DPR: low heritability, low value?

Daughter Pregnancy Rate (DPR) is defined as the percentage of open cows that become in calf during each 21-day cycle. A DPR of  “+1,0” implies that daughters from this bull are 1% more likely to become pregnant during that estrus than a bull with a DPR of zero. Each increase of 1% in PTA DPR equals a decrease of 4 days in PTA days open. Less days open means more income. However the heritability of DPR is very low: only 4%. So should we give much value to it?

Milk yields of dairy cows have steadily increased the recent decades. Selecting for production meant that other traits, like fertility, were ignored. See the below figure.

^{Trends in milk yield (●) and Daughter Pregnancy Rate (○) for US Holsteins. Data are from USDA-ARS Animal Improvement Programs Laboratory, February 2007.} 

The decline in fertility has only recently been stopped. One of the reasons was the introduction of genomics, which made the prediction of fertility traits visible. For a long period fertility declined, but recovery has started. Although genetics is important, other factors like management, environment and nutrition are also very important. The heritability of DPR is low, but DPR should not be neglected.

Breeding caused the problem, but can also help to fix it!