Does dietary supplementation of gamma-aminobutyric acid improve performance in weaner pigs experimentally infected with Escherichia coli and given adrenocorticotropic hormone?

Gamma-aminobutyric acid (GABA) is a non-protein amino acid and a major inhibitory neurotransmitter in the central nervous system. Previous research completed on rats and humans has shown that GABA stimulates voluntary feed intake and regulates stress hormone secretion in humans (Kruk and Pycock 1983). This neurotransmitter also plays important roles in motor function, emotions, appetite regulation and nutrient utilisation efficiency (Lelevich et al. 2009; Zhang et al. 2012). The aim of this study was to use both an enterotoxigenic Escherichia coli (ETEC) infection model and an adrenocorticotropic hormone (ACTH) injection to simulate a pathogenic and endocrine stressful weaning event. We hypothesised that an increased supplementation of GABA in diets of weaned pigs will improve growth performance and reduce cortisol production.

A total of 96 newly weaned male pigs (Large White × Landrace) with the Mucin 4+ allele were stratified into eight treatments based on weaning weight, sow parity and location in the building (eight treatments × 12 pigs = 96 pigs). The study was designed as a 2 × 4 factorial arrangement with respective factors being (1) without/with ETEC infection plus ACTH and (2) four dietary GABA (Sigma-Aldrich; MO, USA) levels (0, 60, 80, 100 mg/kg). All pigs were fed the same base diet (20% protein, 5% fat, 1.2% lysine, 5% crude fibre, 0.85% calcium and 0.4% salt). On d 8 and 9 after weaning, all piglets were orally inoculated with ETEC (0.8 mL via two gelatinised capsules; serotype O149;K88) as well as being given 5 IU ACTH (Synacthen; Juno Pharmaceuticals, Vic., Australia) intramuscularly (IM), which occurred an hour beforehand. Pigs in the non-infected, non-ACTH group were given IM 0.2 mL of sterile saline and sham infected with two gelatinised capsules of phosphate-buffered saline. Faecal consistency score, diarrhoea index, and the number of therapeutic antibiotic treatments were recorded. Faecal β-haemolytic E. coli shedding was measured on d 0, 7, 10, 11 and 14 after weaning. Blood samples were collected on d 6, 9 (1 h after infection) and 14 from eight pigs per treatment. Plasma cortisol was assessed using ELISA from Enzo Life Sciences (Cat. No. ADI-900–071, NY, USA). Data were analysed by two-way analysis of variance using SPSS (v21.0, IBM, Armonk, NY, USA).

There were no differences (P > 0.05) between the four GABA diets for ADG, ADFI or FCR over the 21 days duration of the study (Table 1). Pigs in the non-infected, non-ACTH group gained 35 g/d more than pigs in the ETEC infection plus ACTH group during week 3 (P = 0.098; data not shown). In total, 73.2% of pigs in the infection plus ACTH group developed diarrhoea between d 8 to14 compared to 26.8% in the non-infected, non-ACTH group of pigs (P = 0.001). These data indicate that eliciting both an ETEC infection challenge and an acute stress response after weaning caused no overall detrimental effects on production or diarrhoea; however, further investigation will establish blood measurements more indicative of the stress response during this period.

Table 1.  Effects of dietary treatments, ETEC+ACTH infection or sham-infection on average daily gain (ADG), average daily feed intake (ADFI) and feed conversion ratio (FCR) from d 0 to 21 after weaning