There can be many reasons why a sheep or goat producer may want to collect a blood sample. A blood test can be used for genetic (DNA) testing, to detect antibodies for specific diseases, and to diagnose pregnancy.
One of the most common uses of blood testing is to determine a sheep's susceptibility (or resistance) to scrapie. DNA testing can also determine if a sheep is a carrier for the spider lamb gene.
Many dairy goat producers blood test their animals for the CAE virus. Blood testing is also used to detect OPP, a similar virus, in sheep. While blood testing is not very effective in the early clinical stages, it can be useful for diagnosing Johne's disease in sheep and goats.
Purdue University has developed a fact sheet, "Blood sampling in sheep" that explains how to collect a blood sample. Sheep and goats are among the easiest animal species from which to draw blood, and blood sampling is a management skill that most producers can develop with some experience.
Thanks to Tom Stanley, Virginia Tech Farm Management Extension Agent, for suggesting this blog entry.
Drawing blood - instructions - U-say Ranch
How to blood test your goats - Boer Goats Home
Collecting tissue and other samples - Goat Connection
Guidelines for harvesting blood from livestock [Australia]