Studies on Cooperia curticei (Ransom 1907) a nematode parasite of sheep : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy

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Massey University
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This thesis records in part I studies on the ecology of the free living stages of Cooperia curticei , both under controlled and natural conditions. 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 evaporation. 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.
Cooperia curticei, Nematodes, Sheep parasites