to the oestrogen receptor, based upon
common structural features. Equol is the
major isoflavonoid in plasma of livestock
and appears to be the oestrogenic agent in
clover disease. A unifying feature of oestro-
genic isoflavones is their capacity to
stimulate proliferation of the female repro-
ductive tract. Other indicators of reproduc-
tive derangements include precocious
sexual development, and reduced ovula-
tion rates. For example, ewes grazing on
oestrogenic pastures around the time of
mating, develop ‘temporary infertility’
characterized by low ovulation and con-
ception rates (Adams, 1995). This form of
infertility is reversed within 4–6 weeks of
transfer of ewes to non-oestrogenic grazing.
Temporary infertility may occur in the
absence of overt symptoms, particularly in
Merino ewes. Prolonged comsumption of
oestrogenic pasture can induce permanent
infertility in ewes. Reduced conception
arises from a failure of the cervix to
facilitate transport of spermatozoa follow-
ing insemination. Irreversible changes of
the cervix occur such that it resembles the
histology and function of the uterus. Such
changes are used in the diagnosis of
permanent infertility from tissues obtained
in abattoirs. Isoflavonoids may also impair
male reproductive function by reducing
testicular development and spermato-
genesis.
Reproductive performance in cattle
may be compromised through the ingestion
of needles and buds from western yellow
pine (P. ponderosa). The primary effect is
late-term abortion in beef cattle (Ford et al.,
1997). There is evidence that this syndrome
is a form of premature fetal-induced
parturition rather than a non-specific
abortion. Comparison of the steroid
hormone status of P. ponderosa-fed and
normal cows indicates similar patterns of
periparturient endocrine changes. Thus,
both groups display gradual increases in
oestrogen concentrations which peak at
parturition and decline thereafter. A major
pre-partum difference between these
groups, however, is a striking and progres-
sive decline in blood flow to the gravid
horn in cows fed P. ponderosa needles. The
depression in blood flow specifically in the
caruncular arterial bed results in reduced
nutrient and O 2 supply at the placentome.
The active agents causing these effects are
thought to be the vasoactive lipids isolated
from P. ponderosa needles.
The ergopeptine alkaloid mycotoxins
present in endophyte-infected tall fescue are
the causative agents of ‘fescue summer
toxicosis’ or ‘summer slump’ in cattle.
Effects include delayed onset of puberty and
impaired function of the corpora lutea in
heifers. The corpus luteum of affected
heifers show increased numbers of large
luteal cells, and ultrastructural examination
of these cells reveal higher numbers of mito-
chondria, lipid droplets and secretory
granules. Reduced calving rates may be
associated with endocrine changes such as
lower prolactin status. In ewes, delayed con-
ception, attributed to embryonic mortality
and delayed onset of oestrus rather than to
failure in fertilization, is the primary effect
of fescue toxicosis. The adverse effects
in horses are associated almost entirely
with reduced reproductive performance.
Agalactia, extended gestation length, abor-
tion and thickened placentas are common
observations in affected mares. Placental
abnormalities may include oedema, fibrosis
and mucoid degeneration. It has been
suggested that the effects in the placenta
were the result of hypoxia caused by
reduced blood flow to this organ. Foal losses
have also been reported, 16% for fescue and
<6% for other forages. Endophyte-infected
tall fescue can, in addition, reduce testos-
terone secretion and testicular function in
males, as indicated by studies on beef bulls.
Although lupinosis is essentially a
disorder of the liver, reduced reproductive
performance in ewes has been reported on
administration of phomopsins (Barnes et
al., 1996). Ovulation rate is depressed,
leading to markedly lower conception rates
and numbers of lambs born.A Critique
The occurrence of ANFs and mycotoxins as
co-contaminants in raw materials andAnti-nutritional Factors and Mycotoxins 397