Plasma melatonin and insulin‐like growth factor‐1 responses to dim light at night in dairy heifers

Abstract

The effect of dim (5, 10 and 50 1x) light at night on night plasma melatonin level (NML) and night plasma insulin-like growth factor-1 (IGF-1) level was determined in 12 prepubertal Holstein heifers (245 +/- 16 days age) using a 4 x 4 Latin Square design with 14-day treatment and 14-day recovery periods. Blood samples were collected at 23:00 hr (prior to the 8 hr night treatment which commenced at mid-night) on days 0, 3 and 13, and throughout the night at 01:00, 02:00, 03:00, 04:00, 06:00 and 08:00 hr on days 1, 4 and 14 of treatment. Plasma was analysed by radioimmunoassay for melatonin (all samples) and IGF-1 (samples for day 14, 04:00 hr only). Treatment (P = 0.03) and treatment x time (P = 0.02) were significant for NML. Exposure to 50 lx suppressed NML by 50% during the initial 2 hr of the night, but not thereafter. Exposure to 5 and 10 lx had no effect on NML. The NML response to 50 lx was found on all treatment days studied (treatment x time x day; P = 0.99). There was no treatment effect on plasma IGF-1 level (P = 0.89), but plasma IGF-1 level was higher (P = 0.001) during period 4. Plasma IGF-1 level and NML tended (P = 0.10) to be negatively correlated. Light intensities of 10 lx or less appear safe for use at night in dairy barns where darkness is recommended.

Melatonin concentration in cow’s milk and sources of its variation

“…Melatonin biosynthesis is under the control of light and, in cattle, five to 10 lux seems to be the threshold above which synthesis is inhibited (Muthuramalingam et al 2006). The number of hours of darkness and the photoperiod also dramatically affect synthesis (Dahl 2010).…”

Effects of dim light at night on milk yield, milk composition and endocrine profile of lactating dairy cows

“…In previous studies with Holstein heifers, Lawson and Kennedy (2001) and Muthuramalingam et al (2006) showed that dim light (50 lx) at night reduced plasma melatonin concentration by 50 to 70%. Such a response was not seen in the present study with the application of dim light at night.…”

“…Lawson and Kennedy (2001) and Muthuramalingam et al (2006) previously found that plasma melatonin concentration of Holstein heifers during darkness (0 lx) averaged 50Á60 pg mL…”

“…Exposure of cattle to an extended photoperiod also results in a temporal reduction in melatonin secretion as melatonin release from the pineal gland is inhibited by light (Rieter 1991). Because melatonin has been shown to inhibit IGF-I secretion (Dahl et al 2000;Muthuramalingam et al 2006), temporal reductions in melatonin secretion may contribute at least in part to the increase in milk yield.…”

“…Lawson and Kennedy (2001) found that 50 lx of light was adequate to inhibit the initial nocturnal rise in plasma melatonin concentration from 1640 to 1840, and more recently Muthuramalingam et al (2006) showed that dairy heifers exposed to dim light at night (50 lx) had a 50% suppression of plasma melatonin concentration during the initial 2 h of the night, but not thereafter. Although extending the photoperiod increases milk yield, continuous lighting is not recommended because it eliminates endocrine changes that would be caused by an extended photoperiod (Stanisiewski et al 1988).…”