Reactions of calves to infestation with the stomach worm, Haemonchus placei (Place, 1893) Ransom, 1911

摘要: Studies aimed a t determining the factors responsible for haemonchosis in cattle are reported. Observations on natural populations of Haemonchus placei confirmed conclusions Roberts, O'Sullivan, and Riek (1932) acquisition resistance to this species relationships peak egg counts age animal season year. Most 400 calves which these observations were based developed strong suffered no apparent ill effects; others only became resistant after suffering clinical haemonchosis; about 8 per cent. either failed develop or lost it died. Experiments with single doses, spaced continuous doses larvae showed that H. has comparatively short patent period. The trend assumed by counts, irrespective method infestation, was very similar, reaching its 6th 10th week thereafter rapidly declining remain low levels. Calves 12 : 1 mixture oaten lucerne chaff gave much higher than good quality alone, but infestations did not vary their persistence. A acquired, even from dose larvae. This shown failure test larvae, administered count had been at levels some weeks, cause any increase count; presence, several weeks later autopsy, relatively few adult worms, most undersized females containing eggs. There also numerous fourth stage evidently persisted many weeks. That so immature worms occurred animals may signify young stages could be extremely important epidemiology haemonchosis. "Selfcure", as defined Gordon (1948) contortus sheep, produced experimentally cattle, trends suggest type reaction sometimes occur among before is finally acquired. Circulating antibodies detected infested animals. They found, however, mixed species, probable latter case they associated rather Trichostrongylus Haemonchus. Data relation number female present strongly whilst remains susceptible usually an accurate index degree when occurs little value purpose.