TH; Let's Get it Fixed

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A Genetic Malfunction - Let's Get it Fixed!

   (as published in AMSS Journal Dec '06.)

A Genetic Malfunction - Let’s Get it Fixed!

                               By John Hendrickson

One cannot spend too long around Shorthorns these days without hearing mention of Tibial Hemimelia (TH). Thanks to Dr. Jonathan Beever at the University of Illinois, Dr. Charles Hannon, Food Animal Vet Science and various Shorthorn breeders who chased down and submitted samples. A genetic test for carriers of the defective gene was developed in August of ’05. Since breeders now have a DNA marker test to determine whether or not our cattle are carriers, I feel that the best way to address the defect is head on.

The severe and lethal genetic defect, Tibial Hemimelia is evident in newborn calves that are born with twisted legs with fused joints, have large abdominal hernias and/or a skull deformity. They typically don’t survive at birth but if they do cannot stand to nurse and must be destroyed. Although these calves are a loss for owners, the larger problem for breeders is identifying which normal-appearing animals carry and can pass on the recessive gene.

The ASA (American Shorthorn Association) has been monitoring TH since 1999, when a number of affected calves were submitted to research for scientific review. As more was learned, patterns developed and it was determined that the affected calves had a common ancestral heritage. The research was similar to the genetic disorder in the Galloway cattle, this past experience suggested numerous carriers could be present.

The Shorthorn influence can be found in more than thirty breeds of cattle around the world. Currently, TH has been in Shorthorn cattle and Shorthorn influence cattle, including Maine-Anjou, Chianina and crossbreds.

As breeding selections are made for desirable characteristics, undesirable traits also appear. This situation is not unique to just the Shorthorn breed as genetic defects occur in all breeds. Researchers have cases of defects in other breeds like Mule Foot disease in Simmentals and Holstein; DUMPS, BLAD,& CVM in Holstein; Limber Legs & RVC in Jerseys; Alopecia in polled Herefords; a collagen defect in Angus; and SDM,SMA, Weaver Syndrome in Brown Swiss; as well as Dwarfism in all breeds. Many breeds have genetic defects, but it is how we handle those defects that define our success as stewards of our breed.

However, some of the more popular pedigrees have been identified as carriers of the defective gene, even before a DNA test was available.

Any animal that traces back to the original Deerpark Improver bull imported to the USA in the 1970’s has the potential to be a carrier of the defective TH gene.

TH and Inheritance

The inheritance of TH is simple to understand, especially if you already understand how polledness is inherited. TH is inherited in the same way, with the normal allele (N) being dominant to the defective allele (n). A simple recessive mode of inheritance involves only a single pair of alleles, one

that is passed by the sire and one that is passed by the dam. In the polled/horned example, a calf will inherit one allele, either polled (P) or horned (p) from each of its parents. The polled allele is dominant to the horned allele, so both homozygous (PP) and heterozygous (Pp) animals will be polled. Only homozygous recessive (pp) animal will be horned. Inheritance of the gene for TH works essentially the same way. Both parents pass one allele, either normal (N) or defective (n) to their offspring. The normal allele is dominant to the defective allele, thus heterozygous (Nn) offspring will be normal appearing, but carry the defective allele. This allele could then be passed on to their offspring. Only homozygous (NN) calves will be TH free (THF). An animal must possess two defective copies of the allele in order to display symptoms.

Mating with TH carrier (THC) will result in one of three outcomes.

1. The calf will be free, not carry the defective allele (NN)

2. The calf will appear physically normal, but will be a carrier for the defective TH allele (Nn) Some THC will have curly rougher hair coats.

3. The calf will have the defective allele (nn) and be afflicted with the characteristics described below.

A. Bilateral malformed or absent tibia and abdominal hernia. Twisted rear legs with fused joints.

B. A long shaggy curly hair coat.

C. Retained testicles in males.

D. Meningocele -- protrusions of the coverings of the spinal cord or brain. Skull deformity.

It is important to bear in mind that this is not a genetic defect exclusive to the Shorthorn. The ASA just made people aware of the issue. Dr. Ronald Bolze, former Executive Secretary made every attempt to bring public this defect and made several steps to eradicate it. Genetic Defect Protocols were outlined and approved. The ASA discloses the TH Free (THF) and TH Carrier (THC) and TH Unknown (THH) none tested or TH in ancestry. This “free” and “carrier” males and females are maintained on the ASA website if they are parentally verified. Listing link below.

Registration certificates are still issued regardless of genetic defect status and no indication is placed on ASA registry certificate. Some breeders want change, others want to keep business as usual.

Should I use TH carrier or non tested sires?

When this mutation is present in a herd, it could get carried silently along for generations. Breeders should cull confirmed carriers. Only one way to solve, get rid of it.

This is an expensive, but necessary decision.

Using TH carrier sires can be very risky and potentially expensive. Most A.I. services are now listing THF or THC on bull listings. There are some showy and very popular club calf sires that have been linked to THC.

Some A.I. studs are now posting Caution, Caution this sire is THC.

Unless you are sure a TH carrier sire is bred to only TH free cows, there is a chance of producing defective calves. Even if the TH carrier sire is mated only to TH free dams, by definition each calf has a 50-50 chance of being a TH carrier. 50 percent of the progeny of a carrier parent are carriers when mated to a non-carrier, the other 50 percent are TH freeWhy take the chance!

Mating Strategies

There are a number of different strategies breeders can use to immediately eliminate the chances of producing any defective calves. Ultimately cleanse their herds of defective gene.

Test & Breed to Develop a THF herd.

1. Adopt the simple practice of only using THF sires.

2. Breed TH carriers to TH free animals.

3. Test all bulls and heifer calves born from parents of unknown TH status.

4. Cull THC animals from your herd and not to another breeder.

How can we solve? If we test and logically deal with it, we can easily save ourselves and fellow cattlemen any headaches and heartaches from this TH problem. Hiding the facts or misplacing results will not make the problem go away. Wouldn’t it be great to say in two years time that because of testing and handling effectively this defect; the TH Carriers were prevented from ever becoming a major long term problem? Thousands of Shorthorn cattle are now TH tested. Knowledge is power. We can make informed decisions as breeders and protect the future of our breed. Use THF (negative) bulls.

Many breeders want TH status on registry, such as placing verified THF behind name on registry. Some breeds of cattle have adopted no registry of THC cattle or transfer of animals with TH ancestry until TH Free tested.

This is policy that some Milking Shorthorn breeders are suggesting. Thus, creating a THF genetic pool of MS red, white and roan animals.

Another proposal is all AI sires, donor dams, ET and cloned animals must be DNA genotyped and have status of THF to be papered. This would quickly solve the spread of this genetic plague.

Future Implications

The struggle with genetic defects is not over. Not only must diligent testing and breeding decisions be made to eliminate TH, another defect is affecting Shorthorn cattle. You may have heard reports of “bulldog” calves. Many of which were often mistaken for calves afflicted with TH. The new syndrome is not bulldog. Researchers are currently investigating the physical conditions of the defect and have named it PHA (pulmonary hypoplasia with anasaarca). This second genetic, by all reports, is affecting many other breeds. No DNA test is currently available for PHA, but we know parents of a PHA calf are carriers of the defective gene. Several A.I. groups are now listing bulls as PHA carriers.

Credits and Acknowledgements to this TH article given to:

American Shorthorn Association, 

Dr. Jonathan E. Beever;

 Lana Kaiser, M.D.,DVM; Dr. Chuck P. Hannon;

Dr. Kent A Weigel; Dr. Dave Steffens

 Special Thanks to Shorthorn Breeders whom submitted scores of samples for testing.

After researching TH for 2 ½ years, dealing with two THC herd sires, and since studying various other cattle genetic defects; I decided to submit this review of Tibial Hemimelia (TH) in Shorthorn cattle. 

             John Hendrickson