Animals and experimental design
The study was conducted between March 2017 and August 2018. Each dual-purpose genotype was the cross of a layer breed (White Rock or New Hampshire) and the meat breed Bresse Gauloise, resulting in the following crosses (♂ x ♀): Bresse Gauloise x White Rock (Bresse x WR), White Rock x Bresse Gauloise (WR x Bresse), Bresse Gauloise x New Hampshire (Bresse x NH), and New Hampshire x Bresse Gauloise (NH x Bresse). All purebred parent birds were in possession of Ökologische Tierzucht gGmbH (ÖTZ, Mainz, Rheinland-Palatinate), and the parent flocks for producing the crossbred chicks were assembled specifically for this study by ÖTZ. White Rock and Bresse Gauloise parents for producing the White Rock crosses were kept on an organic laying hen farm in Goch-Hommersum, North Rhine-Westphalia, while New Hampshire and Bresse Gauloise parents for producing the New Hampshire crosses were kept on an organic laying hen farm in Freising, Bavaria. In addition to the crosses, a meat breed and a layer hybrid were included as controls: hatching eggs of purebred Bresse Gauloise (Bresse) came directly from ÖTZ stock (Ueberlingen, Baden-Wuerttemberg), and those of the layer hybrid Lohmann Sandy (Sandy) were purchased from Eiermacher GmbH in Kremsmünster, Austria.
All chicks except the New Hampshire crosses hatched at the same hatchery in Eppingen, Baden-Wuerttemberg. Because of transport limitations due to an outbreak of the avian flu in winter 2016/2017, the New Hampshire crosses hatched in a different hatchery in Blumegg, Baden-Wuerttemberg. All eggs were placed in incubators on February 20, 2017, and the chicks hatched on March 15. Animal husbandry of both the parent flocks and the crosses followed the rules of the European Council Regulation EC 834/2007 (European Union 2007a) and the production guidelines of the organic farming association Demeter (Demeter 2015).
The mixed-sex rearing period took place on an organic farm (Bauckhof Klein Süstedt, Uelzen, Lower Saxony) and lasted from March 15 until June 28, 2017 (15 weeks). Of each genotype, one group of 157–310 chicks of mixed-sex was reared (Bresse x WR: 190; WR x Bresse: 310; Bresse x NH: 157; NH x Bresse: 233; Bresse: 293; Sandy 238). There were no replicates in the sense of several groups of birds per genotype, but for all data measured on individual birds (live weight, welfare indicators), the chicken within the group represent the replicates of the genotype. All chicks were vaccinated against Marek’s disease, Newcastle disease, Salmonella, Mycoplasma, infectious laryngotracheitis, infectious bronchitis, infectious bursitis, coccidiosis, and rhinotracheitis, while the vaccinations against Escherichia coli and egg drop syndrome were only given to the pullets in week 15.
Housing and feeding
The chicks were housed under floor husbandry conditions in a mobile barn of 126 m2 (type Rundbogen, Wördekemper GmbH & Co. KG, Rietberg, North Rhine-Westphalia) divided into six compartments of 17.5 m2 indoor and 12.5 m2 roofed outdoor area each. The pens were separated by wire mesh, and the outdoor runs were separated by fences to avoid mixing of the genotypes. Access to the roofed outdoor area and the adjacent green outdoor area was first granted when the chicks were 6 weeks old. Thereafter, the chickens had access to the roofed outdoor area every day, but access to the green outdoor run was only granted when it did not rain (in total 5 five days without access). The compartments were bedded with wood shavings and equipped with drinkers, troughs, and wooden perches. The feeding regimen was the same for all genotypes and was divided into three periods (see Table 1 for nutrient composition). The feed mixtures were purchased at a commercial feed mill (Meyerhof zu Bakum GmbH, Melle, Lower Saxony) and were of 100% organic origin. Changes from one period to the next were done gradually over a period of 3 days.
At the age of 6 weeks, all birds were marked with foot rings to enable individual documentation of live weight and animal welfare indicators. Data collection included feed consumption, individual live weight and animal welfare indicators, slaughter performance, and animal losses. Feed consumption was documented per genotype (mixed sex) by collecting feed refusals every 3 weeks. All cockerels were weighed at the age of 6 weeks. At the age of 11 and 13 weeks, 20 cockerels of each genotype were randomly selected from all areas of the respective pens and slaughtered, and all remaining cockerels followed at the age of 15 weeks (Bresse x WR: 32; WR x Bresse: 32; Bresse x NH: 22; NH x Bresse: 27; Bresse: 56; Sandy 106). On the days before slaughter, the cockerels were weighed and scored for selected animal welfare indicators based on a simplified version of the Welfare Quality® Protocol (2009) where score “0” indicates an unimpaired state; score “1” indicates minor lesions, dirtiness etc.; and score “2” indicates major lesions, dirtiness etc. The animal welfare indicators included pecking wounds on the comb, breast blisters, cleanliness of back feathers, foot pad lesions, and hock burns. Slaughter performance of the cockerels could only be measured on a group basis on the slaughtering dates in weeks 13 and 15. For each genotype, the sum of the carcasses and the sum of the valuable cuts (whole legs, breast fillet) were weighed.
From every feed mixture fed, one bulk sample was collected and sent to a commercial laboratory for nutrient analysis. The analysis was done according to the European Commission Regulation EC 152/2009 (European Union 2009), and method numbers are given below. The dry matter content of feed was determined by oven-drying at 103 °C (Annex III, A). Ash, ether extracts, sugar, and starch contents were analysed using methods M, H, J, and L of Annex III. Contents of crude protein were calculated from nitrogen content, which was determined according to the Kjeldahl method (Annex III, C). Contents of nitrogen corrected metabolisable energy (AMEN) were calculated according to EC 152/2009 Annex VII. Amino acid concentrations were determined with a chromatographic system according to Annex III, F, using samples that had been hydrolysed in 6 M HCl for 20 h. For analysis of methionine and cysteine concentration, samples were oxidised before hydrolysis to avoid losses.
The experimental design did not include replicates in the sense of several groups of birds per genotype; therefore, the differences in measures taken on individual birds (live weight, daily weight gain, animal welfare indicators) refer to birds kept together in one group per genotype. All statistical analyses were conducted using SAS 9.4. proc glimmix, and P values < 0.05 were interpreted as indicating significant differences.
For the analysis of live weight and daily weight gain, the model included the fixed effects of genotype, week of life (6, 11, 13, 15), and their interaction. Only data from birds that were weighed at least twice remained in the dataset. Slaughter performance of cockerels is given as raw data. Multiple comparisons of means were made using the Tukey’s test.
For the analysis of animal welfare indicators, the frequency of scores 0, 1, and 2 was compared for each sampling date using proc glimmix (chi2 test, multinomial distribution). The model included only the fixed effect of genotype, and P values in multiple comparisons of means were adjusted according to Bonferroni-Holm.