The importance of preparation technique, culture media and incubation time in the embryonation of the infective egg stages of the intestinal nematode parasite Heterakis gallinarum was studied. Mature H. gallinarum worms were isolated from the caeca ofinfected chickens and separated by sex. In a first experiment intact female worms were kept for the development of their eggs in four different media (0.5 formalin, 2 formalin, 0.1 N sulphuric acid, 0.1 potassium dichro-mate) and incubated under constant temperature (20-22°C) for 2,4, 6 or 8 weeks. Afterwards the body of the worms were ruptured and the numbers of unembryo-nated and embryonated eggs were determined using a McMaster egg counting chamber, and the percentage of embryonated eggs wascalculated. After 8 weeks of incubation in 0.5 formalin, 0.1 N sulphuric acid or 0.1 potassium dichro-mate 27.6 , 26.7 and 29.4 of the eggs, respectively, embryonated into third stage larvae (p > 0.05). In contrast, incubation in 2 formalin resulted in an embryonation of 18.6 only (p < 0.05).In a second experiment H. gallinarum eggs were directly harvested from wormuteri and cultivated afterwards in different media (2 formalin, 0.1 N sulphuricacid, 0.1 potassium dichromate) at 20 to 22° C for 6 weeks.An incubation of isolated eggs in 2.0 formalin or 0.1 potassium dichromateduring 6 weeks resulted in a significantly higher percentage of embryonation incomparison to the incubation of intact worms (first experiment).The results suggest that preparation technique, media and time of incubation hasan essential influence on the development rate of H. gallinarum eggs.
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