Date of Graduation


Document Type


Degree Name

Doctor of Philosophy in Poultry Science (PhD)

Degree Level



Poultry Science


Billy M. Hargis

Committee Member

David Caldwell

Second Committee Member

Guillermo Tellez-Isaias

Third Committee Member

Christine Vuong

Fourth Committee Member

John R. Barta

Fifth Committee Member

Robert Beckstead


Histomonosis, Epidemiology


The incidence of histomonosis has been increasing in poultry since the ban of prophylactic and therapeutic compounds. Histomonosis is caused by the protozoa Histomonas meleagridis. The objective of this dissertation was to investigate factors impacting the pathogenesis and transmission of histomonosis and to evaluate compounds that could potentially prevent or reduce the severity of histomonosis in turkeys. In the first study, the effect of sodium chlorate and sodium nitrate on reducing histomonads growth was tested in vitro and added to a basal turkey diet. A decrease in the growth of histomonads in vitro was observed, but no in vivo effect was observed. The second study investigated the influence of Eimeria adenoeides, another cecal protozoan, on the pathology of histomonosis. In experiment 1, a reduction in the severity of histomonosis was observed with pre-inoculation of E. adenoiedes 5 days (day 15) before inoculation of H. meleagridis (day 20). In experiment 2, the same inoculation of E. adenoeides 5 days (day 14) before H. meleagridis (day 19) inoculation was adopted, in addition to inoculation of E. adenoeides 21 days before H. meleagridis (day 35); and inoculation of low doses of oocysts, every 2-3 days during the first three weeks, followed by inoculation of H. meleagridis (day 35). Histomonosis was not affected by the inoculation of E. adenoiedes in experiment 2. In the third study, diets with different compositions and nutritional densities and two different isolates of H. meleagridis and raising conditions were investigated in two pilot experiments and three validation experiments. In pilot experiment 1, one isolate of H. meleagridis (named Buford) was used. Turkeys were fed a low-nutrient density diet corn-soy based (LOW-CS) and raised on floor pens. In pilot experiment 2, another isolate of H. meleagridis was used (named PHL). Turkeys were fed a LOW diet with the addition of wheat middlings (LOW-WM) and raised on floor pens. In experiment 3, conducted on floor pens, both isolates and diets were used in different groups. In experiment 4, turkeys were raised on battery cages; only the PHL isolate was used. Both diets (LOW-WM and LOW-CS) were used, in addition to a diet surpassing the nutritional needs of young poults (turkey started, TS). In experiment 5, conducted in battery cages, only the PHL isolate was used, and the LOW-WM and TS diets were fed to different groups. From all experiments, HT was achieved only with the PHL isolate, with a transmission rate varying depending on the experimental diets. The TS diet had the lowest transmission rate in experiments 4 and 5. Higher variability was observed in the experiments conducted on floor pens. Variation was observed between experiments and within experimental groups. The complexity and multifactorial nature of histomonosis requires further studies.