Egg production and egg quality in free-range laying hens housed at different outdoor stocking densities 1

Egg production and egg quality in free-range laying hens housed at different outdoor stocking densities 1 D. L. M. Campbell,,,2 C. Lee, G. N. Hinch, and J. R. Roberts School of Environmental and Rural Science, University of New England, Armidale, NSW, 2351, Australia; and CSIRO, Agriculture and Food, Armidale, NSW, 2350, Australia ABSTRACT Free-range laying hen systems are increasing egg weight (P = 0.09), percentages of deformed eggs in number within Australia. Variation in out- door stocking densities has led to development of a national information standard on free-range egg labeling, including setting a maximum density of 10,000 hens per hectare. However, there are few data on the impacts of differing outdoor densities on production and egg quality. ISA Brown hens in small (150 hens) flocks were housed in identical indoor pens, each with access (from 21 weeks) to different sized ranges simulating one of three outdoor stocking densities (2 replicates each: 2,000 hens/hectare (ha), 10,000 hens/ha, 20,000 hens/ha). Hen-day production was tracked from 21 through 35 weeks with eggs visually graded daily for external deformities. All eggs laid on one day were weighed each week. Eggs were collected from each pen at 25, 30, and 36 weeks and analyzed for egg quality. There were no effects of outdoor stocking density on average hen-day percentage production (P = 0.67), (P = 0.30), shell reflectivity (P = 0.74), shell breaking strength (P = 0.07), shell deformation (P = 0.83), or shell thickness (P = 0.24). Eggs from hens in the highest density had the highest percentage shell weight (P = 0.004) and eggs from the lowest density had the highest yolk color score (P < 0.001). The amount of cuticle present did not differ between densities (P = 0.95) but some aspects of shell colors (P 0.01) and location of protoporphyrin IX (P = 0.046) varied. Hen age affected the majority of measurements. Stocking density differences may be related to hen diet as previous radiofrequency identification tracking of individual hens in these flocks showed birds used the range for longer in the lowest density and the least in the highest density, including depleting the range of vegetation sooner in the smaller ranges. An additional study assessing the relationship between individual hen range use, nutrition, and egg quality is warranted. Key words: free-range, stocking density, egg quality, cuticle, protoporphyrin 2017 Poultry Science 96:3128 3137 http://dx.doi.org/10.3382/ps/pex107 INTRODUCTION Free-range laying hen (Gallus gallus domesticus) egg production is increasing within Australia in response to consumer demand. This demand is likely driven by the perception that a choice between indoor and outdoor areas with opportunities to access fresh air and more natural surroundings improves hen welfare (Knierim, 2006). At present, the Australian Model Code of Practice for the Welfare of Animals - Domestic Poultry (Primary Industries Standing Committee, 2002) recommends an outdoor stocking density of 1,500 hens per hectare (at simultaneous occupancy) but does not set a maximum density. Thus freerange systems can vary from housing hens with ac- C 2017 Poultry Science Association Inc. Received January 4, 2017. Accepted March 22, 2017. 1 This work was conducted within the Poultry CRC (grant 1.5.6), established and supported under the Australian Government s Cooperative Research Centres Program. 2 Corresponding author: dana.campbell@csiro.au cess to extensive pasture areas, to some larger-scale producers providing less space per individual hen. Because of the large variation in what can be defined as free-range, consumer dissatisfaction increased to a point where the Australian Consumer Affairs Ministers released a free-range egg labelling information standard during 2016 requiring hens to have meaningful and regular access to the outdoors, with outdoor stocking of no more than one hen per square metre (maximum 10,000 hens per hectare). However, there are limited data available from Australia or internationally on free-range systems and the impacts of outdoor range stocking density on hen production and egg quality to define the implications for design, management and efficiency of free-range systems. Research with hens in caged systems has shown stocking density or cage size can impact egg production and egg quality to varying degrees. It is important to note in all following studies, stocking density was modified via group size in comparison to the present study which modified range size and kept group size 3128

EGG PRODUCTION AND OUTDOOR STOCKING DENSITY 3129 constant. Saki and colleagues compared 4 cage densities (2,000, 1,000, 667, and 500 cm 2 /hen) for White Leghorn hens housed in conventional layer cages and found that hens in the highest stocking density had lower egg weight, egg mass, and hen-day egg production although they did have a higher feed conversion ratio, possibly due to restricted movement (Saki et al., 2012). Using a similar experimental design, Sarica et al., (2008) also showed decreased egg production and egg mass in ISA Brown hens at higher cage stocking densities although most egg quality measures were unaffected by cage density. In a further study of hens in conventional cages stocked at either 5 or 7 Hy-Line W36 hens per cage, stocking density had no effect during weeks 28 to 33 of production, but during weeks 33 to 38, hens from the higher stocking density had reduced egg mass (Jahanian and Mirfendereski, 2015). Meng et al., (2015) compared Hy-Line Brown hens in conventional cages (highest stocking density), large or small furnished cages (both the same stocking density but lower than conventional). Results showed egg weight was the same among all cage types, but eggs from the conventional cages had lower Haugh units and albumen heights and egg production was lowest in the large furnished cages (Meng et al., 2015). In contrast, Guo et al., (2012) showed laying rate and egg weight did not differ between hens housed in a conventional cage system and hens housed in furnished cages at small (21 hens) or large (48 hens) flock sizes, both at lower stocking densities than the conventional cage. Hens in the furnished cages did have higher feed intake and poorer feed efficiency than conventional-housed hens (Guo et al., 2012). Finally, recent comparisons of egg production by hens housed in multi-tier aviary systems with access to a veranda showed hens housed at the highest density had the lowest laying percentage but egg weight was the same across all densities (Steenfeldt and Nielsen, 2015). The majority of eggs in the Australian market are brown-shelled eggs where a uniform, dark color is important for consumer satisfaction (Samiullah and Roberts, 2013). Egg shell color is reported to be influenced by a number of variables such as disease, age (Samiullah et al., 2015, 2016), sunlight (Icken et al., 2011), and stress, including stocking density (Walker and Hughes, 1998). Protoporphyrin is the main eggshell pigment in brown-shelled eggs, located primarily in the calcareous portion of the eggshell rather than the cuticle (Samiullah and Roberts, 2013). Free-range eggs are reported to be paler than eggs from caged systems (Samiullah et al., 2014) but to the best of the author s knowledge there are currently no data on the effects of outdoor stocking density on protoporphyrin IX concentrations in free-range laying hens. The cuticle deposited on the eggshell as the outermost layer is important in protecting the egg from external microbes and thus plays a critical role in food safety (Samiullah and Roberts, 2014). Cuticle formation can be reduced by stress and has recently been shown to be lower in free-range versus caged hens (Samiullah and Roberts, 2014; Samiullah et al., 2014) but there are no data on the impacts of free-range outdoor stocking density on the amount of cuticle present. Outdoor stocking density is distinct from indoor stocking density in closed systems as hens have a choice whether to go outside or not, thus the actual stocking densities, both indoor and outdoor, fluctuate across the day. The overall objectives of a large experiment on outdoor stocking density in an experimental freerange laying hen system were to assess behavior, welfare, and production of hens provided different sized outdoor ranges simulating outdoor densities of 2,000, 10,000, or 20,000 hens per hectare. Hens were in small flocks of 150 hens each and assessed until 36 weeks of age. Hens range use was tracked using radio-frequency identification technology that showed, on average, hens spent more time outside each day when more space was available (Campbell et al., 2017). At the conclusion of the trial the majority of hens were in visibly good condition with full feather coverage, no wounds and with minimal differences between stocking densities in basic external health parameters (Campbell et al., 2016). The objectives of the current experiment were to assess the egg production and egg quality including measurements of the amount of cuticle present and protoporphyrin IX concentrations at regular intervals up to 36 weeks of age from the free-range hens housed at one of three stocking densities outdoors. MATERIALS AND METHODS Ethical Statement All research was approved by the University of New England Animal Ethics Committee (AEC14-100) prior to the start of data collection. Hens and Housing Nine hundred ISA Brown floor-raised pullet laying hens (Gallus gallus domesticus) were obtained from a commercial supplier and placed at 16 weeks of age (May 2015) into the University of New England s Laureldale experimental free-range facility located in Armidale, Australia. Hens were distributed between six indoor floor pens (150 birds per pen) with indoor stocking density at nine birds per m 2. Indoor resources per bird either met or exceeded the Australian Model Code of Practice for the Welfare of Animals Domestic Poultry (Primary Industries Standing Committee, 2002) with 15.2 cm of perch space (including the nest box ledge), 160 cm 2 of nest space (six birds per nest box), 1.55 cm of round feeder space (two round feeders per pen), and one nipple drinker per 10 birds (for the indoor pen schematic see Figure 1, Campbell et al., 2017). Barastoc - Premium Top Layer Mash (crude protein: 16.5%, crude fat: 2.5%, crude fibre: 6%, salt: 0.3%, copper: 8.0 mg/kg, selenium: 0.3 mg/kg, calcium: 3.6%,

3130 CAMPBELL ET AL. Figure 1. A map of the six indoor pens and their associated outdoor range areas for the three outdoor stocking density treatments (2,000 hens per hectare (ha), 10,000 hens/ha, 20,000 hens/ha). Melbourne, VIC, Australia) was provided ad libitum. Rice hulls were placed on the floor at an initial depth of approximately 4 cm. The shed was fan ventilated but with no additional environmental control. The average indoor temperature measured at bird height across the trial period was 8.8 C ± SD 4.09 (range: 2.2 to 19.4 C). Incandescent lighting incrementally increased from 15 h (at 16 weeks) to 16 h of light by 20 weeks of age (lights on at 04:00, lights off at 20:00 h). The light inside the pen with the pop-holes closed ranged from 4 to 21 lux (measured at bird height at front, middle, and back of pen, Lutron Light Meter, LX-112850; Lutron Electronic Enterprise CO., Ltd, Taipei, Taiwan), which increased to 5 to 190 lux with the pop-holes open, measured on one cloudy and one sunny day. Each indoor pen was associated with a single wiremesh fenced outdoor area which was initially 100% covered (prior to bird access) with a variety of grass and weeds but no shelter or shade structures were present. The range areas were of different sizes to simulate three outdoor stocking density treatments (with two replicates per treatment) based on maximal occupancy of the range: 2,000 hens per hectare (ha) (5 m 2 /hen), 10,000 hens/ha (1 m 2 /hen), and 20,000 hens/ha (0.5 m 2 /hen, Figure 1). Pop-holes were first opened at 21 weeks of age ( 20% production) with subsequent daily access from 09:00 to 16:30 h across 15 weeks over winter. Birds were not forced onto the range allowing natural range usage patterns. The winter period weather was typically dry (sunny/cloudy with rain on 12% and snow on 2% of days) and outdoor temperatures generally mild (average outdoor temperatures during range access hours were 14.3 C ± SD 5.34; range: 3.5 to 27.9 C). Hens were encouraged to return inside each afternoon using 350 g of poultry grain mix per pen (Barastoc Poultry Grain Mix, Melbourne, VIC, Australia) and all birds were held inside at all other times. Following range access by birds, weekly photos of the range showed ground cover (green vs. brown area) decreased from 100% to 0% coverage within 5 weeks in the 20,000 hens/ha ranges, within 6 weeks in the 10,000 hens/ha ranges, and by 8 weeks, had only dropped as low at 20% in the 2,000 hens/ha ranges and remained at this level for the trial duration. Minimal pasture growth was expected across the winter trial period. Egg Production All eggs were collected by hand each morning and counted per pen from the beginning of lay (19 to 20 weeks) up to the start of 36 weeks of age. All eggs were visually graded (but not candled) to record the numbers of eggs per pen that were normal or deformed (body checked, misshapen, pimpled ( 1 pimple), rough-shelled, or soft-shelled). Across the trial period, only 15 eggs were found laid in the range area (and only in the largest sized ranges). From 21 through 35 weeks of age, all eggs laid within each pen on one day per week were weighed together to obtain the average egg weight per pen. Egg Quality At 25, 30, and 36 weeks of age 90 eggs were collected on one day from each pen (180 eggs per stocking density treatment) to conduct egg quality measurements.

EGG PRODUCTION AND OUTDOOR STOCKING DENSITY 3131 Eggs were unwashed and eggs with substantial shell contamination were not included for analysis. Of the 90 eggs collected from each pen, 30 eggs (60 eggs per stocking density treatment) were analyzed for eggshell and internal quality: shell color by percentage reflectivity, egg shell breaking strength by quasi-static compression, shell deformation to breaking point, and shell weight (egg quality equipment, Technical Services and Supplies (TSS), Dunnington, York, UK). Shell thickness was measured at the eggshell equator in three places using a custom-made gauge based on a Mitutoyo Dial Comparator gauge (Model 2109 10). Percentage shell was calculated from shell weight and egg weight and yolk color was measured using the DSM YolkFan (TSS equipment). All analyses were conducted on or up to two days following egg collection by one person blind to the stocking density treatments. Cuticle Staining and Protoporphyrin IX Concentrations The remaining 30 eggs from each pen were used to separately measure the amount of cuticle and protoporphyrin IX (PP IX) concentrations in the shell. Eggshells were free from extraneous calcareous material. Fifteen unstained eggs per pen (30 per stocking density treatment) were measured using the L a b color space where L has a maximum of 100 (white) and a minimum of 0 (black). For a, green is towards the negative end of the scale and red towards the positive end. For b, blue is towards the negative end and yellow towards the positive end of the scale. The lower the value for L, the darker the eggshell color. The higher the value for a in unstained eggs, the more red in the color of the shells and the higher the value for b, the more yellow in the color of the shells. Using a Konica Minolta hand-held spectrophotometer (CM-2600d, Konica Minolta Sensing, Singapore), readings were taken 3 times per location at 3 locations around the egg equator with the average value recorded. Eggs were then stained with MST cuticle blue dye (MST Technologies, Europe Ltd., Kettering, UK) and the cuticle color was measured. Eggs were immersed for one minute in cuticle blue dye, made according to the manufacturer s recommendation. They were then rinsed in water for 3 seconds, placed on a plastic egg filler, and allowed to dry. The color of the stained egg shell cuticle was measured as described prior. Shell reflectivity was also measured with a shell reflectivity meter (TSS, Dunnington, UK). Following staining with cuticle blue dye, the lower the color for a, the greater the extent of staining and the greater the amount of cuticle present. The difference between the reading for a before and after staining is indicative of the amount of cuticle present. A single score was calculated after the methods of Leuleu et al. (2011) as ΔE ab = [(ΔL ) 2 +(Δa ) 2 +(Δb ) 2 ]where a higher score indicates the presence of more cuticle. The final 15 eggs from each pen (30 eggs per stocking density treatment) were analyzed for PP IX in the cuticle and whole eggshell (including the cuticle). The method described by Poole (1965) was used with some modification as described in Samiullah and Roberts (2013). The absorbance values from the samples were converted into concentration of PP IX in 1 g of eggshell (with and without cuticle present). To determine the amount of PP IX in the cuticle, the values of the eggshell samples without cuticle were subtracted from those samples with the cuticle present. Data and Statistical Analyses The numbers of eggs laid were converted to percentage hen-day production for each pen. The daily values were averaged to provide a weekly percentage henday production value for each pen of birds within each stocking density treatment during the range access period (weeks 21 through 35). Daily grading of normal vs. deformed eggs was converted to a percentage of daily eggs that were deformed and averaged per week during the range access period for each pen within each stocking density. Weekly egg weights were compiled to show the average weekly egg weight for each pen within each stocking density treatment from weeks 21 through 35. The percentage production and percentage abnormal eggs were converted to proportions and arcsine square-root transformed for analysis. Egg quality parameters (percentage shell color reflectivity, egg shell breaking strength, shell deformation, shell thickness, percentage shell and yolk color) were compiled based on hen age and stocking density with percentage values arcsine square-root transformed. General Linear Models with α set at 0.05 were used in JMP 12.1.0 (SAS Institute, Cary, NC), to assess the effects of stocking density, hen age, and the interaction between stocking density and hen age on production, grading, egg quality parameters, cuticle, and PP IX measurements. Where significant differences were present, post-hoc Student t tests were applied to the least squares means with Bonferroni correction applied for more than 3 comparisons. The raw values of transformed data are presented in the results as there was virtually no difference between raw and back-transformed data. RESULTS All birds were in visibly good health throughout the trial (see Campbell et al., 2016 for further details on hen health and welfare measures) with flock-level mortality at 1% over 15 weeks. Egg Production Across the range access period there were no differences in egg production level between stocking

3132 CAMPBELL ET AL. densities (F (2,45) = 0.41, P = 0.67) and no interaction between hen age and stocking density (F (28,45) = 0.35, P = 0.99). However, as expected, production increased as the hens aged with birds in the 2,000 hens/ha stocking densities reaching 97.67% production, birds in the 10,000 hens/ha stocking densities reaching 97.71% production, and birds in the 20,000 hens/ha stocking densities reaching 98.65% production. There were also no differences in average weekly egg weights between stocking density treatments (F (2,45) = 2.52, P = 0.09), no interaction between hen age and stocking density (F (28,45) = 1.27, P = 0.23) but egg weights increased weekly across the trial period (F (14,45) = 430.0, P < 0.0001; 23 weeks: Least squares mean (LSM) ± SEM 51.83 ± 0.23 g, 35 weeks: 67.07 ± 0.23 g). Similarly, there were also no differences between stocking densities in the proportion of deformed eggs (F (2,45) = 1.24, P = 0.30) and no interaction between hen age and stocking density (F (28,45) = 0.61, P = 0.92, Figure 2). There was significant variation between the weeks across the trial duration but there was no consistent pattern (F (14,45) = 7.01, P < 0.0001, Figure 2). Egg Quality Figure 2. The raw values showing the total average percentage (±SE) of deformed eggs (body-checked, misshapen, pimpled, roughshelled, or soft-shelled) laid weekly during the range access period for hens from the three stocking density treatments (2,000 hens per hectare (ha), 10,000 hens/ha, 20,000 hens/ha). Differences were present between weeks of age, but not between stocking densities. There were few effects of stocking density on egg quality measurements, several effects of hen age and no interactions between stocking density and hen age (all P 0.34). Specifically, there were no differences between stocking densities in the percentage shell reflectivity (F (2,531) = 0.30, P = 0.74, Table 1), but there was an overall effect of hen age with the percentage reflectivity being lowest, and thus egg shells darkest, in eggs laid at the earlier stage of 25 weeks (F (2,531) = 15.71, P < 0.0001, Table 1). There was a trend for differences in shell breaking strength across the stocking densities, with strength higher at the higher density (F (2,531) = 2.66, P = 0.07, Table 1), but no changes with hen age (F (2,531) = 1.87, P = 0.16, Table 1). There were no differences between stocking densities in shell deformation (F (2,531) = 0.18, P = 0.83) but there was an effect of hen age (F (2,531) = 9.26, P < 0.0001) with the shortest breaking distance in eggs laid from hens at 36 weeks of age (Table 1). There was no effect of stocking density on shell weight (F (2,531) = 2.20, P = 0.11) but there was an effect of hen age (F (4,531) = 78.35, P < 0.0001) with the highest weight in eggs laid at 36 weeks of age and the lowest in eggs laid at 25 weeks of age (Table 1). In contrast, there was an effect of stocking density on the percentage shell weight (F (2,531) = 5.57, P < 0.004) where eggs laid from hens housed at the highest density showed the highest percentage shell weight (Table 1). There was also an effect of hen age (F (2,531) = 9.06, P = 0.0001) with eggs laid from hens at 36 weeks of age showing the lowest percentage shell weight (Table 1). There was no effect of stocking density on shell thickness (F (2,531) = 1.43, P = 0.24) but there was a trend for a difference in shell thickness with hen age (F (2,531) = 2.38, P = 0.09, Table 1). Finally, there was an effect of stocking density on yolk color (F (2,531) = 33.41, P < 0.0001), eggs laid by hens housed at the lowest stocking density showed the highest color score (Table 1). There was also an effect Table 1. The egg quality measurements (% reflectivity, breaking strength, shell deformation, shell weight, % shell weight, shell thickness, and yolk score) taken on eggs from hens housed at one of three outdoor stocking densities (2,000, 10,000, or 20,000 hens per hectare), sampled at 25, 30, and 36 weeks of age. Dissimilar superscript letters indicate significant differences (P < 0.05) within stocking density or within hen age. Stocking density Hen age 2,000 hens/ha 10,000 hens/ha 20,000 hens/ha 25 weeks 30 weeks 36 weeks % reflectivity 22.32 ± 0.25 22.61 ± 0.29 22.51 ± 0.27 21.27 ± 0.22 b 23.14 ± 0.30 a 23.02 ± 0.26 a Breaking strength (N) 51.43 ± 0.53 51.77 ± 0.53 53.12 ± 0.58 51.99 ± 0.62 52.91 ± 0.55 51.42 ± 0.45 Shell deformation (μm) 308.06 ± 2.85 308.89 ± 2.91 306.61 ± 2.60 310.11 ± 2.91 a 314.86 ± 2.97 a 298.56 ± 2.30 b Shell weight (g) 6.43 ± 0.04 6.46 ± 0.04 6.54 ± 0.04 6.12 ± 0.04 c 6.57 ± 0.04 b 6.74 ± 0.03 a % Shell weight 10.05 ± 0.04 b 10.0 ± 0.04 b 10.20 ± 0.05 a 10.21 ± 0.05 a 10.10 ± 0.04 a 9.94 ± 0.04 b Shell thickness μm 456.74 ± 1.67 457.08 ± 1.53 460.44 ± 1.88 456.16 ± 1.85 461.07 ± 1.71 456.99 ± 1.53 Yolk Score 12.33 ± 0.05 a 11.84 ± 0.07 b 11.69 ± 0.07 b 12.34 ± 0.06 a 11.60 ± 0.06 c 11.94 ± 0.06 b

EGG PRODUCTION AND OUTDOOR STOCKING DENSITY 3133 Table 2. Mean ± SEM spectrophotometric measurements in the L a b space system before and after cuticle staining for eggs from hens housed at one of three outdoor stocking densities (2,000, 10,000, or 20,000 hens per hectare) with samples taken at 25, 30, and 36 weeks of age. The single score is calculated following methods of Leuleu et al. (2011) where a higher score indicates more cuticle present. Dissimilar superscript letters indicate significant differences (P < 0.05) within stocking density or within hen age. Stocking density Hen age 2,000 hens/ha 10,000 hens/ha 20,000 hens/ha 25 weeks 30 weeks 36 weeks L before stain 60.0 ± 0.35 59.50 ± 0.35 60.09 ± 0.35 57.83 ± 0.35 c 60.15 ± 0.35 b 61.62 ± 0.35 a a before stain 18.83 ± 0.20 18.83 ± 0.20 18.59 ± 0.20 19.32 ± 0.20 a 19.10 ± 0.20 a 17.84 ± 0.20 b b before stain 29.45 ± 0.24 a 28.70 ± 0.24 b 28.40 ± 0.24 b 28.61 ± 0.24 29.27 ± 0.24 28.68 ± 0.24 % shell reflectivity 23.11 ± 0.35 22.44 ± 0.35 23.10 ± 0.35 20.91 ± 0.35 c 23.21 ± 0.35 b 24.54 ± 0.35 a a after stain 1.05 ± 0.50 1.09 ± 0.50 1.14 ± 0.50 0.95 ± 0.50 b 1.71 ± 0.50 a 4.05 ± 0.50 c Difference in a 19.89 ± 0.51 19.92 ± 0.51 19.74 ± 0.51 20.27 ± 0.51 b 17.39 ± 0.51 c 21.88 ± 0.51 a Single score 21.23 ± 0.56 21.43 ± 0.56 21.44 ± 0.56 21.59 ± 0.56 b 18.98 ± 0.56 c 23.54 ± 0.56 a of hen age (F (2,531) = 41.54, P < 0.0001), the highest color score was in eggs laid at 25 weeks of age and the lowest in eggs laid at 30 weeks of age (Table 1). Cuticle Staining Within the L a b space system there was no effect of stocking density on the L component before cuticle staining (F (2,261) = 0.80, P = 0.45, Table 2), but there was an effect of hen age (F (2,261) = 29.51, P < 0.0001) with values increasing as the hens aged indicating lighter colored egg shells (Table 2). There was no interaction between stocking density and hen age (F (4,261) = 1.73, P = 0.14). There was also no effect of stocking density on the values of a before cuticle staining (F (2,261) = 0.48, P = 0.62, Table 2). However, there wasaneffectofhenage(f (2,261) = 16.0, P < 0.0001) with values lowest in eggs laid at 36 weeks of age indicating less red in the color of the shell (Table 2). There was no interaction between stocking density and hen age (F (4,261) = 1.66, P = 0.16) but there was an effect of stocking density on the values of b before cuticle staining (F (2,261) = 5.10, P = 0.007, Table 2) with eggs laid from hens at the 2,000 hens/ha density showing the highest values indicating more yellow color in the egg shell. There was no effect of hen age (F (2,261) = 2.27, P = 0.11, Table 2) or interaction between stocking density and hen age (F (4,2) = 1.66, P = 0.16). Similar to the percentage reflectivity measures on the other set of egg samples, there was no effect of stocking density (F (2,261) = 1.21, P = 0.30, Table 2) but there wasaneffectofhenage(f (2,261) = 26.97, P < 0.0001) with the least reflectivity and thus the darkest shells in eggs laid at 25 weeks of age (Table 2). There was no interaction between stocking density and hen age (F (4,261) = 1.51, P = 0.20). There was no effect of stocking density on the values of a following cuticle staining (F (2,261) = 0.008, P = 0.99) but there was an effect of hen age (F (2,261) = 32.85, P < 0.0001) with eggs laid from hens at 36 weeks of age showing the largest negative difference (more cuticle) and eggs laid from hens at 30 weeks of age a positive difference (Table 2). There was a trend for an interaction between stocking density and hen age (F (4,261) = Figure 3. The mean ± SEM differences in a values (in the L a b space system) before and after cuticle staining indicating the amount of cuticle present (higher score = more cuticle) for eggs laid by hens housed at different outdoor stocking densities (2,000, 10,000, and 20,000 hens/ha) at 25, 30, and 36 weeks of age. Dissimilar connecting letters indicate significant differences at P < 0.006. 2.18, P = 0.07). There was no effect of stocking density on the difference in the measure of a (F (2,261) = 0.04, P = 0.96, Figure 4, Table2). There was however, an effect of hen age (F (2,261) = 19.74, P < 0.0001) with eggs laid at 36 weeks showing the highest difference score and thus the most cuticle present, and eggs laid at 30 weeks showing the lowest difference score and thus the least cuticle present (Figure 3, Table2). There was also an interaction between stocking density and hen age (F (4,261) = 2.69, P = 0.03, Figure 3). There was no effect of stocking density on the calculated single score that indicates the amount of cuticle present (F (2,261) = 0.05, P = 0.95) but there was an effect of hen age (F (2,261) = 16.90, P < 0.0001) with eggs laid at 36 weeks of age showing the highest score indicative of the most cuticle present and eggs laid at 30 weeks of age showed the lowest score (Table 2). There was no interaction between stocking density and hen age (F (4,261) = 1.92, P = 0.11).

3134 CAMPBELL ET AL. Protoporphyrin IX Concentrations Within the L a b space system there was no effect of stocking density on the L component with the cuticle present (F (2,261) = 0.83, P = 0.43) but there was an effect of hen age (F (2,261) = 13.03, P < 0.0001) with the highest values in eggs laid by hens at 36 weeks of age, indicating the lightest egg shells and the lowest values in eggs laid by hens at 25 weeks of age (Table 3). There was no interaction between stocking density and hen age (F (4,261) = 0.54, P = 0.71). Following removal of the cuticle, there was an effect of stocking density on the values of L (F (2,261) = 3.85, P = 0.02) with the highest values in eggs laid by hens in the 2,000 hens/ha densities compared to eggs laid by hens in the 10,000 hens/ha densities but neither differed from eggs laid by hens in the 20,000 hens/ha densities (Table 3). There was also an effect of hen age (F (2,261) = 24.68, P < 0.0001) with values increasing and thus egg shell color decreasing, as the hens aged (Table 3). There was no interaction between stocking density and hen age (F (4,261) = 0.33, P = 0.86). In contrast to L, there was an effect of stocking density on the values of a with the cuticle present (F (2,261) = 4.74, P = 0.01) with the lowest values in eggs laid by hens from the 2,000 hens/ha density indicating less red in the color of the shells (Table 3). There was also an effect of hen age (F (4,261) = 7.13, P = 0.001) with the highest values of a in eggs laid by hens at 30 weeks of age (Table 3), but there was no interaction between stocking density and hen age (F (4,261) = 1.22, P = 0.30). There was an effect of stocking density on the values of a following cuticle removal (F (2,261) = 3.86, P = 0.02) with the lowest values in eggs laid by hens from the 2,000 hens/ha densities compared to eggs laid by hens from the 10,000 hens/ha densities although neither differed from eggs laid by hens from the 20,000 hens/ha densities (Table 3). Hen age also impacted the values of a (F (2,261) = 18.59, P < 0.0001) with the lowest values seen in eggs laid by hens at 36 weeks of age (Table 3), but there was no interaction between stocking density and hen age (F (4,261) = 0.16, P = 0.96). There was no effect of stocking density (F (2,261) = 0.06, P = 0.94), hen age (F (2,261) = 1.74, P = 0.18) or interaction between hen age and stocking density (F (4,261) = 1.43, P = 0.22) on the values of b with cuticle present (Table 3). There was no effect of stocking density on the values of b following cuticle removal (F (2,261) = 1.19, P = 0.31) but there was an effect of age (F (2,261) = 16.58, P < 0.0001) with the lowest values in eggs laid at 36 weeks of age (Table 3). There was also a significant interaction between stocking density and hen age (F (4,261) = 2.88, P = 0.02, Figure 4). There was no effect of stocking density on shell percentage reflectivity with the cuticle present (F (2,261) = 0.81, P = 0.45) but there was an effect of hen age (F (2,261) = 7.58, P = 0.0006) with the highest reflectivity in eggs laid by hens at 36 weeks of age (Table 3). Table 3. Spectrophotometric mean ± SEM measurements in the L a b space system with (+) and without (-) cuticle present and concentrations of protoporphyrin IX (PP IX) in the cuticle and calcareous eggshell of eggs from hens housed at one of three outdoor stocking densities (2,000, 10,000, or 20,000 hens per hectare) and sampled at 25, 30, and 36 weeks of age. Dissimilar superscript letters indicate significant differences within stocking density or hen age. Stocking density Hen age 2,000 hens/ha 10,000 hens/ha 20,000 hens/ha 25 weeks 30 weeks 36 weeks L + cuticle 60.70 ± 0.35 60.36 ± 0.35 60.06 ± 0.35 59.19 ± 0.35 c 60.24 ± 0.35 b 61.70 ± 0.35 a L - cuticle 66.23 ± 0.32 a 65.0 ± 0.32 b 65.35 ± 0.32 a,b 64.02 ± 0.32 c 65.36 ± 0.32 b 67.21 ± 0.32 a a + cuticle 18.19 ± 0.19 b 18.83 ± 0.19 a 18.95 ± 0.19 b 18.54 ± 0.19 b 19.21 ± 0.19 a 18.22 ± 0.19 a a - cuticle 16.31 ± 0.18 b 17.01 ± 0.18 a 16.80 ± 0.18 a,b 17.30 ± 0.18 a 17.01 ± 0.18 a 15.82 ± 0.18 b b + cuticle 29.33 ± 0.23 29.42 ± 0.23 29.32 ± 0.23 29.19 ± 0.23 29.70 ± 0.23 29.17 ± 0.23 b - cuticle 28.63 ± 0.22 29.10 ± 0.22 28.76 ± 0.22 29.11 ± 0.22 a 29.57 ± 0.23 a 27.81 ± 0.22 b % shell reflectivity + cuticle 24.03 ± 0.36 23.70 ± 0.36 23.39 ± 0.36 22.90 ± 0.36 b 23.42 ± 0.36 b 24.79 ± 0.36 a % shell reflectivity - cuticle 29.48 ± 0.37 a 28.16 ± 0.37 b 28.71 ± 0.37 a,b 27.62 ± 0.37 b 28.30 ± 0.37 b 30.44 ± 0.37 a PP IX (mm) in 1 g of 1.25 10 7 ± 1.83 10 9 1.28 10 7 ± 1.83 10 9 1.30 10 7 ± 1.89 10 9 1.34 10 7 ± 1.80 10 9a 1.26 10 7 ± 1.97 10 9b 1.25 10 7 ± 1.64 10 9b shell + cuticle PP IX (mm) in 1 g of 1.06 10 7 ± 1.75 10 9 1.12 10 7 ± 1.81 10 9 1.09 10 7 ± 1.87 10 9 1.15 10-7 ± 1.86 10 9a 1.07 10 7 ± 1.84 10 8b 1.04 10 7 ± 1.55 10 9b shell - cuticle PP IX (mm) in 1 g of cuticle 1.96 10 8 ± 1.24 10 9 1.70 10 8 ± 1.02 10 9 2.11 10 8 ± 1.25 10 9 1.84 10 8 ± 1.32 10 9 1.85 10 8 ± 9.75 10 10 2.08 10 8 ± 1.23 10 9

EGG PRODUCTION AND OUTDOOR STOCKING DENSITY 3135 1.18, P = 0.31) and no interaction between stocking density and hen age (F (4,261) = 0.53, P = 0.72, Table 3). DISCUSSION Figure 4. The mean ± SEM of b values (in the L a b space system) following cuticle removal for eggs laid by hens housed at different outdoor stocking densities (2,000, 10,000, and 20,000 hens/ha) at 25, 30, and 36 weeks of age. Dissimilar connecting letters indicate significant differences at P < 0.006. There was no interaction between stocking density and hen age (F (4,261) = 0.72, P = 0.58). In contrast, after the cuticle was removed, there was an effect of stocking density on shell percentage reflectivity (F (2,261) = 3.20, P = 0.04) with the highest reflectivity in eggs laid by hens in the 2,000 hens/ha densities compared to the eggs from hens in the 10,000 hens/ha densities, although neither differed from the eggs laid by hens in the 20,000 hens/ha densities (Table 3). There was also an effect of hen age (F (2,261) = 15.97, P < 0.0001) with the highest reflectivity in eggs laid by hens at 36 weeks of age (Table 3). There was no interaction between stocking density and hen age (F (4,261) = 0.08, P = 0.99). There was no effect of stocking density on the concentration of PP IX in the egg shell with cuticle present (F (2,261) = 1.68, P = 0.19) but there was an effect of hen age (F (2,261) = 8.32, P = 0.0003) with the highest concentrations in eggs laid by hens at 25 weeks of age (Table 3). There was no interaction between stocking density and hen age (F (4,261) = 0.45, P = 0.77) but there was a trend for differences between stocking densities in the concentration of PP IX in the egg shell with the cuticle removed (F (2,261) = 2.70, P = 0.07) and an effect of hen age (F (2,261) = 11.40, P < 0.0001) with the highest concentrations in eggs laid by hens at 25 weeks of age (Table 3). There was no interaction between stocking density and hen age (F (4,261) = 0.19, P = 0.94). Finally, there was an effect of stocking density on the amount of PP IX in the cuticle (F (2,261) = 3.0, P = 0.046, Table 3) with the highest concentrations in the eggs laid by hens from the 20,000 hens/ha densities, the least in the 10,000 hens/ha densities but neither differed from the 2,000 hens/ha densities. There was no effect of hen age (F (2,261) = Outdoor stocking density did not affect hen-day production, egg weight, or egg deformation in these experimental free-range flocks. There were some effects of stocking density on egg quality measurements; eggs laid by hens from the highest stocking density had a higher percentage shell weight and eggs laid by hens from the lowest stocking density had the darkest yolk color. There were some differences between stocking densities in eggshell color and the amount of PP IX in the cuticle but no differences in the amount of cuticle present. Hens in these flocks varied in their range use with hens in the lowest stocking density spending more time outside and hens in the highest density the least time outside (Campbell et al., 2017). Free-range hens have been shown to have reduced egg weight in comparison to conventional caged hens (Samiullah et al., 2014) and free-range systems typically have lower production than caged systems (Miao et al., 2005). Egg production is influenced by a multitude of variables such as disease, nutrition, stress, housing system, and is an energy-costly activity; if more energy is spent roaming outdoors less energy may be used for production (Meng et al., 2015). Thus, we may have expected hens in the lower outdoor density to have lower production. Although not statistically different, the hens in the highest density did reach the highest percentage hen-day production, but all the flocks at all densities surpassed the projected genotype peak of 95% production in alternative production systems (ISA, 2016). Furthermore, the average egg weight by 35 weeks of 67.07 g also surpassed the strain standard of a 62.9 g average egg weight at this age (ISA, 2016). The birds in this study were checked twice daily and always had ad libitum access to feed. The area to roam outside was also less than it would be for larger flocks at the same densities. Thus it is possible that greater differentiation between densities may occur in commercial-scale flocks where there are larger total areas to roam (but see Leenstra et al., 2012 for no relationship between production and use of the outdoor range in commercial farms). Hens in this study were in visibly good condition throughout the trial (Campbell et al., 2016) and it is possible that poor health may exacerbate production differences between the outdoor stocking densities, an issue for experimental clarification. In general, the changes in egg quality with age in this study were consistent with changes observed across the flock cycle of commercial free-range Hy-Line Brown hens in Australian housing systems (Samiullah et al., 2014). The effects of stocking density on egg quality measures of percentage shell weight and yolk color may be related to possible dietary differences. Hens at the

3136 CAMPBELL ET AL. highest stocking density spent the least time outside, with shorter individual visits to the range (Campbell et al., 2017), thus potentially feeding more on the commercial diet rather than foraging outside, consuming insects, or consuming vegetation. Additionally, these birds had the smallest range area and thus depleted initial vegetation faster. Previous research has found varying effects of housing on yolk color (Van Den Brand et al., 2004, Senčić et al., 2006, Sekeroglu et al., 2010), particularly from commercial free-range farms (Samiullah et al., 2014), potentially associated with variation in diet. Hens at the highest outdoor density had the greatest percentage eggshell weight where a dietary reduction in calcium and phosphorus intake may decrease eggshell percentage (Świ atkiewicz et al., 2010). There is also some evidence that dietary corticosterone increases shell thickness in laying hens through possible changes to the shell structure (Kim et al., 2015). By the end of the trial the hens at the highest stocking density showed the highest albumen corticosterone concentrations (Campbell et al., 2016) and the specific effects of corticosterone on egg quality warrant further investigation. There were some effects of stocking density on eggshell color but most effects were associated with age. Similar to differences in egg quality, the differences between stocking densities is possibly associated with variation in the diet of the density groups (Samiullah et al., 2015) although differences could also be linked to stress (Walker and Hughes, 1998; Mertens et al., 2010) withan expectation of greater stress at higher density. Stocking density effects were seen in the values of a and b in one sample pool (of 15 eggs) but not in the other sample pool (of 15 eggs), indicating high within-flock variation. Thus the effects on eggshell color may be multiplicative (Samiullah et al., 2015) and more detailed examination of the cause of individual variation is warranted (Mills et al., 1991; Samiullah et al., 2015). The darker eggshells from hens at 25 weeks of age is consistent with previous findings of age effects in commercial flocks (Samiullah et al., 2014). Differences in the amount of cuticle have previously been found between conventional and freerange flocks (Samiullah et al., 2014) but differences in ranging and/or stress levels in this experiment did not impact cuticle amount. Overall, flocks housed at all outdoor stocking densities showed high production levels, surpassing strain standards. The variation in some egg quality and eggshell color parameters may be associated with differences in range access and range vegetation. Further study that focuses on individual hen ranging, nutrition, and egg production is warranted to determine optimization strategies for production systems that provide hens with a choice of environments. ACKNOWLEDGMENTS This research was conducted within the Poultry Cooperative Research Centre (CRC) (grant 1.5.6), established and supported under the Australian Government s Cooperative Research Centres Program. We thank Sue Belson, Grahame Chaffey, Mandy Choice, Andrew Cohen-Barnhouse, Tim Dyall, Troy Kalinowski, Jim Lea, Dominic Niemeyer, Hélène Pecourt, Mark Porter and Laura Warin for technical and husbandry assistance. Appreciation is expressed towards Matthew Hilliar and Elfira Suawa for conducting the egg quality analyses. REFERENCES Campbell, D. L. M., G. N. Hinch, T. R. Dyall, L. Warin, B. A. Little, and C. Lee. 2017. 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