The experiment was designed to investigate the effects of feed supplementation with essential oils on egg weight and body mass of laying hens. Hens of the laying breed Isa Brown were randomly divided at the day of hatching into 3 groups (n=26) and fed for 45 weeks on diets which differed in kind of essential oil supplemented. Hens were fed from day 1 by the standard feed mixture. Laying hens accepted fodder ad libitum. In the control group hens took feed
mixture without additions, in the first experimental group the feed mixture was supplemented with 0.25 ml/kg thyme essential oil and in the second one hens got hyssop essential oil in the same dose of 0.25 ml/kg. The housing system satisfied enriched cage requirements specified by the Directive 1999/74 EC. The useful area provided for one laying hen presented 943.2 cm2. The equipment of cage consisted of roosts, place for rooting in ashes – synthetic grass, nest and equipment for shortening of clutches. The results showed that the average body weight for a rearing period was in order groups: 736.15±523.49; 747.20±541.6 and 721.95±522.57 (g±SD). Differences between groups were not significant (P>0.05). The average body weight during the laying period was 1763.85±171.46; 1786.08±192.09 and 1729.73±129.12 g for control, thyme
oil and hyssop oil supplementation respectively. During the laying period there were significant differences in body weight between control and experimental group with hyssop essential oil supplementation (P<0.05) and between both experimental groups (P<0.01). No significant differences were found out between control group and experimental groups (P>0.05) in egg weight (58.36±4.91; 58.82±4.95 and 58.26±5.33 g respectively).
