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

摘要

Starch digestion in the small intestine in ruminants isrelatively lower compared with that in monogastric animals,likely due to low pancreatic α-amylase secretion.Previous studies suggested that leucine could increasepancreatic α-amylase secretion in the small intestine ofheifers cannulated with abomasal, duodenal, and ilealcatheters. However, the surgical procedures probablyhave an effect on pancreatic function. Thus, we usedrumen-protected leucine (RP-Leu) to explore its effecton small intestinal digestion of starch in calves withoutany surgery in 3 experiments. The first experiment wasto explore whether RP-Leu could improve post-ruminalstarch digestion in 5-mo-old calves (158 ± 19 kg bodyweight ± standard deviation). We found that RP-Leudid not affect rumen fermentation profile or wholetractstarch digestibility, but it increased blood glucoseconcentration and fecal pH and decreased fecal propionatemolar proportion. Additionally, RP-Leu increasedfibrolytic genera Ruminiclostridium and Pseudobutyrivibrioand decreased the amylolytic genus of Faecalibacterium.The second experiment compared RP-Leu andrumen-protected lysine (RP-Lys) for their effects onpost-ruminal starch digestion in 6-mo-old calves (201± 24 kg body weight). The responses of blood glucoseconcentration, fecal pH, fecal propionate proportion,and starch digestibility to RP-Leu supplementationwere similar to those observed in experiment 1. Cellulolyticfamily Ruminococcaceae and BacteroidalesBS11 gut group tended to be increased by RP-Leu. Incontrast, RP-Lys showed no significant influence on theabove measurements. The third experiment determinedthe interaction between RP-Leu and rumen-escapestarch (RES) on the small intestinal digestion of starchin 8-mo-old calves (289 ± 26 kg body weight). An interactionbetween RP-Leu and RES levels was observed infecal butyrate concentration and the relative abundanceof family Bacteroidaceae, and genera RuminococcaceaeUCG-005 and Bacteroides. We found that RP-Leutended to increase the abundance of fecal Firmicutesand decrease Spirochaetae. In conclusion, RP-Leu, butnot RP-Lys, increased blood glucose concentration anddecreased the amount of starch fermented in the hindgutin a RES dose-dependent manner, suggesting thatRP-Leu might stimulate starch digestion in the smallintestine.