Antibiotics and zinc oxide are therapeutic agents widely used in the livestock industries, reducing significantly the negative effects of weaning by improving the growth rate and decreasing mortality. Although, due to the potential public and environmental risks associated with antibiotic resistance and soil pollution their use in the E.U. has been drastically reduced or banned, thus, alternative solutions been necessary to be develop. The addition of polyphenols to animal feed has shown promising results, as they have a broad antimicrobial activity including against E. coli F4 (K88). Moreover, it has been observed to hold a wide range of beneficial properties such as antidiarrhoeic, anti-inflammatory, and antioxidant activity. In the present study in vitro experiments were performed in order to investigate the antimicrobial activity of several polyphenolic extracts obtained from mustard seed meals of two origins (Poland and Moldavia), grape seed meal, sea buckthorn seed meal, rapeseed meal, and rapeseed meal fermented with S. cerevisiae, against E. coli F4 (K88) proliferation measured at different intervals for 24 hours. The results revealed that polyphenols have a considerable antimicrobial effect in high concentrations. The inhibition was dependent also on polyphenol composition and even the origin place. Withal, it was observed that the polyphenols extracted from rapeseed meal and fermented rapeseed meal presented noticeable differences in inhibition, in similar concentrations, this suggesting that the fermentation process considerably affects the profile of rapeseed meal polyphenols. Likewise for the Moldavian mustard seed extract which significantly inhibited bacterial growth from very low concentrations although it had a low concentration of total polyphenols. Thus, the polyphenolic content of fermented rape seed meal extract presented an enhanced antimicrobial activity against E. coli F4 (K88) compared with the non-fermented rape seed meal extract. Although the total polyphenol concentration was lower in FRSM than in RSM. Polyphenols extracted from Moldavia mustard seed meal exhibited remarkable efficacy in inhibiting bacterial growth. Notably, even at a concentration as low as 3.71 µg/ml, the polyphenols demonstrated significant antimicrobial activity, effectively combating bacterial development. Overall, our study demonstrated that polyphenols represent a promising substitute for antibiotics and zinc oxide and might represent an encouraging long-term solution in overcoming the weaning crisis in pigs. In vivo experimentations are needed to validate these results.
