Measuring the Responses of Different Genotypes of Slow Growing Broilers Toward Short-Term Heat Challenge Test

Abstract

This study was perfonned to evaluate the responds of different genotype of slow growing broilers with regard to heat stress. A number of 102 females from the slow growing broiler hybrids (Hubbard ISA 1657, S757N and 1957) were raised from hatch until week 5 in 3 pens under the same room temperature of 30°C beginning from week 3 until 5. Twenty four experimental birds of each genotype were individually exposed for 15 minutes to a short-tenn heat test at 30°C (control) and 35°C between weeks 3, 4, and 5. The rectal temperatures before and after heat exposure were measured and the latency until panting was recorded. Strain differences were significant for body weight, daily weight gain and relative growth rate (P<0.01). For 1657, S757N and 1957, respectively, body weight in week 5 averaged 815.8±81.2, 924.0±87.9 and 1269.3±136.3 g. Daily gain averaged 22.0±9.8, 25.5±13.1 and 34.9±17.6 g/d, whereas relative growth rate ranged between 11.5±5.5, 13.9±6.9 and 13.0±6.1 %. Rectal temperatures after short-term heat stress were 42.4±0.7°C, 42.4±0.7°C and 42.7±0.7°C, with strains differing significantly (P<0.01). The level of heat stress temperature significantly influenced latency until panting (P<0.01). When e~posed to 35°C, birds started panting within 10.95±2.43 (1657), 12.26±2.61 (S757N) and 10.16±2.36 (1957) minutes. The chi-square analyses revealed significant influences of the heat level and the strain on the frequency of birds panting (P<O.O 1 ). After 35°C test, 96% (1657). 100% (1957) and 67% (S757N) of birds demonstrated panting (P<0.01), while strain differences were not significant for frequency of birds panting exposed to 30°C.