Solution 1:
Early testing to identify animals that are most at risk

Scientists in East Africa have discovered a way of identifying which animals that are likely to suffer most from stomach worms before they look sick. They measured the levels of an antibody called IgA in the blood that shows whether an animal is getting an adequate diet to resist worms.

They found:

• That growing lambs attempt to control parasites by suppressing the worms' size and fertility.
• The lambs do this by producing a local IgA antibody that directly affects the worm.
• The success of this IgA antibody response in controlling the worms is directly related to the level of nutrition (especially protein) that the lambs received.
• A simple test to measure the IgA responses can show whether the lamb is getting enough protein to best resist the effects of the parasite and this can do done before the lambs look sick.

Solution 2:
Feeding extra protein

Measuring the amount of IgA anitbody can show which animals are nutritionally stressed or identify those animals that are relatively resistant to infection. A cheap test is being developed to enable farmers to use so this information in managing their livestock.

Being able to measure the IgA responses of an animal to stomach worms makes it possible to identify animals that are:

• 'at risk' before they develop clinical signs of disease
• on an inadequate diet to protect themselves,
• genetically susceptible to these parasites.

So if animals are found to have low IgA levels they lack sufficient protein in their diets and so are more susceptible to infection. Farmers can counter this by early feeding of extra protein to animals with poor IgA levels in their blood. If extra protein is fed then lambs will be able to grow despite being infected with stomach worms.

Initial support from an NGO, extension service or animal advisor is important in helping livestock keepers with testing and identifying animals liable to need help and supplementation. Assistance will also be needed to identify the best and most cost effective feed and to help identify the lambs needing supplementary protein.

It is not always possible to provide actual figures to show the exact cost and thus benefits of managing young 'at risk' lambs in the way because the costs involved vary between different places. It is however possible to say that the benefits will exceed costs.

Dead, sick or poorly growing animals constitute an opportunity costs from the losses they generate. Not only is there the lost of value from not being able to sell meat or milk from a sick or dead animal but there are losses in time and effort by livestock keepers and veterinarians and maybe drug costs in trying to treat sick animals. Handling ill stock even takes longer. Sick animals carrying large worm burdens are also a threat to other sheep.

Actual costs of supplementary protein feeding depends largely on local circumstances but small ruminants like sheep and goats are often able to use up by products (dried cassava leaves) or plants not directly of use to humans (leguminous fodder/trees) so their 'purchase price' is low.

Being able to help animals control stomach worms before they get sick will mean they grow faster and bigger and reach reproductive age earlier which for females means early breeding and young stock to sell. For males it means early sales.

Keeping healthy livestock is also much easier than sick ones and if all are healthy in a flock then the whole flock is easier to manage. For example if some lambs carry high worm burdens then they will breed later than the healthy ones and that will mean livestock keepers cannot breed the flock at the same time as some animals will not have reached puberty ( breeding ability) in time.

The only risk in this approach to keeping lambs healthy is that the stockman feeds inappropriate or very expensive feed. Protein rich supplements are needed and ones that are not so expensive that they make the exercise one that costs more than the monetary return. This is unlikely as smallholders realize the cost of feed will be of paramount importance. The object would be to identify 'home grown' rather than 'bought in' feeds.

Early action to prevent animals deteriorating and dying will improve overall productivity in flocks and thus the livelihoods of African animal keepers in countries like Kenya and Tanzania where these parasites are a major constraint to production. Scientists are now working to develop cheap and reliable tests that will enable vets or farmers to establish how well their stock are able to resist infection. This information will then let farmers select the most appropriate action to reduce production losses. They could for example treat only those with low resistance.

The goal of this project was to better understand the interaction between diseases and nutrition so that new knowledge could be incorporated into future livestock management strategies. Specifically the researchers wanted to understand the interaction between the level of nutrition and parasites such as Haemonchus in much more detail. Four hypotheses were tested:

• That growing lambs attempt to control parasites by suppressing worm growth and fecundity.
• The major mechanism of resistance is mediated through local IgA antibody responses.
• The level of nutrition (especially protein) influences the IgA response.
• Measuring IgA responses could indicate whether the diet was inadequate to produce optimal parasite resistance.

The project examined over 1000 sheep and found that the results supported all four hypotheses. Growing lambs do attempt to control haemonchosis by suppressing worm growth and fecundity. Increased IgA responses are significantly associated with decreased worm length and fecundity. Animals on protein supplemented diets do produce more IgA. Measuring IgA responses can indicate which animals are on nutritionally inadequate diets. The manifestations and mechanisms of resistance appear very similar in animals infected with haemonchosis and ostertagiasis (the major disease constraint on sheep production in temperate climates). Parasitologists have often assumed that resistant animals control parasites by reducing worm burdens and possibly by reducing the parasite's fecundity as well. These results strongly indicate that in grazing lambs, reducing worm burdens is less important than reducing worm size and fecundity. This knowledge is now being incorporated into livestock management strategies.