The level of inbreeding in Holsteins continues to increase, accelerating to moderate to high levels.
AgSource has been tracking inbreeding levels since 2011, and now has compiled data from more than 1.4 million cows.
The current level of inbreeding in Holsteins calves born in 2019 is 8%, according to the AgSource data. Eight percent is still considered to be a moderate level of inbreeding. “Inbreeding levels less than 3.15% is considered low while inbreeding levels over 12.5% are considered high,” explains Nicole Nehls, with AgSource.
But averages don’t tell the whole story. “There has been a significant shift in distribution in only seven years,” she says. “The majority (76%) of Holstein cows born in 2011 fell in the low to moderate category of 3.15 to 6.25% inbred. However, Holstein calves born in 2018 now fall in the moderate to high category (82%), which is 6.25 to 12.5%.
“Avoiding inbreeding will become harder as selection of top cows and bulls in the Holstein population are made,” she says.
Why the increase?
The use of genomics is one reason inbreeding levels are increasing. The second reason is shorter generation intervals, say geneticists.
“Genomics is a big driver of it,” says Chad Dechow, a dairy geneticist with Penn State University. “We refuse to use bulls that are not the best, and we’re having a tough time using a bull that is $50 less on Net Merit but is still a good bull.”
The problem is all of the top bulls come from pretty much the same families and lineage. Even with more genomic identification of many more females, A.I. companies are having difficulty finding genetic outliers and, as a result, avoiding inbreeding in bull matings becomes more difficult.
Use of genomics is almost a self-fulfilling promise. “If genomics leads to faster genetic progress per year, which it does, then it almost has to lead to more inbreeding,” says Kent Weigel, a dairy geneticist with the University of Wisconsin.
In the past, he notes, the rate of inbreeding was limited by generation interval on the male side. “So even if we made lots of close matings, we couldn’t get inbreeding per year to change too quickly because there were so many years per generation.
“If in the past we made one mating of related animals every five years, and now we’ve cut that in half so we’re making two generations every five years, then even if inbreeding accumulation per generation is constant we will double the rate of inbreeding per year,” he explains.
What to do about it?
At the individual herd level, better animal identification and the use of mating programs designed to limit inbreeding can help, Dechow says. (See sidebar).
Limiting inbreeding on the population level is more problematic. If bull mothers are only being selected from elite families, the genetic diversity that might be available from good (but less than elite) families will be lost. And that is happening quickly, Dechow says.
In groups that study inbred wildlife populations, geneticists there look at “effective future inbreeding” (EFI). EFI is an estimate of how related an individual is to other animals within the population, and genetic diversity conservationists base all mating decisions on that number, he says. “But in livestock genetics, we have not come up with a good policy on dealing with it,” Dechow says.
“The good part about genomics is that more really good bulls are available and their marketable shelf lives are shorter,” says Weigel. “Granted, we can go crazy on some, but the days of 2 million units of Toy Story semen or 3,000 progeny tested sons of Blackstar are probably over.
“We’re accumulating inbreeding through groups of closely related bulls now rather than one individual bull,” he says.
Sidebar: It all starts with identification!
Animal identification is the first step in ensuring good, reliable data. Several steps should be followed to ensure the genetic information you receive from the Council on Dairy Cattle Breeding (CDCB) is accurate.
Step 1) The animal must be identified with a unique, official national animal ID. Animals with a herd management number will not qualify to receive a genetic evaluation.
Step 2) If you tag your animal, make sure to provide the official ID to your technician, or enter the complete official ID number in your herd management software as soon as possible.
Step 3) Enter the complete breeding information. For example, entering a partial NAAB code on a bull, or a bull’s short name, will result in a calf with a sire unknown. Also make sure to enter the correct stud code for conventional versus sorted semen.
Step 4) Ensure the cow’s official ID is transferred to her calf’s official Dam ID. If the official ID of the cow is not transferred to the calf record, it will result in a break in the animal’s pedigree – causing missing inbreeding and incomplete genetic information.
Step 5) If you genotype calves, it is key you enter the same official ID used to receive genomic results in your records and herd management program. If the official ID numbers are different, there is little possibility the animal’s genetic information will be updated and she will receive two different genetic evaluations.
For more on animal identification and inbreeding, go to: https://dairy.agsource.com/2019/07/18/genetics/?dm_i=5A8K,20ZB,13VMNU,6DAC,1