Research Roundup Column
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 the 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 were similar, suggesting the reproductive responses of Bos taurus and Bos indicus 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 season. Reduced pregnancy rate wasn’t overcome by a longer breeding season at the UF site.
In a related study at UF, Brahman-crossbred replacement heifers were evaluated for the effects of acclimation to human handling on reproductive function. The acclimated heifers had reduced plasma cortisol concentrations and reached puberty earlier than non-acclimated heifers.
However, temperament score of the acclimated heifers wasn’t improved post acclimation. This lack of improvement in temperament may have prevented any long-term improvement in the reproductive status of heifers with excitable temperaments.
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 nonaggressive temperaments are advised.
Importance of BCS in cows
Cows maintained at body condition score (BCS) 6 during the last third of gestation had fewer calving losses, more calves weaned, greater pregnancy rate and higher economic return than cows maintained at BCS 4.
In a two-year study, Oregon State University researchers demonstrated the consequences of not maintaining good body condition in cows at the beginning of calving. Two groups of cows were wintered on separate pastures and nutritionally managed to attain a BCS of either 4 or 6. Both groups were fed meadow hay and the BCS 6 cows were supplemented with alfalfa to reach the desired BCS at the beginning of calving.
Following calving, all cows were commingled in pastures and managed as a single herd. Cows were exposed to bulls for a 60-day breeding season. Calves were weaned at approximately 140 days of age and steer calves were finished in a commercial feedlot.
The BCS 6 cows were 136 and 66 lbs. heavier at calving and weaning, respectively, than the BCS 4 cows. Birth weight and weaning weight were greater for calves from BCS 6 dams. In addition, BCS 6 cows weaned 11% more calves and had a higher fall pregnancy rate, 91 vs. 79%.
Feedlot performance and carcass traits of steer calves weren’t affected by dam BCS. Net annual return favored cows maintained at BCS 6 due to more calves weaned and a higher pregnancy rate.
Scott B. Laudert, Ph.D., is a beef cattle technical consultant and former Kansas State University Extension livestock specialist based in Woodland Park, CO. Reach him at 719-660-4473.