Table 3. Plasma concentration of melatonin among different horse ages1)

Neurotransmitter Age of horses
1 to 5 years(n = 5) 6 to 12 years(n = 11) More than 13 years(n = 7)
MEL (pg/mL) 156.6 ± 70.03 127.1 ± 38.32 126.1 ± 47.67
Data represent the mean ± SEM.