Oestrogens
Some subclover varieties contain oestrogens. Particularly, early subclover cultivars contained formononetin, a deleterious phyto-oestrogenic isoflavone that has short to long-term negative effects on reproduction in sheep (Nichols, 2017; Reed, 2016; Pace et al., 2011). Newer cultivars selected to have low formononetin concentration (< 0.2% DM) have no detrimental effect on sheep reproductive performance (Nichols, 2017; Reed, 2016; Pace et al., 2011). When subclover constitutes a high proportion of ewe diets, breeding troubles may occur if subclover is grazed during its early stages of growth, since the formononetin oestrogen is likely to be present only at this stage (Nichols, 2017; Nichols, 2007). Subclover also contains the oestrogenic compounds genistein and biochanin A, but these compounds are of less concern (Nichols, 2017).