Breed Improvement To Use or Not to Use a Carrier?

by Lindsay Upperman, Ph.D., Director of Breed Improvement

Genetic defects have become an important factor in buying and mating decisions within the beef industry. With various defects within and across breeds of cattle, there may be multiple defects to consider. For a producer, this may make breeding season more complicated, and that’s without the traditional decisions to make based on EPDs, indexes and ultimately your operation’s marketing goals. Let’s see if these decisions can be broken down into an easier process!

The first thing to know about genetic defects is that they occur within all species, even humans. So why have producers only really started factoring them into their breeding decisions within the last 10 years or so? Well, most genetic defects are known as simple recessives. Essentially, this means that the animal needs to inherit both recessive copies from their parents in order to cause the defect. Also, this tends to mean that the defect will stay hidden for multiple generations until a mating with inbreeding happens.

Another way of thinking is relevant to how this breed was founded. The black/red color gene has a recessive component as well: the red allele. Remember, an allele is one of two versions of DNA at a given location. An animal inherits one allele from each parent. Thus, in order to have “Red” Angus, the cattle have to have two copies of the red color allele to be visually red.

In the figure, there is a mating depicted between a black-carrier sire and a black-carrier dam, which shows the probability of their offspring having a particular genotype. Each box represents 25% of the offspring or one out of four boxes. Remember, a carrier is an animal that “carries” one copy of the recessive allele and one copy of the dominant allele. In this case, the dominant allele is the black color and the recessive is the red color.

In this figure, 25% of the time their offspring have both copies of the black allele (BB), 50% of the time their off- spring will have one copy of the black allele and one copy of the red allele (Bb), also known as a carrier, and finally, 25% of the time their offspring will have both copies of the red allele (bb). If a producer were to visually see these genotype possibilities, 75% of the time the offspring would be visually black animals (BB, Bb and Bb) and 25% of the time the offspring would be visually red (bb).

Essentially, this is the same inheritance pattern as recessive genetic defects. Ultimately, if two carriers of the same genetic defect are mated, there is a 25% chance the offspring will have the disorder and a 50% chance the offspring is a carrier of the genetic defect. Thus, the best way to proceed with potential matings in your herd is to have the knowledge of which animals are free or carriers of the genetic defects.

Currently, there are 13 genetic defects that occur within Red Angus cattle, with the main six defects being: Arthrogryposis Multiplex (AM), Contractural Arachnodactyly (CA), Developmental Duplication (DD), Alpha-Mannosidosis (MA), Neuropathic Hydrocephlus (NH) and Osteopetrosis (OS). These defects can all be tested for and range from $15 to $25 through the DNA department at RAAA. If you have any questions in regard to defect testing, please feel free to contact dna@redangus.org.

Can I Use a Carrier Bull or Female?

So far, what a genetic defect is and how they are inherited has been discussed, but is it acceptable to use carrier animals within your mating decisions? There are a few questions to consider, for instance is the carrier animal being mated to another carrier animal? Try to avoid mating two carriers together, as this is the only mating that will result in the 25% chance of a calf exhibiting the genetic defect.

However, if the cow herd is free of the genetic defect, but the bull is a carrier, then there will be 0% chance of any offspring exhibiting the genetic defect. Yet, this mating will lead to around 50% of offspring being carriers, which may result in more complicated decisions down the road. In the end, if using carriers in a breeding program, making sure to test those animals that are potential carriers is the safest bet and allows for the best mating decisions to be made. //