Abstract
This study was conducted to investigate effects of diets with varying levels of vitamin premix on egg production, eggshell quality, and vitamin contents in eggs of commercial laying hens. A total of 144 Hy-line Brown layers at 45 weeks old were randomly divided into four groups (six replicates, 6 birds for each group) and fed diets containing different levels of vitamin premix for eight weeks. Laying hens in the control group received diet containing 100% vitamin premix (0.1% in experimental diet). The other three groups received diet containing 75%, 50% or 0% of vitamin premix compared to control, respectively. Egg production and daily egg mass in layers fed diet without vitamin premix were significantly lower (p < 0.01) than those in the control group during the second half of the experiment (four weeks). Linear trend for egg production was determined with increasing dietary vitamin premix levels during the same period. There was no significant difference in feed intake or blood profile among groups. Significant linear and quadratic improvement for eggshell strength and thickness were found with increasing dietary vitamin premix level at 4 and 6 weeks of the experiment (p < 0.05). Concentrations of riboflavin and α-tocopherol in eggs obtained from the control group were significantly higher than those of the group fed a diet without vitamin premix (p < 0.05). These results suggest that reducing more than 50% or withdrawal of vitamin premix in layer diet did negatively affect egg production or egg qualities as the period of deprivation increased. To produce healthy chicken eggs, it is recommended to feed a diet that contains sufficient levels of vitamin premix.