Comparison of two techniques for quantitation of encysted cyathostome larvae in the horse

Haustral portions of intestine of 6 horses were isolated by excising the taeniae coli from the cecum and the ventral colon. Uniform 5-cm X 5-cm sections were cut from the haustra and were illuminated from the serosal side with a strong light source (mural transillumination). Cyathostome larvae encysted in the mucosa and submucosa were observed at 15 X magnification and counted. Two separate counts of the larvae in 80 replicates of tissue by the mural transillumination technique (MTT) revealed no significant (P less than 0.05) difference between sample means. Larvae in tissue sections were counted in situ by MTT, and the mucosal scrapings of the tissue sections were digested in pepsin and HCl to determine larval yields for comparison with the MTT counts. Numbers of larvae recovered by pepsin and HCl digestion for 3 and 6 hours were significantly (P less than 0.01) lower than were numbers originally determined by MTT. Larvae recovered by tissue digestion for 3 or 6 hours were examined individually and given objective scores for morphologic damage. Distribution of scores was time-dependent; increased damage to larvae was associated with a longer time of digestion. Individual 4th-stage cyathostome larvae were dissected from cysts in the large intestinal wall and were incubated in water, 0.9% saline solution, 1.1% HCl, or pepsin (7,000 U of activity/ml). Significantly fewer (P less than 0.05) larvae were recovered from all solutions after 3 and 6 hours. The proportion of dissected larvae that were given high scores after exposure to pepsin was significantly (P less than 0.01) greater than were those held in HCl, saline solution, or water for both periods.