Plasma protein loss in lambs during a mixed infection of T colubriformis and T circumcincta - a consequence of the immune response? A dissertation submitted in partial fulfilment of the requirements for the Degree of Bachelor of Agricultural Science with Honours at Lincoln University

Abstract

Immuno-suppression has been shown to prevent the production losses observed during infection with gastro-intestinal nematode parasites. However, it is not known if this is due to nutrient partitioning on behalf of the animal or if it is a consequence of reduced physical damage resulting in a reduction in plasma protein leakage. The trial examined the effect of immune-suppression on the plasma protein losses in lambs infected with a concurrent infection of Trichostrongylus colubriformis and Telodorsagia circumcincta. Eight parasite naive 6-month-old lambs were given either a mixed infection of the abomasal parasite Telodorsagia circumcincta and the intestinal parasite Trichostrongylus colubriformis for 42 days (group IF, n=4), or were similarly infected while concurrently receiving weekly injections of 1.3mg methylpredisolone acetate/kg live weight in order to suppress immune function (group ISIF, n=4). Plasma protein loss was measured over a seven day period at 13 days pre-infection, and again at day 35 post infection. Dry matter intake, live weight, faecal egg concentration, plasma albumin concentration and total plasma protein concentration were measured weekly. Faecal egg counts increased to 1520 and 4069 eggs/g on day 41 in IF and ISIF sheep, respectively, indicating immuno-suppression treatment of ISIF animals was successful. Voluntary feed intake of the IF lambs was reduced by 18% and 24% on days 28 and 35, of infection, respectively, compared with the ISIF lambs, (P<0.05), however, this did not result in differences in live weight between the two groups. Despite treatment Faecal egg counts increased to 1520 and 4069 eggs/g on day 41 in IF and ISIF sheep, respectively, indicating immuno-suppression treatment of ISIF animals was successful. Voluntary feed intake of the IF lambs was reduced by 18% and 24% on days 28 and 35, of infection, respectively, compared with the ISIF lambs, (P<0.05), however, this did not result in differences in live weight between the two groups. Despite treatment having no effect on total blood protein concentration, plasma albumin concentrations decreased in both groups following infection, although at a greater rate in the IF animals. Plasma protein loss at day 35 was elevated by 310% and 258% in IF and ISIF groups (P<0.05), respectively, compared to day -15, and was not affected by immuno-suppression. In conclusion, immune-suppression failed to significantly affect the occurrence or extent of plasma protein loss during a mixed infection of T colubriformis and T circumcincta in 6-month-old lambs in the current trial. This suggests that mechanical damage by the parasite is responsible for the intestinal pathology of infection and subsequent leakage of plasma proteins, rather than the immune response, as hypothesised.