Animal Science and Technology


Petersson, Katherine

Advisor Department

Fisheries, Animal, and Veterinary Science




Haemonchus contortus; exsheathment; season


Small ruminant farmers have a constant battle with infections of gastrointestinal nematode (GIN) within their grazing sheep and goats. Haemonchus contortus, more commonly called the barber pole worm, is the most pathogenic parasite that feeds on blood, eventually causing anemia and weight loss, and even death. Ruminants have a four-chambered stomach consisting of the reticulum, rumen, omasum, and abomasum. The life cycle of H. contortus begins in the abomasum where the adult worms reside and reproduce, and the resulting eggs are shed out in the feces. The eggs hatch to yield larvae, which grow to the infective third stage (L3). The H. contortus L3 are consumed by grazing sheep and goats. The L3 have a protective sheath covering that must be shed within the rumen in order for the larva to continue development into adults within the abomasum. The shedding of the sheath is called ‘exsheathment’ and is a critical part in the life cycle of H. contortus. Haemonchus contortus have become increasingly resistant to the chemical dewormers (anthelmintics) commonly used to control infections. Increasing anthelmintic resistance in these GIN creates a need for alternative methods of GIN control. Plant secondary compounds have demonstrated anti-parasitic activity and are currently the focus of many studies. Stored larvae are commonly utilized in in vitro and in vivo assays of plant secondary compounds. Although researchers typically do not use L3 that have been stored longer than three months, the effect of season on the viability and exsheathment of stored L3 is unknown. The objective of this study is to determine the effect of season on in vitro and in vivo exsheathment efficacy of stored H. contortus L3. Four donor rams were infected with 10,000 H. contortus L3 on the autumn equinox (fall, n=2) and on the winter solstice (winter, n=2). After the infection reached maturity (~ 4 weeks), fecal matter was collected and cultured for 10 days and the resulting L3 were harvested and stored at 4°C until assay. Each month, the larvae were artificially exsheathed in vitro using CO2 exposure and naturally exsheathed in vivo by the direct placement of ensheathed L3 into rumen fistulated ewes. The average exsheathment over six months for the in vivo and in vitro monthly assays of fall infection was 70 ± 4 (mean ± SEM) and 60 ± 4 respectively. The average exsheathment over three months for the in vivo and in vitro monthly assays of the winter infection was 63 ± 4 and 43 ± 4 respectively. Statistical analysis of the data is pending.