Extended days open aren’t just a problem during a cow’s current lactation.

Researchers in Florida have shown that there’s a carry-over effect. And it’s generally not a good one. That’s because extended days open may increase the risk of over-conditioning cows toward the end of their lactation due to the fact that milk yield is typically lower at this point. These cows may have an increased risk of death or culling around the subsequent calving because of related metabolic problems.

To get the data used in the study, the researchers scoured Dairy Herd Improvement records for 2,075,834 observations of cows calving between 2001 and 2007 in herds located in 36 U.S. states located primarily east of the Mississippi River.

The results show that as days open increased, so did the risk of culling or death.

In addition, the effect of days open on the risk of death was slightly greater for third-lactation cows, for long dry periods, for cows with low test-day milk yield before dry-off before calving and for spring calvings.

The authors say they found an increase in the risk of death and culling as a result of extra days open for 90 percent of the herds included in the study.

When you put some cost figures to these results, the picture is grim, generally due to the opportunity cost of lost income.

For example, an involuntary live cull just after calving has a price tag of about $1,000. A death just after calving is pegged at $1,500.

This is just more proof that it pays to get cows bred on time, and the penalty for failing to do so is costly.

Get more results (scroll down to page five).