Multiple studies have shown that a day length of 16-18 hours and darkness of 6-8 hours have a positive influence on growth and age of sexual maturity in heifers, with no negative influence on the yield potential of the animals. Furthermore, this combination of lighting is thought to affect the dry days and the number of services in a positive way.
Depending on which part of the world you live in, you may need to supplement the daylight with artificial lighting to reach the optimal length of day light. In this case, pay attention to the time shifting to night light – you may have to leave the light on for a few hours longer.
Finding the problem
Check if lighting system is sufficient. If in doubt, we suggest you buy a lux meter and measure the lighting yourself. Or contact your local cattle consultant or an electrician to do this measurement. The measurement should be taken one metre above floor level when comparing with the recommended level.
Causes
The positive effect is due to a signal being transmitted to the brain when light reaches the retina. This signal suppresses the production of melatonin. The rhythm in the production of melatonin is significant for a number of hormones that affect the growth, reproduction, milk yield and health of the animal. This means that the positive effect of lighting is only achieved when the animals go through a period of darkness during the course of a 24-hour period.
If the night lighting consists of leaving a few light sources in the barn on during the night, the lighting level will vary significantly in different parts of the barn. Areas of concentrated pools of light should be avoided in the barn as this will reduce the positive effects of the period of darkness.
Action plan
Lighting in a barn is best reflected from a light and clean environment – clean windows, skylights/windows, roof sheets and internal surfaces.
Focus areas
Cows and heifers should have approx. 16 hours of light (>100 lux)
Cows and heifers should have approx. 8 hours of darkness (<10 lux)
Avoid concentrated pools of light during the hours of darkness.
Source: SEGES, Denmark
