Development and evaluation of an in vitro larval establishment test for Telasordagia circumcincta infections in sheep: A dissertation submitted in partial fulfilment of the requirements for the degree of Bachelor of Agricultural Science with Honours

Abstract

Four trials were conducted to develop and evaluate an in vitro larval establishment test to examine the ability of abomasal tissue to reject establishment of L3 Teladorsagia circumcincta larvae. In the first trial, four mature ewes were drenched and housed and withheld from exposure to gastrointestinal nematode parasites for 75 days. Ewes were then slaughtered and abomasa removed. Tissue (20X20mm) was selected from the fundic, and pyloric ends of the abomasum and also from mid way in between and challenged in vitro with 1200, 2100 or 3200 exsheathed L3 infective T. circumcincta larvae. Tissue was 'rinsed' and then vigorously 'washed' with warm physiological saline before digestion. The solution of 'rinse', 'wash', and 'digest' for each tissue sample was then collected and the number of larvae present in each sample counted. Rejection percentage was calculated by adding the 'rinse' and 'wash' fractions and dividing by the total number of larvae found, which was then multiplied by 100. Rejection did not differ between region with the addition of 1200, viz, 35.3, 24.9 and 29.5% or 2100 larvae, viz, 22.0, 31.8 and 22.6%, for fundic, mid and pyloric tissue, respectively, (p>0.05). Rejection when 3200 larvae were added was greater in the fundic, viz, 53.8%, than mid or pyloric regions, viz, 21.4 and 28.3%, respectively, (p<0.05). The results of trial 1 indicate there is no difference in origin of tissue when 1200 or 2100 larvae are added to animals with low immune ability, however at high concentrations rejection in the fundic tissue may be impaired. It is concluded that 2100 larvae added (held at 4200 m⁻¹ to tissue taken from the folds of either the fundic or mid region is most suitable.