Calving-ease Cows: Optimal or Extreme?
Selection for calving ease often results in decreased calf birth weights, but what are the consequences of selecting heifers based on easier calving and lighter birth weights?
DES MOINES, IOWA (June 23, 2021) — Seedstock breeders and commercial cattle producers often apply genetic selection for calving ease to reduce calving difficulty among first-calf heifers. Scrutiny may be applied to selection of replacement females and the sires to which they are mated. According to Gary Bennett, a recently retired U.S. Meat Animal Research Center (USMARC) scientist, direct or indirect selection of calving ease often results in decreased birth weight of calves. But what might be the consequences when heifer calves are selected on the basis of their genetic potentials for easier calving and lighter birth weight?
Bennett explained relevant USMARC research during the Advancements in Efficiency and Adaptability breakout session of the 2021 Beef Improvement Federation (BIF) Research Symposium & Convention hosted June 22-25 in Des Moines, Iowa. According to Bennett, studies involved lines of cattle selected for calving ease and control lines, with all followed through their fourth calving. Selection for similar yearling weight was applied to cattle from select and control lines. Bulls representing their respective lines were used on heifers, but the same bulls were used on both lines, as cows.
“The principal question addressed by this research is whether a genetic difference in calving ease, independent of growth to yearling age, had negative effects on cow productivity,” reported Bennett.
Sharing the results, Bennett said cows from the select lines representing calving ease exhibited lighter mature weights, smaller hip heights, and the potential for lower maintenance costs on a per cow basis. Select line cows tended to wean more calves and stay in the herd longer.
Select line females were assisted significantly fewer times at calving and, through their years in the herd, produced more pounds of weaned calf. Weaned calf weight per heifer starting the system was significantly greater for the select line due to greater survival rate among their first calves and greater calving success subsequently.
Noting the value of cull animals, Bennett reported that while mature weights were lighter in select lines, marketable cow weight was nearly identical to that of control line cows. Control lines did offer more marketable young cow weight, but select lines yielded more old cow weight.
“No important unfavorable effects of genetic differences in calving ease were identified in this experiment,” stated Bennett.”
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