# Advances in Intestinal Glucose Absorption Regulation for Ruminant Energy Efficiency Improvement

## TL;DR

This review explores how to improve energy efficiency in ruminants by enhancing glucose absorption in the small intestine, focusing on diet, gut microbes, and hormone signaling.

## Contribution

The paper systematically reviews mechanisms and methods to improve intestinal glucose absorption in ruminants, proposing novel strategies like artificial sweeteners and GLP-2 modulation.

## Key findings

- Functional amino acids like Leu and Phe may enhance pancreatic α-amylase activity to improve starch digestion.
- Glucose absorption in ruminants is influenced by diet, age, environment, and gut microbiota, but remains inefficient compared to fermentation.
- Artificial sweeteners and glucagon-like peptide 2-related modulation are proposed as potential strategies to boost glucose absorption.

## Abstract

Ruminant animals such as cattle and sheep mainly obtain energy from microbial digestion in the rumen. Under a high-grain diet, a large amount of starch can reach the small intestine, where digestion could yield more usable energy. However, ruminants have limited capacity to break starch into glucose and to absorb glucose into the body. An enzyme released by the pancreas is central to starch digestion, and certain dietary amino acids may increase this enzyme and improve starch use. The mechanisms enhancing glucose absorption in ruminants are less understood. This review summarizes how diet, age and development, environmental conditions, and gut microbes influence glucose absorption and describes the key sensing signals, transport steps, and hormone control involved. We also compare common methods used to measure glucose absorption and propose practical strategies to improve it, aiming to boost feed efficiency and livestock productivity.

Ruminants can use volatile fatty acids from rumen fermentation for energy, but substantial starch may bypass the rumen and enter into the small intestine under a high-grain diet. In theory, intestinal starch digestion is energetically more efficient than ruminal fermentation. However, ruminants have inherent limits in starch hydrolysis and glucose transport. Small intestinal starch digestion relies on pancreatic α-amylase. Several studies have indicated that functional amino acids (Leu or Phe) may enhance amylase secretion or activity to improve starch digestion. In contrast, strategies to increase glucose absorption efficiency in the small intestine have received less attention. Thus, this review focuses on the effects of diet, ontogeny, environment, and intestinal microbiota on intestinal glucose absorption and their potential mechanisms. The T1R2/T1R3 glucose-sensing pathways, transporting pathways, and related hormones within the small intestine were systematically reviewed. The advantages and limitations of major approaches regarding glucose absorption including portal vein intubation, nutrient perfusion, everted intestinal sacs in vitro, Ussing chamber, brush-border membrane vesicle, D-xylose test, organoid, and nanosensing are also discussed. Importantly, we propose potential strategies to improve small intestinal glucose absorption (e.g., artificial sweeteners and glucagon-like peptide 2-related modulation). Overall, this review summarizes promising regulatory targets to enhance small intestinal glucose absorption and improve energy efficiency in ruminants.