Increase pregnancies by 7 percentage points
By Kimberlee Schoonmaker  |  Wednesday, November 01, 2006

You are probably familiar with the phrase, “Don’t jump the gun.”

That adage was not lost on researchers in a Journal of Dairy Science study published last year. The study found that a 28-day dry period appeared to benefit reproduction. However, “we didn’t have enough animals in that study” to accurately evaluate reproduction, acknowledges Milo Wiltbank, professor of reproductive physiology at the University of Wisconsin.

The study showed cows given a shorter dry period ovulated eight days earlier than cows given a 56-day dry period. Days to first ovulation can be accurately measured, even with the 2o or so cows that they used per treatment, Wiltbank says. Still, they were reluctant to “jump the gun,” and make assumptions about other reproductive variables until more work could be done with more animals.

Now, Wiltbank and his colleagues have data in hand from a 772-cow field trial. Those numbers give them the confidence to say a reduced dry period does indeed benefit reproduction, particularly in cows going into their third or more lactation. Here’s what the research has to say.

Fewer non-cycling cows

During the study, cows given a 34-day dry period ovulated earlier than cows given a 55-day dry period. In fact, short-dry cows averaged 35 days to first ovulation — eight days less than cows on a 55-day dry period. This is consistent with the small-scale study published last year, which showed a reduced dry period shortened the time to first ovulation by eight days.

What’s even more interesting is that at 70 days in milk 92 percent of the short-dry cows were cycling versus 82 percent of the 55-day dry cows. That means, only 8 percent of the short-dry cows were not cycling at 70 days in milk, versus 18 percent of the 55-day dry cows. “The short dry period decreases the number of non-cycling cows,” Wiltbank says. 

Fewer days open

The large commercial herd where the study was done maintained a voluntary waiting period of 45 days. Any animals not bred by 70 days in milk began the Ovsynch program.

The results show time to first insemination was not a problem for the short-dry cows. Those animals averaged 67 days to first service versus 72 days for the 55-day dry cows.

Despite fewer days to first AI, there was no difference in first-service conception rate between the two treatment groups.

However, short-dry cows had 17 fewer days open, says Rick Watters, Ric Grummer’s former graduate student who is now pursuing his doctorate at Cornell University. A trend toward fewer days open was particularly true for cows going into their third or more lactation (For more details on the interaction between stage of lactation and future performance of cows given a reduced dry period, please see the related item on page 44 in Research Track.)

More cows pregnant 

A reduced dry period also improved the percentage of cows pregnant at 150 days in milk.

In fact, 61 percent of the short-dry cows were pregnant at 150 days in milk. In contrast, 54 percent of the 55-day dry cows were pregnant at 150 days in milk. All in all, that translates into a 7 percentage point improvement in the number of animals pregnant at 150 days in milk.

And that’s good news for calving interval, too. “If you have more cows pregnant at 150 days in milk, your actual calving interval should be lessened in animals with a reduced dry period,” Watters says. “Where that was seen was in the 17 fewer days open.”

Another important point is that the reproductive benefits they saw from shortening the dry period were independent of milk production, says Ric Grummer, chair of the dairy science department at the University of Wisconsin-Madison. In other words, the short-dry cows had better reproductive performance, but it’s not because they slacked off in milk production. “Their milk production really compliments the reproduction data,” he says.

So, if you need further motivation to reduce the dry period, particularly for older animals, these reproductive results certainly give you more proof that it benefits cows in their next lactation.

¿Habla Español?

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

The results at a glance