Abstract Arginine (Arg) is a functional amino acid that contributes to intestinal growth as a precursor for nitric oxide and polyamine synthesis. Standardized ileal digestible (SID) Arg requirements may be underestimated in nursery pigs, particularly if gut functionality is considered together with growth performance. The objective of this study was to determine the effect of increasing the ratio of SID Arg to Lys on gut functionality in post-weaning pigs. A total of 24 pigs (initial body weight, 9.20 ± 1.37 kg) were assigned to one of four dietary treatments (ME, 3,380 kcal/pig; CP, 22.7%; SID Lys, 1.34%; n = 6): 1) R75 (SID Arg: Lys, 0.75; n = 6); 2) R90 (SID Arg: Lys, 0.90; n = 6); 3) R105 (SID Arg: Lys, 1.05; n = 6); and 4) R120 (SID Arg: Lys, 1.20; n = 6). These pigs were sourced from a parallel growth performance study, were weaned at 28 d age, and had free access to treatment diets for 7 d. Arginine, above that in the R75 diet, was supplied as crystalline L-Arg; diets were made isonitrogenous with crystalline L-Ala. Upon selection, pigs were fasted for 6 h and an external jugular vein catheter was installed. Following a 2-d recovery from surgery, pigs were fasted for 6 h and then administered an intravenous injection of L-alanyl-L-glutamine dipeptide (500 mg/kg) to assess gut citrulline (Cit) production. Serial blood collection was carried out for 6 h. Pigs were subsequently fed a single meal and euthanized after 1.5 h for postprandial blood sampling and gut tissue collection. Postprandial plasma Arg concentration increased with increasing SID Arg: Lys (R75, 146 ± 19 µmol/L; R120, 202 ± 21 µmol/L; Linear, P 0.05), whereas postprandial Ala concentration decreased with increasing SID Arg: Lys (R75, 863 ± 79 µmol/L; R120, 595 ± 87 µmol/L; Linear, P 0.05). Following the L-alanyl-L-glutamine bolus, there was a rapid increase and subsequent decline in plasma Ala and Gln concentrations (Time, P 0.001). This corresponded to a transient increase in plasma Arg and a prolonged increase in plasma Cit concentrations over 6 h (Time, P 0.001); however, diet did not affect plasma Arg or Cit concentrations (absolute concentrations and area under the curve; P 0.10). In the jejunum, diet did not affect villus height (VH) or crypt depth (CD; P 0.10), but VH: CD tended to increase with increasing SID Arg: Lys (P = 0.10). In the ileum, diet did not affect VH (P 0.10), but CD decreased (Linear, P 0.05) and VH: CD increased (Linear, P 0.01) with increasing SID Arg: Lys. In summary, increasing SID Arg: Lys in nursery diets may augment gut structure in nursery pigs.
Jeffers et al. (Wed,) studied this question.