The effects of hops (Humulus lupulus L.) and silymarin on performance and health of newly weaned pigs
The ban of antimicrobial growth promoters in pig production has resulted in an increased
interest in investigating the effects of different alternatives, which can reduce the problems
post weaning and improve the performance in piglets. Initially two botanical extracts with
different properties were investigated: hops, which have antibacterial properties and
silymarin, which is used for liver disorders.
The first experiment showed that hops and silymarin had beneficial effects on FCR in
piglets (P = 0.014) by 9.6% and 15.8%, respectively. Furthermore, hops significantly
improved someo f the measuredli ver enzymes,s o it was decidedt o focus on hops only.
Two further experiments were carried out examining the effects of different concentrations
of hops and isolated hop compounds (iso-a acids and ß-acids), and the combination with
organic acids in weanerp igs. A higher inclusion level of hops was associatedw ith a better
FCR, and the isolated hop compounds also resulted in an improved FCR (P = 0.027) by
9.2%. The addition of an organic acid mixture did not affect the performance.
An in vitro experiment confirmed that hops and isolated hop compounds had antibacterial
properties. To try and elucidate the mechanism by which the hops and the isolated hop
compounds improved the FCR, the effects on the gut flora were studied in the piglets. Both
the hops and the iso-a acids and ß-acids reduced the level of lactic acid bacteria and the
level of Bacteriodes in one of the two experiments, but no effects were seen on the other
bacteria. This lead to investigate the effects of hops/isolated hop compounds on the level of
volatile fatty acids, digestibility and level of digestive enzymes and level of liver enzymes.
However, none of these parameters gave conclusive results about the mode of action of
hops/isolated hop compounds in the piglet.