The influence of dietary fiber digestibility on the nitrogen requirements of mature horses.

This research article examines whether the digestibility of the fibrous parts of a horse’s diet influences its dietary nitrogen requirements. Mature male (gelding) horses that were not working and were being fed maintenance diets were used in this study.

Study Design

The experiment used a 4 x 4 Latin square design. This is a statistical method often used in experiments which involve comparing multiple treatments or conditions. Here, the researchers wanted to compare the effects of four different diets on the nitrogen requirements of horses.

• Diet 1 contained corn and soybean meal.
• Diet 2 contained corn, corn oil, and urea.
• Diet 3 contained corn, soybean meal, straw, and urea.
• Diet 4 contained corn, alfalfa, and urea.

In diets 2 and 3, urea supplied half of the total nitrogen content, and in diet 4, it accounted for 39% of the total nitrogen. The researchers ensured that each diet was fed according to National Research Council recommendations for daily energy intake for mature horses, and met or exceeded their daily nitrogen requirements.

Nitrogen Digestibility

The researchers used a measure called ‘true absorbed nitrogen’ to understand nitrogen digestibility. This was calculated by subtracting the nitrogen associated with neutral detergent fiber – a measure of the indigestible part of the feed – from the total nitrogen intake. True digestibilities of nitrogen ranged from 92.4% to 95.9%.

Nitrogen Excretion

Even though none of the diets were deficient in nitrogen, the diet containing straw (diet 3) was found to have a significantly lower apparent nitrogen digestibility at 64% when compared to other diets which had nitrogen digestibility ranging between 72.5% to 79.6%. This could be due to the fibrous nature of straw which is harder to digest. Increased fecal excretion of different nitrogen fractions was observed with this diet.

The study suggests that the digestibility of dietary fiber can influence the nitrogen requirements of horses, although further research is required to understand this complex relationship fully.