Reproductive Tract Scores
The reproductive tract scoring (RTS) system was developed to assist beef producers in the selection of herd replacements and to support the timing of estrous synchronization programs . The RTS 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.
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   . Recently, RTS has been found to correlate with artificial insemination pregnancy rate following fixed-time insemination .
An RTS of 1 (see Table 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 a 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.
Table 1. Reproductive tract scores .
|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|
Reproductive tract scoring is a repeatable (between and within veterinarians) and accurate (sensitivity = 82% and specificity = 69%) measure of pubertal status in heifers . Prebreeding evaluations that include assignment of reproductive tract scores and pelvic measurements 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 estrous 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 . This practice allows for better determination of the appropriate estrous synchronization protocol to use and at the same time provides critical information in situations where troubleshooting may be required. It has been reported that RTS were related to both the percentage of beef heifers that became pregnant during the breeding season and the time at which heifers became pregnant .
The reproductive tract scoring system is an effective management tool to avoid attempting to breed immature heifers.
Page derived from a longer work by David Patterson.
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