Investigations on preileal digestion of starch from grain, potato and manioc in horses.

The study investigates how well different forms of starchy feeds, including grain, potatoes, and manioc, are digested before reaching the ileum (a part of the small intestine) in horses.

Methodology

• Seven horses with a fistula in their jejunum (a part of the small intestine before the ileum) were fed a variety of starchy foods including different types of grains, fresh potatoes, and processed manioc.
• The grains were fed in various forms: whole (oats, corn), rolled (oats, barley), crushed, ground, and expanded (corn), while potatoes were given fresh and manioc in a rolled form.
• In one part of the study, ground corn was also fed in combination with an enzyme called amylase, which aids in the digestion of starches.
• The feeds were offered either in isolation or in combination with alfalfa meal or hay.
• Two meals were served per day, 12 hours apart, with the starch intake being mostly about 2 grams per kilogram of body weight per meal, except during one period when oats (3.9 grams of starch per kilogram of body weight) and expanded corn (1.4 grams per kilogram of body weight) were being fed.
• The researchers collected jejunum contents from the horses 11 times from one to eleven hours after the morning meal for 15 minutes each time.
• The amount of starch in the chyme (semi-fluid mass of partly digested food) was determined polarimetrically, a method that measures the rotation of polarized light, which changes when it passes through certain substances like starch.

Results

• The digestibility of the starch in the feeds before it reached the ileum, also known as preileal digestibility, was calculated using two methods: the marker method (using chronic oxide at 0.25% dry matter), and by estimating the total flow of chyme through the jejunoileal part of the intestines during the 12 hours after a meal.
• The results from both methods largely agreed with one another.
• Oat starch was found to be the most digestible form of starch with a preileal digestibility of 80-90%, regardless of the dose, method of preparation, or whether it was combined with hay.
• On the other hand, whole or crushed corn had a preileal digestibility of around 30%, and barley 26%.
• However, the method of preparation could influence digestibility for some feeds: grinding corn increased preileal digestibility to 51%, and expanding it (inflating it with steam) raised it to 90%.
• The addition of amylase improved the digestibility of ground corn by an absolute 10%.
• The preileal digestibility of potato or manioc was notably low at less than 10%.
• Expectably, individual factors in the horse, like the intensity of chewing and the horse’s amylase activity, significantly influenced the preileal digestibility of starch.

Overall, the study provides valuable insights into how different starchy feeds and their method of preparation can impact their digestibility in horses, which has implications for horse nutrition and feed management.