Effect of Dietary Forage: Concentrate Ratio on Pre-Caecal and Total Digestive Tract Digestibility of Diverse Feedstuffs in Donkeys as Measured by the Mobile Nylon Bag Technique.

Abstract

Simple SummaryMore and more researchers are paying attention to the nutrition of donkeys, but the research on the digestion of feed in the prececum and the whole digestive tract of donkeys is very rare. In this study, a Latin square experimental design was applied to determine the effect of dietary forage: concentrate (F:C) ratio on pre-caecal and total digestive tract digestibility of four feedstuffs in donkeys was measured by the mobile nylon bag technique. High-forage diets resulted in the lowest mean retention time of bags at the ileo-caecal junction. Starchy corn meal in comparison with soybean meal encountered greater extent of prececum digestion and prececum fiber digestion in fibrous forages contributed over 50% percent of total tract digestion. The nutrient composition of the feed, especially the fiber content was the main factor that affects the digestibility contribution of the prececum. The domestic donkey is a unique equid species with specific nutritional requirements, however, limited laboratory evidences are available to address the digestibility contribution of the prececum in relation to the total digestive tract. In the present study, six caecum-fistulated adult female Xinjiang donkeys served as the experimental animals in a 3 × 3 Latin square design, and mobile nylon bag technique was applied to determine the effect of dietary F:C ratio on pre-caececum and total digestive tract digestibility of rice straw, alfalfa hay, corn meal, and soybean meal. The dietary treatments included: (1) HF, a high-fiber ration (F:C = 80:20), (2) MF, a medium-fiber ration (F:C = 55:45), and (3), LF, a low-fiber ration (F:C = 35:65). The experiment consisted of three consecutive Latin square periods, and each period lasted 25 days. In each period, the animals were administrated naso-gastrically nylon bags (38 μm pore size) containing aforementioned feeds. After 1.5 h intubation, the bags were checked once an hour and collected at the ileo-caecal junction (small intestine bag, D1) and in the feces (fecal bag, D2). Regardless whatever feeds were introduced, the percentage of bag collected (BC) was quadratically (HF) or linearly (MF and LF) increased against different fixed bag collection time. The highest BC occurred in MF (73.8%), but no significant difference was observed between HF (62.3%) and LF (50.8%). The lowest mean bag retention time was observed in HF (2.7 h), and no significant difference occurred between MF (4.6 h) and LF (5.0 h) diets. For each feed, D1 and D2 digestibility for DM, CP, NDF, and ADF did not differ among three dietary treatments (p > 0.05). Regardless of whatever diets were fed to the donkeys, D2 digestibility for DM and CP among the feeds ranked as: soybean meal > corn meal > alfalfa hay > rice straw (p < 0.01). D1 digestibility for DM among the feeds ranked as: corn meal > soybean meal > alfalfa hay > rice straw (p < 0.01). D1 digestibility for CP among the feeds ranked as: soybean meal > corn meal > alfalfa hay > rice straw (p < 0.01). In summary, dietary forage: concentrate ratio did not affect pre-caecal or total tract nutrient digestibility. The fiber level in feeds was the main limiting factor to affect the digestibility contribution of the pre-caecum in relation to the total digestive tract.