With calf prices climbing, few people think about fertility. Instead, we think about trying to sell more pounds, but that is fertility.

Higher fertility means you will have more calves to sell next year. It also means you can sell more high-priced heifer calves instead of embarking on the costly exercise of turning them into bred heifers.

Fertility can be divided into two major traits - heifer pregnancy and cow pregnancy. Last month, we discussed heifer pregnancy (November BEEF, page 30). In this article, we'll discuss the genetics of cow pregnancy.

For years, geneticists have stated that fertility is not very heritable. We've also talked a lot about nutritional effects on the cow.

A cow's feed requirements differ greatly depending on her productivity. How much does she milk? How big is she? We all want high-production cows, but we want them to weigh 1,050 lbs. and stay fat on a few blades of grass.

In practice, the emphasis on higher growth rates and higher milk production has made our cow herds harder to re-breed. Most of us overcome this with better nutritional management through strategic supplementation, rotational grazing, calving later, weaning earlier, etc. The question is "Can we select for fertile cows that are still high output?"

In the mid '90s, Colorado State University (CSU) set out to get a handle on cow fertility. They developed a unique expected progency difference (EPD) called "stayability." They looked at the probability that a bull's daughters will be in the herd at 6 years of age.

Their reasoning was that daughters leaving the herd prior to 6 years old are probably never profitable. If they leave before then, you never get a chance to recoup your initial investment in the female. So, cows that stay longer make more money.

Based on this logic, CSU developed a statistical approach to estimate an EPD for this stayability trait. The results were surprising. It turned out the trait has acceptable heritability at 0.10, or just less than the heritability for milk.

A lot of people questioned what trait stayability was really measuring. Many of us thought that bulls that produced "poor quality" daughters would end up with low stayability EPDs. But, stayability turned out to be unrelated to quality.

The major reason cows are culled is because they fail to breed, not because they are poor quality. So, in fact, stayability is a good indicator of cow fertility.

Moreover, the variation within the Red Angus breed, as an example, is large. The best bull in the breed has a +20% stayability EPD and the worst bull has a -8% stayability EPD. What does this mean?

Let's assume that on average 70% of your females make it to 6 years of age. Based on their EPDs, we would expect 90% of the daughters sired by the +20% Red Angus bull to still be in our herd at 6 years old compared to just 62% of the daughters sired by the -8% bull. This is a huge difference!

So, what's the next step? We already have EPDs for more than 10 traits in most breeds and more are being created. Moreover, we still have the tough decision of picking the traits to emphasize in our own breeding program.

With any luck, some breeders will soon have the technology to convert all of these EPDs into a single economic figure that tells them how much more one bull should be worth than another based on selected traits. Until then, if you are keeping your own replacement females, I recommend using fertility EPDs first when picking a bull. It's that important.

Select bulls in the top half of the breed for fertility. Then look for the growth and carcass traits you want. If you're developing an index, place one-third of your selection pressure on growth, one-third on carcass and one-third on fertility. This is the basis of our program at Leachman Cattle Co.

As you shop for bulls this spring, encourage your bull suppliers to give you this stayability and heifer pregnancy information. If they don't have it, let them know that they may need it to keep your future business.