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Originally Published IVD Technology June 2001

POC testing in the health maintenance of livestock animals

Jerry K. McVicker


Jerry K. McVicker, MS, is the manager of R&D at Midland BioProducts Corp. (Boone, IA). His research interests include the development of novel diagnostic products and their applications in veterinary healthcare.
Getting the results of tests for animal condition and disease states quickly and on-site offers advantages to everyone with a stake in sound livestock management.

A significant current trend in medical diagnostics is the shift away from dependence on centralized, high-throughput clinical laboratories and toward the use of point-of-care (POC) testing. The development of POC technologies has reduced costs related to shipping and receiving samples and has made possible more direct physician control of patient care, monitoring, and treatment. POC tests are generally easy to use and interpret and provide the luxury of timely results.

The Quick Test Colstrum IgG (Midland BioProducts; Boone, IA) measures the concentration of IgG in colostrum directly.
POC testing is also evolving as a viable tool for animal healthcare. In the livestock industry, veterinary care provided on a herd basis is generally giving way to diagnosis and treatment of individual animals. The POC test format is an ideal methodology for livestock healthcare because of its convenience, ease of interpretation, cost, and timeliness of results. Since most livestock veterinary care is delivered on the farm or ranch, the format offers the medical practitioner and the stock producer considerable convenience by comparison with clinical laboratory methods. Samples do not need to be preserved and transported to the laboratory. Instead, they are tested on-site. Diagnosis can be made and treatments implemented at once, eliminating the need for a return call by the practitioner and further handling of the animal later.

For the livestock industry, the necessary justification of the cost of administering a diagnostic test is that it should add value to the animal. That is, the financial gain likely as a result of using the diagnostic must be higher than the cost of the assay and associated animal handling. This advantage is not always easy to determine with specificity. Beyond the obviously increased value of an ailing animal that is appropriately treated, there could be indirect benefits from the test. For example, the timeliness, effectiveness, and cost of subsequent veterinary treatments might be optimized. Targeted treatment of individual animals before they can cause problems for other animals in a herd also would be financially beneficial to the business. In many situations, POC testing of livestock is highly cost-efficient and offers great utility to both the veterinary practitioner and the stock producer.

The Need to Monitor Passive Transfer in Calves

Unlike human infants, calves are born virtually without any detectable level of specific immunity. This is because no immunoglobulins are transferred across the placenta. Consequently, the neonatal calf's immunity to infectious agents relies on the ingestion and absorption of maternal immunoglobulins from colostrum. This process, called passive transfer, is a critical determinant of the calf's immediate and long-term health.

When immunoglobulin ingestion or absorption is not adequate, the calf is characterized by a condition termed failure of passive transfer (FPT). FPT is defined as a concentration of immunoglobulin G (IgG) in the calf's blood of less than 1000 mg/dl.

Figure 1. Typical distribution of serum IgG values in calves.
The condition may occur as a result of inadequate suckling, poor absorption of IgG, low levels of IgG in colostrum, or environmental stress. The incidence of FPT varies among herds, but it is not uncommon to find herds with 40% of the calves falling under the classification (see Figure 1). In fact, 41% of the calves enrolled in the U.S. Department of Agriculture's National Dairy Heifer Evaluation Project were found to have IgG levels below 1000 mg/dl.1

Morbidity and mortality rates increase significantly when effective immunity is lacking. In addition, low levels of IgG in newborn calves may lead to slower rates of weight gain and lower milk production in adult animals. An economic analysis of 2016 Holstein bull calves, performed by Land O'Lakes Inc., found that a bull calf with adequate passive transfer was worth an additional $23.04 in the first four weeks of age.2 Therefore, the management and care of the neonate is vital to ensuring the profitability and productivity of the livestock enterprise.

A calf's ability to absorb IgG is optimal at birth, then progressively declines. The highest rate of absorption occurs during the earliest hours of life. The rate gradually slows through the first 12 hours, and between 12 and 24 hours the absorption efficiency declines substantially. At about 24 hours, IgG will no longer be absorbed across the gut into the bloodstream (see Figure 2). Ingesting high-quality colostrum in the first hour of life is therefore essential for healthy calf development. Studies have indicated that approximately 100 g of colostral IgG must be fed to the animal within the first three to six hours after birth in order for a calf to develop an adequate level of IgG concentration.

Figure 2. Percent absorption of IgG in the calf.

The simplest way to reduce FPT is to improve herd management practices. The traditional recommendation has been to feed the calf 2 qt of colostrum at birth and repeat 12 hours later. However, this general recommendation ignores several important specific factors: the quantity of IgG in the colostrum, the timing of the first feeding, and the weight or size of the calf. The development and implementation of both colostrum- and calf-management programs that involve monitoring of IgG levels will help to minimize morbidity and mortality problems in livestock herds.

Systems for Quantifying IgG

In Colostrum. The level of IgG in colostrum can be estimated with the use of a hydrometer. That instrument will measure the specific gravity of the colostrum and thereby provide an estimation of the total protein/IgG concentration. It does not actually quantitate the IgG concentration. In fact, a large study by researchers at Washington State University (Pullman, WA) found that the hydrometer overestimated IgG concentrations by about 40%.4

Because most livestock veterinary care is administered on the farm, POC testing is an invaluable aid. POC testing on-site minimizes animal handling and enables the practitioner to make immediate treatment decisions.

The Quick Test Colostrum IgG, a POC method available from Midland BioProducts Corp. (Boone, IA), measures the concentration of IgG in colostrum directly. The test is performed by first diluting a colostrum sample in supplied diluent by means of a pipette that is also provided as part of a kit. The dilution is mixed and applied to the sample well of the measurement device. The sample flows through complexing reagents in the cassette, and results are interpreted in 20 minutes.

In Calf Blood. A similar POC test from the same source can be used to detect the IgG status of the calf (that is, the quality of passive transfer) before or after colostrum feeding. The Quick Test Calf IgG can be used either in conjunction with the Quick Test Colostrum IgG test or as an independent measure of IgG status.

The test is performed by diluting a blood sample from the calf in the diluent vial using a provided pipette, mixing, and then applying the diluted blood sample to the sample well of the test device. The application of the diluted blood to the sample well initiates the flow of the sample through the complexing reagents. Results again can be interpreted after 20 minutes.

The format lends itself to convenient use in the vicinity of the calf. The timely results facilitate the application of any intervention treatments that may be necessary.

The Future of Livestock POC Testing

This handheld refractometer can be used to estimate total protein levels in the serum of newborn calves. The IgG levels can then be correlated to the total protein estimates. Serum is placed on the refractometer's slide and held to the eye for reading.

Good management practices employed in the first 24 hours of its life can have a significant positive influence on a calf's future. Risks of disease and death can be substantially reduced by feeding high-quality colostrum to the animal in a timely manner and in sufficient quantities. Stock producers and veterinarians have been aware of these facts for years, but they have lacked satisfactory tools for monitoring the calves or the colostrum provided to them. The introduction of POC testing methods such as the Quick Test kits described here into the routine of early-stage calf management will improve productivity for both the growers and the veterinarians.

The management of FPT in calves is only one application for POC diagnostic tests in animal healthcare. The fundamental principle of POC testing has broad implications for livestock health management.

Methods can and will be developed for the purposes of monitoring management practices, general animal health, and disease states. Uses for the tests on the farm and in interstate commerce are apparent. There are also environmental testing needs and applications associated with livestock production. Later, once the harvested animals have entered the food supply, POC testing can be used for food safety evaluations. And detection of nutritional markers and genetic selection markers will improve with the application of this quick, on-site test technology.

Conclusion

Producers and consumers alike are increasingly confronting issues of animal welfare, food quality, food safety, and the cost of maintaining these desirable qualities. Proliferating regulatory demands and the burden of complying with them together call for the development of accurate, timely, user-friendly, and cost-effective assay methods.

The rapid point-of-care assays described in this article have streamlined dairy calf management practices around the world. POC methodologies can and will have an even greater role to play in the future as we continue to strive to improve our ability to ensure the quality and availability of food sources for a growing global population.

References

1. "Transfer of Maternal Immunity to Calves: A National Dairy Heifer Evaluation Project Fact Sheet." (Washington, DC: U.S. Department of Agriculture, Animal & Plant Health Inspection Service, Veterinary Services, 1993).

2. MA Fowler, "What Is It Worth to Know a Calf's IgG Level?" in Proceedings of the 3rd Annual PDHGA Conference (Savoy, IL: Professional Dairy Heifer Growers Association, 1999), 31–38.

3. JK McVicker, "Evaluation of a Lateral Flow Device for the Determination of IgG Colostrum" (abstract), in Proceedings of the American Dairy Science Association 42 (2001): 97.

4. LC Pritchett et al., "Evaluation of the Hydrometer for Testing Immunoglobulin G1 Concentrations in Holstein Colostrum," Journal of Dairy Science 77 (1994): 1761–1767.

Photo Courtesy Midland Bioproducts Inc.

The Quick Test Colostrum IgG (Midland BioProducts; Boone, IA) measures the concentration of IgG in colostrum directly.

Photo Courtesy Midland Bioproducts Inc.

Photo Courtesy Midland Bioproducts Inc.

Photo Courtesy Midland Bioproducts Inc.

Copyright ©2001 IVD Technology