Assessment of the antibacterial activity of chestnut (Castanea sativa) and cloves (Syzygium aromaticum) herbal extracts as an alternative to antibiotics use during post-hatching period of chicks

Bacterial infections of newly hatched chicks are the most common cause of their death in the initial period of rearing. These infections are always treated with antibiotics. The aim of the study was to investigate the antimicrobial activity of herbal extracts of chestnut (Castanea sativa) and clove (Syzygium aromaticum) against bacterial infections i.e. Escherichia coli, Enterococcus faecalis, Staphylococcus aureus, Klebsiella pneumonice in comparison to antibiotics. The results of the microbiological analyses showed that the Castanea sativa and Syzygium aromaticum extracts had a slighter antibacterial activity in comparison to antibiotics. The diameter of zone inhibition of the culture’s growth of gram-negative bacteria (i.e. Escherichia coli and Klebsiella pneumoniae) and gram-positive bacteria (i.e. Staphylococcus aureus and Enterococcus faecalis) was 6–13 mm for these extracts in comparison to 15–30 mm for antibiotics. However, some bacterial strains presented full resistance to the selected antibiotics, e.g., wild strains of Enterobacteriaceae to amoxicillin or Staphylococcus aureus and Enterococcus faecalis to florfenicol, colistin, and doxycycline. In the second experiment, the effect of the herbal extract mixture added into drinking water on the growth and mortality of chicken broiler during the first rearing week was investigated. There was found that the use of herbal extracts improved the chickens’ body weight (157.4 g; P ≤ 0.008) and decreased mortality rate (2.4%) compared to the control group (144.1 g and 3.9%, respectively) but not to the group treated with antibiotic (161.5 and 0.6% respectively; P ≤ 0.009). In summary, the use of herbal extracts as a nutritional supplement for poultry seems to have a positive effect on weight gain of young birds, and to some extent reduce mortality in the first week of rearing.