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Sunday, April 10, 2011

Temperament and Pregnancy

By Scott B Laudert, Ph.D., beef cattle technical consultant.

Undesirable temperament in feedlot cattle has been reported to reduce slaughter and carcass weights by 40 lbs. and 17 lbs., respectively (BEEF, June 2010, “Research Roundup”).  Since temperament is a moderately heritable trait in cattle, one would rightfully conclude that excitable feedlot steers and heifers are the progeny of excitable
Sires and dams.  Now researchers from the University of Florida (UF) and Oregon State University (OSU) are studying the effect of temperament on reproductive function of beef cows and heifers.

Prior  to the start of cattle- breeding season at both universities, cows were classified by a final temperament score of 1 to 5 with 5 being extremely excitable and 1 being calm.  The final score was an average of observations recorded while the cows were restrained in a squeeze chute for a blood draw, exiting the squeeze chute and crossing a holding pen.  Cows scoring 4 or 5 were considered to have excitable temperaments.

UF cows were Brahman crossbreds and were exposed to bulls for a 90- day breeding season.  OSU cows were British crosses and were either exposed to bulls for a 50-day breeding season or estrus synchronized and timed-AI followed by 50 days of bull exposure.

Results at both locations suggested  that reproductive responses of cattle with excitable temperaments are similar.  Plasma cortisol concentration was elevated in cows with an excitable temperament.  An elevated level of this hormone is known to interfere with reproduction. 

Cows with excitable temperaments at both locations were less likely to become pregnant during the breeding.  Reduced pregnancy rate wasn’t overcome by a longer breeding season at the UF site.

Management strategies that improve temperament will benefit overall herd reproductive efficiency and productivity.  Aggressive culling of animals with excitable temperaments and selection of replacements with non-aggressive temperaments are advised.