Collecting Samples for Genetic Tests

An excellent management decision for sheep producers includes testing their sheep to identify any genetic issues or diseases within their flock. Genetic testing helps to maintain a healthy flock and ensures buyers that the sheep are free from specific problems. Producers have different options for testing protocols, ranging from tissue to blood samples. Some tests require specific collection methods, so always check with your testing laboratory for their preferred method. 

Producers commonly collect tissue samples for testing. They can collect tissue samples using a method that collects the tissue by itself, or they can collect the sample when an animal gets tagged. This method punches a hole in the ear and pushes the sample and the punch piece into a collection vial. If the sample is collected at the same time as tagging, a special tagging tool attaches the tag while punching the tissue into a collection vial. Once the animal has been tagged, the collection vial can be removed from the tagger. The tag and collection vial bear the same identification number. This improves the accuracy of matching a sample to an animal. Some companies offer the option to match a collection vial with an RFID tag. Taggers and collection vials can be purchased through testing laboratories or animal health supply companies.

Once tissue samples have been collected, they can be shipped immediately or kept for up to three years. This gives producers the flexibility to make decisions about retaining or culling lambs later. 

An important consideration when collecting tissue samples in vials is the shipping method. Tissue samples do not require refrigeration, so they can be shipped in a padded envelope or a box. Do not ship samples in a paper envelope because the envelope will likely tear during shipment, resulting in lost samples.

Other producers may prefer to submit blood samples for analysis. Blood samples can be submitted on blood cards or as whole blood samples. Blood cards can be purchased from the testing lab, and blood tubes can be purchased from an animal supply company or your local veterinarian. The blood cards, also called dried blood spot cards, have an area where two to three blood droplets should be placed

Most blood cards will have a circle or square where the blood droplets should be placed. Blood is taken from an ear by nicking a vein in the ear with a sharp object such as a lancet or needle. Always use a new lancet or needle for each sample to avoid contamination. Allow two to three droplets to fill the circle, but do not oversaturate. Then, allow ample time for the blood samples to dry before packaging and shipping. Be sure to move the blood cards to a location where they will not become contaminated with dust or barn dirt. Blood cards, like tissue samples, can be stored at room temperature and may be kept for several years.

In contrast, whole blood samples are drawn from the jugular vein into a test tube and shipped in the tube. There are two different types of tubes used for collecting whole blood samples, and they are specific to the type of test you wish to have performed. Most producers refer to them by the color of the rubber stopper at the top of the tube: purple or red.

Purple top tubes contain the EDTA additive that prevents blood samples from clotting. These tubes should be used when testing for scrapie, callipyge, dwarfism, hairy lamb syndrome, myostatin, spider lamb syndrome, TMEM 154, or Booroola. Producers should collect two to three cc's from an animal, place the blood in the tube, and gently invert the tube to mix with the EDTA additive. Do not shake the tube! 

Red top tubes do not contain an additive and should be used for serum lab tests. The testing lab will centrifuge the samples; producers do not need to do this before shipping. These tubes are primarily used when testing for Johne's Disease or Ovine Progressive Pneumonia (OPP). These tests also require two to three cc's of blood but do not require inverting the tube.

All tubes should be refrigerated after collecting the blood samples. Tubes should be shipped with an ice pack during the summer, and the shipment should be delivered within one to two days. At other times of the year, the blood tubes can be shipped without an ice pack and delivered in three to five days. All samples should be shipped within seven to ten days after collection.

Testing is a great way to identify any sheep within a flock that serve as carriers for genetic diseases. They can then be removed from the flock to prevent spreading the problem. Now is a great time to test lambs and yearlings before selling animals for breeding stock.

First published in the Dorset Connection, the magazine produced by the Continental Dorset Club