This article topic also appears in El Lechero. This article has been written specifically for dairy owners and herdsmen. The article in El Lechero is written for dairy employees.
Editor’s note: In a previous Progressive Dairyman article (Nov. 30, 2008 issue), veterinarian Bruce Hoffman discussed the importance of identifying and eliminating persistently infected BVD animals. The following article by Hoffman’s colleague Kevin Crandall, an independent veterinarian, discusses how he has defined protocols to control BVD through the combined use of testing, vaccination and biosecurity.
In my five years of experience working with large dairies, I have determined there are three major categories regarding the cow in which dairies must do well in order to survive. This is not to discredit the importance of milk marketing, contracting, income over feed costs, etc. However, the three major cow categories are high milk production, high reproductive efficiency (how many cows are getting pregnant and how soon) and low involuntary cull rate (the number of cows leaving the herd because they get sick or are not productive). From a cow perspective, these three items are critical to the success of any large dairy. Everything a dairy owner, manager, herdsman, veterinarian, or nutritionist does should be focused on improving these three areas.
What does this have to do with testing and eliminating BVD persistently infected (PI) animals from the herd? If there was one disease that could significantly impact all three areas it would be bovine viral diarrhea (BVD). There are no hard, fast numbers, only estimates, of how much BVD impacts milk production, reproduction and herd health. Part of the reason is that these areas have many things that affect them, including diet, cow comfort, management, breeding and transition performance, just to name a few. Plus, every dairy is different. Even in the absence of hard, fast numbers, most experts (even those that don’t work for vaccine companies and testing laboratories) agree that BVD has a significant negative impact on cow performance.
The reason BVD even came up for consideration on my client’s dairy was that we were experiencing a higher-than-normal amount of what I classify as, immune-suppressed diseases. These diseases included adult cow pneumonia in the face of proper vaccination, metritis, environmental mastitis and undiagnosed gastrointestinal disorders across the herd. While we were trying to solve those problems the reproduction, which historically had been a strength, started to slip and even crashed and burned for a period of time. After careful consideration and looking at all the possibilities, including reviewing and deeming adequate the vaccination protocols, the decision was made to find out if there were any BVD PI animals in the herd and eliminate them.
Commitment to eliminating PIs from the dairy
The first and most important [factor] is if you decide to eliminate PI animals you have to commit to a program that screens all animals. There is no half-way, partial or “almost 100 percent”. Do not waste your time and money if you are not dedicated 100 percent to eliminating PI animals and remaining PI-free.
For herds that are just getting started on a program, it will require a good vaccination protocol (using a reputable vaccine with the correct timing of vaccination), one-time whole herd testing and then continual vigilant testing on all animals entering the herd – this includes purchased replacements (heifers or milk cows), newborn heifers and any bulls used for breeding.
My suggestion is to build a team of people you trust that includes your veterinarian, vaccine company representative and a proven testing laboratory. Having a good working relationship with all three of these people is key to having a successful program.
We started with the milking string to make sure that PIs were not present. We felt the easiest way to test all of the milking animals was to send in individual milk samples. It is also appropriate to do string samples and then only test the positive pens individually. With either method, coordinate it with your regular DHI or weigh day test. Our dairy is on a DHI test so we just had the DHI lab send the test samples directly to the lab.
On the same day we tested the milk, we started ear-notching every newborn animal on the dairy. This included all live heifers and bulls as well as any late-term abortion and calves born dead. The theory was we would test all the milking animals and then by testing the newborns we could indirectly screen all of the first-calf heifers and dry cows that didn’t have a milk sample at the time of test. Shortly after the milk test about 800 heifer calves that were still in hutches were ear-notched and tested.
When the results came back, we had eight adult cows show up positive and another dozen or so that were suspect. We then ear-notched all the positive and suspect animals, which resulted in three confirmed adult PI animals. Two of these animals were in their first lactation and one was in her second. These three animals were immediately sold. From the initial calf ear-notching and continual ear-notching programs for the newborn calves, we found we had 10 PI-positive calves, five bulls and five heifers. All of the PI newborn calves were from first-calf heifers.
These results were shared with the vaccine company, and they have since bent over backwards to reimburse the dairy for failed vaccinations and run further tests on the PI animals to determine the exact BVD strain.
The animals that remained to be tested were all of the replacement heifers and the feedlot. Instead of ear-notching every heifer dairy management decided to eliminate PI cases over time by testing every newborn calf. The program has been modified slightly since we started testing, so now the dairy ear-notches every heifer calf and once a week takes a milk sample from the fresh cow pen to screen for BVD. If a positive newborn heifer is found, then an ear notch is taken from her mother as a double-check on the milk sample.
There are a few other minor, but important things to consider when carrying out your program. First, ear-notching newborn animals and tracing PI positive calves to their mother is only effective when proper maternity records are kept. If a calf is not correctly matched up with its true dam, then testing the improperly recorded dam will yield negative test result, when the real dam could be positive and enter the herd undetected.
On large dairies calving 20 to 60 animals a day, I would say it is nearly impossible to be 100 percent accurate in correctly identifying mothers and their calves. As a safety net, consider sampling the milk from the fresh pen as often as needed, depending on how long they stay in the fresh pen. If they stay in the fresh pen only four to five days, then a milk sample needs to be taken every three days.
Second, how fast you want to eliminate PI animals from your herd will determine how aggressive you are in testing youngstock. I would say you have the biggest bang for your buck testing only the pre-breeding heifers and younger. If PI animals are eliminated before they are bred then that drastically reduces the BVD exposure to the rest of the heifers and theoretically will improve reproduction and health in your youngstock.
Third, always remember that BVD can circulate in a herd even in the absence of PI animals, but especially if you find PI animals. Finding and eliminating PI animals is the most important step to decreasing exposure. However, just because the PI animals have been eliminated does not guarantee more PI’s won’t be created. Although not common, low level circulating BVD in non-PI animals can still produce PI animals. Therefore it is critical that constant testing be a part of the elimination program.
The idea behind testing and eliminating PI animals is to build a barrier between any animals entering the herd (either by calving or purchase) and the milking herd. That is why it takes 100 percent dedication. If one PI animal slips by undetected, then BVD can continue to negatively affect herd performance. The use of a good vaccine helps decrease the number of PI cases. Only by combining the two strategies of vaccination and testing do you maximize your ability to eliminate PI animals from your herd and significantly decrease the negative impact BVD has on the areas of milk production, reproduction and herd health.
Positive economic results
Since the dairy has started testing and eliminating BVD PI animals from the herd, our milk production hasn’t changed, but our reproduction has improved significantly. When we were at our lowest, our pregnancy rate hovered between 12 to 14 percent. Since we have eliminated the PI animals our pregnancy rate has climbed to 19 to 20 percent. The herd somatic cell count has dropped about 80,000 from the month before we tested until now as well as about 50,000 from this time last year. The herd has seen a decrease in the number of pneumonia cases, as well as metritis. Undiagnosed gastrointestinal problems have not improved significantly. Involuntary cull rate has improved by 6 percent since the month before we tested, but it is not significantly improved over the same time last year.
Do I contribute all of the improvement in the herd to the elimination of PI animals? Definitely not! There are no silver bullets, just good consistent monitoring and management. There have been other changes and improvements made in other areas that have also positively impacted the dairy.
Do I think that eliminating the PI animals and significantly decreasing BVDV exposure has helped? You bet! I firmly believe it is worth the time and money. PD