Evaluation of Reproudctive Soundnesss of Yearling Heifers
Reproductive Tract Scores
Table 1. Reproductive Tract Scores29
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Age at puberty can be determined fairly closely in a laboratory setting by measuring blood progesterone levels from samples
taken every 10 days (or more frequently). Of course, this method is not practical for production herds and another method
of determining onset of puberty was needed. The reproductive tract scoring (RTS) system was developed to subjectively classify
puberal status using size of the uterus and ovaries estimated by palpation per rectum.29 The system assigns a score to each heifer using a 5-point scale where a score of 1 is considered an immature tract and scores
of 4 and 5 are considered a cycling tract (Table 1).
A RTS of 1 is used to describe heifers with infantile reproductive tracts that are not near the time of puberty when palpated.
These heifers have small, flaccid tracts and small ovaries with no significant structures. Heifers may be assigned a RTS of
1 because: 1) they are simply too young to fit into the breeding season being planned, 2) they are too light to reach their
target weight and are not able to express their genetic potential for reaching puberty, 3) they were implanted with a growth-promotant
near the time of birth. Heifers assigned a RTS of 2 have slightly larger uterine diameter but tone is still lacking and the
ovaries have very small follicles. Heifers described as having a RTS of 3 have some uterine tone and larger uterine diameter
than heifers with more immature scores. These heifers are subjectively evaluated as being close to cycling (within 6 weeks).
Heifers assigned either a score of 4 or 5 are considered cycling as indicated by good uterine tone and size, and easily palpable
ovarian structures. RTS 4 is assigned to heifers that although they have large follicles present, do not have a palpable corpus
luteum (CL) either because they are in their puberal cycle or the CL is not detected by palpation. Heifers with a RTS of 5
are similar in uterine and ovarian size, tone, and structure when palpated per rectum as compared to RTS 4 heifers except
that a CL is identified.
The scores assigned with the RTS system are able to predict the reproductive performance of yearling heifers, especially for
pregnancy percentage following synchronized breeding and to pregnancy percentage at the end of the breeding season. Heifers
with more mature reproductive tracts had higher pregnancy percentages and calved earlier.
Heifers should be evaluated for reproductive tract score about six to eight weeks prior to the breeding season. If deficiencies
are found, management changes instituted this far ahead of the breeding season can result in an increased number of heifers
reaching puberty by the start of the breeding season. If the heifers are evaluated too far ahead of the breeding season (>
8 weeks), the heifers are likely to be young and to have lower tract scores than is a true reflection of their potential to
reach puberty before the breeding season.
A reasonable goal is to have at least 80% of replacement heifers cycling before the start of the breeding season. A group
is considered to be properly developed to reach this goal if at least 60% of the heifers are scored as a RTS 4 or 5 and most
of the remainder of the heifers are RTS 3 when evaluated six to eight weeks before breeding. Because progesterone or melengestrol
acetate (MGA) will induce puberty in some heifers that are near puberty, a lower percentage (50%) of heifers with RTS 4 or
5 when evaluated six to eight weeks prior to breeding is adequate to meet the 80% goal at breeding if using MGA® or CIDR®.
In order to reach the goal of at least 80% of heifers in a replacement pool cycling at the start of the breeding season, nutrition
must remain adequate for continued growth from the time of RTS evaluation until breeding.
If a low percentage of heifers are cycling at the time of RTS evaluation and many of the heifers are scored less than a 3,
management changes must be instituted immediately. These changes may include: 1) increasing the plane of nutrition so that
increased weight gain will allow the heifers to reach target weight by the start of the breeding season, 2) increasing the
plane of nutrition and delaying the start of the breeding season by several weeks, 3) holding the heifers over to bred six
months later to calve in the fall (for spring-calving herds), 4) marketing the heifers for feeder cattle and finding another
source of replacements.
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