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A review of the effects of stocking density on turkey behavior, welfare, and productivity
A review of the effects of stocking density on turkey behavior, welfare, and productivity M. A. Erasmus1 Department of Animal Sciences, Purdue University, West Lafayette, IN 47907 Scientific research into stocking density effects on turkey behavior, welfare, and productivity have been conducted in experimental settings with flock sizes that are much different from those in the commercial turkey industry. There is currently little information available regarding how much space turkeys require for particular behavioral activities. This paper reviews the current industry guidelines and standards as well as scientific literature pertaining to stocking densities for commercial turkeys.
ABSTRACT Stocking density, the amount of space available per animal, greatly affects the welfare of commercial turkeys. For example, stocking density has been found to affect behavior such as injurious pecking; production, such as growth rates and feed efficiency; and health-related aspects, such as leg health and the incidence of airsacculitis. Current industry guidelines and standards for turkey space requirements and stocking densities vary, and they are different from those that have been examined scientifically.
Key words: Stocking density, turkey, behavior, welfare, productivity 2017 Poultry Science 0:1–6 http://dx.doi.org/10.3382/ps/pex075
INTRODUCTION
view). Certification programs such as American Humane Certified (American Humane Association, 2013) and Certified Humane (Humane Farm Animal Care, 2014) also focus on the ability of birds to stand, turn around, and stretch their wings. The number of animals housed within a particular area affects how much space is available to any one animal within the group, as well as how each animal is able to use the available space. Therefore, it is difficult to separate the effects of space, group size, and stocking density (space per animal or average body weight per unit of space; discussed in Marchewka et al., 2013; also see Estevez et al., 2007; Leone et al., 2010). These 3 factors are often confounded in the scientific literature. Although stocking density has been identified as one of the main factors affecting turkey welfare (Marchewka et al., 2013), specific stocking density recommendations for turkeys vary widely among industry guidelines and certification programs. This paper reviews the scientific literature pertaining to the impacts of stocking density on turkey behavior, welfare, and productivity, with a focus on stocking density recommendations in North America. The majority of the world’s live turkeys are produced in North America (243.2 million in 2014, representing over 52% of the world’s live turkey production), followed by Europe (110.8 million turkeys), South America (65 million), Africa (23.7 million), and Asia (14.6 million) (Food and Agriculture Organization of the United Nations, 2017). An understanding of the effects and importance of stocking density can help to optimize stocking density recommendations for commercially housed turkeys.
The amount of space that farm animals require has been a contentious issue for the past several years, as indicated by the increase in legislation regarding housing and space requirements for laying hens, gestating sows, and veal calves (e.g.: in the United States, Proposition 2 of 2008 in California and Public Act 117 of 2009 in Michigan; in Europe, Council Directive 1999/74/EC for laying hens and Council Directive 2008/120/EC for pigs). In addition to more legislation, the number of animal welfare certification programs for farm animals has increased in recent years. Although there has not been similar legislation specifying space requirements for turkeys, the importance of space for turkeys is reflected in industry guidelines and standards, which focus on behavioral requirements. For example, the National Turkey Federation guidelines state that turkeys “must have enough space at each stage of production to stretch, move about comfortably, preen, grow, and produce normally” (National Turkey Federation, 2012). The Canadian Codes of Practice similarly state that “birds must have enough space to move freely, be able to stand normally, turn around and stretch their wings without difficulty” (Canadian Agri-Food Research Council, 2015; currently under re-
C 2017 Poultry Science Association Inc. Received December 19, 2016. Accepted March 20, 2017. 1 Corresponding author: [email protected]
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ERASMUS Table 1. General stocking density standards and guidelines for meat turkeys. Information has been adapted from the National Turkey Federation (2012), Canadian Codes of Practice (Canadian Agri-Food Research Council, 2015; under review), Certified Humane (Humane Farm Animal Care, 2014), Global Animal Partnership (2011), and the “Ag Guide” (Federation of Animal Science Societies, 2010). Source
Category or description
Maximum stocking density∗ lb/ft2 kg/m2
National Turkey Federation Federal Animal Science Societies Guide (“Ag Guide”)
To be used as a “measurable standard”
15
73.2
< 0.7 lb (< 0.3 kg) 0.7–4.4 lb (0.3–2.0 kg) 4.4–6.6 lb (2.0–3.0 kg) 6.6–13.2 lb (3.0–6.0 kg) 13.2–17.6 lb (6.0–8.0 kg) 17.6–26.4 lb (8.0–12.0 kg) 26.4–35.2 lb (12.0–16.0 kg) 35.2–44.1 lb (16.0–20.0 kg) Broilers (up to 13.7 lb, 6.2 kg) Hens (13.7–23.8 lb, 6.2–10.8 kg) Light toms (23.8–29.3 lb, 10.8–13.3 kg) Heavy toms (> 29.3 lb, 13.3 kg) Step 1 Step 2 Step 3 Steps 4 & 5 Maximum for broilers, hens, toms and heavy toms
2.3 1.2-7.3 4.9-7.3 4.4-8.8 6.6-8.8 5.9-8.8 6.9-9.3 8.4-10.5 9.2 9.2 11.3 12.3 10 7.5 6.5 6 7.5
11.2 (0.026 m2 /bird) 5.9–35.6 (0.058 m2 /bird) 23.9–35.6 (0.081 m2 /bird) 21.5–43.0 (0.14 m2 /bird) 32.2–43.0 (0.19 m2 /bird) 28.8–43.8 (0.27 m2 /bird) 33.7–45.4 (0.35 m2 /bird) 41.0–51.3 (0.39 m2 /bird) 45 45 55 60 48.8 36.6 31.7 29.3 36.6
Canadian Codes of Practice Global Animal Partnership Certified Humane
∗ Space requirements and stocking densities are reported differently depending on the source of information. Therefore, stocking densities in lb/ft2 and kg/m2 were calculated for ease of comparison. Space per bird is included in the table if it was provided in the original source.
Current Recommendations and Standards In Europe, the Council of Europe does not provide specific stocking density guidelines for turkeys. Rather, the Council of Europe Recommendation Concerning Turkeys (2001) states that factors such as turkeys’ age, sex, and weight should be considered such that turkeys are able to “move around freely” and “perform normal social behavior.” Within North America, the recommended stocking densities for turkeys vary among organizations and certification programs. For example, the National Turkey Federation (2012) suggests a standard density of 73.2 kg/m2 (15 lbs/ft2 ), whereas the Global Animal Partnership (2011) standards range from 29.3 to 48.8 kg/m2 (6 to 10 lbs/ft2 ) depending on the level of certification. Current standards and recommended densities for North America are summarized in Table 1 (meat turkeys) and Table 2 (breeder turkeys). The units in which density or space requirements are stated differ among industry standards, which are often reported in weight per unit of space (E.g. NTF, 2012; AHA, 2013), and scientific studies, which typically state densities as space available per bird (m2 /bird) or as the number of birds per area (birds/m2 ). There is a large variation in the group sizes, space allocations and ages of turkeys that have been used in experimental studies, making comparisons among studies difficult. A summary of the available literature for male turkeys is provided in Table 3.
Space Requirements Poultry should have enough space to be able to perform certain types of behavior, such as being able
to walk normally, get up and lie down, turn around, and preen (Jankowski et al., 2015). In order to assess how much space turkeys need, Ellerbrock and Knierim (2002) measured the area occupied by stationary turkeys using photographs. Turkeys at 11 (7.6 kg; 16.7 lb) and 21 (21.8 kg; 48.0 lb) wk of age occupied between 0.08 m2 (0.9 ft2 ) and 0.20 m2 (2.1 ft2 ) when stationary (Ellerbrock and Knierim, 2002). Ellerbrock and Knierim (2002) propose that as turkeys become larger, the amount of space required per unit of body weight decreases. Therefore, it is possible that larger turkeys “require less floor area per kilogram liveweight than smaller ones” (Ellerbrock and Knierim, 2002). However, the aforementioned measurements are for standing, stationary turkeys and space requirements vary depending on the behavior and activity of the bird. Currently, the effects of stocking density on space use and how space use changes with increasing age are unknown.
Space and Stocking Density Effects on Turkey Behavior and Welfare The effects of stocking density and group size on turkey behavior and welfare have recently been reviewed by Marchewka et al. (2013), and center on aggression, feather pecking and behavioral disturbances. There do not appear to be any recently published studies comparing the effects of stocking density on aggression and pecking behavior of turkeys in large groups. However, there is some information available pertaining to the incidences of aggression, head, back and vent wounds for turkeys in commercial flocks where thousands of birds are housed together (see Marchewka et al., 2015).
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STOCKING DENSITY, TURKEY WELFARE, AND PRODUCTIVITY Table 2. Stocking density standards and guidelines for breeder turkeys. Maximum stocking density∗ lb/ft2 or ft2 /bird kg/m2 or m2 /bird
Source
Category or description
National Turkey Federation
“Adequate roaming space; birds free to roam throughout growing area. Birds can stand up, sit down and spread their wings.”
Federation of Animal Science Societies Guide (“Ag Guide”)
Breeder Breeder Breeder Breeder Breeder Breeder
Certified Humane
Breeder females up to 8 wk 1.5 ft2 /bird Breeder females (grower house) 2.5 ft2 /bird Breeder females (darkening phase) 3.5 ft2 /bird Breeder females (laying phase) 5.5 ft2 /bird Breeder males up to 8 wk 2 ft2 /bird Breeder males 8–16 wk 6 ft2 /bird Breeder males > 16 wk 10 ft2 /bird “Additional space must be provided as needed to maintain bird welfare”
females < 17.6 lb (< 8.0 kg) females 17.6–26.4 (8.0–12.0 kg) females > 26.4 (> 12.0 kg) males < 26.4 (< 12.0 kg) males 26.4–37.4 (12.0–17.0 kg) males > 37.4 (> 17.0 kg)
5.9 lb/ft2 4.4–6.6 lb/ft2 5.3 lb/ft2 6.6 lb/ft2 5.3–7.5 lb/ft2 > 6.2 lb/ft2
28.8 (0.28 m2 /bird) 21.5–32.2 (0.37 m2 /bird) > 25.9 (0.46 m2 /bird) 32.2 (0.37 m2 /bird) 25.8–36.6 (0.46 m2 /bird) > 30.3 (0.56 m2 /bird) 0.14 m2 0.23 m2 0.33 m2 0.51 m2 0.19 m2 0.56 m2 0.90 m2
Information has been adapted from the National Turkey Federation (2012), Canadian Codes of Practice (Canadian Agri-Food Research Council, 2015; under review), Certified Humane (Humane Farm Animal Care, 2014), Global Animal Partnership (2011), and the “Ag Guide” (Federation of Animal Science Societies, 2010). ∗ Space requirements and stocking densities are reported differently depending on the source of information. Therefore, stocking densities in lb/ft2 and kg/m2 were calculated for ease of comparison. Space per bird is included in the table if it was provided in the original source.
Marchewka et al. (2015) assessed the welfare of turkeys on 10 commercial farms where the flock size ranged from 6,460 to 8,462 birds and the stocking density was 3.5 birds/m2 (0.29 m2 /bird) to 3.6 birds/m2 (0.28 m2 /bird) at 6 wk of age when birds were placed. Head wounds were present in 3.4 ± 1.0% and 3.5 ± 1.0% of turkeys as recorded by two observers, respectively (Marchewka et al., 2015). The observers also recorded the percentages of turkeys with back wounds (observer 1: 0.4 ± 0.1%; observer 2: 0.3 ± 0.1%), vent wounds (0.1 ± 0.1% for both observers) and the percentages of turkeys that were featherless (0.02 ± 0.01% for both observers). Cumulative mortality across all flocks was 15 ± 1.4% at 19 to 20 wk of age (Marchewka et al., 2015). Although Marchewka et al. (2015) did not compare stocking densities, their study is the first to examine the incidence of various welfare problems at commercial stocking densities. Up to a certain group size, turkeys are able to distinguish between familiar and unfamiliar conspecifics, which affects the level of aggression. Buchwalder and Huber-Eicher (2004; 2005) examined the relationships among group size, space, and aggression in turkey toms. Their research revealed that when an unfamiliar tom was introduced into a group of turkeys, group size influenced aggression. Specifically, the level of aggression directed at the unfamiliar tom was higher when the tom was introduced into a group of 6 vs. 30 toms, suggesting that turkeys are limited as to how many individuals they can distinguish among, which Buchwalder and Huber-Eicher refer to as the “limiting group size” (Buchwalder and Huber-Eicher, 2005). Space was also important in determining aggression: turkey toms reacted more aggressively toward an unfamiliar tom when the unfamiliar tom was introduced into a smaller vs. a larger pen (Buchwalder and Huber-Eicher, 2004). In an-
other study, Moran (1985) reported that mortality rates due to fighting were higher for turkey toms reared at a lower density (0.89 m2 /bird; 9.6 ft2 /bird) compared to a higher density (0.44 m2 /bird; 4.7 ft2 /bird). In addition to affecting levels of aggression, stocking density may impact other injurious behavior such as feather pecking. One study reported higher levels of feather damage in turkeys housed at a density of 0.74 vs. 1.86 m2 /bird (0.8 vs. 2.0 ft2 /bird; Gill and Leighton, 1984). Feather pecking is a multifactorial problem that is affected by many other factors (reviewed in Dalton et al., 2013) and further research is needed to understand the impacts of stocking density on feather-pecking behavior. With increasing stocking density, there is a greater potential for birds to be disturbed by others in the group. Martrenchar et al. (1999) reported that the amount of time that turkeys were able to rest without being disturbed was shorter at 9 wk of age when turkeys were housed at 5 birds/m2 (129.4 ± 22.9 sec) vs. 8 birds/m2 (67.1 ± 10.7 sec). There is some evidence from research with broiler chickens that increased disturbance is associated with reduced feed efficiency and reduced carcass quality due to bruises and scratches (Cornetto et al., 2002), but the effects of disturbances on turkey productivity and carcass quality are as yet unknown. In addition to behavior, a stocking density that is too high can increase the risk for leg and foot problems, mortality, breast blisters, and airsacculitis. Indeed, Martrenchar et al. (1999) reported that the incidence of footpad lesions increased and gait worsened as the amount of space available per male turkey decreased from 0.40 m2 /bird (10.7 lb/ft2 ) to 0.25 m2 /bird (6.4 lb/ft2 ) from 12 to 16 wk. Berk and Hahn (2000) reported that the percentage of turkeys with breast
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Table 3. Summary of published literature examining stocking density effects on male turkey welfare and productivity. Publication
Age
Group size
Space provided (m2 /bird)
Calculated stocking density at end of study (lb/ft2 )∗
Moran (1985)
0–38 d
120 60 30 15
0.077 (120 birds) 0.15 (60 birds) 0.44 (30 birds) 0.89 (15 birds)
5.1 lb/ft2 (0.44 m2 /bird) at 18.7 wk 2.6 lb/ft2 (0.89 m2 /bird) at 18.7 wk
38–131 d Noll et al. (1991)
0–20 wk
13 28
0.21 (13 birds) 0.46 (28 birds)
13.2 lb/ft2 (0.21 m2 /bird) at 20 wk 5.7 lb/ft2 (0.46 m2 /bird) at 20 wk
Zuidhof et al. (1993)
8–16 wk
75 38 Turkeys removed weekly
Space ranges: 0.18 (for 75 birds)– 0.27 (for 51 birds) 0.36 (for 38 birds)– 0.53 (for 26 birds)
5.12 lb/ft2 (0.27 m2 /bird) at 16 wk 10.25 lb/ft2 (0.53 m2 /bird) at 16 wk
Perkins et al. (1995)
8–12 wk
75 37 50 25 317 439 540 317 439 540
0.18 0.36 0.27 0.54 0.24 0.19 0.15 0.40 0.31 0.25
8.5–8.9 lb/ft2 (0.27 m2 /bird) at 16 wk 4.1–4.2 lb/ft2 (0.54 m2 /bird) at 16 wk
12–16 wk Martrenchar et al. (1999)
0–12 wk
12–16 wk
(75 birds) (37 birds) (50 birds) (25 birds) (317 birds) (439 birds) (540 birds) (317 birds) (439 birds) (540 birds)
Berk and Hahn (2000)
0–20 wk
27 63
0.65 (27 birds) 0.28 (63 birds) Free range access provided from 6 wk
Jankowski et al. (2014)
1–126 d
28 34
Marchewka et al. (2015)
6 wk
Between 6,460 and 8,462
0.36 (28 birds) 0.29 (34 birds) – birds were heat stressed 0.28–0.29 when placed at 6 wk
Data collected at 19–20 wk
Experiment 1: 6.43 lb/ft2 (0.40 m2 /bird) at 16 wk 8.67 lb/ft2 (0.31 m2 /bird) at 16 wk 10.71 lb/ft2 (0.25 m2 /bird) at 16 wk Experiment 2: 6.49 lb/ft2 (0.24 m2 /bird) at 16 wk 8.57 lb/ft2 (0.19 m2 /bird) at 16 wk 10.17 lb/ft2 (0.15 m2 /bird) at 16 wk Body weights not reported
10.5 lb/ft2 (0.36 m2 /bird) at 18 wk 12.3 lb/ft2 (0.29 m2 /bird) at 18 wk Bird numbers at 19–20 wk not reported Commercial study: stocking densities were not compared
∗ Stocking density in lb/ft2 was calculated using the final reported body weights divided by the area of space provided so that densities would be comparable to how densities are typically reported in the U.S. turkey industry.
blisters was higher for turkeys housed at 3.5 birds/m2 (11.6%) compared to 1.5 birds/m2 (5.3%). Mortality rates were also higher at the higher density (Berk and Hahn, 2000). Similarly, Noll et al. (1991) reported that mortality rates tended to be higher (5.4% vs. 3.1%) at a higher stocking density (0.46 vs. 0.21 m2 /bird; 13.2 vs. 5.7 lb/ft2 at 20 wk). Higher stocking densities may also be associated with respiratory problems. The incidence of airsacculitis was higher (25% vs. 11.7% of turkeys) when turkeys were housed at a density of 0.46 m2 /bird (13.2 lb/ft2 at 20 wk) compared to 0.21 m2 /bird (5.7 lb/ft2 at 20 wk; Noll et al., 1991). Furthermore, the severity of lung lesions tended to be greater in turkeys housed at a higher density (5.5 turkeys/m2 vs. 2.8 turkeys/m2 ; 8.5 to 8.9 lb/ft2 vs. 4.1 to 4.2 lb/ft2 at 16 wk; Perkins et al., 1995). However, another study reported no differences in lung lesions between densities of 5.5 and 2.8 turkeys/m2 (10.3 lb/ft2 vs. 5.1 lb/ft2 at 16 wk; Zuidhof et al., 1993). It is possible that turkeys that are housed at higher stocking densities experience greater levels of stress, which contribute to the development of respiratory problems (Perkins et al., 1995). Turkeys housed at higher densities may also be less capable of coping with additional environ-
mental stressors such as elevated environmental temperatures: Perkins et al. (1995) reported that a higher percentage of turkeys were gasping (31% of turkeys at 5.5 turkeys/m2 vs. 6% of turkeys at 2.8 turkeys/m2 ) when the environmental temperature was raised to 30˚C for 1 h.
Stocking Density Impacts on Productivity of Turkeys Productivity parameters that have been evaluated in relation to stocking density include body weight, feed conversion, and carcass characteristics. Martrenchar et al. (1999) conducted 2 experiments examining the impacts of stocking density on productivity of turkeys. Turkeys were housed at one of 3 stocking densities from 0 to 12 wk (0.24, 0.185, or 0.15 m2 /bird) then provided with more space from 12 to 16 wk (0.40 m2 /bird (6.4 lb/ft2 at 16 wk), 0.31 m2 /bird (8.6 lb/ft2 at 16 wk) or 0.25 m2 /bird (10.7 lb/ft2 at 16 wk), respectively). Body weights were highest for turkeys provided with 0.24 to 0.40 m2 /bird (Experiment 1: 13.4 ± 0.1 kg;
STOCKING DENSITY, TURKEY WELFARE, AND PRODUCTIVITY
Experiment 2: 13.5 ± 0.11 kg) compared to turkeys provided with 0.185 to 0.31 m2 /bird (Experiment 1: 13.1 ± 0.1 kg; Experiment 2: 12.9 ± 0.11) or 0.15 to 0.25 m2 /bird (Experiment 1: 13.1 ± 0.96 kg; Experiment 2: 12.4 ± 0.13 kg). Similarly, Noll et al. (1991) reported higher body weights at both 16 (10.3 kg vs. 10.0 kg) and 20 wk (13.5 kg vs. 12.8 kg) for turkeys housed at 2.2 birds/m2 (5.7 lb/ft2 at 20 wk) compared to turkeys housed at 4.8 birds/m2 (13.2 lb/ft2 at 20 wk). The effects of stocking density on feed conversion were similar: turkeys housed at 2.2 birds/m2 (4.1 g feed/g weight gain) had improved feed conversion compared to turkeys housed at 4.8 birds/m2 (4.3 g feed/g weight gain; Noll et al., 1991). In contrast, Moran (1985), comparing 0.44 vs. 0.89 m2 /bird (5.1 vs. 2.6 lb/ft2 at 19 wk), and Perkins et al. (1995), comparing 0.27 vs. 0.54 m2 /bird (8.5 to 8.9 vs. 4.1 to 4.2 lb/ft2 at 16 wk), reported no differences in male turkey weights due to stocking density. Zuidhof et al. (1993) reported that a low ventilation rate (225 L/s) in combination with a high stocking density (0.53 m2 /bird or 10.25 lb/ft2 ) resulted in lower weight gains compared to the same ventilation rate but a lower stocking density (0.27 m2 /bird or 5.12 lb/ft2 ), indicating that environmental factors may interact with stocking density to affect productivity. A recent experimental study examined the effects of stocking density and heat stress on body weight, feed intake, and skeletal characteristics of turkeys from 1 d to 19 wk of age (Jankowski et al., 2015). Turkeys reared at a higher density (3.4 birds/m2 or 0.29 m2 /bird) combined with a higher environmental temperature (5◦ C higher than the control group) had a lower average body weight at 18 wk (17.7 ± 0.47 kg vs. 18.4 ± 0.43 kg) compared to turkeys housed at a density of 2.8 birds/m2 (0.36 m2 /bird) and breeder (Aviagen Turkeys) recommended temperatures (Jankowski et al., 2015). The increased stocking density together with increased temperature negatively affected bone length and bone weight after 4 wk and bone strength at 18 wk, indicating lower skeletal quality and potentially greater problems with locomotion (Jankowski et al., 2015). Because the effects of temperature and stocking density were confounded, it is not possible to determine how stocking density alone affected body weight and bone characteristics. Lastly, there is some evidence that carcass composition is also affected by stocking density. Carcasses from turkeys reared at a lower density of 0.46 m2 /bird had a greater percentage of abdominal fat (1.24 vs. 1.05%), lower carcass moisture content (63.2 vs. 64.2%) and more total breast meat (1.53 vs. 1.46 kg; but breast meat as a percentage of bodyweight did not differ among densities) compared to turkeys reared at 0.21 m2 /bird (Halvorson et al., 1991). The authors postulate that the amount of carcass fat was likely higher in the low density group because turkeys in the low density group consumed excess feed (Halvorson et al. 1991).
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CONCLUSION Stocking density standards and guidelines for turkeys vary depending on body weight and stage of production. Stocking densities range from as low as 5.9 kg/m2 (1.2 lb/ft2 ; Federation of Animal Science Societies, 2010) to as high as 73.2 kg/m2 (15 lb/ft2 ; National Turkey Federation, 2012) for meat turkeys, and as low as 21.5 kg/m2 (4.4 lb/ft2 ; Federation of Animal Science Societies, 2010) to 30.3 kg/m2 (6.2 lb/ft2 ; Federation of Animal Science Societies, 2010) for breeder turkeys. Certified Humane standards for breeder turkeys are even higher, ranging between 0.14 and 0.90 m2 /bird (Humane Farm Animal Care, 2014). There is little overlap between industry standards and densities that have been evaluated scientifically, which range from 12.7 kg/m2 (2.6 lb/ft2 ; Moran, 1985) to 64.4 kg/m2 (13.2 lb/ft2 ; Noll et al., 1991). Densities as high as 73.2 kg/m2 have not been evaluated, and the majority of scientific studies were conducted over a decade ago with genetic lines of turkeys that may differ from modern genetic lines in feed efficiency and growth rates. However, a review of the literature provides insight into potential effects of stocking density on turkey productivity, behavior and welfare. In general, higher densities (greater than 29.3 kg/m2 or 6 lb/ft2 ) are associated with reduced body weight, reduced feed efficiency, and increased mortality rates. Moreover, higher stocking densities lead to increased risks of footpad dermatitis, breast blisters, and respiratory problems. Higher stocking densities also lead to disturbances of resting birds and may increase levels of aggression and feather pecking. While industry standards and guidelines focus on providing turkeys with adequate space to perform particular behaviors, there is currently no scientific information available as to the amount of space turkeys need for particular behaviors. It is important to note that many welfare issues of turkeys are multifactorial in nature and are not influenced by stocking density alone, but are also influenced by other factors, such as environmental and management factors. Welfare issues resulting from management and environmental factors can be further aggravated by high stocking densities. For example, with a higher stocking density, more waste is produced, which necessitates judicious management and appropriate ventilation to maintain an appropriate level of litter quality. Further research is needed to understand the interactions among management, stocking density, and turkey behavior in order to inform space and stocking density standards.
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Berk, J., and G. Hahn. 2000. Aspects of animal behaviour and product quality of fattening turkeys influenced by modified husbandry. Arch. Tierz. 43: 189–195. Buchwalder, T., and B. Huber-Eicher. 2004. Effect of increased floor space on aggressive behaviour in male turkeys (Meleagris gallopavo). Appl. Anim. Behav. Sci. 89:207–214. Buchwalder, T., and B. Huber-Eicher. 2005. Effect of group size on aggressive reactions to an introduced conspecific in groups of domestic turkeys (Meleagris gallopavo). Appl. Anim. Behav. Sci. 93: 251–258. Canadian Agri-Food Research Council, 2015. Recommended code of practice for the care and handling of farm animals: chickens, turkeys and breeders from hatchery to processing plant. Accessed Mar. 2016. https://www.nfacc.ca/pdfs/codes/chickens turkeys breeders code of practice.pdf. Cornetto, T., I. Estevez, and L. W. Douglass. 2002. Using artificial cover to reduce aggression and disturbances in domestic fowl. Appl. Anim. Behav. Sci. 75:325–336. Dalton, H. A., B. J. Wood, and S. Torrey. 2013. Injurious pecking in domestic turkeys: development, causes and potential solutions. World. Poult. Sci. J. 69: 865–875. Ellerbrock, S., and U. Knierim. 2002. Static space requirements of male meat turkeys. Vet. Rec. 151: 54–57. Estevez, I., I. E. Andersen, and E. Nævdal, 2007. Group size, density and social dynamics in farm animals. Appl. Anim. Behav. Sci. 103:185–204. Federation of Animal Science Societies, 2010. Guide for the Care and Use of Agricultural Animals in Research and Teaching. 3rd Ed. Chapter 9 Poultry. Accessed Mar. 2016. http://www.fass.org/docs/agguide3rd/Chapter09.pdf. Food and Agriculture Organization of the United Nations, 2017. FAOSTAT. Accessed Feb. 2017. http://www.fao.org/ faostat/en/#data/QA. Gill, D. J., and A. T. Leighton, Jr. 1984. Effects of light environment and population density on growth performance of male turkeys. Poult. Sci. 63:1314–1321. Global Animal Partnership, 2011. Global Animal Partnership’s R Animal Welfare Rating Standards for Turkeys v2.0. 5-Step Accessed Mar. 2016. http://glblanimalpartnership.blob.core. windows.net/standards/Turkey%20Welfare%20Standards% 20V2.0.pdf.
Humane Farm Animal Care, 2014. Animal care standards: turkeys. Accessed Mar. 2016. http://certifiedhumane.org/wpcontent/uploads/2015/09/Std14.Turkeys.1A.pdf. Halvorson, J. C., P. E. Waibel, E. M. Oju, S. L. Noll, and M. E. El Halawani. 1991. Effect of diet and population density on male turkeys under various environmental conditions. 2. Body composition and meat yield. Poult. Sci. 70:935–940. Jankowski, J., D. Mikulski, M. R. Tatara, and W. Krupski. 2015. Effects of increased stocking density and heat stress on growth, performance, carcase characteristics and skeletal properties in turkeys. Vet. Rec. 176:21–26. Leone, E. H., M. C. Christman, L. Douglass, and I. Estevez. 2010. Separating the impact of group size, density, and enclosure size on broiler movement and space use at a decreasing perimeter to area ratio. Behav. Process. 83:16–22. Marchewka, J., T. T. N. Watanabe, V. Ferrante, and I. Estevez. 2013. Review of the social and environmental factors affecting the behavior and welfare of turkeys (Meleagris gallopavo). Poult. Sci. 92:1467–1473. Marchewka, J., I. Estevez, G. Vezzoli, V. Ferrante, and M. M. Makagon. 2015. The transect method: a novel approach to on-farm welfare assessment of commercial turkeys. Poult. Sci. 94:7–16. Martrenchar, A., D. Huonnic, J. P. Cotte, E. Boilletot, and J. P. Morisse. 1999. Influence of stocking density on behavioural, health and productivity traits of turkeys in large flocks. Br. Poult. Sci. 40:323–331. Moran, E. T. 1985. Effect of toe clipping and pen population density on performance and carcass quality of large turkeys reared sexes separately. Poult. Sci. 64:226–231. National Turkey Federation, 2012. Animal care best management practices. Available online: http://www.eatturkey.com/sites/ default/files/welfarm2012.pdf. Noll, S. L., M. E. El Halawani, P. Waibel, P. Redig, and K. Janni. 1991. Effect of diet and population density on male turkeys under various environmental conditions. 1. Turkey growth and health performance. Poult. Sci. 70:923–934. Perkins, S. L., M. J. Zuidhof, J. J. R. Feddes, and F. E. Robinson. 1995. Effect of stocking density on air quality and health and performance of heavy torn turkeys. Can. Agr. Eng. 37:109–112. Zuidhof, M. J., J. J. R. Feddes, and F. E. Robinson. 1993. Effect of ventilation rate and stocking density on turkey health and performance. J. Appl. Poult. Res. 2:123–129.
ABSTRACT Stocking density, the amount of space available per animal, greatly affects the welfare of commercial turkeys. For example, stocking density has been found to affect behavior such as injurious pecking; production, such as growth rates and feed efficiency; and health-related aspects, such as leg health and the incidence of airsacculitis. Current industry guidelines and standards for turkey space requirements and stocking densities vary, and they are different from those that have been examined scientifically.
Key words: Stocking density, turkey, behavior, welfare, productivity 2017 Poultry Science 0:1–6 http://dx.doi.org/10.3382/ps/pex075
INTRODUCTION
view). Certification programs such as American Humane Certified (American Humane Association, 2013) and Certified Humane (Humane Farm Animal Care, 2014) also focus on the ability of birds to stand, turn around, and stretch their wings. The number of animals housed within a particular area affects how much space is available to any one animal within the group, as well as how each animal is able to use the available space. Therefore, it is difficult to separate the effects of space, group size, and stocking density (space per animal or average body weight per unit of space; discussed in Marchewka et al., 2013; also see Estevez et al., 2007; Leone et al., 2010). These 3 factors are often confounded in the scientific literature. Although stocking density has been identified as one of the main factors affecting turkey welfare (Marchewka et al., 2013), specific stocking density recommendations for turkeys vary widely among industry guidelines and certification programs. This paper reviews the scientific literature pertaining to the impacts of stocking density on turkey behavior, welfare, and productivity, with a focus on stocking density recommendations in North America. The majority of the world’s live turkeys are produced in North America (243.2 million in 2014, representing over 52% of the world’s live turkey production), followed by Europe (110.8 million turkeys), South America (65 million), Africa (23.7 million), and Asia (14.6 million) (Food and Agriculture Organization of the United Nations, 2017). An understanding of the effects and importance of stocking density can help to optimize stocking density recommendations for commercially housed turkeys.
The amount of space that farm animals require has been a contentious issue for the past several years, as indicated by the increase in legislation regarding housing and space requirements for laying hens, gestating sows, and veal calves (e.g.: in the United States, Proposition 2 of 2008 in California and Public Act 117 of 2009 in Michigan; in Europe, Council Directive 1999/74/EC for laying hens and Council Directive 2008/120/EC for pigs). In addition to more legislation, the number of animal welfare certification programs for farm animals has increased in recent years. Although there has not been similar legislation specifying space requirements for turkeys, the importance of space for turkeys is reflected in industry guidelines and standards, which focus on behavioral requirements. For example, the National Turkey Federation guidelines state that turkeys “must have enough space at each stage of production to stretch, move about comfortably, preen, grow, and produce normally” (National Turkey Federation, 2012). The Canadian Codes of Practice similarly state that “birds must have enough space to move freely, be able to stand normally, turn around and stretch their wings without difficulty” (Canadian Agri-Food Research Council, 2015; currently under re-
C 2017 Poultry Science Association Inc. Received December 19, 2016. Accepted March 20, 2017. 1 Corresponding author: [email protected]
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ERASMUS Table 1. General stocking density standards and guidelines for meat turkeys. Information has been adapted from the National Turkey Federation (2012), Canadian Codes of Practice (Canadian Agri-Food Research Council, 2015; under review), Certified Humane (Humane Farm Animal Care, 2014), Global Animal Partnership (2011), and the “Ag Guide” (Federation of Animal Science Societies, 2010). Source
Category or description
Maximum stocking density∗ lb/ft2 kg/m2
National Turkey Federation Federal Animal Science Societies Guide (“Ag Guide”)
To be used as a “measurable standard”
15
73.2
< 0.7 lb (< 0.3 kg) 0.7–4.4 lb (0.3–2.0 kg) 4.4–6.6 lb (2.0–3.0 kg) 6.6–13.2 lb (3.0–6.0 kg) 13.2–17.6 lb (6.0–8.0 kg) 17.6–26.4 lb (8.0–12.0 kg) 26.4–35.2 lb (12.0–16.0 kg) 35.2–44.1 lb (16.0–20.0 kg) Broilers (up to 13.7 lb, 6.2 kg) Hens (13.7–23.8 lb, 6.2–10.8 kg) Light toms (23.8–29.3 lb, 10.8–13.3 kg) Heavy toms (> 29.3 lb, 13.3 kg) Step 1 Step 2 Step 3 Steps 4 & 5 Maximum for broilers, hens, toms and heavy toms
2.3 1.2-7.3 4.9-7.3 4.4-8.8 6.6-8.8 5.9-8.8 6.9-9.3 8.4-10.5 9.2 9.2 11.3 12.3 10 7.5 6.5 6 7.5
11.2 (0.026 m2 /bird) 5.9–35.6 (0.058 m2 /bird) 23.9–35.6 (0.081 m2 /bird) 21.5–43.0 (0.14 m2 /bird) 32.2–43.0 (0.19 m2 /bird) 28.8–43.8 (0.27 m2 /bird) 33.7–45.4 (0.35 m2 /bird) 41.0–51.3 (0.39 m2 /bird) 45 45 55 60 48.8 36.6 31.7 29.3 36.6
Canadian Codes of Practice Global Animal Partnership Certified Humane
∗ Space requirements and stocking densities are reported differently depending on the source of information. Therefore, stocking densities in lb/ft2 and kg/m2 were calculated for ease of comparison. Space per bird is included in the table if it was provided in the original source.
Current Recommendations and Standards In Europe, the Council of Europe does not provide specific stocking density guidelines for turkeys. Rather, the Council of Europe Recommendation Concerning Turkeys (2001) states that factors such as turkeys’ age, sex, and weight should be considered such that turkeys are able to “move around freely” and “perform normal social behavior.” Within North America, the recommended stocking densities for turkeys vary among organizations and certification programs. For example, the National Turkey Federation (2012) suggests a standard density of 73.2 kg/m2 (15 lbs/ft2 ), whereas the Global Animal Partnership (2011) standards range from 29.3 to 48.8 kg/m2 (6 to 10 lbs/ft2 ) depending on the level of certification. Current standards and recommended densities for North America are summarized in Table 1 (meat turkeys) and Table 2 (breeder turkeys). The units in which density or space requirements are stated differ among industry standards, which are often reported in weight per unit of space (E.g. NTF, 2012; AHA, 2013), and scientific studies, which typically state densities as space available per bird (m2 /bird) or as the number of birds per area (birds/m2 ). There is a large variation in the group sizes, space allocations and ages of turkeys that have been used in experimental studies, making comparisons among studies difficult. A summary of the available literature for male turkeys is provided in Table 3.
Space Requirements Poultry should have enough space to be able to perform certain types of behavior, such as being able
to walk normally, get up and lie down, turn around, and preen (Jankowski et al., 2015). In order to assess how much space turkeys need, Ellerbrock and Knierim (2002) measured the area occupied by stationary turkeys using photographs. Turkeys at 11 (7.6 kg; 16.7 lb) and 21 (21.8 kg; 48.0 lb) wk of age occupied between 0.08 m2 (0.9 ft2 ) and 0.20 m2 (2.1 ft2 ) when stationary (Ellerbrock and Knierim, 2002). Ellerbrock and Knierim (2002) propose that as turkeys become larger, the amount of space required per unit of body weight decreases. Therefore, it is possible that larger turkeys “require less floor area per kilogram liveweight than smaller ones” (Ellerbrock and Knierim, 2002). However, the aforementioned measurements are for standing, stationary turkeys and space requirements vary depending on the behavior and activity of the bird. Currently, the effects of stocking density on space use and how space use changes with increasing age are unknown.
Space and Stocking Density Effects on Turkey Behavior and Welfare The effects of stocking density and group size on turkey behavior and welfare have recently been reviewed by Marchewka et al. (2013), and center on aggression, feather pecking and behavioral disturbances. There do not appear to be any recently published studies comparing the effects of stocking density on aggression and pecking behavior of turkeys in large groups. However, there is some information available pertaining to the incidences of aggression, head, back and vent wounds for turkeys in commercial flocks where thousands of birds are housed together (see Marchewka et al., 2015).
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STOCKING DENSITY, TURKEY WELFARE, AND PRODUCTIVITY Table 2. Stocking density standards and guidelines for breeder turkeys. Maximum stocking density∗ lb/ft2 or ft2 /bird kg/m2 or m2 /bird
Source
Category or description
National Turkey Federation
“Adequate roaming space; birds free to roam throughout growing area. Birds can stand up, sit down and spread their wings.”
Federation of Animal Science Societies Guide (“Ag Guide”)
Breeder Breeder Breeder Breeder Breeder Breeder
Certified Humane
Breeder females up to 8 wk 1.5 ft2 /bird Breeder females (grower house) 2.5 ft2 /bird Breeder females (darkening phase) 3.5 ft2 /bird Breeder females (laying phase) 5.5 ft2 /bird Breeder males up to 8 wk 2 ft2 /bird Breeder males 8–16 wk 6 ft2 /bird Breeder males > 16 wk 10 ft2 /bird “Additional space must be provided as needed to maintain bird welfare”
females < 17.6 lb (< 8.0 kg) females 17.6–26.4 (8.0–12.0 kg) females > 26.4 (> 12.0 kg) males < 26.4 (< 12.0 kg) males 26.4–37.4 (12.0–17.0 kg) males > 37.4 (> 17.0 kg)
5.9 lb/ft2 4.4–6.6 lb/ft2 5.3 lb/ft2 6.6 lb/ft2 5.3–7.5 lb/ft2 > 6.2 lb/ft2
28.8 (0.28 m2 /bird) 21.5–32.2 (0.37 m2 /bird) > 25.9 (0.46 m2 /bird) 32.2 (0.37 m2 /bird) 25.8–36.6 (0.46 m2 /bird) > 30.3 (0.56 m2 /bird) 0.14 m2 0.23 m2 0.33 m2 0.51 m2 0.19 m2 0.56 m2 0.90 m2
Information has been adapted from the National Turkey Federation (2012), Canadian Codes of Practice (Canadian Agri-Food Research Council, 2015; under review), Certified Humane (Humane Farm Animal Care, 2014), Global Animal Partnership (2011), and the “Ag Guide” (Federation of Animal Science Societies, 2010). ∗ Space requirements and stocking densities are reported differently depending on the source of information. Therefore, stocking densities in lb/ft2 and kg/m2 were calculated for ease of comparison. Space per bird is included in the table if it was provided in the original source.
Marchewka et al. (2015) assessed the welfare of turkeys on 10 commercial farms where the flock size ranged from 6,460 to 8,462 birds and the stocking density was 3.5 birds/m2 (0.29 m2 /bird) to 3.6 birds/m2 (0.28 m2 /bird) at 6 wk of age when birds were placed. Head wounds were present in 3.4 ± 1.0% and 3.5 ± 1.0% of turkeys as recorded by two observers, respectively (Marchewka et al., 2015). The observers also recorded the percentages of turkeys with back wounds (observer 1: 0.4 ± 0.1%; observer 2: 0.3 ± 0.1%), vent wounds (0.1 ± 0.1% for both observers) and the percentages of turkeys that were featherless (0.02 ± 0.01% for both observers). Cumulative mortality across all flocks was 15 ± 1.4% at 19 to 20 wk of age (Marchewka et al., 2015). Although Marchewka et al. (2015) did not compare stocking densities, their study is the first to examine the incidence of various welfare problems at commercial stocking densities. Up to a certain group size, turkeys are able to distinguish between familiar and unfamiliar conspecifics, which affects the level of aggression. Buchwalder and Huber-Eicher (2004; 2005) examined the relationships among group size, space, and aggression in turkey toms. Their research revealed that when an unfamiliar tom was introduced into a group of turkeys, group size influenced aggression. Specifically, the level of aggression directed at the unfamiliar tom was higher when the tom was introduced into a group of 6 vs. 30 toms, suggesting that turkeys are limited as to how many individuals they can distinguish among, which Buchwalder and Huber-Eicher refer to as the “limiting group size” (Buchwalder and Huber-Eicher, 2005). Space was also important in determining aggression: turkey toms reacted more aggressively toward an unfamiliar tom when the unfamiliar tom was introduced into a smaller vs. a larger pen (Buchwalder and Huber-Eicher, 2004). In an-
other study, Moran (1985) reported that mortality rates due to fighting were higher for turkey toms reared at a lower density (0.89 m2 /bird; 9.6 ft2 /bird) compared to a higher density (0.44 m2 /bird; 4.7 ft2 /bird). In addition to affecting levels of aggression, stocking density may impact other injurious behavior such as feather pecking. One study reported higher levels of feather damage in turkeys housed at a density of 0.74 vs. 1.86 m2 /bird (0.8 vs. 2.0 ft2 /bird; Gill and Leighton, 1984). Feather pecking is a multifactorial problem that is affected by many other factors (reviewed in Dalton et al., 2013) and further research is needed to understand the impacts of stocking density on feather-pecking behavior. With increasing stocking density, there is a greater potential for birds to be disturbed by others in the group. Martrenchar et al. (1999) reported that the amount of time that turkeys were able to rest without being disturbed was shorter at 9 wk of age when turkeys were housed at 5 birds/m2 (129.4 ± 22.9 sec) vs. 8 birds/m2 (67.1 ± 10.7 sec). There is some evidence from research with broiler chickens that increased disturbance is associated with reduced feed efficiency and reduced carcass quality due to bruises and scratches (Cornetto et al., 2002), but the effects of disturbances on turkey productivity and carcass quality are as yet unknown. In addition to behavior, a stocking density that is too high can increase the risk for leg and foot problems, mortality, breast blisters, and airsacculitis. Indeed, Martrenchar et al. (1999) reported that the incidence of footpad lesions increased and gait worsened as the amount of space available per male turkey decreased from 0.40 m2 /bird (10.7 lb/ft2 ) to 0.25 m2 /bird (6.4 lb/ft2 ) from 12 to 16 wk. Berk and Hahn (2000) reported that the percentage of turkeys with breast
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ERASMUS
Table 3. Summary of published literature examining stocking density effects on male turkey welfare and productivity. Publication
Age
Group size
Space provided (m2 /bird)
Calculated stocking density at end of study (lb/ft2 )∗
Moran (1985)
0–38 d
120 60 30 15
0.077 (120 birds) 0.15 (60 birds) 0.44 (30 birds) 0.89 (15 birds)
5.1 lb/ft2 (0.44 m2 /bird) at 18.7 wk 2.6 lb/ft2 (0.89 m2 /bird) at 18.7 wk
38–131 d Noll et al. (1991)
0–20 wk
13 28
0.21 (13 birds) 0.46 (28 birds)
13.2 lb/ft2 (0.21 m2 /bird) at 20 wk 5.7 lb/ft2 (0.46 m2 /bird) at 20 wk
Zuidhof et al. (1993)
8–16 wk
75 38 Turkeys removed weekly
Space ranges: 0.18 (for 75 birds)– 0.27 (for 51 birds) 0.36 (for 38 birds)– 0.53 (for 26 birds)
5.12 lb/ft2 (0.27 m2 /bird) at 16 wk 10.25 lb/ft2 (0.53 m2 /bird) at 16 wk
Perkins et al. (1995)
8–12 wk
75 37 50 25 317 439 540 317 439 540
0.18 0.36 0.27 0.54 0.24 0.19 0.15 0.40 0.31 0.25
8.5–8.9 lb/ft2 (0.27 m2 /bird) at 16 wk 4.1–4.2 lb/ft2 (0.54 m2 /bird) at 16 wk
12–16 wk Martrenchar et al. (1999)
0–12 wk
12–16 wk
(75 birds) (37 birds) (50 birds) (25 birds) (317 birds) (439 birds) (540 birds) (317 birds) (439 birds) (540 birds)
Berk and Hahn (2000)
0–20 wk
27 63
0.65 (27 birds) 0.28 (63 birds) Free range access provided from 6 wk
Jankowski et al. (2014)
1–126 d
28 34
Marchewka et al. (2015)
6 wk
Between 6,460 and 8,462
0.36 (28 birds) 0.29 (34 birds) – birds were heat stressed 0.28–0.29 when placed at 6 wk
Data collected at 19–20 wk
Experiment 1: 6.43 lb/ft2 (0.40 m2 /bird) at 16 wk 8.67 lb/ft2 (0.31 m2 /bird) at 16 wk 10.71 lb/ft2 (0.25 m2 /bird) at 16 wk Experiment 2: 6.49 lb/ft2 (0.24 m2 /bird) at 16 wk 8.57 lb/ft2 (0.19 m2 /bird) at 16 wk 10.17 lb/ft2 (0.15 m2 /bird) at 16 wk Body weights not reported
10.5 lb/ft2 (0.36 m2 /bird) at 18 wk 12.3 lb/ft2 (0.29 m2 /bird) at 18 wk Bird numbers at 19–20 wk not reported Commercial study: stocking densities were not compared
∗ Stocking density in lb/ft2 was calculated using the final reported body weights divided by the area of space provided so that densities would be comparable to how densities are typically reported in the U.S. turkey industry.
blisters was higher for turkeys housed at 3.5 birds/m2 (11.6%) compared to 1.5 birds/m2 (5.3%). Mortality rates were also higher at the higher density (Berk and Hahn, 2000). Similarly, Noll et al. (1991) reported that mortality rates tended to be higher (5.4% vs. 3.1%) at a higher stocking density (0.46 vs. 0.21 m2 /bird; 13.2 vs. 5.7 lb/ft2 at 20 wk). Higher stocking densities may also be associated with respiratory problems. The incidence of airsacculitis was higher (25% vs. 11.7% of turkeys) when turkeys were housed at a density of 0.46 m2 /bird (13.2 lb/ft2 at 20 wk) compared to 0.21 m2 /bird (5.7 lb/ft2 at 20 wk; Noll et al., 1991). Furthermore, the severity of lung lesions tended to be greater in turkeys housed at a higher density (5.5 turkeys/m2 vs. 2.8 turkeys/m2 ; 8.5 to 8.9 lb/ft2 vs. 4.1 to 4.2 lb/ft2 at 16 wk; Perkins et al., 1995). However, another study reported no differences in lung lesions between densities of 5.5 and 2.8 turkeys/m2 (10.3 lb/ft2 vs. 5.1 lb/ft2 at 16 wk; Zuidhof et al., 1993). It is possible that turkeys that are housed at higher stocking densities experience greater levels of stress, which contribute to the development of respiratory problems (Perkins et al., 1995). Turkeys housed at higher densities may also be less capable of coping with additional environ-
mental stressors such as elevated environmental temperatures: Perkins et al. (1995) reported that a higher percentage of turkeys were gasping (31% of turkeys at 5.5 turkeys/m2 vs. 6% of turkeys at 2.8 turkeys/m2 ) when the environmental temperature was raised to 30˚C for 1 h.
Stocking Density Impacts on Productivity of Turkeys Productivity parameters that have been evaluated in relation to stocking density include body weight, feed conversion, and carcass characteristics. Martrenchar et al. (1999) conducted 2 experiments examining the impacts of stocking density on productivity of turkeys. Turkeys were housed at one of 3 stocking densities from 0 to 12 wk (0.24, 0.185, or 0.15 m2 /bird) then provided with more space from 12 to 16 wk (0.40 m2 /bird (6.4 lb/ft2 at 16 wk), 0.31 m2 /bird (8.6 lb/ft2 at 16 wk) or 0.25 m2 /bird (10.7 lb/ft2 at 16 wk), respectively). Body weights were highest for turkeys provided with 0.24 to 0.40 m2 /bird (Experiment 1: 13.4 ± 0.1 kg;
STOCKING DENSITY, TURKEY WELFARE, AND PRODUCTIVITY
Experiment 2: 13.5 ± 0.11 kg) compared to turkeys provided with 0.185 to 0.31 m2 /bird (Experiment 1: 13.1 ± 0.1 kg; Experiment 2: 12.9 ± 0.11) or 0.15 to 0.25 m2 /bird (Experiment 1: 13.1 ± 0.96 kg; Experiment 2: 12.4 ± 0.13 kg). Similarly, Noll et al. (1991) reported higher body weights at both 16 (10.3 kg vs. 10.0 kg) and 20 wk (13.5 kg vs. 12.8 kg) for turkeys housed at 2.2 birds/m2 (5.7 lb/ft2 at 20 wk) compared to turkeys housed at 4.8 birds/m2 (13.2 lb/ft2 at 20 wk). The effects of stocking density on feed conversion were similar: turkeys housed at 2.2 birds/m2 (4.1 g feed/g weight gain) had improved feed conversion compared to turkeys housed at 4.8 birds/m2 (4.3 g feed/g weight gain; Noll et al., 1991). In contrast, Moran (1985), comparing 0.44 vs. 0.89 m2 /bird (5.1 vs. 2.6 lb/ft2 at 19 wk), and Perkins et al. (1995), comparing 0.27 vs. 0.54 m2 /bird (8.5 to 8.9 vs. 4.1 to 4.2 lb/ft2 at 16 wk), reported no differences in male turkey weights due to stocking density. Zuidhof et al. (1993) reported that a low ventilation rate (225 L/s) in combination with a high stocking density (0.53 m2 /bird or 10.25 lb/ft2 ) resulted in lower weight gains compared to the same ventilation rate but a lower stocking density (0.27 m2 /bird or 5.12 lb/ft2 ), indicating that environmental factors may interact with stocking density to affect productivity. A recent experimental study examined the effects of stocking density and heat stress on body weight, feed intake, and skeletal characteristics of turkeys from 1 d to 19 wk of age (Jankowski et al., 2015). Turkeys reared at a higher density (3.4 birds/m2 or 0.29 m2 /bird) combined with a higher environmental temperature (5◦ C higher than the control group) had a lower average body weight at 18 wk (17.7 ± 0.47 kg vs. 18.4 ± 0.43 kg) compared to turkeys housed at a density of 2.8 birds/m2 (0.36 m2 /bird) and breeder (Aviagen Turkeys) recommended temperatures (Jankowski et al., 2015). The increased stocking density together with increased temperature negatively affected bone length and bone weight after 4 wk and bone strength at 18 wk, indicating lower skeletal quality and potentially greater problems with locomotion (Jankowski et al., 2015). Because the effects of temperature and stocking density were confounded, it is not possible to determine how stocking density alone affected body weight and bone characteristics. Lastly, there is some evidence that carcass composition is also affected by stocking density. Carcasses from turkeys reared at a lower density of 0.46 m2 /bird had a greater percentage of abdominal fat (1.24 vs. 1.05%), lower carcass moisture content (63.2 vs. 64.2%) and more total breast meat (1.53 vs. 1.46 kg; but breast meat as a percentage of bodyweight did not differ among densities) compared to turkeys reared at 0.21 m2 /bird (Halvorson et al., 1991). The authors postulate that the amount of carcass fat was likely higher in the low density group because turkeys in the low density group consumed excess feed (Halvorson et al. 1991).
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CONCLUSION Stocking density standards and guidelines for turkeys vary depending on body weight and stage of production. Stocking densities range from as low as 5.9 kg/m2 (1.2 lb/ft2 ; Federation of Animal Science Societies, 2010) to as high as 73.2 kg/m2 (15 lb/ft2 ; National Turkey Federation, 2012) for meat turkeys, and as low as 21.5 kg/m2 (4.4 lb/ft2 ; Federation of Animal Science Societies, 2010) to 30.3 kg/m2 (6.2 lb/ft2 ; Federation of Animal Science Societies, 2010) for breeder turkeys. Certified Humane standards for breeder turkeys are even higher, ranging between 0.14 and 0.90 m2 /bird (Humane Farm Animal Care, 2014). There is little overlap between industry standards and densities that have been evaluated scientifically, which range from 12.7 kg/m2 (2.6 lb/ft2 ; Moran, 1985) to 64.4 kg/m2 (13.2 lb/ft2 ; Noll et al., 1991). Densities as high as 73.2 kg/m2 have not been evaluated, and the majority of scientific studies were conducted over a decade ago with genetic lines of turkeys that may differ from modern genetic lines in feed efficiency and growth rates. However, a review of the literature provides insight into potential effects of stocking density on turkey productivity, behavior and welfare. In general, higher densities (greater than 29.3 kg/m2 or 6 lb/ft2 ) are associated with reduced body weight, reduced feed efficiency, and increased mortality rates. Moreover, higher stocking densities lead to increased risks of footpad dermatitis, breast blisters, and respiratory problems. Higher stocking densities also lead to disturbances of resting birds and may increase levels of aggression and feather pecking. While industry standards and guidelines focus on providing turkeys with adequate space to perform particular behaviors, there is currently no scientific information available as to the amount of space turkeys need for particular behaviors. It is important to note that many welfare issues of turkeys are multifactorial in nature and are not influenced by stocking density alone, but are also influenced by other factors, such as environmental and management factors. Welfare issues resulting from management and environmental factors can be further aggravated by high stocking densities. For example, with a higher stocking density, more waste is produced, which necessitates judicious management and appropriate ventilation to maintain an appropriate level of litter quality. Further research is needed to understand the interactions among management, stocking density, and turkey behavior in order to inform space and stocking density standards.
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