Evaluation of the meat quality of broilers subjected to heat stress, at 21 days of age

Introduction

Brazil, as many other countries, has great weather variations, resulting in temperature oscillations. Heat waves, resulting from global warming, happen at any time, directly affecting animal production, mainly the poultry industry, because birds are more susceptible to heat stress.
There are different types of agents capable of leading animals to a condition characterized by stress. Such agents include: mechanical (trauma, contention, surgery), physical (heat, cold, sound), chemical (drugs for disease treatments and growth and production stimulation) and psychological (management or environmental changes).
Factors such as age, sex, nutrition and mainly stress may affect the composition and the quality of animal carcasses. The concept of meat quality is quite complex and varies according to the features of each consumer, besides other variables which have to do with the nutritional composition, health, physical characteristics, presentation, packing and ease of use.
Hence, the bird''''s behavior under thermal stress conditions plays an important role in simulating real field conditions in different regions of the country. This study evaluates the effect of the bird''''s exposure to heat stress in the quality of meat from 21-day-old broilers.

Materials and Methods

The experiment was conducted in experimental chambers of the Poultry Sector, Animal Husbandry Department, College of Agrarian and Veterinary Sciences, CAV, UNESP, Jaboticabal Campus, SP, Brazil. Part of the animals (100 birds) were reared in a thermoneutral chamber during 21 days (control group). The remaining animals (400 birds), to be subjected to various periods of heat stress were housed in another chamber in which, during periods of stress, the chamber temperature was up-regulated to 32ºC.

Animals were subjected to heat stress during different periods i.e., 0, 24, 48 and 72 hours, according to the following treatments: T1 (controls)- birds reared in a thermoneutral temperature, up to 21 days, and not subjected to stress; T2 - birds reared at a thermoneutral temperature, up to 21 days, and subjected to heat stress during 24 hours; T3 - birds reared at a thermoneutral temperature, up to 21 days, and subjected to heat stress during 48 hours; T4 - birds reared at a thermoneutral temperature, up to 21 days, and subjected to heat stress during 72 hours.

At experiment completion, the birds were taken to the processing plant, observing welfare standards. After a resting period, the chickens were subjected to the flow diagram in the plant. After slaughter, the carcasses were submitted to the Animal Product Technology (TPOA) lab, FCAV/UNESP, Jaboticabal Campus.

After slaughter, the Pectoralis major muscle was removed then subjected to the following analyses: pH, color, and R value. The pH was determined by means of a direct muscle ion electrode, using a Digimed portable pH meter (model DM 21). The color was determined by means of a Minolta Chrome Meter CR-300, using the CIELAB (L, a* e b*) system. Finally, the R value was determined according to the methodology described by Honikel & Fischer (1977). A totally randomized design was used and the means and variables were compared using the AgroStat software.

Results & Discussion

Table 1, shows the pH results, as well as the R values of heat-stressed poultry meat. Color results are are shown in Table 2.

Table 1. pH means and R values in the meat of chickens subjected to heat stress

*Periods*	pH	*Value of R*
Control	Stress	Test F	Control	Stress	Test F
0h	5,61^Aa	5,61^Aa	0,75^NS	1,39^Aa	1,33^Aa	0,27^NS
24h	5,99^Aa	5,60^Ba	39,22**	1,12^Aa	1,04^Aa	0,35^NS
48h	5,63^Aa	5,54^Aa	0,11^NS	0,98^Aa	1,22^Aa	3,42^NS
72h	5,62^Aa	5,52^Aa	0,13^NS	1,08^Aa	1,15^Aa	0,34^NS
Test F		0,58^NS			1,84^NS

^{In the same column, means followed by the same low-case letters, do not differ (5%); In one line, means followed by the same capital letters do not differ; **(P<0,01); NS = Not significant.}

Table 1, shows that the group of birds subjected to heat stress, have lower pH values, when subjected to a 24-hour heat stress. This is highly significant when compared to the control group. Souza et al. (2010), found similar heat stress values in broilers, during summer time, when high temperatures also occur. When compared with the controls, the R values showed no significant differences.

Table 2. Color means of the meat from chickens subjected to heat stress

*Periods*	*Color L*	*Color a*	*Color b*
Control	Stress	Test F	Control	Stress	Test F	Control	Stress	Test F
0h	48,85^Aa	48,84^Aa	0,00^NS	2,91^Aa	2,91^Aa	0,00^NS	2,67^Aa	2,67^Aa	0,00^NS
24h	50,52^Aa	49,99^Aa	0,09^NS	3,39^Aa	3,05^Aa	0,27^NS	3,02^Aa	2,73^Aa	0,30^NS
48h	51,79^Aa	50,09^Aa	0,94^NS	4,21^Aa	3,83^Aa	0,36^NS	2,91^Aa	2,15^Aa	1,97^NS
72h	49,64^Aa	49,24^Aa	0,05^NS	4,78^Aa	4,35^Aa	0,44^NS	2,43^Aa	3,21^Aa	2,06^NS
Test F		0,24^NS			2,20^NS			1,27^NS

^{In the same column, means followed by the same low-case letters, do not differ (5%); In one line, means followed by the same capital letters do not differ; **(P<0,01); NS = Not significant.}

Table 2, shows no difference between the control group and the groups of birds subjected to heat stress. Nonetheless, when compared to the controls, lower yellowness (b) values are seen in the meat of broilers under heat stress during 24 and 48 hours. Fischer et. al. (2010), also found lower yellowness values (

Conclusion

Under conditions of this experiment, one can conclude that heat stress does not affect broiler meat quality, at 21 days of age.

Bibliography

Fischer PC, Brossi C, Golineli BB, Contreras-Castillo C. 2010. Qualidade de peito de frango submetido a estresse térmico agudo. Disponível em: www.usp.br/siicusp/Resumos/14Siicusp
/2996.pdf. Acesso em 24/01/2011.

Honikel OK & Fischer CA. 1977. A rapid method for the detection of PSE and DFD porcine muscles. Journal of Food Science 42(6):1633-1637.

Souza VLF, Buranelo GS, Gasparino E, Cardozo RM, Barbosa MJB. 2010. Efeito da automatização nas diferentes estações do ano sobre os parâmetros de desempenho, rendimento e qualidade da carne de frangos de corte. Acta Scientiarum. Animal Sciences Maringá 32(2):175-181.

Evaluation of the meat quality of broilers subjected to heat stress, at 21 days of age

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