Apparent and true prececal and total digestibility of protein in diets with different protein levels in equines

This work aimed to determine the apparent prececal, postileal and total digestibility of crude protein (CP) in diets for equines and to estimate the true prececal, postileal and total digestibility of CP. Five ileum fistulated foals, were ad libitum fed, three times a day (8 a.m., 2 p.m. and 8 p.m) with five diets with 50:50 forage:concentrate ratio. The diet consisted on coast-cross hay and concentrate of corn, premix and different levels of soybean meal. Samples of ileal digesta were collected in the morning period, 30 minutes after diet supply and successively at 60 minutes, with the total of six samples for each animal, by each period. A completely randomized block design was used with five treatments (levels of CP) and four blocks (periods). The true digestibility of protein in several segments was estimated regressing the quantity of nitrogenous compound (N) apparently prececal and total digested, on the quantity of N intake, and the quantity of N apparently postileal digested, on the quantity of N that arrived in the large intestine. The levels of CP in the diet were negatively related to the prececal digestibility of dry matter. The average apparent prececal digestibility of protein was calculated in 44.81% and the apparent postileal digestibility of protein linearly increased in function of the levels of dietary CP. The total apparent maximum digestibility of CP of 79.98% was estimated with the level of 17.92% of ingested CP. The true prececal, postileal and total digestibility of CP were estimated as 53.97, 96.5 and 95.11%, respectively. The small intestine was the place where the greater digestion of dietary CP occurred.