Over the last 50 years in the chicken industry, the average age for pullets to begin laying eggs to 50% production has improved from 24 weeks to 20 weeks. They reduced age to maturity to begin the productive cycle of their life earlier. Part of their story is nutrition and lighting, but genetics played an important role.
In the dairy industry, the age to maturity has changed very little. We’ve certainly lowered the age at first breeding so that we now have many Holstein heifers that calve between 22 and 24 months of age. Better reproductive strategies have helped us focus on getting semen in heifers faster. We also know that if we dip below 22 months to 19-21 months, we have heifers that fall through the cracks. But there are some heifers that do not; there are outliers that seem to do just fine calving earlier. These outliers are the ones that are the most interesting to me.
In the dairy industry, we’ve known that a cow gets close to maximum size from 48-54 months. In a 2015 study (see chart), Canadian researchers put the mature size of Holsteins at 1562 lbs. Using 55% of mature weight as a target for breeding, that would lead to a target of 859 lbs. at 13.6 months. The current popular literature has done a great job pointing out that when the mature body weight is 1650, we may need to breed at higher weights (908 lbs.) with the same minimum age floor. Even though she hits 850 lbs. much earlier than 13.5 months, we likely need to wait. She isn’t physiologically mature. But this is not true for all breeds. The Jersey reaches mature size earlier, and Brown Swiss later. In the same Canadian study, it showed Jerseys reach the target of 55% maturity weight by 12.6 months; she can safely calve a month early.
Hasn’t this changed over the last 100 years in the dairy industry? In 1934, a small bulletin out of Iowa documented weights of cattle from various breeds. The Holsteins peaked at 1345 lbs. and reached 55% of mature body weight by 14 months. That’s not far from the 13.6 months in 2015, about 80 years later. Smaller cows grew along a similar growth curve. In the same bulletin, Jerseys and Ayrshires showed the same trend as modern cows. Jerseys were faster and Ayrshires were slower to the target breeding date. In 1954, another bulletin showed that Holsteins were reaching larger mature weights (1410 lbs) but age to target breeding weight was again 14 months.
Could we lower the Age to Maturity (ATM) and have a lower age to first breeding? Could we take our outliers and make them mainstream? Could we calve Holsteins at 20 months with no one falling through the cracks? Maybe, and that’s on the wish list.
How might we accomplish this? Could we look at outliers that do well at a 20-month calving age? Having a lot of heifers falling off the wagon is an expensive way to identify your target animals. Perhaps a more tedious method is needed. Could we measure individuals and measure age to maximum weight? If we had a large foundation of weights, could we correlate ATM to genetic markers? Once these markers were in place, progress could happen quickly.
Why bother? If we could shave off 60 days to first calving, that could mean $150/hd in savings ($2.50/hd/day). Would this be enough to outweigh genetic progress on other production traits?
A wish list is of course something for the future. Please remember I don’t think we can calve all Holstein heifers at 20 months today; the genetics aren’t there. But, the challenge goes out to the genetics industry: can we do this for the future?
Paul Dyk, MSc, PAS provides independent nutrition and management consulting through GPS Dairy Consulting, LLC to dairy clients with a focus on listening to and meeting his client’s goals.
