Relationship between hen age, body weight, laying rate, egg weight and rearing system

Relationship between hen age, body weight, laying rate, egg weight and rearing system S.WĘŻYK, J. KRAWCZYK, CALIK J. and K. POŁTOWICZ National Research Institute of Animal Production, 32-083 Balice n. Kraków (Poland) Corresponding author: wezyk@interia.pl A total of 246 Polish ASTRA H (H) and 246 Polish ASTRA S (S) hens were studied from 20 to 63 weeks of age. Hens (150 S and 150 H) were assigned to 10 replications of 15 birds and kept on litter at a stocking density of 4.2 birds/m 2. The remaining 152 hens were allocated to 4 replications of 28 birds and placed in a 3-tier battery of individual cages at a stocking density of 1150 hens/m 2. The following parameters were evaluated during the experiment: body weight, egg production, mean weight of eggs laid, daily feed intake per layer, and health status. The mortality of H and S hens kept on litter was high (13% and 18%) compared to that of birds in cages, which was 9.6% and 3.1%, respectively. The aggression in hens kept on litter in the initial period of egg production increased the number of eggs laid outside nests. H hens were later to go into egg production, and production was relatively low (63.4%). Caged S layers showed a significantly (P<0.05) higher laying rate (82.4%) than H hens kept on litter (69.6%). The weight of H hens kept in both systems increased by approx. 1000 g on average in relation to the weight at 20 weeks of age, while the weight of lighter S layers increased by just 500 g. In H and S hens, a relationship was found between egg weight and layer age, with heavier eggs being laid by caged H layers than by caged S layers. The mean egg weight during the whole experimental period was similar in all the groups. The housing system had a statistically significant (P 0.05) effect on daily feed intake per layer. Caged hens of both lines ate significantly (P 0.01) less feed than hens kept on litter. For both lines of hens, a significantly (P 0.05) lower profitability of litter housing compared to cage housing was found. The highest profitability was obtained from caged S hens. Introduction Restrictive Council Directive 1999/74/EC concerning laying hens, which is being implemented in European Union countries, has forced egg producers to switch from conventional cages to alternative non-cage systems. Producers of table eggs are well aware of the fact that this radical change in egg production technology will affect production profitability and egg quality. It is predicted that the population of laying hens will considerably decrease (by approx. 20%), with increasing costs and higher wholesale and retail hen prices, and deteriorating egg hygiene, especially for eggs obtained on free range. The paper entitled The present and future state of European egg production and egg quality following the implementation of the European layer welfare Directive 1999/74/EC, which was presented in November 2004 by 10 European poultry organizations, shows that further studies are necessary to provide an objective list of all the advantages and disadvantages of alternative layer hen rearing technologies. The aim of the present study was to determine the relationship between the age of laying hens, rate of egg production and egg weight in cage and litter management systems. Material and methods The study involved 246 ASTRA H (H) black-feathered Polish laying hens and 246 ASTRA S (S) brown-feathered laying hens from 20 to 63 weeks of age. Hens of both lines are useful for intensive rearing in cages and on litter. A total of 150 hens of each line were assigned to 10 replications of 15 birds and kept on litter at a stocking density of 4.2 hens/m 2. The remaining 152 hens were assigned to 4 replications of 28 birds, which were placed in a 3-tier battery of individual cages at a stocking

density of 1150 cm 2 /hen. Hens were fed ad libitum with a standard layer diet. Both rearing systems were used in a windowless poultry house, increasing the amount of light from 9 h/day at 18 weeks of age to 16 h/day after 30 weeks of age. Because of the incidence of feather-picking and cannibalism, light intensity was reduced in these groups between 24 and 36 weeks of age to 10 lux at the hens back height and a vitamin-mineral concentrate was added to the feed. During the experiment, the following parameters were evaluated every 4 weeks: body weight, egg production, mean weight of eggs laid, daily feed intake and health status. The results obtained were analysed statistically with one-way analysis of variance using Statgraphic 4.0 Plus software. Results As is evident from Table 1, the growth rate of H hens was significantly higher (P<0.05) in the litter than in the cage system, with a difference of 5.52% for the whole period of egg production. S hens laid more eggs than H hens in both systems, with a mean egg production rate of 82.4% in cages and 69.58% on litter. Table 1. Average rate of egg production (%) depending hen age and management system (weeks) 20-23 15.86 B + 2.86 71.80 C + 2.41 68.77 B + 4.82 89.95 A + 3.28 79.57 b + 4.55 87.98 a + 3.52 75.92 AB + 3.91 85.15 B + 3.77 68.45 B + 5.99 86.10 C + 2.51 64.55 Ab + 4.50 86.30 B + 1.50 65.55 A + 2.33 83.53 B + 2.89 64.24 A + 2.64 78.33 B + 2.45 64.90 A + 3.17 81.35 B + 2.48 64.94 A + 3.47 79.20 B + 3.26 64.24A + 5.44 76.38 B + 2.03 39.90 A + 6.92 84.83 AC + 4.09 85.55 a + 2.42 80.28 a + 2.64 77.7 A + 0.85 73.93 Aa + 2.04 65.50 A + 2.17 61.65 Aa + 3.14 63.88 A + 1.65 62.68 A + 3.74 61.88 A + 4.86 Average 68.9 a 63.38 82.4 Bb 69.58 a a, b - values in rows with different letters differ significantly (P<0.05) Table 2. Average body weight of hens kept in cages and on litter, according to age (weeks) Cage litter Cage Litter 20 1901 A + 65.32 1872 A + 74.49 1556 B + 16.60 24 2090 Aa + 76.36 1981 Ab + 108.39 1595 B + 20.60 28 2231 A + 79.61 2178 A + 92.34 1598 B + 47.26 32 23.41 A + 76.53 2302 A + 128.02 1656 B + 72.89 36 2472 A + 81.87 2398 A + 149.80 1770 B + 73.28 40 26.77 A + 80.06 2580 A + 125.54 1944 B + 43.48 44 2820 A + 124.83 2656 Ab + 147.48 1969 B + 50.27 52 2845 A + 157.02 2742 A + 211.81 2001 B + 52.89 60 2999 Aa + 172.09 2775 Ab + 270.92 2057 B + 45.53 1456 B + 111.80 1462 B + 64.17 1596 B + 53.19 1709 B + 38.10 1861 B + 112.77 1902 B + 57.41 1912 B + 94.63 1825 B + 57.15 1905 B + 76.12 Average 2486 A 2387 A 1794 B 1736 B Hens body weight increased consistently with age, although H layers were markedly heavier than S layers in both systems. Regardless of origin, hens kept on litter were considerably heavier than those kept in cages (Table 2). Table 3. Egg weight depending on hen genotype, age and management system 47.97 D + 3.45 79.56 C + 4.90 82.08 b + 2.56 78.44 A + 2.77 73.32 AB + 4.48 69.45 A + 8.30 68.36 A + 7.40 77.10 Ab + 5.05 67.07 A + 5.70 67.14 A + 4.28 64.95A +3.99

20-23 46.58 ac + 1.75 51.15 + 0.85 55.28 + 1.00 59.23 + 1.11 62.05 A + 0.94 63.13 A + 0.98 64.15 + 1.19 65.18 + 0.88 66.70 a + 0.99 66.90 a + 0.70 66.70 a + 0.91 44.86 Ab + 1.29 47.53 Ba + 1.06 45.81 bc + 0.99 51.31 + 1.01 51.78 + 1.13 51.68 + 0.76 56.14 ab + 1.24 54.75 Ac + 0.62 57.0 Bb + 0.80 58.95 + 1.78 58.25 + 053 59.76 + 1.25 62.57 a + 1.31 63.18 + 1.09 64.24 B + 0.66 63.78 + 1.32 64.38 + 1.53 65.11 ab + 1.22 64.84 + 1.86 63.75 b + 1.63 64.35 + 0.95 64.81 + 1.65 63.23 a + 1.40 64.47 + 1.39 65.95 ac + 1.88 63.68 ab + 1.72 64.54 a + 1.23 66.15 a + 1.78 64.35 ab + 1.48 65.34 + 1.13 66.49 a + 2.39 64.23 a + 1.38 64.46 + 1.28 Average 60.6 60.5 59.8 60.7 With age, egg weight increased in both lines of hens from approx. 45 g at 20 weeks of age to approx. 65-66 g at the end of the experiment, with no clear differences between lines or rearing systems in each 4-week period (Table 3). Table 4. Daily intake of feed by layer depending on hen age, genotype and management system (weeks) 20-23 115.6 A + 1.10 138.5 A + 0.95 131.0 A + 0.84 143.1 A + 1.84 140.3 A + 0.32 143.3 A + 2.88 127.1 A + 2.08 127.8 A + 3.06 113.0 A + 2.00 110.7 A + 2.88 120.7 A + 1.52 152.9 B + 0.30 100.7 A + 0.15 158.1b + 15.80 2578 B + 1.00 130.3 A + 0.20 167.3 B + 26.60 176.2 B + 8.10 120.7 A + 0.53 168.1 B + 10.60 174.3 B + 11.50 131.0 A + 0.10 169.4 B + 28.90 187.6 B + 12.40 132.2 A + 0.06 171.2 B + 17.90 154.5 B + 6.27 126.0 Ab + 2.64 152.4 B + 12.50 149.0 B + 4.54 108.7 C + 0.65 136.0 A + 0.68 136.0 B + 4.10 110.7 B + 1.50 133.7 A + 5.27 133.7 B + 4.20 102.3 A + 4.50 128.8 B + 3.61 134.9 B + 3.34 102.7 A + 2.08 131.7 B + 2.05 130.5 A + 4.17 106.7 B + 1.52 131.2 A + 8.23 Average 128.3 153.4 B 115.6 A 149.8 B With age, daily feed intake showed an upward trend in both lines of layers. The highest mean daily intake of feed was characteristic of H layers kept on litter (153 g/hen), and the lowest (115.6 g/hen) of caged S hens (Table 4). As can be seen from Tables 2 and 3, the increasing body weights of H and S hens with age in both rearing systems, was parallel to increasing mean egg weight. Discussion Mortality in the litter system was high (13% in H and 18% in S hens) compared to the cage system, in which there was 9.6% and 3.1% mortality, respectively. The results of veterinary tests showed cannibalism to be the main cause of mortality. These results concur with the findings of Yngvesson et al. (2004), Arandelović and Vukić-Vranješ (2004) and McAdie et al. (2005). Despite the use of feed with higher levels of protein, minerals and vitamins at the peak of egg production, the incidence of cannibalism and feather-picking in layers on litter persisted until as late as 47 weeks of age, contributing to a considerable reduction in the egg production rate (Table 1). These vices were also the reason for an increased number of eggs being laid outside nests. In H layers after 40 weeks of age, the proportion of eggs laid on litter decreased to 2% per 4 weeks, and in S layers it decreased from 28% in the initial period of egg production to 5.7-9.4% at the end of the experiment, depending on the replication.

H hens were later to come into egg production, maintaining production at an initially low level in the litter system to increase it later on, but never reaching the egg production of caged S hens (Table 1). The lower egg production level of both groups of hens kept on litter could result from the light intensity, which was reduced to make layers less aggressive. Caged S layers achieved a significantly higher rate of egg production (82.4%), differing significantly (P<0.05) or highly significantly (P<0.01) in all the test periods from S hens kept on litter (69.6%) and from H hens, regardless of the rearing system. In both systems, the body weight of H hens increased from 20 weeks of age by an average of 1000 g, while in lighter S layers it increased by only 500 g (Table 2). In all the 4-week periods there were differences (P<0.01) in body weight between the two lines of hens. Mean egg weight was found to vary according to the age of hens of both lines, with heavier eggs laid by caged H layers than caged S layers (Table 3). Similar results were reported by Premavalli and Viswanathan (2004a). The same authors (2004b) obtained heavier eggs (50.35 g) from caged White Leghorn hens than from those kept on litter (46.59 g). The mean egg weight in the whole experimental period was similar in all the groups, contrary to the generally accepted notion that layers in the litter system produce heavier eggs. The rearing system had an effect (P<0.05) on the daily intake of feed per layer (Table 4). In each 4-week period, hens of both lines consumed less (P<0.01) feed in the cage system than hens kept on litter. The differences of 25 g/day/layer (H) and 43.2 g/day/layer (S) resulted from the fact that hens spilled feed from feeding troughs. These results concur with the study of Fiks-Ven Nieuk et al. (2003), who found that hens in the non-cage system require more energy to move, thus eating more feed and laying lighter eggs. In both lines of hens, the litter system was less profitable (P<0.05) than the cage system. Horne and Bondt (2003) believe that full implementation of the Council Directive 1999/77/EC by 2012 will maintain egg production costs at 0.80/kg, which may cause severe perturbations in the European egg industry considering that production of eggs in Brazil and India is 3% and 10% cheaper, respectively. Fisher and Bowles (2002) emphasize that with a production cost for 1 egg of 0.06 in the EU and 0.04 in the USA, it is profitable for the USA to export eggs from the cage system to the EU despite the high customs duties and expensive transport. Marzone (2003) and Guémené (2004) believe that growing costs related to increasing hen welfare standards increase the risk of the loss of competitiveness. Meanwhile, the Secretaries of Agriculture of the EU member states are against blocking imports into the EU market of eggs and egg products from countries where hen welfare standards are not met (Windhorst, 2001). Bibliography ARANDELOVIĆ D. and VUKIĆ-VRANJEŠ M. (2004) Opis slučaja pojave kanibalizma kod matičnog jaja těske linije i alternativni aspekt lečenia. Živinarstvo 39(5):14-19 HORNE P.L.M. VAN, and BONDT N. (2003) - The Hague, LEI, FIKS-VAN NIEKERK T.G.C., VAN EMOUS R.A. and REUVEKAMP B.F.J. (2003) Experiences with production and egg quality in alternative systems and large enriched cages for laying hens in the Netherlands. Proc. of XVIth European Symposium on the Quality of Poultry Meat & Xth European Symposium on the Quality of Eggs and Eggs products. September 23 rd -26 th, 2003 Saint-Brieuc, France, vol.iii:210-216. GUÉMENÉ D. (2004) Poultry production, welfare and European legislation. Proc. of World Poultry Congress & Exhibition, June 8-13, 2004, Istanbul, Turkey FISHER CH. and BOWLES D. (2002) Hardboiled reality- 2001 2012 a dozen years crucial to agriculture and trade reform. Animal welfare-friendly egg production in a global market. EUROGROUP for animal welfare, RSPCA, 2002 McADIE T.M., KEELING L.J., BLOKHUIS H.J. and JONES R.B. (2005) Reduction of feather pecking and improvement of feather conditions with presentation of string device to chickens. Applied Animal Behaviour Science 93(1/2):67-80 MAGDELAINE P. and L. MIRABITO (2003) Changes in demand for eggs and eggs products and influence of changes in welfare regulations. Proc. of XVIth European Symposium on the Quality of

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