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Studies of sheep fed soy
Lactation
in rams grazing subterranean clover.
Meyer EP
Aust
Vet J 1970 Jul 46:7 305-7
Hormone
studies on ewes grazing an oestrogenic (Yarloop clover) pasture during
the reproductive cycle.
Obst JM,
Seamark RF
Aust J
Biol Sci 1975 Jun 28:3 279-90
Abstract
The
endocrine function of Merino and Corriedale ewes grazing an oestrogenic
(Yarloop clover) pasture has been studied during the oestrous cycle,
pregnancy and parturition, and the results compared with those from a
study of similar ewes grazing a neighbouring grass pasture. Plasma
progesterone, oestrogen and corticoids were measured using competitive
protein binding assay procedures. During the oestrous cycle clearly
anomalous patterns in hormone content were evident in ewes grazing
Yarloop, and this related to their significantly poorer (P less than
0.001) fertility. The first mating, when ewes were 1-1/2 years of age,
was particularly affected. Successful conception took place in only 27%
of ewes mated on Yarloop, compared with 95% on grass. Evidence of
disturbance in the normal patterns of both plasma oestrogen and
progesterone was found in infertile ewes, including a shortened period
of luteal function. Disturbance of endocrine function caused by Yarloop
clover ingestion was also found in pregnant ewes, with the mean plasma
progesterone concentrations during the latter half of pregnancy reduced
(P less than 0.05) and the plasma oestrogen and corticoid levels
tending to be higher in these animals. In detailed hormone studies in
the periparturant period, both groups showed a similar fall in plasma
progesterone and rise in plasma oestrogen prior to parturition. Where
excessive time was taken for parturition (more than 30 min) this was
reflected in higher plasma corticoid levels (P less than 0.05) within 8
h of birth.
Cervical
mucus changes in infertile ewes previously exposed to oestrogenic
subterranean clover.
Adams NR
Res Vet
Sci 1976 Jul 21:1 59-63
Abstract
Characteristics
of cervical mucus were compared between groups of ewes which had
previously grazed for long periods on either potently oestrogenic
clover pasture (group A), mildly oestrogenic pasture (group B) or
non-oestrogenic pasture (group C). No phytooestrogens were fed at the
time of the study. The chloride content of mucus from group A ewes was
significantly decreased, on a dry weight basis. The motility and
survival of ram spermatozoa appeared similar in cervical mucus from
groups A and B. There was no statistically significant difference
between groups of ewes in either the total wet weight of mucus, the
proportion of dry weight, or the degree of arborisation of mucus, at
the time of oestrus. Mucus from group A ewes had a significantly
decreased spinbarkheit, and a decreased ability to orientate sperum
migration, when compared with group B. The group B ewes had a
significantly smaller spinbarkheit than group C. Measurement of
cervical mucus spinbarkheit offers promise as a diagnostic test for
permanent clover infertility.
Morphological
changes in the organs of ewes grazing oestrogenic subterranean
clover.
Adams NR
Res Vet
Sci 1977 Mar 22:2 216-21
Abstract
The
morphological effects of phytooestrogen exposure were determined in 10
ewes exposed to subterranean clover for 60 days, compared with 10
controls. In a second experiment, the time course of the development of
the changes was studied. Typically oestrogenic changes were observed in
ovary, oviduct, uterus, cervix, vagina and mammary glands. There was an
early increase in cervical mucus, followed by a decrease. The delta
basophils of the pituitary became degranulated, and hyperactive in
appearance. The adrenal and thyroid glands increased in weight, and
thyroid epithelium increased in height. There appeared to be a
temporary increase in neurophysin storage in the hypothalamus, and
shrunken, hyperchromatic neurones were observed in the hypothalamus of
some affected ewes. All changes were observed within three weeks of
exposure.
Permanent
clover infertility in ewes.
Rizzoli DJ,
Moran AR
Aust
Vet J 1977 Apr 53:4 190-1
Permanent
infertility in ewes exposed to plant oestrogens.
Adams NR
Aust
Vet J 1990 Jun 67:6 197-201
Abstract
In
Australia, more than 1 million ewes have permanently damaged
reproductive tracts because they have been grazed on oestrogenic
pasture. These effects occur in the absence of classical clinical
''clover disease''. The lesions result from an ''organisational''
action of oestrogen, causing a mild sexual transdifferentiation to
occur in ewes during adult life, with the main lesion being found in
the cervix. Diagnosis of the problem depends primarily on detection of
the pathological changes, rather than history or clinical signs. On
average, affected flocks have around a 10% increase in non-pregnant
ewes, but most farmers can achieve an acceptable lambing rate by
increasing their management and feed inputs to produce more twin lambs.
Agronomic approaches have been used in the past to combat ''clover
disease'', but further progress with the present problem may depend on
the development of animal-based solutions.
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