In conclusion, phytogenic feed additives are claimed
to exert antioxidative, antimicrobial, and growth-promoting effects in livestock, actions that are partially
associated with enhanced feed consumption, supposedly because of improved palatability of the diet.
Whereas available results do not support a specific amelioration of palatability, the antioxidative efficacy of
some phytogenic compounds to protect the quality of
feed, as well as that of food derived from animals fed
those substances, cannot be ruled out. With respect to
antimicrobial action, some observations in vivo support
the assumption that the general potential of phytogenic
feed additives is to contribute to a final reduction of
intestinal pathogen pressure. When compared with antimicrobial feed additives and organic acids, the phytogenic substances currently used in practice similarly
seem to modulate relevant gastrointestinal variables,
such as microbial colony counts, fermentation products
(including undesirable or toxic substances), digestibility of nutrients, gut tissue morphology, and reactions
of the gut-associated lymphatic system. Furthermore,
some isolated observations seem to support the claimed
enhancements of digestive enzyme activity and absorption capacity through phytogenic compounds. In addition, phytogenic products may stimulate intestinal mucus production, which may further contribute to relief
from pathogen pressure through inhibition of adherence to the mucosa. Unfortunately, respective experimental results are available only from commercial products containing blends of phytogenic substances. Therefore, there is still a need for a systematic approach to
explain the efficacy and mode of action for each of type
and dose of active compound, as well as its possible
interactions with other feed ingredients. Nevertheless,
the current experience in feeding such compounds to
swine and poultry seems to justify the assumption that
phytogenic feed additives may have the potential to
promote production performance and productivity, and
thus add to the set of nonantibiotic growth promoters,
such as organic acids and probiotics.