What if you could grow heifers faster and still get good milk production when they freshen? Skeptics would say it can’t be done easily. Heifers simply get too fat when grown at a fast rate, and they don’t milk when that happens. 

However, you may be able to “have your cake and eat it, too,” thanks to extended lighting.

It’s well documented that lactating cows benefit from extended or long-day lighting, which is defined as 16 hours of light and eight hours of dark. Research also shows that growing heifers benefit from extended lighting before puberty and during their first lactation. Here’s what the research has to say.

Accelerates puberty

Researchers have known for more than 25 years that extended lighting accelerates puberty without hurting mammary development — a major drawback associated with growing heifers at faster rates of gain.

One of the most recent studies confirms that extended lighting boosts lean growth and gets heifers to puberty at an earlier age. The study, done at the University of Illinois and reported in the December 2005 Journal of Dairy Science, shows these results:

  • Lean growth. Heifers exposed to 16 hours of light grew slightly faster (2.7 pounds of gain per day versus 2.5 pounds for heifers exposed to only eight hours of light per day). “This is actually lean growth that you’re seeing,” says Geoff Dahl, extension dairy specialist at the University of Illinois. In other words, the heifers hit puberty with a leaner body composition. This is important because when you grow heifers rapidly, it can promote fat accumulation, which is believed to impair mammary development and future milk yield.
  • Earlier puberty. Heifers exposed to 16 hours of light per day reached puberty 24 days earlier. This did not impair skeletal growth, another common problem associated with the rapid rearing of heifers.
Researchers at the University of Illinois exposed heifers to 16 hours of light per day from weaning until puberty. The heifers reached puberty 24 days earlier and gave more milk during their first lactation than heifers exposed to only eight hours of light.

The heifers in the University of Illinois study were exposed to extended lighting from about three months of age until puberty. Dahl’s group did not analyze heifer body size or composition at breeding. However, they followed the animals into their first lactation in order to assess the impact of lighting on first-lactation milk yield.

More milk, too

During the lactation segment of the study, reported in the June 2006 Journal of Dairy Science, Dahl’s group examined the effect of extended lighting on first-lactation milk yield. They found:

  • Heifers exposed to 16 hours of light were taller and heavier at calving.
  • These heifers gave more energy-corrected milk during the first five months of lactation. (Please see “More light, more milk” on page 24.)
  • Data projected over the entire lactation also show that the long-day heifers gave 1,654 pounds more fat-corrected milk during their first lactation than the short-day heifers.
  • However, there was no difference in peak milk or average somatic cell count between the two groups.

Turn on the lights

So, should you string up the lights in your heifer barn? Sure, chances are good that you’ll recover the cost of extra lighting with more milk during the first lactation. And if heifers give more milk during the first lactation, they’re likely to do so in subsequent lactations.

But keep a few things in mind. The study size during the Illinois experiment was small. They followed only 32 heifers into lactation, which is a small number of animals for a lactation study, Dahl says. This study also is the only one that shows the effect of long-day lighting before puberty on future milk yield.

However, previous studies have shown that extended lighting benefits mammary growth, so there’s a good chance you’ll see a positive impact on milk yield. “The mammary growth data out there are supportive of this being a true effect,” Dahl says.

Bottom line: Extended lighting holds promise as a tool to accelerate heifer growth and puberty without hurting mammary development or future milk yield.


You can learn more about extended-day lighting on the Internet,