Let there be light (and darkness)

You'll get an increase in milk production when cows get 16 hours of light, alternating with 8 hours of dark

Holstein dairy cows.

If our cows still lived out in the wild, they would likely have a calf each spring. Calving in spring makes sense with lots of lush, spring grass to support milk production. Trying to make milk while foraging for last year’s dried up grass underneath snow wouldn’t have been very successful.

The spring grass usually gets all the credit for milk production, but lighting should not be overlooked. When the cows were dry in the winter months, daylight was short, about 8 hours on a good day. But in the spring, daylight hours get longer as the season progresses, reaching about 16 hours in mid-summer.

Lighting and production

For more than 25 years, research has been tweaking the use of controlled lighting to increase milk production in dairy cattle. Initially, the work focused on lactating cows. Study after study have shown an increase in milk production when cows receive 16 hours of light, alternating with 8 hours of dark.

Generally, milk yields increase 5-10% or more over the production of cows receiving shorter or longer light periods.

Learn more

The Midwest Planning Service’s Dairy Freestall Housing and Equipment publication has an excellent section on lighting for the entire dairy facility. It contains information about lighting levels needed, light types, mounting heights and coverage areas. A copy of this publication may be available for review at your county Extension Office, or can be purchased at www-mwps.sws.iastate.edu/.

Dry cows too

Work then shifted to look at the impact of lighting (photoperiod) on dry cows. Research at the University of Illinois documented that a shorter light period for dry cows increased milk production in the following lactation.

Cows exposed to 8 hours of light and 16 hours of dark during the whole dry period responded with increased milk production in the following lactation. This response was seen in cows that received either long-day light or ambient (existing daylight) treatments after calving.

Even heifers

What about springing heifers? Heifers showed the same response if they were exposed to short day photoperiods for 60 days before calving. A study looking at short day photoperiods for just the last 21 days of the dry or prefresh period did not show the same increased milk production response.

Why? So, what causes this response? Researchers believe that greater mammary growth, improved immune response and increased dry matter intake is related to hormonal changes. Prolactin levels circulating in the blood decrease and sensitivity increases in dry cows exposed to short photo periods compared to cows exposed to long periods of light.

Put it to use

Is it practical to provide milking cows with 16 hours of light and 8 hours of dark each day? Absolutely, and we shouldn’t let that opportunity for increased milk production pass.

How practical is limiting dry cow light to 8 hours a day? Shouldn’t be hard in the dead of winter, but can be challenging, if not impossible, in many facilities the rest of the year.

The dark period must be contrasted with 8 hours of light measuring 15 to 20 foot-candles 3 to 4 feet off of the ground. This is actually pretty bright. A few incandescent bulbs or old fluorescent tubes will not do the trick. When considering light sources, look at energy efficient alternatives such as metal halide or mercury lights.

If it is dark for 16 hours a day in the dry cow/transition cow barns, how do we keep track of cows that are calving? Turn those barns into a red-light district. Fifteen watt or lower red lightbulbs will provide enough light to monitor cows while the cows do not perceive the red light as “light” that interferes with their prolactin response. Putting red screens over existing, higher wattage lights (while creative!) will still interfere with the prolactin response.

Real life application

Is this practical for all farms? No. Is it practical for your farm? Maybe, look around.

Will it work where dry cows are currently housed? Will it work somewhere else on the farm if groups are shifted around a bit?

If you are planning to do some building, this is worth taking a serious look at while plans are being developed. Take a few minutes to take an objective look at the lighting for your lactating cows, dry cows and prefresh pens. Is there enough light for 16 hours to achieve that milk response in the milking pens? If there are enough light fixtures, are they clean or covered with dust?

Are all the bulbs working? Is the timer working with correct on/off times?


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