Table 3. Effect of supplementation level of RPL-T on serum melatonin and gastrointestinal hormone concentration in Holstein steers

		Control	RPL-T 191.1 mg/kg BW	RPL-T 95.6 mg/kg BW	RPL-T 19.1 mg/kg BW
Hormone	Melatonin (pg/mL)	64.41 ± 0.72 3^b	67.04 ± 0.728^ab	67.67 ± 0.963^a	66.68 ± 0.856^ab
	Cholecystokinin (ng/mL)	1.51 ± 0.069^b	1.81 ± 0.090^a	1.76 ± 0.072^a	1.74 ± 0.052^a
	Secretin (ng/mL)	1.94 ± 0.059	1.91 ± 0.098	1.84 ± 0.079	2.00 ± 0.081

Each value is presented as mean ± SE (n = 4).
Values with different superscripts in the same row differ significantly at p < 0.05.
RPL-T, rumen-protected L-tryptophan; BW, body weight.