Effects of prolonged exposure of ewes to oestrogenic pasture 2. Occurrence of abnormalities of the external genitalia and altered mating performance

Abstract

Romney ewes grazed pasture initially containing 0 (C), 30 (M), or 60% (P) Pawera red clover for c. 6 months per year (spring-autumn) during the first 4 (P) or 5 (M) years of a 6-year study. When not grazing red clover, all animals grazed C-type pastures. In Years 3-6, ewes were scored on a subjective 0-3 scale for vaginal abnormalities. More of the animals grazing M pasture scored 1 or higher each year compared to the ewes on C pasture (P < 0.001). Similarly, more of the ewes grazing P herbage were scored 2 or higher than either of the other two groups (P < 0.001). A greater proportion of the ewes on the P sward were mated more than once at each joining, compared with the other two groups (P < 0.01 in Year 3; P < 0.001 in all other years) and consequently there were differences in the mean number of times each ewe was mated. Long-term grazing of oestrogenic red clover results in both a high incidence of abnormalities of the external genitalia and decreased mating performance in ewes. However, these effects appear to be independent of each other. A93026

Fertility of Herbivores Consuming Phytoestrogen-containing Medicago and Trifolium Species

“…Histological examination of the cervix revealed that subclinical infertility was widespread in Western Australian flocks [72]. With isoflavone-containing red clover varieties, ewes exposed long-term had a high incidence of abnormalities of the external genitalia, decreased mating performance and fewer multiple births [73,74].…”

Dietary red clover (Trifolium pratense) induces oviduct growth and decreases ovary and testes growth in Japanese quail chicks

“…Red clover contains the phytoestrogens formononetin, biochanin A, and to a lesser extent, daidzein, and genistein [42–45]. Red clover was found to cause vaginal abnormalities and altered mating behavior in ewes [8], leading to permanent flock infertility [7], when ewes were fed red clover during periods in the first 4–5 years of their lives. Immature rats exhibited up to a 200% increase in uterine growth when fed 2 g red clover per day for 5 days [11].…”

“…Phytoestrogens are a subset of plant secondary compounds (SPCs, so-called because they have no function in the primary roles of growth and development in plants), and include several classes of chemicals [6]. While phytoestrogens have been shown to exert endocrine disrupting effects on many species of vertebrates, including livestock [7,8], rodents [9–11], fish [12], and birds [13,14], little is known about the evolutionary function of these chemicals in plants. It has been suggested, however, that phytoestrogens have evolved as a chemical defense against vertebrate herbivory [15–17], similar to the well-studied ecdysteroidal disruption that plants exert on certain insects [18].…”

“…Red clover ( Trifolium pratense ) is commonly eaten by California quail [33], and contains the phytoestrogens formononetin and biochanin A [34]. Livestock grazing on red clover and other subterranean clovers can exhibit what is known as “clover disease” resulting in behavioral and physiological reproductive disruption in both males and females, leading to infertility [7,8,35]. Although the phytoestrogen genistein has been shown to act as an estrogen in zebra finch and chickens [13,36], few studies have considered the endocrine disruptive effects of whole estrogenic plants in birds (or, for that matter, any other vertebrate).…”

Prospects for Trifolium Improvement Through Germplasm Characterisation and Pre-breeding in New Zealand and Beyond

“…Further research showed a strong link between high levels of phytoestrogens, specifically formononetin, in red clover, and decreased efficiency in ewe fertility ( Rumball et al, 1997 ). Grazing management has allowed better control over the exposure to formononetin ( Shackell et al, 1993a , b ). However, the more recent red clover cultivars have been bred with lower levels of phytoestrogen.…”