Animal Health Series: It’s all in the genes

Assembled by Peggy Joseph-Potter RN, BSN, MHA

For anyone registering cattle, perusing pedigrees, or checking out potential semen donors, you may have found some unfamiliar notations following the animal’s name. Recent changes implemented by the American Hereford Association may affect both registration and management of your breeding program. In November 2010, the American Hereford Association implemented a mandatory DNA testing policy for all future walking sires. All Hereford sires born after January 1, 2011, need to be DNA genotyped at the official American Hereford Association DNA laboratory before their progeny can be registered. The intent of the policy is to improve the quality control of pedigrees and to test for three non-lethal genetic abnormalities. The same requirement for all AI sires and donor dams was previously implemented. Why the change you may ask? According to Joe Roybal of Beef Magazine, it was prompted by the difficulties and expense in determining sires in the standard breeds. The issue with genetic testing was most likely prompted by the Angus industry when Arthrogryposis Multiplex, a very popular sire, lead to the genetic evaluation of 10,000 direct sons and daughters after it was discovered he carried the lethal gene for Curly Calf Syndrome.

Recessive genes are responsible for the development of three genetic abnormalities known to be present in Hereford cattle, Dilutor-Rat Tail, Hypotrichosis and Idiopathic Epilepsy. Therefore, an animal seemingly normal in appearance can produce offspring that demonstrate recessive gene abnormalities. Genetic abnormalities are inherited defects, their form may be extreme, showing visible signs with a lethal result or they may be less obvious, causing premature abortion, early embryonic death or produce animals that are weak, slow growing with lower vigor, fertility and longevity.
Recessive inheritance can cause a parent to carry the defective gene and appear normal; the parent is then known as a carrier. If both parents pass the defective gene to the offspring, the genetic defect shows up and the genetic condition in the offspring is called homozygous recessive. The defective gene in the carrier animal is present along with the normal gene and this condition is termed heterozygous. The underlying problem of genetic defects is that parents that appear to be perfectly normal can be carriers and so can produce offspring that are defective. Parents that never produce defective progeny are in the majority and are called homozygous normal. At first glance, it seems that if we could identify carrier animals and eliminate them from the breeding population the problem of recessive genetic defects would be solved. However, it is necessary to explore the problem a little further before deciding that identifying carriers is necessarily worth the money and effort.

Symptoms of the Dilutor-Rat Tail gene are as follows: Carrier Hereford bulls or females when mated to black cattle can produce offspring with a hair coat that is gray, smokey or chocolate color. Hypotrichosis gene: Partial to almost complete lack of hair. Affected calves are often born with very short, fine, kinky hair that may fall out leaving bare spots or areas particularly susceptible to rubbing. The condition may vary in expression as the animal matures and is usually less noticeable in older animals. The hair coat will sometimes appear “frosted” or “silverish.” Tail switch may be underdeveloped.
Idiopathic Epilepsy gene: Age of onset or first seizure can be variable, ranging from birth to several months of age. Occurrence and persistence of seizure may be influenced by environmental stressors such as temperature extremes or increased physical activity. Upon initial onset of seizure episodes individuals will typically lie on their sides with all limbs extended in a rigid state. Manual flexing of the limbs is possible, but return to the extended position occurs after release. Seizure episodes may last from several minutes to more than an hour. Carrier Free (F) identifies the animal as tested and the results indicate that the animal is not a carrier.

Breeders wanting to have their animals tested must use the AHA official lab, Maxxam Analytics. All samples submitted for parentage will also be tested for genetic abnormalities. The cost for DNA testing of less than 50 animals is $32/head for hair samples and $37/head for semen, blood or tissue. In order to test your animals, call the AHA office, 816-842-3757, and request a DNA kit. You will need to have your animal’s registration number available. You will receive a Genetic Marker Test form. Each form is specifically bar coded to the registration number of the animal.

Instructions for obtaining a hair sample: Pull hair samples above the tail switch. Do not cut the hair. The hair root contains the materials needed for DNA testing. Pull 20-25 hairs evenly and directly from the tail so the hair does not break. The switch must be dry and brushed clean of all debris. The lab suggests wrapping the hair around a pencil and then pulling.

According to Jonathan Beever, a leader in cattle genetics, the issue is one of management and accurately identifying carriers through genetic testing; eliminating the gene source is contrary to overall breed improvement. In the absence of DNA testing, genetic abnormalities can be minimized by utilizing outbreeding and examining pedigrees to avoid mating of animals with common ancestors within at least two or three generations. In addition, the practice of turning over the sires after one or two breeding seasons and using fewer cows per bull reduces the chances of producing animals with inherited defects. No matter which process you use to protect your herd be aware of the possibility of genetic abnormities and plan you program accordingly.

Bibliography:
American Hereford Association. AHA implements new DNA policy for walking herd sires. Retrieved May 1, 2011, from The Pairie Star.
Causes of Gentic Abnormalities in Cattle. Retrieved May 1, 2011, from Petahia.
DNA Testing Procedures. Retrieved May 1, 2011, from American Hereford Association.
Roybal, J. Avoiding THE WORST. Retrieved May 1, 2011, from BEEF.
Biography:
Peggy and her husband, Bob Potter, own and operate PJ Ranch LLC in Winton, California. They have been Miniature Hereford owners and active participants in the MHBA since 2002. She is employed as a critical care nurse for a local medical center.

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