Dairy cow reproduction has improved significantly over the past decade, but virgin heifer reproduction has remained relatively flat. Why?
In this episode of Ruminate This, Scott Zehr explores whether mycotoxins in virgin heifer TMRs could be quietly influencing heifer conception rates and dairy fertility. While dairies have made major advances in reproductive protocols, genetics, and technology, heifers may represent one of the biggest remaining opportunities for improvement.
Scott explores why heifer diets are often among the least-tested rations on the farm, how multiple mycotoxins can affect immune function and hormone signaling, and why young animals may actually have less margin for error than many assume.
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If heifer fertility has plateaued, maybe it isn’t a protocol problem at all, maybe it’s a fundamentals problem.
Scott Zehr: All right. Hey, welcome everybody to another episode of Ruminate This with Agrarian Solutions. I’m your host, Scott Zehr, and today we are gonna be talking about virgin heifer reproduction. One of my passion topics here.
Over the last decade, dear reproduction in the US has seen incredible gains. If I think back to 2013, 2016, the years I was breeding cows man, if we had a 44% conception rate on cows and 68% heat detection rate, we were doing good.
Put you at about a 30 preg rate, and that was exceptional actually. Now we fast forward to 2026 and we’re seeing first service conception rates in mature cows, 50 to 55% pretty regularly. We have preg rates over 40 in a lot of herds. High thirties if nothing else.
And I think the industry has just gotten way better at getting cows pregnant over the last 10 to 12 years. Genetics is a big part of that. I think we’ve learned better how to feed cows. No doubt. That’s why we’re seeing eight pounds of components and herds shipped out the door.
But today I want to talk more about the Virgin Heifers. I recall a conversation I had with somebody at select Sires at the time. This is probably 10 years ago. And, the conversation basically, the guy told me that the largest opportunity for repro improvement in US dairies is in the Virgin Heifer population. And I could still make that same argument today.
And it’s not, I’m not trying to paint a real broad brush. There are certainly outliers in every dataset. But for the most part, if I go back to 2013 through 2018 as when I was breeding cows, we’re using gender sorted semen on virgin heifers, and we were achieving 46 to 55% conception rate? Depending on the farm.
And I think that’s just about where we’re still at today. We may have some herds in the sixties. But for the most part, I would say heifer reproduction in the US over the last decade is honestly plateaued from my perspective. So it raises the question why is this happening? Or why has it happened?
And we all look at things through a different lens. We have so many things going for us to help us get heifers bred more efficiently. Better protocols than we had 15 years ago. The introduction of monitoring systems used a lot over the last decade, it’s becoming more and more common in, in the Virgin Heifer population.
But when I look internally at Agrarian Solutions, one of the things that we don’t see is we do not see very many TMR samples being sent in from mycotoxin analysis from our virgin heifers. And, to me that begs the question one, why is that? Number two, the next question I think about is, are mycotoxins a contributing factor to this plateau?
You know, I think we just assume sometimes that virgin heifers are, they’re young, they’re healthy, they’re resilient, and they’re low risk. And looking at the, through the lens of mycotoxins.
But I think sometimes because of that assumption, we treat their nutrition a little bit differently. We don’t test regularly for mycotoxins. We feed refusals, so we have a chance for increased wild yeast in the TMR. And then you contrast that with the cows. A lot of herds are testing their forages on a weekly basis.
A lot of herds that we work with Agrarian Solutions are testing their TMRs on a monthly basis. We test the fresh pen, we test the lactating pens. We test the dry cows even, which is a big step forward. But the heifers, it’s rare.
Oftentimes the only time we see a heifer TMR sample come in is if myself or Chad Christensen out in the Midwest. Jeff Hostetter in the south. If we actually are on the farm and we just pull the sample ’cause we’re testing every TMR group while we’re there. So what happens when we actually take a look? We find mycotoxins. Routinely.
We’re not necessarily seeing mycotoxins come through at catastrophic levels in these virgin heifer TMRs. Generally it’s more the low to moderate contamination. But oftentimes we’re seeing multiple mycotoxins. It stands to reason. If we’re seeing more and more samples come through of our corn silage or of our, our lactating TMR with DON present, zearalenone present, fumonisin present. T-2 Present. It stands to reason we’re gonna have multiple mycotoxins show up in the virgin heifer feed stuff.
And why is this important? Right? It matters biologically because mycotoxins are going to drain nutrients. They’re gonna challenge the immune function of that animal. Zearalenone’s going in disrupting hormone signaling. It creates a competition for energy needed for growth and reproduction. I would say our heifer reproduction, for the most part, is not failing loudly. We’re not seeing big crashes. We’re seeing this plateau. And I’ll come back to it, you know, the myth that we talk about with heifers being younger and more resilient.
They’re still growing. They’re building body reserves, they’re developing mammary tissue, they’re developing their reproductive system. They actually don’t have any extra nutrients to waste on fighting a chronic mycotoxin exposure. The youth doesn’t necessarily mean resilience. It actually probably means less margin for error.
Mature cows have a stronger adaptive capacity. Heifers are allocating nutrients to frame growth, mammary development, immune function, as I mentioned, reproductive maturity, mycotoxins attack all of those systems simultaneously. So it brings us back to that plateau.
You know the industry as a whole, we have improved our AI protocols immensely, as I mentioned. The semen technology, the monitoring systems, genetics. But I still come back to heifer reproduction hasn’t moved nearly as much as our cow reproduction. And I can’t help but wonder if this glass ceiling is a false ceiling.
So as I mentioned we all look at things through a different lens. But I’m gonna come back to, are we missing something in the heifer TMR that’s holding us back? And again, if we’re not sampling, we can’t measure what that thing is. So as I wrap up this episode I wanna just give some practical takeaways.
Number one, start testing. And, you hear me talk about that a lot. If we’re not testing, we don’t know what we’re dealing with. We can’t make a plan for mitigation. We really shouldn’t assume that just because, you know, virgin heifers are young and perhaps more resilient that we don’t need to pay closer attention to those TMRs and what we’re doing with them.
If we think about the fundamentals of rearing animals, right? We wanna provide enough nutrients when they’re young for growth and development. And we’re trying to hit average daily gain numbers. We wanna get these animals bred efficiently, turned around and in the milking herd by 22, 23 months or sometimes less.
What are we doing to defend and protect that virgin heifer to make sure that she flows through the program the way we’re trying to get her to do that? We focused a lot in the last 10 years on non-completion rates in heifers, and I would argue that still today, the same as 10 years ago, one of the reasons virgin heifers leave the herd probably the most predominant reason is they don’t get breaded.
So I would just challenge you as listeners to, to think about, how do we come up with a better solution for managing our virgin heifer TMRs? Let’s take a look at it. Let’s test it. Let’s know what we’re dealing with. And if nothing else, if we routinely test that TMR even once a month, once every six weeks, routinely, we can either check mycotoxins off the box as, “Hey, we’re not seeing any.” Or we can have a discussion about how we’re gonna handle the mycotoxin exposures there.
I would be hard pressed to think that the next gains and heifer reproduction are gonna come from better protocols or sorted semen is going to become all of a sudden, as effective, if not more effective than conventional semen.
And also we’re seeing a rise in embryo implantation. Which is going to have a lesser conception rate for the most part than sort of semen would. So let’s think about what’s going into the front end of our virgin heifers. Let’s have a conversation about how DTX can potentially be a solution to mitigate the chronic exposure from mycotoxins and these heifer TMRs.
And, lastly, I wanna say it again. The dairy industry has done an incredible job over the last decade of modernizing cow reproduction. We have some of the best genetics in the world. In our virgin heifer population. Beef on dairy, as far as helping improve reproduction, it has given us this opportunity to rather than shotgun genetics across the population, it has driven us into a more rifled approach where we’re breeding the best of the best in creating the best.
And in doing so, we’ve created this amazing genetically driven animal. And I guess my challenge would be to, let’s think about applying that same strategy to the TMR, that rifled approach.
Maybe the next improvement in virgin heifer reproduction doesn’t come from another protocol. Maybe it comes from us respecting and understanding the biology of the animals that we’re assuming are fine. So maybe, and this is a what if question. What if virgin heifer reproduction isn’t what has plateaued? What if it’s our assumptions?
Again, I’m gonna come back to it, folks, test those TMRs, send them in, we’ll test them complimentary. And let’s have a conversation about how we can defend and protect those virgin heifers from these environmental challenges. And break that glass ceiling on Virgin Heifer reproduction. Hey, if you found value in today’s podcast, please share it with a friend, and we look forward to talking to you again soon.
