This study aimed to determine the effects of in-feed inclusion of humic substances (HS) and/or calcium carbonate (CaCO3) on the performance and welfare of laying hens. A total number of 144 Hy-Line Brown laying hens (55 weeks old) were randomly assigned to four treatments, T1-T4 (36 birds per treatment). T1 hens were fed on a control diet without HS or CaCO3, T2 hens were fed on the control diet + 2.00 g per bird per day CaCO3, T3 hens were fed on the control diet + 0.20% HS and T4 hens were fed on the control diet + 0.20% HS + 2.00 g/bird/day CaCO3. The experiment started after 15 days of adaptation and lasted 8 weeks. The parameters evaluated were percentage of hen-day egg production, food consumption, mortality, egg quality parameters and heart rate variability (welfare indicator). Hens in the T3 group showed a significantly lower feed intake than those in the other three groups, however, significantly higher daily egg production was recorded in groups T3 and T4 compared to T1 and T2. Eggshell quality characteristics were significantly improved by HS supplementation and eggs laid by hens in groups T1, and T4 presented paler yolk and shell color than those in the other groups. In conclusion, these results indicated that in-feed inclusion of HS had a beneficial effect on laying hens' productive performance including egg production and eggshells quality.
Keywords: Eggshell; Feed additive; Sympathovagal balance.
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