Excess dietary Lys reduces feed intake, stimulates jejunal CCK secretion and alters essential and non-essential blood AA profile in pigs

Abstract

Background: Commercial diets are frequently formulated to meet or exceed nutrient levels including those of limiting essential amino acids (AA) covering potential individual variations within the herd. However, the provision of dietary excess of AA, such as Lys, may lead to reduced appetite and growth in pigs. The mechanisms modulating these responses have not been extensively investigated. This study evaluated the effect of Lys dietary excesses on performance and satiety biomarkers in post weaning pigs.

Methods: Twenty-four pigs aged 21 d and weighing 6.81 ± 0.12 kg (mean ± SEM) were individually housed and offered 1 of 4 dietary treatments for 3 weeks: a diet containing a standardized ileal digestible Lys reaching 100% (T0), 120% (T1), 150% (T2) or 200% (T3) of the NRC (2012) requirements. At the end of the experiment, blood samples from the cephalic vein of the T0 and T3 groups were obtained for AA analysis. In addition, primary intestinal cultures from T0 pigs were used, following their humane killing, to evaluate the effect of Lys on gut hormone secretion and AA sensors gene expression under ex vivo conditions.

Results: Feed intake was linearly reduced (P < 0.001) and the weight gain to feed ratio reduced (P < 0.10) with increased dietary levels of Lys during the third- and first-week post weaning, respectively. Cholecystokinin concentration (P < 0.05) and the metabotropic glutamate receptor 1 and the solute carrier family 7 member 2 (P < 0.10) gene expression was enhanced in proximal jejunum tissues incubated with Lys at 20 mmol/L when compared to the control (Lys 0 mmol/L). Plasma Lys and Glu (P < 0.05) concentration increased in the T3 compared to T0 pigs. In contrast, plasma levels of His, Val, Thr, Leu (P < 0.05) and Gln (P < 0.10) were lower in T3 than T0 pigs.

Conclusion: The present results confirm that excess dietary Lys inhibits hunger in pigs. Moreover, the results provide evidence of pre- and post-absorptive mechanisms modulating these responses. Lys dietary excesses should be narrowed, when possible, to avoid negative effects of the AA on appetite in pigs.

Keywords: Amino acid; Blood; Cholecystokinin; Feed intake; Lysine; Pig; Satiety.

Fig. 1

Blood levels of essential amino acids (EAA) in pigs fed Lys dietary excesses. Effect of dietary Lys levels (100% of requirements (T0) vs. 200% of requirements (T3)) on EAA (Lys (A), His (B), Ile (C), Leu (D), Met (E), Phev(F), Thr (G), Trp (H) and Val (I)) plasma levels in young pigs. Data are presented as the mean ± SEM (n = 6). ^***P ≤ 0.001, ^**P ≤ 0.01, ^*P ≤ 0.05

Fig. 2

Blood levels of non-essential amino acids (NEAA) in pigs fed Lys dietary excesses. Effect of dietary Lys levels (100% of requirements (T0) vs. 200% of requirements (T3)) on NEAA (Ala (A), Arg (B), Asn (C), Asp (D), Cys (E), Gln (F), Glu (G), Gly (H), Pro (I), Ser (J) and Tyr (K)) plasma levels in young pigs. Data are presented as the mean ± SEM (n = 6). ^*P ≤ 0.05, tendency = 0.05 ≤ P ≤ 0.10

Fig. 3

Cholecystokinin (CCK) and glucagon-like peptide 1 (GLP-1) concentration in porcine intestinal cultures exposed to Lys. CCK and GLP-1 secretion using an ex vivo jejunum (A) or ileum (B) culture from young pigs. Tissue cultures were incubated for 1 h with a KRB/HEPES buffer containing 0 (control), 10, 20 and 30 mmol/L Lys. Data are presented as the mean ± SEM of 3 biological replicates per pig (n = 5). ^*P ≤ 0.05

Fig. 4

Gene expression of AA sensors in porcine jejunum exposed to Lys. Gene expression (mRNA abundance) of AA receptors and transporters (T1R1 (A), T1R3 (B), CaSR (C), mGluR1 (D), mGluR4 (E), SLC7A1 (F) and SLC7A2 (G)) in the proximal jejunum of young pigs following 1 h incubation with a KRB/HEPES buffer containing 0 (control) or 20 mmol/L Lys. Data are presented as mean ± SEM (n = 6). P values indicate a statistical trend: 0.05 ≤ P ≤ 0.10