Farm Newsletter May 2004

Nematodirus Battus Alert

N. battus is a round worm of sheep

During May and June 2003 the Veterinary Investigation Centres in England and Wales diagnosed a large number of deaths and diarrhoea in young lambs due to N. battus infestation. In the first quarter of 2004 a small number of similar reports were received, mainly in the South. The period of risk can vary enormously because the trigger for hatching of the eggs depends on weather conditions as well as requiring the presence of susceptible lambs and contaminated pasture. It is likely that pastures that carried lambs in the last two years, particularly where clinical disease was diagnosed, will be heavily contaminated with N. battus eggs.

Clinical signs:

It is a disease of young lambs, typically 4 – 12 weeks of age. Clinical signs are due to larval stages. Ingestion of large numbers of infective larvae leads to mass invasion and destruction of the intestinal lining. Weight loss, diarrhoea, collapse through dehydration and sudden death can all occur. Death rates are often high in affected animals.

Life cycle:

This differs from other parasites of sheep in that the infective larvae develop inside the egg. The egg is a tough little devil and is very resistant. It can survive on pasture for TWO years. Hatching requires special environmental stimuli, usually chilling followed by average temperatures over 10°C. This results in mass hatching and huge numbers of infective larvae appear on the pasture. The life cycle is typically from one year’s crop of lambs to the next, but calves may also be infected and contribute to pasture contamination. Therefore, lambs are at greatest risk where they are grazing pastures used for lambs (or calves) in the previous year. In sheep, age resistance to N. battus occurs at 10 to 12 weeks of age and is strong by six months. Therefore, although a mass appearance of larvae can occur in most years, it is the timing of this (together with the presence of susceptible lambs) that leads to disease.

Diagnosis:

Post-mortem examination and the identification of the worms are diagnostic. Faecal samples are essential – low numbers of eggs are very significant because the adult does not produce many eggs at all. The absence of eggs DOES NOT RULE OUT the diagnosis, as the immature worms do the damage but are not yet old enough to lay eggs.

Treatment:

Most modern wormers will work, but the injectable ivermectins or injectable moxidectin WILL NOT WORK.

Doramectin requires an increased dose.

No anthelmintic has a persistent effect against N. battus so several treatments may be necessary over the risk period. Resistance has not yet occurred in the UK.

Avoidance:

Aim to graze lambs of 1 to 3 months of age on pastures where there have not been lambs of a similar age (or calves) in the last TWO years.

Warning:

A number of diseases cause diarrhoea in young lambs, not just N. battus. Don’t forget coccidiosis for example. You must bring in faecal samples or take dead lambs straight to the VIC in Thirsk and get a diagnosis. Treatment for these two conditions is entirely different.

Energy Deficiency in Dairy Cows

There has been a lot of this during the past winter and spring months. We are going to try and hold a meeting for vets, farmers and nutritionists in August or September to highlight certain issues and throw some ideas about. However, two things to think about:-

Dry cows:

Often they are too fat. When they calve, these fat cows cannot eat enough because the rumen is too small as the abdomen is full of fat! Thin cows mean hungry cows. Calve them down thin. This means dry them off thin. Watch the intake of a late lactation but early to mid pregnancy cow. Watch that she doesn’t get too fat in the last 3 to 4 months before drying off. Talk to us about controlled diets for your dry cows if they are too fat.

Get the vet, the nutritionist, the milk records and anyone else you feel may be useful to sit around a table in the late summer and early autumn and chat. Make sure they look at the cows too. May be even condition score a few groups and note group changes. Cows should not lose more than ½ a condition score during the first 4 to 6 weeks after calving. Ideally they shouldn’t lose at all. The vet doesn’t need blood samples to diagnose the problem. A loss of more than one condition score after six weeks into a lactation will often indicate energy deficiency either due to a fat cow at calving or an energy deficient diet (or both).

May Means Magnesium

As well as lots of colics at this time of year we attend quite a few staggers cases. Put magnesium chloride flakes in the water or onto supplementary diets. It is very bitter so don’t use too much. Have a stock of Magnijects to hand. If you are in any doubt put one under the skin. Roll the swelling flat with the bottle when you have run it in. It will absorb quicker.

 Never put magnesium directly into a vein. It will stop the heart and kill the cow.

Erythrocin Intra-Mammary Tubes

There has been quite a bit of advertising of this product recently. It is not a broad spectrum antibiotic. It does not deal with E.coli. It does do Staphs and Streps however. Each farm has its own problem bugs. Talk to us before you decide to use it