Keel bone fractures are more prevalent in White Leghorn hens than in Red Jungle fowl hens—A pilot study

Fractures and deviations to the keel bone are common in commercial laying hens, with reported variations in occurrence across strains and breeds. The aetiology is not fully understood, however, modern genetics and selection for efficient egg production has been claimed to be important factors for the keel bone fractures. To explore this further, we investigated keel bones from two different breeds, representing different degrees of selection for egg production: Red jungle fowl (n = 82), and White Leghorn (n = 32), where the latter is a selected laying breed which is the origin for many modern laying hen hybrids. Keel bones from a total of 116 birds, 53 hens and 63 roosters, were examined by necropsy at 80 weeks of age. All birds were raised in modified aviaries in the same holding facility. Overall, 24.5% of the hens had one or more fractures to the keel, with a difference in the prevalence between hens from the two breeds (p<0.01): 10% (95% CI: 3.7–24%) in the Red Jungle fowl hens and 69% (95% CI: 37–90%) in the White Leghorn hens. No roosters, regardless of breed, had keel bone fractures. Mild to moderate keel bone deviations were present in 54% (95% CI: 25–80%) of the hens and 4.7% (95% CI: 0.5–30%) of the roosters, all White Leghorns.

A Comparative Study of Pathology and Host Immune Response Induced by Very Virulent Infectious Bursal Disease Virus in Experimentally Infected Chickens of Aseel and White Leghorn Breeds

Indigenous breeds of young chickens in India are believed to be resistant to the classical strain of infectious bursal disease virus (IBDV). However, the mechanism underlying this resistance is obscure. Innate immunity is a key factor in defining the clinical course and pathology of microbial infections. The present study is aimed to compare the pathology of very virulent IBDV (vvIBDV) and immunological host response in experimentally infected - vaccinated and unvaccinated indigenous Aseel and commercial White Leghorn chickens. The viral loads and innate immune gene expression profiles of MDA-5, Mx, IFN-α, and IFN-β in different lymphoid organs were analyzed by quantitative PCR. The histopathological scores in Aseel birds were lower than in White Leghorns despite comparable viral loads. The degrees of histopathological lesions were fewer in vaccinated birds than in unvaccinated birds of both breeds. Analysis of innate immune response genes revealed that the cytoplasmic pattern recognition receptor MDA-5 gene was overexpressed mainly in the cecal tonsils of both vaccinated and nonvaccinated White Leghorn chickens. An increase in the expression of the IFN-α gene was seen in the cecal tonsils of Aseels, and an increase in IFN-β gene expression was seen in the thymuses of White Leghorns following vvIBDV challenge both in vaccinated and nonvaccinated birds. In addition, we observed that the Mx gene plays a minimal role, if any, in vvIBDV infection of the breeds under study. It remains interesting and important that although vvIBDV causes disease in indigenous Aseel birds, the faster clearance and reduced pathology of the virus in Aseel birds compared to White Leghorn chicken indicate some unidentified innate immune factors that are limiting IBDV in this breed. Further studies will be required to correlate kinetics of humoral and cellular immune response in relation to the virus load in different organs to illuminate the mechanism of genetic resistance in native breeds of chicken.

Comparing the innate and humoral immune responses of different chicken lines to Infectious Bronchitis Virus (IBV) infection

Infectious Bronchitis Virus (IBV) is a gammacoronavirus that is prevalent in commercial chicken flocks, resulting in characteristic clinical signs including snicking, rales, decreased tracheal ciliary activity, reduced weight gain and reduced egg production. Preliminary results indicate that there is a different clinical response to IBV infection in different chicken lines. Therefore, we aim to determine whether there is a differential innate or humoral immune response to IBV between chicken lines. A series of in vivo experiments were conducted comparing brown leghorns (Rhode Island Red, RIR (Roslin)) to white leghorns (from Valo and Ovagen). Trachea and bursa were collected from infected and control birds at four-, six- and fourteen-days post infection (dpi). There was a difference in snick rate and rales between the RIRs and the white leghorns (both lines). However, no difference was observed in ciliary activity. Viral load was determined by absolute quantification using qRT-PCR. The viral load in the trachea of RIRs was significantly lower (p<0.05) at 6 dpi compared to 4 dpi, unlike in Ovagen birds where there was no significant difference between the timepoints. Relative gene expression of IFN-α, IFN-β, IFN-γ, IL-6 and IL-1β in these tissues will be measuredby qRT-PCR. Serum was processed from whole blood collected at zero and ten dpi for use in IBV specific ELISAs which will measure antibody responses in the chicken lines. This project aims to explore immune responses against IBV as well as identifying the causes of variability in experimentation using chickens to investigate IBV infection.