This thesis records in part I studies on the ecology of the free
living stages of Cooperia curticei , both under controlled and natural
At constant temperatures free living stages developed throughout
the temperature range of 10-37c. At all temperatures each larval stage
occupied the same proportion of the total developmental time to reach
the infective stage. The relationship between the rate of development
in log days and temperature was found to be linear. Under natural
conditions the rate of development was most strongly correlated with
mean maximum air temperature and was not significantly different to that
observed under controlled conditions. When faecal cultures were kept at
10°C, 27°C and 37°C a higher proportion of eggs completed development
to the infective stage at 27°C than at the other temperatures. Under
natural conditions the percentage recovery was influenced by weather
conditions particularly rainfall.
Submergence of the free living stages in water inhibited their
further development. First and second stage larvae survived longest at
temperatures between 5°C and 15°C but for a much-shorter time than infective
larvae. Between the extremes of -6 and 52°C, the longest survival
of infective larvae was 312 days at 10°C.
Techniques are described for the recovery of Cooperia curticei
larvae from sample units of pasture, soil and faecal pellets. Under
natural conditions the maximum survival of larvae from monthly experiments
ranged from 9 - 26 weeks. Maximum survival was particularly
influenced by temperature. Infective larvae survived through the
winter. There was an exponential relationship between the percentage
survival and percentage of larvae recovered from the herbage. Vertical
migration of larvae appeared to be primarily affected by rainfall and
It is concluded that infective larvae of Cooperia curticei
are available to grazing sheep throughout the year. Theoretically
the nematode can complete from 9 - 11 generations in each year.
Part II of this thesis records experiments on the relationship
between Cooperia curticei and the host sheep.
Experiments carried out in vivo and in vitro demonstrated that
infective larvae of C. curticei exsheath under conditions provided by
the rumen. The process of exsheathment was similar to that described
for H. contortus.
A series of experimental observations were made on the effect of
Cooperia curticei infection in sheep using animals of differing ages, on
different diets and with various sizes of infection. The prepatent
period of infection was 14- 16 days. Peak egg counts were recorded 5 - 7
days after infection became patent . There after they declined gradually
in sheep given 10,000 larvae but in sheep given 50,000 to 100,000 larvae
the decline was more abrupt. The egg output per female worm was
found to range up to 1,958 eggs per day.
No clinical sign of infection was observed from any experimental
animal. Body weights, wool growth and blood analyses showed no
significant changes and no gross lesions or significant histopathological
changes were observed. The results indicate a well balanced
relationship between C. curticei and the sheep.
The distribution of the C. curticei in the small intestine was
skewed, and most of the worms were recovered from 5- 10 feet from the
gastric pylorus. A predominance of female worms was observed at all
levels of the small intestine. Maximum percentage recovery of C. curticei
was observed in sheep given 10,000 larvae. Experimental animals
with higher doses besides giving a lower rate of recovery showed inhibition
of development and stunted growth of worms.
Serum and intestinal mucus samples from infected animals were
tested for precipitating antibodies by gel diffusion against five
antigens. Antigens were prepared from first stage, second stage,
ensheathed third stage, exsheathed third stage larvae and exsheathing
fluid. Variable numbers of precipitin lines were obtained with serum
and mucus from infected sheep more than 6-7 months old. Sheep 2-3
months old showed no such response but did show evidence of an
acquired resistance to infection.