Enhancing FTAI Outcomes in Beef Cows: Integrating Estrus Expression and Reproductive Tract Scoring

Despite high fertilization potential with a single insemination, average pregnancy rates following fixed-time artificial insemination (FTAI) in beef cattle remain around 50%. The discrepancy reflects biological variability influenced by estrus expression, uterine environment, and embryonic survival. Two practical tools, estrus detection and reproductive tract size and position scoring (SPS), have gained attention for their combined predictive value in improving fertility outcomes¹. 

Recent work in multiparous Nelore and Angus cows demonstrates that pregnancy success at day 30 post-FTAI is influenced by the interaction between estrus activity and reproductive tract anatomy, rather than either factor alone². 

Estrus Expression: A Biological Signal of Fertility 

Estrus expression at the time of AI is more than a behavioral marker—it reflects a favorable endocrine state dominated by elevated estradiol (E2). This hormonal peak enhances: 

• Preovulatory follicle maturation 

• Uterine receptivity 

• Sperm transport efficiency 

• Corpus luteum development and progesterone production 

Cows expressing estrus before FTAI consistently demonstrate improved pregnancy rates in both beef and dairy systems^1,2. 

In Nelore and Angus populations, estrus expression rates vary depending on synchronization protocol, but the association with improved fertility remains consistent when estrus is present. 

Reproductive Tract Size and Position Score (SPS) 

The SPS system classifies mature cycling cows using rectal palpation: 

• SPS1: Small, compact uterine horns resting within the pelvic cavity 

• SPS2: Moderate size, partially outside pelvic cavity 

• SPS3: Larger uterine horns positioned mostly outside the pelvic cavity 

In lactating dairy cows, smaller reproductive tract size has been associated with higher pregnancy per AI ^3,4. Similar patterns are now evident in beef populations. 

Anatomically, smaller and more compact uterine horns may enhance sperm transport efficiency and reduce the distance sperm must traverse to reach the oviduct—potentially improving fertilization success. 

The Critical Interaction: Estrus × SPS 

The most clinically relevant finding is that estrus expression and SPS interactively influence fertility outcomes. 

Day 30 pregnancy rates were greatest in cows that¹: 

• Expressed estrus prior to FTAI 

• Were classified as SPS1 

Cows with favorable anatomy (SPS1) but no estrus expression did not achieve comparable pregnancy rates. Likewise, estrus-active cows with larger reproductive tracts (SPS2/SPS3) showed reduced pregnancy rates compared to estrus-active SPS1 cows². 

This interaction suggests that: 

• Estrus reflects endocrine readiness 

• SPS reflects anatomical suitability 

• Optimal fertility requires both factors working synergistically 

Pregnancy Loss: Limited Association 

Pregnancy loss between early and later gestational checkpoints was not significantly influenced by estrus activity or SPS in these beef populations². 

In contrast, some dairy data have reported increased pregnancy loss in cows lacking estrus at FTAI, potentially due to altered steroid metabolism and luteal function under high metabolic demand⁴. However, in beef cows, the primary benefit of combining estrus detection and SPS appears to be enhanced pregnancy establishment rather than reduced embryonic loss. 

Clinical Application: Stratifying Breeding Decisions 

The practical takeaway is clear—FTAI should not be approached as a uniform strategy. Incorporating estrus detection patches and assigning SPS at breeding enables precision-based semen allocation. 

Suggested Field Framework: 

High Fertility Tier 

• SPS1 + Estrus active 

• Prioritize sexed semen or elite sires 

Moderate Fertility Tier 

• SPS1 + No estrus 

• SPS2 + Estrus active 

• Use conventional semen 

Lower Fertility Tier 

• SPS2/SPS3 + No estrus 

• Consider high-fertility bulls or reassess breeding strategy 

This stratified approach can improve overall pregnancy outcomes while maximizing return on genetic investment. 

Vet Pearls 

1. Add SPS to your FTAI checklist. 
Rectal palpation-based scoring is quick, low-cost, and clinically informative. 

2. Estrus patches are decision tools—not just compliance tools. 
Use estrus activity to guide semen allocation. 

3. Not all synchronized cows are equally fertile. 
Synchronization controls timing—not uterine anatomy or endocrine competence. 

4. Focus on multiparous cows. 
Variation in reproductive tract size becomes more evident with parity, making SPS particularly valuable. 

5. Improve precision, not just pregnancy rate. 
Better candidate selection reduces wasted semen doses and enhances herd genetic gain. 

Conclusion 

Pregnancy success following FTAI in beef cows is not determined by synchronization protocol alone. It is significantly influenced by the interaction between estrus expression and reproductive tract size and position. Cows that are both estrus active and possess small, compact uterine horns within the pelvic cavity demonstrate the highest likelihood of pregnancy establishment. Integrating estrus detection with reproductive tract scoring at the time of breeding enables veterinarians and producers to move toward precision reproductive management—optimizing fertility outcomes while strategically allocating genetic resources. 

References  

1. Speckhart SL, Oliveira Filho RV, Franco GA, Vasconcelos JL, Schrick FN, Edwards JL, Pohler KG. Influence of estrus activity and reproductive tract size and position scores on fertility in Bos indicus and Bos taurus suckled beef cows. Journal of Animal Science. 2022 Jun 1;100(6):skac141. https://academic.oup.com/jas/article-pdf/100/6/skac141/43917672/skac141.pdf  

2. Liles HL, Schneider LG, Pohler KG, Oliveira Filho RV, Neal Schrick F, Payton RR, Rhinehart JD, Thompson KW, McLean K, Edwards JL. Positive relationship of rectal temperature at fixed timed artificial insemination on pregnancy outcomes in beef cattle. Journal of Animal Science. 2022 Jul 1;100(7):skac100. https://pmc.ncbi.nlm.nih.gov/articles/PMC9246666/pdf/skac100.pdf  

3. Young CD, Schrick FN, Pohler KG, Saxton AM, Di Croce FA, Roper DA, Wilkerson JB, Edwards JL. A reproductive tract scoring system to manage fertility in lactating dairy cows. Journal of Dairy Science. 2017 Jul 1;100(7):5922-7. https://www.sciencedirect.com/science/article/pii/S0022030217303788  

4. Madureira AM, Poole RK, Burnett TA, Guida TG, Edwards JL, Schrick FN, Vasconcelos JL, Cerri RL, Pohler KG. Size and position of the reproductive tract impacts fertility outcomes and pregnancy losses in lactating dairy cows. Theriogenology. 2020 Dec 1;158:66-74. https://www.sciencedirect.com/science/article/am/pii/S0093691X20304623