Sandy Johnson, extension beef specialist, Colby
Producers know the importance of reproductive performance to the bottom line. Those who use artificial insemination (my type of AI) want to maximize the number of AI-sired calves. This raises the question: what are reasonable expectations for AI and season-long pregnancy rates? While industry-wide data on fertility is limited, several pieces of information shed light on this question.
First, consider a hypothetical herd of 100 cows, 60% of which conceive in the first 21 days, leaving 40 cows to breed in the second cycle. If the conception rate remains the same for the second cycle, then 24 (40 x .6) additional cows would be bred, leaving 16 head. Using the same logic for the 3rd 21 days, 10 (16 x .6) cows would calve in the third cycle for a total of 94 of 100 bred in three cycles. These values are similar to the calving distributions reported by NDSU in their CHAPS database. The summary includes 88,000 cows from 2010 to 2017 and reports 60% and 87% calving by 21 and 42 days of the season, respectively. For yearling heifers, they report 42% calving early, 76% at 21 days, and 88% at 42 days. The overall pregnancy rate is reported at 93.7%.
Data from the Show-Me-Select Heifer program (personal communication Thiago Martins) provides information on season-long heifer pregnancy rates. The overall average from 2010 to 2024, spring and fall seasons, is 85.6% with a range of 77 to 89%. The length of the breeding season is generally 60 days, but is not part of the data set.
How do AI and natural service inseminations compare? A report from Australian dairies from 1973 and 1974 found the first service pregnancy rate to AI was 57.5 ± 9.2 % (n=13,942 inseminations) and 58 ± 13.1% (n=6,310) for natural service.
A review summarized results from fixed-time artificial insemination studies in beef cattle from 1995 to 2021 (Monterio et al., 2023). A total of 228 manuscripts and 272,688 timed inseminations were included, and a minimum of 100 animals per treatment were required for inclusion.
Figure 1 shows box and whisker plots, which illustrate the distribution of the data. Briefly, the shaded box represents 50% of the values, the line that divides the shaded box is the median (50% of values above this line and 50% below), and the “x” is the mean or average. The point at which the vertical lines end represents the upper and lower values, and the dots represent values considered to be outliers.
For Bos taurus cattle, average fixed-timed AI pregnancy rates were 55.1 % for heifers (nulliparous), 52.5% for first-calf heifers (primiparous), and 51.6% for mature cows (multiparous). Pregnancy rates in Bos indicus females with fixed-timed AI were 47% for heifers, 39.4% for first-calf heifers, and 50.9% for mature cows. Most of the inseminations were in Brazil, 56%, and largely Bos indicus breeding, followed by 36% in the US, representing a majority of Bos taurus genetics. Pregnancy per timed-AI increased 4.6% in Bos taurus females from the 2006-2010 period (52.9%) to the 2016-2021 period (55.1%). The increase during the same period was 6.6% in Bos indicus cattle.
Fixed-time AI pregnancy rates between 2010 to 2017 were compiled from the Show-Me-Select Heifer program. Heifers with infantile reproductive tracts were excluded. The most common protocol used was the 14-day CIDR+PG. Heifers considered pubertal by reproductive tract scoring four to six weeks before AI had an average fixed-time AI pregnancy rate to this protocol of 52% (11,674/22,625), and those classified as pre- or peripubertal were 46% (4,765/10,280) for an overall average of 50%.
How did your expectations align with the data presented? Are you above average or below average? There are numerous factors that influence fertility outcomes, from cow and bull factors to the ways people interact with the process along the way. For classical reviews on this topic, see these proceedings from Mike Smith and George Perry at the 2011 ARSBC. Planning for improvements in reproductive performance is a year-round process.
References
Bonacker, R., J. Thomas, J. Locke, E. Knickmeyer, J. Decker, S. Poock, and D. Patterson. 2023. The Missouri Show-Me-Select Replacement Heifer Program: II. Comparing pregnancy rates resulting from fixed-time artificial insemination based on reproductive tract score and estrous synchronization protocol. J. Anim. Sci. Suppl. S3. 96:89
Williamson, N.B., R.S. Morris, and G.A. Anderson. 1978. Pregnancy rates and non-return rates following artificial and natural breeding in dairy herds. Aust. Vet. Journal 54:111-114.
Monteiro, P.L.J., Consentini, C.E.C., Andrade, J.P.N., Beard, A.D., Garcia-Guerra, A., Sartori, R., and M.C. Wiltbank. 2023. Research on timed AI in beef cattle: Past, present and future, a 27-year perspective. Therio 211:161-171. doi: 10.1016/j.theriogenology.2023.07.037