Yolk vitamin D content and eggshell quality traits as affected by hen genotype and housing system

A novel approach to fortify egg with vitamin D consists in sunlight exposure of hens as they are capable of endogenous vitamin D synthesis. The present study aimed to investigate the yolk vitamin D content and the eggshell quality traits of 5 hen genotypes (GT): 2 Italian local breeds (Bionda Piemontese [BP], Robusta Maculata [RM]) and their respective crossbreeds (CB) with a commercial strain (Sasso) compared to Lohmann brown (LB) as well as the effect of the housing system (HS) (enriched-cage [EC] vs. free-range [FR]). 300 hens were raised from 18 to 66 wks of age in EC and FR (3 replicates of 10 hens/GT/HS) and fed the same commercial feed (vitamin D = 3,000 IU). 100 eggs/ GT/HS were collected in fall, spring and summer for the evaluation of eggshell breaking strength (EBS) and eggshell/egg proportions. Yolk vitamin D3 and 25(OH) D3 content was analyzed in 2 pools/GT/HS of 5 yolks each collected at the same sampling times. Data were submitted to two-way ANOVA (main effects: GT and HS) with interaction. Overall, vitamin D3 and 25(OH)D3 content of yolks from LB, BP and RM was increased (+109, 116 and 385%, and +108, 400 and 200% respectively; P< 0.01) when hens were housed in FR rather than in EC. HS did not affect yolk vitamin D content of both CB. EBS was positively influenced by the HS (EC < FR), although significant differences were observed only for LB and RM (4.44 [43.5] vs. 4.84 [47.5] and 3.69 [36.2] vs. 4.00 [39.2] kg [N], respectively for EC and FR) whereas eggshell/ egg proportions were not remarkably affected. In conclusion, the sunlight exposure of hens raised in FR stimulated vitamin D synthesis with positive repercussion on yolk enrichment and EBS in all seasons, even though the effect was deeply influenced by the hen genotype.