Failure of sperm transport in relation to ewe infertility following prolonged grazing on oestrogenic pastures

Abstract

Sixteen ewes were drawn from each of two ewe flocks, one of which had grazed on oestrogenic pastures for annual periods over the previous 5 years ("clover" treatment) while the other grazed on green oats ("oats" treatment). Fertility of ewes on the clover treatment had decreased progressively, whereas in those on the oats treatment it had remained high. Oestrous ewes were allocated alternately to receive either two or eight services then killed 24 hr post coitus and the numbers of sperm in the cervix, uterus, and fallopian tubes determined. There was no difference in ovarian activity between the two groups; however, highly significant differences were found in the numbers of sperm recovered from the cervix, uterus, and fallopian tubes. Average sperm numbers per fallopian tube were 17,160 and 350 for ewes on the oats and clover treatments respectively. In addition to the reduction in sperm numbers, both the percentage of motile sperm flushed from the cervix and the proportion of recovered ova with sperm attached to the zona pellucida were lower in ewes on the clover treatment. The results suggest that primary failure of sperm transport in ewes on the clover treatment occurred when sperm did not enter the cervix in adequate numbers following service. The significance of these observations in relation to possible causal mechanisms is discussed.

Infertility in Ewes caused by Prolonged Grazing on Oestrogenic Pastures: Oestrus, Fertilization and Cervical Mucus

“…Results from the present study, showing that ewes affected with clover disease had a lower fertilization rate and fewer sperm on the zona pellucida of recovered eggs, are in agreement with previous reports (Turnbull et al 1966;Lightfoot et al 1967;Kaltenbach and Davies 1970) concerning the nature of the permanent infertility in ewes following prolonged grazing on oestrogenic pastures. New evidence was presented to show that the duration of oestrus in affected ewes is comparable with that in control animals.…”

“…Since the original work of Bennetts et al (1946), it has been established that the major cause of permanent infertility in ewes affected with clover disease as the result of prolonged grazing on oestrogenic pastures is failure of fertilization due to impaired transport of spermatozoa through the genital tract (Turnbull et al 1966;Lightfoot et al 1967;Kaltenbach and Davies 1970). It is not known, however, why sperm transport is affected, although changes in the anatomy of the tract or in the nature of its secretions or both could be involved.…”

“…In particular, cervical mucus seemed worthy of further study. Lightfoot et al (1967) noted a lower proportion of motile sperm in mucus from clover-affected ewes and it is known (Gibbons and Mattner 1966;Mattner 1966) that the establishment and maintenance of the cervical sperm population in the ewe is dependent on the rheological properties of cervical mucus.…”

Fertility of Herbivores Consuming Phytoestrogen-containing Medicago and Trifolium Species

“…Permanent infertility results, mainly from disruption of the cervix which undergoes a uterus-like differentiation [70]. Diminished cervical folds hinder transportation of spermatozoa [71]. There is an increase in the cross-sectional area of lamina propria tissue lying underneath the cervical folds, mid-cervix.…”

Hypothalamic-Pituitary Function in Normal Ewes and Ewes which Grazed Oestrogenic Subterranean Clover for Several Years

“…A consequence of this oestrogen-rich diet is the development of 'clover disease' which is reflected by poor reproductive performance in flocks so affected. A number of physiological changes and clinical manifestations of the condition have been described; including cystic hyperplastic endometritis (Bennetts et al 1946), metaplasia resulting in cervical tissue looking more like uterine tissue (Adams 1976), variability in oestrous cycle length (Adams et al: 1975), production of large volumes of watery cervical mucus (Smith 1971) which can be associated with reduced sperm transport (Lightfoot et al 1967), and alterations in luteal function (Adams et al 1980). The availability of synthetic gonadotrophin releasing hormone (GnRH) made it possible to test a limited number of ewes with a history of permanent clover infertility for possible alterations to normal hypothalamic-pituitary function (Findlay et al 1973).…”