EVALUATION OF A RAPID BLOOD LEUKOCYTE DIFFERENTIAL FOR CALF HEALTH MANAGEMENT- AAD

Mortality in young dairy calves exceeds 10% (USDA 2010), and historical losses are worse in warmer climates such as the Southeast (rref 3). A South Carolina study showed dairy calf mortality from birth to 3 months or birth to 1 year ranged from 6.5 to 22.0% (Jenny, 1981). Heifer health, including sickness and death, was reported as the top challenge rated very important by 92.5% of dairy calf-raisers in a recent study (USDA, 2011). Yet only half of dairy calf-raising operations reported testing heifers for any disease during 2010 (USDA, 2011). Producers need low-cost, on-farm tests that give near immediate results that can be used to dictate treatment (personal interviews). Such tests do not currently exist. The testing used is typically specific to a particular disease and requires submission to central labs that take days or weeks to provide results.The blood leukocyte differential (BLD) could meet producer needs for testing. Blood leukocytes, or white blood cells, play a crucial role in defense against infection (Blumenreich). The total number and percentages of leukocyte types change at the onset of and different stages of disease (Berend 2001). Thus, the leukocyte differential has become widely accepted in human hematology and it is commonly used for screening, case finding, diagnosis, and monitoring of hematologic and nonhematologic disorders (Berend 2001). The number and type of cells not only indicate the presence of infection or disease but also differentiate between bacterial, viral and parasitic infections. Similarly, in companion animals the differential is a useful triage tool that improves the rapid diagnosis and care of pets (Idexx training tool). Such a tool would be useful in calf management to reduce mortality and morbidity, improve overall animal health, improve producer profitability and minimize the opportunity for antibiotic resistance.Technology from Advanced Animal Diagnostics (AAD) is well-suited to provide a rapid BLD test that can identify the presence of a disease or infection and indicate the causative agent (bacteria, virus or parasite) in less than one minute from a single drop of blood. Given the limited number of therapeutics available, accurate treatment decisions can be made by confirming the presence of disease and identifying the causative agent. AAD has developed similar technology to perform a leukocyte differential in milk. The company is preparing for commercial sales of a reader instrument that acts as a rapid robotic cytologist. With different software customized for blood, the company could use the existing system to produce a BLD.The College of Veterinary Medicine, North Carolina State University, and AAD intend to collaborate on a project to develop the framework for using total and differential leukocyte counts from calf blood. The intended field use is the development of protocols to use the technology to effectively improve health management of calves, such as to identify calves with specific disease or to indicate whether antibiotic treatment is warranted. Technical objectives include: Step 1: Longitudinal BLD Values for Healthy Calves: Determine normal values for dairy calves by age (up to 6 months) using AAD's BLD. Differentials change over time as the immune system develops, so normal ranges by age must be determined first to eventually interpret "abnormal." Step 2: BLD Values for Key Calf Diseases: Determine the BLD patterns (totals and percentages) for dairy calves to be used in the detection of three serious calf diseases:Septicemia, the life-threatening presence of bacteria in the blood stream,Pneumonia ,an infection of the calf's lungs, andDiarrhea, the most common health problem for young calves.For pneumonia and diarrhea, patterns for infections caused by both bacteria and viruses will be identified so the producer can understand whether antibiotic treatment is warranted.AAD has the development, manufacturing and dairy sales and customer support infrastructure to quickly leverage the results of this research into a successful commercial product.