Ascorbic acid and citric flavonoids for broilers under heat stress: effects on performance and meat quality

Ascorbic acid and citric flavonoids for broilers under heat stress: effects on performance and meat quality

Peña JEM; Vieira SL; López J; Reis RN; Barros R; Furtado FVF; Silva PX

Departamento de Zootecnia, Universidade Federal do Rio Grande do Sul. Porto Alegre, RS, Brasil

^{Mail Address}

ABSTRACT

The aim of this study was to evaluate the effects of increasing doses of ascorbic acid (AA) and citric flavonoids (quercetin and rutin) on the performance and meat quality characteristics of broilers submitted to cyclic heat stress. Four-hundred one-day-old female Ross 308 were housed in 40 battery cages a in temperature controlled room. Treatments consisted of 0, 250, 500, and 1000 g/ton on of AA + citric flavonoids. Birds were fed ad libitum until 32 day of age. Beginning on day 14 post-hatch until the end of the experiment, in order to simulate cyclic heat stress, the temperature inside the room was increased to 32°C for 5 hours, and decreased until reaching the comfort temperature corresponding to the age of the animals. Birds were slaughtered at 33 days of age, and carcass and commercial cuts yields were determined. Thighs and boneless breast samples were collected and frozen for subsequent analyses of pH, cooking loss, shear force, color, and Thiobarbituric Acid Reactive Substances (TBARS). Significant differences (p <0.05) were found for feed efficiency from 1 to 7 days of age, with the best values for the birds fed 0 and 250 g/ton on of AA + citric flavonoids. At the end of the experiment, there were no differences in other performance variables, carcass and parts yields, pH, shear force, color and TBARS. The meat of the birds supplemented with 250 g/ton on of product presented the lowest cooking loss.

Keywords: Ascorbic acid, broiler, heat stress, flavonoids.

INTRODUCTION

Poultry production in tropical countries is affected by the combined effects of high environmental temperature and humidity during most month of the year. As the ratio between humidity and environmental temperature exceeds the thermal comfort zone, birds become more susceptible to heat stress, which negatively influences performance and the efficiency of the immune system (Thaxton & Siegel, 1970; Borges et al., 2003).

During stress, body and immune system cells undergo enzymatic or self-oxidative peroxidation through actions that involve free radicals, oxygen-reactive species, resulting in destabilization of the cell wall, and consequently, cell function loss (Puthpongsiripom et al., 2001). Excessive levels of free radicals may lead to lipid peroxidation, leading to several pathologies in the animals, and affecting meat organoleptic characteristics (Silva et al., 2002; Fellenberg & Speisky, 2006).

The use of several dietary alternatives has been recommended to alleviate of high environmental temperature impact, such as changes in feeding and drinking water management. In addition, dietary nutritional changes, including replacing carbohydrates by lipids or reducing crude protein level, and the use of salts and additives in the drinking water have shown positive effects (Dale & Fuller, 1978; Mendes et al., 1997; Borges et al., 2003).

The use of traditional antioxidants, such as ascorbic acid (AA) has been recommended, and, in some cases, has presented promising effects in the attenuation of heat stress on performance (Stilborn et al., 1988). Alternatively, some compounds with antioxidant activity, such as flavonoids, may also be beneficial. Flavonoids (quercetin and rutin) are obtained by the fermentation of citrus, and polyphenolic substances widely distributed in plants. Many biological effects have been attributed to flavonoids as they may act as antioxidants in the liver and protector of blood vessels (Silva et al., 2002; Tieppo, 2007). According to Bianchi & Antunes (1999), the combined use of antioxidants can reduce the effects of stress due to its oxi-reduction properties, which may have an important role in free radical quenching and neutralization, in addition to improving meat organoleptci characteristics and quality (Peterson & Dwyer, 1998).

The present study aimed at evaluating the effect of increasing AA and citric flavonoid doses on live performance and meat quality traits of broilers submitted to cyclic heat stress.

MATERIAL AND METHODS

A total number of 400 female Ross 308 broilers (44 ± 0.5 g) were used. Birds were distributed in randomized block design, with four treatments of 10 replicates of 10 birds each. The experiment was carried out in a temperature-controlled room. Birds were housed in metal cages (0.80m x 0.90m) equipped with a feeder and a drinker each. Mash feeds were formulated with corn and soybean meal according to the recommendations of Rostagno et al. (2005), and are shown in Table 1. Treatments consisted of diets containing graded levels of AA and citric flavonoids, as presented in Table 2. The commercial product Biocitro^® (Quinabra, São José dos Campos, Brazil), obtained by citrus fermentation, was used. It contains 10.0% AA and 0.7% flavonoids (50% quercetin and 50% rutin). The feeding program was divided in two phases: starter, fed from 1 to 20 days, and grower, fed from 21 to 32 days.

Performance was weekly assessed, measuring body weight, feed intake, feed conversion ratio, and mortality. Initial room temperature was 32° C, which was then daily adjusted until 25° C at 13 days of age. From day 14 until the end of the experimental period, room temperature simulated cyclic heat stress: it remained 32° C for 5 hours, and then was slowly reduced (1° C every 12 min) until reaching the comfort temperature that corresponded to bird age.

Broilers were slaughtered at 33 d of age after 8 hours of fasting. Carcasses were chilled according the official regulations (Regulamento Técnico de Inspeção Tecnológica e Higiênico Sanitária de Carne de Aves; Brasil, 1998). Carcasses were then processed, and the following cuts were produced: deboned breast meat, breast fillet, thighs, legs, wings, and back. Breast and thighs were individually packaged in gas-impermeable plastic film (BB300-Cryovac^®), and stored in a freezer at -18° C for 230 days. All cuts were individually weighed and expressed relative to empty carcass weight.

Breast meat pH, cooking loss (Chrystall et al., 1994), and shearing force (Liu et al., 2004) were determined. Meat color was measured in the center of the Pectoralis major (internal face) using a MINOLTA Chroma Meter CM 508-d spectrometer. L*, a*, and b* parameters were read according to the ICE (International Commission on Illumination) system. Thigh samples were submitted to TBARS assessment (Tarlagdis et al., 1960).

Data were submitted to analysis of variance and regression using SAS (2001) package, and means that presented statistical difference were compared by the test of Tukey at 5%.

RESULTS AND DISCUSSION

Live performance: No treatment effect was detected on body weight, feed intake, or mortality (p>0.05) (Table 3). General mortality was high, above the values commonly found under commercial production conditions. In the absence of health problems, this was probably consequence of the heat stress imposed to birds in all treatments.

Feed conversion ratio was statistically different (pd< 0.001) for the period of 1 to 7 days of age, with broilers fed 0 and 250 g/ton Biocitro^® presenting better feed conversion ratio as compared to those fed 500 and 1000 g/ton (Table 4).

The lack of treatment effects maybe related to the difficulty to determine the degree of stress to which the birds are experimentally submitted (Mckee & Harrison, 1995; Whitehead et al., 2003). Puron & Santamaria (1994) did not observe differences in weight gain, feed intake, feed conversion ratio or mortality of broilers fed 200 ppm AA, and attributed these results to the temperatures and times applied (35-38° C for 4 hours and 26-34° C for 6 hours, respectively), as the beneficial effects of AA and flavonoids supplementation are most likely to be observed at higher temperatures. However, cyclic heat stress temperatures and times used in the study of Sahin et al. (2003) were higher (34°C for 8 h/d), and resulted in lower feed intake and worse feed conversion ratio in quails fed a diet supplemented with 250 mg L-AA.

Consistent with Vathana et al. (2002), favorable temperatures and light provided for the entire 24-h day period may explain the lack of differences in body weight, weight gain, and feed intake among the experimental birds. Birds may have also suffered changes during the acclimation process, and therefore, did not suffer heat stress (Arjona et al., 1988).

AA supplementation showed positive effects on the reduction of corticosterone plasma levels ando n the heterophil/lymphocyte ratio, as evaluated by Mckee & Harrison (1995) in birds submitted to heat stress (33° C) and supplemented with 150 and 300 ppm AA in the diet.

Meat yield and meat quality traits: No statistical differences were detected among the analyzed treatments for carcass and cut yields of 33-day-old birds (p>0.05) (Table 5).

The use of body energy reserves during heat stress periods may vary with dietary carbohydrate and fat levels or with AA dietary supplementation, as well as with corticosteroid synthesis and the production of thyroid hormones (Dale & Fuller, 1980; Mckee et al., 1997). Although plasma hormone concentrations were not measured in the present study, these probably were not significant as no differences in abdominal fat yield were detected (p>0.05).

Data presented in Table 6 showed that the experimental treatments did not cause any significant differences in breast pH at the different measurement times. However, pH tended to decline as a function of time. After rigor mortis resolution (4 h post-mortem), breast meat pH is commonly between 5.7 and 5.9, and must remained unchanged after this time. A slight increase is expected after long storage times due to the formation of basic substances (Souza, 2006). As pH was not measured 24 h post-mortem, it was not possible to establish if values were lower than those obtained at 4 h. considering that these values were close to those recorded at that time, meat probably presented normal behavior and that birds were not sufficiently stressed to present meat changes, such as those observed in PSE or DFD pork, present in poultry meat with pH higher than 6.2 at 24 h post mortem or below 5.7 during the first 45 min after slaughter (Aks'it et al., 2006).

Nevertheless, as shown in Table 7, there were significant differences in cooking loss of thawed weight loss both in grams and in percentage (pd<0.037 and pd<0.020, respectively), with the treatment 1000 g/ton promoting the highest loss.

These results have no relation with pH values, as the pH highest value seems to indicate a slower decline, leading to higher water retention capacity. According to Souza (2006), breast meat cooking loss varies between 18 and 29%, which is consistent with the results obtained in the present study.

No significant differences were observed in shear force (p>0.05) (Table 8).

However, this parameter has no relation with the results obtained for cooking loss, as meat texture is closely linked to intramuscular water content (Lawrie, 2005). According to Souza (2006), breast meat shearing force values are approximately 2.50 to 5.00 kgf. The low values obtained in the present study could be related to the chemical and centesimal composition of the muscle, which changes with bird age and genetics (Olivo & Olivo, 2005).

Data presented in Table 8 show that the experimental treatments did not result in significant differences for L*, a*, or b* values. Several authors relate meat color to pH and to water retention capacity (Yang & Chen, 1993; Fletcher, 1995; Moreira, 2005; Olivo & Olivo, 2005). According to Zapata et al. (2006), freezing seems to produce a marked darkening, reducing chicken mean luminosity. However, in the present study, results indicate that meat was normal with L* values between 44 and 53, and a pH of 5.7. The a* and b* color components indicate that the meat samples were dark red and yellowish, This was possibly due to partial cell breakdown and blood migration caused by the slow freezing process or to the oxidation of the meat pigment, which stability depends on animal species, muscle biochemical characteristics, and some external parameters (Lyon & Lyon, 2002).

Table 8 shows mean TBARS levels of the frozen thigh meat samples. Samples of birds fed 250 and 1000 g/ton of the product presented the highest values, and those of treatments 0 and 500 g/ton had the lowest values. However, data analysis did not show any influence of treatments on this parameter.

CONCLUSIONS

The addition of graded AA and citric flavonoids (quercitin and rutin) levels to the broiler diets did not affect live performance, commercial cut yield, carcass yield or meat quality trait parameters. However, differences were found in feed conversion ratio and thawed weight loss. The addition of graded levels of the product impaired feed conversion ratio of birds during the first week of age, and increased breast water loss of birds processed at 32 days of age.

ACKNOWLEDGEMENTS

The authors thank the company Quinabra for funding and for supplying the commercial product; the Center for Meat Education, Research and Technology (Centro de Ensino, Pesquisa e Tecnologia de Carnes - CEPETEC), UFRGS; and the Center of Meat Technology (Centro de Tecnologia de Carnes - CTC) of Instituto de Tecnologia de Alimentos (ITAL), SP, for their help in meat quality analysis and interpretation of the results.

Arrived: April/2008

Approved: June/2008

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Publication Dates

• Publication in this collection
  26 Sept 2008
• Date of issue
  June 2008

History

• Accepted
  June 2008
• Received
  Apr 2008