PHOTOPERIODIC MODULATION OF CIRCADIAN OSCILLATIONS OF IMMUNE PARAMETERS OF BROILER CHICKS DURING BROODING PHASE: IMPLICATIONS FOR IMMUNE FUNCTION AND HEALTH.

Abstract

An experiment was conducted to study the effect of photoperiod on the circadian rhythms of immune cells/organs of broiler chicks during brooding. A total of Forty-eight clinically healthy day-old broiler chicks were assigned to two groups; continuous lighting (CL) and restricted lighting (RL). Extended lighting was provided in CL group using LED bulbs at dawn (18.00 h) till dusk. At day-15 of brooding, four broiler chicks from each group were randomly selected, weighed, humanely slaughtered and 3.5mL of blood collected at five-hour intervals over a 24 h period. The bursae of Fabricius and spleens were harvested from the sacrificed broiler chicks and weighed. The data generated were analysed (Student T-Test) and the Single cosinor application®. The results from haematology and lymphoid organs did not show any significant (P > 0.05) differences in both groups. However, the analyzed results from the Single cosinor application® showed the mesors, amplitudes and acrophases in the CL group for heterophil and lymphocyte to be; 26.6 ± 3.50 %, 7.3 %, 09.10 h; 70.0 ± 3.97 %, 6.0 %, 19.7 h and for RL group as 26.0 ± 1.06 %, 0.4 %, 02.30 h; 68.0 ± 3.80 %, 9.7 %, 13.20 h, respectively. It was concluded that CL delayed the acrophases of the heterophils and lymphocytes (early photophase and scotophase), respectively, while the acrophases of heterophil and lymphocyte were restricted to the late scotophase and mid-photophase in the RL group. These findings show that continuous lighting disrupts rhythm of immune cells which may lead to poor immune response and disease resistance in brooded broiler chicks