When looking at inbreeding holistically, Cole emphasized that inbreeding affects different traits in different ways and is a natural consequence of mating related animals in a finite population. Overall, inbreeding can be managed but not avoided entirely.
Why does “new inbreeding” matter more than “old inbreeding” with a population of millions of Holsteins? In 2008, with the advent of genomic information from high-density DNA marker panels, we no longer had to assume the proportion of alleles that were proportionally inherited in each generation. Genomic information enabled us to determine the exact proportion of alleles that were inherited. Recent inbreeding will produce long stretches of homozygosity, which will help us look at specific places in the genome that can lead to the frequency of harmful loci appearing and pairing up. As an example, Holstein Haplotype 1 (HH1) in the Holstein population, a bull that was a carrier of the haplotype, was heavily used in the Holstein population. As more inbreeding was done with that bull, it increased the likelihood that you have two copies of the alleles in the population, in the case of HH1, a decrease in fertility. In the case of older inbreeding, the harmful loci have typically been purged from the population, and the desirable alleles have been maintained.
How much should we be worried about inbreeding? As Cole stated, “We don’t know how much is too much. We worry in part because we don’t know when we are going to have a manageable situation to an unmanageable situation. The upside is that we don’t do single-trait selection anymore. Single-trait selection can get us into trouble very quickly,” Cole said.” We don’t know if we will see slow, steady erosion in performance or a sudden crash in performance because of inbreeding.”
Yet, it is not all negative news. The change in phenotypic performance for every 0.25% increase in inbreeding — the current average in the Holstein population — remains negative for individual traits, but the change in genetic potential when selecting on an index, in the example given of Net Merit $, outpaces the consequences of the negative phenotypic depression of inbreeding. Additionally, our ability to detect genetic defects has changed thanks to the advent of genomic data.
Cole discussed many options that the industry can evaluate on how to best manage the inbreeding in the future, with some having more practical applications and others that will require leaps in technology to achieve. Concluding the webinar, Cole summarized that when we do intensively inbreed our cattle without the ability to control the effects, we cause harmful defects.
To watch the webinar, visit the Iowa State University dairy extension page.
