Trim 20 days off the dry period. give cows less light. Get more milk.

It sounds like a plausible combination, and now there’s research that proves it works.

The research, presented this past summer at the annual meeting of the American Dairy Science Association, shows that cows exposed to less light during a 42-day dry period gave more milk during their next lactation. Here’s what the research has to say.

A 7-pound advantage

During the study, researchers at the University of Illinois exposed 20 dry cows to only eight hours of light per day for 42 days. A control group of 20 cows received 16 hours of light per day during that same time. At calving, all of the cows were exposed to natural lighting.

When lactation began, the researchers recorded milk production through 120 days in milk.

The results show the less-light, short-dry combination gave cows an edge over their peers. In fact, those cows gave about 7 pounds more milk per cow per day during the first 120 days in milk than the “long-day, short-dry” cows.

Comparable results

The milk production response of the short-dry cows in the Illinois study compares favorably to the response seen in cows exposed to short-day lighting for an entire 60-day dry period, says Geoff Dahl, professor and chair of the animal sciences department at the University of Florida, and formerly with the University of Illinois.

Previous research shows cows exposed to eight hours of light during a traditional 60-day dry period gave about 5 pounds more milk per cow per day during the next lactation than cows exposed to 16 hours of light per day during a 60-day dry period. 

Stick to a 42-day regimen

So, can you get by with fewer than 42 days of reduced lighting during the dry period?

Not yet.

“We know we can go as low as 40 days” of less light and still get a good milk-production response, Dahl says. Going much below that hasn’t yielded consistent results yet.

So, at this point, aim for at least six weeks of less light during the dry period — and that’s good news for those of you who give cows a dry period that’s similar in length.

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This article is available in Spanish at www.dairyherd.com


 A snapshot of the research

Here’s how cows responded to eight hours of light per day during a 42-day-dry-period study at the University of Illinois:

  • They ate about 2 pounds more dry matter per cow per day during the dry period than cows exposed to 16 hours of light per day. Dry matter intake did not differ after calving.
  • They calved almost five days earlier than long-day cows (37 days dry versus 42 days dry, respectively.)
  • They gave 7 pounds more milk per cow per day during the first 120 days of lactation than cows exposed to 16 hours of light per day.
  • Researchers did not examine the effect of this strategy on metabolic problems, reproductive performance or udder health.