Page 72 - The Veterinary Care of the Horse

larvae in the milk. This is only necessary on studs where these parasites reach high numbers

and are a problem. In these situations, the foals may be routinely wormed at an early age (1–
VetBooks.ir 2 weeks) but the vet should be consulted as not all treatments are appropriate for young foals.

BOTS – Gasterophilus intestinalis and Gasterophilus nasalis

Adult size and colour The adult is an insect that looks rather like a bumble bee (Figure 2.21).

Figure 2.21 Adult bot fly

Life cycle In the summer months the adult insects hover round the horses and lay their eggs

on the horse’s legs, chest, shoulders, mane and under their throats. The adult flies usually live
for only a few days. The cream-coloured eggs are firmly attached to the horse’s coat. The

larvae begin to develop inside the egg and are ready to hatch after a few days. Some do not
hatch until they are eaten or licked by the horse. The larvae then penetrate the mucosa of the

tongue and mouth and migrate towards the pharynx where they can cause severe irritation
and then to the horse’s stomach. Here they attach to the stomach lining (Figure 2.22) and

cause inflammation and ulceration. After approximately 9 months the large red or yellow
larvae are passed in the faeces the following spring and summer. Following a period of 6
weeks pupation, the adult fly emerges.