Two experiments were carried out to investigate the effect of varying levels of black seed (Nigella sativa) powder supplementation on performance, thermoregulatory performance, blood profile and histopathology of broiler chickens during hot season. The first experiment had a total of 180 one week old broiler chicks which were randomly assigned to four treatments.

 The birds in each group were further divided into three (3) replicates with 15 chickens in a completely randomized design (CRD). Birds in all the treatment groups were fed same diet for the starter phase and then supplemented with Nigella sativa powder at 0, 5, 10 and 15 g/kg of diet to the end of 4weeks, on the last day the growth performance, thermoregulatory parameters and the haematology were investigated. Also at the finisher phase the same diet was given to all the treatments with the same design and supplementations were varied at 0, 10, 20, and 30g/kg for treatment 1 to 4 respectively. Results of the first experiment showed that supplementation of Nigella sativa in hot season significantly (P<0.05) increased the final body weight, weight gain and daily weight gain with decreased mortality as in the supplemented groups compared to the control. Also both the thermoregulatory parameters and the Haematological parameters were better in the supplemented groups compare to the control. In the second experiment the results of the performance showed better final weight and relative weight of the liver, gizzard, proventriclus, spleen, kidney and the thymus compared to the control. 

Thermoregulatory parameters measured at the end of 8weeks showed significant (P<0.05) decrease in both the body temperature and the respiratory rate on the supplemented groups compared to the control. Haematological parameters also indicated significant (p<0.05) for PCV, Hb, WBC and RBC of while Total protein, albumin and globulin showed no significant difference at (p>0.05). The histopathological findings clearly depicts no toxic effect as all tissues were not distorted. In conclusion, black seed can be supplemented to broiler chickens during hot season to improve performance, thermoregulation, and blood profile without any detrimental effect to broiler chickens as shown by the Histopathology.