Manipulating light exposure at strategic points in the life cycle of cattle could be a non-invasive technique to improve performance, health, and well-being. Pulsed alternating wavelengths system (PAWS; Xiant Technologies, CO) is a recently developed technology based on delivering specific light wavelengths and patterns. The objective of this small-scale study was to compare the hormonal (melatonin and cortisol) and neurotransmitter (serotonin) levels in PAWS exposed vs. unexposed control calves. Holstein heifer calves (3 d old) were housed individually in polyethylene hutches with a front yard of 2.25 m² with sand bedding and assigned into 1 of 2 treatments: (1) control (CON; n = 4); and (2) PAWS exposed (PAWS; n = 4). Hutches in the PAWS group had interior lamps affixed to the hutch roof and were constantly on. All the study calves had free access to the enclosed front yard. Calves were fed and managed according to farm management program. Blood samples were collected for determination of serum melatonin and serotonin concentration at 0600 h, 1200 h, 1800 h, and 2400 h on d 0 (enrollment), d 2, d 4, and d 14. Hair was sampled for cortisol determination on d 0, d 14, d 40, and d 60. No group differences for cortisol concentration were determined. Table 1 presents mean (SE) melatonin and serotonin serum concentrations for the overall monitoring period, by day, and by day at 2400 h, which was the time of maximum exposure to the treatment. Data from this initial small-scale study indicate a significant effect for PAWS on melatonin concentration. A larger study is needed to further explore these associations. Table 1 (Abstr. T9).

Time	Melatonin (mean SE; pg/mL)		P-value	Serotonin (mean SE; ng/mL)		P-value
CON	PAWS	CON	PAWS
Overall	5.47 ± 1.86	11.6 ± 1.85	0.02	1,644 ± 91.5	1,462 ± 91.6	0.16
Day average
d 0	2.66 ± 2.08	9.98 ± 2.08	0.02	1,406 ± 118	1,268 ± 119	0.42
d 2	4.58 ± 2.27	10.3 ± 2.27	0.08	1,926 ± 196	1,850 ± 196	0.78
d 4	4.99 ± 2.36	9.80 ± 2.36	0.16	1,369 ± 192	1,279 ± 192	0.74
d 14	9.10 ± 6.80	17.0 ± 6.80	0.41	1,870 ± 172	1,458 ± 172	0.10
Sample at 2400 h
d 0	4.56 ± 7.66	22.6 ± 7.66	0.14	1,781 ± 311	1,458 ± 311	0.49
d 2	5.13 ± 7.13	23.7 ± 7.13	0.11	2,700 ± 405	2,543 ± 405	0.79
d 4	10.1 ± 9.06	20.8 ± 9.07	0.43	2,169 ± 470	1,758 ± 470	0.55
d 14	4.45 ± 9.62	15.4 ± 8.33	0.43	1,803 ± 320	1,925 ± 277	0.78