The objective of this trial was to study the effects of different dietary levels of crude protein (CP) on intake and apparent total tract, intestinal, and ruminal digestibilities of nutrients in Holstein x Zebu steers. The diets contained [dry matter (DM) basis]: 10.5, 12, 13.5, or 15% of CP and a forage (Tifton 85):concentrate ratio of 65:35. Four castrated animals averaging 487.3 kg of body weight at the beginning of the trial and fitted with both abomasum and rumen cannulas were randomly assigned to a 4 x 4 Latin square. Each experimental period lasted 20 days with 10 days for diet adaptation and 10 days for sample collection (feces, abomasum digesta, ruminal content, and urine). Chromium oxide was used as the external marker for determination of fecal excretion. Increasing dietary levels of CP did not change significantly the intakes of dry matter (DM), organic matter (OM), neutral detergent fiber (NDF), and total digestible nutrients (TDN). However, intake of CP increased while that of ether extract (EE) and non-fiber carbohydrate (NFC) decreased with the increment of dietary CP. Apparent total tract digestibilities of DM, OM, and CP all increased linearly by increasing the dietary CP from 10.5 to 15%. Except for intestinal digestibility of CP that increased 2.77 percentage units for each 1% increment in the diet CP, the different dietary CP levels did not affect intestinal and ruminal digestibilities of all remaining nutrients in the current trial.
neutral detergent fiber; acid detergent fiber; neutral detergent insoluble nitrogen; acid detergent insoluble nitrogen; nonfiber carbohydrate; lignin
