By Tom Shelton, M.S., D.V.M., Merck Animal Health and Michael Coe, DVM, PhD, Animal Profiling International, for Progressive Dairyman
The dairy industry continues to change as the numbers of farms are decreasing and the numbers of cows per farm are increasing. Introducing new animals to a herd can increase the risk for a Bovine Viral Diarrhea (BVD) persistently infected (PI) animal to enter the herd and negatively impact reproduction, health and performance.
This makes biosecurity increasingly important. However, less than 20 percent of farms have routine biosecurity protocols for new animals entering the herd, according to the National Animal Health Monitoring System (NAHMS).
There is a new approach that makes BVD monitoring easier and more cost effective thanks to the sensitivity of real-time reverse transcriptase polymerase chain reaction (rt RT PCR). In lieu of sampling individual cows, dairy producers can take pooled bulk milk tank samples. Because PI cows shed a large amount of BVD virus in milk, the PCR test effectively identifies BVD in a bulk tank milk sample. This is a good first step in identifying the presence of a PI animal in the milking herd and an economical way to periodically monitor the herd to assure a negative status. BVD monitoring pays dividends
Identifying and removing PI animals from milking strings can increase productivity between $20 to $88 per cow per year by reducing negative effects of maintaining this endemic, subclinical disease in a herd.¹ Negative effects include impact on reproduction, mastitis, culling rates, slaughter value and mortality, as well as reduced milk production.
A positive bulk milk tank sample can be reflective of the number of calves that are born persistently infected. Identifying and removing these calves at birth, as well as removing adult PIs would eliminate the primary source of BVD as an endemic disease in dairy herds. Incidence highest on large dairies
In 2007, NAHMS conducted bulk milk tank tests in 527 dairies across the United States, and found a 1.7 percent positive-BVD rate. Large dairies (more than 500 cows) were positive 12.8 percent of the time. Small dairies (less than 100 head) had no positives and medium dairies (101 to 499 cows) tested 3.5 percent positive. Regionally, there was a higher percentage of positive results in Western dairies (7.7 percent) vs. Eastern dairies (1.1 percent).
In 2011 to 2013, Merck Animal Health in conjunction with Animal Profiling International, a testing laboratory in Portland, Ore., performed a similar bulk milk tank testing program targeting mostly large dairies (more than 500 cows) from Vermont to California.
Bulk tank samples were collected from dairies in 18 states: Arizona, California, Florida, Iowa, Indiana, Illinois, Kansas, Minnesota, New York, Ohio, Oregon, Pennsylvania, South Dakota, Utah, Vermont, Washington, and Wisconsin. Veterinarians and herdsman collected samples and submitted them to Animal Profiling International for processing.
The actual size of the dairies represented ranged from 45 to 15,000 cows. Some dairies submitted quarterly samples in an effort to ensure that all cows in the herd would have at least one sample tested over the course of the year. A data sheet accompanied the first sample that asked key questions related to management, herd health and BVD control measures.
In addition, individual samples from neonatal calves were collected from some of these same dairies, as well as regional calf facilities over time. These samples were tested in a pooled fashion and individual BVD-positive animals were identified. PI animals have profound effect
The Merck Animal Health/Animal Profiling International program included 182 dairies of which 18 percent tested positive for BVD. Looking just at the 118 large dairies (more than 500 cows), the testing revealed 28 percent were positive for BVD. Western dairies were 24 percent positive for BVD and Eastern dairies had 8 percent positive for BVD.
The study showed an increased rate of positive BVD PI animals across all tested dairies, which was appreciable compared to the 2007 NAHMS test. Some of the dairies in the Merck Animal Health/Animal Profiling International survey conducted multiple tests over time in order to reflect a more representative population. Of those dairies, one in 10 tested negative a single time but then tested BVD-positive on a subsequent test.
The incidence of PI calves was reflective of the percent positive bulk tanks by region. Where positive bulk tank tests are found, the number of calves born persistently infected varied from less than two out of 1,000 to levels approaching five out of 1,000. Although these numbers may seem small, PI calves can have profound effects on their developing cohort, and in group-management conditions, they have the potential to affect exponentially more animals.
During 2013, six large dairies (ranging in size from 1,800 to 6,000 cows) in three states initiated a BVD bulk milk tank monitoring program to identify and remove BVD-PI cows from the lactating herd.
In all six dairies, only one or two cows (less than one in 1,000) were identified as BVD-PI. This speaks to the high sensitivity of the test, as well as the negative impact that one or two BVD-PI cows can have on the health and productivity of the entire herd. Conclusions
With the advent of rt RT PCR testing for BVD, sampling costs are much less expensive. We can now test the whole herd or groups of calves by pooling individual samples for screening. This has allowed us to “pull back the covers” on a subclinical disease that manifests itself in insidious and economically adverse ways.
Eliminating BVD from our dairy herds requires effective vaccination programs, reasonable biosecurity to reduce reintroduction and cost-effective monitoring and management. Only by combining all of these factors can we obtain the benefits of increased production efficiency and, thus, a higher return on investment
Future articles will chart the costs, return on investments and do’s and don’ts required to deal with those herds that have been found BVD-positive.
1. VanLeewun, J. Impact of BVD on Dairy Herd Profitability. Center for Epidemiological Research, Atlantic Veterinary College, UPEI, Canada.
Tom Shelton Senior Technical Services Veterinarian Merck Animal Health email@example.com
Tom Shelton, M.S., D.V.M. is a senior technical services veterinarian for Merck Animal Health from Washington, Utah. He specializes in calf health and performance, vaccinology and immunology.
Michael Coe, DVM, PhD VP Animal Health Animal Profiling International Inc. firstname.lastname@example.org
Michael Coe, DVM, PhD is the Vice President of Animal Health for Animal Profiling International from Logan, Utah. He specializes in health management, nutrition, microbiology, and production medicine.