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Performance, Livability, and Carcass Yield of Slow- and Fast-Growing Chicken Genotypes Fed Low-Nutrient or Standard Diets and Raised Indoors or with Outdoor Access

A. C. Fanatico^*, P. B. Pillai^*, P. Y. Hester, C. Falcone, J. A. Mench, C. M. Owens^* and J. L. Emmert^*,1

^* Center for Excellence in Poultry Science, University of Arkansas, Fayetteville 72701; Department of Animal Sciences, Purdue University, West Lafayette, IN 47907; and Department of Animal Science, University of California, Davis 95616

¹ Corresponding author: jemmert{at}uark.edu

	ABSTRACT

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION REFERENCES

 
Two experiments were conducted to assess the effect of genotype, production system, and nutrition on performance and livability of meat chickens for niche markets. Slow-growing (SG) and fast-growing genotypes (FG) were raised for 91 and 63 d, respectively, in experiment 1 (females) or 84 and 56 d, respectively, in experiment 2 (males). In each trial, SG were placed before FG to achieve a similar BW at processing. In experiment 1, each genotype was assigned to 8 pens of 20 birds each, with 4 pens within each genotype raised indoors in a conventional research facility or in a small facility with outdoor access. All birds were fed a low-nutrient diet. In experiment 2, genotype assignment to pens was as in experiment 1; however, 4 pens within each genotype were fed a low-nutrient diet or a conventional diet, and birds were raised indoors. Birds were gait-scored and commercially processed; legs were examined for tibial dyschon-droplasia lesions and scanned for bone mineral density. In experiment 1, FG gained more weight than SG (P < 0.05) even though they were placed later. Outdoor access increased feed intake, and feed efficiency was poorer (P< 0.05). Fast-growing genotypes had higher breast meat yield, whereas SG had higher wing and leg yields (P < 0.05). In experiment 2, the low-nutrient diet reduced (P< 0.05) gain of the SG; FG increased feed intake of the low-nutrient diet such that their gain was unaffected (P> 0.05). For FG, the low-nutrient diet resulted in a poorer (P < 0.05) feed efficiency. Although weight gain of the FG was maintained on the low-nutrient diet, breast yield was reduced (P < 0.05). Genotype affected bone health in both experiments, with SG having better gait scores and less tibial dyschondroplasia (P < 0.05). Outdoor access and the low-nutrient diet also resulted in better gait score (P < 0.05). These data indicate differences among genotypes and provide information about the efficiency and potential for alternative poultry systems.

Key Words: broiler • free range • organic • growth performance • livability

	INTRODUCTION

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION REFERENCES

 
Interest in alternative animal production systems and alternatively produced products has increased at a rapid rate in recent years. Alternative animal production systems are typically designed to address a variety of concerns held by consumers and independent producers. Although alternative poultry production systems vary greatly in size and composition, most systems are designed to address one of the foremost concerns of some consumers: access to the outdoors. Products from these systems are often labeled as free range, which although not specifically defined by the USDA may be used on labels after a review process, in which the producer submits written documentation that describes how outdoor access is provided (USDA, 2006a). In addition to outdoor access, many consumers are interested in obtaining organic poultry products. For organic production, a strict set of standards must be followed in addition to outdoor access, including the use of 100% organic feed grown without synthetic chemicals and without growth promotants or antibiotics (USDA, 2006b). European alternative production systems are typically governed by more comprehensive standards, which in some cases even dictate the genotype and dietary nutrient levels that can be used (European Union, 1991). The Label Rouge program, for example, requires the use of slow-growing genotypes and dictates that a high level of cereal grains be used, thus limiting the amount of protein that is provided (Ministère de L’Agriculture, 1996).

As interest in alternative poultry production continues to grow in the United States; it is possible that more strictly defined production systems could develop, in which the use of certain genotypes or specified dietary nutrient levels is dictated, similar to some European systems. In the United States, the conventional broiler from a cross of Cornish and White Rock chickens is typically used in both conventional and alternative poultry production; it is an efficient bird that reaches market weight in 42 d. However, it was primarily developed for use in indoor, climate-controlled conditions. Alternative production systems are influenced by concerns about animal behavior and welfare, which includes the incidence of leg disorders and livability. A slower-growing genotype that shows more foraging behavior and has a different body conformation could be more suitable for production systems that provide outdoor access.

Very little data about growth performance and carcass yield are available for slow-growing genotypes. Furthermore, the effect of feeding low-nutrient diets, similar to those fed in the Label Rouge program, on growth performance in alternative and conventional chicken genotypes has not been assessed in alternative production systems in the United States. Fanatico et al. (2005) described growth patterns for slow-, medium-, and fast-growing genotypes fed an industry-type diet, but information about the effect of outdoor access was limited, and low-nutrient diets were not tested. The potential use of alternative genotypes is not strictly a performance-based decision, but as the alternative market grows in response to increased consumer concerns, there is a need to quantify the effect of production system and diet on growth performance. This information would provide producers with realistic data to use in their production decisions. The objective of this study was to investigate the effect of production system (indoor vs. access to outdoors), genotype (fast- vs. slow-growing), and diet (conventional vs. low-nutrient) on growth, livability, bone health, and carcass yield of meat-type chickens.

	MATERIALS AND METHODS

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION REFERENCES

 
Two experiments were conducted at the University of Arkansas Poultry Research Farm from August to November 2004. All procedures were approved by the University of Arkansas Institutional Animal Care and Use Committee. In both experiments, a slow-growing genotype (S & G Poultry LLC, Clanton, AL) and a typical fast-growing genotype (Cobb, Siloam Springs, AR) were compared. Although commercial slow-growing products are widely available in Europe, there is little availability in the United States. The company S & G Poultry recently developed a slow-growing chicken that requires approximately 12 wk to achieve the typical BW of an 8-wk-old commercial broiler chicken but with a poorer feed efficiency and lower breast yield (Fanatico et al., 2005). Because of the difference in growth rate, chick placement dates in both experiments were staggered in an attempt to reach a similar final BW at the time of processing, as previously reported (Fanatico et al., 2005). In both experiments, 4 replicate pens per treatment containing 20 birds per pen were used. Birds and feed were weighed for the determination of weight gain, feed intake, and feed efficiency (adjusted for mortality). Feed and water were freely available in both trials. The fast-growing birds were gait-scored at 56 d and the slow-growing at 84 d with the 0 to 5 gait score system of Garner et al. (2002), with a score of 0 assigned to birds with no obvious gait impairment and a score of 5 assigned to lame birds that cannot walk (Garner et al., 2002). Birds were also examined for foot pad dermatitis using a 0 to 2 score system (Algers and Berg, 2001), with a score of 0 representing no or very small and superficial lesions and a score of 2 representing a severe lesion with ulcers or scabs, signs of hemorrhages, or a swollen food pad.

At trial termination, all birds were commercially processed at the University of Arkansas Pilot Processing Plant. Feed was withheld for 10 h before slaughter, and birds were weighed individually at the plant. Automated equipment was used for stunning, scalding, picking, vent opening, and evisceration. Birds were electrically stunned (11 V, 11 mA, 10 s) followed by scalding at 53°C for 120 s. Carcasses were prechilled at 12°C for 15 min and chilled (immersion) at 1°C for 1 h. After chilling, carcasses were aged on ice and breast fillets deboned from the carcass at 4 h postmortem. Weights of breast (boneless, skinless), wings, legs, and frame (carcass including skin but with breast, wings, and legs removed) were recorded. Yield was expressed as a percentage of chilled, ready-to-cook (RTC) weight.

The incidence of tibial dyschondroplasia (TD) was determined for all birds at the time of processing. The drums were removed from the thighs at the femoral joint during cut-up, and the proximal end of the tibiotarsus bone was cut longitudinally to observe cartilage formation using the following visual scoring: 0 = normal growth plate with smooth contour and off-brown tincture; 1 = mild to moderate with translucent cartilage thickened approximately to twice the size of normal; and 2 = severe with opaque white cartilage widened to span more than twice the size of a normal growth plate, indented or extending into the metaphyses (Rath et al., 2004). The left wing and drumstick were collected from an average of 2 birds per replicate pen per treatment, resulting in a sample size of 6 to 11 observations per treatment. Samples were frozen and express-mailed in dry ice to Purdue University, where they were thawed and scanned with muscle and skin intact using dual-energy x-ray absorptiometry for determination of bone mineral density (BMD; Hester et al., 2004).

Experiment 1: Production System

The objective of experiment 1 was to evaluate the effect of production system (indoor vs. outdoor access) on the performance of female slow- and fast-growing genotypes, which were raised for 91 or 63 d, respectively. Birds were randomly assigned to pens in a conventional indoor facility or a portable facility with outdoor access. The 4 treatments consisted of slow-growing birds given outdoor access, slow-growing birds that were confined indoors, fast-growing birds given outdoor access, and fast-growing birds that were confined indoors.

Indoor treatments were grown in floor pens in a conventional poultry research facility that contained a concrete floor, side curtains, and fans for ventilation and cooling. Thermostatically controlled heater and gas brooders, which extended along the length of the house, were used to provide additional heat during brooding. Indoor pens measured 1.8 m x 1.8 m (6.2 birds/m²) and contained 1 bell waterer and hanging tube feeder. New wood shavings were used as litter. A constant photoperiod of 24 h was provided.

Birds with outdoor access were grown in a small portable facility measuring 3.7 m x 5.5 m. The portable facility was not moved during the trial. The facility was insulated and naturally ventilated but had no access to power. Propane space heaters were used to keep nighttime temperatures above 15.5°C inside the house. No artificial lighting was used, with photoperiod being limited to natural daylight. The house was subdivided into 8 indoor pens that opened to 8 separate yards, which were surrounded by electric net fencing. The indoor area of each pen measured 1.2 m x 1.5 m (11.1 birds/m²). All pens allowed outdoor access to grassy yards through bird exits (0.6-m width x 0.5-m height). Birds were allowed access to the outdoors during daytime hours, with the exception of 2 d during the study period in which the outdoor temperature was less than 4.4°C. The outdoor portion of each pen had an area of 9.3 m² and was completely covered with grassy vegetation. The indoor portion of each pen contained 1 fount-type waterer and hanging tube feeder, and the floor was covered with fresh wood shavings. The outdoor portion of each pen contained 1 waterer and a range-type tube feeder with a rain shield.

All chicks were brooded in the indoor facility; chicks in the treatments with outdoor access were moved to the portable facility after 21 d of age. The temperature inside the portable house during the study period ranged from a high of 23.9°C to a low of 13.9°C; the temperature outside ranged from a high of 22°C to a low of 2°C. There were 30 d of precipitation during the 71-d period when the birds had access to the outdoors. The total precipitation was 27.82 cm.

All birds were provided with multistage diets (Tables 1 and 2) that were formulated to be low in protein and energy, similar to those used in the French Label Rouge program (Lewis et al., 1997) for slow-growing birds. This study was not conducted under USDA organic requirements, which require the use of 100% organic nonmedicated feed. Although animal by-products were not used, anticoccidial medication was included in the feed.

The objective of experiment 2 was to evaluate the effect of dietary nutrient level (conventional vs. low-nutrient) on the growth performance and bone health of male slow-and fast-growing genotypes, which were raised for 84 or 56 d, respectively. Birds in experiment 2 were raised for a shorter period of time than birds in experiment 1 (conducted concurrently), because processing capacity dictated that the 2 experiments be terminated on different days. Moreover, because of sex and diet differences, males used in experiment 2 were expected to grow at a faster rate than the females used in experiment 1. All birds were housed in the conventional indoor facility described above. Birds were randomly assigned to pens according to experimental diet, which consisted of either a low-nutrient diet (low in amino acids and energy as used in experiment 1) or a more conventional diet that was formulated according to NRC (1994) recommendations (Table 1). Diets were provided in multiple phases (Table 1), and the 4 treatments consisted of slow-growing birds fed the low-nutrient diets, slow-growing birds fed the conventional diets, fast-growing birds fed the low-nutrient diets, and fast-growing birds fed the conventional diets. Specific ages associated with each diet are shown in Table 2.

Statistical Analysis

Data were subjected to ANOVA using the GLM procedure (SAS Institute, 2003) appropriate for a completely randomized design. A factorial arrangement of treatments was used. Treatment means were separated using Fisher’s protected least significant difference multiple comparison procedure. The proportions of gait and TD scores were compared using a ² test for equality of distributions except in those cases in which small expected counts may have substantially affected the approximate P-value from the ². In those cases, Fisher’s exact test was used (Fleiss, 2003). Because BW as a covariant was significant, the BMD was analyzed using analysis of covariance with the factorial arrangement of treatments and type of bone (tibia and humerus) as a subplot within the individual bird (Steel et al., 1997). The mixed procedure of the SAS system was used in the BMD analysis (SAS Institute, 2003).

	RESULTS AND DISCUSSION

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION REFERENCES

 
Many factors affect growth performance of poultry including genotype, production system, diet, age, sex, stocking density, photoperiod, temperature, and activity. Although stocking density, lighting, and temperature varied and could have affected the results, the analysis was limited to the controlled factors of interest, namely genotype (slow- or fast-growing), nutrient level (low or conventional), and production system.

Growth Performance

The type of production system tested did not affect weight gain, but weight gain of the fast-growing genotype exceeded (P < 0.05) that of the slow-growing birds, even though an attempt was made to reach a similar market BW (Table 3). Previous research (Gordon and Charles, 2002; Fanatico et al., 2005) indicated that 84 to 91 d was sufficient for the slow-growing birds to reach a live weight of 2.0 to 2.5 kg, which is a typical live weight for specialty poultry production. Fast-growing broilers have been selected for rapid early growth and reach this market weight in roughly 42 d, depending on diet and growing conditions. Overall feed intake was not affected (P > 0.05) by genotype. The outdoor access production system increased (P < 0.05) feed intake of both genotypes but had a greater effect on the feed intake of slow-growing birds. As expected, feed conversion of the fast-growing birds was better (P < 0.05) than that of the slow-growing birds. Feed conversion was worsened (P < 0.05) by outdoor access in both genotypes, and the effect was more pronounced in the slow-growing birds.

Birds of experiment 2 were raised indoors and were fed a low-nutrient diet or a conventional diet (Table 1). When compared with the conventional diet, the low-nutrient diet did not affect (P > 0.05) weight gain of the fast-growing birds and reduced (P < 0.05) weight gain of the slow-growing genotype (Table 4). Total weight gain of the slow-growing birds fed the conventional diet was similar (P > 0.05) to that of the fast-growing birds fed either diet. Weight gain responses are readily explained by the interaction of diet composition and feed intake. Fast-growing broilers were able to increase (P < 0.05) consumption of the low-nutrient diet to the extent that weight gain was maintained, although feed conversion was worsened (P < 0.05). In contrast, slow-growing broilers apparently lacked the ability to increase feed consumption, so that feed conversion worsened, although not significantly. Overall, the fast-growing broilers exhibited reduced (P < 0.05) total feed intake and improved (P< 0.05) feed conversion compared with the slow-growing genotype.

It is clear from experiment 2 that the genotypes responded differently to diet, thus in part explaining why final BW of slow- and fast-growing birds in experiment 1 were different. The degree of effect of the low-nutrient diet on weight gain of the slow-growing birds was somewhat surprising in light of their body composition. As evident in both experiments and in previous research (Fanatico et al., 2005), the slow-growing birds are much less heavily muscled (Tables 7 and 8) than the fast-growing birds; however, the slow-growing birds appear to have a greater proportion of feathers relative to their BW, which could conceivably affect sulfur amino acid requirements.

Livability

The slow-growing birds had much lower mortality than the fast-growing genotype (Table 3 and 4). In both experiments, birds became infected with Escherichia coli at approximately 4 wk of age and were treated with oxytetracycline administered in water. Although the USDA prohibits the use of antibiotics in organic production, this study was not intended to be conducted under organic conditions. Slow-growing birds were not affected, although they presumably received the same exposure and were given the same antibiotic treatment. Consequently, in both trials, the fast-growing birds had a much higher mortality. Although the slow-growing birds had no mortality in experiment 1, the fast-growing birds averaged 10% mortality in experiment 1 and 14% mortality in experiment 2 (Tables 3 and 4). Although the mortality was variable within treatment and likely due in part to the Escherichia coli infection, these data agree with Lewis et al. (1997), who found no mortality in slow-growing birds and 11% in fast-growing birds. Slow-growing Label Rouge birds have been reported to have 3% mortality compared with 6% mortality of conventional flocks, even though the slow-growing birds are in production twice as long (J. M. Faure, Institut National de la Recherche Agronomique, Nouzilly, France, personal communication). In addition to the effect on the number of birds available for processing, livability is a welfare issue of concern to some consumers and could affect purchasing decisions and therefore perceived product value.

In experiment 1, there was no effect of genotype on BMD after adjusting for BW (P > 0.05; Table 3). There was also no effect (P > 0.05) of production system on BMD, even with the slow-growing broilers that foraged extensively when outdoors. In experiment 2, the conventional diet resulted in a higher BMD (P < 0.05) in both genotypes (Table 4). Calcium and phosphorus levels in the conventional and low-nutrient diets were similar in the grower II and finisher diet phases, with Ca being higher in the conventional diet during the starter and grower I phases.

The prevalence of bone and joint disorders in broiler chickens continues to be a concern (Mench, 2004). Both infectious and noninfectious skeletal conditions are seen in commercial broilers, but the incidence varies widely from one flock to another. Among the most common disorders are bacterial chondronecrosis, angular deformities (e.g., valgus-varus), and TD. All of these disorders can impair mobility. Although their causes are complex and multifactorial, fast growth is certainly a contributing factor (Mench, 2004). Slower-growing birds have a lower incidence of bacterial chondronecrosis (McNamee and Smythe, 2000), and slowing growth in the first 15 to 20 d of life can reduce incidence of angular bone deformity and dyschondroplasia (Classen and Riddell, 1989). Slow-growing genotypes are reported to have less varus-valgus deformity than fast-growing genotypes (Leterrier et al., 1998).

In the present study, gait scores and incidence rates for TD showed clear advantages for the slow-growing birds in both experiments (Tables 5 and 6). In experiment 1, the slow-growing birds all had gait scores of 0, whereas the fast-growing birds had higher scores (P < 0.05); birds with gait scores of 4 and 5 were culled for lameness during the course of the trial. In the fast-growing genotype, birds in the production system with outdoor access had better gait scores than the indoor birds (P < 0.05). In experiment 2, again the slow-growing birds had much better gait scores (P < 0.05). For both genotypes, the conventional diet resulted in worse gait scores (P < 0.05). The gait score results could have been affected by genotype differences in both growth rate and in conformation, because the larger breast size of fast-growing strains causes their center of gravity to shift forward, resulting in a more inefficient and tiring gait pattern (Corr et al., 2003). The outdoor access most likely resulted in better gait score due to the opportunity for exercise; Falcone et al. (2004) found that the walking ability of broilers can be improved in more complex environments that promote activity.

Carcass Yield

Carcass weights reflect differences in weight gain, with the production system with outdoor access having no effect (P > 0.05) on carcass weight and with the fast-growing birds having higher carcass weights (P < 0.05) than the slow-growing birds (Table 7). Similarly, RTC yield was higher (P < 0.05) for the fast-growing birds. Interestingly, the overall effect of production system on RTC yield was significant (P < 0.05) because of the effect on the slow-growing birds, which had a lower RTC yield when provided outdoor access as compared with the conventional indoor production system. There was no effect (P > 0.05) of outdoor access on breast weight and breast yield (pectoralis major and pectoralis minor), but both were affected by genotype, with the fast-growing birds exhibiting far superior values (P < 0.05) in both categories. Wing yield was reduced and leg yield increased (P < 0.05) by outdoor access; for both parameters, the effect of outdoor access was greater in the slow-growing birds. There was a significant genotype effect on wing, leg, and frame yield; slow-growing broilers had a higher percentage (P < 0.05) yield in each category, which is reflective of the large percentage difference in breast yield.

Lewis et al. (1997) found that a low stocking density increased breast yield compared with a high stocking density; Fanatico et al. (2005) observed a nonsignificant increase in breast yield for fast- and slow-growing broilers provided outdoor access. However, in experiment 1, we failed to note a similar trend in birds provided outdoor access, which had a much greater area in which to grow. Rather, production system had a greater effect on leg yield of the slow-growing genotype, perhaps due to increased activity of these birds when provided outdoor access.

The low-nutrient diet reduced the carcass weight of the slow-growing birds as compared with carcass weights among birds of other treatment groups (P < 0.05; Table 8). The low-nutrient diet reduced RTC yield in fast-growing, but not slow-growing, birds (genotype x diet interaction, P < 0.05). Similar to experiment 1, in experiment 2, breast weight and breast yield were affected substantially by genotype, with the fast-growing birds exhibiting far superior values (P < 0.05) in both categories (Table 8). Breast weight and breast yield were reduced (P < 0.05) in birds fed the low-nutrient diet, and the effect on breast yield was more pronounced in the fast-growing broilers. As in experiment 1, wing and frame yields in experiment 2 were higher (P < 0.05) for the slow-growing birds, but in contrast to the first experiment, there was no effect (P> 0.05) of genotype on leg yield. Dietary regimen (low-nutrient vs. conventional) had no effect (P > 0.05) on wing, leg, or frame yield (Table 8).

Although weight gain of the fast-growing broilers was maintained on the low-nutrient diet (Table 4), breast yield was reduced (Table 8). Therefore, although nutrient intake was sufficient to maintain overall BW, it appeared that the nutrient level was insufficient to support maximum breast yield. Some researchers have suggested that amino acid needs for maximum breast yield exceed those needed for maximum growth performance (Sibbald and Wolynetz, 1986; Moran and Bilgili, 1990; Bilgili et al., 1992; Schutte and Pack, 1995; Dozier et al., 2000), whereas other researchers have not reported similar results (Kidd et al., 1999, 2003, 2004; Garcia et al., 2006). Our data on breast yield are in agreement with that of Gordon and Charles (2002), who reported that the reduction in breast meat yield of broilers fed a low-nutrient diet was not as large in slow-growing broilers as in fast-growing broilers.

In agreement with the findings of Fanatico et al. (2005), in which similar genotypes were used, results of both trials highlight basic growth and carcass differences between the fast- and slow-growing broilers. Indicative of their classification, slow-growing broilers had a much slower and less efficient pattern of growth and were much less heavily muscled. In particular, there was a striking difference in breast meat quantity and yield, which reflects the years of genetic improvements in breast meat quantity that have led to the present-day fast-growing broiler. Although there are differences in trial design, our results are similar in many ways to those of Havenstein et al. (1994, 2003), who conducted a series of studies to assess the effect of genetics and diet on growth performance of slower-growing 1957 broilers and faster-growing 1991 or 2001 broilers. They cited large differences in growth rate, and most of the difference was attributed to genetics, with 10 to 15% of the difference brought about through improved diets.

Alternative poultry producers are aware that outdoor access can affect growth performance and efficiency. However, an increasing number of consumers are interested in purchasing poultry products that were produced in alternative systems that typically provide outdoor access; recently, nearly 10% of Americans surveyed reported that they regularly consume organic products (Hisey, 2004). Consumers must be willing to pay a premium for alterative poultry products to overcome inefficiencies in the production system.

In some countries, alternative production systems such as free-range and organic must adhere to standards that define stocking density, outdoor access, genotype, and diet. In the Label Rouge program in France, the use of slow-growing genotypes and low-nutrient diets is required (Ministère de L’Agriculture, 1996). Currently, alternative production systems in the United States are not standardized, and producers have more freedom in defining their production system. However, the choice of genotype in an alternative production system is not a simple question. It is influenced not only by bird growth and feed efficiency but also by livability, welfare, behavior, and consumer preferences. Despite poorer performance and efficiency, slow-growing birds had better livability with lower mortality and fewer leg disorders. Further, from a behavioral standpoint, slow-growing birds may be more adapted to an alternative production because they forage more actively, but availability of specialty slow-growing genetics is currently limited in the United States.

The issue then is the amount of premium consumers are willing to pay and the type of product they expect to receive. Producers that elect to purchase and raise slow-growing broilers with low-nutrient diets will raise fewer flocks per year, and resulting broiler carcasses will not have the meaty appearance of fast-growing commercial broilers. However, for some consumers, this may be acceptable and even desirable. For these consumers, the production system, the genotype, and the diet may all be part of a total package that is desired. It would seem, however, for alternative production systems in which further processing will be conducted, a more heavily muscled genotype could be beneficial. An intermediate-type bird may be of interest; in France, a medium-growing genotype that is harvested at 56 d has gained market share (Beaumont et al., 2004).

In conclusion, the production system with outdoor access resulted in increased feed intake and poorer feed conversion compared with a conventional system. The fast-growing birds had superior growth performance and breast yield, whereas the slow-growing birds had less mortality and improved bone health, which is important in an alternative system. The use of a low-nutrient diet improved gait score in fast- and slow-growing birds, although it reduced BW in slow-growing birds and breast yield in fast-growing broilers. Alternative poultry producers need to understand the expectations and willingness of target consumers to pay a premium price to assess whether it is possible to offset the higher cost of production associated with slow-growing genotypes.

	ACKNOWLEDGMENTS

 
We would like to thank the USDA Southern Region Sustainable Agriculture Research and Education program and the US Poultry and Egg Association (Tucker, GA) for providing funding for this research. Funding for this project was also provided by the National Research Initiative of the USDA Cooperative State Research, Education and Extension Service, grant number 2001-35204-10800, to J. A. Mench. We also thank N. C. Rath with the USDA Agricultural Research Service (Fayetteville, AR) for TD analysis and P. Talaty (Purdue University, West Lafayette, IN) for technical assistance in use of dual-energy x-ray absorptiometry.

Received for publication December 11, 2006. Accepted for publication February 8, 2008.

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