Sampling Strategies

Herd Sampling Strategies - Individual vs. Pooled

Few would argue the strength of individual analysis in metabolic profile analysis. Indeed the gold standard for analytical analysis would be to measure a large percent of the population of interest as individuals. Decisions made in grouping and approach strategies will define the suggested number of individuals within a group to be sampled.

Statistical modeling would suggest at least 8 individuals from a population is representative (mean analysis), though 12 or 13 samples are best for threshold analysis using the targeted diagnostic approach. Though statistics may show a minimum number of samples needed to represent a population, the best way to truly characterize a population is to obtain more samples. The goal in metabolic profile testing is to appropriately balance quality of information derived from the testing process with analytical costs.

In the original protocol for the CMP, mean analyte values within physiologic groupings were used for interpretation. These mean values were arithmetically determined from individual samples. Use of individual sampling resulted in the high associated costs of this procedure. In place of individual analysis, can pooled samples be used to reduce the cost and provide some valid method of herd assessment? In a number of preliminary studies using individual samples, pooled samples from these individuals were found to accurately represent arithmetic means from pool sizes ranging from 5 to 20 animals. If sufficient animals are available within a large group, consider taking multiple pooled samples to account for a greater number of animals and provide some degree of variation assessment within the group.

Literature and Resources for Sampling Strategies:

Application of Pooled Sample Metabolic Profiles as a Herd Screening Tool

Robert J. Van Saun, DVM, MS, PhD, Diplomate ACT and ACVN

Department of Veterinary Sciences, Pennsylvania State University

http://vbs.psu.edu/research/docs/rvs-metabolic-screen-tool.pdf

Methodologies used in metabolic profiling have ranged from mean analysis of multiple analytes to proportional analysis of single analytes. Perparturient disease is a result of the cow's inability to maintain coordinated metabolism between lipid, glucose and amino acids. Use of pooled samples was evaluated as a method to collect usable information on herd metabolic status encompassing multiple parameters without the high cost of individual sampling. Aim of this study was to determine if diagnostic interpretation guidelines can be established for pooled metabolic profile samples.

Interpretation of pooled metabolic profiles for herd assessment

Davidek, J., Van Saun, R.J.  Pp. 24, In: Oral and Poster Abstracts 25th Jubilee 25th World Buiatrics Congress, Budapest, Hungary, July 6-11, 2008.

http://vbs.psu.edu/ext/resources/pdf/Interpretation-Czech.pdf/

Interpretation of Pooled Metabolic Profiles for Evaluating Transition Cow Health Status (Poster)

Robert J. Van Saun, DVM, MS, PhD, Diplomate ACT and ACVN

Department of Veterinary Sciences, Pennsylvania State University

http://vbs.psu.edu/ext/Resources/pdf/pubs/rvs-pooled profile-WBC2006.pdf

Monitoring and Testing Dairy Herds for Metabolic Disease

Garrett R. Oetzel, DVM, MS, Associate Professor, Department of Medical Sciences, School of Veterinary Medicine, University of Wisconsin-Madison

http://dairynutrient.wisc.edu/images/28/Herd-Testing.pdf

Metabolic disease incidence typically increases as milk production increases and as herds become larger. These factors favor the use of rigorous, quantitative monitoring of metabolic disease whenever possible. Fortunately, recent developments of herd-based tests plus new appliications of some old tests are now available for use in routine herd monitoring and for investigating dairy herds with metabolic disease problems. This allows the herd consultant to make recommendations based on objective data rather than subjective impressions alone.

Herd-Based Biological Testing for Metabolic Disorders (Power Point)

Garrett R. Oetzel, DVM, MS, Associate Professor, Department of Medical Sciences, School of Veterinary Medicine, University of Wisconsin-Madison

http://www.wcds.afns.ualberta.ca/Proceedings/2003/PowerPoint/22 Oetzel Metabolic Disorders.pdf