Effect of temperature on survival of free-living stages of Haemonchus contortus.

One percent or more unembryonated eggs of Haemonchus contortus survived in sheep fecal pellets less than 0.5 hour at -95 C, 2 hours at -28 C, 1 hour at -10 C, 4 days at 4 C, and 1 hour at 45 C. One percent or more embryonated eggs survived 1 hour at -95 and -28C, 12 hours at -10 C, 64 days at 4 C, and 12 hours at 45 C. Over half the unembryonated and embryonated eggs survived only 1 and 4 days, respectively, at 4 C. One percent or more 1st-stage larvae did not survive 0.5 hour at -95 C but did survive 0.5 hour at -28 C, 8 hours at -10 C, 16 days at 4 C, and 1 hour at 45 C. Less than 1% of 2nd-stage larvae survived up to 2 days at -95 C; all were dead by 4 days. Second-stage larvae survived 32 days at -28 C, 8 days at -10 C, 64 days at 4 C, and 2 hours at 45 C. One percent or more 3rd-stage larvae survived 256 days at -95 C, 16 days at -28 C, 32 days at -10 C, more than 256 days at 4 C, 128 days at 20 C, 64 days at 25 and 35 C, and 4 days at 45 C. Thus, the increasing order of survival was unembryonated eggs, 2nd-stage larvae, 1st-stage larvae, embryonated eggs, and 3rd-stage larvae.