More bunk space, please

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Bunk space in the pre-fresh pen may hold the answer to why fresh-cow performance falters.

That’s a strong statement, but it shows just how convinced Ken Nordlund is about pre-fresh cows needing at least 30 inches of bunk space instead of 24 inches. Nordlund, a veterinarian at the University of Wisconsin, says there is good reason to stock the pre-fresh pen based on bunk space per cow instead of cows per stall.

This way of thinking is not widely used. Stocking density is often based on the number of stalls or headlocks in the pen. After all, you need to get as many cows in there to keep overhead down. And from time to time you’re going to have more cows ready to freshen than you have room for them. However, field data analyzed by Nordlund and his colleagues at the UW-Madison School of Veterinary Medicine present a compelling case for giving cows 6 more inches of bunk space in the pre-fresh pen.

Here’s why you should rethink it, too.

Cows want their space

The natural behavior of cows is to space themselves 12 feet apart, Nordlund says. Confinement housing does not make this pasture-based instinct practical. Still, cows crave more space at the bunk.

When they don’t get it, bad behavior erupts. Cows jostle for a place at the bunk like kids in a cafeteria lunch line. In the end, it’s the meek cow that relinquishes her spot at the bunk to the bully.

Nordlund and colleagues have collected hundreds of hours of video footage that prove it. Many others have, too. 

Do those subordinate cows eat less, or do they come back later and get their fill?

“We believe they will eat less,” Nordlund says. He points to data collected on two New Mexico dairies that show as headlock density increases, feed intake drops. (Please see “Overcrowding hurts pre-fresh feed intake” at right.)

In contrast, the more room at the bunk, the fewer displacements that happen.

A September 2006 Journal of Dairy Science study documents this quite well. Far fewer cows were displaced from the bunk when eating space increased from 25 inches to 36 inches per cow. Partitions between adjacent cows, or “feed stalls,” improved time at the bunk, too.

Although the study involved lactating cows, the benefits of adequate bunk space are not limited to lactating cows. Pre-fresh cows need plenty of access to feed in order to minimize the drop in feed intake that occurs as calving approaches.

The 1.6-pound effect

The damage from overcrowding pre-fresh cows at the bunk is particularly acute for subordinate animals.

“If bunk space is restricted, it’s the low-rank animals that pay the price,” Nordlund says.

Field data analyzed by Nordlund’s colleague Gary Oetzel, also a veterinarian at the University of Wisconsin School of Veterinary Medicine, document the severity of the problem. Here’s what it found:

In a pre-fresh pen with 24-inch headlocks, each 10-percent increase in headlock occupancy above 80 percent resulted in a 1.6-pound loss in daily milk yield in the cow’s next lactation.

Take note that this production loss starts at an 80-percent stocking density. “This means that there are production losses even in two-row pre-fresh pens where every cow has a stall, but not all cows can eat at the same time,” Nordlund says.

Look at it this way. If you have a 12-foot panel with six headlocks in a two-row pen stocked at 150 percent of stalls, you have nine cows for every 12-foot panel. Video studies of feeding behavior show that cows fill 24-inch headlocks to a maximum of 80 percent in peak feeding periods. In other words, each panel provides simultaneous feeding space for 4.8 cows. That leaves four cows without access to the bunk during peak feeding periods. Usually, those are the subordinate cows.

This 150-percent stocking density creates an 11-pound milk loss per cow per day for the lowest ranked one-third of cows in the pen.

Here’s the math:

150 % —  80 % = 70 %

Remember, each 10 percent increment above an 80-percent stocking density costs you 1.6 pounds of milk per cow per day.  

70 % ÷ 10 % = 7 increments

7 increments x 1.6 lbs =

11.2 lbs of milk lost per cow per day.

Cows need 30 inches of bunk space in the pre-fresh pen. “Quit counting headlocks and start counting inches,” Nordlund says.

Are you up to the challenge?


How to give cows 30 inches of bunk space

Increasing bunk space from 24 to 30 inches doesn’t necessarily mean you need to tear out your existing headlocks and buy 30-inch ones. You can still achieve 30 inches of bunk space per pre-fresh cow by under-stocking the pen.

Here’s how:

Let’s say you have a 12-foot panel with six headlocks. The headlocks are 24-inches apart, from the center of one to the center of the other. To find out how many cows can eat at once and still receive 30 inches of bunk space per cow, simply divide the length of the panel by 2.5 feet (i.e., 30 inches).

Here’s the math using a 12-foot panel:  

12 ft ÷ 2.5 ft = 4.8  cows

That means, about five cows can eat at once, and each receives 30 inches of bunk space. Stock your pre-fresh pens according to the number of cows that can eat at once, not cows per stall.



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