Does early thermal conditioning sometimes fail to improve the resistance of broilers to heat stress?

Abstract

-Early age thermal conditioning (TC) by exposing young chicks to 40o C for 24 hours reduces body temperature (Tb) and improves long-term broiler resistance to heat stress. Three experiments were performed under semi-controlled tropical environmental conditions to evaluate the factors affecting TC efficacy. The addition of infrared bulbs during TC reduced growth and increased water intake compared to gas heaters at similar ambient temperatures (Ta). TC consistently reduced the Tb of chickens at 7 and 40 days of age independently of the heat source (-0.22 o C on average). During heat stress after 40 days of age, significant reduction in mortality was observed in the TC chickens when only gas heaters were used in the second experiment. The use of infrared bulbs during the first week of age never resulted in reduced mortality. The third experiment demonstrated late acclimatization when chickens were exposed to natural climatic conditions (Ta varying daily from 26 to 36 o C) compared to maximal Ta limited to 31 o C by air-conditioning from 30 to 40 days of age. Chickens exposed to natural climatic conditions had lower Tb (-0.16 o C) and resisted heat stress at 38 ± 2 o C at 41 days of age, although 12.6% of the air-conditioned chickens died. The TC effects were maintained on Tb in late acclimatized chickens but no differences in mortality due to TC occurred during heat stress. Inconsistencies between TC experiments arise from an imprecise definition of TC and heat stress conditions, and from the environmental conditions perceived by chickens after TC, which can induce late acclimatization. Persistent reductions in Tb after TC have been consistently measured but these might not be directly responsible for resistance to heat stress. Conversely, of the 525 heat stressed chickens studied during the 3 experiments, 64% of those who had a Tb lower than 40.8 o C at 4 days of age (prior to TC exposure) survived heat stress although only 47% of the chicks having a Tb higher than 40.8 o C at 4 days did. Further research is warranted on the Tb of newly hatched chicks. Résumé -L'acclimatation précoce échoue-t-elle parfois à renforcer la résistance des poulets de chair à un stress thermique chaud ? L'acclimatation précoce (TC) qui consiste à exposer des jeunes poussins à 40 o C pendant 24 heures, fait baisser la température corporelle (Tb) et améliore durablement la résistance des poulets de chair à un coup de chaleur. Trois expériences conduites dans un environnement tropical semi-contrôlé évaluent des facteurs de variation de l'efficacité de TC. Par rapport à une source unique de chaleur au gaz pendant TC, l'adjonction d'ampoules infra rouges a diminué la croissance et augmenté la consommation pour une même température ambiante (Ta). Quelle que soit la source de chaleur, Tb mesurée à 7 et 40 jours d'âge, était toujours diminuée par TC (-0,22 o C en moyenne). TC n'a réduit la mortalité pendant un stress thermique après l'âge de 40 jours que lorsqu'il était appliqué avec des éleveuses à gaz au cours de la seconde expérien...

Hematological parameters and productive performance of heat-stressed laying hens as influenced by early heat shock program, sodium bicarbonate and/or vitamin C supplementation

“…Heat exposure program (at 3-5 days of age, 4 and 8 weeks of age) might enhance thermo-tolerance of laying hens that would face severe heat stress in advanced or later ages (Yahav and McMurtry, 2001). These results agree with the results of Morsy (2013); Nagwa, Ahmed et al, 2004El-Moniary et al (2010); Zulkifli et al, 2003Zulkifli et al, & 2009De Basilio et al, 2002& 2003Faisal et al (2008);El-Badry et al (2009); Star et al (2009) and Mahmoud, Hanan (2006), they used heat shock exposure programs to acclimate birds to heat stress and enhance some physiological responses of birds.…”

“…Nowadays, heat shock exposure during earlier age (growth period) is unconventional procedure to increase thermo-tolerance and acclimate birds to heat stress which led to minimize heat-related mortality, improve productive performance and feed conversion and enhance immunity responses (Emam, 2013;Morsy, 2013;Nagwa, Ahmed et al, 2004El-Moniary et al, 2010;El-Badry et al, 2009;Star et al, 2009;Zulkifli et al, 2003Zulkifli et al, & 2009Faisal et al, 2008;Mahmoud, Hanan, 2006;Rahimi, 2005;De Basilio et al, 2002;Yalcin et al, 2001;Yahav and Plavnik, 1999;Yahav et al, 1997;Yahav and Hurwitz, 1996;Davis et al, 1991 andArjona et al, 1988). Emam (2013) reported that exposure of laying hens to heat shock program (40±1 °C for 4 h from 12:00-16:00 for 3 consecutive days) at 3 days and 8 weeks of age or at 3 days, 8 and 16 weeks of age (growth period) alleviated the negative effects of heat stress on productive performance of laying hens during egg production period.…”

Genotype Interaction X Seasons of the Year on Meat Production Characters on Campero Chicken

“…Se ha otoño, comportamiento de clara trascendencia documentado el impacto negativo del stress calórico económica. En términos de los caracteres a la faena, sobre la tasa de crecimiento y el consumo de alimento los valores observados son los habituales en este tipo en diferentes poblaciones comerciales de aves para de aves, informados en estudios previos (32) e carne (23,24,25,26) y se han informado independientemente del genotipo, las aves criadas en modificaciones de parámetros fisiológicos (27) de primavera si bien presentaron menor peso corporal síntesis proteica y de grasa periférica subcutánea en registraron mayor proporción de pata-muslo, esas condiciones (28). depusieron menor proporción de grasa y presentaron mayor rendimiento a la faena.…”

Summer ventilation of poultry house for chicken fattening in CFD modelling

“…If the relative humidity is out of the ideal range of 60 to 70 %, the temperature within the hall needs to be adjusted. For example, if RH is near 50 %, the temperature has to be increased to 33 ºC on the first day [8]. In all stages of growth of the chicken we have to observe and ensure that chickens perceive appropriate temperature [9].…”