Story: Diseases of sheep, cattle and deer
Page 3 – Sheep footrot and poisonous plants
Footrot is caused by the anaerobic bacteria Fusobacterium necrophorum, and its transmitting agent, Dichelobacter nodosus. Warm, moist conditions encourage the spread of footrot, which is highly contagious among sheep. As the disease spreads in the hoof it destroys tissue, and the horny part can become almost completely detached. Sheep become lame and are less inclined to graze, resulting in weight loss, scantier wool and poorer lambing performance. They become prone to fly strike (where blowflies lay eggs in the wool and maggots develop), especially where infected hooves have been in contact with the fleece. If not treated, footrot leads to a slow and painful death.
New Zealand’s early sheep flock was founded on Merinos, which are more likely to get footrot than other breeds. Farmers in wetter areas had trouble with the disease from the outset. The problem increased on the big stations after farmers fenced the land and sowed improved pasture, and the intensity of grazing increased.
A variety of treatments were tried. A popular method was to run sheep through a foot bath of bluestone (copper sulfate) and arsenic. However, the cure rate was poor. The problem was only eased temporarily in dry seasons, when the disease went into remission naturally.
The problem of footrot in Merinos encouraged farmers to introduce British sheep breeds that were less susceptible. Footrot remains a major problem in Merino and other fine-woolled breeds when it is wet, although vaccinations are now available. Other methods of control include culling susceptible animals, genetically selecting animals that show resistance to the disease, paring hooves to remove infected tissue, using foot baths containing a disinfecting agent, and dosing with antibiotics.
Foot abscess is an infection of the joints in the foot, generally by Fusobacterium necrophorum and/or Arcanobacter pyogenes. Wet and muddy underfoot conditions predispose the condition. Treatment involves draining the abscess, bandaging and antibiotics.
In the early days of settlement, thousands of sheep newly landed off ships from Australia, or sheep being driven to new grazing areas, died after eating tutu (Coriaria arborea). Some farmers claimed to have lost one-quarter of their flock to tutu poisoning. Tutu has been responsible for most plant poisonings of stock in New Zealand.
The blood cure
Bleeding was the recommended cure for sheep poisoned by tutu. Early runholder Mark Pringle Stoddart wrote: ‘cure is instantaneous if applied in time, and consists simply by boldly cutting across the bars of the palate – the swallowing of blood brings immediate relief.’ 1
This treatment would certainly not be advocated today.
Tutu grows throughout New Zealand on riverbanks and tussock lands, and among scrub. Stock can eat a small amount without any ill effects, but larger quantities can be lethal.
Many other plants can kill sheep, including acorns, yew, St John’s wort, ngaio, oleander, rhododendron, laburnum, delphinium, Iceland poppy, cestrum, foxglove, goat’s rue, ragwort, and blue lupin. Some sheep become sick after grazing on specialist feed crops. They can get nitrate or nitrite poisoning and red gut from grazing lucerne, skin scald from rape, and haemoglobinuria from brassicas (such as swedes and kale).
Sheep can also be poisoned if pasture is contaminated with superphosphate fertiliser. The fluorine in superphosphate is largely the cause.