Scientists Encourage Greater Genetic Diversity in Livestock
When Penn State scientists dug into the family trees of North America’s Holstein herd and found that 99.75 percent of modern-day Holstein bulls were descended from two born in the 1880s, it raised concerns about too little genetic diversity in livestock.
This Holstein bull, Neptune H, was the granddaddy of them all. Not literally, but if you include Hulleman, another bull from the 1880s, it’s safe to say these two are the granddaddies of nearly them all.
Pennsylvania State University associate professor Chad Dechow and two colleagues dug into the family trees of North America’s Holstein herd and reported in 2015 that 99.75 percent of modern-day bulls were descended from those two.
Chad Dechow, Dairy Cattle Genetics, Pennsylvania State University: “Everybody kind of had an idea that the lines would consolidate quite a bit but …nobody had really described the extent to which that would be the case so it was a little bit of an eye opener of how much the male lineages contracted….It’s maybe not quite as alarming as it first sounds, but at the same time, there has been a rise in inbreeding… and there are concerns related to that.”
More than a century ago, word-of-mouth would push some Holstein bulls onto the national stage. The advent of artificial insemination, rapidly adopted in the 1960s by the dairy industry, brought even more widespread use of just a few popular bulls.
Hulleman’s son, Pawnee Farm Arlinda Chief, a bull born in 1962, sired 16,000 daughters thanks to artificial insemination. However, a harmful mutation was quietly being passed along with the bull’s many positive traits. USDA and University of California-Davis scientists had, by 2016, pinpointed the mutation and confirmed that, when the mother also passed on the mutation, it caused some unborn calves to die in the womb.
The industry losses from the mutation, now rapidly being weeded out of the national Holstein herd, were an estimated $420 million. That amount is dwarfed by the $30 billion in economic gains associated with the line’s increased milk production. So, the question becomes: does it matter?
Chad Dechow, Dairy Cattle Genetics, Pennsylvania State University: “That’s one of the tricky questions we want to know, you know: at what level is inbreeding problematic? And there’s kind of the running joke of: If it works, it’s line breeding. And if it doesn’t, it’s inbreeding, right?
Andy Snyder, a territory sales manager in eastern Iowa for the genetics company GENEX, says many dairy producers feel they have to focus first on selling enough milk and milk fats to make a living. A few are searching for “outcross” bulls, animals outside mainstream genetic lines.
Andrew Synder, territory sales manager, Genex, Cascade, Iowa: “They are constantly looking for that outside bull but he has to measure up. If you bring in a bull that the daughters milk ten pounds less and give five pounds less fat a day, we’re not making progress…It’s amazing how efficient the American dairy farmer has become and our genetics are sought around the world…It’s hard to get bulls that rank extremely high outside those lines.”
One of Snyder’s customers, Doug Roth of Hilltop Dairy near Wayland, Iowa, tried crossing Holsteins with another dairy breed but was unhappy with the results.
Hilltop Dairy pairs now most of their Holstein cows and heifers with Angus bulls using artificial insemination. Thirty percent, however, are bred to Holstein bulls using a sex-sorting technology to ensure most offspring are heifer calves. Hilltop gets assistance from Neogen, a genomics company, to help decide which females are worth spending the money on for this more expensive approach.
Doug Roth, producer, Hilltop Dairy, Wayland, Iowa: “They’ll send us results back with production traits… with type traits, any recessive mutations you know so that we can get rid of those calves right away… and the ones we breed are according to genomics. Now we don’t necessarily use the genomic results to choose our bulls. We use our genomic results to determine which ones we keep to breed, and that’s about the extent of it.”
GENEX, which has about 200 Holstein bulls available, and others in the dairy industry have software to pinpoint when a cow and a bull are too closely related.
Doug Roth, producer, Hilltop Dairy, Wayland, Iowa: “We’re paid for fat and protein…So I use bulls that are high fat and high protein bulls. And then of course, I don’t want to give up functional type. … I want to make sure we still maintain sound feet and legs and also udders. Stature? I’ve went the other way: we used be breeding bigger, bigger, bigger and now we are trying to maintain just a moderate-sized cow.”
While the genomic mapping of cows, in 2009, has been helpful in locating both mutations and positive traits, Dechow isn’t convinced high-tech, data-based tools will eliminate the obsession with a few bulls.
Chad Dechow, Dairy Cattle Genetics, Pennsylvania State University: “That’s had both its upsides and downsides. Certainly, from a genetic-progress standpoint, we are making faster genetic progress in milk yield and in health and fertility so that’s all been great, but a consequence of that has also been …that that particular system and using DNA markers actually accelerates the pace of inbreeding a little bit.”
Although there are differences, Dechow says other livestock industries need to be paying attention as well so breeders avoid losing positive traits needed in the future.
Turkey producer Tim Graber, who also farms in rural Wayland, Iowa, asks the two turkey genetics companies that provide his poults to look for larger breasted turkey lines as this is a key trait for processors. But Graber wonders about the turkeys losing hardiness and disease-resistance.
Tim Graber, turkey producer, Tim Graber Farms, Wayland, Iowa: “I can choose which genetic company and then I can work with them and tell them, ‘Hey this is what I’d like to see more in the future, maybe a more hardy bird, better feed conversion, maybe one that has better bone structure.’ And they take that and they listen to us and work with us.”
Graber makes sure only about half of his birds come from any one genetic line, a measure that was important when avian influenza hit the region.
Tim Graber, turkey producer, Tim Graber Farms, Wayland, Iowa: “To me, it makes sense not to have all your eggs in one basket so to speak.”
Chad Dechow, Dairy Cattle Genetics, Pennsylvania State University: “Losing genetic diversity limits our agility. And that to me is kind of the biggest problem.”
By Colleen Bradford Krantz, firstname.lastname@example.org