Objective: Our objective was to determine the relative percentages of calves sired by either natural service sire or fixed time artificial insemination (FTAI) sire within the same estrous period.
Study Description: During two consecutive years, heifers and cows were synchronized and inseminated using the 7-day CO-Synch + CIDR FTAI protocol. All females were exposed to natural service bulls immediately following insemination. After calving, DNA was collected from a random subset of calves born in the first 21 days of the calving season for parentage analysis. Calves born from heifers totaled 59 in Year 1 and 82 in Year 2; calves born from cows totaled 89 in Year 1 and 102 in Year 2.
Results: In Year 1, among calves born from heifers, the percentage sired by natural service was 5.1% (n = 3/59). Among calves born from cows, the percentage sired by natural service was 14.6% (n = 13/89). In Year 2, among calves born from heifers, the percentage sired by natural service was 9.8% (n = 8/82). Among calves born from cows, the percentage sired by natural service was 20.6% (n = 21/102).
The Bottom Line: If commercial producers use FTAI followed by immediate bull exposure in beef females, it can be expected that natural service bulls may sire 5 to 20% of calves born early in the calving season while reducing time and labor associated with bull turnout.
The full research report is available. Hartman, A. R.; McCabe, E. D.; Jacobs, D. R.; Fike, K. E.; and Grieger, D. M. (2023) “Sire Distribution of Calves in a Beef Herd with Use of Fixed Time Artificial Insemination Followed by Immediate Bull Exposure for Natural Service in Cows and Heifers,” Kansas Agricultural Experiment Station Research Reports: Vol. 9: Iss. 1. https://doi.org/10.4148/2378-5977.8418