Avian coccidiosis remains an economically important disease affecting the poultry industry worldwide. The dearth of information on haematological changes resulting from field cases of coccidiosis in commercial layer chickens necessitated this research. One hundred and twenty commercial layer chickens sampled from different farms in Zaria, diagnosed of coccidiosis at early, mid/peak and late production stages were used for this study. Results showed a significant (p < 0.05) decline in almost all haematological parameters (except for elevated MCV) of commercial layer chickens which were diagnosed of coccidiosis at the different production stages when compared to corresponding values of other apparently healthy layers that served as controls. The mean corpuscular volume (MCV) values in the layers diagnosed of coccidiosis at all production stages were significantly higher than the values obtained from the corresponding apparently healthy ones that served as control, whereas the MCHC showed significant decreases across all layer chickens diagnosed of coccidiosis at different production stages when compared to the corresponding values of the apparently healthy control layers. Thus, the erythrocytic indices of the layer chickens with coccidiosis showed the RBCs were macrocytic and hypochromic. On the basis of mean PCV, layer chickens at early production stage (PCV: 24.51 ± 3.17%) were most severely affected by coccidiosis, following closely by the layers at mid/peak production stage (PCV: 24.66 ± 1.64%). The highest mean WBC (19.15 ± 2.99 x109/L) was recorded in layers with coccidiosis at mid/peak production stage, which showed they were better in mounting inflammatory response when compared to the mean values of layers at early (14.92 ± 2.85 x109/L) and late (17.99 ± 2.70 x109/L) stages of production. In conclusion, coccidiosis in commercial layer chickens caused significant haematological alterations which could necessitate dietary supplementation to prevent occurrence of anaemia and decline in egg production
Key words: Coccidiosis, Haematological changes, Layer chickens, Production stages
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