Performance, carcass yield, and meat quality of broilers supplemented with organic or inorganic zincABSTRACT
A total of 640 one-day-old Cobb broiler chicks, half male and half female, were reared up to 49 days of age. A completely randomized 2 × 4 factorial design was used. Experimental treatments consisted of four levels of organic zinc supplementation and one control (inorganic zinc supplementation) and two levels of sex (female and male), with four replicates of 16 birds per experimental plot. Animal performance, carcass and cut yields, and meat quality were evaluated. Feed intake increased with zinc supplementation. Broilers that received the lowest level of organic zinc showed better feed conversion than those fed an equivalent level of inorganic zinc. Increased levels of organic zinc reduced the abdominal fat content in females but impaired the oxidative stability of meat. The results showed that male broilers have better performance, carcass yield, and meat quality than females and that organic zinc improves broiler feed conversion and reduces abdominal fat but increases lipid oxidation in meat.
Keywords: birds; color; lipid oxidation; oligoelement; organic minerals; meat pH
RESUMO
Foram alojados 640 pintainhos de corte, sendo metade de machos e metade de fêmeas, da linhagem Cobb, de um a 49 dias de idade. Foi adotado um delineamento inteiramente ao acaso, em esquema fatorial 2 × 4. Os tratamentos experimentais consistiram em quatro níveis de suplementação de zinco orgânico e um controle inorgânico, e diferentes sexos, com quatro repetições de 16 aves por parcela experimental. Foram avaliados o desempenho, a característica da carcaça e dos cortes, bem como a qualidade de carne dos frangos. O aumento dos níveis de zinco elevou o consumo de ração dos frangos. Os frangos que receberam zinco orgânico na exigência mínima apresentaram melhor conversão alimentar comparados àqueles que receberam ração de fonte inorgânica. O aumento nos níveis de zinco orgânico proporcionou redução no teor de gordura abdominal para fêmeas, mas níveis de zinco orgânico prejudicaram a estabilidade oxidativa da carne. Conclui-se que frangos machos apresentam melhor desempenho, carcaça e qualidade de carne em relação às fêmeas, e que o zinco orgânico melhora a conversão alimentar dos frangos, reduz a gordura abdominal, porém eleva a oxidação lipídica da carne.
Palavras-chave: aves; cor; minerais orgânicos; oxidação lipídica; oligoelemento; pH da carne
INTRODUCTION
Modern poultry farming has been characterized by the production of broilers with high growth rates and weight gain. Research on breeding, nutrition, sanitation, and management practices has been carried out to promote the development of the poultry production chain. Minerals are of great importance for bird development, acting as structural components of organs and tissues, electrolytes, and catalysts of enzymatic and hormonal processes (Maiorka and Macari, 2002). Zinc participates in the catalytic site of several enzymes, such as DNA and RNA polymerases, and binds to receptor sites in target cells. The mineral is involved in cell proliferation; protein synthesis; metabolism of carbohydrates, proteins, and lipids; and production, storage, and secretion of hormones, such as insulin, testosterone, and cortisol (González and Silva, 2006).
The use of organic minerals has received great attention in animal nutrition because of their greater bioavailability compared with that of inorganic mineral sources (Oliveira et al., 2010). Absorption can take place via two ways: the mineral attaches to the brush border of the small intestine and is absorbed by the epithelial cell or, as occurs in most cases, the chelating agent is absorbed and transports the mineral through the intestinal cell wall (Kratzer and Vohra, 1996).
Zinc is a constituent of superoxide dismutase, an enzyme involved in the stabilization of structural membranes and in cell protection against lipid peroxidation (Meunier et al., 2005). Lipid oxidation affects the stability of meat, consequently impacting shelf life, which can be enhanced by the addition of antioxidants to animal diet (Murakami, 2009).
Some animal feed components are not antioxidants but are essential to endogenous antioxidant systems (Papas, 1999). Zinc is such a component; it has antioxidant effects and thus can increase the oxidative stability of meat. Male and female broilers present different growth curves: males have a lower growth rate than females and take longer to reach their maximum growth rate for weight gain and breast weight, but they exhibit higher fat and muscle deposition. Because of these differences, male and female broilers have different nutritional requirements (Scheuermann et al., 2003).
Moro et al. (2005) evaluated four commercial broiler strains and observed that males had better weight gain, average daily gain, feed intake, feed conversion ratio, and production efficiency index than females. Male broilers have higher muscle fiber density, a factor that can influence the quality of poultry meat (Scheuermann et al., 2003). Females have fewer muscle fibers, larger myofiber cross-sectional area, and, consequently, higher glycolytic potential, which can negatively affect meat quality. The aim of this study was to evaluate the performance, carcass and cut yields, and meat quality of male and female broiler chickens supplemented with different sources and levels of zinc.
MATERIAL AND METHODS
The experiment was conducted at the Bird Nutrition Research Unit and the Laboratory of Carcass Analysis of the Farm School of Londrina State University, Paraná, Brazil, and at the Laboratory of Animal Nutrition of Londrina State University, Paraná, Brazil. A total of 640 one-day-old Cobb broiler chicks, half male and half female, were used in this study. Birds were housed and received water and feed ad libitum during the 49-day experimental period. The period was divided into three phases: starter (1-21 days), grower (22-42 days), and finisher (43-49 days). The following production data were evaluated: feed intake, weight gain, feed conversion ratio, and livability.
Experimental diets (Table 1) met the minimum requirements for each sex, as described by Rostagno et al. (2005). Chicks were supplemented with inorganic or organic zinc, according to the following treatments: control, 66, 60, and 46mg/kg inorganic zinc; B, 33, 30, and 23mg/kg organic zinc; C, 66, 60, and 46mg/kg organic zinc; D, 99, 90, and 69mg/kg organic zinc; and E, 132, 120, and 92mg/kg organic zinc (starter, grower, and finisher phases, respectively). The source of inorganic zinc was zinc oxide. Bioplex® Zn was the source of organic zinc. The vitamin-mineral premix did not contain zinc in its formulation. A completely randomized 2 × 4 factorial design was used. Experimental treatments consisted of four levels of organic zinc supplementation and a control (inorganic zinc supplementation) and two levels of sex (female and male), with four replicates of 16 birds per experimental plot.
On day 50 two broilers from each plot were weighed and killed, representing the average weight of the plot, totaling 8 birds per treatment. The broilers were analyzed for carcass yield, cut yield, and meat quality. Prior to slaughter, broilers were fasted for 10h. Broilers were killed by electrical stunning using a Fluxo FX 2.0 equipment, followed by bleeding, scalding, and evisceration. Carcasses were cut into retail cuts for yield analysis. Carcass yield was obtained by weighing birds before slaughter and after evisceration and removal of the head, neck, and feet. Cut yield was determined by dividing the weight of the legs (thigh and drumstick), back, wings, and breast by the weight of the eviscerated carcass.
For meat quality analysis, chicken breasts were harvested and placed in an ice water bath at 4°C for 24h. pH was determined by insertion of a pH electrode (Testo 205 pHmeter) into the cranioventral side of the pectoralis major muscle, according to Olívo et al. (2001). Color was measured at three points on the ventral side of the pectoralis major using a Konica Minolta CR-10 colorimeter. Results were expressed as CIELab color parameters L* (lightness), a* (redness), and b* (yellowness). Water-holding capacity (WHC) was determined by the filter paper press method (Barbut, 1996). Briefly, a 2g sample of breast meat was placed between two filter papers and compressed with a 10kg weight for 5min. Then, the breast meat was weighed, and the amount of water released was determined by calculating the difference in weight before and after compression. WHC was expressed as the percentage of released water relative to the initial weight of the sample. Cooking loss was determined according to the method of Cason et al. (1997). Breast meat samples were weighed, packed, and placed in a water bath at 85°C for 30min. Then, samples were cooled to room temperature and weighed. Cooking loss was determined as the difference between the initial and final weight. Thiobarbituric acid reactive substances (TBARS) content was determined in breast samples after 90 days of storage at −20°C, according to the method described by Pikul et al. (1989). Briefly, samples (10g) were homogenized with 50mL of 7.5% (v/v) trichloroacetic acid solution. The supernatant was filtered, and 4mL aliquots were mixed with 5mL of thiobarbituric acid solution, placed in boiling water, cooled, and read at 538nm.
Results were submitted to analysis of variance followed by Tukey’s test at the 5% significance level. Results of the different treatments were submitted to polynomial regression analysis. Comparison between treatments and the control was carried out by Dunnett’s test at the 5% significance level. This research was approved by the Ethics Committee on the Use of Animals (process no. 23/10).
RESULTS AND DISCUSSION
The results of broiler performance from 1 to 49 days of age (Table 2) showed that there was no significant effect of organic zinc level on weight gain, feed conversion ratio, or livability. Furthermore, no interaction effect was found between zinc level and bird sex. Dietary supplementation with high levels of zinc, however, increased feed intake, as expressed by the linear regression equation y= 5229.99 + 5.3787x with R 2= 0.76.
Jahanian et al. (2007) obtained similar results using different organic zinc levels and sources (zinc acetate, zinc methionine, and zinc lysine). The authors observed an increase (P< 0.01) in feed intake with zinc supplementation and reported that zinc methionine gave the best results. Osman and Mohan (2007) reported that broilers fed a diet supplemented with 400 or 500mg/kg zinc had higher feed intake than non-supplemented birds.
According to Medeiros et al. (2011), increased zinc levels may influence the production of angiotensin-converting enzyme (ACE), responsible for the conversion of angiotensin I to angiotensin II, which induces vasoconstriction in the brain, kidneys, lungs, and skeletal muscles and stimulates the release of aldosterone from the adrenal gland, increasing blood pressure by enhancing sodium and water reabsorption. This metabolic response results in higher energy expenditure and increased feed intake.
Dunnett’s test revealed no significant differences in feed intake, weight gain, and livability between control broilers (supplemented with inorganic zinc) and broilers supplemented with organic zinc. However, feed conversion ratio differed significantly between the groups. Broilers that received the lowest level of organic zinc showed better feed conversion than those fed an equivalent level of inorganic zinc. This result can be explained by the higher bioavailability of organic minerals compared with that of inorganic mineral sources (Oliveira et al., 2010), as the chelating agent is easily absorbed and transports the metal ion through the intestinal cell wall. Hess et al. (2001) studied female broiler diets supplemented with different zinc sources and concluded that feed conversion was improved by supplementation with zinc amino acid complexes.
Rossi et al. (2003), who studied the effects of five graded levels of organic zinc (0, 15, 30, 45, and 60mg/kg), and Gomes et al. (2008), who analyzed the effects of six graded levels of organic zinc (12, 37, 62, 87, 112, and 137mg/kg), found similar results to those of the present study: that zinc supplementation did not improve (P> 0.05) broiler weight gain.
Interestingly, male broilers showed significantly higher feed intake and weight gain and lower feed conversion ratio than female broilers. However, no differences (P> 0.05) in livability were observed between male and female birds. According to Fanatico et al. (2005), broiler sex influences muscle development and differences in weight between sexes increase with age. These observations are in accord with of Gonzales and Sartori (2008), who noted that androgens, hormones responsible for muscle anabolism, contribute to broiler development and are found in higher concentrations in males. Almeida and Zuber (2002), Mendes and Saldanha (2004), and Dalanezi et al. (2005) also evaluated broiler development by sex and reported that males perform better than females.
Carcass and cut yields (Table 3) were not influenced by organic zinc levels or sources. Dunnett’s test did not reveal any significant difference in yield between organic zinc treatments and the control (P> 0.05). These results can be attributed to the lack of significant difference in weight gain between treatments, which resulted in similar carcass and cut yields. Rossi et al. (2007), Trindade Neto et al. (2010), and Medeiros et al. (2012) investigated the effect of different levels of organic zinc on broiler performance and concluded that carcass and cut yields were not influenced by zinc supplementation. Male broilers had higher leg yield than females (P<0.01). This result is in agreement with the data of Dalanezi et al. (2005).
Abdominal fat yield was higher (P<0.01) in females than in males. Similar results were obtained by Mendes et al. (2004) and Murakami et al. (2010). Females undergo specific physiological maturation processes for reproduction, including fat accumulation, which is known to increase with age (Gaiotto, 2004). As female broilers have more adipocytes than males, they have greater fat deposition capacity (Langslow and Lewis, 1974).
However, female broilers showed a reduction (P<0.01) in abdominal fat content with increasing zinc concentration. The relationship was best described by the quadratic equation y= 6.6037 − 0.1055x + 0.0007x 2 with R 2= 0.99. The minimum value of y is given by organic zinc supplementation at 91.99mg/kg during the finisher phase.
Osman and Mohan (2007) supplemented broiler diets with 300, 400, or 500mg/kg zinc methionine and found no significant differences in carcass yield, cut yield, and abdominal fat deposition at 49 days of age. The authors did not find a decrease in abdominal fat yield in female broilers with increased levels of organic zinc, as observed in the present study (Table 4).
The deiodinase type II enzyme, responsible for the peripheral deiodination of thyroxine (T4) to the active form triiodothyronine (T3), may be zinc dependent (Nishiyama et al., 1994). Thus, elevated zinc levels might have promoted the conversion of T4 to T3, increasing metabolic rate, thermogenesis, and oxygen consumption. Furthermore, elevated zinc levels stimulate ACE production, which culminates in the secretion of aldosterone (Valee and Falchuk, 1993). The hormone increases blood pressure and the metabolic rate of several organs, leading to greater energy expenditure. Thus, two zinc-dependent mechanisms are able to increase feed intake and reduce abdominal fat content.
Organic zinc supplementation and broiler sex had no interaction effects on meat quality. Meat pH, color, WHC, and cooking loss were not influenced by zinc sources or levels (Table 5 and 6). Zinc level had a linear effect (P< 0.01) on lipid oxidation, according to the equation y= 0.5403 + 0.077x with R 2= 0.94; that is, lipid oxidation increased with increasing levels of zinc.
The mechanism by which zinc supplementation might have increased lipid oxidation is related to other minerals. In excess, zinc may exert negative effects on copper homeostasis and consequently on the antioxidant system (Harris, 1992), because copper is a cofactor for the enzyme superoxide dismutase (Cu-Zn-SOD), which is an essential defense against free radicals (Signorini and Signorini, 1995). Another copper-dependent enzyme, ceruloplasmin, is a free radical scavenger. According to Schümann et al. (2002), chronic excessive intake of zinc interferes with the absorption and metabolism of other trace elements, such as iron and copper, which are transported and stored by ceruloplasmin. By keeping iron and copper ions bound to its structure, ceruloplasmin reduces oxidative stress by inhibiting the Fenton reaction (Gutteridge, 1985), which in turn prevents or minimizes free radical generation (Schümann et al., 2002) and lipid and phospholipid oxidation (Gutteridge, 1985). In short, excessive zinc intake can lead to copper deficiency, affecting iron absorption, reducing superoxide dismutase and ceruloplasmin levels, increasing free radical generation and meat oxidation. The only meat quality parameter affected by broiler sex was WHC (Table 6). Male broilers had higher (P< 0.05) WHC than females. Therefore, the meat of male broilers had greater juiciness than the meat of females.
CONCLUSION
Male broilers perform better than female broilers. Dietary supplementation with high levels of organic zinc reduces abdominal fat deposition in female broilers but shortens the shelf life of meat. Male broilers yield higher quality meat with higher WHC and, thus, improved sensorial quality.
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Publication Dates
-
Publication in this collection
03 Apr 2020 -
Date of issue
Jan-Feb 2020
History
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Received
22 Sept 2017 -
Accepted
12 Nov 2018
