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Gastrointestinal nematode parasites is the correct terminology for what is commonly referred to as worms.  Gastrointestinal nematode parasitism is one of the most important production-limiting diseases of Deer in New Zealand.

Internal parasites can be thought of as 'silent thieves' as the loss in production caused by parasitism often goes unnoticed. Gastrointestinal parasitism can be classed as either clinical or sub-clinical.

Clinically affected animals are easy to identify as they show more obvious symptoms including illthrift, scours, anaemia and weight loss. It is the subclinically affected animals which pose the greatest challenge to farmers as they are more difficult to identify generally with slower decreases in weight gain. While clinical parasitism may be associated with losses in deer, it is the subclinical animals bearing low levels of infection which result in the greatest economic losses.

Deer are treated for gastrointestinal nematode parasites by either pour-on, injectable or oral anthelmintic products, the choice of product is normally decided by weighing up effectiveness, ease of use, cost, reliability and available product support.