Phylogenic versus selection effects on growth development, egg laying and egg quality in purebred laying hens

The aim of the present study was to assess the performance traits of chicken lines with different performance level and phylogenetic origin. Selection for high performances may change unselected traits related to animal health and well-being. However, long before intense selection started to act leading to contemporary high performing genotypes, founder populations on egg laying breeds with white and brown egg shell had been separated for many generations and have evolved independently. We have started to set up a comprehensive collaborative effort at the Friedrich-Loeffler-Institut to approach research question related to the capacity of high selected chicken lines to cope with limited metabolic resources. As a first step, four genotypes of purebred laying hens (WLA, BLA, R11 and L68) were used, which were divided by their divergence in performance and phylogeny. For the first time these genotypes were characterized according to their performance and growth development in the first 16 weeks of age in a rearing trial, a pre-laying period of 6 weeks and a following performance trial of 13 laying months (23 rd to 74 th week of age). The investigated performance traits were significantly affected by genotype, age and their interaction (p ≤ 0.001). As a result of selection for high laying performance, selected strains showed a significantly higher performance than the non-selected ones. The high performing genotypes had an average laying intensity of 85 to 90%, a daily egg mass production of approximately 50 g/hen/d and a feed to egg mass ratio of 2.1 to 2.3 kg/kg. However, the low performing genotypes had an average laying intensity of 52 to 56%, a daily egg mass production of approximately 26 to 31 g/hen/d and a feed to egg mass ratio of approximately 3.0 kg/kg. Concerning average egg weight only R11 (50 g/egg) differed from the other experimental lines (55 to 58 g/egg). Independently of their performance brown hens showed a significantly higher body weight than white hens during the whole trial. Egg quality analyses showed that high performing lines had a significantly higher albumen proportion (57.1 to 62.4%) and a significantly lower yolk proportion (26.8 to 29.8%) than the low performing lines (albumen: 55.3 to 57.4%, yolk: 30.3 to 33.5%). White hens (10.8 to 13.6%) had significantly higher proportion of egg shells than brown hens (10.3 to 12.9%). In summary, the studied genotypes showed clear differences in performance level that made them well suitable for the established experimental design. With that design further studies should be carried out under varying environmental conditions (e.g. feeding, housing, infectious diseases). Thereby the studies will examine the question whether selection on high performance (WLA, BLA) leads to a reduced adaptability to varying environmental conditions.