Ileal digestibility and endogenous protein losses of milk replacers based on whey proteins alone or with an enzyme-treated soybean meal in young dairy calves

摘要

Our objective was to measure and compare apparentileal digestibility, standard ileal digestibility, andtrue ileal digestibility of crude protein (CP) and aminoacids (AA) in milk replacers (MR) containing all milkproteins (WPC) or with 50% of the CP provided byan enzyme-treated soybean meal (ESBM). A T-cannulawas placed in the ileum of 9 Holstein calves (8 malesand 1 freemartin female) at approximately 15 d of age.After 2 wk postsurgery, calves were randomly assignedto a 3 × 3 replicated Latin square with 5-d periods.Calves were fed twice daily at a rate of 2% (dry matter)of body weight (1.25 kg/d on average), reconstitutedto 15% solids, and adjusted weekly. No starter was offeredto minimize rumen development. Digesta sampleswere collected continuously during 12 h on d 4 and5 of each period. Basal endogenous losses of AA andCP were estimated by feeding an N-free MR to eachcalf during 1 period. Total endogenous losses (basal +specific; END_(total)) were estimated by multivariate regressionof the chi-squared distances between digestaand reference protein AA profiles. Ileal digesta pH withthe ESBM diet was lower than that with the WPCdiet. According to the piecewise nonlinear model ofpH fluctuation, digesta pH during ESBM decreasedmore slowly after feeding and reached its nadir laterthan with the WPC diet. Diet did not affect averagedaily gain, but calves on the ESBM diet showed a biggerincrement of withers height and lower mean fecalscores. The basal endogenous losses of AA and CP were13.9 ± 1.1 and 22.4 ± 1.1 g/kg of dry matter intake,respectively. The estimated END_(total) of AA and CPwas higher with ESBM than with WPC. Accordingly,apparent ileal digestibility and standard ileal digestibilityof most AA, CP, and total AA were lower ortended to be lower with ESBM. However, true ilealdigestibility did not differ between diets for CP and allAA except Ala and Ile, which were greater with WPC,and Arg, which tended to be greater with ESBM. Inagreement with the estimated differences in END_(total),we found that flows of digesta DNA and crude mucinwere greater with ESBM. Substitution of 50% of theprotein from whey with enzymatically treated soybeanmeal did not affect major nutrient digestibility or calfgrowth and even improved fecal consistency. Adjustingdigestibilities of CP and AA in MR by endogenousprotein losses is crucial when comparing bioavailabilityof alternative proteins and milk proteins.