Postruminal casein infusion and exogenous glucagon-like peptide 2 administration differentially stimulate pancreatic a-Amylase and small intestinal a-Glucosidase activity in cattle

Authors: TROTTA, RONALD - University Of Kentucky; SWANSON, KENDALL - North Dakota State University; Klotz, James; HARMON, DAVID - University Of Kentucky

Submitted to: Journal of Nutrition
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/4/2023
Publication Date: 8/10/2023
Citation: Trotta, R.J., Swanson, K.C., Klotz, J.L., Harmon, D.L. 2023. Postruminal casein infusion and exogenous glucagon-like peptide 2 administration differentially stimulate pancreatic a-Amylase and small intestinal a-Glucosidase activity in cattle. Journal of Nutrition. https://doi.org/10.1016/j.tjnut.2023.08.009.
DOI: https://doi.org/10.1016/j.tjnut.2023.08.009

Interpretive Summary: Conventionally raised cattle are typically finished on a high concentrate diet that contains high levels of soluble carbohydrates or starch to allow for more growth and improved product quality. Ruminants are well equipped to ferment structural carbohydrates in forage-based diet in their foregut. When grain-based diets containing large amounts of starch are fed, significant amounts of starch can escape rumen fermentation of the foregut and enter the small intestine for potential digestion. Because this is a departure from what the ruminant was designed to digest, it has been shown that ruminant small intestinal starch digestion could be limited by inadequate pancreatic and/or intestinal carbohydrase enzymatic activity and is a possible area to improve production efficiency. The milk protein casein has been shown to increase pancreatic mass in ruminants and administration of the hormone glucagon-like peptide 2 has been shown to increase small intestinal growth. The objective of this experiment was to use post-ruminal casein infusion and glucagon-like peptide 2 administration to study limitations of small intestinal starch disappearance in cattle receiving a continuous infusion of starch. This work demonstrated that cattle receiving the casein treatment had increased pancreatic mass and the those that received the glucagon-like peptide 2 treatment had increased small intestinal mass. These treatments also had respective increases in enzymatic activities associated with starch digestion. This study provided a novel in vivo model to study physiological mechanisms that could be used to improve small intestinal starch digestion in cattle consuming a high-grain diet and will be of interest to other researchers looking to improve the production efficiency of cattle.

Technical Abstract: Small intestinal (SI) starch digestion in ruminants is potentially limited because of insufficient activity of pancreatic and/or SI carbohydrases. The objective was to use postruminal casein infusion and glucagon-like peptide 2 (GLP-2), known stimulators of pancreatic and SI function, to evaluate limitations of SI starch digestion by determining their effects on organ growth, carbohydrase activity, and postruminal starch digestion. Holstein steers (n=24; 250 ± 23 kg BW) were limit-fed an alfalfa cube-based diet. Steers received continuous abomasal infusion of 3.94 g/kg of BW of raw corn starch combined with either 0 or 1.30 g/kg of BW of casein. Steers received subcutaneous injections in two equal portions daily of excipient (0.5% bovine serum albumin) or 100 µg/kg of BW GLP-2 per day. This resulted in four treatments: control, casein, GLP-2, and casein + GLP-2. At the end of the 7-d treatment period, steers were slaughtered for tissue collection. Data were analyzed using the MIXED procedure of SAS. Postruminal casein infusion increased (P = 0.03) pancreatic mass by 12.6%, total pancreatic a-amylase activity by 50%, and postruminal starch disappearance from 96.7% to 99.3%. Exogenous GLP-2 increased (P < 0.01) total SI mass and SI mucosal mass by 1.2 kg and 896 g, respectively. Relative to control, GLP-2 and casein + GLP-2 increased (P = 0.04) total SI a-glucosidase activity by 83.5%. Total SI maltase, isomaltase, and glucoamylase activity was 90%, 100%, and 66.7% greater for GLP-2 and casein + GLP-2 steers compared with control. These data demonstrate that casein increased pancreatic a-amylase activity, GLP-2 increased SI a-glucosidase activity, and the combination of casein and GLP-2 increased both pancreatic a-amylase activity and SI a-glucosidase activity. This approach provides a novel model to understand physiological mechanisms that might improve SI starch utilization and efficiency of cattle consuming high-grain diets.