Effects of two different light programs on milk yield, prolactin, IGF-1 and sleep in dairy cows

Abstract: The aim of this study was to investigate the relationship between sleep, photoperiod, milk yield and hormones connected to milk formation. Variations of prolactin (PRL) and Insulin-Like growth factor-1 (IGF-1) in plasma were measured during two different light programs. The light programs consisted of either 24 hours of light (L24:D0) or four hours of light and 20 hours of darkness (L4:D20). Five cows of the Swedish Red breed were used in a cross-over experiment and each light program consisted of five days. Milk yield was measured at every milking and milk samples were analyzed with regard to fat, lactose and protein. The difference between morning and evening milking in a 12-hour milking interval was also examined. Blood samples were collected via a permanent catheter during milking and after periods of sleep during the last 36 hours of each light program. There were no significant differences in milk yield or milk composition between the light programs, neither did morning or evening milk yield vary. There were small variations in amounts of sleep between the two light programs. Plasma PRL did not differ significantly between the light programs besides at 1 min and 11 min after start of milking. Levels of IGF-1 were significantly higher during L4:D20. There was no significant effect of sleep on IGF-1. Sleep, light and milk formation needs to be further studied in order to investigate possible connections and underlying mechanisms.