When it comes to calving ease, your chances are better if your cow's pelvis is the right size. "The data nationally would indicate still that anywhere from a low of 18 percent to a high of 28 percent of first-calf heifers have to be assisted at calving," David Patterson, professor of animal science and beef reproduction specialist for the University of Missouri Extension said. "And a high percentage of those assisted births are because either the calf is too big or the pelvic area is too small, or it's a combination of the two."
Asked if breed people recognize the importance of pelvic measurement, Patterson explained, "In some circles, yes, and in some circles no." But Patterson and his colleagues do recognize it, and it's an important part of their on-farm heifer development and management program.  
Many quality management programs offer reproductive evaluation of the heifers prior to their first breeding season. Heifers need to meet a minimum requirement of 150 sq. cm. of overall pelvic area. If they don't those heifers should be flagged and they need to be remeasured within a defined time period.
There are a number of reasons why heifers could be shy of that 150 sq. cm. standard. The animal may be too young for the upcoming breeding period, or could be late maturing.  
Patterson said, "Typically what will happen is at or around the time those heifers do reach puberty, there's a relatively large and rapid increase in pelvic growth. And so, part of the reproductive exam in conjunction with the pelvic exam is also an assessment of whether the heifers are cycling or not, defined as a reproductive track score."
The score is on a 1-5 scale, with 1 indicating that the animal is infantile, and 5 that it's ovulating; in many instances, a heifer with a pelvic areas less than 150 sq. cm. will have a track score of 3 or less, indicating she is not yet cycling. He said, "Those heifers, once they're remeasured, in most cases will be fine."
But there are a couple of other possibilities. One is inadequate nutrition; the program recommends heifers be measured six weeks before the breeding season begins, so that provides time for those animals to receive the proper supplements and catch up. But another is genetics.  
"Pelvic area or pelvic growth is a fairly highly heritable trait," said Patterson, "so it's not uncommon for us to find situations — and we have — where there'll be a number of half-sisters that are all sired from the same bull, and that particularly sire may be abnormally small or abnormally structured in terms of his pelvic dimensions, and as a result that transmits to his progeny."  
"There's a lot of people who don't believe in taking the measurements, but the fact of the matter is if it's included as part of a program where you're evaluating heifers at different time-points, it can really give you some useful information and be a good screening point."


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