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Paying attention to age at first calving is worth your time

Robert Fourdraine Published on 24 August 2015

Optimal age at first calving has been debated for many years. There are many factors that can influence when a heifer calves for the very first time. Having a good heifer-raising program, coupled with an effective breeding program, are key elements.

There has been discussion about how early heifers can, or should, calve for the first time. Various studies have reported lifetime production gains, but there are also increases in calving problems that could offset those production gains.



Most producers have experimented with calving heifers earlier, and depending upon their personal experiences, have established what works best for them. An often overlooked factor that could have a much bigger impact is how consistently heifers are calved for the first time.

The question becomes, then: How consistent is the heifer-raising and breeding program on the farm? One way to evaluate this is by looking at the percentage of heifers actually calved by a producer-set calving age goal and the distribution of calvings outside of this goal. Analyzing close to 500,000 AgSource calving records since January 2013 can help us shed some light on what we typically see and how individual herds can differ.

Overall trends

Analysis of calving records shows that herds on 2X milking average 24.9 months old at first calving, while herds on 3X milking average 23.4 months. However, there are significant differences based on herd size. Figure 1 shows the average calving age by herd size. As herd size increases, average age at calving decreases, with the exception being large herds milking twice.

calving age by herd size

The overall distribution of calvings is shown in Figure 2. Herds on 2X milking show a greater spread compared to herds on 3X milking. Past research conducted by Dr. Pat Hoffman at the University of Wisconsin using calving and lifetime production data, shows increasing lifetime production losses as calving age increases.


calving distribution

For herds milked three times, heifers calving at 25 months versus 24 months produce approximately 1,200 pounds less over their lifetime, while heifers calving at 29 months versus 24 months produce roughly 6,000 pounds less lifetime milk.

As shown in Figure 3, for herds milked three times, there are significant differences of calving distributions based on herd size. Larger herds have fewer outliers, reducing lifetime production losses.

3x milking calving distribution

Differences by herd

Analysis of data shows there are significant differences between herds. Given those differences, what is the economic impact of having a more consistent calving distribution? Using calving records of two herds on 3X milking, we will try to answer this question.

When comparing Herd 1 to Herd 2, there is a difference in calving pattern. Herd 1 has a much tighter pattern than Herd 2. If both herds’ goal is to have heifers calve by 24 months, Herd 1 had 20 percent of heifers that calved 24 months or later, while Herd 2 had 27.6 percent of heifers calving 24 months or later.


By itself, that is not a big difference, but when taking into consideration the distribution and associated lifetime production losses, assuming $20 per hundredweight milk price, lifetime losses for Herd 1 average $144 per cow, while Herd 2 averaged losses of $340 per cow (for heifers calving at 24 months or greater).

How to analyze your heifer management program

It is unrealistic to expect all heifers to calve within the desired range, but managing the number of outliers can present you with some significant financial opportunities. Figure 4 shows a guide to compare a herd’s age at first calving pattern with herds of similar size and times milked.

age at first calving guide

To use Figure 4, you must have data on the total number of heifers you calved in the past year and the distribution of how many calved by each age category. Select from Figure 4 the column that best reflects your herd size and times milked.

Multiply the percent listed in each cell with the total number of heifers that calved in the year and divide by 100. Place this value in the column labeled “Expected # Heifers” and insert the actual number of heifers that calved in the column labeled “Your Herd.”

For example, if your herd size is 300 cows and you milk 2X per day, select the column labeled 250 to 500 cows. If you calved 100 heifers in the past year, the expected number of heifers calving at, for example, 26 months would be: (9.0 x 100)/100 – or 9 heifers. Follow this step for every cell.

To evaluate how consistent your calving pattern is, compare your actual numbers with the expected number. If your target is 23 months, compare your number with the expected number for heifers calved 24 months or greater.

If your number is greater than the “expected number,” then there is an opportunity to improve your heifer management. As stated before, the higher the age at calving, the greater the opportunity is.

1000+ herd milking distribution


Evaluating the consistency of your heifers’ age at first calving can lead to significant lifetime production gains. Lifetime production losses increase as calving age increases past 23 to 24 months old.

Use the figure to compare your calving pattern over the past year with the pattern of herds of equal size. This will give you an indication of how large the financial gains are you can obtain through greater consistency of calving age. PD

Robert Fourdraine is the vice president of DHI Operations with AgSource Cooperative Services. He can be contacted by email.