The impact of diet and arginine supplementation on pancreatic mass, digestive enzyme activity, and insulin-containing cell cluster morphology during the estrous cycle in sheep

Abstract

To determine the effect of feed intake and arginine treatment during different stages of the estrous cycle on pancreatic mass, digestive enzyme activity, and histological measurements, ewes (n = 120) were randomly allocated to 1 of 3 dietary groups; control (CON; 2.14-Mcal metabolizable energy/kg), underfed (UF; 0.6 × CON), or overfed (OF; 2 × CON) over 2 yr. Estrus was synchronized using a controlled internal drug release device for 14 d. At controlled internal drug release withdrawal, ewes from each dietary group were assigned to 1 of 2 treatments; Arg (L-Arg HCl, 155-μmol/kg BW) or Sal (approximately 10-mL saline). Treatments were administered 3 times daily via jugular catheter and continued until slaughter on d (day) 5 and 10 of the second estrus cycle (early luteal phase, n = 41 and mid-luteal phase, n = 39; yr 1) and d 15 of the first estrus cycle (late luteal phase, n = 40; yr 2). A blood sample collected from jugular catheters for serum insulin analysis before slaughter. The pancreas was then removed, trimmed of mesentery and fat, weighed, and a sample snap-frozen until enzyme analysis. Additional pancreatic samples were fixed in 10% formalin solution for histological examination of size and distribution of insulin-containing cell clusters. Data were analyzed as a completely randomized design with a factorial arrangement of treatments. Diet, treatment, and diet × treatment were blocked by yr and included in the model with initial BW used as a covariate. Day of the estrous cycle was initially included in the model but later removed as no effects (P > 0.10) were observed for any pancreatic variables tested. Overfed ewes had the greatest (P < 0.001) change in BW, final BW, change in BCS, and final BCS. A diet × treatment interaction was observed for change in BW and final BW (P ≤ 0.004). Overfed and CON had increased (P < 0.001) pancreas weight (g) compared with UF ewes. Protein concentration (g/pancreas) was the lowest (P < 0.001) in UF ewes, whereas protein content (mg/kg BW) was greater (P = 0.03) in UF than OF ewes. Activity of α-amylase (U/g, kU/pancreas, U/kg of BW, and U/g protein) and trypsin (U/pancreas) was greater (P ≤ 0.003) in OF than UF ewes. Serum insulin was the greatest (P < 0.001) in OF ewes. No effects were observed for pancreatic insulin-containing cell clusters. This study demonstrated that plane of nutrition affected several measurements of pancreatic function; however, the dosage of Arg used did not influence pancreatic function.

Effect of dietary energy substrate and days on feed on apparent total tract digestibility, ruminal short-chain fatty acid absorption, acetate and glucose clearance, and insulin responsiveness in finishing feedlot cattle1

“…In muscle tissue, insulin normally increases the energy consumption by increasing AA uptake and protein synthesis and reducing proteolysis (Hocquette et al, 1998;Richardson et al, 2004). Keomanivong et al (2017) has reported increased serum insulin in overfed ewes compared with underfed and control ewes, whereas no difference was observed in pancreatic insulin-containing cell clusters. Because of the pancreatic exhaustion due to continuous stimulation to produce excess insulin and its effects on target tissues for anabolic responses, insulin resistance may be considered one of the major contributing factors to the decreased feed efficiency associated with late finishing stages.…”

Nutritional and Physiological Constraints Contributing to Limitations in Small Intestinal Starch Digestion and Glucose Absorption in Ruminants

“…Responses in pancreatic α-amylase activity to individual amino acids have varied with the type of amino acid, length of infusion, and animal species. Arginine administration through jugular blood did not influence pancreatic α-amylase activity in non-pregnant ewes [93]. Similarly, dietary rumen-protected Arg supplementation to ewes during mid-to late-gestation did not influence pancreatic α-amylase activity of lamb offspring at 54 d of age [109].…”

“…More recent studies have evaluated the effects of dietary intake restriction on pancreatic α-amylase activity in ruminants. Dietary intake restriction decreased pancreatic α-amylase activity in nonpregnant ewes [93], pregnant ewes [94,95], and pregnant beef cows [96,97]. Changes in pancreatic α-amylase activity in response to changes in dry matter or energy intake may be related to the abundance and activity of pancreatic proteins involved in energy metabolism.…”

Influence of maternal nutrient restriction and rumen-protected arginine supplementation on post-ruminal digestive enzyme activity of lamb offspring

“…Increasing dietary levels of arginine results in increased hepatopancreatic α-amylase and trypsin activities in the Jian carp (Chen et al, 2012). Arginine administration through jugular infusion had no influence on pancreatic αamylase activity in nonpregnant ewes (Keomanivong et al, 2017b). However, it is unclear if maternal arginine supplementation could potentially influence offspring digestive enzyme activity in the pancreas or small intestine of ruminants.…”