THERMO-TOLERANCE OF TWO BREEDS OF COMMERCIAL BROILER CHICKENS USING THE HETEROPHIL-LYMPHOCYTE RATIO

Abstract

Two hundred and thirty-two (232) four weeks old broiler chickens were housed in two separate pens of 116 birds (52 Cobb 500 and 64 Ross 308) per pen in a split-plot experimental design. Each breed served as a treatment that was replicated 4 times, with 13 Cobb 500 and 16 Ross 308 chickens per replicate. The two pens were labelled controlled (40±1ºC) and natural (32.54ºC) heat-stress pens. Controlled heat stress was induced throughout the experiment (4 to 8 weeks of age) by increasing the temperature of the pen to 40 ± 1ºC for four hours daily (11:00am to 3:00pm). The controlled heat stress condition that was applied in this study was an attempt to mimic the increase in atmospheric temperature that is expected in the next seven decades in the study area due to climate change. Haematological traits measured included Heterophils (H), Lymphocytes (L) and Heterophils-Lymphocytes ratio (H:L). Data obtained were analyzed using the General Linear Model procedure of Statistical Analysis System and means separated by Tukey Test. Significant (p<0.05) breed differences were observed for H, L and H:L with Cobb 500 having the lowest and the best values for H:L in both the natural (0.52) and controlled (0.80) heat stress condition. The results of this study showed better thermo-tolerance of Cobb 500 chickens compared to Ross 308 across the heat stress conditions as it recorded lower values for H:L. Therefore, Cobb 500 is the most suitable breed for rearing till 8 weeks of age under the present-day climatic extremes (heat stress) and that of the next seven decades.