‘The truth about caustic and urea treated grain,and rumen PH’

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The use of slow-release rumen conditioners like Acid Buf to optimise rumen pH and reduce the risk of sub-acute ruminal acidosis (SARA) has become widespread in recent years, and for good reason.

More effective in buffering the acid produced from highly fermentable feeds such as rolled cereals, these conditioners have largely superseded traditional mineral-based rumen buffers, such as sodium bicarbonate, limestone flour and magnesium oxide.

There’s also now evidence that the way in which sodium bicarbonate in particular lowers acid loading in the rumen will negatively affect feed conversion efficiency (FCE).

The recently promoted claims that feeding caustic - or urea-treated grains can act as a substitute for a high quality slow-release rumen conditioner is therefore highly questionable. It is also not supported by scientific data.

With caustic-treated grain, the addition of water plus sodium hydroxide (caustic soda at rates between 3-5%) causes a chemical reaction that de-lignifies the seed coat (helping to increase digestibility) and results in the production of small amounts of sodium bicarbonate as a by-product, mostly in the form of free sodium.

The bigger concern is that free sodium and sodium bicarbonate – whether from caustic soda-treated cereals or when added directly as a buffer – reduce acid loading by speeding up feed passage through the rumen. There might be less starch fermented in the rumen, and so less acid is produced, but much of that starch remains encapsulated in fibre and cannot be utilised by the lower digestive tract.

The result is a loss of fermentable energy as both fibre and starch end up in the manure. This energy loss also limits how much of the additional protein available in caustic-treated grains can be captured by rumen microbes.

This overall reduction in feed conversion efficiency (FCE) when feeding these treated cereal grains is supported by research carried out by the US Agricultural Research Service that was published as long ago as 1993. More recently, a 2012 study at the University of Georgia highlighted a 8.8% reduction in FCE (see Figure 1a) and a 4.5% drop in fat corrected milk (see Figure 1b) when using sodium bicarbonate compared to the higher performing slow-release rumen conditioner Acid Buf.

Treating grains by adding urea, traditionally used as a preservative to help store the grain and prevent spoilage, is common practice. As a result, the added non-protein nitrogen from the urea can increase crude protein contents and slightly increase pH. However, this slight increase in pH of the grain is unlikely to provide sufficient rumen buffering on its own.

When urea-treated grains are fed, total starch levels are generally increased on the basis that it is safer as a result of the higher pH. However, research data from Michigan State University shows that the acid load produced as a by-product of rumen fermentation is still up to five times higher than the effect from the pH of the feeds themselves. Therefore, in reality the potential pH benefits of the feed are going to be relatively low in comparison to the total acid load produced in the rumen by fermentation, especially when overall diet starch levels are being increased.

So whilst treating cereal grains with different products is a useful way to store grain and increase grain feed value (by improving digestibility and protein content), when it comes to rumen pH buffering capacity, there’s little to be gained.

Just remember to base buying decisions on the facts, backed by sound scientific data.