EFFECT OF THERMAL CONDITIONS ON WELFARE OF BROILER CHICKENS OF DIFFERENT ORIGIN (original) (raw)

the objective of the study was to determine the effect of the stress factor of elevated air tempera- ture during the second rearing period on health, duration of tonic immobility, blood corticosterone levels and heterophil to lymphocyte ratio in commercial broilers representing three commercial lines. day-old hybro, hubbard flex and ross 308 broiler chickens were assigned to 6 groups. in the experimental groups, birds were exposed to elevated air temperature (30°c) in the rear- ing area from 30 to 34 days of age (4 days), and to standard thermal conditions (20–18°c) from 34 to 42 days of the experiment. the control groups consisted of broilers maintained throughout rearing under standard thermal conditions, with the air temperature of 31–33°c during the first days being gradually decreased to 20–18°c at 6 weeks of age. broiler mortality was monitored in all the groups throughout the experiment. the concentration of plasma corticosterone was deter- mined at 30, 34 and 42 days of the experiment in 7 birds from each group. blood smears were also performed to count lymphocytes (l) and heterophils (h), which made it possible to determine the h:l ratio. at 30, 34 and 42 days of the experiment, the duration of tonic immobility (ti) was exam- ined in 7 birds from each group. the thermal factor applied in the second rearing period elicited a stress reaction in the chickens of all lines, as indicated by the increased level of blood corticos- terone. however, ross 308 broilers were less tolerant of reduced welfare levels associated with elevated air temperature compared to hybro and hubbard flex broilers, as evidenced by higher mortality, the highest increase in blood corticosterone, longer duration of ti, as well as increased heterophil to lymphocyte ratio after the thermal factor was applied. the results of the present experiment show that ross 308 chickens are probably the least suitable for rearing during the summer production cycles.

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