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.