We have recently updated an article about trends in age at first calving using records obtained from DRMS for all first-lactation Holsteins in Pennsylvania during 2015.
In Pennsylvania Holstein herds, the herd-average age at calving has been hovering around 25.5 months for several years. The 2015 data included records for 110,280 heifers with age at calving ranging from 18 to 30 months (average 24 months, standard deviation 2.24 months). More heifers calved at 24 months than any other age, which we have seen for a number of years now. Nearly 75% of heifers calved at 25 months or less and 66% were between 22 and 25 months of age at calving, 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.
Actual 305-day lactation records from these heifers showed that average milk production was 19,150 pounds. 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, 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.
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. If your heifers aren't calving by 24 months of age, you have an opportunity to improve your returns from investments in rearing costs.