Proceedings of the World Congress on Genetics Applied to Livestock Production, 884 Investigation of Genetic Resistance to Newcastle Disease in Local Chickens in Tanzania using Natural Challenge by Field Velogenic NDV Strains A.P. Muhairwa 1* , G.C. Chiwanga 1 , J.R. Mushi 1 , P.L.M Msoffe 1 , E.N. Amuzu-Aweh 2 , J. Dekkers 3 , R. Gallardo 4 , S.J. Lamont 3 , T. R. Kelly 5 , and H. Zhou 6 1 Sokoine University of Agriculture, Morogoro, Tanzania * apm@suanet.ac.tz (Corresponding Author) 2 Department of Animal Science, University of Ghana, Ghana 3 Department of Animal Science, Iowa State University, Ames, IA 50011, USA 4 School of Veterinary Medicine, University of California, Davis, 95616, USA 5 One Health Institute, University of California, Davis, 95616, USA 6 Department of Animal Science, University of California, Davis, 95616, USA Summary Genetic resistance to Newcastle disease among three ecotypes of Tanzanian local chickens, Ching’wekwe, Kuchi and Morogoro MEDIUM was investigated by natural challenge with endemic velogenic strains of Newcastle disease virus (vNDV). The study was designed to determine variations in susceptibility and response to NDV among the three ecotypes. Naturally NDV-infected seeders were introduced into flocks of susceptible chickens under a controlled environment. For each bird, body weights were measured at 0, 7, 9, 11, 13, 15, 17, and 25 days post-exposure. Flock mortality was assessed every 8 hours for the first three days and then every 12 hours thereafter until 29 days post-exposure. Date and time of death was recorded, and post-mortem examinations performed for each dead chicken. Lesions on the trachea, proventriculus, intestines, and caecal tonsils were scored for severity ranging from 0 to 3. Linear models were used for survival days, post-exposure growth rate and average lesion score. Preliminary results indicate that post-exposure weight reduction in Ching’wekwe was significantly less than in Morogoro Medium and Kuchi. No significant differences were observed in the lesion scores and survival times among the three ecotypes after exposure. More data is being collected for more comprehensive analysis. Keywords: Newcastle disease, innate resistance, natural infection, local chicken ecotypes Introduction Poor husbandry and diseases limit village scavenging chicken production in Africa, thus significantly compromising income generation and a source of protein to the growing population. According to Kitalyi et al. (1998), Newcastle disease (ND) accounts for more than 80% mortality among village chickens. Preserving the village chicken population by preventing ND, is envisaged to be the first step in improving productivity and commercial value of local chickens in Africa, this is because outbreaks of ND can decimate all unvaccinated chickens in the village. Given the diversity of local chickens, it is of interest to know how the different ecotypes cope with the disease and to select for strains of chickens that can survive NDV infection. Cole and Hutt (1961) provided one of the earliest known associations between animal genetics and disease resistance by showing existence of innate resistance to Newcastle disease, however, limited studies with modern genetic tools have been made. Initial investigations by Msoffe et al. (2001) provided insights on variations in susceptibility to disease among local ecotypes in Tanzania. This study was designed to compare susceptibility and response to NDV of three common ecotypes of chickens namely Ching’wekwe (Ching), Kuchi and Morogoro medium (MoroMed).