Increased use of artificial insemination has increased attention to estrous cycles.  Cycles of 18 to 24 days are considered "normal".  Cycles of  7 to 12 days (short cycles) have been observed in both heifers and cows, but most have been in post-calving cows. 
            Researchers have reported that weaning calves within 24 hrs. after birth increased the proportion of cows with abnormal estrous cycles.  They reported 7 of 14 weaned cows had short cycles while only 2 of 14 lactating cows had short cycles.  Last year we noted that weaning post-calving, non-cycling cows increased the number with short cycles; 77.8% of the cows in estrus within 10 days after early weaning had short cycles (average 8 days). 
           Lack of understanding and interest in short cycles prompted Kansas State University animal scientists to see if they could determine if short cycles are increased by weaning calves from early postpartum non-cycling cows. Eighty-eight crossbred Simmental cows were checked for estrus three times daily from calving until the end of the experiment.  Thirty-three (19 to 68 days postpartum) that had not been detected in estrus and did not have a palpatable corpus luteum by May 10,  were selected for the experiment.  Twenty-five had their calves weaned May 10; the remaining 8 continued suckling their calves.  All cows were artificially inseminated about 12 to 18 hours after estrus was detected.  Weaning calves from cows that had not cycled after calving caused a higher percentage of cows to show heat in the next 25 days than cows suckling calves.  However, 78.3% of the nonsuckling cows had short cycles (7-10 days) compared with 16.6% of the cows suckling calves.  A short cycle does not appear to be clinically abnormal when heat occurs with the first ovulation after calving.  The percentage of cows having a heat with the first ovulation, and thus a short cycle, increases drastically when calves are weaned. 
          Although non-cycling cows can be induced to cycle by weaning their calves, the first estrus after weaning is relatively infertile.  Source: Ward, S. and co-workers. 1979 Cattleman's Day. Kansas State University, Manhattan.