With Pat Hoffman, University of Wisconsin-Madison dairy extension specialist
For years, dairy producers have been told they should target specific breeding weights and lower the average breeding age of their heifers.
But according to Pat Hoffman, University of Wisconsin dairy extension specialist, there’s just one small problem with this school of thought.
“No single heifer calves at the ‘average’ age. Dairy farmers calve distributions of heifers, not the average,” he said.
In other words, a dairy farm may set a goal of breeding heifers at 13 months of age and, on average, might come close to meeting that goal. However, due to common delays in breeding dairy heifers such as light body weights, missed heats and re-breedings, many heifers actually become pregnant many months later than they should. Hoffman said these delays are common, but they do come with significant economic costs. Hoffman suggest that, for each heat cycle delay, an additional cost of $60 maybe incurred due to increased days on feed.
Current research at the University of Wisconsin-Madison suggests breeding dairy heifers can be approached from a different angle. Instead of looking at individual heifers and targeting a specific breeding weight for each heifer, the goal should be to “reduce the age variance associated with getting dairy heifers pregnant.” In other words, aim to get as many heifers bred as close to the target age as possible.
Two factors can have a big influence on the age variance at pregnancy. The first factor is growth variance, which is most often associated with dairy calf and early postweaning health issues. This is the most common reason growth to breeding falls behind. The goal should be to do everything you can to keep calves and pre-breeding heifers healthy because each disease outbreak is usually accompanied by a drop in performance. The more frequently a calf or young heifer is sick, the further behind she’ll be at breeding age.
The second factor maybe more human-induced with the assumption that every heifer must be bred at exactly the same body weight. Genetically, this is not logical because some heifers are simply larger or smaller than others. Thus, an acceptable breeding weight range will work equally well as one specific body weight target.
For example, examine the herd’s genetic characteristics for body size and decide it’s realistic for almost all heifers to be between 850 and 900 pounds at 12 months of age. If that range seems reasonable, then all heifers that are within or reasonably near that range can be bred at the first standing heat after 13 months. This is a simple example of adding age back into the heifer breeding criteria. Doing so reduces the variance of pregnancy age and ultimately reduces the variance of days on feed, age of first calving and rearing cost.
This small philosophical change in the heifer breeding criteria can ultimately have an effect on the entire heifer program. In addition to a starting age criteria, an ending age breeding criteria can also help reduce heifer days on feed. For example, dairy producers may want to put three- or four-straw limits on trying to get a heifer bred. Currently, many dairy producers are considering or have adopted ending breeding criteria because feed costs are high. It may be better to cull the heifer and simply cut future losses.
Limiting the variance of age at pregnancy on dairy heifers starts with excellent calf management and good, quantifiable breeding criteria, and ends with good reproductive management. For calves, dry bedding, adequate space, good nutrition, fresh air and optimal care will result in heifers reaching the breeding criteria as uniformly as possible.
To help dairy producers see the variance in their herds, Hoffman and his colleague, Dr. Victor Cabrera, designed the “Heifer Pregnancy Rate” spreadsheet tool. Click here to access this tool on the UW Department of Dairy Science website. The tool is easy to use and gives dairy producers a quickly look at variances associated with breeding and calving dairy heifers.
“Historically we’ve placed a great deal of emphasis on managing dairy heifers by body weight,” Hoffman summarized, “but we can’t forget how important days on feed is. Those factors are equally important and we need to control the variance of both.”