The demographics of today’s average beef producer are either that is aging or doing it part time.
That is why, in general, producers do not want to deal with calving difficulties any more than is absolutely necessary, especially in first-calf heifers. As we continue with breeding season, are you sure you are using calving ease sires where they are needed? Are you using the right tools to select a calving ease sire?
Way too many producers still rely on actual birth weight (BW) when selecting a calving ease sire. This is the absolute worst indicator of calving ease to base selection upon. Studies have shown that a 10 degree temperature drop during the last third of gestation can result in a 10 pound increase in BW, so fall calves cannot be compared to spring calves, and the same for winter versus late spring. One year’s birth weights will be up and the next down due to the weather. On average, southern calves will weigh much less than northern calves. Age of dam has an effect on BW, so Beef Improvement Federation (BIF) estimates a mature cow’s calf will weigh 6 pounds more than a first-calf heifer. That is why calves are put in contemporary groups and adjusted for age of dam for breed associations’ genetic evaluations.
Body condition score (BCS) or “feed” can have some effect on birth weight, but not nearly to the extent people think. Although this is somewhat controversial, I firmly believe, based on my own experience, research and literature review, that you cannot feed on BW. You can increase calving difficulties by excessive BCS by filling the pelvic canal with fat. You can decrease BW by decreasing BCS to the low 4 and below. If this happens, calf vigor, passive immunity and female rebreeding will be compromised. It is never a good idea to limit feed as a management tool to decrease BW.
What tool to use then?
First and foremost it should be an EPD (expected progeny differences). This allows you to compare purebreds and hybrids within a breed (not between breeds) for genotypic differences for the trait of economic relevance. In the case of BW, it is literally the pound difference between sires if you breed them to an infinite of number of genetically similar cattle within the breed (straightbred). In reality, the best way to use them is to go to the breed’s website and look at the percentile charts and see how the animal ranks within the breed.
Second is to decide which is the economically relevant trait (ERT). Most breed associations print EPDs at least for BW and calving ease direct (CED). If I had to guess, I would say the vast majority of breeders use BW EPD as their ERT for calving ease, and this is the wrong decision. CED EPD is the right answer and is defined as the percent probability a sire’s calves will be born unassisted. You compare sires just like the above
BW example by knowing something about the breed and how they rank within the breed. Birth weight is an indicator of calving ease, but the ERT is calving ease. Since BW is a good indicator, every breed association that I know of except Gelbvieh use BW as a correlated trait when they calculate CED EPDs, so all the information from BW EPD is in the CED EPD. The basis for CED is calving ease scores on the BIF scale for first-calf heifers. First-calf heifers are used because they have the most problems and are watched the closest.
Obviously, if you have the chance to artificially inseminate your cattle to high accuracy EPD bulls, your chances for calving ease success will be exponentially higher. Although low accuracy EPDs are many times more reliable than actual BW or ratios, they still come with a fair amount of risk because, by definition, they are low accuracy. It is a fact of life that young bulls get bought and must be used to breed yearling heifers. My best rule of thumb in using unproven bulls for calving ease is to not get too greedy on growth. Often these potential big spread bulls are also short gestation bulls. If they don’t always breed true, then every fifth calf´s BW that goes long gestation will be a whopper. I am sure many of you can think of examples amongst breeds. On the other hand, do not go overboard with little tiny calves, especially if you are you using proven sires. Calves should be big enough to be thrifty and have some growth in them.
The take-home message is not to use indicator traits like actual BW or even the vastly better BW EPD, but to go straight to the ERT of
CED EPD, especially since it already contains BW. Beware of going to extremes like getting greedy with growth on low-accuracy bulls or the other extreme or tiny calves that lack vigor. Stay in the middle of the road and stay in bed next spring. — R.L. “Bob” Hough, Ph.D.
[Dr. Bob Hough has served for 10 years as the executive vice president of the Red Angus Association of American and more recently as executive vice president of the North American Limousin Foundation from 2009 to early 2011. He is now a consultant, freelance writer and semi-retired. He can be contacted at bobhough1@ aol.com]