"A bull whose daughters have high milk production is incorrectly referred to as a maternal bull. Milk is not a maternal trait. It's a growth trait," says Kit Pharo, seedstock and commercial producer from Cheyenne Wells, Colo. "The only reason a rancher would select for more milk production would be to increase the preweaning growth of his calves."

For the most part, Mr. Pharo considers milk to be a relatively inefficient way to produce growth. Research has shown that it requires 15 to 25 percent less feed to feed the cow and calf separately than it does to feed the cow and let her feed the calf.

"Don't get me wrong, I believe milk production is important, but we only need enough to get the calf to the point that it can utilize forages on its own," says Mr. Pharo.

Remember that milk expected progeny differences measure pounds of growth. Milk EPDs measure the expected difference in the calves a bull's daughters will produce. These weights are taken at, or adjusted to, 205 days of age.

So what's the difference between a bull with a "0" milk EPD and a bull with a "+20" milk EPD? A difference of 20 pounds will actually produce an extra weight gain of less than one-tenth of a pound per day. "That's probably not something I would lose much sleep over," says Mr. Pharo.

So what is a maternal trait? Things that come to mind for Mr. Pharo include, but are not limited to, calving ease, mothering ability, fleshing ability and udder conformation.

"Ultimately, though, fertility is the only genuine maternal trait," says Mr. Pharo. "Within a maternal cowherd everything else must take a back seat to fertility."