A supplement of selected amino acids can mitigate some aspects of the stress response and improve feed conversion efficiency in piglets exposed to stressors associated with weaning

This study tested the hypothesis that gamma-aminobutyric acid (GABA) supplementation in the drinking water, together with supplementation of glutamine (Gln), glutamate (Glu) and tryptophan (Trp) in the diet, would reduce indices of the stress response and improve growth performance in post-weaned piglets subjected to a mixing stress and short-term feed deprivation. At weaning, 72 male piglets were allocated to pens with their littermates (3 piglets/pen) and allowed to acclimate for 14 days, after which time they were allocated to a 2 × 2 factorial arrangement of treatments with factors being (1) with/without feed deprivation for 12 h (Fast, NoFast) and (2) with/without supplementation of the selected amino acids (Supplement, NoSupplement). All piglets were mixed with non-littermates at 0600 h on day 14 to create a mixing challenge, and at this time piglets were either taken off feed for 12 h (Fast) or were not deprived of feed (NoFast). At 1800 h on the same day, one half of the piglets was supplemented with 50 mg/pen/day GABA in the drinking water (from days 14-18) and 0.3% L-Glu, 0.1% L-Gln and 0.34% L-Trp added to their diet (from days 14-21). From day 21 all piglets were fed the same diet without any supplementation, and the study finished on day 28. Weekly live weights and feed intakes were measured, blood was collected at days 11, 14 (1800 h) and 18, and a sugar absorption test (SAT) was conducted in Fast-NoSupplement piglets and Fast-Supplement piglets on days 14 and 22. On day 14, 12 h after feed deprivation, there was a trend ( P = 0.063) for an interaction such that Fast piglets offered NoSupplement had the highest cortisol concentration compared to all other treatments (14.2 ng/ml). Plasma glucose concentration at this time was higher ( P < 0.001) in NoFast piglets compared to Fast piglets (main effect; 6.3 vs 5.7 mmol/L); however, this difference was reversed by day 18 (6.6 vs 7.1 mmol/L, P = 0.024). The Fast piglets had higher ( P < 0.001) concentrations of NEFA compared to NoFast piglets on day 14 only (main effect; 0.33 vs 0.09 mmol/L). A trend ( P = 0.072) for a main effect for concentrations of brain-derived neurotrophic factor was seen on day 14 (5.3 vs 2.6 ng/ml), and on day 18, a significant interaction ( P = 0.005) occurred with SupplementFast piglets having the highest concentration compared to all other treatments (7.9 ng/ml). At day 22, piglets offered Supplement tended ( P = 0.090) to have a higher plasma D-mannitol concentration compared to NoSupplement piglets (174 vs 128 nmol/L), and there was a trend ( P = 0.092) for a positive change in citrulline concentration between days 14 to 22 between the Supplement and NoSupplement piglets (change, 11.2 vs 2.0 ng/ml). Feed conversion ratio from day 15-21 was lower ( P = 0.007) in Supplement piglets compared to NoSupplement piglets regardless of feed deprivation (main effect; 1.27 vs 1.42). These results provide partial evidence that mixing stress and (or) short-term feed deprivation induces acute psychological and metabolic changes in piglets, and supplementation with this combination of selected amino acids can potentially modulate aspects of intestinal function and improve feed efficiency after weaning.