella flares up into serious clinical disease as the result of stress or some other challenge to the horse’s health.

Clinical salmonellosis can be serious and even fatal to both horses and humans. After an outbreak, vets often screen other horses on the premises to detect carriers or those incubating the disease. They also assess the human health risk.

In California, a shire mare succumbed to salmonellosis after colic surgery. University vets investigating the horse’s premises found evidence of the specific salmonella they had cultured from the sick shire across the farm.

The pet dog was infected, 6 of the 8 horses were carriers, several wild turkey samples were positive and so were the dung heap and some water troughs.

The owners asked about the risk to their vegetable plot, since they used horse manure to fertilise the ground. Sure enough, salmonella was found in the soil. The scientists monitored this soil for the next year, with no more manure being applied. The pathogenic salmonella persisted for 7 months.

These findings show that while horse manure might be good for roses and shrubs, it should be viewed with caution for growing edible plants.