Reproductive Tract Scores

BACKGROUND. Heifers that calve early during their first calving season have higher lifetime production than those that calve late (Lesmeister et al., 1973; Perry and Cushman, 2013). Because most beef calves are weaned at a fixed time rather than on a weight-constant or age-constant basis, calves born late in the normal calving season are usually lighter than those born early. This tends to decrease the total lifetime productivity of their dams (Lesmeister et al., 1973). Furthermore, cows that calve late one year tend to calve late or fail to calve the subsequent year (Burris and Priode, 1958). Therefore, the age at which a heifer reaches puberty is highly correlated with the date at which conception occurs, and conception date during a heifer’s first breeding period is correlated with lifetime fertility and reproductive longevity.

REPRODUCTIVE TRACT SCORES. The reproductive tract scoring system (RTS, Table 1; Anderson et al., 1991) was developed to assist beef producers in the selection of herd replacements and to support the timing of estrous synchronization programs (Patterson et al., 2013a). The reproductive tract scoring system is used to estimate pubertal status. Scores are subjective estimates of sexual maturity, based on ovarian follicular development and palpable size of the uterus. An RTS of 1 is assigned to heifers with infantile tracts, as indicated by small, toneless uterine horns and small ovaries devoid of significant structures. Heifers scored with a RTS of 1 are likely the furthest from reaching puberty at the time of examination. Heifers assigned a RTS of 2 are thought to be closer to puberty than those scoring 1, primarily due to larger uterine horns and ovaries. Those heifers assigned an RTS of 3 are thought to be on the verge of estrous cyclicity based on uterine tone and the presence of palpable follicles. Heifers assigned a score of 4 are considered to be estrous cycling as indicated by uterine tone and size, coiling of the uterine horns, as well as the presence of a preovulatory size follicle. Heifers assigned a score of 4 do not have an easily distinguished corpus luteum. Heifers with an RTS of 5 are similar to those scoring 4, except for the presence of a palpable corpus luteum. Prebreeding examinations that include RTS furnish the opportunity to assess reproductive development, but further provide an appraisal of possible aberrant situations that may detract from a heifer’s subsequent reproductive potential (Patterson et al., 1999; Lamb, 2013; Patterson et al., 2013b).

Table 1. Reproductive tract scores (RTS; Anderson et al., 1991) RTS Reproductive status Uterine horns Ovarian length (mm) Ovarian height (mm) Ovarian width (mm) Ovarian structures 1 Prepubertal, infantile tract Immature, < 20 mm diameter, no tone 15 10 8 No palpable follicles 2 Prepubertal, > 30 days to puberty onset 20-25 mm diameter, no tone 18 12 10 8 mm follicles 3 Peripubertal, < 30 days to puberty onset 20-25 mm diameter, slight tone 22 15 10 8-10 mm follicles 4 Pubertal, follicular phase 30 mm diameter, good tone 30 16 12 10 mm follicles, CL possible 5 Pubertal, luteal phase > 30 mm diameter >32 20 15 CL present

Figure 1 represents a modified interpretation of the conceptual model for puberty onset in the heifer presented by Day and Anderson (1998). This model combines the associated endocrine and ovarian changes that occur as heifers approach puberty, in addition to the corresponding RTS that would be assigned at respective points in development. An RTS of 1 corresponds to the point at which the pattern of luteinizing hormone (LH) release is characterized by low-frequency, high amplitude pulses. This is due to the fact that the hypothalamic-pituitary axis is highly responsive to negative feedback from estradiol. Reproductive tract scores of 2 and 3 are associated with the pre- and peri-pubertal phase, at which time responsiveness to estradiol negative feedback begins to decrease, causing increases in LH pulse frequency, follicular growth, and estradiol secretion. The decline in estradiol negative feedback and increase in LH secretion result in significant increases in follicular growth, and elevated concentrations of estradiol sufficient to induce estrus and the preovulatory LH surge. Reproductive tract scores of 4 and 5 are assigned to heifers that have reached puberty, but differ in stage of the estrous cycle at the time of the prebreeding examination (follicular phase, RTS = 4; luteal phase, RTS = 5).

Figure 1. Endocrine and ovarian changes associated with puberty onset (adapted from Anderson et al., 1991; Day and Anderson, 1998; Patterson et al., 1999). 

TIMING AND RECOMMENDED USE. Reproductive tract scoring is a repeatable (between and within veterinarians) and accurate (sensitivity = 82% and specificity = 69%) measure of pubertal status in heifers (Rosenkrans and Hardin, 2003). Research has shown that RTS is a predictor of heifer fertility, compares well with other traits used as predictors of production outcomes, and is likely to be a good predictor of lifetime production of the cow (Pence and BreDahl, 1998; Pence et al., 2007; Holm et al., 2009). Recently, RTS has been found to correlate with AI pregnancy rate following fixed-time AI (Patterson and Thomas, 2019). Prebreeding evaluations that include assignment of reproductive tract scores and pelvic examinations should be performed four to six weeks prior to the scheduled start of the breeding season. This timing provides a check on the development status of heifers, and allows time to provide adjustments to nutritional programs when needed. Beef heifers in many cases are placed on estrous synchronization protocols to facilitate use of artificial insemination during the first breeding season. A standard measure of success of the postweaning to prebreeding period is when a minimum of 50% of the heifers in a given group are estrous cycling based on RTS. This benchmark indicates that heifers are adequately developed and ready to be placed on an estrus synchronization protocol and that acceptable pregnancy rates can be expected. At the time RTS are assigned, pelvic measurements should also be obtained and results of these two measures of development should be considered in total (Patterson and Bullock, 1995). This practice allows for better determination of the appropriate estrus synchronization protocol to use and at the same time provides critical information in situations where troubleshooting may be required. Pregnancy diagnoses should be performed within 90 d from the start of the breeding period, which then provides the opportunity to assess relationships between RTS and how scores relate to not only if heifers became pregnant, but more importantly when (Patterson et al.,2018; Patterson and Thomas, 2019). These conclusions are supported by studies reported by Hall (2005) and Gutierrez et al. (2014) which involved comparison of heifers that were inseminated on the basis of FTAI followed by a natural service clean-up period versus natural service only. Gutierrez et al. (2014) reported that RTS influenced both the number of beef heifers that became pregnant during the breeding season and the time at which heifers became pregnant. All heifers enrolled in the Missouri Show-Me-SelectTM Replacement Heifer Program are required to undergo prebreeding examinations that include RTS and pelvic exams (Patterson et al., 2018). These assessments have improved performance of heifers entering the herd and provide the opportunity to compare RTS with other important reproductive endpoints. The reproductive tract scoring system has yet to be utilized for the estimation of genetic merit in national cattle evaluations. While RTS can effectively be used to evaluate pubertal status in phenotypic selection to cull heifers that are delayed in achieving puberty, its greatest value would be inclusion into national cattle evaluations.

REFERENCES

Anderson, K. J., D. G. LeFever, J. S. Brinks, and K. G. Odde. 1991. The use of reproductive tract scoring in beef heifers. Agri-Practice 12:19–26.

Burris, M. J., and B. M. Priode. 1958. Effect of calving date on subsequent calving performance. J. Anim. Sci. 17:527–533.

Day, M. L., and L. H. Anderson. 1998. Current concepts on the control of puberty in cattle. J. Anim. Sci. 76:1–15.

Gutierrez, K., R. Kasimanickam, A.Tibary, J. M. Gay, J. P. Kastelic, J. B. Hall, and W. D. Whittier. 2014. Effect of reproductive tract scoring on reproductive efficiency in beef heifers bred by timed insemination and natural service versus only natural service. Theriogenology. 81(7):918-924.

Hall, J. B. 2005. Reproductive evaluation of heifers. Proc Applied Reproductive Strategies in Beef Cattle. p. 279-283.

Holm, D. E., P. N. Thompson, and P. C. Irons. 2009. The value of reproductive tract scoring as a predictor of fertility and production outcomes in beef heifers. J. Anim. Sci. 87:1934–1940.

Lamb, G. C. 2013. Criteria for selecting replacements at weaning, before breeding, and after breeding. Vet. Clin. North Am. Food Anim. Pract. 29:567–578.

Lesmeister, J. L., P. J. Burfening, and R. L. Blackwell. 1973. Date of first calving in beef cows and subsequent calf production. J. Anim. Sci. 36:1–6.

Patterson, D. J., and K. D. Bullock. 1995. Using prebreeding weight, reproductive tract score and pelvic area to evaluate prebreeding development of replacement beef heifers. Proc. Beef Improvement Federation Meeting. Sheridan, WY. pp. 174-177.

Patterson, D. J., D. S. Brown, W. J. Sexten, J. E. Decker, and S. E. Poock. 2013a. Management Strategies for Adding Value to Replacement Beef Heifers: A Working Model. Vet. Clin. North Am. Food Anim. Pract. 29:653–666.

Patterson, D. J., and J. M. Thomas. 2019. Control of estrus and ovulation in beef heifers and cows. Theriogenology. In press.

Patterson, D. J., J. M. Thomas, N. T. Martin, J. M. Nash, and M. F. Smith. 2013b. Control of Estrus and Ovulation in Beef Heifers. Vet. Clin. North Am. Food Anim. Pract. 29:591–617.

Patterson, D. J., S. L. Wood, and R. F. Randle. 1999. Procedures that support reproductive management of replacement beef heifers. In: Proc. Am. Soc. Anim. Sci.

Patterson, D. J., J. M. Thomas, J. W. C. Locke, E. R. Knickmeyer, R. C. Bonacker, and M. F. Smith. 2018. Control of estrus and ovulation in beef heifers. In: Proceedings, Applied Reproductive Strategies in Beef Cattle. August 29-30. Ruidoso, NM.

Pence, M., and R. BreDahl. 1998. Clinical use of reproductive tract scoring to predict pregnancy outcome. In: Proc. 31st Annu. Con. AABP. Am. Assoc. Bov. Pract., Spokane, WA. p. 259–260.

Pence, M., D. Ensley, R. Berghaus, J. Rossi, T. Wilson, and P. T. Cannon. 2007. Improving reproductive efficiency through the use of reproductive tract scoring in a group of beef replacement heifers. Bov. Pract. 41:35.

Perry, G. A., and R. Cushman. 2013. Effect of age at puberty/conception date on cow longevity. In: Veterinary Clinics of North America: Food Animal Practice. Vol. 29. Elsevier. p. 579–590.

Rosenkrans, K. S., and D. K. Hardin. 2003. Repeatability and accuracy of reproductive tract scoring to determine pubertal status in beef heifers. Theriogenology 59:1087–1092.