The role of preparation technique, culture media and incubation time for embryonation of Heterakis gallinarum eggs

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 of infected 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 dichromate) and incubated under constant temperature (20-22 degrees C) for 2, 4, 6 or 8 weeks. Afterwards the body of the worms were ruptured and the numbers of unembryonated and embryonated eggs were determined using a McMaster egg counting chamber, and the percentage of embryonated eggs was calculated. After 8 weeks of incubation in 0.5% formalin, 0.1 N sulphuric acid or 0.1% potassium dichromate 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 worm uteri and cultivated afterwards in different media (2% formalin, 0.1 N sulphuric acid, 0.1% potassium dichromate) at 20 to 22 degrees C for 6 weeks. An incubation of isolated eggs in 2.0% formalin or 0.1% potassium dichromate during 6 weeks resulted in a significantly higher percentage of embryonation in comparison to the incubation of intact worms (first experiment). The results suggest that preparation technique, media and time of incubation has an essential influence on the development rate of H. gallinarum eggs.