Thesis Abstract

Tolerance to African animal trypanosomosis (AAT) among several animal species involves a wide milieu of factors which modulate the animal’s response to the disease and is considered a breed attribute. To investigate the effect of breed on tolerance/resilience to trypanosome infection on pubertal boars, nine (9) Nigerian Native and nine (9) Large-White x Landrace crossbreed boars were experimentally inoculated with laboratory samples of Trypanosoma brucei brucei. Their comparative responses with regard to clinical symptoms, growth parameters, histopathological and histometrical features of the testis, Sertoli and germ cell numbers and spermatogenic output including cell ratios and daily sperm production were studied over two study periods- 63 days post infection (63d p.i.) and 98 days post infection (98d p.i.). Results obtained indicated that infected boars of both breeds were clearly parasitaemic in the first study period, with a significant (P<0.05) reduction observed in the native boars by 98d p.i. The general trend in the results obtained showed significant (P<0.05) differences in the various parameters, with the Nigerian Native boars exhibiting strong marginal gains by the second study period. This was not the case with the exotic Large-White x Landrace boars and suggested that the native boars possessed a superior ability to mitigate the more severe effects of the pathology and a tendency to return to normal. With respect to the clinical features investigated, the Nigerian Native boars presented significantly (P<0.05) higher values with respect to parasitaemia log values, rectal temperatures, as well as packed cell volume. Histopathological findings revealed that lesions, including tubular distortion, denudation of basement membrane, seminiferous epithelial damage led to the distortion of the architecture of the seminiferous epithelium as well as degradation of the inter-tubular comrpartment and values were significantly (P<0.05) lower among the native boars. The parameters on growth showed the nutrient-parasite interaction was influenced by breed attributes. Biometrical and linear body measurements were affected significantly (P<0.05) less in the native boars than in the exotic boars. Weight loss was minimized among the native boars with a tendency to significantly (P<0.05) increase growth rate as during the second study period, whereas this trend was not clearly observed among the exotic boars. The effect of the infection on clinical and histopathological features, as well as growth responses and especially in relation to the testes’ capacity for spermatogenesis was studied. We observed significant (P<0.05) reductions in testes weight, somatic and germ cell populations and also significant (P<0.05) reductions in the overall kinetics of spermatogenesis and daily sperm production. The mechanisms of action implicated in breed responses to the pathology appeared to relate to phenotypic characteristics as well as innate mechanisms which are known to modulate the pathogenesis of trypanosomosis. Equally the lowered parasitaemia observed among the native boars suggested that toxicological effects of trypanosomes on this breed of boars were limited. It was concluded that the Nigerian Native boars possessed an attribute that could reverse the adverse patho-physiological effects of T. b. brucei infection and were therefore more resilient to T. b. brucei infection than the exotic Large-White x Landrace boars.

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