Bloat
Like many other forage legumes such as alfalfa or other clover species, red clover may cause bloat in livestock. This risk depends on intake and there are several ways to reduce it. It may be preferable to avoid pure stands of red clover and prefer mixed stands of red clover with grasses or legume species that are not prone to produce bloat, such as chickpea and sainfoin. Hungry livestock should be prevented from entering pure stands of red clover, for instance by feeding dry forages to them beforehand. Another method consists in preventing consumption peaks by keeping livestock in the stand at night. Risk of bloat decreases with plant age: livestock entering a full-bloom red clover stand have less risk of bloat than animals grazing a younger stand (Dalto et al., 2009; Kopp, 2003).
Urolithiasis
Red clover, as other clovers and forage legumes, may cause an increase in urinary calculi (clover stones) in sheep (Nagy, 2009; Hall, 2007). This may be due to the presence of benzocoumarins (a class of phytoestrogens) (Hall, 2007).
Reproductive disorders
Red clover contains several isoflavones, including daidzein, genistein, formononetin and biochanin A (Steinshamn, 2010; Saviranta et al., 2008; Cox et al., 1974). Cultivars with high isoflavone levels may have estrogen-like effects on animals. These compounds may disrupt reproductive cycles or impair fertility in sheep (McDonald et al., 1994). Reproductive disorders were also observed in sows fed red clover (Ballarini et al., 1977). In ewes, isoflavones were more concentrated in certain tissues (kidneys) than in muscles, making it unlikely that such compounds can be found in meat (Urpi-Sarda et al., 2008). Cattle appear to be less sensitive to these compounds (Dewhurst et al., 2009). Feeding red clover to dairy cows might increase concentrations of formononetin, daidzein and equol (an isoflavandiol metabolized from daidzein) in milk (Andersen et al., 2009; Mustonen et al., 2009; Steinshamn et al., 2008a). However, the intake of red clover had no influence on the equol content of meat (Moorby et al., 2004). As noted in Environmental impact, the excretion of isoflavones raises environmental concerns (Tucker et al., 2010).
Anthelmintic effect
In finishing lamb systems, red clover, like other legume forages, can contribute to the control of nematode parasites. Lambs grazing red clover had lower faecal egg counts and improved live-weight gains compared to lambs grazing ryegrass. However, red clover pasture increased re-infection of grazing lambs with Trichostrongylus species compared to ryegrass following anthelmintic treatment (Marley et al., 2005).