In-bred holsteins are a problem.
May 28, 2021 4:53:35 GMT -5
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Post by Christine on May 28, 2021 4:53:35 GMT -5
De WSJ 05282021
Trick question: How many Holsteins—the black-and-white dairy cows prized for the quality and quantity of their milk—are in the U.S.?
a. Nine million
b. Fewer than 50
c. Both a and b
Holsteins give more milk than any other dairy cow in the country, with the average female producing around 23,000 pounds of milk over 305 days, according to the Holstein Association USA. The entire population provides 94% of the nation’s milk.
But selective breeding—allowing farmers to mate only animals with the most desirable traits—has led to so much inbreeding that virtually all Holsteins in the U.S. and abroad descend from just two bulls.
So, while there are roughly nine million Holsteins in the U.S., the breed’s effective population—a measure of genetic diversity—is just 43, according to an estimate published last year in the peer-reviewed Journal of Dairy Science.
“Effective population represents the unique pedigrees within a breed,” said Les Hansen, a professor of dairy-cattle genetics at the University of Minnesota. “All the others are different permutations of those.”
In the wild, animals with an effective population of less than 50 are considered at immediate risk of extinction because of the increased risk of miscarriages, stillbirths and genetic abnormalities.
Holsteins, whose breeding cycles are strictly managed by the agriculture industry, aren’t on the verge of disappearing, but their level of inbreeding concerns some geneticists.
“We’re not seeing a problem, but the average cow lactating today is probably 7.3% inbred,” Dr. Hansen said. “For heifer calves born early this year, it’s up to 9%.”
The percentages estimate the probability that a pair of genes are identical because they descended from an ancestor shared by both parents. The more often near relatives mate, the higher the percentage.
In the past, geneticists recommended the average shouldn’t surpass 6.25% for commercial livestock, Dr. Hansen said. But now, some suggest the inbreeding of Holsteins shouldn’t be a concern until it exceeds 10%.
At the current rate, that could happen in about two years.
The two bulls that most Holsteins descend from are Round Oak Rag Apple Elevation and Pawnee Farm Arlinda Chief—Elevation and Chief for short. Each was born in the 1960s and was used as a sire, providing semen for artificial insemination. The DNA of their recent descendants now permeate the breed.
“These bulls have incredible global impact,” Dr. Hansen said. “A bull in production for 10 years will produce up to two million units of semen and a tremendous number of daughters.”
Along with maximizing milk production, selective breeding boosts longevity, mobility, leg and foot health, and dozens of other positive traits.
But it’s also responsible for the proliferation of some diseases.
Cholesterol deficiency, an incurable disorder first documented in 2015, causes calves to suffer from chronic diarrhea and, typically, die between three weeks and six months after birth.
The recessive genes that cause the condition have been traced back to Maughlin Storm, a Canadian bull born in 1991 whose offspring have been used world-wide. The deficiency is one of at least 15 genetic disorders that adversely affect Holsteins, according to the U.S. Department of Agriculture. (Tests are used to detect and eliminate them from the population.)
“There are individual examples like cholesterol deficiency that are devastating,” said Christine Baes, who holds the Canada Research Chair in Livestock Genomics at the University of Guelph in Ontario, and who, with colleagues, has estimated the effective population of the breed. “But the benefits generally outweigh the costs.”
Still, the worry is that the dwindling diversity of Holsteins could permanently undermine the breed’s fitness. But rather than slowing down, the pace of inbreeding has accelerated.
Traditionally, livestock were bred based on the pedigrees recorded in herdbooks, the official record of a recognized breed that traces the lineage of registered animals.
“A potential bull would be born, and you had to wait until it had milk-producing offspring to tell how good it was,” Dr. Baes said. “Now, you can look at its DNA.”
The process, known as genomic selection, allows geneticists to identify desirable traits in very young animals, and because of that, the average age when Holsteins have offspring has shrunk.
In 1990, sires of bulls were 8 years old, on average, according to Dr. Baes’s research. By 2016, they were 2.32 years old. Sires of cows were, on average, 7.67 years old in 1990. By 2016, they were 3.75.
Females changed similarly.
When birthing a bull, they were 2.24 years old, on average, in 2016, down from 5.74 in 1990. When birthing a heifer, they were 3.25 years old in 2016, down from 4.49.
Before genomic selection was introduced in the U.S. in 2008, Holstein inbreeding increased at an average rate of 0.11% each year, according to Dr. Hansen’s research.
In 2019, the average rate of increase was 0.46%.
“Without correction, it will keep on,” Dr. Hansen said. “Maybe they can tolerate high inbreeding. We don’t know.”
One potential solution might fix the cows but water down the milk.
“If you’re desperate, you crossbreed,” Dr. Baes said. “You won’t have that Cadillac of milk production anymore. But you’ve immediately solved your inbreeding problem.”
Write to Jo Craven McGinty at Jo.McGinty@wsj.com
Trick question: How many Holsteins—the black-and-white dairy cows prized for the quality and quantity of their milk—are in the U.S.?
a. Nine million
b. Fewer than 50
c. Both a and b
Holsteins give more milk than any other dairy cow in the country, with the average female producing around 23,000 pounds of milk over 305 days, according to the Holstein Association USA. The entire population provides 94% of the nation’s milk.
But selective breeding—allowing farmers to mate only animals with the most desirable traits—has led to so much inbreeding that virtually all Holsteins in the U.S. and abroad descend from just two bulls.
So, while there are roughly nine million Holsteins in the U.S., the breed’s effective population—a measure of genetic diversity—is just 43, according to an estimate published last year in the peer-reviewed Journal of Dairy Science.
“Effective population represents the unique pedigrees within a breed,” said Les Hansen, a professor of dairy-cattle genetics at the University of Minnesota. “All the others are different permutations of those.”
In the wild, animals with an effective population of less than 50 are considered at immediate risk of extinction because of the increased risk of miscarriages, stillbirths and genetic abnormalities.
Holsteins, whose breeding cycles are strictly managed by the agriculture industry, aren’t on the verge of disappearing, but their level of inbreeding concerns some geneticists.
“We’re not seeing a problem, but the average cow lactating today is probably 7.3% inbred,” Dr. Hansen said. “For heifer calves born early this year, it’s up to 9%.”
The percentages estimate the probability that a pair of genes are identical because they descended from an ancestor shared by both parents. The more often near relatives mate, the higher the percentage.
In the past, geneticists recommended the average shouldn’t surpass 6.25% for commercial livestock, Dr. Hansen said. But now, some suggest the inbreeding of Holsteins shouldn’t be a concern until it exceeds 10%.
At the current rate, that could happen in about two years.
The two bulls that most Holsteins descend from are Round Oak Rag Apple Elevation and Pawnee Farm Arlinda Chief—Elevation and Chief for short. Each was born in the 1960s and was used as a sire, providing semen for artificial insemination. The DNA of their recent descendants now permeate the breed.
“These bulls have incredible global impact,” Dr. Hansen said. “A bull in production for 10 years will produce up to two million units of semen and a tremendous number of daughters.”
Along with maximizing milk production, selective breeding boosts longevity, mobility, leg and foot health, and dozens of other positive traits.
But it’s also responsible for the proliferation of some diseases.
Cholesterol deficiency, an incurable disorder first documented in 2015, causes calves to suffer from chronic diarrhea and, typically, die between three weeks and six months after birth.
The recessive genes that cause the condition have been traced back to Maughlin Storm, a Canadian bull born in 1991 whose offspring have been used world-wide. The deficiency is one of at least 15 genetic disorders that adversely affect Holsteins, according to the U.S. Department of Agriculture. (Tests are used to detect and eliminate them from the population.)
“There are individual examples like cholesterol deficiency that are devastating,” said Christine Baes, who holds the Canada Research Chair in Livestock Genomics at the University of Guelph in Ontario, and who, with colleagues, has estimated the effective population of the breed. “But the benefits generally outweigh the costs.”
Still, the worry is that the dwindling diversity of Holsteins could permanently undermine the breed’s fitness. But rather than slowing down, the pace of inbreeding has accelerated.
Traditionally, livestock were bred based on the pedigrees recorded in herdbooks, the official record of a recognized breed that traces the lineage of registered animals.
“A potential bull would be born, and you had to wait until it had milk-producing offspring to tell how good it was,” Dr. Baes said. “Now, you can look at its DNA.”
The process, known as genomic selection, allows geneticists to identify desirable traits in very young animals, and because of that, the average age when Holsteins have offspring has shrunk.
In 1990, sires of bulls were 8 years old, on average, according to Dr. Baes’s research. By 2016, they were 2.32 years old. Sires of cows were, on average, 7.67 years old in 1990. By 2016, they were 3.75.
Females changed similarly.
When birthing a bull, they were 2.24 years old, on average, in 2016, down from 5.74 in 1990. When birthing a heifer, they were 3.25 years old in 2016, down from 4.49.
Before genomic selection was introduced in the U.S. in 2008, Holstein inbreeding increased at an average rate of 0.11% each year, according to Dr. Hansen’s research.
In 2019, the average rate of increase was 0.46%.
“Without correction, it will keep on,” Dr. Hansen said. “Maybe they can tolerate high inbreeding. We don’t know.”
One potential solution might fix the cows but water down the milk.
“If you’re desperate, you crossbreed,” Dr. Baes said. “You won’t have that Cadillac of milk production anymore. But you’ve immediately solved your inbreeding problem.”
Write to Jo Craven McGinty at Jo.McGinty@wsj.com