Effect of the rearing system (barn vs. free range) on eggshell quality traits, yolk vitamin D3 content and keel bone damage in Leghorn hens.

This study aimed to assess the effects of rearing system on egg quality traits, eggshell characteris-tics including eggshell breaking strength (EBS), yolk vitamin D3 (YD3) content and keel bone dam-age (KBD) occurrence. Sixty White Leghorn hens (18–week-old) were raised in either indoor barn or free-range system (BA and FR, respectively; 3 replicates of 10 hens) and fed a basal diet for 52 weeks. Egg production was monitored daily, while feed intake was registered weekly. In both autumn-winter and spring-summer periods, 204 eggs/rearing system were collected to assess egg and eggshell quality traits. The YD3 content was determined on six eggs/rearing system/period, while KBD occurrence was evaluated on all hens. FR hens presented a lower feed consumption than BA ones in both periods, resulting in a reduced Ca and vitamin D3 supply. During the autumn-winter, FR eggs showed similar YD3 content than BA ones (19.63 vs. 17.83 lg/100 g DM yolk; p ¼ 0.33), while EBS tended to be lower (4.29 vs. 4.38 kg, respectively; p ¼ 0.08). In spring-sum-mer, FR eggs had identical EBS (3.63 vs. 3.63 kg; p ¼ 0.97) and higher YD3 content than BA (25.39 vs. 20.81 lg/100 g DM yolk; p < 0.01). The estimated endogenous vitamin D3 synthesis accounted for 22% and 43% of the total YD3 content in autumn-winter and spring-summer, respectively. KBD occurrence was similar in both periods. These findings suggest that sunlight exposure in free-range system can positively affect eggshell quality traits (particularly EBS) and yolk vitamin D3 content likely by stimulating vitamin D3 synthesis, although with seasonal variations.