Effects of different rearing systems and age on laying hens' performance, egg characteristics and synthesis of heat shock protein 70

This study was carried out to investigate the performance of laying hens that reared in the conventional cage and organic system and this study also aimed to determine possible age-related changes in egg external and internal quality characteristics, egg yolk fatty acids, cholesterol, Vitamin A, D, E, K and malondialdehyde (MDA), furthermore, aim to determine possible age-related changes in synthesis of Heat Shock Protein 70 kDa (HSP70) which is known as a stress protein. The research was conducted on organic and conventional flocks of a commercial laying hen company. For the performance data of the study, 4 different layer hybrid Bovans White flocks were monitored from both systems. A total of 360 eggs were examined for investigate the effects of rearing systems and age (30 and 60 weeks) on egg external and internal quality characteristics and a total of 48 samples were examined for egg yolk compositions. A total of 48 liver tissues were used for the analysis of HSP70 by western blot method. Egg production (hen-day) and dirty egg ratio were found high in the organic system (P<0.05). In the conventional system, 50% yield age, peak of laying age and peak production of lay (hen-day) was calculated as 156 days, 218.75 days and 95.98%, respectively, and 155.75, 201.50 ve %96.56 in the organic system respectively (P>0.05). It was determined that weights of egg, albumen, yolk and shell were high in organic and 60 weeks of age group (P<0.001). Shape index and yolk color were found higher in the organic and 30 weeks groups (P <0.001), crude ash ratio of the egg shell was higher in the conventional system (P<0.05), shell ratio was high in conventional (P<0.05) and 30 week of age group (P<0.001), albumen ratio was high in 30 weeks group, and the yolk ratio was high in the 60 weeks group (P <0.001). Total polyunsaturated (PUFA), omega-3 (n-3) and omega-6 (n-6) fatty acids were high in organic and 30 weeks groups while monounsaturated (MUFA) fatty acids were higher in the conventional system (P <0.05). Egg yolk malondialdehyde (MDA), Vit D2 and K2 levels were high in the organic system and alpha-tocopherol (α-tok) levels were high in the conventional system (P <0.01). MDA and α-tok values were high at 60 weeks old and Vit D2 value was high at 30 weeks old groups (P <0.01). Stress protein HSP70 level was only affected by the rearing system and this value was found high in the organic system (P<0.001). As a result, in general, it has been found that the organic system can be regarded as advantageous in terms of egg production and quality and it can be said that the eggs which collected from young hens exhibited better characteristics. The high level of HSP70 in the organic system could be an indicator that hens might be more affected than environmental conditions or the hens reared in the organic system had the strong antioxidant defense system.