The Moos Room™

00;00;11;03 - 00;00;41;10
Speaker 1
And welcome to The Moos Room, Brad, here on a rainy afternoon podcasting today from actually in western Minnesota. Kind of beginning with the state fair this week. It's been crazy here. I think the weather is it's just wild. It just seems to rain every other day here. It's hard to get alfalfa up, hard to get any forage up for the cows.

00;00;41;12 - 00;01;13;01
Speaker 1
It's been a challenge this year, but we move on. We face somatic cell count issues, you name it. But we're trying to figure out those challenges and move on with our dairy herd. And it also kind of brings me to another one that we've been having. And it's not one that I haven't talked about before. And I wanted to provide a little bit of an update today on where we are with the valve bovine leukemia virus or Lucas's.

00;01;13;04 - 00;01;42;28
Speaker 1
And I know I talked about this way back in November, so almost a year ago where we were doing some testing in our herd. But I wanted to give you an update. We did some other testing, and we also did some testing in the winter time to kind of look at flies and maybe we'll talk about here later on in the podcast about is it really flies that's causing the valve transmission in our herd.

00;01;42;28 - 00;02;15;01
Speaker 1
But first off, here's a few highlights on valve. It's a retrovirus that infects B cells and integrates into an animal's DNA, which leads to immune dysfunction. Infected cows can experience loss of production somewhere in the 2 to $400 range. So there is a monetary loss for dairy farmers. And it also can increase other health issues in a herd.

00;02;15;03 - 00;02;43;08
Speaker 1
So transmission can be either vertically. So that's from the dam to the calf. Or it can be horizontally which is among cattle via blood transfer. And this is maybe where we're thinking flies. We know that 90 over 90% of dairy herds have at least one B of infected animal. The prevalence rate in herds is around 46%. So which is actually quite high.

00;02;43;10 - 00;03;16;25
Speaker 1
And to manage this we need to do some testing, which we'll talk about working with your veterinarian and implementing hygiene protocols to reduce transmission. Because it really affects cattle. They have reduced immune responses, which impacts their overall health and lots of other issues. And so maybe some of the other issues that we see in our dairy herd related to mastitis, high somatic cell counts, you name it, I'm not blaming it all on the environment.

00;03;16;25 - 00;03;48;12
Speaker 1
There could be some things with glucose that are causing these. So let's talk about what we found and what we did for our testing. First before we get into the winter testing. So we tested again in May. So at the end of May we tested 317 cows, all lactating in our herd. This was by Elisa testing. So with DHEA we can figure out who's Eliza positive or Eliza negative.

00;03;48;12 - 00;04;21;28
Speaker 1
So of the 317 cows, we had 96 that were Eliza positive and we had 11 cows that were Eliza suspect. So that brings our herd prevalence rate to about 30%, which is maybe a little bit less than maybe the national average. So let's consider back when we did testing in June of 2024. So a little more than a year ago, we were at 29% positive.

00;04;22;02 - 00;04;52;14
Speaker 1
And one year later we were at 30% positive. So we didn't really reduce the prevalence rate in our herd, which we tried to do through some culling and getting rid of the high positive cows. But did it work? Who knows. But based on this test, there, of the 317 or so there were 53 of them were previously positive for glucose.

00;04;52;14 - 00;05;39;07
Speaker 1
This 111 them were never tested before, so we had 101 animals that were newly tested in our herd. And we had 33 new infections. So we're still getting infections of glucose in our herd. So if we look at our herd on May 29th of this year, kind of our lactation distribution, we have about 37% of the cows are in first lactation, 27% are in second lactation, 18% are third lactation and 17% of them are in fourth or greater lactation.

00;05;39;09 - 00;06;10;16
Speaker 1
If we look at the the lives of positive cows by lactation, about 12% of the Lucas is positive. Cows are in first lactation. So we're still getting we're getting some young animals that are showing high positive for the process. 37% are positive in second lactation, 31% in third lactation, but 60% of the fourth in greater lactation. Cows are positive for glucose.

00;06;10;18 - 00;06;50;24
Speaker 1
So we have about 60 cows roughly that are fourth lactation or greater, and 60% of them are positive. So well over 30 plus animals in fourth and greater lactation are positive for glucose. So very high positivity rate for the older cows, not much for the younger animals. We haven't really done some testing in young heifers yet. I would like to expand this to actually test all of the heifers on our site to see are they glucose as positive when they're heifers, and how can we control that?

00;06;50;26 - 00;07;18;24
Speaker 1
We did have some animals that were really high for Belva. Some were high before a lot of the cows that were really high for concentrations of BV are in second lactation and some are in first lactation, which is kind of crazy as well. So we're going to have to look at these cows to determine what might be happening.

00;07;18;24 - 00;07;50;20
Speaker 1
And if we should call some of them based on their high titer rates for BV, there was also a handful of cows that were Elisa positive. So from the milk test, but they lacked detectable levels of BV at the time of blood sampling. So where they positive or not, maybe those were suspects as well. So if we remember back the year ago, we decided we were going to cull some animals that had really high levels of BV.

00;07;50;22 - 00;08;24;25
Speaker 1
We did that and others certainly were considered for removal. It's one of the ways that I help with culling bv positive animals, if they have other health issues, tend to get called as well. We were going to freeze frozen colostrum to calves born from BV positive Dam, so we would not be feeding valve positive colostrum to calves. Certainly I've been probably breeding more glucose as positive animals to beef.

00;08;24;27 - 00;08;48;12
Speaker 1
And so that's how we've kind of tried to manage this in our herd. We're working with the researchers at Michigan State on this. And we also had some questions, I guess, on what was really happening in our herd. And one of the ideas was for glucose is how important are biting flies? And will flies transmit to the classes.

00;08;48;14 - 00;09;21;11
Speaker 1
So we know that BV can be transmitted among cattle by blood exchange either direct secretions milk and colostrum, intrauterine transmission, sexual contact and biting flies. So we were really curious are flies causing the BV spread in our herd? Biting flies actually give painful bites which disrupt feeding behavior, blood loss, tissue damage, and sometimes cause other reactions in cows.

00;09;21;11 - 00;10;07;16
Speaker 1
We know that past research studies have kind of found that having no fly control program was really associated with high BV prevalence in herds. There was some Japanese studies that were recently done where BV infections were more common in the summertime. But really, they said flight control was probably a major importance in controlling BV transmission. Michigan State had done a field trial a while ago, maybe ten plus years ago, where they looked at some herds, a grazing herd and conventional herds that participated in a BV trial.

00;10;07;19 - 00;10;33;20
Speaker 1
The cows were Eliza tested in the spring, in the fall to determine the rate of new infection. So if infections could be compared between the summer and the winter months, the grazing herd had new infections that were twice as high in the summer as compared with the winter exposure period. The other two herds, which were conventional so showed no seasonal differences.

00;10;33;20 - 00;10;59;05
Speaker 1
So basically it showed that quite possibly flies could be contributing to the number of new infections during the summertime, because obviously we don't really have many flies in the winter time or biting flies in the upper Midwest. So we wanted to look at a field trial here at our University of Minnesota herd in Morris grazing herd and see what was going on along with this additional testing.

00;10;59;05 - 00;11;26;05
Speaker 1
So obviously we tested animals in June of 2024. So a year and a half ago figured out who was positive, who was negative. And then I collected a sample in December 2024. So six months after we'd done the initial testing, I collected another milk sample and froze them and waited to see what would our test results be in May.

00;11;26;05 - 00;12;00;04
Speaker 1
So we tested again in May of this year. So we had all of those samples. So again 317. And then we went back and looked at okay the animals that were negative in June of 2024. And now they were positive in May of 2025. What was their status during the winter time? It's really assumed that 30 days are required for an exposure to induce antibody levels in cattle.

00;12;00;06 - 00;12;33;07
Speaker 1
So basically during this summer exposure period, as we'll call it, we had five months with flies, two months without flies. So we had 37 cows that showed up positive in May of this year that were negative last year. So we dug those milk samples out of the freezer, decided to test them, and we had 37 cows that went from negative to suspect or positive from May to December.

00;12;33;07 - 00;13;11;07
Speaker 1
So that's 95%. So that's quite a pretty high prevalence rate. So we had a lot of new infections possibly during the summertime. So 30 of the 37 went positive during the summertime. Five of the 37 went suspect during the summer. So we counted those 35 as positive and suspects. But we still had some suspects. So if we consider we have 35 new infections over a six month period times those 37 cows, that leads us to about a 16% new infection rate per cow per month, which is really high.

00;13;11;09 - 00;13;40;13
Speaker 1
If we look at the winter exposure time, we had five months without any flies. We had one cow that went negative to positive from December 24th to May of 2025, and we had one cow that went from negative to suspect. So two of five cows went from suspect to positive. In the winter time, it's about 40%. So we had two new infections during the winter period.

00;13;40;13 - 00;14;18;15
Speaker 1
So about 25% infection rate during the winter period. So to kind of summarize that if you're confused, there were 37 allies and negative cows at the start of summer 2024. All but two of them were Eliza suspect or positive by December 2024. So 95% of them were suspect or positive after just one summer. And of the two remaining negative cows, one became positive and the other became suspect before the next spring.

00;14;18;18 - 00;14;51;22
Speaker 1
So obviously is 37 cattle enough to make a comparison for any sort of meaningful conclusions? Maybe yes, maybe no. Obviously it's one herd trying to figure out what's going on, but it really kind of grabs you a little bit that 95% of the negative cows became suspect or positive after one summer. So clearly we need more work on the seasonality of the of presence.

00;14;51;22 - 00;15;25;18
Speaker 1
So we need to compare seasonal rates, maybe do some more studies within our herd to see, you know, more testing to see what's really causing this as we think about this and flies and our flies causing this, it can become scary for me because whole man, if flies are transmitting the closest in our herd, then we've really got to ramp up our management of fly prevalence in our herd to try and reduce the fly load to help reduce the cost of spread.

00;15;25;20 - 00;15;54;21
Speaker 1
But obviously we need to remember that glucose is important in animals. It's increasing in prevalence. We see that a lot of the research is showing it is increasing in prevalence. We know that it impacts the bottom line. The economics of a dairy herd. It has implications for animal welfare and public health. We know that the percentage of cows infected within herds is increasing.

00;15;54;23 - 00;16;27;21
Speaker 1
Back in 1975, you'll find about the prevalence was about 10%, 1996 41%. And we figure now it's approaching 50% of cows in herds are infected with bovine leukemia virus. It has been eradicated from all cattle in 20 European countries, New Zealand and Western Australia. And really this is done by testing and culling the antibody positive cows so it can be controlled in herds.

00;16;27;28 - 00;16;56;05
Speaker 1
Obviously it impacts the herd in very important ways with milk production, loss and decreased longevity of cattle. And it's because of a impaired immune response. A study has shown that first lactation cattle didn't show a significant drop in milk production associated with glucose test positive, so it seems to take some time for the disease to progress to induce an immune response.

00;16;56;07 - 00;17;21;07
Speaker 1
And we probably see that even in our herd, where we have very few cows that are positive in first lactation, and as the cows get older, the disease progresses. And now we see more cows showing up positive if we think about life span. If you are believe positive, you are 23% more likely to leave the herd than if you are bovine negative.

00;17;21;07 - 00;17;59;01
Speaker 1
So B of positive cows tend to have less survival in the herd, whether farms are calling them or they have other immune responses and disease challenges. So it's been estimated that the annual loss for BV is about 3 to $400 per milking cow, which is actually quite a lot. If you consider, herd size. You know, if we consider we have 100 positive cows, well, that's a lot of money, 40 to $50,000 in loss just for our herd.

00;17;59;03 - 00;18;35;17
Speaker 1
So what do we do about it? Well, we're going to develop our culling plan again to see if we can help reduce the transmission of Blvd. Our herd. We're going to be looking at other ways that we can prevent transmission. Looking at not feeding colostrum from cows that are BV positive, and looking at ways to increase our flight control measures to help reduce BV and that might be the biggest challenge for us for especially for a grazing herd to help reduce fly population.

00;18;35;19 - 00;19;03;02
Speaker 1
So hopefully you learned a little insights today about our field testing and how it's ongoing and how we really have it reduce the spread of BV at our herd and we probably need to look at other ways and think about other ways to help reduce that transmission. But I know we'll get there if we work on this problem and we'll see a much healthier herd in the future.

00;19;03;05 - 00;19;25;29
Speaker 1
So with that, if you have any comments, questions or scathing rebuttals, feel free to let me know at the newsroom. That's m o s r o m at edu or contact us on the web at University of Minnesota Extension Livestock. And with that, we'll talk to you later. Bye.