The analyses aimed at determining the effect of replacing the antibiotic in feed mixes with various herbal additives on the core chicken breeding parameters such as weight gain, FCR, mortality rate, EEI, selected carcass slaughter parameters and some strength and morphometric parameters of the tibia bone on broiler chickens. 400 one-day-old Ross 308 male chicks were split into 8 groups of 10 chicks each in 5 repetitions. The chicks were allocated at random to the control group (negative – without AGP), I – receiving AGP, and to groups given 2% herbal additives: hop – II, lime – III, lemon balm – IV, pansy – V, peppermint – VI and nettle – VII. The study involved herbs contained essential oils of: hop cones (0.42%), lemon balm leaves (0.077%), peppermint leaves (2.92%), as well as flavonoids: pansy herb (0.37%), and lime flower (0.78%). During the experiment chickens’ body weight was controlled on the 21st, 35th and 42nd days of breeding, set FCR, EEI and postslaughter evaluation were performed on 10 male chicks selected from each group. The right-leg tibia was sampled for analysis from chickens slaughtered on day 42. The bones were mechanically stripped of soft tissues, weighed (with 0.1 g accuracy), packed into labeled plastic bags and frozen (at a temperature of –25°C) until the beginning of analyses. An Instron Universal Testing Machine (Model 3369) was used to determine bone ultimate strength and maximum elastic strength and yielding deformation, bending point resistance and load-to-deformation ratio. The geometric properties of bones (cross-section area, second moment of interia, mean relative wall thickness) and cortical indexes (cortical layer, cortical index, cortical surface, cortical surface index) were estimated on the basis of measuring the external and internal horizontal and vertical axes in the cross section of the bones at the site of fracture. Bone mineralization was degreased and dried to a constant weight in a muffle furnace and mineral content was determined. On 21st day of life the body weight of chickens receiving an admixture of lemon balm and nettle was significantly higher (P < 0.01) compared to the body weight of birds fed with AGP, hop and lime and control groups. The highest slaughter weight was recorded in chickens fed on a mix with an addition of nettle (2435 g), while significantly lower body weight (P < 0.05) was revealed in the control group (2112 g) and the group receiving hops (2109 g). The addition of lime, lemon balm, pansy and nettle significantly (P < 0.05) increased the slaughter yield of chicks compared to the control group, the AGP group and the group receiving hops. The largest increase in bone elasticity occurred as a result of using additives such as hop, pansy and nettle in the mixes. The value of the dy in these groups compared to the control group and the group receiving an antibiotic were on average more than 20% higher. The value of the Wf in the group receiving pansy compared to the control group and the group receiving AGP were higher by 22.4% and 21.9% respectively (P < 0.05). Regardless of the species of herb added higher values were recorded for the following parametres: Ix, A, CS and Wy/dy. A 2% addition of hop, nettle and pansy increased the dy value, whereas an addition of hop, lemon balm and pansy contributed to increased Wy compared to bone properties measured in the control group and in the group receiving the antibiotic. The body weight of chicks in experimental groups (except for the group fed on nettle) on the 42nd day of breeding was similar to the body weight of control chicks and chicks fed on mixes with an antibiotic. Moreover, the conversion of feed per 1 kg of weight gain with the use of lime, lemon balm and/or nettle did not deviate from the conversion of feed by birds in the control group and the group receivig antantibiotic. The introduction of lime, lemon balm, pansy and nettle increased the slaughter yield and the addition of pansy, mint and nettle contributed to a reduction in the share of abdominal fat compared to the AGP group.
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