Herd Data Key to Managing Dairy Replacement Heifers
Posted: November 5, 2012
Today’s higher feed costs impact not only the lactating herd, but the replacements being raised as well. This increased investment cost for replacement animals has producers examining their heifer inventories and replacement needs. New tools like genomic testing have improved a producer’s ability to identify the genetic potential of their heifers, but there are several factors that need to be considered when examining heifer inventories.
Internal Herd Growth
Knowing how many replacements you need annually to achieve your dairy’s goals (maintain herd size, expand, or downsize) is a key starting point to managing heifer inventories. This number is easy to calculate with a few key herd metrics: herd size (HS; milking and dry cows), average age at first calving (AFC), herd cull rate (CR), and the non-completion rate of heifers (NCR; heifers that enter the replacement growing business but do not enter the dairy herd). The formula is: HS × (AFC ÷ 24) × CR × (1 + NCR). This will yield the number of heifers a herd would need annually to maintain their current herd size based on the age animals enter the herd and the rate cows and heifers leave the operation.
Let’s look at an example 100-cow dairy herd. Heifers calve in at 25 months, cull rate is 35%, and the non-completion rate for heifers is 10%. Plugging those into the formula we have 100 × (25 ÷ 24) × 0.35 × (1 + 0.1) = 40 heifers annually, or a total heifer inventory of 80. It is important to realize changes in culling rate and non-completion rate in heifers can have a significant impact on this number over time. Evaluating an operation's cull rate and non-completion rate history to see trends and fluctuations is beneficial in determining how accurate the calculation will be over time.
Another key to heifer inventory is identifying how many heifers you can expect annually. Again, having a good understanding of several herd metrics will make this determination easier. To do this, herd size (HS), calving interval (CI), calf sex ratio (SR), calf mortality rate (CM), and age at first calving (AFC) are needed. The formula includes the time period (1 year for comparison) as well. The formula is: 1 (time period) × HS × 12 ÷ CI × SR × (1 – CM) × AFC ÷ 24. So if our example herd had a calving interval of 13 months, a calf sex ratio of 50%, and calf mortality of 10%, we would have: 1 × 100 × 12 ÷ 13 × 0.5 × (1 – 0.1) × 25 ÷ 24 = 44. So, if this herd’s metrics and ratios remain consistent, after one year’s time they would have 4 heifers more than what they would need as replacements. This gives them a few options: grow the herd, cull more cows, or sell heifers.
Monitoring and Evaluating Heifers
At some point there may be enough heifers on hand to easily handle the needs of the milking operation, so the question arises who should leave and when. Genomics can be very useful to help identify the heifers with greater genetic potential or identify heifers with lower genetic potential. This should not be the only factor considered. Health events and growth rates for these heifers can also be very useful to create a complete picture of heifers with the greatest potential to do well in the lactating herd. The more factors available to assess a heifer’s potential and value, the better decision can be made. To do this, heifer records will need to be maintained and monitored routinely to provide the quality data needed to make such assessments.
Controlling costs is just as important as ensuring the quality and quantity of heifers entering the dairy herd. Understanding a herd’s unique heifer need and availability based on key herd metrics can achieve insight into potential limitations or excess availability of heifers. Controlling these metrics to improve access to replacement opens the dairy business to greater control of quality of heifers becoming their next lactating herd participants.
- Extension Associate, Penn State Extension, Department of Animal Science