Inbreeding has become a hot topic in recent years…
Producer concern is on the rise over whether genomics is creating too much inbreeding in the dairy cattle population. The worry is that there will soon be limited options to which a herd can be bred to avoid negative effects of inbreeding. Mating an animal to her father or brother is certainly not desirable, but we need to ask what the real goal is in terms of inbreeding. Should we aim for zero percent inbreeding or rather manage it to maximize profit?
The linear effect of inbreeding depression
As animals become more related to each other, inbreeding depression or sub-par productive performance can occur. Inbreeding depression is not ideal, but it should still be weighed against the potential added value from genetic gain.
A common misconception is there is a magic level of inbreeding that we should never go beyond for any given mating. In reality, numerous studies over time have shown the effects of inbreeding depression to be linear.
For every 1% increase in inbreeding for a mating, you will realize $22-24 less profit over the life of the resulting offspring. The same cost, or loss, is predicted when going from 9% to 10% inbreeding as is expected between 1% and 2%.
It’s well-documented that inbreeding has been on the rise since the mainstream adoption of AI. Despite this increase, dairy cattle have made significant strides in production traits like milk, fat, and protein. It’s safe to say that producers would not trade today’s high producing cows for the less inbred, but also lower producing, cows of the 1960’s.
Let’s look into the records of a random cross-section of 10 upper Midwest dairies averaging 1,500 cows, who implement a mating program on their farm. This analysis shows how cows with superior genetics are more productive than cows with inferior genetics, despite the more highly productive group also being more inbred.
In this analysis, cows born between 2005 and 2010, with at least one lactation on record were included. Each individual herd was first analyzed separately, and cows were split into quartiles based on their individual level of inbreeding.
|Total # of cows||% Inbred||NM$||Milk Deviation||1st Lact 305-Day Milk||PTA DPR||Avg. 1st Lact Preg Rate||PTA PL|
|25% MOST inbred from each herd||3810||7.0||158||649||28258||0.4||22.5||1.4|
|25% LEAST inbred from each herd||3784||4.5||121||296||27875||0.4||22.6||0.9|
Here, you can see the difference in genetics, 1st lactation milk production, and NM$ between the top 25% most inbred from each herd and top 25% least inbred animals from each herd. The most highly inbred quartile of cows was also the most genetically superior group of cows in each of these ten herds.
Despite the elevated inbreeding in the most highly inbred quartile of each herd, the genetics more than make up for that when their actual performance is measured. The NM$ levels, pounds of milk and milk deviations were all favorable for the more highly inbred, but also more genetically superior group.
This is not to say that selecting a mating resulting in a 25% inbreeding level is the best option, but rather that when managed properly as part of a program, excellent genetics can more than make up for predicted inbreeding depression.
What many producers also don’t realize is that current proof values of a bull already account for the level of predicted future inbreeding. Adjustments are made in favor of a bull that is considered an outcross sire, and a bull that is more closely related to the average population will see a negative impact on his PTAs because of these adjustments.
Manage inbreeding to maximize profit
To manage inbreeding, we look to an example to see how managing, rather than avoiding inbreeding is the best route.
The example below shows three options to use for a mating in your herd. Sire 1 and sire 2 both offer high Net Merit $ levels. However, their 8% and 6.5% inbreeding levels would be above the suggested 6.25% industry standard, which would eliminate them as potential mating sires in many breeding programs. Sire 3 would be a logical outcross mating in this example, resulting in a mere 1% inbreeding.
|Sire Option||Sire NM$||Inbreeding % with cow being bred||Economic loss due to inbreeding||Adjusted NM$ for level of inbreeding|