Relationship between neonatal glutamine supplementation, post-weaning growth and immune cell parameters in blood in a lipopolysaccharide challenge model in low birth weight piglets

A lipopolysaccharide (LPS) challenge is used as an experimental model to assess how pigs respond to a bacterial infection [1]. Glutamine (Gln) supplementation has been shown to improve post-weaning bodyweight (BW) and the immune response to an LPS challenge [1], and we have previously reported that Gln supplementation from 1 – 11 days of life (d) increased the BW of low birthweight (L) piglets[2]. However, the effects beyond the cessation of Gln supplementation remain to be studied. Therefore, the objective of this study was to investigate the effect of Gln supplementation
from 1 – 11 d on pre- and post-weaning BW development, and the immunological response to an LPS challenge. We hypothesized that Gln supplementation of L piglets is associated with improved pre- and post-weaning BW development and enhances blood leukocyte profiles in response to an LPS challenge.
Methods: At birth (0 d), 10 pairs of L (0.8–1.2 kg) and normal birthweight (N: 1.4–1.8 kg) male German Landrace littermates, born to first parity sows, were selected. At 24 hours (h) post farrowing, litter sizes were standardized to 12 piglets, and L and N piglets randomly assigned to Gln (1 g/kg BW/d; n = 20) or Alanine (Ala, 1.22 g/kg BW/d; isonitrogenous to Gln; n = 20) supplementation groups. Piglets were supplemented with 33% of their respective daily dose three times daily, until 11 d, and were suckled by their birth sow until weaning (28 d). At weaning, piglets were housed
according to supplementation group (Gln or Ala), and at 33 d transferred to individual pens for the remainder of the study. Bodyweight was recorded daily from 0 until 12 d, weekly from 14 to 56 d and immediately prior to euthanasia (62 d). Post-weaning feed intake was recorded daily. At 54 d, blood samples (1.5 mL) were collected via venepuncture at -15, 360, and 720 min relative to an LPS challenge (100 μg/kg BW i.p.). Flow cytometry was performed to quantify
total leucocyte count and Pappenheim stained blood smears were used to differentiate leucocytes (banded and segmented neutrophils, eosinophils, lymphocytes and monocytes). Data was analysed using the MIXED procedure of SAS. The fixed effects were supplementation (Gln and Ala), birth weight class (L and N), the supplementation × BC interaction and a random sow effect, with repeated measures used where appropriate. Least square means were separated using the Tukey test (P<0.05).
Results: Pre-weaning (0 – 28 d), L piglets were lighter compared with N, and Gln supplementation was associated with lower body weight in N-Gln than N-Ala at 28 d (P<0.05). Post-weaning, L-Ala (35 d; P<0.10, 42 - 56 d; P<0.05) and L-Gln (56 d; P<0.05) were lighter than their N littermates. Prior to the LPS challenge, L piglets were lighter that N (P<0.05) and during the challenge (1 – 24 h) L piglets (Ala P<0.05; Gln; P<0.10) were lighter than N littermates. At 360 min post LPS challenge, the lymphocyte % was lower in N-Ala than L-Ala piglets (P = 0.012) and tended to
be lower than in N-Gln piglets (P = 0.085). Additionally at 360 min, the neutrophil to lymphocyte ratio was higher in L-Gln than N-Gln, and lower in L-Ala than N-Ala piglets (P = 0.010), also it tended to be higher in N-Ala than N-Gln (P = 0.076). Whilst, also at 360 min, the total leukocyte count was higher in N-Gln than N-Ala (P = 0.031) and L-Gln than L-Ala (P = 0.050) piglets. From pre (-15 min) to 720 min post LPS challenge there was a decrease in lymphocytes and segmented neutrophils, and an increase in banded neutrophils and the neutrophil to lymphocyte ratio (P < 0.001) in all four groups. At 360 min post-LPS challenge, L-Gln rectal temperature was higher than L-Ala (P<0.001).
Conclusions: These results suggest that in this study, oral Gln supplementation during the neonatal period does not appear to improve L piglet pre- or post-weaning BW. Moreover, neonatal Gln supplementation did not alleviate the clinical signs of LPS challenge.