STOMACH WORMS IN LAMBS AND THEIR CONTROL        271

Six Blackface ewes and their twelve twin Greyface lambs approximately six
weeks old were put into one half of the field on 25th May 1932, and allowed to
graze over the whole 1½ acres up to the 28th August 1932.

                                                TABLE II.

Showing the number of eggs per gram of fœces from lambs at 6 weeks old.

An equal number of ewes and lambs were allowed to graze only 1-10th of the
other half at one time, the ewes and their lambs being changed to clean sections at
10-day intervals. A temporary fence of sheep stakes and wire-netting served to
confine the animals.

Both groups of lambs were selected as nearly alike as possible with respect to
age, weight and condition. The average weights of the progressional and non-pro-
gressional groups were 23.4 lbs. and 23.9 lbs. respectively.

Prior to the commencement of the experiment the ewes and lambs were sub-
mitted to fæcal examination for the presence of stomach worms. Fæcal cultures
demonstrated the presence of a moderate to heavy infestation of both H. contortus
and O. circumcincta in all the ewes.

Three lambs from each group were submitted to egg counts by the Stoll method
(Table II). The fæces were removed by hand, the method being to insert the small
finger into the rectum.

Since it is not possible from an examination of eggs to determine the species of
worms present, fæcal cultures were made. Approximately 90 per cent. of the
migrating larvæ were identified to be O. circumcincta, the remaining 10 per cent.
being Nematodirus and Trichostrongylus species. A lamb from the same source and
similar in age and weight to those submitted to fæcal examination was autopsied
and examined for helminths. The abomasum yielded 76 O. circumcincta but no
H. contortus, while the small intestine, colon and cæcum contained no helminths.
It may be concluded therefore that both groups of lambs commenced the experi-
ment with an initial infection of helminths consisting almost entirely of O. circum-
cincta.

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