Assessment of oestrogenic activity of pastures by means of increase of teat length in sheep

Abstract

The use of increase in teat length for bioassay of oestrogens in sheep has been investigated. In wethers injected intramuscularly with stilboestrol dipropionate the best precision was obtained by measurement of the increase 9 days after the beginning of oestrogen administration. The range of doses over which the log dose-response relationship was linear was rather narrow (4–16 µg stilboestrol dipropionate per day). Applied in the field, the technique provides a means of assessing the effective intake of oestrogens by grazing sheep. Marked seasonal fluctuations in the oestrogen intake of wethers grazing a red clover pasture were recorded; the lowest level was in May and peaks occurred in August and December–February.

Investigation of the vaginal smear (Allen-Doisy) assay of oestrogen in ovariectomized ewes

“…In 1961, Braden, Southcott, and Moule (1964) observed peaks of oestrogenic activity in red clover pasture at Chiswick in February, August, and December, and troughs in May and October. They used the method of change in teat lengths of wethers grazing on the pasture.…”

“…Lamond and Southcott (1962) showed that the uterine weight increase after administration of stilboestrol could be the basis of a useful assay, and Davies and Bennett (1962) used the assay in assessing differences in oestrogenic potency between subterranean clover varieties (Trifolium subterraneum). Braden, Southcott, and Moule (1964) examined the increase in teat length in wethers and ovariectomized ewes after oestrogenic stimulation, and concluded that the response could be used for detecting oestrogens in pasture and under certain circumstances would also provide a measure of the oestrogenic potency. Morley, Bennett, and Axelson (personal communication) have found that mammary gland growth and a lactation score in ewes may be related to dose of oestrogen.…”

The oestrogenic activity of white clover (Trifolium repensL.)

“…2. Where sufficient material was available (Samples 2 and 4), feeding to Romney wethers, and recording the changes in teat length (Braden et al 1964).…”

“…White clover (T. repens L.), by contrast, possesses little or none of these isoflavones (Francis et at. 1967), and is generally not considered to be an oestrogenic forage Braden et at. 1964).· However, oestrogenic effects of this clover in sheep and cattle have occasionally been reported in the U.S.A. (Sanger and Bell 1961;Wright 1960), Japan (Ochi et at.…”

Forage plant estrogens

“…Because of their results, some workers have utilized sheep rather than laboratory animals in bioassays (Bennett and Dudzinski, 1967;Bennetts et al, 1968;Braden et al, 1967;Francis and Millington, 1965). Among the criteria used to measure the estrogenic response in sheep are uterine weight increase, vaginal cornification (Braden et al, 1964), teat length (Millington et al, 1964a(Millington et al, , 1964b, lactation in ewes (Clark, 1964;McKeown, 1962), and nucleic acid in samples of uterine tissue (Little and Lamboume, 1976;Little, 1976) (Table 4). …”