Effect of a free-range raising system on growth performance, carcass yield, and meat quality of slow-growing chicken 1

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1 Effect of a free-range raising system on growth performance, carcass yield, and meat quality of slow-growing chicken 1 K. H. Wang, 2 S. R. Shi, T. C. Dou, and H. J. Sun Poultry Institute, Chinese Academy of Agricultural Sciences, Yangzhou, Jiangsu Province, , P. R. China ABSTRACT Experiments were conducted to evaluate the effect of free-range raising systems on growth performance, carcass yield, and meat quality of slowgrowing chickens. Slow-growing female chickens, Gushi chickens, were selected as the experimental birds. Two hundred 1-d-old female chicks were raised in a pen for 35 d. On d 36, ninety healthy birds, with similar BW (353.7 ± 32.1g), were selected and randomly assigned to 2 treatments (indoor treatment and free-range treatment, P > 0.05). Each treatment was represented by 3 groups containing 15 birds (45 birds per treatment). During the indoor treatment, the chickens were raised in floor pens in a conventional poultry research house (7 birds/m 2 ). In the free-range treatment, the chickens were housed in a similar indoor house (7 birds/m 2 ); in addition, they also had a free-range grass paddock (1 bird/m 2 ). All birds were provided with the same starter and finisher diets and were raised for 112 d. Results showed that the BW and weight gain of the chickens in the free-range treatment were much lower than that of the chickens in the indoor floor treatments (P < 0.05). There was no effect of the free-range raising system on eviscerated carcass, breast, thigh, and wing yield (P > 0.05). However, the abdominal fat yield and tibia strength (P < 0.05) significantly declined. The nutrient composition (water, protein, and fat), water-holding capacity, shear force, and ph of the muscle were largely unaffected (P > 0.05) by the free-range raising system. The data indicated that the free-range raising system could significantly reduce growth performance, abdominal fat, and tibia strength, but with no effect on carcass traits and meat quality in slow-growing chickens. Key words: free range, slow-growing chicken, growth performance, carcass yield, meat quality INTRODUCTION Organic and natural food are very popular sources of food. Poultry products are also an important food source. The raising of poultry receives a lot of attention regardless if the birds are raised without the use of antibiotics for growth, without animal by-products, and in the case of organic, without synthetic chemicals. Some consumers are also interested in birds raised with access to the outdoors (free range). Many consumers buy these products because they believe that the products have superior sensory qualities and report that they taste better (Latter-Dubois, 2000). Although some countries (European Union, United States) have very specific definitions for free-range and other specialty production, China does not. Production systems vary widely from large stationary houses with yards to 2009 Poultry Science Association Inc. Received October 1, Accepted May 16, This work was financially supported by the Public Welfare Industry Project of Ministry of Agriculture, P. R. China. 2 Corresponding author: sqbreeding@126.com or ssr236@163.com 2009 Poultry Science 88 : doi: /ps small portable houses that are moved frequently to new pastures. Conventionally confined systems lead to animal stress (Jones and Millis, 1999), resulting in physiological and behavioral responses (Marin et al., 2001) and poor performance (Mendl, 1999). Outdoor production systems, without any confinement on birds, could decrease stress conditions and allow selection of strains that may increase comfort and bird welfare. Furthermore, the outdoor production system increases the flavor of chicken better than the conventionally confined systems (Lewis et al., 1997; Fanatico et al., 2006). Based on these advantages, birds have been raised in outdoor systems. This new approach has led the Chinese agriculture departments to implement legal policies concerning the criteria for the production and certification of bird quality (DB3210/T , China). Many factors affect growth and performance of specialty birds, including genotype, age, sex, diet, density, environment, exercise, and pasture intake (Gordon and Charles, 2002). A better understanding of these factors and their interactions will help improve the performance in free-range production, in which unpredictable conditions may result in variations in the size of dressed 2219

2 2220 carcasses and parts. The purpose of the present study is to evaluate the effect of a free-range raising system on growth performance, carcass yield, and meat quality of slow-growing chickens. MATERIALS AND METHODS Experimental Design and Bird Management This trial was carried out at the Poultry Institute, Chinese Academy of Agricultural Sciences (Yangzhou) from March to July A slow-growing female chicken, Gushi chicken, was selected as the experimental bird. Gushi chicken is also called local chicken in China and is popular among Chinese people for its more delicious meat compared with that of the commercial broilers. Two hundred 1-d-old female chicks were raised in a pen for 35 d. On d 36, ninety healthy birds, with similar BW (353.7 ± 32.1 g), were selected and randomly assigned to 2 treatments [indoor treatment and free-range treatment (P > 0.05)]. Each treatment was represented by 3 groups containing 15 birds (45 birds per treatment). Chickens in the indoor treatment were raised in floor pens in a conventional poultry research house that contained a concrete floor, side curtains, and fans for ventilation and cooling. The raising density of each pen was 7 birds/m 2, where the temperature was 20 ± 3 C, the RH was 65 to 75%, and the photoperiod was 12 h. Chickens in the free-range treatment were housed in a similar indoor house (7 birds/m 2 ). In addition, they also had a free-range grass paddock (1 bird/m 2 ). Feed and water were also provided outdoors using trough feeders and water pans with reservoirs. Ground predators were excluded by electric net fencing, and overhead predators were excluded by netting over the paddocks. Birds were confined to indoor pens at night. Chicks were fed the same diet (1 to 35 d: starter; 36 d to slaughter: finisher; Table 1). Feed and water were freely available, and all diets were formulated to contain adequate nutrient levels as defined by the NRC (1994). Sample Collection and Analytical Determination Birds and feed were weighed weekly to determine BW, feed intake, and feed efficiency. Weight gain and feed efficiency were adjusted for mortality. At 112 d, after fasting for 10 h before slaughter, all birds were weighed individually and killed by manual exsanguination. After the birds were manually eviscerated, the eviscerated carcass, abdominal fat, breast meat (including pectoralis major and pectoralis minor), and leg meat (including thigh and drumstick) were equally measured. Eviscerated carcass percentage was calculated as the ratio between the eviscerated carcass and live BW after fasting. The weight percentages of breast meat, leg meat, Wang et al. and abdominal fat were calculated as a percentage of eviscerated carcass weight. Left drumsticks of 5 birds from each replicate pen were deboned. Bone-breaking strength of the tibia was determined with a texture analyzer (TMS-2000, American FTC Co., Sterling, VA) at 72 h postmortem. Muscle samples were collected from the left side of the pectoralis major muscle for meat quality analysis. Physicochemical characteristics of breast muscle samples, such as water, protein, fat, water-holding capacity, ph, and shear force, were evaluated. Water-holding capacity (WHC) was estimated by determining expressible juice using modification of the filter paper press method described by Wiebicki and Deatherage (1958) as follows. A raw meat sample weighing 1,000 mg was placed between 18 pieces of 11-cm-diameter filter paper and pressed at 35 kg for 5 min. Expressed juice was defined as the loss in weight after pressing and presented as a percentage of the initial weight of the original sample (Bouton et al., 1971). Total water content was determined in duplicate according to AOAC (1990) procedures. The WHC was calculated as the fraction of water retained by the meat [(expressible juice/total moisture content)] (Allen et al., 1998). Shear force was determined using a texture analyzer and a Warner-Bratzler device (C-LM 2, Northeast Agricultural University Ltd., Harbin, China). Muscle samples were stored at 4 C for 24 h and were then individually cooked in a water bath at 80 C in plastic bags to an internal temperature of 70 C. The samples then were removed and chilled to room temperature. Strips [1.0 cm (width) 0.5 cm (thickness) 2.5 cm (length)] parallel to the muscle fiber were prepared from the medial portion of the meat and sheared vertically (Molette et al., 2003). Shear force was expressed in kilograms. The ultimate ph values of the pectoralis muscles were measured 45 min postmortem, using a portable ph meter (IQ150, IQ Scientific Instruments Inc., Carlsbad, CA) equipped with an insertion glass electrode. Before measurement, the ph electrode was calibrated, using 3 buffers with ph values of 4.01, 7.00, and The samples were always measured at the same place. The average ph value was defined through 3 times on the same muscle samples. Table 1. Analyzed nutrient composition of trial diet 1 Nutrient Starter Finisher CP (%) ME (MJ/kg) Crude fiber (%) Calcium (%) Available phosphorus (%) Methionine (%) Lysine (%) Diet and analyzed nutrient composition were both provided by Yangzhou Hope Feed Co. (Yangzhou, China).

3 Table 2. Effect of raising system on BW and G:F 1 Raising system BW (g) Weight gain (g) G:F (g/g) Indoor 1,610.5 ± a 1,256.8 ± 94.4 a 3.95 ± 0.29 b Free-range 1,419.4 ± b 1,065.7 ± 57.6 b 4.41 ± 0.43 a a,b Values within a column with no common superscript differ significantly (P < 0.05). 1 Results are means with n = 3 per treatment. EFFECT OF FREE-RANGE RAISING SYSTEM 2221 Water, protein (nitrogen), and fat contents of feed and muscle were determined by AOAC (1990) methods. Statistical Analysis Data were analyzed by 1-way ANOVA (SPSS Inc., Chicago, IL). When appropriate, differences among treatment means were compared by Duncan s multiple range test. Differences were considered significant at P < RESULTS AND DISCUSSION Growth Performance Body weight (average cumulative BW) and G:F of chickens in 2 raising systems are shown in the Table 2 and Figure 1. The BW and weight gain of chickens in the free-range treatment were significantly lower than those of chickens in the indoor treatment (P < 0.05). The birds in the free-range treatment showed higher G:F than birds in the indoor treatment (P < 0.05). The free-range raising system has many factors, such as temperature, photoperiod, and light intensity, which are not controlled and are inherently variable. Furthermore, birds raised in a free-range raising system have access to pasture and the various forages, insects, and worms, which may be available. It was expected that the performance of birds in a free-range raising system would be inferior to that of birds in a more controlled environment because the free-range birds would be exposed to fluctuating temperatures and increased exercise in yards, thus increasing their energy requirement with a consequent increase of feed conversion (which was exhibited in current study). Castellini et al. (2002) also found the same result that growth rates and feed efficiencies with outdoor organic treatments were lower than with conventional treatments. But it was reversed with the result by Santos et al. (2005) that BW gain in the semiconfined system was higher than that in the confined system, due to improved bird comfort and welfare. Carcass Yield Mean yields of eviscerated carcass, breast, thigh, and wing of chickens in 2 raising systems are shown in Table 3. In the present study, although stocking density was lower in the free-range treatment, there was no effect of the production system on eviscerated carcass, breast, thigh, and wing yield (P > 0.05), which was consistent with Fanatico et al. (2005b). In contrast, Ricard (1977) and Castellini et al. (2002) found that percentages of breast and thigh meat increased when birds had an outdoor access and a lower stocking density in an organic production system because of forced motor activity. The abdominal fat yield of chickens in the free-range system was significantly lower than chickens in the indoor treatment (P < 0.05). The greater motion reduced the abdominal fat and favored muscle mass development in agreement with Ricard (1977), Lewis et al. (1997), and Castellini et al. (2002). Tibia strength of chickens in 2 raising systems is also shown in Table 3. Production system had an effect on bone-breaking strength as indicated by the more tender tibias in the free-range birds (P < 0.05). However, this differs from the result of Fanatico et al. (2005b), who thought perhaps the lower density and exercise in outdoor treatment led to stronger bones. Lewis et al. (1997) also found a tendency toward more total bone in birds with a low stocking density compared with high density as well as increased breast meat yield. The current study found that the relative low calcium level of the diet could not satisfy the necessary calcium requirement for more exercise in the free-range system, which Table 3. Effect of raising system on carcass performance and tibia strength 1 Raising system Eviscerated carcass yield 2 (%) Breast Thigh Wing Abdominal fat Tibia strength (kg) Indoor ± 2.04 a ± 2.92 a ± 0.50 a ± 0.62 a 6.50 ± 3.19 a 5.04 ± 0.88 a Free-range ± 1.12 a ± 0.83 a ± 1.12 a ± 0.79 a 3.01 ± 1.13 b 3.46 ± 0.58 b a,b Values within a column with no common superscript differ significantly (P < 0.05). 1 Results are means with n = 3 per treatment. 2 Calculated as a percentage of live BW. 3 Calculated as a percentage of eviscerated carcass weight.

4 2222 induced the calcium first to flow to the blood as blood calcium and reduce the density and strength of bone (John and Albert, 1981). Also, there were many other factors that could affect it, such as vitamin D intake, lighting, and behavior. Additional study is needed in this area to yield more details. Meat Quality Wang et al. Effect of the free-range raising system on meat quality is presented in Table 4. There was no difference in the nutrient composition of the muscle (water, protein, and fat) among the raising system (P > 0.05), which was consistent with the result by Fanatico et al. (2005a) that an outdoor (free range) production system had a limited effect on DM and fat (P > 0.05). According to Gordon and Charles (2002), temperature fluctuations could cause variations in carcass quality. Heat may increase abdominal fat. And in cold temperatures, less fat and meat are deposited. The present study was conducted in mild temperatures; this may have resulted in a similar nutrient composition between production systems. Water-holding capacity is important in whole-meat and further-processed meat products. If WHC is poor, whole-meat and further-processed products will lack juiciness. Free-range raised birds did not have different WHC from indoor birds (P > 0.05), whereas Castellini et al. (2002) and Fanatico et al. (2007) found that an outdoor (free range) production system resulted in significantly lower WHC (P < 0.05). Lower WHC indicated losses in the nutritional value through exudates that were released and this resulted in drier and tougher meat (Dabes, 2001). The causes were due to the temperature fluctuation, especially the relative high temperature during the latter part of the experiment (above 32 C in July), which had affected the water content of the muscle in both groups. Among the organoleptic characteristics, tenderness, which can be defined as how easy the meat can be chewed or cut, is considered as the most important by consumers. In the present study, the free-raising system did not influence tenderness (P > 0.05). This finding agreed with the work of Fanatico et al. (2005a) that production system had no effect on tenderness of the slow-growing birds. However, Castellini et al. (2002) found different results; they concluded that the production system affected the shear force that was higher in either the breast or drumstick of the organic birds (P Figure 1. Average cumulative BW. < 0.05), presumably as a consequence of their greater motor activity. Farmer et al. (1997) observed the same tendency for breast meat from birds reared under a lower stocking density. Muscle ph is a significant parameter in terms of preservation and stability of meat; it is known that a high muscle ph results in shorter shelf life stability, especially as it pertains to microbial growth. Postmortem ph decline is one of the most important events in the conversion of muscle to meat due to its effect on meat tenderness, color, and WHC (Aberle et al., 2001). The rate of ph decline is dependent on the activity of glycolytic enzymes just after death; the ultimate ph is determined by the initial glycogen reserves of the muscle (Bendall, 1973). At present, although not significant (P > 0.05), the ph of free-range birds was lower than that of indoor-raised birds. It was emphatically confirmed by Fanatico et al. (2007) that outdoor access resulted in a lower ph in slow-growing birds (P < 0.05). Exercise and the environment are likely to affect muscle metabolism due to the amount of foraging (Farmer et al., 1997). Culioli et al. (1990) and Castellini et al. (2002) also had similar results; but in contrast, Alvarado et al. (2005) found that a free-range raising system resulted in a higher ph. From these results, it is concluded that rearing slowgrowing chickens by the free-range system seems to be a possible alternative to the conventional method. This was due to a significant reduction in growth performance, abdominal fat, and tibia strength. There was no effect on carcass traits and meat quality. Further Table 4. Effect of raising system on meat quality 1,2 Raising system Water (%) Protein (%) Fat (%) Water-holding capacity (%) Shear force (kg) ph Indoor ± ± ± ± ± ± 0.31 Free-range ± ± ± ± ± ± There are no significant differences in each column (P > 0.05). 2 Results are means with n = 3 per treatment.

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