Inbreeding: Keeping your herd in the "safe zone"
For generations we have been selectively breeding our cattle to get the best herds possible. In school, I recall my professor Dr. Roger Shanks stressing that the only way to make genetic progress was to actively select who was going to be a parent.
He also stressed that, “Fences were the first tool of animal breeding.” What he meant by this is that the by establishing fences we now had the ability to control which animals were bred together.
When seeking out the best animals possible it makes sense to mate the best to the best, and, in fact, this is what we have been doing for generations.
Oftentime’s linebreeding, a softer form of inbreeding, has been utilized to capitalize on these superior genes. We have traditionally identified the amount of inbreeding based on the pedigree of the animal. However, genomics has allowed us to identify the exact DNA makeup of each animal, and thus their level of relatedness.
What we have found is that the level of inbreeding in our dairy herds is greater than what we originally thought. Young genomic bulls are 13.27% related and the U.S. cow population is on average 7% inbred.
Genetic theory recommends an inbreeding level of 6% or less. How is this higher level of inbreeding affecting our dairy industry? At this point it is hard to say. What we do know is that inbreeding increased the amount of homozygosity at various alleles in the animal’s genome.
What does this mean in English? It means that the more inbred an animal becomes the less diversity there is in the animal’s genes or genetic make-up. If this occurs in good genes then we see a positive effect. However, if this happens in bad genes we see negative effects.
The fear is that if a new disease emerges there will not be enough diversity in the cattle population to fight it off. The main problem with inbreeding is that we have no control over what genes are passed from parent to offspring, therefore we run the risk of increasing homozygosity at both good and bad genes.
So, the main question every dairy producer should be asking is, “Is it possible to avoid inbreeding?” At this point it is not. The race to create the best herds has resulted in increasing the inbreeding in all current active sires in the U.S. What this means is that any bull in the current active sire list of any stud will likely be related to your herd.
There are steps individual farms can take to decrease the inbreeding in their herd though. It is important to start by identifying the current level of inbreeding in your herd; then work on a mating program that will keep your average inbreeding levels steady.
This will require looking deeper into the pedigree of the sires you are thinking of using. The stud books usually only list two generations for each bull, while the co-ancestry may be at deeper levels.
Work with your stud company to identify your herd’s level of inbreeding and the pedigree of potential sires. Producers could also consider bringing in foreign genetics such as Dutch, Canadian or New Zealand genetics.
It is important to remember that genomics and animal breeding has allowed us to achieve great genetic progress. Genomics has also identified more accurately the level of inbreeding in our herds.
As a producer you must strive to work on keeping your herd in the “safe zone”, obtaining genetic progress while maintaining genetic diversity. Utilizing your tools, such as selectively mating to limit inbreeding, genomics testing, and foreign genetics will help you educate yourself and keep control of inbreeding on your farm.
Schlesser has served as the Dairy Agent for Marathon County since 2012.