Effect of chronobiological manipulation of lactation in the dairy cow

The objective of this study was to determine if chronobiological manipulation of the environment through the use of skeletal photoperiods could enhance milk production of the dairy cow. Cows in their 8th mo of gestation were maintained in either a control light regimen (12 to 13 h continuous light) or three skeletal photoperiods exposed to a total of 8 h of light. Cows in the skeletal photoperiods received 6 h of light from 0500 to 1100 h and a 2 h light pulse between 1500 and 1700 h (pulse 1500 to 1700 h), 1800 and 2000 h (pulse 1800 to 2000 h), or 2100 and 2300 h (pulse 2100 to 2300 h). Cows were milked twice daily and milk weights recorded. Weekly milk samples were analyzed for fat, protein, lactose, and SCC. Milk progesterone was monitored for the first 60 d after calving to determine return to estrus. Total electrical consumption for lighting the different light regimens were monitored throughout the lactation. Cows in the light regimen of pulse 1800 to 2000 h exhibited a higher persistency of lactation and a higher feed efficiency than the cows in the other light regimens. There were no differences between treatments in milk fat, protein, lactose, or SCC. The total electricity used to light pulse 1800 to 2000 h was 50% less than that used to light the control light regimen. It is concluded that light is essential between 13 to 15 h after subjective dawn for increasing persistency of lactation. Further, milk production of the dairy cow can be profitably enhanced through the use of chronobiological principles.