Phytoestrogens are hormone-like substances in plants
that can substantially influence human health (positively
or negatively), and when fed to dairy cows are
partly transferred to their milk. The aim of this study
was to investigate the effects of varying the botanical
composition and regrowth interval of legume-grass
silage on phytoestrogen intake and milk phytoestrogen
concentrations. In one experiment, 15 Swedish Red
dairy cows were fed 2- or 3-cut red clover-grass silage,
or 2-cut birdsfoot trefoil-grass silage. In a second experiment,
16 Norwegian Red dairy cows were fed short-term
ley silage with red clover or long-term ley silage with
white clover, and the effects of supplementation with
α-tocopherol were also tested. High concentrations of
formononetin and biochanin A were found in all silage
mixtures with red clover. The milk concentration of
equol was highest for cows on the 2-cut red clover-grass
silage diet (1,494 μg/kg of milk). Because of the metabolism
of biochanin A, genistein, and prunetin, their
concentrations in milk and the apparent recovery were
low. Coumestrol was detected in only short-term and
long-term ley silage mixtures, and its milk concentration
was low. Concentrations of secoisolariciresinol and
matairesinol were higher in 2-cut birdsfoot trefoil-grass
and long-term ley silage mixtures, those with legume
species other than red clover, and the highest grass
proportions. The 2-cut birdsfoot trefoil-grass silage
diet also resulted in higher enterolactone concentration
than the other diets (226 μg/kg of milk). Lengthening
the regrowth interval increased the intake of secoisolariciresinol
and decreased the recovery of lignans. Feeding
long-term ley silage resulted in higher milk lignan
concentrations but lower milk isoflavone concentrations
than feeding short-term ley silage. The apparent recovery
of all phytoestrogens except prunetin was highest
on the 2-cut birdsfoot trefoil-grass silage diet. No effect
of α-tocopherol supplementation was observed on milk
concentrations of any of the measured phytoestrogens.
Variations were observed in milk concentrations of
phytoestrogens, especially of equol, among cows, which
could not be explained by variations in diet composition
or phytoestrogen intake. The results show that
milk phytoestrogen concentration is strongly influenced
by silage botanical composition, but questions regarding
phytoestrogen metabolism remain to be answered.
Key words: Trifolium species , Lotus corniculatus ,
estrogen receptor , ruminant
Phytoestrogens are hormone-like substances in plantsthat can substantially influence human health (positivelyor negatively), and when fed to dairy cows arepartly transferred to their milk. The aim of this studywas to investigate the effects of varying the botanicalcomposition and regrowth interval of legume-grasssilage on phytoestrogen intake and milk phytoestrogenconcentrations. In one experiment, 15 Swedish Reddairy cows were fed 2- or 3-cut red clover-grass silage,or 2-cut birdsfoot trefoil-grass silage. In a second experiment,16 Norwegian Red dairy cows were fed short-termley silage with red clover or long-term ley silage withwhite clover, and the effects of supplementation withα-tocopherol were also tested. High concentrations offormononetin and biochanin A were found in all silagemixtures with red clover. The milk concentration ofequol was highest for cows on the 2-cut red clover-grasssilage diet (1,494 μg/kg of milk). Because of the metabolismof biochanin A, genistein, and prunetin, theirconcentrations in milk and the apparent recovery werelow. Coumestrol was detected in only short-term andlong-term ley silage mixtures, and its milk concentrationwas low. Concentrations of secoisolariciresinol andmatairesinol were higher in 2-cut birdsfoot trefoil-grassand long-term ley silage mixtures, those with legumespecies other than red clover, and the highest grassproportions. The 2-cut birdsfoot trefoil-grass silagediet also resulted in higher enterolactone concentrationthan the other diets (226 μg/kg of milk). Lengtheningthe regrowth interval increased the intake of secoisolariciresinoland decreased the recovery of lignans. Feedinglong-term ley silage resulted in higher milk lignanconcentrations but lower milk isoflavone concentrationsthan feeding short-term ley silage. The apparent recoveryof all phytoestrogens except prunetin was higheston the 2-cut birdsfoot trefoil-grass silage diet. No effectof α-tocopherol supplementation was observed on milkconcentrations of any of the measured phytoestrogens.Variations were observed in milk concentrations ofphytoestrogens, especially of equol, among cows, whichcould not be explained by variations in diet compositionor phytoestrogen intake. The results show thatmilk phytoestrogen concentration is strongly influencedby silage botanical composition, but questions regardingphytoestrogen metabolism remain to be answered.Key words: Trifolium species , Lotus corniculatus ,estrogen receptor , ruminant
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