Bloat
White clover can cause bloat in ruminants when they graze clover-rich swards or pure clover. It can be prevented by gradually introducing livestock to the pasture, and by supplementing them with hay or straw. In extreme situations, anti-foaming agents can be administered directly into the rumen (Lane et al., 2000; Jouglar et al., 1983).
Phytoestrogens
White clover may contain low levels of phytoestrogens (0.02-0.06% of DM) compared to red clover (Trifolium pratense) (1-2.5%) (Saloniemi et al., 1995). Coumestrol is sometimes the main active agent (Carlsen et al., 2008). However, the phytoestrogen level is too low to have adverse effects on reproduction.
Hydrogen cyanide poisoning
White clover is polymorphic for cyanogenesis; cyanogenic and acyanogenic plants can exist in the same population, and the cyanide concentration can change during the growing season (OGTR, 2008; Stochmal et al., 1997). Some varieties rich in HCN are not recommended, especially for lactating animals (Lehmann et al., 1991).
Other secondary metabolites
Several other secondary compounds are present in white clover: saponins, condensed tannins, isoflavones and isoflavanones all have various effects on ruminants. However, these effects are generally limited because of the low level of secondary metabolites and because white clover is mostly used as a component of pasture with other forages. The effects of these compounds are well described in Carlsen et al., 2008.