γ-aminobutyric acid (GABA) is a natural stress-reducing substance and is actively used as a human health supplement. However, minimal research has been conducted on its use in cattle. This study was conducted to evaluate the effects of GABA on the growth performance, complete blood count, blood metabolites, and carcass characteristics of fattening Hanwoo steers. Twenty-one fattening steers were randomly assigned to one of three treatments: control (basal diet: concentrate feed + rice straw), T1 (basal diet + GABA supplement at 0.8% of feed/head/day), and T2 (basal diet + GABA supplement at 1.6% of feed/head/day). Feed intake and conversion ratio did not differ among the treatments. However, the average daily gain during the early fattening period increased linearly to 0.80 kg, 0.86 kg, and 0.92 kg in the control, T1, and T2 groups (p<0.05). Plasma γ-glutamyl transferase (37.5, 58.2, 42.8 U/ℓ) and creatinine (1.32, 1.34, 1.49 ㎎/㎗) levels in the GABA supplement group were increased compared to those in the control group. The carcass weight (422.7, 427.1, 454.1 kg), rib eye area (86.67, 92.57, 91.14 cm2), and marbling score (3.67, 4.29, 4.14) were numerically higher in the GABA supplement group than in the control group. Thus, GABA supplementation positively affected the average daily gain and carcass characteristics of Hanwoo steers. However, the effect of the GABA supplement level of GABA was small, and further research using rumen-protected coating technology on GABA is necessary.

Sparassis latifolia (formerly S. crispa) is used in food and nutraceuticals or dietary supplements, as rich in flavor compounds and β-glucan. Some previous studies have reported the effects of mushroom on brain function, including its neuroprotective effect. Thus, for this mushroom to be used as an effective nutraceutical for brain function, it would be desirable for it to contain other compounds such as γ-aminobutyric acid (GABA) in addition to β-glucan. In this study, the enhancement of growth and GABA production in the mycelium of medicinal and edible mushroom S. latifolia was investigated. Amino acids were added externally as the main source of nutrition, and the effects of amino acids were investigated using liquid medium, specifically amino acid-free potato dextrose broth (PDB). The amino acids added were L-glutamic acid (named PDBG medium) and L-ornithine (named PDBO medium). The growth of mycelia was determined to be 0.9 ± 0.00 g/L, 2.2 ± 0.16 g/L, and 1.93 ± 0.34 g/L PDBG respectively. The GABA content was 21.3 ± 0.9 mg/100 g in PDB medium, and it in PDBG 1.4% medium, at 115.4 ± 30.2 mg/100 g. However, the PDBO medium was not effective in increasing the GABA content of mycelia. Amino acids had little effect on the β-glucan content of mycelia. The β-glucan content was 39.7 ± 1.4 mg/100 mg, 34.4 ± 0.2 mg/100 mg, and 35.2 ± 9.2 mg/100 mg in PDB, PDBG 1.8% and PDBO 1.4% media, respectively. Addition of glutamic acid and ornithine positively affected the growth of S. latifolia mycelia, and glutamic acid positively affected GABA production; no degradation of GABA was observed with addition of glutamic acid.