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The effect of perch availability during pullet rearing and egg laying on musculoskeletal health of caged White Leghorn hens
The effect of perch availability during pullet rearing and egg laying on musculoskeletal health of caged White Leghorn hens P. Y. Hester,*1 S. A. Enneking,* B. K. Haley,* H. W. Cheng,† M. E. Einstein,* and D. A. Rubin‡ *Department of Animal Sciences, Purdue University, West Lafayette, IN 47907; †USDA-Agricultural Research Service, Livestock Behavior Research Unit, West Lafayette, IN 47907; and ‡Biological Sciences, Illinois State University, Normal 61790 age. Treatment 3 chickens had access to perches only during the pullet phase (0 to 16.9 wk of age). Treatment 4 chickens had perch access throughout their entire life cycle (0 to 71 wk of age). Musculoskeletal health was assessed by measuring muscle weights, bone mineralization, bone fracture incidence, and keel bone deviations. Muscle deposition of 71-wk-old hens increased when given access to perches as pullets. Bone mineralization of 71-wk-old hens also increased if given perch access as adults. However, the disadvantage of the adult perch was the higher incidence of keel deviations and keel fractures at end of lay. The increase in bone mineralization of the keel bone as a result of perch access during the pullet and laying phases was not great enough to prevent a higher incidence of keel bone fractures at end of lay. Perch redesign and placement of perches within the cage to minimize keel fractures and deviations are possible solutions.
Key words: osteoporosis, bone mineralization, perch, keel fracture, muscle deposition 2013 Poultry Science 92:1972–1980 http://dx.doi.org/10.3382/ps.2013-03008
INTRODUCTION Skeletons experiencing osteoporosis demonstrate a progressive decrease in mineralized structural bone (Whitehead, 2004). Pullets approaching sexual maturity deposit medullary bone in the marrow of some bones to provide a quick labile source of calcium for shell formation. Whereas medullary bone deposition increases with age in reproductively active female hens, structural bone mineralization gradually deteriorates (Whitehead and Wilson, 1992; Hudson et al., 1993). Age-related loss of structural or compact bone, which is generalized throughout the skeleton, eventually leads to osteoporosis and increases the probability of bone breakage (Whitehead and Wilson, 1992). ©2013 Poultry Science Association Inc. Received January 2, 2013. Accepted March 31, 2013. 1 Corresponding author: [email protected]
One contributing factor to the development of osteoporosis in egg-laying strains of chickens may be that they have been genetically selected for many years for small body frames so as to improve egg production and feed efficiency. Genetically selecting for high and low bone strength lines of chickens for 9 generations resulted in marked differences in bone quality traits and susceptibility to osteoporosis (Bishop et al., 2000; Fleming et al., 2006). Using bone indexes as the selection criteria, a heritability estimate of 0.40 was reported (Bishop et al., 2000), demonstrating the influence of genetics on skeletal integrity. In addition to genetics, exercise affects skeletal quality. Birds that exercise have fewer osteoclasts resorbing the endosteal bone surface than nonactive birds (Fleming et al., 2006). However, this suppression of osteoclastic activity does not persist throughout life. As hens age, the differences in the number of osteoclasts between active and nonactive hens dissipate. Ultimately, at some point in the aging process, exercise fails
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ABSTRACT A major skeletal problem of conventionally caged hens is increased susceptibility to osteoporosis mainly due to lack of exercise. Osteoporosis is characterized by a progressive decrease in mineralized structural bone. Whereas considerable attention has been given to enriching laying cages, little research has been conducted on providing caged pullets with furnishments, in particular perches. The objective of the current study was to determine if metal perches during all or part of the life cycle of White Leghorns affected hen musculoskeletal health, especially at end of lay. Treatments during the pullet phase (hatch to 16.9 wk) entailed cages with and without perches. Four treatments were used during the laying phase (17 to 71 wk of age). Treatment 1 chickens never had access to perches at any point during their life cycle, typical of egg industry practices in the United States for conventional cages. Treatment 2 chickens had access to perches only during the egg-laying phase, which was from 17 to 71 wk of
MUSCULOSKELETAL HEALTH OF CAGED HENS WITH PERCHES
anterior latissimus dorsi through hyperplasia and hypertrophy of muscle fibers (Sola et al., 1973). Therefore, the objective of the current study was to determine if perch availability during all or part of the life cycle of caged White Leghorns affected hen musculoskeletal health, especially at the end of lay. Our hypothesis was that early use of perches as pullets compared with no perch would lead to long-term improvement in musculoskeletal health in aging hens, as demonstrated through increased bone mineralization and greater muscle deposition.
MATERIALS AND METHODS Birds and Management One-day-old White Leghorn hatchlings (n = 1,064) of the Hy-Line W36 strain were housed in 28 pullet cages at the Purdue University Poultry Research Farm in West Lafayette, Indiana. Fourteen pullet cages had 2 perches/cage arranged parallel to the feeder mounted 8.9 cm from the cage floor, whereas the remaining 14 pullet cages were without perches. Information on cage size, placement of the perches, number of birds assigned to each cage, floor space allocation, feeder space, and perch space per chicken during the pullet phase were described by Enneking et al. (2012a). Pullets (n = 324) were transferred to 36 metal laying cages at 17 wk of age. The chickens were housed in a single room of the Layer Research Unit at Purdue University. One-half of the laying cages contained 2 perches mounted 8.9 cm from the cage floor, whereas the other 18 cages lacked perches. With the exception of length, the perches were identical to the perches used in the pullet cages. The 32-mm diameter perches were round and circular, made of galvanized steel with a smooth surface. Perch placement and cage dimensions within the conventional laying cage were described by Hester et al. (2013). From 17 to 71 wk of age, stocking density, perch space/ chicken, and feeder space/chicken were 439 cm2, 16.9 cm, and 8.4 cm per hen, respectively. The 16.9 cm of perch space/hen provided the opportunity for all hens to perch at the same time if desired. Each laying cage contained 2 nipple drinkers. The diets and lighting protocol were described by Hester et al. (2013). Standard management and vaccination practices were used. The Purdue University Animal Care and Use Committee approved the protocol.
Treatments Treatments during the pullet phase entailed 14 cages with perches and 14 cages without perches (controls). For the laying phase (17 to 71 wk of age), a 2 × 2 factorial arrangement was used in which the factors were the pullet versus the laying phase and the presence or absence of the perch, resulting in a total of 4 treatments. Treatment 1, which served as the control, never had access to perches at any point during their life cycle,
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to maintain the suppression of osteoclastic resorption leading to bone loss. Another possibility for bone loss with aging hens is the downregulation of the osteoblastic estrogen receptor, which may contribute to exercise having less of an effect on maintaining skeletal quality (Fleming et al., 2006). The type of housing and furnishments in cages can influence chicken activity levels, which consequently affect skeletal health. For example, the major skeletal problem of conventionally caged hens, compared with other loose housing systems, is the increased susceptibility to osteoporosis mainly due to lack of exercise (Rowland and Harms, 1970, 1972; Meyer and Sunde, 1974; Knowles and Broom, 1990; Nørgaard-Nielsen, 1990; Fleming et al., 1994; Tauson and Abrahamsson, 1994a; Tauson, 1998; Whitehead and Fleming, 2000; Jendral et al., 2008). Even though bone strength is greater, hens in extensive housing have more old fractures than caged hens due to greater freedom of movement (McLean et al., 1986; Gregory et al., 1990; Abrahamsson and Tauson, 1995; Tauson et al., 1999; Wilkins et al., 2004; Fleming et al., 2004, 2006). Little attention has been given to evaluating the use of enrichments in the pullet cage. Caged pullets given access to front and back perches immediately following hatch began using perches as early as 2 wk of age, though perching was rare at this age (P. Y. Hester, unpublished data). Perch use increased with age, peaking at 12 wk of age and maintaining this level of perching activity until the end of the observations at 16 wk of age (Enneking et al., 2012b). Our laboratory uses dual energy x-ray absorptiometry (DEXA) to measure skeletal mineralization in poultry. The DEXA scans are the standard method used in human medicine to assess bone mineral density (BMD) and osteoporosis (see review of Hester et al., 2004). It has been successfully applied both in vivo and ex vivo in poultry. A moving x-ray generator produces photons over a broad spectrum of energy levels. The photons are filtered as they pass through the test sample to produce 2 distinct peaks, enabling the densitometer to distinguish bone from soft tissue (Hester et al., 2004). The use of DEXA as a tool for monitoring skeletal integrity throughout the life cycle of chickens has been validated (Onyango et al., 2003; Schreiweis et al., 2003, 2004, 2005; Hester et al., 2004). High correlations (r = 0.82 to 0.94, P < 0.001) existed between bone scans conducted in live birds compared with respective excised bones (Schreiweis et al., 2005). It is unknown if the use of perches as pullets has a long-term benefit in improving hen musculoskeletal health during the laying phase. In 12-wk-old caged White Leghorns, the bone mineral content (BMC) of the tibia, keel, and humerus and the gross leg muscle weight increased as a result of perch access compared with pullets without perches, suggesting that perch use contributed to increase mineralization and muscle deposition through increased exercise (Enneking et al., 2012a). Chickens responded to weight loading of the
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typical of current egg industry practices in the United States. Treatment 2 chickens had access to perches only during the egg-laying phase of the life cycle, which was from 17 to 71 wk of age. Treatment 3 chickens had access to perches only during the pullet phase (0 to 16.9 wk of age). Treatment 4 chickens had perch access throughout their entire life cycle (0 to 71 wk of age). Each cage housed 9 hens, and for each of the 4 treatments, there were 9 cages for a total of 36 cages.
Measurements
Statistical Analysis The design was completely randomized (Steel et al., 1997). The MIXED model procedure of SAS Institute (2008) was used to analyze the data. A 2 × 2 factorial arrangement was used in which the presence or absence of the perches within the pullet or laying cages were the main plots. An analysis of covariance, using BW as the covariate, with repeated measures over the age of the hen (30 to 70 wk of age), was used for each bone scanned from the live hens. Mineralization of each bone collected at 71 wk of age was also subjected to an analysis of covariance using BW as a covariate. Muscle
RESULTS DEXA Scans of Live Hens from 30 to 70 Wk of Age The monitoring of live hens throughout their egg production cycle showed that the BMD of the keel (Figures 1 and 2) was the only bone affected by perch treatment with no effect on the humerus, radius, ulna, and tibia (data not presented in figures or tables). The BMD of the keel of 50-wk-old hens that had access to perches as pullets from 0 to 16.9 wk of age increased compared with hens with no pullet perch (P = 0.07 using the SLICE option, Figure 1). All other ages were not significant for BMD of the keel bone (pullet treatment × age interaction, P = 0.003, Figure 1). There was also an increase in BMD of the keel of 60-wk-old hens that had access to perches during egg laying from 17 to 71 wk of age compared with controls with no perch (P = 0.04 using the SLICE option, Figure 2). All other ages were not significant for mineralization of the keel bone (laying hen treatment × age interaction, P = 0.056, Figure 2). The Tukey-Kramer test was unable to partition differences among means for both of the interactions. The BMD of the tibia, humerus, ulna, keel, and radius of hens generally increased with age with the lowest value for all bones occurring at 40 wk of age, which was during the month of July (P < 0.0001, Figure 3). The BMC of the ulna increased as a result of perch access during egg laying (mean ± SEM of 0.99 ± 0.02) compared with controls without perches during egg production (mean ± SEM of 0.94 ± 0.02, P = 0.04) with no effect on the BMC of the humerus, radius, tibia, and keel (data not presented in tables or figures). Similar to BMD, the BMC of the tibia, humerus, ulna, keel, and radius increased as the hens aged (P = 0.0002, data not presented in tables or figures).
DEXA Scans of Bones at 71 Wk of Age The interaction between the presence or absence of perches during either the pullet or laying phases of 71-wk-old hens was not significant for BMD and BMC (Tables 1 and 2); however, the main effects of pullet or
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To monitor changes in bone mineralization (BMD and BMC) as hens aged, the same 2 live hens/cage were scanned using DEXA at 30, 40, 50, 60, and 70 wk of age. Hens used for scanning were selected randomly at 30 wk of age, and a colored leg band was placed on the shank for easy identification on subsequent scans. Individual BW were collected from each of the 72 hens immediately before the scan of the left tibia/fibula, left wing (humerus, ulna, and radius), and keel. At 71 wk of age, chickens were sedated using sodium pentobarbital (30 mg of pentobarbital/kg of BW injected into the brachial vein). Individual BW was determined followed by euthanasia using cervical dislocation. The left wing, left thigh, left drum, and breast were retrieved, placed in a plastic bag, labeled, and frozen for later DEXA scans and muscle deposition. After thawing the carcass parts, the humerus, ulna, radius, wing phalange (III carpometacarpal), femur, tibia/fibula, and keel were scanned using DEXA with muscle, skin, and feathers intact, similar to scanning a live bird (Hester et al., 2004), to quantify BMD and BMC. After scanning, feathers, and skin were removed from the left thigh, left drum, and breast. The weight of the skeletal muscles and tendons of each carcass part were determined after excising from bone. Muscle weight was expressed relative to BW. The left tibia, femur, and keel were examined for fresh and old healing fractures similar to Mazzuco and Hester (2005). The keel bone was evaluated for deformations using a scoring system of values ranging from 1 to 4 points, with 1 being the worst condition and 4 being representative of a normal keel (Tauson et al., 1984; see Hester et al., 2013 for details on scoring).
weights, keel fractures, and keel scores were subjected to an ANOVA. Treatment (factors of pullet vs. the laying phase and the presence or absence of the perch) and age of the hen were considered fixed effects. The variability of least squares means was reported as the SEM. For percentage data, transformations of arcsine square root were used and the data reanalyzed. Because statistical trends were similar for both transformed and untransformed data, the untransformed results were presented. The Tukey-Kramer test was used to partition differences among means (Oehlert, 2000), and the 2-way interactions were subjected to the SLICE option (Winer, 1971).
MUSCULOSKELETAL HEALTH OF CAGED HENS WITH PERCHES
laying hen access to perches compared with no perch resulted in increases for bone mineralization. The presence of a perch during the pullet phase had no effect on BMD of any of the bones at 71 wk of age (Table 1). With the exception of the tibia (P = 0.10), the BMD of the wing bones (humerus, ulna, radius, and phalange, P < 0.0001), keel (P < 0.0001), and femur (P = 0.03) increased due to the presence of the perch
Figure 3. The effect of age (P < 0.0001) on bone mineral density of the tibia, humerus, ulna, keel, and radius of caged White Leghorns at 30, 40, 50, 60, and 70 wk of age. Values represent the least squares means ± 0.002 adjusted for BW. Means within a bone for each age lacking a common letter (a–c) differ (P < 0.05). Within a bone, means were averaged over treatments with 70 to 71 observations per age.
during egg laying compared with 71-wk-old hens with no perch during the egg-laying phase (Table 1). The keel of 71-wk-old hens had greater BMC as a result of the presence of a perch during the pullet phase compared with pullets with no perch (P = 0.006, Table 2). The BMC of the other bones (humerus, ulna, radius, phalange, femur, and tibia) were not affected by the perch treatment during the pullet phase (Table 2). The presence of a perch compared with hens with no perch during egg laying increased BMC of all bones (humerus, ulna, radius, phalange, and keel, P < 0.0001) including the leg bones (femur, P = 0.016 and tibia, P = 0.010, Table 2).
Muscle Deposition at 71 Wk of Age
Figure 2. The bone mineral density of the keel of caged White Leghorns at 30, 40, 50, 60, and 70 wk of age. The hens of the perch treatment had access to perches as laying hens from 17 to 71 wk of age, whereas the control hens did not have access to perches during egg laying. The SLICE option, used to differentiate means of the laying hen × age interaction (P = 0.056), only showed a difference between treatments at 60 wk of age (P = 0.04) as indicted by the asterisk (*). All other ages were not significant. Values ± SEM represent the least squares means adjusted for BW.
The interaction between the presence or absence of perches during either the pullet or laying phases of 71-wk-old hens was not significant for muscle weights, but main effects for the presence or absence of perches in cages either during the pullet or egg-laying phases were significant for some of the muscles that were measured (Table 3). Providing access to perches compared with no perch during the pullet phase increased the muscle weights of the breast (P = 0.0002), left thigh (P < 0.0001), relative left thigh (P = 0.03), left drum (P < 0.0001), total left leg muscle (P < 0.0001), and relative left leg muscle (P = 0.04) of 71-wk-old hens. Relative breast and relative left drum muscle weights were not affected by the perch treatments during the pullet phase (P = 0.14 and 0.20, respectively). The opposite effect occurred during the laying phase where perch access compared with no perch reduced muscle weights of the breast (P < 0.0001), left thigh (P < 0.0001), left drum (P < 0.0001), and total left
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Figure 1. The bone mineral density of the keel of caged White Leghorns at 30, 40, 50, 60, and 70 wk of age. The hens of the perch treatment had access to perches as pullets from hatch to 16.9 wk of age, whereas the control hens did not have access to perches as pullets. The SLICE option, used to differentiate means of the pullet × age interaction (P = 0.003), only showed a difference between treatments at 50 wk of age (P = 0.07) as indicted by the asterisk (*). All other ages were not significant. Values ± SEM represent the least squares means adjusted for BW.
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Table 1. The effect of perch access on bone mineral density of caged White Leghorns at 71 wk of age Left wing bones Item
0.157 0.157 0.001 131 0.89 0.154b 0.161a 0.001 131 <0.0001 0.154 0.160 0.154 0.161 0.001 65 0.51
Ulna
0.112 0.113 0.001 150 0.59 0.108b 0.117a 0.001 150 <0.0001 0.108 0.116 0.108 0.118 0.002 75 0.33
Radius
Phalange
0.0809 0.0808 0.0005 148 0.97 0.0783b 0.0834a 0.0005 148 <0.0001 0.0787 0.0830 0.0778 0.0838 0.0007 74 0.25
0.0948 0.0958 0.0008 139 0.38 0.0911b 0.0995a 0.0008 139 <0.0001 0.0915 0.0981 0.0907 0.1009 0.0011 70 0.09
Keel
0.112 0.112 0.014 152 0.99 0.109b 0.115a 0.006 152 <0.0001 0.111 0.114 0.109 0.115 0.021 76 0.98
Femur
0.267 0.264 0.003 139 0.40 0.261b 0.270a 0.003 139 0.03 0.263 0.271 0.259 0.268 0.004 70 0.80
Tibia
0.231 0.231 0.002 139 0.86 0.229 0.233 0.002 139 0.10 0.223 0.233 0.230 0.233 0.002 70 0.86
a,bLeast
squares means (adjusted for BW) within a column for the laying phase lacking a common superscript differ (P < 0.05). number of observations per least squares means during the pullet phase, laying phase, or the interaction for pullet with laying phases. 2Control-control chickens never had access to perches during their life cycle; control-perch chickens had access to perches only during the egg-laying phase of the life cycle (17 to 71 wk of age); perch-control chickens had access to perches only during the pullet phase (0 to 16.9 wk of age); and perchperch chickens always had access to perches (0 to 71 wk of age). 1Average
leg muscle (P < 0.0001) of 71-wk-old hens, but when expressed relative to BW, each of these muscles were not affected by the perch treatment during egg laying (breast, P = 0.88, left thigh, P = 0.15, left drum, P = 0.63, and left total leg, P = 0.45, Table 3).
Bone Fractures and Keel Bone Deviations at 71 Wk of Age The perch pullet treatment had no effect on keel fracture incidence or keel scores (P = 0.96 and 0.49,
Table 2. The effect of perch access on bone mineral content of caged White Leghorns at 71 wk of age Left wing bones Item Treatment (g) During pullet phase Control Perch SEM n1 P-value During laying phase Control Perch SEM n1 P-value Interaction (pullet-laying)2 Control-control Control-perch Perch-control Perch-perch SEM n1 P-value a,bLeast
Humerus
1.21 1.23 0.01 131 0.15 1.19b 1.26a 0.01 131 <0.0001 1.19 1.24 1.19 1.27 0.01 65 0.38
Ulna
0.711 0.729 0.008 150 0.14 0.684b 0.757a 0.008 150 <0.0001 0.681 0.741 0.686 0.772 0.012 75 0.28
Left leg bones
Radius
0.0809 0.0808 0.0005 148 0.97 0.0783b 0.0834a 0.0005 148 <0.0001 0.0787 0.0830 0.0778 0.0838 0.0007 74 0.25
Phalange
0.347 0.356 0.005 139 0.20 0.326b 0.376a 0.005 139 <0.0001 0.328 0.365 0.325 0.387 0.007 70 0.08
Keel
1.41b 1.48a 0.02 152 0.006 1.35b 1.53a 0.02 152 <0.0001 1.33 1.49 1.38 1.58 0.03 76 0.53
Femur
2.11 2.12 0.02 139 0.75 2.08b 2.16a 0.02 139 0.016 2.08 2.15 2.09 2.16 0.03 70 0.99
Tibia
2.79 2.82 0.02 139 0.22 2.77b 2.84a 0.02 139 0.010 2.75 2.83 2.79 2.85 0.03 70 0.77
squares means (adjusted for BW) within a column for the pullet or laying phases lacking a common superscript differ (P < 0.05). number of observations per least squares means during the pullet phase, laying phase, or the interaction for pullet with laying phases. 2Control-control chickens never had access to perches during their life cycle; control-perch chickens had access to perches only during the egg-laying phase of the life cycle (17 to 71 wk of age); perch-control chickens had access to perches only during the pullet phase (0 to 16.9 wk of age); and perchperch chickens always had access to perches (0 to 71 wk of age). 1Average
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Treatment (g/cm2) During pullet phase Control Perch SEM n1 P-value During laying phase Control Perch SEM n1 P-value Interaction (pullet-laying)2 Control-control Control-perch Perch-control Perch-perch SEM n1 P-value
Humerus
Left leg bones
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MUSCULOSKELETAL HEALTH OF CAGED HENS WITH PERCHES Table 3. The effect of perch access on muscle deposition of caged White Leghorns at 71 wk of age
Item
Relative breast1 (%)
177b 185a 2 152 0.0002 186a 176b 2 152 <0.0001 183 171 189 181 2 76 0.35
10.31 10.44 0.06 151 0.14 10.38 10.37 0.06 151 0.88 10.39 10.23 10.38 10.50 0.09 76 0.12
Relative left thigh1 (%)
Left thigh (g)
69.6b 73.4a 0.6 140 <0.0001 74.0a 69.0b 0.6 140 <0.0001 72.0 67.2 76.0 70.8 0.9 70 0.84
4.08b 4.14a 0.02 140 0.03 4.13 4.09 0.02 140 0.15 4.11 4.04 4.15 4.14 0.03 70 0.34
Relative left drum1 (%)
Left drum (g)
46.7b 49.0a 0.4 140 <0.0001 49.1a 46.5b 0.4 140 <0.0001 47.7 45.7 50.5 47.4 0.5 70 0.30
2.74 2.77 0.02 140 0.20 2.75 2.76 0.02 140 0.63 2.73 2.75 2.77 2.77 0.02 70 0.65
Total left thigh + drum (g)
116.2b 122.4a 0.9 140 <0.0001 123.2a 115.5b 0.9 140 <0.0001 119.7 112.7 126.6 118.2 1.3 70 0.61
Relative total left thigh + drum1 (%)
6.81b 6.91a 0.03 140 0.04 6.88 6.84 0.03 140 0.45 6.84 6.78 6.92 6.90 0.05 70 0.64
a,bLeast
squares means (adjusted for BW) within a column for the pullet or laying phases lacking a common superscript differ (P < 0.05). of breast, left thigh, left drum, and total left thigh + left drum expressed relative to BW (g of muscle/g of BW × 100). 2Average number of observations per least squares means during the pullet phase, laying phase, or the interaction for pullet with laying phases. 3Control-control chickens never had access to perches during their life cycle; control-perch chickens had access to perches only during the egg-laying phase of the life cycle (17 to 71 wk of age); perch-control chickens had access to perches only during the pullet phase (0 to 16.9 wk of age); and perchperch chickens always had access to perches (0 to 71 wk of age). 1Weights
respectively, Table 4) at 71 wk of age. In contrast, keel fractures increased (P = 0.009) and keel scores were worse (P = 0.0003) in 71-wk-old hens because of the presence of perches compared with no perch during the egg-laying phase (Table 4). The incidence of keel fractures was high (>80%, Table 4), and the majority of the fractures were old. The interactions between the presence or absence of perches during either the pullet or laying phases of 71-wk-old hens were not significant for keel fracture incidence and keel scores (Table 4). Out of 278 left femurs examined at 71 wk of age, only 3 were broken, each from a different treatment group for an overall incidence of 1%. There was 1 (old fracture) broken left tibia.
DISCUSSION Adult White Leghorns of the current study demonstrated high use of perches, especially at night (P. Y. Hester, unpublished data), which is expected given the strong motivation that egg-laying strains of chickens have for perching (Lambe and Scott, 1998; Olsson and Keeling, 2002). Pullet perch use was also high for the chickens of this study (Enneking et al., 2012b). The addition of perches to conventional laying cages increased bone mineralization of 71-wk-old hens for all bones measured in the study except for the BMD of the tibia (Tables 1 and 2). These results of increased BMD and BMC are in agreement with other studies that reported an increase in bone strength of caged hens as a result of perch access during egg laying (Hughes
Table 4. The effect of perch access on keel bone fracture and scores in caged White Leghorns at 71 wk of age % Fractured
Item Treatment During pullet phase Control Perch SEM n2 P-value During laying phase Control Perch SEM n2 P-value Interaction (pullet-laying)3 Control-control Control-perch Perch-control Perch-perch SEM n2 P-value
88 88 2 18 0.96 83b 92a 2 18 0.009 85 91 82 93 3 9 0.42
Keel score1
3.15 3.08 0.08 152 0.49 3.32a 2.91b 0.08 152 0.0003 3.40 2.91 3.24 2.91 0.11 76 0.49
a,bLeast squares means within a column for the laying phase lacking a common superscript differ (P < 0.05). 1Score for keel ranged from 1 to 4. A score of 1 represented severe keel bone deviations, and a score of 4 represented normal keels. 2Average number of observations per least squares means during the pullet phase, laying phase, or the interaction for pullet with laying phases. 3Control-control chickens never had access to perches during their life cycle; control-perch chickens had access to perches only during the egglaying phase of the life cycle (17 to 71 wk of age); perch-control chickens had access to perches only during the pullet phase (0 to 16.9 wk of age); and perch-perch chickens always had access to perches (0 to 71 wk of age).
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Treatment During pullet phase Control Perch SEM n2 P-value During laying phase Control Perch SEM n2 P-value Interaction (pullet-laying)3 Control-control Control-perch Perch-control Perch-perch SEM n2 P-value
Breast (g)
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an increase in mineralization as a result of perch access during the pullet phase was the BMD of the keel of 50-wk-old hens (Figure 1) and the BMC of the keel of 71-wk-old hens (Table 2). Unfortunately, this increase in mineralization as a result of pullet access to perches did not lead to a reduction in keel fracture incidence at 71 wk of age (Table 4). The BMD and BMC of all other bones (including live scans conducted over the life cycle of the hen as well as the BMD and BMC of bones collected from 71-wk-old hens) were not affected by pullet access to perches. In addition, the treatment interaction (perch or no perch during the pullet or laying phases) was also not significant for BMD (Table 1) and BMC (Table 2). The tibia was the only bone out of 7 examined that did not increase in BMD at 71 wk of age as a result of perch access during the laying phase. Appleby et al. (1992) also reported no improvement in tibial bone strength as a result of perch access in caged brown hybrids with no correlation between perching time and tibial strength. The fact that the BMD of the tibia did not respond to perching may have more to do with perch elevation than the type of bone. Perches in the current study were mounted 8.9 cm from the cage floor. If a perch of higher elevation had been used, it may have required hens to jump higher, leading to more exercise and increased mineralization. To support this hypothesis, the humerus of hens was stronger in getaway cages with higher perches compared with hens in furnished cages with lower perches most likely due to more wing flapping (Tauson and Abrahamsson, 1994b). Providing perches to pullets compared with no perches had long-term benefits in increasing gross and relative thigh and total leg muscle deposition of 71-wk-old hens (Table 3). Muscle growth during development was perhaps stimulated by the jumping on and off perches during light hours. As additional evidence that pullet perches stimulated muscle deposition, pullets from this same experiment were sampled at 12 wk of age and those with perch access had greater BW and gross left leg muscle weights than pullets without perches (Enneking et al., 2012a). The pullets with perches may also have had a larger skeletal frame as indicated by larger bones at 12 wk of age. Based on larger pullet BW, gross leg muscle weights, and bone area at 12 wk of age (Enneking et al., 2012a), it is suspected that the chickens with perches during the pullet phase began egg laying as larger birds compared with pullets with no perches. This ultimately led to heavier BW of 71-wk-old hens with prior access to pullet perches compared with hens that had no exposure to perches as pullets (Hester et al., 2013). Muscle weights did not continue to increase as a result of perching activity as adults. In fact, gross breast, thigh, and drum muscle weights (Table 3) as well as BW (Hester et al. 2013) decreased as a result of perching activity as adults. Unlike the pullet perch effect, when adjusted for BW, the relative muscle weights were similar between hens with and without access to perches
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and Appleby, 1989; Duncan et al., 1992; Tauson and Abrahamsson, 1994b; Abrahamsson and Tauson, 1997; Barnett et al., 1997; Jendral et al., 2008; Tactacan et al., 2009). Because in vivo BMD scans were positively correlated with bone-breaking force (Schreiweis et al., 2005), it is assumed that the increase in bone mineralization observed in the current study would also lead to greater bone strength. Less bone breakage would also be anticipated because as BMD decreased in Leghorns, the incidence of bone breakage increased (r = −0.54, P < 0.05, Mazzuco and Hester, 2005). However, this was not the case for the keel bone of the current study. The increase in BMD and BMC of the keel bone as a result of perch access compared with no perch during egg laying was not great enough to prevent a higher incidence of keel bone fractures. The unexpectedly high incidence of keel bone fractures (mostly old breaks) in caged 71-wk-old Leghorns with (92%) and without perches (83%) is a welfare concern because of possible chronic pain resulting from fracture-associated activation of specific nociceptors and inflammation (Carstens and Moberg, 2000; Underwood, 2002; Kuenzel, 2007). The incidence of old keel breaks of hens in noncage systems has been reported in the range from 52 to 73% (Freire et al., 2003; Nicol et al., 2006) and is likely due to the increased mobility and bumping of the keel bone when hens move from litter to raised slats or access the nest boxes (DEFRA, 2006). Although keel fracture incident was high in the current study (Table 4), fractures of the femur and tibia were rare for all treatment groups. Metal perches in cages not only caused higher keel fractures, but also resulted in more keel bone deviations. At resting, perching hen places pressure on her keel causing it to curve or deviate (Abrahamsson and Tauson, 1993; Tauson and Abrahamsson, 1994b, 1996; Abrahamsson et al., 1996; Tauson, 1998; Vits et al., 2005). Pullets given perches throughout rearing did not alleviate the poorer keel bone scores of caged hens with perches (Table 4). In contrast, floor rearing with perches compared with cage rearing reduced keel bone damage of laying hens in furnished cages (Moe et al., 2004). Redesign of the perch to minimize keel fracture and deviation is needed. Materials commonly used in the construction of perches for use by hens of the commercial egg industry include wood, plastic, and metal. For keel bone lesions, plastic versus wooden perches had no effect on keel scores (Tauson and Abrahamsson, 1994b). Soft round polyurethane perches resulted in less peak force and more contact area with the keel bone compared with round steel, mushroom shaped plastic, and flattened round perches (Pickel et al., 2011). However, surrounding wooden perches with a rubber lining did not reduce keel bone lesions compared with wooden perches of equal diameter without a rubber lining (Tauson and Abrahamsson, 1996). There has been very little research conducted on the effect of the material composition of perches on keel bone fracture incidence. Early pullet exposure to perches did little to improve hen skeletal mineralization. The only results showing
MUSCULOSKELETAL HEALTH OF CAGED HENS WITH PERCHES
ACKNOWLEDGMENTS Support for this project was provided by Agriculture and Food Research Initiative competitive grant no. 2011-67021-30114 from the USDA National Institute of Food and Agriculture. Appreciation is extended to F. A. Haan and B. D. Little of Purdue University in West Lafayette, Indiana, for the care and management of the chickens. T. L. Pollard of Big Dutchman donated the perches used in the study (Holland, MI). Chicks were donated by Hy-Line Hatchery (Warren, IN). Mention of trade names or commercial products in this article is solely for the purpose of providing specific information and does not imply recommendation or endorsement of the USDA. The USDA is an equal opportunity provider and employer.
REFERENCES Abrahamsson, P., and R. Tauson. 1993. Effect of perches at different positions in conventional cages for laying hens of two different strains. Acta Agric. Scand. A Anim. Sci. 43:228–235. Abrahamsson, P., and R. Tauson. 1995. Aviary systems and conventional cages for laying hens: Effects on production, egg quality, health and bird location in three hybrids. Acta Agric. Scand. A Anim. Sci. 45:191–203. Abrahamsson, P., and R. Tauson. 1997. Effects of group size on performance, health and birds’ use of facilities in furnished cages for laying hens. Acta Agric. Scand. A Anim. Sci. 47:254–260.
Abrahamsson, P., R. Tauson, and M. C. Appleby. 1996. Behaviour, health and integument of four hybrids of laying hens in modified and conventional cages. Br. Poult. Sci. 37:521–540. Appleby, M. C., S. F. Smith, and B. O. Hughes. 1992. Individual perching behaviour of laying hens and its effects in cages. Br. Poult. Sci. 33:227–238. Barnett, J. L., P. C. Glatz, E. A. Newman, and G. M. Cronin. 1997. Effects of modifying layer cages with perches on stress physiology, plumage, pecking and bone strength of hens. Aust. J. Exp. Agric. 37:523–529. Bishop, S. C., R. H. Fleming, H. A. McCormack, D. K. Flock, and C. C. Whitehead. 2000. Inheritance of bone characteristics affecting osteoporosis in laying hens. Br. Poult. Sci. 41:33–40. Braastad, B. O. 1990. Effects on behaviour and plumage of a keystimuli floor and a perch in triple cages for laying hens. Appl. Anim. Behav. Sci. 27:127–139. Carstens, E., and G. P. Moberg. 2000. Recognizing pain and distress in laboratory animals. ILAR J. 41:62–71. DEFRA (Department for Environment, Food, and Rural Affairs). 2006. The welfare effects of different methods of depopulation on laying hens. DEFRA Publications, London UK. Accessed Dec. 2012. http://randd.defra.gov.uk/Default.aspx?Menu=Menu&M odule=More&Location=None&ProjectID=11925&FromSearch= Y&Publisher=1&SearchText=aw0231&SortString=ProjectCode &SortOrder=Asc&Paging=10#Description. Duncan, E. T., M. C. Appleby, and B. O. Hughes. 1992. Effect of perches in laying cages on welfare and production of hens. Br. Poult. Sci. 33:25–35. Enneking, S. A., H. W. Cheng, K. Y. Jefferson-Moore, M. E. Einstein, D. A. Rubin, and P. Y. Hester. 2012a. Early access to perches in caged White Leghorn pullets. Poult. Sci. 91:2114– 2120. Enneking, S. A., P. S. Wakenell, J. P. Garner, and P. Y. Hester. 2012b. Mortality and behavior of caged White Leghorn pullets with access to perches. CD Paper in Proc. XXIV World’s Poult. Congr., Salvador, Brazil. World’s Poult. Sci. J. (Suppl. 1):134– 136. Fleming, R. H., D. Korver, H. A. McCormack, and C. C. Whitehead. 2004. Assessing bone mineral density in vivo: Digitized fluoroscopy and ultrasound. Poult. Sci. 83:207–214. Fleming, R. H., H. A. McCormack, L. McTeir, and C. C. Whitehead. 2006. Relationships between genetic, environmental and nutritional factors influencing osteoporosis in laying hens. Br. Poult. Sci. 47:742–755. Fleming, R. H., C. C. Whitehead, D. Alvey, N. G. Gregory, and L. J. Wilkins. 1994. Bone structure and breaking strength in laying hens housed in different husbandry systems. Br. Poult. Sci. 35:651–662. Freire, R., L. J. Wilkins, F. Short, and C. J. Nicol. 2003. Behaviour and welfare of individual laying hens in a non-cage system. Br. Poult. Sci. 44:22–29. Glatz, P. C., and J. L. Barnett. 1996. Effect of perches and solid sides on production, plumage and foot condition of laying hens housed in conventional cages in a naturally ventilated shed. Aust. J. Exp. Agric. 36:269–275. Gregory, N. G., L. J. Wilkins, S. D. Eleperuma, A. J. Ballantyne, and N. D. Overfield. 1990. Broken bones in domestic fowls: Effects of husbandry system and stunning method in end-of-lay hens. Br. Poult. Sci. 31:59–69. Hester, P. Y., S. A. Enneking, K. Y. Jefferson-Moore, M. E. Einstein, H. W. Cheng, and D. A. Rubin. 2013. The effect of perches in cages during pullet rearing and egg laying on White Leghorn hen performance, foot health, and plumage. Poult. Sci. 92:310–320. Hester, P. Y., M. A. Schreiweis, J. I. Orban, H. Mazzuco, M. N. Kopka, M. C. Ledur, and D. E. Moody. 2004. Assessing bone mineral density in vivo: Dual energy X-ray absorptiometry. Poult. Sci. 83:215–221. Hudson, H. A., W. M. Britton, G. N. Rowland, and R. J. Buhr. 1993. Histomorphometric bone properties of sexually immature and mature White Leghorn hens with evaluation of fluorochrome injection on egg production traits. Poult. Sci. 72:1537–1547. Hughes, B. O., and M. C. Appleby. 1989. Increase in bone strength of spent laying hens housed in modified cages with perches. Vet. Rec. 124:483–484.
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during egg laying (Table 3). Lower BW for caged hens with perch access compared with no perches has been reported in other studies as well (Tauson, 1984; Braastad, 1990; Tauson and Abrahamsson, 1994b; Glatz and Barnett, 1996). The lower BW of caged hens with access to perches during egg laying compared with those that did not have perches could have been due to less fat deposition as adults because of increased movement on perches during the photoperiod. There is much more movement on and off floor perches during daylight compared with night (Lambe and Scott, 1998). During the day, hens spend most of their time standing followed by preening, sitting, and walking on the perch (Struelens et al., 2008). The perch effect on muscle deposition during the pullet phase was much greater than the laying phase. Older hens may step on and off perches, whereas younger pullets may jump on and off perches. The height of perches from the cage floor was 8.9 cm for both the pullet and laying cages. Growing pullets, especially at younger ages, would have to generate more effort to mount perches than adult hens. In conclusion, the pullet and adult perches stimulated leg muscle deposition and bone mineralization, respectively. However, these improvements of the musculoskeletal system were not great enough to prevent a higher incidence of keel bone fractures and deviations in 71-wk-old hens with access to adult perches. Perch redesign and placement within the cage to minimize keel fractures and deviations are possible solutions.
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Hester et al. Schreiweis, M. A., J. I. Orban, M. C. Ledur, D. E. Moody, and P. Y. Hester. 2005. Validation of dual-energy X-ray absorptiometry in live White Leghorns. Poult. Sci. 84:91–99. Sola, O. M., D. L. Christensen, and A. W. Martin. 1973. Hypertrophy and hyperplasia of adult chicken anterior latissimus dorsi muscles following stretch with and without denervation. Exp. Neurol. 41:76–100. Steel, R. G. D., J. H. Torrie, and D. A. Dickey. 1997. Principles and Procedures of Statistics: A Biometrical Approach. 3rd ed. McGraw Hill Book Co., New York, NY. Struelens, E., F. A. M. Tuyttens, L. Duchateau, T. Leroy, M. Cox, E. Vranken, J. Buyse, J. Zoons, D. Berckmans, F. Ödberg, and B. Sonck. 2008. Perching behaviour and perch height preference of laying hens in furnished cages varying in height. Br. Poult. Sci. 49:381–389. Tactacan, G. B., W. Guenter, N. J. Lewis, J. C. Rodriguez-Lecompte, and J. D. House. 2009. Performance and welfare of laying hens in conventional and enriched cages. Poult. Sci. 88:698–707. Tauson, R. 1984. Effects of a perch in conventional cages for laying hens. Acta Agric. Scand. A Anim. Sci. 34:193–209. Tauson, R. 1998. Health and production in improved cage designs. Poult. Sci. 77:1820–1827. Tauson, R., and P. Abrahamsson. 1994a. Effects on production, health and behaviour in three SCWL strains in an EMC model in comparison with other modified and conventional cages. Pages 41–53 in Modified Cages for Laying Hens. C. M. Sherwin, ed. Universities Federation for Animal Welfare, Potters Bar, UK. Tauson, R., and P. Abrahamsson. 1994b. Foot and skeletal disorders in laying hens: Effects of perch design, hybrid, housing system and stocking density. Acta Agric. Scand. A Anim. Sci. 44:110– 119. Tauson, R., and P. Abrahamsson. 1996. Foot and keel bone disorders in laying hens. Effects of artificial perch material and hybrid. Acta Agric. Scand. A Anim. Sci. 46:239–246. Tauson, R., T. Ambrosen, and K. Elwinger. 1984. Evaluation of procedures for scoring the integument of laying hens-Independent scoring of plumage condition. Acta Agric. Scand. A Anim. Sci. 34:400–408. Tauson, R., A. Wahlstrom, and P. Abrahamsson. 1999. Effect of two floor housing systems and cages on health, production, and fear response in layers. J. Appl. Poult. Res. 8:152–159. Underwood, W. J. 2002. Pain and distress in agricultural animals. J. Am. Vet. Med. Assoc. 221:208–211. Vits, A., D. Weitzenburger, H. Hamann, and O. Distl. 2005. Production, egg quality, bone strength, claw length, and keel bone deformities of laying hens housed in furnished cages with different group sizes. Poult. Sci. 84:1511–1519. Whitehead, C. C. 2004. Overview of bone biology in the egg-laying hen. Poult. Sci. 83:193–199. Whitehead, C. C., and R. H. Fleming. 2000. Osteoporosis in cage layers. Poult. Sci. 79:1033–1041. Whitehead, C. C., and S. Wilson. 1992. Characteristics of osteopenia in hens. Pages 265–280 in Poultry Science Symposium 23: Bone Biology and Skeletal Disorders in Poultry. C. C. Whitehead, ed. Carfax Publishing Co., Abington, Oxfordshire, UK. Wilkins, L. J., S. N. Brown, P. H. Zimmerman, C. Leeb, and C. J. Nicol. 2004. Investigation of palpation as a method for determining the prevalence of keel and furculum damage in laying hens. Vet. Rec. 155:547–549. Winer, B. J. 1971. Statistical Principles in Experimental Design, 2nd ed. McGraw-Hill Inc., New York, NY.
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Jendral, M. J., D. R. Korver, J. S. Church, and J. J. R. Feddes. 2008. Bone mineral density and breaking strength of White Leghorns housed in conventional, modified, and commercially available colony battery cages. Poult. Sci. 87:828–837. Knowles, T. G., and D. M. Broom. 1990. Limb bone strength and movement in laying hens from different housing systems. Vet. Rec. 126:354–356. Kuenzel, W. J. 2007. Neurobiological basis of sensory perception: Welfare implications of beak trimming. Poult. Sci. 86:1273– 1282. Lambe, N. R., and G. B. Scott. 1998. Perching behaviour and preferences for different perch designs among laying hens. Anim. Welf. 7:203–216. Mazzuco, H., and P. Y. Hester. 2005. The effect of an induced molt and a second cycle of lay on skeletal integrity of White Leghorns. Poult. Sci. 84:771–781. McLean, K. A., M. R. Baxter, and W. Michie. 1986. A comparison of the welfare of laying hens in battery cages and in a perchery. Res. Dev. Agric. 3:93–98. Meyer, W. A., and M. L. Sunde. 1974. Bone breakage as affected by type housing or an exercise machine for layers. Poult. Sci. 53:878–885. Moe, R. O., D. Guéméné, H. J. S. Larsen, M. Bakken, S. Lervik, H. Hetland, and R. Tauson. 2004. Effects of pre-laying rearing conditions in laying hens housed in standard or furnished cages on various indicators of animal welfare. Page 329 in Book of Abstracts of the XXII World’s Poultry Congress, Istanbul, Turkey. WPSA Turkish Branch. Nicol, C. J., S. N. Brown, E. Glen, S. J. Pope, F. J. Short, P. D. Warriss, P. H. Zimmerman, and L. J. Wilkins. 2006. Effects of stocking density, flock size and management on the welfare of laying hens in single-tier aviaries. Br. Poult. Sci. 47:135–146. Nørgaard-Nielsen, G. 1990. Bone strength of laying hens kept in an alternative system, compared with hens in cages and on deeplitter. Br. Poult. Sci. 31:81–89. Oehlert, G. W. 2000. Comparing models: The analysis of variance. Pages 44–52 in A First Course in Design and Analysis of Experiments. W. H. Freeman and Co., New York, NY. Olsson, I. A., and L. J. Keeling. 2002. The push-door for measuring motivation in hens: Laying hens are motivated to perch at night. Anim. Welf. 11:11–19. Onyango, E. M., P. Y. Hester, R. L. Stroshine, and O. Adeola. 2003. Bone densitometry as an indicator of percent tibia ash in broiler chicks fed varying dietary calcium and phosphorus levels. Poult. Sci. 82:1787–1791. Pickel, T., L. Schrader, and B. Scholz. 2011. Pressure load on keel bone and foot pads in perching laying hens in relation to perch design. Poult. Sci. 90:715–724. Rowland, L. O., Jr., and R. H. Harms. 1970. The effect of wire pens, floor pens and cages on bone characteristics of laying hens. Poult. Sci. 49:1223–1225. Rowland, L. O., Jr., and R. H. Harms. 1972. Time required to develop bone fragility in laying hens. Poult. Sci. 51:1339–1341. SAS Institute. 2008. SAS Proprietary Software. Version 9.2. SAS Inst. Inc., Cary, NC. Schreiweis, M. A., J. I. Orban, M. C. Ledur, and P. Y. Hester. 2003. The use of densitometry to detect differences in bone mineral density and content of live White Leghorns fed varying levels of dietary calcium. Poult. Sci. 82:1292–1301. Schreiweis, M. A., J. I. Orban, M. C. Ledur, D. E. Moody, and P. Y. Hester. 2004. The effect of the ovulatory and egg laying cycle on bone mineral density and content of live White Leghorns as assessed by dual-energy X-ray absorptiometry. Poult. Sci. 83:1011–1019.
Key words: osteoporosis, bone mineralization, perch, keel fracture, muscle deposition 2013 Poultry Science 92:1972–1980 http://dx.doi.org/10.3382/ps.2013-03008
INTRODUCTION Skeletons experiencing osteoporosis demonstrate a progressive decrease in mineralized structural bone (Whitehead, 2004). Pullets approaching sexual maturity deposit medullary bone in the marrow of some bones to provide a quick labile source of calcium for shell formation. Whereas medullary bone deposition increases with age in reproductively active female hens, structural bone mineralization gradually deteriorates (Whitehead and Wilson, 1992; Hudson et al., 1993). Age-related loss of structural or compact bone, which is generalized throughout the skeleton, eventually leads to osteoporosis and increases the probability of bone breakage (Whitehead and Wilson, 1992). ©2013 Poultry Science Association Inc. Received January 2, 2013. Accepted March 31, 2013. 1 Corresponding author: [email protected]
One contributing factor to the development of osteoporosis in egg-laying strains of chickens may be that they have been genetically selected for many years for small body frames so as to improve egg production and feed efficiency. Genetically selecting for high and low bone strength lines of chickens for 9 generations resulted in marked differences in bone quality traits and susceptibility to osteoporosis (Bishop et al., 2000; Fleming et al., 2006). Using bone indexes as the selection criteria, a heritability estimate of 0.40 was reported (Bishop et al., 2000), demonstrating the influence of genetics on skeletal integrity. In addition to genetics, exercise affects skeletal quality. Birds that exercise have fewer osteoclasts resorbing the endosteal bone surface than nonactive birds (Fleming et al., 2006). However, this suppression of osteoclastic activity does not persist throughout life. As hens age, the differences in the number of osteoclasts between active and nonactive hens dissipate. Ultimately, at some point in the aging process, exercise fails
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ABSTRACT A major skeletal problem of conventionally caged hens is increased susceptibility to osteoporosis mainly due to lack of exercise. Osteoporosis is characterized by a progressive decrease in mineralized structural bone. Whereas considerable attention has been given to enriching laying cages, little research has been conducted on providing caged pullets with furnishments, in particular perches. The objective of the current study was to determine if metal perches during all or part of the life cycle of White Leghorns affected hen musculoskeletal health, especially at end of lay. Treatments during the pullet phase (hatch to 16.9 wk) entailed cages with and without perches. Four treatments were used during the laying phase (17 to 71 wk of age). Treatment 1 chickens never had access to perches at any point during their life cycle, typical of egg industry practices in the United States for conventional cages. Treatment 2 chickens had access to perches only during the egg-laying phase, which was from 17 to 71 wk of
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anterior latissimus dorsi through hyperplasia and hypertrophy of muscle fibers (Sola et al., 1973). Therefore, the objective of the current study was to determine if perch availability during all or part of the life cycle of caged White Leghorns affected hen musculoskeletal health, especially at the end of lay. Our hypothesis was that early use of perches as pullets compared with no perch would lead to long-term improvement in musculoskeletal health in aging hens, as demonstrated through increased bone mineralization and greater muscle deposition.
MATERIALS AND METHODS Birds and Management One-day-old White Leghorn hatchlings (n = 1,064) of the Hy-Line W36 strain were housed in 28 pullet cages at the Purdue University Poultry Research Farm in West Lafayette, Indiana. Fourteen pullet cages had 2 perches/cage arranged parallel to the feeder mounted 8.9 cm from the cage floor, whereas the remaining 14 pullet cages were without perches. Information on cage size, placement of the perches, number of birds assigned to each cage, floor space allocation, feeder space, and perch space per chicken during the pullet phase were described by Enneking et al. (2012a). Pullets (n = 324) were transferred to 36 metal laying cages at 17 wk of age. The chickens were housed in a single room of the Layer Research Unit at Purdue University. One-half of the laying cages contained 2 perches mounted 8.9 cm from the cage floor, whereas the other 18 cages lacked perches. With the exception of length, the perches were identical to the perches used in the pullet cages. The 32-mm diameter perches were round and circular, made of galvanized steel with a smooth surface. Perch placement and cage dimensions within the conventional laying cage were described by Hester et al. (2013). From 17 to 71 wk of age, stocking density, perch space/ chicken, and feeder space/chicken were 439 cm2, 16.9 cm, and 8.4 cm per hen, respectively. The 16.9 cm of perch space/hen provided the opportunity for all hens to perch at the same time if desired. Each laying cage contained 2 nipple drinkers. The diets and lighting protocol were described by Hester et al. (2013). Standard management and vaccination practices were used. The Purdue University Animal Care and Use Committee approved the protocol.
Treatments Treatments during the pullet phase entailed 14 cages with perches and 14 cages without perches (controls). For the laying phase (17 to 71 wk of age), a 2 × 2 factorial arrangement was used in which the factors were the pullet versus the laying phase and the presence or absence of the perch, resulting in a total of 4 treatments. Treatment 1, which served as the control, never had access to perches at any point during their life cycle,
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to maintain the suppression of osteoclastic resorption leading to bone loss. Another possibility for bone loss with aging hens is the downregulation of the osteoblastic estrogen receptor, which may contribute to exercise having less of an effect on maintaining skeletal quality (Fleming et al., 2006). The type of housing and furnishments in cages can influence chicken activity levels, which consequently affect skeletal health. For example, the major skeletal problem of conventionally caged hens, compared with other loose housing systems, is the increased susceptibility to osteoporosis mainly due to lack of exercise (Rowland and Harms, 1970, 1972; Meyer and Sunde, 1974; Knowles and Broom, 1990; Nørgaard-Nielsen, 1990; Fleming et al., 1994; Tauson and Abrahamsson, 1994a; Tauson, 1998; Whitehead and Fleming, 2000; Jendral et al., 2008). Even though bone strength is greater, hens in extensive housing have more old fractures than caged hens due to greater freedom of movement (McLean et al., 1986; Gregory et al., 1990; Abrahamsson and Tauson, 1995; Tauson et al., 1999; Wilkins et al., 2004; Fleming et al., 2004, 2006). Little attention has been given to evaluating the use of enrichments in the pullet cage. Caged pullets given access to front and back perches immediately following hatch began using perches as early as 2 wk of age, though perching was rare at this age (P. Y. Hester, unpublished data). Perch use increased with age, peaking at 12 wk of age and maintaining this level of perching activity until the end of the observations at 16 wk of age (Enneking et al., 2012b). Our laboratory uses dual energy x-ray absorptiometry (DEXA) to measure skeletal mineralization in poultry. The DEXA scans are the standard method used in human medicine to assess bone mineral density (BMD) and osteoporosis (see review of Hester et al., 2004). It has been successfully applied both in vivo and ex vivo in poultry. A moving x-ray generator produces photons over a broad spectrum of energy levels. The photons are filtered as they pass through the test sample to produce 2 distinct peaks, enabling the densitometer to distinguish bone from soft tissue (Hester et al., 2004). The use of DEXA as a tool for monitoring skeletal integrity throughout the life cycle of chickens has been validated (Onyango et al., 2003; Schreiweis et al., 2003, 2004, 2005; Hester et al., 2004). High correlations (r = 0.82 to 0.94, P < 0.001) existed between bone scans conducted in live birds compared with respective excised bones (Schreiweis et al., 2005). It is unknown if the use of perches as pullets has a long-term benefit in improving hen musculoskeletal health during the laying phase. In 12-wk-old caged White Leghorns, the bone mineral content (BMC) of the tibia, keel, and humerus and the gross leg muscle weight increased as a result of perch access compared with pullets without perches, suggesting that perch use contributed to increase mineralization and muscle deposition through increased exercise (Enneking et al., 2012a). Chickens responded to weight loading of the
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typical of current egg industry practices in the United States. Treatment 2 chickens had access to perches only during the egg-laying phase of the life cycle, which was from 17 to 71 wk of age. Treatment 3 chickens had access to perches only during the pullet phase (0 to 16.9 wk of age). Treatment 4 chickens had perch access throughout their entire life cycle (0 to 71 wk of age). Each cage housed 9 hens, and for each of the 4 treatments, there were 9 cages for a total of 36 cages.
Measurements
Statistical Analysis The design was completely randomized (Steel et al., 1997). The MIXED model procedure of SAS Institute (2008) was used to analyze the data. A 2 × 2 factorial arrangement was used in which the presence or absence of the perches within the pullet or laying cages were the main plots. An analysis of covariance, using BW as the covariate, with repeated measures over the age of the hen (30 to 70 wk of age), was used for each bone scanned from the live hens. Mineralization of each bone collected at 71 wk of age was also subjected to an analysis of covariance using BW as a covariate. Muscle
RESULTS DEXA Scans of Live Hens from 30 to 70 Wk of Age The monitoring of live hens throughout their egg production cycle showed that the BMD of the keel (Figures 1 and 2) was the only bone affected by perch treatment with no effect on the humerus, radius, ulna, and tibia (data not presented in figures or tables). The BMD of the keel of 50-wk-old hens that had access to perches as pullets from 0 to 16.9 wk of age increased compared with hens with no pullet perch (P = 0.07 using the SLICE option, Figure 1). All other ages were not significant for BMD of the keel bone (pullet treatment × age interaction, P = 0.003, Figure 1). There was also an increase in BMD of the keel of 60-wk-old hens that had access to perches during egg laying from 17 to 71 wk of age compared with controls with no perch (P = 0.04 using the SLICE option, Figure 2). All other ages were not significant for mineralization of the keel bone (laying hen treatment × age interaction, P = 0.056, Figure 2). The Tukey-Kramer test was unable to partition differences among means for both of the interactions. The BMD of the tibia, humerus, ulna, keel, and radius of hens generally increased with age with the lowest value for all bones occurring at 40 wk of age, which was during the month of July (P < 0.0001, Figure 3). The BMC of the ulna increased as a result of perch access during egg laying (mean ± SEM of 0.99 ± 0.02) compared with controls without perches during egg production (mean ± SEM of 0.94 ± 0.02, P = 0.04) with no effect on the BMC of the humerus, radius, tibia, and keel (data not presented in tables or figures). Similar to BMD, the BMC of the tibia, humerus, ulna, keel, and radius increased as the hens aged (P = 0.0002, data not presented in tables or figures).
DEXA Scans of Bones at 71 Wk of Age The interaction between the presence or absence of perches during either the pullet or laying phases of 71-wk-old hens was not significant for BMD and BMC (Tables 1 and 2); however, the main effects of pullet or
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To monitor changes in bone mineralization (BMD and BMC) as hens aged, the same 2 live hens/cage were scanned using DEXA at 30, 40, 50, 60, and 70 wk of age. Hens used for scanning were selected randomly at 30 wk of age, and a colored leg band was placed on the shank for easy identification on subsequent scans. Individual BW were collected from each of the 72 hens immediately before the scan of the left tibia/fibula, left wing (humerus, ulna, and radius), and keel. At 71 wk of age, chickens were sedated using sodium pentobarbital (30 mg of pentobarbital/kg of BW injected into the brachial vein). Individual BW was determined followed by euthanasia using cervical dislocation. The left wing, left thigh, left drum, and breast were retrieved, placed in a plastic bag, labeled, and frozen for later DEXA scans and muscle deposition. After thawing the carcass parts, the humerus, ulna, radius, wing phalange (III carpometacarpal), femur, tibia/fibula, and keel were scanned using DEXA with muscle, skin, and feathers intact, similar to scanning a live bird (Hester et al., 2004), to quantify BMD and BMC. After scanning, feathers, and skin were removed from the left thigh, left drum, and breast. The weight of the skeletal muscles and tendons of each carcass part were determined after excising from bone. Muscle weight was expressed relative to BW. The left tibia, femur, and keel were examined for fresh and old healing fractures similar to Mazzuco and Hester (2005). The keel bone was evaluated for deformations using a scoring system of values ranging from 1 to 4 points, with 1 being the worst condition and 4 being representative of a normal keel (Tauson et al., 1984; see Hester et al., 2013 for details on scoring).
weights, keel fractures, and keel scores were subjected to an ANOVA. Treatment (factors of pullet vs. the laying phase and the presence or absence of the perch) and age of the hen were considered fixed effects. The variability of least squares means was reported as the SEM. For percentage data, transformations of arcsine square root were used and the data reanalyzed. Because statistical trends were similar for both transformed and untransformed data, the untransformed results were presented. The Tukey-Kramer test was used to partition differences among means (Oehlert, 2000), and the 2-way interactions were subjected to the SLICE option (Winer, 1971).
MUSCULOSKELETAL HEALTH OF CAGED HENS WITH PERCHES
laying hen access to perches compared with no perch resulted in increases for bone mineralization. The presence of a perch during the pullet phase had no effect on BMD of any of the bones at 71 wk of age (Table 1). With the exception of the tibia (P = 0.10), the BMD of the wing bones (humerus, ulna, radius, and phalange, P < 0.0001), keel (P < 0.0001), and femur (P = 0.03) increased due to the presence of the perch
Figure 3. The effect of age (P < 0.0001) on bone mineral density of the tibia, humerus, ulna, keel, and radius of caged White Leghorns at 30, 40, 50, 60, and 70 wk of age. Values represent the least squares means ± 0.002 adjusted for BW. Means within a bone for each age lacking a common letter (a–c) differ (P < 0.05). Within a bone, means were averaged over treatments with 70 to 71 observations per age.
during egg laying compared with 71-wk-old hens with no perch during the egg-laying phase (Table 1). The keel of 71-wk-old hens had greater BMC as a result of the presence of a perch during the pullet phase compared with pullets with no perch (P = 0.006, Table 2). The BMC of the other bones (humerus, ulna, radius, phalange, femur, and tibia) were not affected by the perch treatment during the pullet phase (Table 2). The presence of a perch compared with hens with no perch during egg laying increased BMC of all bones (humerus, ulna, radius, phalange, and keel, P < 0.0001) including the leg bones (femur, P = 0.016 and tibia, P = 0.010, Table 2).
Muscle Deposition at 71 Wk of Age
Figure 2. The bone mineral density of the keel of caged White Leghorns at 30, 40, 50, 60, and 70 wk of age. The hens of the perch treatment had access to perches as laying hens from 17 to 71 wk of age, whereas the control hens did not have access to perches during egg laying. The SLICE option, used to differentiate means of the laying hen × age interaction (P = 0.056), only showed a difference between treatments at 60 wk of age (P = 0.04) as indicted by the asterisk (*). All other ages were not significant. Values ± SEM represent the least squares means adjusted for BW.
The interaction between the presence or absence of perches during either the pullet or laying phases of 71-wk-old hens was not significant for muscle weights, but main effects for the presence or absence of perches in cages either during the pullet or egg-laying phases were significant for some of the muscles that were measured (Table 3). Providing access to perches compared with no perch during the pullet phase increased the muscle weights of the breast (P = 0.0002), left thigh (P < 0.0001), relative left thigh (P = 0.03), left drum (P < 0.0001), total left leg muscle (P < 0.0001), and relative left leg muscle (P = 0.04) of 71-wk-old hens. Relative breast and relative left drum muscle weights were not affected by the perch treatments during the pullet phase (P = 0.14 and 0.20, respectively). The opposite effect occurred during the laying phase where perch access compared with no perch reduced muscle weights of the breast (P < 0.0001), left thigh (P < 0.0001), left drum (P < 0.0001), and total left
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Figure 1. The bone mineral density of the keel of caged White Leghorns at 30, 40, 50, 60, and 70 wk of age. The hens of the perch treatment had access to perches as pullets from hatch to 16.9 wk of age, whereas the control hens did not have access to perches as pullets. The SLICE option, used to differentiate means of the pullet × age interaction (P = 0.003), only showed a difference between treatments at 50 wk of age (P = 0.07) as indicted by the asterisk (*). All other ages were not significant. Values ± SEM represent the least squares means adjusted for BW.
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Table 1. The effect of perch access on bone mineral density of caged White Leghorns at 71 wk of age Left wing bones Item
0.157 0.157 0.001 131 0.89 0.154b 0.161a 0.001 131 <0.0001 0.154 0.160 0.154 0.161 0.001 65 0.51
Ulna
0.112 0.113 0.001 150 0.59 0.108b 0.117a 0.001 150 <0.0001 0.108 0.116 0.108 0.118 0.002 75 0.33
Radius
Phalange
0.0809 0.0808 0.0005 148 0.97 0.0783b 0.0834a 0.0005 148 <0.0001 0.0787 0.0830 0.0778 0.0838 0.0007 74 0.25
0.0948 0.0958 0.0008 139 0.38 0.0911b 0.0995a 0.0008 139 <0.0001 0.0915 0.0981 0.0907 0.1009 0.0011 70 0.09
Keel
0.112 0.112 0.014 152 0.99 0.109b 0.115a 0.006 152 <0.0001 0.111 0.114 0.109 0.115 0.021 76 0.98
Femur
0.267 0.264 0.003 139 0.40 0.261b 0.270a 0.003 139 0.03 0.263 0.271 0.259 0.268 0.004 70 0.80
Tibia
0.231 0.231 0.002 139 0.86 0.229 0.233 0.002 139 0.10 0.223 0.233 0.230 0.233 0.002 70 0.86
a,bLeast
squares means (adjusted for BW) within a column for the laying phase lacking a common superscript differ (P < 0.05). number of observations per least squares means during the pullet phase, laying phase, or the interaction for pullet with laying phases. 2Control-control chickens never had access to perches during their life cycle; control-perch chickens had access to perches only during the egg-laying phase of the life cycle (17 to 71 wk of age); perch-control chickens had access to perches only during the pullet phase (0 to 16.9 wk of age); and perchperch chickens always had access to perches (0 to 71 wk of age). 1Average
leg muscle (P < 0.0001) of 71-wk-old hens, but when expressed relative to BW, each of these muscles were not affected by the perch treatment during egg laying (breast, P = 0.88, left thigh, P = 0.15, left drum, P = 0.63, and left total leg, P = 0.45, Table 3).
Bone Fractures and Keel Bone Deviations at 71 Wk of Age The perch pullet treatment had no effect on keel fracture incidence or keel scores (P = 0.96 and 0.49,
Table 2. The effect of perch access on bone mineral content of caged White Leghorns at 71 wk of age Left wing bones Item Treatment (g) During pullet phase Control Perch SEM n1 P-value During laying phase Control Perch SEM n1 P-value Interaction (pullet-laying)2 Control-control Control-perch Perch-control Perch-perch SEM n1 P-value a,bLeast
Humerus
1.21 1.23 0.01 131 0.15 1.19b 1.26a 0.01 131 <0.0001 1.19 1.24 1.19 1.27 0.01 65 0.38
Ulna
0.711 0.729 0.008 150 0.14 0.684b 0.757a 0.008 150 <0.0001 0.681 0.741 0.686 0.772 0.012 75 0.28
Left leg bones
Radius
0.0809 0.0808 0.0005 148 0.97 0.0783b 0.0834a 0.0005 148 <0.0001 0.0787 0.0830 0.0778 0.0838 0.0007 74 0.25
Phalange
0.347 0.356 0.005 139 0.20 0.326b 0.376a 0.005 139 <0.0001 0.328 0.365 0.325 0.387 0.007 70 0.08
Keel
1.41b 1.48a 0.02 152 0.006 1.35b 1.53a 0.02 152 <0.0001 1.33 1.49 1.38 1.58 0.03 76 0.53
Femur
2.11 2.12 0.02 139 0.75 2.08b 2.16a 0.02 139 0.016 2.08 2.15 2.09 2.16 0.03 70 0.99
Tibia
2.79 2.82 0.02 139 0.22 2.77b 2.84a 0.02 139 0.010 2.75 2.83 2.79 2.85 0.03 70 0.77
squares means (adjusted for BW) within a column for the pullet or laying phases lacking a common superscript differ (P < 0.05). number of observations per least squares means during the pullet phase, laying phase, or the interaction for pullet with laying phases. 2Control-control chickens never had access to perches during their life cycle; control-perch chickens had access to perches only during the egg-laying phase of the life cycle (17 to 71 wk of age); perch-control chickens had access to perches only during the pullet phase (0 to 16.9 wk of age); and perchperch chickens always had access to perches (0 to 71 wk of age). 1Average
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Treatment (g/cm2) During pullet phase Control Perch SEM n1 P-value During laying phase Control Perch SEM n1 P-value Interaction (pullet-laying)2 Control-control Control-perch Perch-control Perch-perch SEM n1 P-value
Humerus
Left leg bones
1977
MUSCULOSKELETAL HEALTH OF CAGED HENS WITH PERCHES Table 3. The effect of perch access on muscle deposition of caged White Leghorns at 71 wk of age
Item
Relative breast1 (%)
177b 185a 2 152 0.0002 186a 176b 2 152 <0.0001 183 171 189 181 2 76 0.35
10.31 10.44 0.06 151 0.14 10.38 10.37 0.06 151 0.88 10.39 10.23 10.38 10.50 0.09 76 0.12
Relative left thigh1 (%)
Left thigh (g)
69.6b 73.4a 0.6 140 <0.0001 74.0a 69.0b 0.6 140 <0.0001 72.0 67.2 76.0 70.8 0.9 70 0.84
4.08b 4.14a 0.02 140 0.03 4.13 4.09 0.02 140 0.15 4.11 4.04 4.15 4.14 0.03 70 0.34
Relative left drum1 (%)
Left drum (g)
46.7b 49.0a 0.4 140 <0.0001 49.1a 46.5b 0.4 140 <0.0001 47.7 45.7 50.5 47.4 0.5 70 0.30
2.74 2.77 0.02 140 0.20 2.75 2.76 0.02 140 0.63 2.73 2.75 2.77 2.77 0.02 70 0.65
Total left thigh + drum (g)
116.2b 122.4a 0.9 140 <0.0001 123.2a 115.5b 0.9 140 <0.0001 119.7 112.7 126.6 118.2 1.3 70 0.61
Relative total left thigh + drum1 (%)
6.81b 6.91a 0.03 140 0.04 6.88 6.84 0.03 140 0.45 6.84 6.78 6.92 6.90 0.05 70 0.64
a,bLeast
squares means (adjusted for BW) within a column for the pullet or laying phases lacking a common superscript differ (P < 0.05). of breast, left thigh, left drum, and total left thigh + left drum expressed relative to BW (g of muscle/g of BW × 100). 2Average number of observations per least squares means during the pullet phase, laying phase, or the interaction for pullet with laying phases. 3Control-control chickens never had access to perches during their life cycle; control-perch chickens had access to perches only during the egg-laying phase of the life cycle (17 to 71 wk of age); perch-control chickens had access to perches only during the pullet phase (0 to 16.9 wk of age); and perchperch chickens always had access to perches (0 to 71 wk of age). 1Weights
respectively, Table 4) at 71 wk of age. In contrast, keel fractures increased (P = 0.009) and keel scores were worse (P = 0.0003) in 71-wk-old hens because of the presence of perches compared with no perch during the egg-laying phase (Table 4). The incidence of keel fractures was high (>80%, Table 4), and the majority of the fractures were old. The interactions between the presence or absence of perches during either the pullet or laying phases of 71-wk-old hens were not significant for keel fracture incidence and keel scores (Table 4). Out of 278 left femurs examined at 71 wk of age, only 3 were broken, each from a different treatment group for an overall incidence of 1%. There was 1 (old fracture) broken left tibia.
DISCUSSION Adult White Leghorns of the current study demonstrated high use of perches, especially at night (P. Y. Hester, unpublished data), which is expected given the strong motivation that egg-laying strains of chickens have for perching (Lambe and Scott, 1998; Olsson and Keeling, 2002). Pullet perch use was also high for the chickens of this study (Enneking et al., 2012b). The addition of perches to conventional laying cages increased bone mineralization of 71-wk-old hens for all bones measured in the study except for the BMD of the tibia (Tables 1 and 2). These results of increased BMD and BMC are in agreement with other studies that reported an increase in bone strength of caged hens as a result of perch access during egg laying (Hughes
Table 4. The effect of perch access on keel bone fracture and scores in caged White Leghorns at 71 wk of age % Fractured
Item Treatment During pullet phase Control Perch SEM n2 P-value During laying phase Control Perch SEM n2 P-value Interaction (pullet-laying)3 Control-control Control-perch Perch-control Perch-perch SEM n2 P-value
88 88 2 18 0.96 83b 92a 2 18 0.009 85 91 82 93 3 9 0.42
Keel score1
3.15 3.08 0.08 152 0.49 3.32a 2.91b 0.08 152 0.0003 3.40 2.91 3.24 2.91 0.11 76 0.49
a,bLeast squares means within a column for the laying phase lacking a common superscript differ (P < 0.05). 1Score for keel ranged from 1 to 4. A score of 1 represented severe keel bone deviations, and a score of 4 represented normal keels. 2Average number of observations per least squares means during the pullet phase, laying phase, or the interaction for pullet with laying phases. 3Control-control chickens never had access to perches during their life cycle; control-perch chickens had access to perches only during the egglaying phase of the life cycle (17 to 71 wk of age); perch-control chickens had access to perches only during the pullet phase (0 to 16.9 wk of age); and perch-perch chickens always had access to perches (0 to 71 wk of age).
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Treatment During pullet phase Control Perch SEM n2 P-value During laying phase Control Perch SEM n2 P-value Interaction (pullet-laying)3 Control-control Control-perch Perch-control Perch-perch SEM n2 P-value
Breast (g)
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an increase in mineralization as a result of perch access during the pullet phase was the BMD of the keel of 50-wk-old hens (Figure 1) and the BMC of the keel of 71-wk-old hens (Table 2). Unfortunately, this increase in mineralization as a result of pullet access to perches did not lead to a reduction in keel fracture incidence at 71 wk of age (Table 4). The BMD and BMC of all other bones (including live scans conducted over the life cycle of the hen as well as the BMD and BMC of bones collected from 71-wk-old hens) were not affected by pullet access to perches. In addition, the treatment interaction (perch or no perch during the pullet or laying phases) was also not significant for BMD (Table 1) and BMC (Table 2). The tibia was the only bone out of 7 examined that did not increase in BMD at 71 wk of age as a result of perch access during the laying phase. Appleby et al. (1992) also reported no improvement in tibial bone strength as a result of perch access in caged brown hybrids with no correlation between perching time and tibial strength. The fact that the BMD of the tibia did not respond to perching may have more to do with perch elevation than the type of bone. Perches in the current study were mounted 8.9 cm from the cage floor. If a perch of higher elevation had been used, it may have required hens to jump higher, leading to more exercise and increased mineralization. To support this hypothesis, the humerus of hens was stronger in getaway cages with higher perches compared with hens in furnished cages with lower perches most likely due to more wing flapping (Tauson and Abrahamsson, 1994b). Providing perches to pullets compared with no perches had long-term benefits in increasing gross and relative thigh and total leg muscle deposition of 71-wk-old hens (Table 3). Muscle growth during development was perhaps stimulated by the jumping on and off perches during light hours. As additional evidence that pullet perches stimulated muscle deposition, pullets from this same experiment were sampled at 12 wk of age and those with perch access had greater BW and gross left leg muscle weights than pullets without perches (Enneking et al., 2012a). The pullets with perches may also have had a larger skeletal frame as indicated by larger bones at 12 wk of age. Based on larger pullet BW, gross leg muscle weights, and bone area at 12 wk of age (Enneking et al., 2012a), it is suspected that the chickens with perches during the pullet phase began egg laying as larger birds compared with pullets with no perches. This ultimately led to heavier BW of 71-wk-old hens with prior access to pullet perches compared with hens that had no exposure to perches as pullets (Hester et al., 2013). Muscle weights did not continue to increase as a result of perching activity as adults. In fact, gross breast, thigh, and drum muscle weights (Table 3) as well as BW (Hester et al. 2013) decreased as a result of perching activity as adults. Unlike the pullet perch effect, when adjusted for BW, the relative muscle weights were similar between hens with and without access to perches
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and Appleby, 1989; Duncan et al., 1992; Tauson and Abrahamsson, 1994b; Abrahamsson and Tauson, 1997; Barnett et al., 1997; Jendral et al., 2008; Tactacan et al., 2009). Because in vivo BMD scans were positively correlated with bone-breaking force (Schreiweis et al., 2005), it is assumed that the increase in bone mineralization observed in the current study would also lead to greater bone strength. Less bone breakage would also be anticipated because as BMD decreased in Leghorns, the incidence of bone breakage increased (r = −0.54, P < 0.05, Mazzuco and Hester, 2005). However, this was not the case for the keel bone of the current study. The increase in BMD and BMC of the keel bone as a result of perch access compared with no perch during egg laying was not great enough to prevent a higher incidence of keel bone fractures. The unexpectedly high incidence of keel bone fractures (mostly old breaks) in caged 71-wk-old Leghorns with (92%) and without perches (83%) is a welfare concern because of possible chronic pain resulting from fracture-associated activation of specific nociceptors and inflammation (Carstens and Moberg, 2000; Underwood, 2002; Kuenzel, 2007). The incidence of old keel breaks of hens in noncage systems has been reported in the range from 52 to 73% (Freire et al., 2003; Nicol et al., 2006) and is likely due to the increased mobility and bumping of the keel bone when hens move from litter to raised slats or access the nest boxes (DEFRA, 2006). Although keel fracture incident was high in the current study (Table 4), fractures of the femur and tibia were rare for all treatment groups. Metal perches in cages not only caused higher keel fractures, but also resulted in more keel bone deviations. At resting, perching hen places pressure on her keel causing it to curve or deviate (Abrahamsson and Tauson, 1993; Tauson and Abrahamsson, 1994b, 1996; Abrahamsson et al., 1996; Tauson, 1998; Vits et al., 2005). Pullets given perches throughout rearing did not alleviate the poorer keel bone scores of caged hens with perches (Table 4). In contrast, floor rearing with perches compared with cage rearing reduced keel bone damage of laying hens in furnished cages (Moe et al., 2004). Redesign of the perch to minimize keel fracture and deviation is needed. Materials commonly used in the construction of perches for use by hens of the commercial egg industry include wood, plastic, and metal. For keel bone lesions, plastic versus wooden perches had no effect on keel scores (Tauson and Abrahamsson, 1994b). Soft round polyurethane perches resulted in less peak force and more contact area with the keel bone compared with round steel, mushroom shaped plastic, and flattened round perches (Pickel et al., 2011). However, surrounding wooden perches with a rubber lining did not reduce keel bone lesions compared with wooden perches of equal diameter without a rubber lining (Tauson and Abrahamsson, 1996). There has been very little research conducted on the effect of the material composition of perches on keel bone fracture incidence. Early pullet exposure to perches did little to improve hen skeletal mineralization. The only results showing
MUSCULOSKELETAL HEALTH OF CAGED HENS WITH PERCHES
ACKNOWLEDGMENTS Support for this project was provided by Agriculture and Food Research Initiative competitive grant no. 2011-67021-30114 from the USDA National Institute of Food and Agriculture. Appreciation is extended to F. A. Haan and B. D. Little of Purdue University in West Lafayette, Indiana, for the care and management of the chickens. T. L. Pollard of Big Dutchman donated the perches used in the study (Holland, MI). Chicks were donated by Hy-Line Hatchery (Warren, IN). Mention of trade names or commercial products in this article is solely for the purpose of providing specific information and does not imply recommendation or endorsement of the USDA. The USDA is an equal opportunity provider and employer.
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