312           Important Helminth Parasites of Horses

Kamala may be administered in capsules of 30 grm. to adult horses
after the animal has been fasted for 24 to 36 hours. The drug has a
purgative action and seldom needs to be followed by a purgative. It
should not be given to very young or old and weak animals or those suffering
from febrile diseases, such as influenza, strangles and infectious anaemia.

Oleoresin of male fern may be given to adult horses in doses of 3 to 6
drm. (10 to 20 grm.) in capsules after fasting the animal for 24 hours.
It should be immediately preceded or followed by a quart of linseed oil.

All these drugs should be given to animals in good condition which can
presumably withstand their effects.

No definite prophylactic measures can be formulated until the life-history
of the parasite has been established. However, proper disposal of excreta
in which mature segments and eggs are voided should be practised, as suggest-
ed in the case of round-worm infestation.

                           ROUND-WORMS

Of the helminths infesting the horse, round-worms are by far the most
common and important. These vary considerably in their size, structure,
biology and injuriousness. For the completion of the life-cycle some of these
require an intermediate host in which they undergo a part of their develop-
ment, while other species are transmitted from one animal to another directly
by eggs or by their infective larvae. The majority are transmitted directly,
without the agency of an intermediate host. Some of these worms are blood
suckers, others do damage in various ways : all of them probably tend to
produce unthriftiness, in some cases going on to cachexia.

                              ASCARIDS

The large intestinal round-worm— Parascaris equorum—is a large
yellowish worm, sometimes a foot long, which is often passed in the droppings.
It inhabits usually the upper part, occasionally the middle and lower parts,
of the small intestine. At times they are found in the caecum and the stomach.
The infestation may be heavy and is particularly harmful to foals and young
horses.

Eggs are produced in large numbers by the female worms and are voided
with the faeces. They are very resistant to adverse conditions, like drying
and freezing and to chemicals, and may remain viable for several years, but
hot dry conditions destroy them in a few weeks. The thick egg-shell protects
the contained larva against various unfavourable influences. Ordinarily
sufficient moisture is present in horse manure for the development of the
eggs. Droppings which appear dry on the surface usually contain enough
moisture in the middle to permit normal development of these eggs. Under
suitable conditions of temperature and moisture the eggs develop to the in-
fective stage in about two weeks. They do not hatch and the infective larvae
remain inside the egg-shell until they reach the gut of the host.