Toxicity of urea and ammonia-treated straws
Treating straw with urea or ammonia can cause toxicity in ruminants. Large amounts of urea entering the rumen may result in the production of excess NH3 by the rumen bacteria. Part of this ammonia cannot be fully detoxified by the liver and passes into the blood stream, causing ataxia (at 29 mg/L blood in cattle) or death (at 42 mg/L in cattle and 32 mg/L in sheep) (Rogers, 1999). It is thus important that livestock is progressively introduced to treated straws so that rumen bacteria can adapt to the increased levels of urea, thus preventing the sudden release of NH3 in the rumen (Suttie, 2000; Rogers, 1999).
Other concerns
Concerns about straws tend to be specific. For instance, some straws (wheat, barley) contain awns that may lower their palatability. Some legumes, like faba bean (Vicia faba) have coarse, woody stems (Suttie, 2000). The high fibre content of oat straw is known to cause digestive and bowel occlusions (phytobezoars) in horses (Kohnke et al., 1999). The straw of chickpea (Cicer arietinum) has a very high oxalic acid content, is unpalatable, and reputed to be toxic (Suttie, 2000).