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Chaff slows eating.

Horses are naturally adapted to eat roughage. It takes longer to eat and digest than concentrate feed.

It has become popular to add chaff or chopped straw to concentrate feed to make horses eat it more slowly. But there has been little scientific work to demonstrate that the practice has the desired effect.

Now a study by Dr Andrea Ellis, of Nottingham Trent University, and co-workers at Waltham and Spillers shows that it does.

They measured the time taken for horses to eat 1kg of various feeds and the average number of chews per minute. They evaluated the effect of including 10%, 20% or 30% of straw, chopped into either 2.5cm or 4cm lengths, to a trial pellet fibre mix (containing 10% short cropped lucerne).

The rate of chewing remained about the same regardless of the type of food fed. But the type of food had a significant effect on the rate of intake and the total number of chews per kg.

Diets containing added straw were eaten much more slowly than their normal diet mix, (containing 50% pellets, 15% lucerne-straw chaff, and 35% soaked sugar beet pulp), their normal diet and the trial pellets on their own. There was no significant effect of increasing the straw content above 20%, although the intake rate did decrease, leading to an increased time spent on feed intake for 1kg of feed as illustrated below.

So adding chaff can result in horses spending more time eating their concentrate ration.

This could have health benefits for the horse. Increased buffering by saliva in the stomach may reduce the risk of stomach ulcers. Choke may be less likely because of more saliva being mixed with the bolus of food, and the food being eaten more slowly and chewed more thoroughly.

One interesting finding was that the normal diet mix was eaten more quickly than a trial diet containing similar amounts of chaff (but without the sugar beet pulp). The investigators suggest that this was probably due to the higher moisture content when the soaked sugar beet pulp was included. Chopped straw may only have a beneficial effect in slowing intake if it is added to a high dry matter diet. The investigators suggest that this is an area that needs more research.

Source: Equine Nutrition Conference, Hannover.

Further reading: Adding chopped straw to concentrate feed: The effect of inclusion rate and particle length on intake behaviour of horses. Andrea D Ellis, Samantha Thomas, Kate Arkell, Patricia Harris. Proc Equine Nutrition Conference Pferdeheilkunde (2005) 21, 35 - 37.

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