The Moos Room™

 Welcome to The Moo's Room. Just back from the state fair tonight. I was there the last five days working with the 4-H shows and calculating all the total merits my grad students did and working with a lot of 4-H-ers. Plus, my daughter had a Holstein cow there. Didn't do as good as what we liked, of course, but she wasn't on the bottom, so that's always a good thing.

But we, we did okay, and, uh, everything's good. We're all back home. Everybody's tired, which is a typical fair. Things, you know, I think about our genetics all the time, especially with all of the total merits, and maybe we'll summarize some of those things as we get into the future and kind of look at what the genetics of a 4-H show is into the future.

It's kind of interesting. We didn't have any genetic merit winners in the Jersey breed because we don't give out awards for negative numbers. The Milking Shorthorns were the same, no genetic awards in the Milking Shorthorn show because all of the animals were negative net merit. But anyways, we'll move on and talk about something else.

Today, I really wanted to talk about heifers and something that sounds pretty simple, and that's age at first calving. And we've talked about for years about getting Holstein heifers calved in at twenty-two, twenty-three, maybe twenty-four months. But there was a new study that was done by Mike Overton at Zoetis, and that really looked at a large data set of almost one hundred and thirty thousand cows from seventy-four dairy herds.

And really what I like about this study is it makes us really look beyond first lactation milk production. And if we only looked at three oh five milk, we might convince ourselves that waiting a little longer is better But once we kind of follow the cows and account for who stays in the herd and look at the economics, maybe the answer changes a little bit.

So we're gonna walk through some of the things that was measured, why maybe milk production might matter a little bit, what happened to replacement risk, and where maybe the practical target lands for age at first calving. Obviously, we'll talk about some of the limitations, because this really was an observational study, and age is probably not the only factor that makes a heifer ready to calve.

So what did they actually do? Well, this was a retrospective study, so they looked at dairy comp records from the seventy-four farms that gave permission to use their records. The cows were Holstein. They were born from January of twenty twenty through June of twenty twenty-one, so we had to make them last a long time as well for productive life.

And the authors kept heifers that calved from twenty-one to twenty-seven months of age. And then they followed production and survival through three hundred and five days of second lactation when they had records available. So it's actually a quite a large data set, and it certainly accounted for a lot of different factors that go along with these cows, as well as herd, month of birth, any health problems, twins, stillbirths, things like that And age at first calving, as we know, is connected to growth, uh, breeding management, health, fertility, genetics, and culling decisions.

So we're gonna kind of look at these outcomes and how they're associated with age at first calving

So they used three measures in this paper as far as how milk was looked at. First, they looked at 305-day milk production. Obviously, this is kind of our standard that we've had throughout the industry However, cow leaves a herd early, obviously we can still project their milk to three hundred and five days.

The second measure was cumulative, and that was the milk that was produced through three hundred and five days of first lactation or until the animal left the herd

And then they had cumulative one and two, so they had milk production from first lactation and added it to milk production from second lactation if they were actually in the herd and, and didn't get culled or died before that. So cumulative milk really asks how much the herd received while the cow was present in the herd Although neither metric is really useless, but when we're talking about economics of age at first calving, maybe the cumulative milk production captures the survival a little bit more that maybe milk projection to three hundred and five days can hide.

So if we look at projected three hundred and five day milk, the age at first calving group that I would say were the highest was twenty-six months at first calving, and their predicted yield was a little over eighteen thousand pounds of milk

The 23-month group was not much less, really only about 150 pounds of milk of projected 305 days. So we're not talking a lot. It's not a huge difference. Obviously, older heifers were also heavier, bigger heifers, which probably gave them more intake capacity, less nutrient demand for continued growth. So biologically, it probably fits.

But I wouldn't say that we should base this on and say, "Oh, well, we need to hold our heifers so they calve at 26 months just to get more milk production." That was certainly not the goal as well. Obviously, they only had body weight available on a few farms, so it's really hard to kind of look at that difference between body weight and milk production.

But alas, the milk production was the highest at 26 months. It was an interesting result, obviously not the whole result. The practical question is whether these cows stayed in the herd long enough to have enough milk and calves generate for revenue So if we look at cumulative, now the answer really changes.

So when they totaled milk production produced through second lactation, the peak moved to 23 months of age. So that group produced about 37,000 pounds of milk as a cumulative measure. You know, these are first lactation cows, so productions can be a little bit less on average across 75 farms. But the 26-month group was about 2,000 pounds left.

Twenty-seven months was well over 6,000 pounds of milk, so a lot. So the difference between the 23- and 26-month group was roughly 2,400 pounds or 1,000 kilos of milk. The difference between 23 and 27 months was almost 6,000 pounds of milk or 2,600 kilograms. So why did this really happen? It's not because the 23-month-old cows had the highest projected first lactation milk yield, because they didn't.

It really happened because more of the younger calving cows remained in the herd and accumulated more days in milk. So really the metric is kind of doing exactly what it's designed to do, and that's add up all the milk production. So a cow that is sold or dies stops contributing milk. So that's why I think the cumulative milk might be a more useful metric for this kind of question, especially when we're trying to connect heifer management to survival and economics

But they looked at replacement risk, and the replacement risk increased from about 17% for the 21-month group to 35% for the 27-month group

Basically, it says that The heifers calving at 27 months may have had slower growth, poorer fertility, more disease, little bit different genetics, management history was a little bit different, and that all affected survival. And really, basically it said the older calving cows were more likely to leave the herd early, so obviously that affected their projected milk production and increased replacement costs for that group.

So the older an animal was, you have more replacement cost and they were culled a lot sooner They also looked at stillbirth. That didn't really rise with calving age, not much difference at all. 21 months, 4%, 26 months about 3%. If we think 24 months, about 3% as well. So really not much difference in age at first calving for stillbirth

If you look at net income, so net income was kind of flat through 23 months, from 21 to 23 months. The 21, 22, and 23 were really identical, around $5,000 in the modeled net income. But I wouldn't really look at this study and say that every farm has to hit exact day or exact month for calving. The meaningful change really started at 24 months of age, where the net income really started to decline, and it declined to about $4,388, so $4,388 at 27 months.

And this economic model included milk, calf value, feed, replacement cost, any other additional cost of keeping a heifer in the rearing pen. So it really... Actually, the direction makes sense. So delayed entry into the milking string added cost every single day and had higher replacement cost, and that higher replacement cost shortens the productive period over which the initial investment of this heifer can be recovered.

So really the takeaway was 22 to 23 months from a net income perspective Why was 27 months maybe lower? Well, the total revenue was $52 lower than the 23-month group. And if you really put everything together and model net income, it was about $650 lower at 27 months

So really the milk production difference didn't really overcome the extra rearing days or the extra replacement cost. And so calving them later and having milk production did not reduce the higher replacement cost that we saw in this study So basically, this study supports a target of around twenty-two to twenty-three months of age at first calving only when the heifers are grown adequately.

So we really have to think about average daily gain and trying to breed heifers at sixty percent of mature body weight, and first calving is around eighty-two to eighty-five percent mature body weight. So maybe you would much rather breed a well-grown heifer at the right size than breed every heifer on the same day.

That kind of goes for calving as well. So delaying a small heifer is not really a growth program, but pushing age lower without adequate body weight is really not optimizing things either. Obviously, body weight wasn't available on farms, so it's really hard to figure this out. But really on farms, the practical question is whether the heifers are reaching both age and size targets consistently without having excess body condition.

So we really need to think about taking some measurements when we're doing this Sort of one management point I would take away from this study is to look at the tail of the age at first calving distribution and maybe not just the average. So a herd can average twenty-three months and still have meaningful number of heifers calving at twenty-six, twenty-seven or twenty-eight months

And this kind of study had also looked at a small University of Idaho study that surveyed 40% farms that limited breeding to 90 to 120 days during the breeding season. And the study found that really we didn't look at a breeding window intervention. So maybe we need to think about breeding and heifer growth and age all at the same time, and do we keep breeding in growth or health and or we start using some different strategies for our replacements

So what do we do with this study on a farm? First, I would probably look at the distribution of age, age at calving, and you can plot that on your farm pretty easy in farm software or DHI. The average can look fine, while a costly tail, so those on the extremes, are kind of hiding some things. Second, I would probably pair age at first calving with actual body weight or if you, if you have body weights or kind of trying to figure out what a proxy for mature size is.

If heifers are not reaching the breeding and calving weight targets in our herd, that's maybe a question that we need to look at and evaluate our heifer growth program. Third, I'd probably look at cumulative performance. You know, projected 305 milk is okay, but maybe we should look at cumulative days and how much milk they get from first to second lactation, and actually looking at the economics of trying to pay back that replacement cost.

So this study really gives us a reason to kind of look at our age at first calving and kind of examining those ones that are late calvings way out there and kind of try to make the best decision on our heifers and try to be more consistent and have better information. So really the bottom line is that 22 to 23 months looked like a practical target for Holstein heifers when they're actually grown and ready to calve.

The economics were identical from 21 to 23 months, so I wouldn't really obsess over one exact month. You know, if you calved them at 23 months, you're probably gonna be just fine. What I would try to avoid is deliberately delaying a ready heifer because of older animals might project a little more milk production.

The cumulative milk replacement risk and economic results all showed that against later calving groups, really especially when we got past 24 months. At the same time, age is not a substitute for growth. We need heifers to reach body weights, stay healthy, and become pregnant quite quickly and enter the milking string with enough body size to produce without sacrificing things.

So hopefully this gives you a few things to look at in your own heifer program and hopefully you have the data and are able to look at that. So if you have any comments, questions, or scathing rebuttals, feel free to contact me at The Moo's Room. That's T-H-E-M-O-O-S-R-O-O-M @umn.edu, or find us on the web at University of Minnesota Livestock Extension or UMN WCROC Dairy.

And with that, hope you have a great week. Bye.