Technical note: Establishment of an ileal cannulation technique in preweaning calves and use of a piecewise regression approach to evaluate effects on growth and pH fluctuation of ileal digesta

Nutrient digestibility and endogenous protein losses in the foregut and small intestine of weaned dairy calves fed calf starters with conventional or enzyme-treated soybean meal

The aims of this experiment were (1) to compare the effects of a soybean meal with an enzymatic treatment (ESBM) to reduce the concentration of antinutritional factors versus a standard soybean meal (SBM) on foregut and small intestine digestion in weaned dairy calves and (2) to estimate the endogenous losses of crude protein (CP) in the small intestine. Our hypothesis was that a diet containing ESBM instead of SBM would improve ruminal and small intestine digestion and absorption of nutrients. A T-cannula was placed in the duodenum, and a second T-cannula was installed in the distal ileum of 12 Holstein calves at approximately 3 wk of age. Calves were weaned on d 42, and on d 50 they were assigned randomly to a quadruplicated 3 × 3 Latin square with 10-d periods. Digesta samples were collected on d 7 and 8 from the ileum and d 9 and 10 from the duodenum. The diets were fed for ad libitum intake and consisted of a calf starter (CS) of 20% CP with SBM as the main source of protein (CTRL), and an isonitrogenous CS with an ESBM instead of SBM (ENZT). A third diet with a low content of CP (10%) and no soy protein was fed to estimate endogenous N losses and digestibilities of test ingredients. Flows and digestibilities of nutrients were compared between CTRL and ENZT and their test ingredients (SBM vs. ESBM, respectively). Duodenal net flows of CP and total AA as well as ruminal microbial protein synthesis per kilogram of digested CP were greater, and flow of nonprotein N and CP true (corrected by endogenous and microbial flows) foregut digestibility were lower with ENZT than CTRL. The apparent small intestine digestibilities of CP and total AA were greater for ESBM than SBM, but there were no differences between the CTRL and ENZT diets. We observed no differences in digestibilities at the duodenum or ileum of starch or NDF, but true small intestine digestibilities of CP and all AA were greater with ENZT than CTRL. Total endogenous protein losses in the small intestine estimated from calves fed the low-CP with no soy protein diet were 37 ± 1.5 g of CP and 29 ± 1.4 g of AA/kg of DMI. These values may be considered the basal endogenous losses as they are similar to values obtained with the regression method, which estimates N losses when dietary N is null. Our results indicated that the inclusion of an ESBM improved the efficiency of ruminal microbial protein synthesis per digested kilogram of organic matter and CP, and increased CP and AA absorption in the small intestine despite a greater proportion of undigested dietary protein entering the duodenum.

Short communication: A pilot study to describe duodenal and ileal flows of nutrients and to estimate small intestine endogenous protein losses in weaned calves

The aims of this pilot study were (1) to evaluate the effect of an ileal and duodenal cannulation surgery on body weight and dry matter intake, (2) to estimate endogenous losses of crude protein (CP) and AA in the small intestine, and (3) to describe duodenal and ileal flows of nutrients in weaned dairy calves. Three Holstein male calves were fitted at 7 wk of life with a T-cannula at the terminal ileum and another cannula at the proximal duodenum. On wk 14 of life, calves were randomly assigned to a single 3 × 3 Latin square with 10-d periods. The 3 diets were fed ad libitum and consisted of a control calf starter (CS) with conventional soybean meal (SBM) as the main source of protein (CTRL), an isonitrogenous (20% CP) CS with an enzyme-treated SBM as the main source of protein (ENZT), and a CS with low content of CP (10%) and no soy protein (LOCP). Flows and digestibilities of nutrients were compared between the soy-based high-protein diets (HICP) and LOCP, and between CTRL and ENZT. Final data were only available from 2 calves per diet (n = 2) because cannulas from 1 calf became inoperative after the first collection period. Duodenal flows of CP, total AA, nonprotein nitrogen, microbial N, and fatty acids, as well as apparent duodenal digestibility of starch, were greater for HICP than for LOCP, indicating a greater foregut microbial activity and digestion. The apparent ileal digestibility (AID) of organic matter, CP, and total AA were greater for HICP than for LOCP. Duodenal net flow of CP was greater for ENZT than for CTRL, but flow of AA was not different. On the other hand, duodenal flow of microbial N was greater, and flows of nonprotein N and starch were lower for the ENZT diet, suggesting a more efficient microbial activity in the rumen. Even though CTRL had a greater AID when compared with ENZT, the AID of CP and AA were greater for enzyme-treated SBM than for SBM. Endogenous losses in the small intestine per kilogram of duodenal dry matter flow were 47 ± 15 and 37 ± 12 g/d, and the true ileal digestibilities for the HICP diets were 86 ± 0.1 and 87 ± 0.1% for CP and AA, respectively. An optimal supply of CP and the inclusion of an enzyme-treated SBM improved the efficiency of microbial digestion and increased AA absorption. Although further research with greater biological replication is needed, our results indicate that there is potential to improve digestion and absorption of proteins through dietary strategies in young weaned calves.

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

Our objective was to measure and compare apparent ileal digestibility, standard ileal digestibility, and true ileal digestibility of crude protein (CP) and amino acids (AA) in milk replacers (MR) containing all milk proteins (WPC) or with 50% of the CP provided by an enzyme-treated soybean meal (ESBM). A T-cannula was placed in the ileum of 9 Holstein calves (8 males and 1 freemartin female) at approximately 15 d of age. After 2 wk postsurgery, calves were randomly assigned to 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), reconstituted to 15% solids, and adjusted weekly. No starter was offered to minimize rumen development. Digesta samples were collected continuously during 12 h on d 4 and 5 of each period. Basal endogenous losses of AA and CP were estimated by feeding an N-free MR to each calf during 1 period. Total endogenous losses (basal + specific; ENDtotal) were estimated by multivariate regression of the chi-squared distances between digesta and reference protein AA profiles. Ileal digesta pH with the ESBM diet was lower than that with the WPC diet. According to the piecewise nonlinear model of pH fluctuation, digesta pH during ESBM decreased more slowly after feeding and reached its nadir later than with the WPC diet. Diet did not affect average daily gain, but calves on the ESBM diet showed a bigger increment of withers height and lower mean fecal scores. The basal endogenous losses of AA and CP were 13.9 ± 1.1 and 22.4 ± 1.1 g/kg of dry matter intake, respectively. The estimated ENDtotal of AA and CP was higher with ESBM than with WPC. Accordingly, apparent ileal digestibility and standard ileal digestibility of most AA, CP, and total AA were lower or tended to be lower with ESBM. However, true ileal digestibility did not differ between diets for CP and all AA except Ala and Ile, which were greater with WPC, and Arg, which tended to be greater with ESBM. In agreement with the estimated differences in ENDtotal, we found that flows of digesta DNA and crude mucin were greater with ESBM. Substitution of 50% of the protein from whey with enzymatically treated soybean meal did not affect major nutrient digestibility or calf growth and even improved fecal consistency. Adjusting digestibilities of CP and AA in MR by endogenous protein losses is crucial when comparing bioavailability of alternative proteins and milk proteins.

Decreased amylolytic microbes of the hindgut and increased blood glucose implied improved starch utilization in the small intestine by feeding rumen-protected leucine in dairy calves

Starch digestion in the small intestine in ruminants is relatively lower compared with that in monogastric animals, likely due to low pancreatic α-amylase secretion. Previous studies suggested that leucine could increase pancreatic α-amylase secretion in the small intestine of heifers cannulated with abomasal, duodenal, and ileal catheters. However, the surgical procedures probably have an effect on pancreatic function. Thus, we used rumen-protected leucine (RP-Leu) to explore its effect on small intestinal digestion of starch in calves without any surgery in 3 experiments. The first experiment was to explore whether RP-Leu could improve post-ruminal starch digestion in 5-mo-old calves (158 ± 19 kg body weight ± standard deviation). We found that RP-Leu did not affect rumen fermentation profile or whole-tract starch digestibility, but it increased blood glucose concentration and fecal pH and decreased fecal propionate molar proportion. Additionally, RP-Leu increased fibrolytic genera Ruminiclostridium and Pseudobutyrivibrio and decreased the amylolytic genus of Faecalibacterium. The second experiment compared RP-Leu and rumen-protected lysine (RP-Lys) for their effects on post-ruminal starch digestion in 6-mo-old calves (201 ± 24 kg body weight). The responses of blood glucose concentration, fecal pH, fecal propionate proportion, and starch digestibility to RP-Leu supplementation were similar to those observed in experiment 1. Cellulolytic family Ruminococcaceae and Bacteroidales BS11 gut group tended to be increased by RP-Leu. In contrast, RP-Lys showed no significant influence on the above measurements. The third experiment determined the interaction between RP-Leu and rumen-escape starch (RES) on the small intestinal digestion of starch in 8-mo-old calves (289 ± 26 kg body weight). An interaction between RP-Leu and RES levels was observed in fecal butyrate concentration and the relative abundance of family Bacteroidaceae, and genera Ruminococcaceae UCG-005 and Bacteroides. We found that RP-Leu tended to increase the abundance of fecal Firmicutes and decrease Spirochaetae. In conclusion, RP-Leu, but not RP-Lys, increased blood glucose concentration and decreased the amount of starch fermented in the hindgut in a RES dose-dependent manner, suggesting that RP-Leu might stimulate starch digestion in the small intestine.