Heifers are an expensive part of the dairy business. By most accounts, heifer rearing costs are the third largest contributor to the total cost of milk production, behind feed for the milking cows and labor.
Studies show that the age of the heifer at calving has a profound impact on what it costs to raise that heifer. In addition, we know that body weight at calving and rate of growth before puberty impact the first-lactation production potential of that heifer. Heifers seem to get more attention now than they did several years ago, partly because of these factors and partly because we are doing a better job of controlling heifer diets and management.
We obtained records from DRMS for all first-lactation Holsteins in Pennsylvania during 2015. We also accessed DRMS Dairy Metrics for the average age at first calving by herd. The graphs presented here give us a closer look at what is happening to age at first calving in Pennsylvania.
In Pennsylvania Holstein herds, average age at calving has been hovering around 25.5 months for several years and is trending lower over the last 12 months. Data from DRMS Dairy Metrics indicate that herd-average age at calving was 25.66 months in 2007, 25.51 months in 2009, 25.48 months in 2011, and 25.68 months in 2013. In 2015 the average age at calving was 25.51 months, and Figure 1 shows the current trend from April of 2015 through April of 2016. Age of first lactation cows has been less than 25.5 months over the past year.
Figure 1. Age of first lactation Holsteins (months) in Pennsylvania from April of 2015 through April of 2016. Data from Dairy Metrics, DRMS, Raleigh, NC; May 2016.
Figure 2 shows the number of Holstein heifers who calved at various ages during 2015. This graph represents 110,280 heifers with age at calving ranging from 18 to 30 months (average 24 months, standard deviation 2.24 months; records collected by DRMS). In 2015, there were more PA heifers calving at 24 months than any other age, which we have seen for a number of years now. The aspect of this graph that has been changing is the number of heifers calving at less than 24 months. As you can see, in 2015 more heifers calved at 23 months than at 25 months, and the number calving at 22 months was more than the number calving at 26 months.
Figure 2. Distribution of age at calving of 110,280 first-lactation Holstein heifers in Pennsylvania in 2015. Data from DRMS, Raleigh, NC.
While there are a few that calve very late--30 months and beyond (not shown here), they are a small number in comparison. In fact of these Holstein heifers from 2015, 60% calved at 24 months or less and 74% calved at 25 months or less. The other noticeable aspect of this graph is that most of the heifers (66%) are clustered between 22 and 25 months, meaning they are getting bred in a relatively short interval. This may be enhanced by improved reproduction management and grouping or more aggressive culling of problem breeders.
Figure 3 shows the actual 305-day lactation records from the heifers in Figure 2. This data set is based on a calendar year, so many heifers had not yet completed their first lactation. The actual average days in milk was 281, with a range of 45 to 305 days. Even with this variability, we see that heifers calving at 21 months of age made the same amount of milk as older heifers, demonstrating that heifers can calve early and still make the milk that we want. Average milk production (again, including incomplete records) was 19,150 pounds for the 2015 heifer crop.
Figure 3. Average actual 305-day milk production by age at calving of first-lactation Holstein heifers in 2015 in Pennsylvania. Data from DRMS, Raleigh, NC.
Another way of looking at the milk production data is presented in Figure 4. In this graph, each X represents a single heifer. Again, it is clear that heifers calving before 24 months of age can achieve high yields. However, a close look at the solid section near the top of each column shows that the number of heifers milking at the highest levels increases for each age category from 20 months through 23 months and then decreases through 28 months.
Figure 4. Actual 305-day milk production and age at calving of first-lactation Holstein heifers in 2015 in Pennsylvania. Each X represents an individual heifer. Data from DRMS, Raleigh, NC.
Obviously, the concept of producing the same amount of milk from younger animals is the driving force behind reducing age at calving. This quick look at Pennsylvania DHI records shows that it can be done successfully. From these graphs you can see there were very few Holsteins calving at 20 months or less, and those calving at young ages did not produce as well. However, from 21 months on the results appear very positive. These data do not allow us to evaluate the number of heifers that calve but do not complete their first lactation, but past research has shown that heifers calving too early have a higher risk of being culled in the first lactation. Calving at 22 to 24 months of age is recommended.
Take a look at your herd's age at calving. Studies show that for every month beyond 24 months, heifers cost you an additional 5% per month to keep them in the heifer barn. In that case, once heifers get out towards 30 months before calving, they are costing you an additional 30% or more just to get them in the milking string. This likely does not pay for any farm.
Said another way, heifers that calve at 30 months or more were successfully bred at the age they could have been calving. That amounts to trading nine months of milk income for extra feed. A select group of heifers with exceptional genetic merit may be able to recoup these costs, but for the vast majority of heifers we need to focus on breeding by 13 to 15 months and consider culling those that fail to breed within that window.
This is an updated and expanded version of an article published in Hoard's Dairyman, April 25, 2013. Reviewed by Rob Goodling, Penn State and Logan Horst, Penn State.