­When Ken Birker sold off 15 percent of his herd a few years ago, he naturally expected the milk in his bulk tank to go down, at least temporarily. Funny thing is, it never happened.

“We were milking about 400 cows at the time, and made a strategic decision to focus on our better animals and switch to three-times-a-day milking,” the Vinton, Iowa, dairyman explains. “It was our hope that we could eventually return to the same level of production with fewer cows, but certainly did not expect that it would happen so quickly– essentially overnight.”

In retrospect, Birker believes the remaining cows responded to an improvement in stocking density – easier access to feed and water; higher per-cow feed intake; and improved free stall accessibility, which allowed for more hours of rest per day, improved rumination and healthier feet and legs.

His experience is no surprise to Chris Hill, nutritionist for Poulin Grain, Inc., who consults with dairies throughout Vermont’s Champlain Valley. Prior to his current job, Hill managed three dairies and worked on a number of others – some large, some small, and with varying priorities regarding animal behavior and cow comfort. “After working on several dairies, I was impressed by the improvements in herd healh, reproduction and milk production I saw on the farms with excellent cow comfort and stall availability,” he says.

Lessons in cow comfort

Motivated by these observations, Hill returned to graduate school at the University of Vermont and chose to place his research emphasis on stocking density and animal behavior. His trial work was conducted at the nearby Miner Institute at Chazy, N.Y., where he collaborated with Peter Krawczel, PhD, who is now in the Department of Animal Science at the University of Tennessee.

Both researchers attempted to identify the ideal stocking density that would allow cows to behave naturally, for the best possible health and productivity outcomes. Among the results they found were:

1. Cows will choose rest over eating. Cows need between 10 and 14 hours of resting time per day, and three to five hours for eating. The remainder of the time is allocated to travelling to and from the parlor; milking; drinking water; grooming; social behavior and estrous activity. But they prefer rest over all other behaviors, and if adequate resting space is not available, they will sacrifice time for other activities to rest when they can. Krawczel cites a study that also showed an increase in the level of the stress hormone cortisol, and a decrease in growth hormone, in cows that were deprived of adequate resting time. And, in their work at the Miner Institute, they found an advantage of 3.7 pounds of milk per day for each extra hour of resting time that cows received. “It is a fallacy that if cows aren’t lying down it is a good thing, because that must mean they are up and eating,” says Hill. “I’ve spent a lot of time observing cows at all hours of the day and night, and too often we see cows just standing around doing nothing. They are interested in resting, not eating, but they cannot find the space to lie down. They simply run out of hours in the day to get it all done.”

2. Overstocking can cause an illusion of good stall comfort. Cows will use virtually any stall if they are forced to do so, but that doesn’t mean they enjoy it. University of British Columbia (UBC) research showed that standing versus lying time is longer in uncomfortable stalls. In other words, cows will climb right in, lie down and stay down in comfortable stalls, but will stand longer if they are uncomfortable. Another sign of discomfort is a high incidence of cows “perching” with two feet in a stall – whether occupied or unoccupied by another cow. Krawczel says researchers at the UBC found that cows would use less-preferred stalls more frequently when preferred stalls were blocked, indicating that it was a “forced” choice. For this reason, Hill feels that the Stall Use Index (SUI) provides a better assessment of comfort in overcrowded situations than either the Cow Comfort (CCI) or Stall Standing Indices (SSI) because SUI acccounts for all cows in the pen that are not eating and not just those occupying a stall.

3. Bedding and stall maintenance matter. Excellent bedding and stall maintenance can compensate for many other imperfections, including small stalls. Hill says a deep, clean, inviting surface will encourage cows to readily lie down. The type of bedding matters, too. UBC research found a 23.8 percent incidence of hock lesions when sand bedding was used, compared to 69.7 percent with sawdust and 91.7 percent with mattresses. Numerous mastitis studies also have shown a lower incidence of environmental mastitis with sand bedding compared to organic materials. Hill says sand usually is less expensive and more available than other types of bedding. He adds that he has seen farms develop a number of creative ways to keep sand out of the mechanics of manure removal equipment, which is often a factor that creates reluctance to use sand. “I tell people, you can break your manure equipment, or you can break your cows,” advises Hill. “A machine can’t feel pain and discomfort, but the cows definitely can.”

4. Feeding behavior is affected, too. Cows have a tremendous propensity to eat, and overstocking at the feedbunk can drive cows to the point of physical injury. Research has shown that cows will willingly exert more than 500 pounds of pressure against the feed barrier while eating. Tissue damage occurs at 225 pounds of pressure, meaning that cows can permanently wear the scars of overcrowding at the bunk. “When you walk onto a farm and see cows with massive calluses on their necks, it is more likely to be a feed bunk push-up or design problem than a stall problem,” says Hill.

5. Heifers and lame cows will suffer first. Natural animal behavior dictates that dominant animals will gain more ready access to stalls. In Hill’s research, he found that milk production started to drop in first-calf heifers mixed with older cows when they were just 15 percent overstocked. He found that lame cows started to lose production at the same threshold of 15 percent overstocking when mixed with healthy cows.

It depends…

So what is the ideal stocking density? “Unfortunately, there is no ‘magic number,’” says Krawczel. “It really comes down to adjusting up and down from your current level.” Barn design, stall design, 2X or 3X milking, location of waterers, weather, bedding and a host of other factors have bearing on the decision, he says, noting that 120 percent is a reasonable number to work around in many cases.

At the Birker Dairy in Iowa, they have arrived at a stocking density of 120 percent for first-calf heifers and 112 percent for higher-parity cows. Ken Birker adds that those numbers always are fluid, and are regularly re-evaluated based on current weather, feed and cow health conditions.”

Hill says his experience has shown that stocking density is intricately linked to virtually every aspect of cow health and performance – milk production; udder health and milk quality; fresh-cow health; foot and leg health; estrus expression and reproductive efficiency, and more. Less-than-optimal results in any of those areas could be linked to overstocking.

For example, “a lot of people try switching to 3X milking and are disappointed that they don’t see much of a response,” shares Hill. “The reason could be that the herd’s stocking density is too high, and then they are asking even more of their cows. The cows get even less rest, and they just can’t respond with higher production. I firmly believe the most successful dairies are the ones that make their decisions based on what is best for the cow,” he says. “If the cows are comfortable and healthy, everybody wins.”