Utilization of laying-type cockerels as coquelets : Influence of genotype and diet characteristics on growth performance and carcass composition

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1 Arch.Geflügelk., 76. S , 2012, ISSN Verlag Eugen Ulmer, Stuttgart Utilization of laying-type cockerels as coquelets : Influence of genotype and diet characteristics on growth performance and carcass composition Nutzung männlicher Legehybriden als Stubenküken: Der Einfluss der Herkunft und der Futtervarianten auf Wachstumsleistung und Schlachtkörperzusammensetzung Mirjam Koenig 1, Gisela Hahn 1, K. Damme 2 and M. Schmutz 3 Manuscript received 25 November 2010, accepted 31 August 2011 Introduction oultry breeding has undergone enormous changes during the last decades. The antagonistic relationship between meat and laying performance led the poultry industry to the separation of two lines of production: meat production or egg production (SIEGMANN and NEUMANN, 2005). Cocks of layer type chicken lines cannot be used economically for fattening, and thus they are killed at hatch. The present study refers to the announcement of a Directive about advancement of innovations to improve livestock breeding in the context of laying-hen reproduction. In Germany, over 40 million male one-day-old layer chicks are culled every year. This culling presents a serious ethical problem nowadays. Other solutions to this dilemma do not yet exist. In ovo-sex determination is currently not ready for practice. A dual-purpose breed is not economic (BRODMANN et al., 2001), since laying and meat performance are antagonistic. The long fattening period and the unfavourable feed conversion render egg-type cockerels unprofitable. (JAENECKE, 1996, MURAWSKA et al., 2005, SCHÄUBLIN et al., 2005, DAMME and RISTIC, 2003). From an economical point of view under German conditions, standard broiler production is much more remunerative than the rearing of egg-type cockerels. Standard broiler production costs amounted to 0.79 per kg life weight in 2008/2009 (GEFLÜGELJAHRBUCH, 2011). A technological-economical calculation of laying-type cockerels production cost resulted in more than 4 per kg life weight (unpublished data). In respect of this discrepancy, it is difficult to find an economically rewarding alternative to culling. Such an alternative may be the rearing of the male layer chicks as coquelets. This production implies a shorter fattening period with an acceptable feed conversion (KOENIG et al., 2010). A coquelet is defined as a chicken of less than 650 g carcass weight without giblets, head and feet (cf. marketing standards for poultry meat, Regulation (EC) No. 543/ 2008). A shorter fattening period with an acceptable feed conversion would be a prerequisite to render the fattening of male layer chicks from layer breeds as economical. This study evaluates the conditions to rear male layer chicks and 1 Max Rubner-Institute, Federal Research Institute of Nutrition and Food, Kulmbach, Germany 2 Bavarian Institute for Agriculture, Kitzingen, Germany 3 Lohmann Tierzucht, Cuxhaven, Germany use them as coquelets. The study thus provides information necessary to develop a possible solution to culling. The entire study was divided into several steps to investigate efficiency, suitable management factors, and product characteristics. In a first trial was looked for differences between several genotypes of laying-type cockerels. In order to find out the most appropriate genotype growth performance, carcass quality, and meat quality were assessed. Overall Lohmann Brown (, Lohmann Tierzucht GmbH, Cuxhaven, Germany) had better fattening performance and carcass composition, while Lohmann Selected Leghorn (, Lohmann Tierzucht GmbH, Cuxhaven, Germany) had better meat quality (KOENIG et al., 2010). Hy-Line Brown (Hy-Line International, West Des Moines, USA) and Dekalb White (Broederij ter Heerdt b.v., AC Babberich, Netherlands) was found to perform less on all characteristics and was not considered any further. Overall, the results of different assessments showed advantages of regarding fattening performance and carcass composition and of regarding meat quality. The second trial, which is presented here, examined the influence of genotype and diet characteristics on growth performance, carcass composition and meat quality. The aim of this trial was to ascertain possibilities to improve fattening performance. Materials and Methods A total of 4700 male layer chicks were reared, with 2350 each of two genotypes: medium-heavy, brown-eggshell Lohmann Brown laying-type cockerels (), and light, whiteeggshell Lohmann Selected Leghorn laying-type cockerels (). Both genotypes were produced by Lohmann Tierzucht GmbH, Cuxhaven, Germany. The animals were reared in a confinement housing system at the Bavarian Agricultural Research Institute, Kitzingen (Germany). The birds were assigned to 20 pens of the same poultry house with 235 chicks per pen, i.e. 10 pens per genotype. Stocking density was 25 animals per m 2. The lightening program was constant light for the first 72 h, and from the fourth day an alteration of 8 h light and 4 h darkness. Two different diets were examined, each without anticoccidiostats (Table 1). The animals were fed either commercial broiler diet (), or a rearing diet for laying hens (). From day 1 to day 21 two, different starters were offered. In comparison to starter-composition, starter-composition contained slightly more metabolizable ener-

2 198 Koenig et al.: Utilization of laying-type cockerels as coquelets Table 1. Main characteristics of feeding diets Wichtige Inhaltsstoffe der Futterrezeptur Ingredient Starter Finisher Starter Finisher Crude protein (%) ME (MJ/kg) Methionine (%) Calcium (%) hosphorus (%) Sodium (%) = broiler diet, = laying hen diet gy (ME), but less crude protein (C). From day 22, the animals were fed with two different finishers, of which the composition was high-energy with a higher crude protein content. The ground feed and drinking water were provided ad libitum all over the fattening period. For each genotype, the animals from 5 pens each were fed with or. At the end of the fattening period, immediately before slaughter, all birds were weighed in groups. A random sample of 240 birds, 12 out of every pen, was manually slaughtered in the slaughterhouse of the Bavarian Agricultural Research Institute. Slaughter was at 49 days of age. Feed was withdrawn 12 h before slaughter. The chickens were stunned by concussion. After bleeding, the birds were scalded (60 sec., 53 C) and plucked (plucking machine). Remaining feathers were plucked by hand. After the dissection of head and feet, the carcasses were manually eviscerated. Carcass weights of 240 animals were registered immediately after slaughter, and after 24-h chilling at +4 C. After packaging, the refrigerated carcasses were transported to the Max Rubner-Institute, location Kulmbach, for assessment of carcass composition and meat quality. The packaged carcasses were stored deep-frozen. To assess carcass composition, the frozen carcasses were first thawed under standardised conditions. Then, they were dissected into breast, back, wings, thigh, and drumstick according to a standard method of dissection of turkey carcasses (HAHN and SINDLER, 2002). After that the weights of the parts were recorded. The valuable parts, i.e. breast, thigh and drumstick, were fully dissected into meat, bones, skin, subcutaneous fat, and tendons. These tissue components were weighed and are expressed as percentage of the respective parts. For the calculating of growth performance, the weights of all coquelets were recorded each week starting with day 1 by assessing the average weights per pen. In addition, the weekly feed and water uptake per pen were recorded. Fattening performance was calculated from animals weight development, growth rates, and feed conversion. Carcass composition is characterized by the weight and tissue composition of valuable parts. Weight and carcass data were pooled for 240 or 12 animals of each pen, which gives 5 replicates per combination of genotype and feed variant. Data were analyzed by Analysis of Variance (ANOVA). For fattening performance, oneway ANOVA was applied using SAS 9.1 (SAS Institute, Carey NC, with genotype and feeding variant as fixed effects. Differences between treatment means were compared by the Tukey-Test. Carcass composition was analyzed with STATISTICA 7.1 (STATSOFT INC., with genotype and diet and their interactions as fixed effects. Results Growth development of laying-type cockerels differed significantly between genotypes and mainly feeding regime in the course of the fattening period (Table 2). One-dayold chicks had similar starting weights in all experimental groups. There was just a small genetic difference between medium-heavy and light at day 1. From day 21 through 49, weighed more than. Within the feed variants, there was a significant difference between and, except for the first day. A significant interaction of genotype and diet was found from day 21 through 42. At slaughter, i.e. day 49, the egg-type cockerels differed in body weight. group had 11% better growth performance than. The pattern of was 9% higher than for. At slaughter there was no more an interaction between the groups. Feed conversion rates (FCR) differed between all experimental groups (Table 3). performed better, with a FCR of 2.43, followed by 11% higher. The groups fed had a FCR of 2.35 and the groups fed 16% higher. Overall, the groups fed had a lower feed uptake and a higher weight increase compared to the groups fed. Within feed types, chicken had lower FCR than. Even relevant interactions could be detected between the main effects, genotype and diet. Overall, attained higher carcass weight than, and fed groups higher weight than groups fed with (Table 4). Also the weight and proportions of valuable parts (i.e. breast, thigh, and drumstick) differed between experimental groups. had %-points higher proportions than for thigh and drumstick, but 1.4%-points lower for breast. Diet did not influence the carcass composition with regard to the separate valuable parts. Noticeably, abdominal fat had a nearly twofold proportion in compared to fed groups. The absolute weight of all valuable parts (i.e. breast, thigh and drumstick) as well as their absolute meat content were highest for within genotypes, and for within feed groups (Table 4). The relative tissue distribution (meat, bones, skin with fat, tendons) of valuable parts of the carcasses referred to the weights. The tissue distribution of valuable parts (breast, thigh, drumsticks) was rather similar between all experimental groups (Table 5). About two-thirds of all valuable parts was meat, followed by bones just below 20%, skin with fat < 10%, and tendons < 3%. In the current study, the light had a higher meat and lower bone percentage than the heavy. The feeding regime did not affect these tissue components, but skin-with-fat was higher for. A significant interaction of genotype and diet for tendons

3 Koenig et al.: Utilization of laying-type cockerels as coquelets 199 Table 2. Development of body weight of male layer chicks of two different genotypes (, ) reared with two feed variants (, ) (n = 10/group) Körpergewichtsentwicklung männlicher Legehybriden (n = 10/Gruppe) verschiedener Herkünfte (, ) unter dem Einfluss zweier Futtervarianten (Broilermastfutter und Legehennen-Aufzuchtfutter) Genotype Diet Genotype Diet Day a Day Day Day a Day a Day a Day a Day a 37.5 b b 287 b 374 b 492 b 616 b a a < a < a < a < a < a b 120 b 196 b 276 a 365 b 485 b 610 b < < < < < < < < < er-day data with no common superscripts are different with p < 0.05 = Lohmann Brown, = Lohmann Selected Leghorn; = broiler diet, = laying hen diet Table 3. Feed conversion rate (FCR) and feed intake of male layer chicks from different genotypes (; ) influenced by two feed variants (, ) (n = 10/group) Futterverwertung und Futteraufnahme männlicher Legehybriden (n = 10/Gruppe) verschiedener Herkünfte (, ) unter dem Einfluss zweier Futtervarianten (Broilermastfutter, und Legehennen-Aufzuchtfutter, ) arameter Genotype Diet Genotype Diet Feed intake (g) Weight increase (g) FCR (g feed/g increase) a 2.43 a b 2.73 b < a < a b 2.81 b < <0.001 <0.008 Data with no common superscripts are different with < 0.05 = Lohmann Brown, = Lohmann Selected Leghorn; = broiler diet, = laying hen diet appears to be a spurious effect that cannot be interpreted due to missing main effects. Overall, the cockerels strain was the crucial factor to affect carcass composition, especially with respect to meat content. The diet regime influenced skin-with-fat content, while no relevant interactions could be detected between the main effects, genotype and diet. Discussion In this trial, feeding regime influenced growth performance. Growth development was more influenced by feeding regime than by genotype. During the whole fattening period groups fed performed better. Just from day 21 through 49 genetic differences were relevant. From day 21 through 42 significant interactions were detected. During the final fattening period, groups fed were significantly different from the other groups. The special feed composition of, with higher contents of crude protein and metabolizable energy may have caused these differences (cf. GERKEN et al., 2003). All groups and their interactions differed significantly (Table 3) in regard to feed conversion rate (FCR). Feeding regime as well as genotype was able to influence FCR. This rate could be determined for pooled batches of animals only, for which average individual feed uptake and weekly weight increase could be measured for replicated pens of the experimental groups. The fed groups had a lower feed uptake and a higher weekly weight increase than the

4 200 Koenig et al.: Utilization of laying-type cockerels as coquelets Table 4. Aspects of carcass composition of egg-type cockerels from different genotypes (, ) influenced by two feed variants (, (n = 240) Aspekte der Schlachtkörperzusammensetzung männlicher Legehybriden (n = 240) verschiedener Herkünfte (, ) unter dem Einfluss zweier Futtervarianten (Broilermastfutter und Legehennen-Aufzuchtfutter); 5 Wiederholungen je Versuchsgruppe arameter Genotype Diet Genotype Diet Carcass Weight (g) 402 a Breast (%) 25.5 b (0,1) Thigh (%) 19.6 a Drumstick (%) 16.5 a Back (%) 22.6 Wings (%) 15.1 b Abdominal fat (%) 0.24 Valuable parts (g) 248 a Meat of valuable 165 a parts (g) 356 b 26.9 a 19.3 b 15.8 b a b 149 b < a < < < b < a < a 361 b a 223 b 149 b < < < Data with no common superscripts are different with p < 0.05 For each group, 60 chicken are pooled in 5 replicate batches of 12 from separate compounds = Lohmann Brown, = Lohmann Selected Leghorn; = broiler diet, = laying hen diet Table 5. ercentage of tissue components for valuable parts (breast, thigh and drumstick) of egg-type cockerels of different genotypes (, ) influenced by two feed variants (, (n = 240) Anteile der Gewebekomponenten der wertvollen Teilstücke männlicher Legehybriden verschiedener Herkünfte (, ) unter dem Einfluss zweier Futtervarianten (Broilermastfutter, und Legehennen-Aufzuchtfutter, ); 5 Wiederholungen je Versuchsgruppe (n = 240) arameter Genotype Diet Genotype Diet Meat (%) 66.4 b Bones (%) 19.6 b (0,2) Skin/fat (%) 8.35 Tendons (%) a 18.1 a < < b a a 2.81 b < Data with no common superscripts are different with < 0.05 For each group, 60 chicken are pooled in 5 replicate batches of 12 from separate compounds = Lohmann Brown, = Lohmann Selected Leghorn; = broiler diet, = laying hen diet fed groups. This can be explained by the special feed composition of higher raw protein content and higher metabolizable energy. Consequently, lower weight increase and higher feed uptake of the fed groups was caused by the lower nutrient content of the laying hen diet (cf. RISTIC et al., 2003). In general, higher feed uptake is necessary to balance lower nutrient content of a diet in order to satisfy the nutritional requirement. Our results show that it was possible to improve FCR by feeding. In comparison to earlier studies (JAENECKE, 1996, DAMME and RISTIC, 2003) the present results of feed conversion appear to be acceptable. DAMME and RISTIC (2003) evaluated an average FCR

5 Koenig et al.: Utilization of laying-type cockerels as coquelets 201 of egg-type male hybrids of 3.0 (1 28 days of age) or 2.8 (1 70 days). In our study, the overall average feed conversion was 2.6 (1 49 days). HAVENSTEIN et al. (2003) compared the performance of old and popular genotypes fed with dietary regimes representative for 1957 or The 2001 diets contained higher protein and energy levels than the 1957 diets. Growth performance of the popular strains was better with 2001 than 1957 feed. A change in diet increased growth rate and indicated improvements in nutrition. Also in our study, diets differed in protein and energy levels. As expected, the fed groups showed a better growth performance than the fed groups. These findings corroborate results of other studies on low-protein diets (cf. BREGENDAHL et al., 2002). The adequate choice of cockerel genotype may result in better carcass composition. The differences we found between medium-heavy strain and light strain were to be expected (cf. GERKEN et al., 2003). But both attained lower body weights compared to the egg-type cockerels of the commercial, heavy laying-hen genotype Astra S, fed with standard broiler diet in a study by MURAWSKA et al. (2005). This difference highlights the importance of genotype. Also JAENECKE (1996) determined cockerel genotype as the determining factor to influence the tissue composition of carcasses. The relative tissue distribution was at a similar level throughout all groups. About two-thirds of the tissue was meat, followed by bones, skin with fat and tendons. MURAWSKA et al. (2005) found a similar tissue distribution for egg-type cockerel carcasses. In the present study, the light achieved the most favourable relative meat content. But with regard to absolute meat content of the valuable parts, performed less than, which is a consequence of the different constitution of the two genotypes. The medium heavy of our study had advantages in growth performance and carcass quality compared to other studies (GERKEN et al., 2003, JAENECKE, 1996). But feeding regime was not able to influence carcass quality in our study. All in all, cockerel genotype was the most determining factor to improve growth performance as well as carcass quality. Feeding regime was just influencing growth performance. Conclusion To sum up, the use of conventional broiler diet is meaningful in order to improve the growth performance of egg-type cockerels. But carcass composition was hardly influenced by the feeding type, rather than by the cockerels strain. In the finally third step of this project, genetic aspects were studied based on the antagonistic relationship of meat and laying performance. The correlation between egg-type cockerels fattening performance and agnate laying-hens laying performance was calculated. The analysis of these data is going on. All in all, by the development of sustainable, ethically justifiable production methods an alternative to the culling of one-day-old male layer chicks would be principally possible. However, also economic aspects are to be taken into account. The male layer chicks are not well suited for fattening, compared with broilers. The long fattening period and the unfavourable feed conversion are not worthwhile. By rearing coquelets the fattening period of the layingtype cockerels shortens, thus inducing an acceptable fattening performance, which causes an improved efficiency. However, this study is a first stocktaking and might contribute to tackle an urgent ethical problem in the production of laying hens by developing a profitably acceptable niche product. Acknowledgements This project refers to the announcement of a directive about advancement of innovations to improve livestock breeding funded by the German Federal Ministry of Food, Agriculture and Consumer rotection. The authors acknowledge the support of the Bavarian Agricultural Research Institute, and the Lohmann Tierzucht Company. Summary The aim of the study was to find an alternative to the present culling of one-day old male layer chicks in the context of laying hen reproduction. The development of a new ethically justifiable production system for the rearing of layingtype cockerels to produce coquelets could be a solution of this ethical problem. To this end, a project was initiated to determine economic efficiency and suitable management factors of coquelet production. After appropriate genotypes for laying-type cockerels had been determined in a preceding trial, we analyzed fattening performance and carcass quality in order to evaluate the potential to optimize coquelet production. The experiment was performed with the medium-heavy genotype Lohmann Brown () and the light genotype Lohmann Selected Leghorn (). The cockerels were reared on deep litter and were fed on standard diets for broilers () or laying-hens (). After a rearing period of 49 days, fattening performance and carcass quality were analyzed with genotype and feeding regime and their interactions as main effects. The development of body weight is more influenced by feeding regime than by genotype. Further results of growth performance, feed conversion and carcass quality showed the influence of the two different feeding regimes. Standard appeared to be more appropriate for cockerel feeding because it improved the fattening performance compared to. However, carcass composition was not affected by the different feeding regimes. But with regard to tissue composition and percentage of valuable parts, cockerel genotypes differed. In most aspects of carcass quality, the medium-heavy performed better than the light. The results of this study outline the economic feasibility of coquelet-production. The project thus contributes to link the production of a high-quality niche product with the solution of an ethical problem in animal production. Key words Laying-type cockerel, coquelet, growth performance, carcass quality, ethics, feeding variants Zusammenfassung Nutzung männlicher Legehybriden als Stubenküken Der Einfluss verschiedener Futtervarianten auf die Mastleistung und Schlachtkörperqualität Das Ziel der vorliegenden Studie war es, eine Alternative zur praxisüblichen Tötung männlicher Eintagsküken im Rahmen der Reproduktion von Legehennen zu finden. Die Entwicklung eines neuen, konventionellen und ethisch vertretbaren roduktionssystems zur Aufzucht männlicher Legehybriden und deren Nutzung als Stubenküken könnte als Lösung eines ethischen roblems in der Tierproduktion dienen. Im Zuge mehrerer Mastdurchgänge wurden die Wirt-

6 202 Koenig et al.: Utilization of laying-type cockerels as coquelets schaftlichkeit, geeignete Managementfaktoren sowie die rodukteigenschaften untersucht. Nachdem im ersten Durchgang die am besten geeigneten Legehybridherkünfte ermittelt wurden, indem Untersuchungen zur Mastleistung, Schlachtkörper- und roduktqualität durchgeführt wurden, zielte der zweite Durchgang darauf ab, die Fütterung anzupassen, um Mastleistung sowie Schlachtkörperzusammensetzung zu optimieren. Der mittelschwere Braunleger Lohmann Brown () sowie der leichte Weißleger Lohmann Selected Leghorn () wurden in den Versuch mit einbezogen. Die Haltung der Tiere erfolgte in Bodenhaltung mit ad libitum-fütterung aus konventionellem Broilermastfutter () bzw. Legehennen-Aufzuchtfutter (). Nach einer Mastdauer von 49 Tagen wurden Mastleisung und Schlachtkörperzusammensetzung mit den Effekten Herkunft, Fütterung und deren Interaktion untersucht. Die Fütterung hatte einen erheblichen Einfluss auf die Körpergewichtsentwicklung. Die Gruppe der Tiere, denen das Broilermastfutter verabreicht wurde, schnitten im gesamten Mastverlauf besser ab. Die weiteren Ergebnisse zu Körpergewichtsentwicklung, Futterverwertung und Schlachtkörper-zusammensetzung zeigten, dass die Futtervariante und auch der Genotyp Einfluss nehmen konnte. Möchte man eine Verbesserung der Mastleistung erzielen, so war der Einsatz des Broiler-Mastfutters sinnvoll. Auf die Schlachtkörperzusammensetzung hingegen konnte die Futtervariante keinen Einfluss ausüben. In diesem unkt waren die Unterschiede in der Genetik der mittelschweren und der leichten die bestimmenden Faktoren, wobei die Braunleger die vorteilhafteren Ergebnisse erzielten. Auf der Basis der Stubenkükenproduktion könnte dieses rojekt einen Beitrag dazu leisten, die roduktion eines Nischenprodukts mit der teilweisen Lösung eines ethischen roblems in der heutigen Tierproduktion zu verbinden. Stichworte männliche Legehybriden, Stubenküken, Wachstumsleistung, Schlachtkörperqualität, Ethik, Futtervarianten References BREGENDAHL, K., J.L. SELL, D.R. ZIMMERMANN, 2002: Effect of lox-protein diets on growth performance and body composition of broiler chicks. oultry Science 81, BRODMANN, N., E. FRÖHLICH, H. HIRT,. OSTLER, 2001: rojekt Zweinutzungshuhn, Schlussbericht zum Fortsetzungsbericht, Februar 1999 Mai FiBL, CH-5070 Frick. DAMME, K., M. RISTIC, 2003: Fattening performance, meat yield and economic aspects of meat and layer type hybrids. World s oultry Science Journal 59, GEFLÜGELJAHRBUCH, 2011: Schwerpunkt: Nachhaltiges Wirtschaften. Jahrbuch des Zentralverbandes der deutschen Geflügelwirtschaft e.v. und seiner Mitgleidsverbände. Eugen Ulmer, Stuttgart. GERKEN, N., D. JAENECKE, M. KREUZER, 2003: Growth, behaviour and carcass characteristics of egg-type cockerels to male broilers. World s oultry Science Journal 59, HAHN, G., M. SINDLER, 2002: Method of dissection of turkey carcases. World s oultry Science Journal 58, HAVENSTEIN, G.B.,.R. FERKET, M.A. QURESHI, 2003: Growth, livability, and feed conversion of 1957 versus 2001 broilers when fed representative 1957 and 2001 broiler diets. oultry Science 82, JAENECKE, D., 1996: Comparison of fattening performance, carcass and product quality, nutrient uptake and behaviour with male layers and broilers. Göttingen, Univ., Thesis. KOENIG, M., G. HAHN, K. DAMME, M. SCHMUTZ, 2010: Utilization of laying-type cockerels as coquelets Growth performance and carcass quality. Fleischwirtschaft 90 (2), MURAWSKA, D., R. BOCHNO, D. MICHALIK, M. JANIZEWSKA, 2005: Age-related changes in the carcass tissue composition and distribution of meat and fat with skin in carcasses of laying-type cockerels. Archiv für Geflügelkunde 69, RISTIC, M., G. BELLOF, E. SCHMIDT, 2003: Einfluss von Genotyp und Fütterung auf den Schlachtkörperwert von Broilern im Ökologischen Landbau. Ressortforschung für den ökologischen Landbau 2004: Statusseminar der Ressortforschungseinrichtungen des BMVEL am 5. März 2004 in der BBA, Kleinmachnow. Landbauforschung Völkenrode Sonderheft 273, SAS, 2002/2003: SAS/STAT User s Guide. Version SAS Institute Inc. Cary, NC, USA. SCHÄUBLIN, H., H. WIEDMER, R. ZWEIFEL, 2005: Schlussbericht Versuchsprojekt M 405 Vergleich der Mastleistungen und Fleischqualität von Hähnen ausgewählter Legelinien mit einem extensiven Masthybriden , Aviforum, CH 3052 Zollikofen ( SIEGMANN, O., U. NEUMANN, 2005: Kompendium der Geflügelkrankheiten, Schlütersche Verlagsgesellschaft, Hannover. STATISTICA Version 7.1: StatSoft Europe GmbH, (www. statsoft.de). STATISTISCHES BUNDESAMT, 2007: ( Correspondence: Mirjam Koenig, Max Rubner-Institut, Federal Research Institute of Nutrition and Food, E.-C.-Baumann-Str. 20, Kulmbach, Germany; mirjamkoenig@gmx.de