Dairy researchers have seen the light; farmers should, too


We’re going to do it. A whole column that doesn’t mention the two four-letter words we are growing to hate: f_ _ d and c _ _ t.

No magic answers for the issues they represent. But, it doesn’t hurt to revisit some non-feed opportunities to support and increase milk production. Let’s look at the light.

For more than 20 years now, 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 has shown an increase in milk production when cows receive 16 hours of light alternating with eight hours of dark. Generally, milk yields increase 8 percent to 10 percent over the production of cows receiving shorter or longer light periods.

Dry cows

In the past few years, work has shifted to look at the impact of lighting (photoperiod) effects on dry cows. Geoff Dahl, when working at the University of Illinois, documented that a shorter light period for dry cows increased milk production in the following lactation.

Cows exposed to eight 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 long-day light or ambient (existing daylight) treatments after calving.

What about 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 the last 21 days of the dry or pre-fresh period did not show the same increased milk production response.

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.


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

Dry cows stuck in a dingy corner of the old bank barn may be getting plenty of dark. But how much light and air they get is usually questionable!

The dark must be contrasted with eight hours of light measuring 15-20 foot-candles 3-4 feet off of the ground. This is actually pretty darned bright. A few incandescent bulbs will not do the trick.

When considering light sources, we need to be looking at energy efficient alternatives such as fluorescent, metal halide or mercury lights. Tunnel ventilated barns are actually the most likely candidates for providing short day photoperiods.

Dry cows and heifers on pasture? Forget the photoperiod thing.

Little red lights

So, 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? Little red light bulbs. Fifteen watt or less red light bulbs will provide enough light to monitor cows while they 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 interfere with the prolactin response.

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.


Up-to-date agriculture news in your inbox!

Previous articleOhio's dairy labeling law goes to court
Next articleThat’s Mrs. Quixote to you
Dianne Shoemaker is an OSU Extension field specialist in dairy production economics. You can contact her at 330-533-5538 or shoemaker.3@osu.edu.



We are glad you have chosen to leave a comment. Please keep in mind that comments are moderated according to our comment policy.

Receive emails as this discussion progresses.