Dietary gamma-aminobutyric acid supplementation does not mitigate stress responses in weaner pigs given adrenocorticotropic hormone and experimentally infected with enterotoxigenic Escherichia coli

Abstract

Gamma-aminobutyric acid (GABA) is a non-protein amino acid, a major inhibitory neurotransmitter in the central nervous system that stimulates feed intake and inhibits the hypothalamic-pituitary-adrenal (HPA) axis. We hypothesised that: (1) GABA supplementation in the diet would reduce markers of the stress response in weaned pigs injected with adrenocorticotropic hormone (ACTH) and inoculated with enterotoxigenic Escherichia coli (ETEC); and (2) this reduction in stress responses would improve performance after weaning. A total of 96 newly-weaned male pigs (Large White x Landrace) were stratified into a two by four factorial arrangement with respective factors being (i) with/without ACTH injection and ETEC infection (challenge versus non-challenge) and (ii) four dietary GABA levels (0, 60, 80, 100 mg/kg). On days 8 and 9 after weaning, piglets were orally inoculated with ETEC (0.8 ml via two gelatinized capsules; serotype O149; F4) as well as being given 5 IU ACTH intramuscularly (IM), which occurred an hour before ETEC inoculation. Pigs in the non-challenged group were given IM 0.2 mL of sterile saline and sham infected with two capsules of PBS. Faecal consistency scores were recorded daily, pigs and feed were weighed weekly to determine performance and blood samples were collected at days 6, 9 and 14. GABA supplementation did not reduce plasma cortisol. However challenged pigs had higher levels compared to the non-challenge group at day 9 (P = 0.001). Performance was not influenced by GABA supplementation (P > 0.05). Between days 8–14, 54.3% of pigs in the challenge group developed diarrhoea compared to 5.6% in the non-challenged group (P = 0.001). These data indicate that eliciting both an ETEC infection challenge and an acute stress response after weaning initiated an endocrine stress response. The use of GABA in feed did not reduce this stress response, reduce diarrhoea or improve production performance.