Studies on Acquired Immunity to Nematodirus battus Infection in Lambs

Ali, Daud Ahmad Israf (1995) Studies on Acquired Immunity to Nematodirus battus Infection in Lambs. PhD thesis, University of Glasgow.

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Several experiments were conducted using housed sheep with the aim of obtaining information regarding the immune response of young lambs to Nematodims battus infection, the influence of protein supplementation and the persistence of the response. Field observations were conducted also over a two year grazing period to determine the seroepidemiology of natural infections using an ELISA developed against worm antigens. Prior to commencement of the main housed experiments, the results of a preliminary trial conducted by Dr.W.D.Smith prior to commencement of this PhD research project were evaluated to assess the kinetics of worm loss following a single infection of N.battus, essential information before 'trickle infection-challenge' experiments can commence. Four groups of young lambs were infected with a single dose of 30,000 L3 and each group was killed after 7, 14, 21 or 28 days post-infection (PI). The worm burdens were significantly reduced in number after 28 days PI. Individual variation in burdens was evident after 21 days PI and therefore, in view of these findings, lambs in future experiments were killed at 9 or 10 days post-challenge (PC) to minimize between animal variation. The housed 'trickle infection-challenge' trials followed a standard infection regime. Lambs were infected with escalating doses of L3 over several weeks, treated with anthelmintic and challenged with a single dose of 30,000 L3 a week later. Challenge controls did not receive a primary trickle infection. All groups were killed on either day 9 or 10 PC to obtain worms, blood and intestinal tissue. Blood samples were taken frequently throughout the primary infection period for peripheral blood eosinophil counts and antibody level determination. Two trials were conducted to assess the influence of supplemention of an adequate basal diet with a rumen bypass protein (fish meal). Both had a similar design except for differences in the levels of dietary protein, the age of lambs and the duration of infection. Previously infected and challenge control groups were offered either a basal diet (trial 1, 132 g CP kg-1 DM; trial 2, 125 g CP kg-1 DM) or a supplemented one (trial 1, 183 g CP kg+ DM; trial 2, 178 g CP kg-1 DM CP). The results of both trials showed trends for enhancement of responsiveness without significant effects. Previous infection significantly enhanced immunity as characterized by reduced worm size and burdens, elevated antibody levels, increased numbers of tissue mast cells and eosinophils. Supplementation significantly enhanced antibody but not inflammatory responses. Re-analysis of the results showed that lambs could be segregated into high- and low- responders based on their worm burden. However, the degree of responsiveness was not reflected in the inflammatory and antibody responses studied. A trial was conducted to determine the persistence of the immune response described in the dietary trials. Six groups of lambs (3 infected, 3 challenge controls) were subjected to the standard design outlined above. An infected and control group was challenged either one, 6 or 12 weeks post-treatment and killed 10 days PC. The results showed an ability to respond without antigenic stimulus for up to 12 weeks which was expressed by retardation in development of the worm populations and also by worm expulsion. Field trials were conducted over a two year grazing period to determine any difference in serum anti-worm antibodies of lambs and ewes and whether this could be correlated to developing immunity. The use of serum fructosamine concentration as a general index of gastrointestinal damage was also investigated. The results showed that antibody responses of ewes were maintained at high levels throughout the grazing period with no indication of a periparturient relaxation in immunity. Lambs developed increasing antibody levels over time and the FEC declined when the peak levels were reached. However, lamb antibodies were significantly lower in comparison to ewes. Serum fructosamine was not altered despite periods of clinical nematodirosis.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Additional Information: Adviser: Bob Coop
Keywords: Veterinary science, Animal diseases, Parasitology
Date of Award: 1995
Depositing User: Enlighten Team
Unique ID: glathesis:1995-74644
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 13 Nov 2019 15:58
Last Modified: 13 Nov 2019 15:58

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