Abstract
The aim of the study was to evaluate the effects of strain and stocking density on heat tolerance of broiler chickens. A total of 318-day-old broiler chicks of two commercial strains, Cobb 500 and Ross 308, were used in a 2 x 2 factorial experiment arranged in a Completely Randomized Design (CRD) with three replicates per treatment. The two stocking densities investigated were low density (18 birds per replicate) and high density (35 birds per replicate). Data were collected from day 1 to day 56 on body weight, rectal temperature (°C), pulse rate (beats/min), respiratory rate (breathes/min). Data collected were subjected to Two-way Analysis of Variance using the IBM SPSS Version 25.0, and significant means were separated using Duncan's Multiple Range Test at 5% level of significance. Results showed that strain had a significant (P<0.05) effect on pulse rate, with Ross 308 recording a significantly (P<0.05) higher pulse rate (51.46±0.17 beats/min) compared to Cobb 500 (50.51±0.17 beats/min). The interaction was significant (P<0.05) for pulse rate. Cobb 500 birds at low density had significantly (P<0.05) lower pulse rate (49.94±0.28 beats/min) compared to Cobb 500 birds at high density (51.08±0.21 beats/min) and Ross 308 birds at both density levels. It can be concluded that Ross 308 exhibited a significantly higher pulse rate than Cobb 500. Cobb 500 strain is recommended for broiler production in hot environments due to its better physiological response to heat stress. Lower stocking density is advisable, as it tends to reduce physiological stress.