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Animal Health & Nutrition

RSS By: Rick Lundquist, Dairy Today

Rick Lundquist is an independent nutrition and management consultant based in Duluth, Minn. He provides livestock production advice.

Dark Days Ahead

Nov 07, 2011

Concerned over stagnant milk production in the fall? Among possible reasons for this phenomenon, decreased day length and photoperiod response are worth watching.

I was talking with a dairy producer who was disappointed with his herd’s stagnant milk production this fall. He decided to feed some of his top-quality alfalfa hay to try to jump-start his cows. Nothing happened, so he took it out.
I’ve heard the concern over stagnant milk production in the fall for years. The weather cools off, but the cows don’t “take off.” There are several possible reasons for this phenomenon.
1.       Many herds freshen heavily in the fall. The average days in milk doesn’t reflect the scatterplot of the herd -- lots of fresh cows that haven’t come into milk yet, plus lots of stale cows getting ready to dry off.
2.       Cows may also be restoring body condition after the summer, so a larger portion of the energy consumed is used for tissue growth and restoration.
3.       Day length is decreasing rapidly. This is what I want to concentrate on here.
Photoperiod affects hormones, which, in turn, affect lactation, reproduction and growth. Melatonin is a hormone that is directly responsive to light and dark. It influences the secretion of insulin-like growth factor and prolactin. Both of these hormones affect the mammary gland and are associated with increased milk production. Concentrations of both of these hormones are reduced when days are short compared to longer days.
In a review on this topic, Geoffrey Dahl at the University of Florida reported that milk production increased an average of 5 lb./cow/day with long-day length compared to short-day length. This response was regardless of stage of lactation.
The effects of day length on milk production should be more pronounced in animals that are housed outside, such as dry lots or pasture. Artificial lighting can alleviate some of this malaise. Dahl recommends 16-18 hours of light at 15-20 footcandles, 3’ from the floor of the stall. But it is also critical to have at least six hours of complete darkness.
Ironically, short days benefit dry cows. Dry cows respond to short days by decreasing circulating prolactin, but at the same time, receptors for prolactin are more responsive. This response increases mammary gland growth and improves immune function. Dry cows housed under short days produced 7 lb./day more milk after freshening relative to dry cows housed under long days. This response was irrespective of day length after freshening. The dry cows housed under short days also had lower somatic cells counts and improved mammary health after calving.    
Growing animals grow faster when days are longer. Heifers put on more lean tissue, grow taller and reach puberty faster when days are long compared to shorter day length.
So, this photoperiod response probably explains a lot of the frustration over slow milk responses in the fall. It happens every year. It’s still hard to tell an anxious dairy producer, “Just wait till January.”
Reference: Geoffrey E. Dahl. Let There be Light: Photoperiod Management of Cows for Production and Health. 2005. Proceedings 42nd Florida Dairy Production Conference.
Contact Rick Lundquist at
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