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Independent Article
 
   
 
   
 
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.