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ENVIRONMENT, WELL-BEING, AND BEHAVIOR |
* MTT Agrifood Research Finland, Animal Production Research, FI-31600 Jokioinen, Finland; and Finnish Food Safety Authority, EVIRA, Animal Diseases and Food Safety Research, Mustialankatu 3, FI-00790 Helsinki, Finland
1 Corresponding author: eija.valkonen{at}mtt.fi
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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Key Words: laying hen • furnished cage • dietary energy • production • well-being
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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The effects of group size and bird density in cages have been under study for decades. Generally, increased group size and increased density in cages both result in lower egg production and feed use (Adams and Craig, 1985; Sohail et al., 2001, 2004). However, in a study with a constant cage area (364 cm2) and feeder space (10 cm) perhen, Carey et al. (1995) reported no effects of group size on egg production rate and feed conversion, but reported significantly higher feed consumption in groups of 12 and 24 hens than in groups of 6 and 8 hens. In agreement with these results, Abrahamsson and Tauson (1997) found no effects of group size from 5 to 8 hens on performance in FC with constant space allowance and constant feeder space per hen.
It is well established that hens generally adjust their feed intake according to their energy requirements. However, the results of studies of the effects of dietary energy on the laying rate are conflicting. For example, Çiftci et al. (2003) found that decreasing the energy content of feed from 2,751 to 2,641 kcal of ME/kg increased the laying rate from 86.44 to 88.27%. But Mathlouthi et al. (2002) reported increased laying rates at an energy content of 2,753 kcal of ME/kg of feed compared with 2,653 kcal of ME/kg of feed.
Responses of egg weight to changes in feed energy content are typically insignificant (Vogt, 1986; Summers and Leeson, 1993; Keshavarz and Nakajima, 1995; Grobas et al., 1999b; Mathlouthi et al., 2002; Çiftci et al., 2003). However, some authors have reported significant, although small, increases in egg weight caused by increased dietary energy (Marsden et al., 1987; Peguri and Coon, 1991). According to Bish et al. (1985), differences in the BW of layers may partly account for the effects of feed energy content on egg weight. In addition, if the feed energy increase is due to supplemental fat, fat supplements per se may cause increased egg weight (Vogt, 1986; Grobas et al., 1999b).
The literature includes reports of studies in which lower feed intake is observed in hens housed in cages equipped with perches than in hens kept in CC without a perch (Tauson and Jansson, 1988; Braastad, 1990; Glatz and Barnett, 1996). In studies comparing CC and FC feed intake, the results are conflicting. For example, Hetland et al. (2004) report higher feed consumption in 8- or 16-hen FC in comparison with 3-hen CC. On the other hand, Hetland et al. (2003) found higher feed use in 16-hen FC, but not in 8-hen FC, than in 3-hen CC. Elson and Croxall (2006) reported lower feed intake in FC than in CC. Results from an earlier study in our institute (Valkonen et al., 2006) also showed lower feed intake in 8-hen FC than in 3-hen CC. Plumage cover affects a bird’s energy requirements and thus its feed intake (Tauson and Svensson, 1980; Peguri and Coon, 1993). In FC, increased group size may negatively affect plumage cover (Appleby et al., 2002; Hetland et al., 2003; Weitzenbürger et al., 2006). On the other hand, the provision of perches and litter material may diminish feather damage (Braastad, 1990; Abrahamsson and Tauson, 1997). Bird activity tends to increase with increasing group size when associated with larger total cage area (Carey et al., 1995), whereas furnishing cages with perches tends to decrease activity (Braastad, 1990; Matsui et al., 2004).
On the basis of this background, it is conceivable that the energy and nutrient requirements of hens may differ in CC and FC. Only a few reports on different feeding strategies in FC and CC have been published. The objective of this experiment was to compare the 2 different production systems (CC and FC) and to examine the effects of dietary energy content on the egg production and egg quality of hens kept in either CC or FC.
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MATERIALS AND METHODS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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A total of 1,088 Lohmann Selected Leghorn-Classic Layer pullets (Lehtosen Kasvattamo Ky, Somero, Finland) were housed at 16 wk of age in an environmentally controlled windowless room in either 8-hen FC or 3-hen CC. During the first week following housing, the hens received 8.5 h of light per day. After that, the photoperiod was gradually increased each week by 0.5 h per day to 14.5 h daily at 25 wk of age. The temperature in the hen house was adjusted to 20°C, but it fluctuated between 18 and 27°C during the spring and summer months (May to August) at 54 to 68 wk of age. However, the daily variation in temperature did not exceed 6°C. During the autumn and winter, the temperature was more uniform, with a maximum daily variation of 3.5°C.
From housing at 16 wk of age until the beginning of the experiment at 21 wk of age, the hens received a feed mix composed of barley (460 g/kg), oats (300 g/kg), a commercial feed concentrate for laying hens (160 g/kg), and limestone (80 g/kg). The calculated ME and protein content of the feed were 2,477 kcal/kg and 163 g/kg, respectively. From the beginning of the experiment, the hens received 1 of the 2 experimental diets (see Experimental Treatments and Procedures section). Table 1
shows the composition of the experimental feeds. The grain ingredients were ground in a roller mill, and the feeds were mixed and cold-pelleted in batches of 2 tons. A chain feeder ran once a day to provide hens their feed. To ensure ad libitum access to feed, the hens were offered approximately twice the amount of feed that they were expected to consume daily; thus, the trough was never empty. Leftover feed was automatically collected separately for each experimental unit and reused for the same unit. A row of 6 CC or a pair of FC constituted an experimental unit. Nipple drinker lines supplied water to the birds. Water and feed were available ad libitum both before and during the experiment.
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Experimental Treatments and Procedures
There were 32 replicates of both CC and FC, and these were randomized in the 2 dietary treatments, yielding 16 replicates per treatment. The experiment began at 21 wk of age and lasted for 52 wk, or 13 four-week periods. During the experiment, the hens received either a low-or high-energy diet series (from 2,342 to 2,414 kcal/kg or from 2,581 to 2,629 kcal/kg; Table 1
) consisting of 3 feeding phases of 20, 16, and 16 wk, respectively. Feed energy and protein content were decreased in stages from one feeding phase to the next. The experimental diets were formulated to contain equal amounts of other nutrients per kilocalorie of ME.
Egg weight and number were recorded daily, and the mean production was calculated for each 4-wk period. Feed consumption was measured for each period. The hens were weighed 4 times during the experiment: at the beginning of each new feeding phase and at the end of the experiment. Mortality was recorded daily, and cumulative mortalities were calculated at the end of the experiment. The dead hens were sent to the Finnish Food Safety Authority for autopsies.
Egg quality was assessed 3 times during the experiment, at 36, 54, and 68 wk of age. Each time, the egg weight, albumen height, specific weight, and shell strength of 8 eggs per replicate were measured. The weights and proportions of the albumen, yolk, and shell of an additional 8 eggs per replicate were also measured. Thick albumen height was measured with a digital tripod micrometer (York Electronic Center, Technical Services and Supplies Limited, York, UK) and converted to Haugh units. The shell-breaking force was measured as compressive fracture force by using a Canadian eggshell tester (OTAL Precision Company Limited, Ottawa, Ontario, Canada; Hamilton, 1982). The assessment of the eggs’ specific gravity was based on Archimedes’ principle. The mass of the water (22°C) displaced by the egg was weighed by placing the egg in a wire basket, which was supported from the outside, in a water bowl that was on a scale. Specific gravity is the quotient of the egg mass and the mass of the water displaced by the egg. To weigh the egg components, the eggs were first weighed and broken, and the yolk was then separated from the albumen. The yolk was rolled on a tissue to remove remaining albumen and then weighed. The shell was dried with a tissue and weighed. Albumen weight was calculated by subtracting the shell and yolk weights from the egg weight.
The eggs were sent to a commercial egg-packing plant, where they were candled to grade them according to normal commercial practice. The total number and the proportion of dirty and cracked eggs were determined, as well as the distribution of grade-A eggs according to different weight classes. The results of the egg grading were received weekly for each experimental treatment. The data from the packing plant were not analyzed statistically because there was only one observation per treatment each time. Experimental procedures were evaluated and approved by the Animal Care Committee of the MTT Agrifood Research Finland.
Analytical Procedures
Samples were taken at the feed mill from every feed batch. Before analysis, the samples were passed through a hammer mill fitted with a 1-mm mesh and then dried. The crude fat and ash contents were determined by standard methods (AOAC, 1990), and the crude fiber content was determined by a modified AOAC method (method 962.09) by using glass wool instead of a ceramic fiber filter. The feed nitrogen content was analyzed by the Dumas method with a Leco FP 428 nitrogen analyzer (Leco Corporation, St. Joseph, MI). The CP content of the feeds was calculated by multiplying the nitrogen content by 6.25. Amino acid analysis was performed with a Biochrom 20 amino acid analyzer (Biochrom Limited, Cambridge, UK). The calcium and phosphorus concentrations of the feeds were determined with an ICP emission spectrophotometer (Thermo Jarrell Ash-Baird, Franklin, MA; Luh Huang and Schulte, 1985).
Statistical Procedures
We assumed that the observations were independent because the 2 different housing systems were placed parallel to each other in the same room. The experimental design was thus regarded as a completely randomized 2 x 2 factorial design. However, because the different housing systems could not be randomized over the 2 batteries, some caution is warranted in interpreting the results concerning the effects of the housing system. Statistical analyses were performed by using the GLM procedure of SAS (SAS Institute Inc., Cary, NC). Production parameters were subjected to repeated measures ANOVA with the following model: Yij = µ + ti + 
i + pj + (p x t)ij + 
ij, where Yij is the observation, µ is the general mean, ti is the effect of treatment (i = 1, ..., 4), i is the error term for the effect of treatment, pj is the effect of period (j = 1, ..., 13), and ij is the experimental error term. Egg quality parameters and live weights were evaluated by ANOVA with the following model: Yij = µ + ti + i, where Yi is the observation, µ is the general mean, ti is the effect of treatment (i = 1, ..., 4), and i is the experimental error term. The treatment effects were separated into 3 orthogonal contrasts as follows: C1—CC vs. FC (groups 1 and 2 vs. groups 3 and 4), C2—high feed energy content vs. low feed energy content (groups 1 and 3 vs. groups 2 and 4), and C3—interaction between cage type and dietary treatments (C1 x C2). Residuals were plotted against fitted values to ascertain the normality of the experimental data. Arcsine transformations were made when required to attain normality of the data. In the tables, the original means and SEM are presented.
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RESULTS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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The mean cumulative production exceeded the breeder’s performance goal of 21 kg per hen in every treatment. Mortality was highest in treatment 2 (CC, high-energy diet), at 4.3%. A typical diagnosis at autopsy was fatty liver and liver rupture (43% of all autopsies), and salpingitis (25% of all autopsies).
No significant interaction occurred between the effects of housing and of dietary treatment on production, except in the laying rate during the second feeding phase (P < 0.01; Table 2). During this phase, the CC hens on the high-energy diet had a higher production rate than the hens on the low-energy diet, whereas FC hens showed an opposite response to dietary energy. No interaction between the effects of cage type and of dietary treatment on egg quality was found.
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Hens housed in FC were heavier at the beginning of the experiment (21 wk of age; P < 0.001) and also at every subsequent weighing (P < 0.05; Table 3). It is not known whether this difference was possibly due to heavier birds being initially housed by chance in FC at 16 wk of age or because the pullets housed in FC gained more weight than those housed in CC during the 5 wk before the experiment started.
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). During the third feeding phase, the production rate was smaller in FC than in CC (P < 0.01). During the third feeding phase, the hens in FC consumed less feed and had lower calculated energy intake than their counterparts in CC (P < 0.01). Over the entire experiment, housing had no significant effects on production parameters.
At the age of 36 wk, eggs laid in FC had smaller specific weights than those laid in CC (Table 4). At 54 wk of age, shell proportion was smaller and albumen proportion was greater in eggs from FC than in those from CC (Table 5). A similar effect of cage system on shell proportion (P < 0.05), and shell-breaking strength (P < 0.001) was evident at the age of 68 wk. However, there was no evidence of increased cracking in eggs from FC, because the proportion of downgraded eggs was lower in FC than in CC.
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During each feeding phase and over the entire experiment, the hens receiving the low-energy diet consumed more feed (P < 0.001) than those fed the high-energy diet (Table 2). Metabolizable energy intake was equal in both diets, except during the second feeding phase, when the ME intake in the high-energy diet was higher than that in the low-energy diet (P < 0.01). An effect of dietary ME on the production rate was evident during the third feeding phase (P < 0.05) and over the entire experiment (P < 0.05): the hens receiving low-energy feed had lower production rates than the hens on the high-energy diet. Dietary energy had no significant effects on egg weight. During each feeding phase and over the entire experiment, the high-energy diet resulted in a better feed conversion ratio than did the low-energy diet (P < 0.001). Dietary energy had no effect on energy efficiency.
For egg quality measurements (Table 4) at 54 wk of age, hens fed the high-energy diet had the greatest specific weight. At 36 and 68 wk, there were no effects of dietary energy on egg quality.
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DISCUSSION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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It appears more likely that the greater live weight in FC at the beginning of the experiment was a consequence of birds growing more rapidly in FC during the 5-wk period following housing than that initially heavier birds were housed in FC by chance. This leaves the questions of the hens’ energy requirements and energy expenditure for different purposes in different cage types open to speculation.
In the current study, the effects of group size and enrichment in cages intermingle. However, it is typical that group sizes in CC are, in practice, smaller than those in FC. The results of the present study should thus be interpreted as a comparison of the 2 production systems. In the current experiment, the 2 housing systems also had different feed trough lengths per hen. The available feeding space may affect the hens’ feed intake (Cunningham, 1982) or feed conversion ratio (Anderson et al., 1995). However, feeder space effects were negligible in the current experiment because the feed intake was greater in FC than in CC during the first feeding phase, whereas the feed intake was lower in FC than in CC during the third feeding phase, and the feed conversion ratios were equal in the 2 systems. Greater feed intake in FC during the first feeding phase probably resulted from the greater live weights in FC than in CC. Lower feed consumption in FC than in CC during the third feeding phase may be accounted for by the better plumage condition observed in FC (data not shown).
In the literature, suggested reasons for the lower feed consumption observed in FC than in CC include energy savings because of lower activity, better insulation because of better plumage, and roosting side by side (Tauson and Abrahamsson, 1994). On the other hand, the larger group size and total cage area in FC than in CC would presumably have an opposite effect on feed consumption (Carey et al., 1995). In agreement with our results, Hetland et al. (2003) reported no difference in feed consumption or feed conversion ratio between 3-hen CC and 8-hen FC. In 16-hen FC, the feed consumption and feed conversion ratio were higher than in smaller groups (Hetland et al., 2003). In contrast, Hetland et al. (2004) reported that birds in 3-hen CC consumed less feed than those in FC in groups of either 8 or 16 birds, but the authors stated that the difference could have been due to poorer plumage in FC in the study in question. In many cases, differences in feather cover may explain the conflicting results in experiments on feed consumption in FC and in CC. Meanwhile, the reasons for conflicting results on plumage condition in FC and in CC are far more complex. Factors affecting feather cover include the incidence of feather pecking, the amount of mechanical abrasion, nutrition, and air humidity (Tauson, 1986). Feather pecking is a very intricate phenomenon including at least genetic, behavioral, social, hormonal, environmental, and nutritional aspects (Sedla
ková et al., 2004). Our results on production rate and egg weight in the different cage systems agree with those of Abrahamsson et al. (1995) and of Abrahamsson and Tauson (1997), who also reported equal layer performance in FC and CC.
Indications of weaker eggshell strength in FC than in CC in the present study are in agreement with the findings of Glatz and Barnett (1996) and Short et al. (2001) in studies with cages equipped with perches. However, despite weaker shell strength and lower specific weights in FC at various ages in the present study, there was a smaller proportion of cracked eggs in FC than in CC according to the packing plant reports. This finding is in contrast to those of Abrahamsson et al. (1995), Abrahamsson and Tauson (1997), Wall et al. (2002), and Guedson and Faure (2004), who all reported a higher incidence of cracked eggs in FC than in CC. Cage design may affect the risk of egg cracking. The FC model used in the present experiment had a floor inclination of 10%, which is a relatively gentle slope in comparison with the 14% slope allowed by Council Directive 1999/74/EC (Commission of the European Communities, 1999). In CC, the slope was 12%. Based on the cage measurements given in the studies of Abrahamsson et al. (1995), Abrahamsson and Tauson (1997), and Wall et al. (2002), these studies had a slope in FC of 12%, but they did not indicate the slope in CC or sufficient information to calculate it. In the study by Guedson and Faure (2004), the floor slopes were approximately 6.3 and 9.4% for the 2 standard cage models, respectively, and 7.9 and 9.6% for the 2 FC models, respectively. The difference in slopes between cage types may be a factor in the incidence of cracked eggs in the present experiment.
Effects of Dietary Energy
Our findings on the effects of dietary energy on production rate are consistent with those of Keshavarz and Nakajima (1995) and Mathlouthi et al. (2002), who found an increased production rate with higher feed energy content. These results, however, are in contrast to those of Vogt (1986) and Çiftci et al. (2003). Concerning dietary energy effects on egg weight, our results agree with those of Summers and Leeson (1993), Keshavarz and Nakajima (1995), Grobas et al. (1999b), Mathlouthi et al. (2002), and Çiftci et al. (2003), who reported that the effects of dietary energy on egg weight were not significant.
Supplemental fat has often resulted in increased egg weight (Whitehead et al., 1991, 1993; Grobas et al., 1999b). Moreover, the literature attributes the effects of supplemental fat to its linoleic acid content. In the present study, the different ME contents of diets were mainly achieved through the inclusion of different amounts of rapeseed oil. The rapeseed oil content of high-energy diets was from 33 to 39 g/kg. Even then, there were no effects of supplemental fat on egg weight. In the studies by Keshavarz and Nakajima (1995) and Grobas et al. (1999b), the amount of supplemental fat was 40 g/kg of feed. Whitehead et al. (1993) reported a significant effect on egg weight at 40 g/kg of supplemental fat, but not at 20 g/kg of supplemental fat. In the present study, the calculated linoleic acid concentrations of the diet series were different. However, these differences were not very great because the low-energy diets contained greater amounts of oats than did the high-energy diets (Table 1). According to the NRC (1994) Nutrient Requirements of Poultry, even the low-energy diets had sufficient amounts of linoleic acid. Linoleic acid concentrations in our low-energy diets were apparently high enough so that no increase in egg weight occurred when dietary ME was increased by rapeseed oil addition.
Whitehead et al. (1991) reported that supplemental fat increased the proportion of albumen at 32 wk of age. This result agrees with the results of the present experiment at 36 wk of age. Moreover, Grobas et al. (1999a) found increased albumen and yolk weights owing to supplemental fat but no effects of dietary energy on the weight of egg components. However, Grobas et al. (2001) reported no significant effects of supplemental fat on egg component weights when dietary energy was increased by fat supplements. Our results agree with those of Grobas et al. (2001), except for yolk weight at 36 wk of age; in our results, hens fed the low-energy diet laid eggs with greater yolk weights than did the hens on the high-energy diet. In agreement with Grobas et al. (2001), Keshavarz and Nakajima (1995) also found no effects of supplemental fat or higher dietary energy on albumen and yolk weights.
According to the results of the present experiment, the effects of dietary energy on egg production and quality are generally independent of the cage system used. Moreover, the results of this study add evidence of equal production and feed conversion ratios in FC and CC. The effects of different equipment in FC on hen energy and nutrient requirements warrant further investigation.
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ACKNOWLEDGMENTS |
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Received for publication June 12, 2007. Accepted for publication February 7, 2008.
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