Nitrate poisoning
Like other cereal forages, wheat forage can accumulate nitrates and careful attention must be paid to nitrate content, particularly when feeding pregnant livestock. Forages containing 350-1130 mg/kg (DM basis) of NO3 nitrogen should be limited to 50% of the total diet for pregnant animals to prevent early term abortion or reduced breeding performance (Cash et al., 2002). In hay, nitrate accumulation may be an issue if high levels of N fertilizer have been applied. Ensiling wheat forage is safer than making hay because it reduces nitrate levels provided that the fermentation process lasts more than 30 days (Boyles et al., 2010).
Bloat
Wheat pastures are known to cause frothy bloat, which occurs when rumen gasses are trapped in the rumen fluid instead of being removed by eructation. In the USA, frothy bloat is known to cause death in young cattle grazing wheat pastures and high losses have been reported in the past. Bloat typically happens on lush wheat pastures, with low dry matter and fibre content, and high protein and soluble nitrogen fractions. These conditions may occur in autumn or early spring. In order to prevent bloat, hungry cattle should not enter the stand and/or should be supplemented with fibrous roughages (KSU, 1998; Horn et al., 1977).
Grass tetany
Grass tetany generally affects dairy cattle, beef cattle, sheep and goats in the temperate regions of the world when they receive inadequate available Mg in the diet (Dalley, 2004). Wheat forage, like other lush growing pastures, may have a low Mg content after intensive growth even during winter (KSU, 1998; Bohman et al., 1983). This problem often occurs when the crop has received large amounts of water (rainy spring) and has been heavily fertilized with nitrogen and potassium because Mg is leached by water and fertilizer. In some cases, the Mg level is adequate, but Mg availability is reduced if the K:(Ca+Mg) ratio exceeds 2.2 (Agdex, 2009). Livestock grazing unbalanced pasture, or pasture with a low Mg content, have low Mg in their blood. This phenomenon is of utmost importance in high producing animals, which require more Mg for fat mobilization and subsequent milk production. The recommended safe level of Mg in forage is 2.0 g/kg DM for lactating or pregnant cattle (Grunes et al., 1970; NRC, 2000). However, if N and K contents are high, the Mg concentration should be at least 2.5 g/kg DM (Grunes et al., 1984). This results in grass tetany symptoms: nervousness, twitching and further staggering, collapsing and convulsions that may cause death (Dalley, 2004). It is possible to prevent the problem by applying Mg fertilizer to the sward. It is also possible to feed the animal with an adequate mineral supplement. An adequate energy feed supplementation may also help in solving the problem (Agdex, 2009; KSU, 1998).
Hay irritation
Rough-awned varieties of wheat may cause soreness and irritation to the mouth, lips, gums and lower surface of the tongue in cattle. Ensiling (rather than baling) such crops may alleviate this problem. This issue may also be reduced by harvesting at the late-boot stage rather than at the dough stage (Boyles et al., 2010).