Breeding your top females to the best bulls available may seem like a solid strategy for genetic improvement, but if those matings are closely related, it could have a negative impact on your herd.
Dr. Les Hansen, University of Minnesota dairy genetics specialist, recently released a paper, “Random Use of Holstein Semen on Holstein Females is Becoming Risky,” in which he warns dairymen of the consequences associated with even a slight annual increase in inbreeding among the Holstein breed.
Progressive Dairyman caught up with Hansen to learn why inbreeding is a big deal and what dairy producers can do to manage it.
1. Why should dairymen care about inbreeding?
HANSEN: Mating of close relatives increases the doubling up of recessive genes at single locations on chromosomes. When not paired with a dominant gene, recessive genes are able to fully express themselves. The expression of inbreeding from a single pair of recessive genes can be huge (embryo death, stillbirth, genetic abnormalities). On the other hand, the accumulation of effects from many pairs of recessive genes – each with more modest impact – across all chromosomes can also be substantial even if none are singly lethal (resulting in embryo loss, stillbirth or calf death).
2. With the advancement of genomics, we have more genetic information available today than ever before, yet inbreeding is increasing. Why?
HANSEN: Genetic advancement from genomics is almost completely due to the shortened generation intervals. Genetic theory tells us genetic relationships within a breed will automatically increase with shortened generation intervals. Yes, more lowly ranked males and females could be picked to avoid accumulation of genetic relationships within a breed, but no one seems to be interested in doing that. Therefore, we are mating "the best to the best as fast as we can," and consequently, the highest ranked animals are becoming more and more related to each other.
3. You note that the average annual increase in inbreeding for Holstein females is only 0.2 percent. That doesn’t seem like a significant number. Why is it cause for concern?
HANSEN: "Only 0.2 percent annually" might not seem like very much to those unaccustomed to genetic programs of livestock. However, the 0.2 percent annual rate equates to a full 1 percent increase every five years. It's important to keep in mind that the upper limit for inbreeding isn't 100 percent. A bull mated to his own daughter results in 25 percent inbreeding, and everyone agrees mating a bull to his own daughter is the epitome of inbreeding. Mating of half-siblings (brothers and sisters) gives inbreeding of 12.5 percent. Therefore, placed in context, our increase of average inbreeding of Holsteins from 5.7 percent in 2010 to 6.5 percent in 2015 is a dramatic increase of average inbreeding in just five years. At the current rate of increase, average inbreeding will be 8.5 percent within 10 years.
4. What is genomic future inbreeding (GFI) and how can a dairyman use it to manage inbreeding and maximize genetic potential?
HANSEN: Genomic future inbreeding (GFI) is a wonderful tool developed by USDA scientists. At the gene level (not based only on pedigree inspection), GFI estimates the expected inbreeding if an animal is mated to a typical animal in the breed. Currently, the bull with the highest relationship to the Holstein breed is Picston Shottle, and his GFI is 9.9 percent. That means mating Shottle to a typical Holstein in the breed will result in inbreeding of almost 10 percent. The bull Shottle died recently, but his impact on the genetic composition of Holsteins has been incredible.
Genetic selection (improvement) is all about letting top individuals have a high impact on a breed. However, extraordinary impact of a bull (which is more likely with genomics through his many high-ranking descendants) can lead to considerable economic loss via inbreeding depression that may counteract the positive effects of individual genes that the bull transmits. PD
