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Levels of T4 and tri-iodothyronine (T3), the activated hormone, correspond to thyroid function, but are also affected by changes in environment and physiological status (Suttle 2010). This paper reports serum and plasma T4 concentrations recorded in cattle and sheep in health monitoring and diagnostic projects.
The Edinburgh University Dairy Herd Health and Productivity Service (DHHPS) surveyed plasma or serum samples from adult dairy cows throughout the UK, throughout their production cycles, for the assessment of nutritional status (Macrae and others 2006). The DHHPS laboratory found no difference between plasma and serum samples for T4 estimation (unpublished data). Samples numbering 3475, from October 1992 to September 1993, were obtained from animals' blood sampled on a routine basis to check nutritional status (‘routine’) where T4 status was not specifically requested. Samples numbering 3512, from October 1993 to September 2005, were tested for T4 at the request of the farmer, veterinary surgeon, or feed advisor (‘request’). The DHHPS T4 analysis was a competitive immunoassay using direct chemiluminescent technology (Bayer), employing a Bayer Operon analyser wet chemistry system.
The Veterinary Laboratories Agency (VLA) analysed 1761 serum samples submitted from dairy and beef cattle and calves between January 2004 and October 2005, and 455 serum samples submitted from sheep between December 2000 and January 2006. Samples were submitted …