Ethological Study of Free-Range Hens with Zinc and Vitamin C Supplemented Diet

1 Trakia University, Faculty of Veterinary Medicine, BG-6000 Stara Zagora, Bulgaria
2 Agricultural University, Department of Animal Science, BG-4000 Plovdiv, Bulgaria


Bozakova, N., V. Gerzilov and L. Sotirov, 2017. Ethological study of free-range hens with Zinc and vitamin C supplemented diet. Bulg. J. Agric. Sci., 23 (2): 289–297

The study was designed to examine the effects of a dietary supplementation with zinc (35 mg/kg) and vitamin C (250 mg/kg) on the behaviour and plasma corticosterone in New Hampshire NG-line hens reared under free range conditions (sleeping pens and outdoor walking yards) during cold (7°C), thermoneutral and hot (31°C) subperiods. Hens’ behaviour was recorded by video cameras. Blood plasma corticosterone was assayed by ELISA. In all birds, both low and high ambient temperatures, combined with high light intensity, induced a signifi cant increase in plasma corticosterone compared to the thermoneutral period (P < 0.01). During those periods hens were more aggressive which indicated poorer welfare. Hens supplemented with either zinc or zinc + vitamin C had lower plasma corticosterone than controls. Dietary zinc, either alone or co-administered with vitamin C, reduced plasma corticosterone and increased the number of egg-laying, dust bathing and preening birds during the cold and hot periods. The aggressive behaviour was reduced (P< 0.01) indicating a higher welfare level. The group supplemented with zinc + vitamin C showed more intensive preening and resting, as well as less aggression and movement than the zinc-supplemented group (P < 0.05), suggesting a synergistic action of both supplements towards alleviating stress and therefore, a possibility for improving hen welfare.

Key words: poultry welfare, behaviour, corticosterone, zinc and vitamin C, stress

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