By Mark Z. Johnson
In a normal year in Oklahoma, sometime during the spring, replacement heifers would be selected from the yearling females coming off wheat pasture. Individual producers selection criteria and breeding objectives would determine which heifers were to be retained. It would be safe to assume most heifers coming off wheat pasture would have achieved a target weight of reaching 65% of their mature weight by 14-15 months of age and accordingly, over 90% would be fully pubertal and ready for their first breeding season. At worst (in a normal year), heifers would reach 55% of their mature weight and the majority of those heifers would be ready for breeding. However, the past year or two haven’t been “normal” with regard to precipitation and wheat pasture grazing. As a result producers may be evaluating a group of replacement heifers that are a little behind schedule with regard to target weights and body condition.
If this sounds familiar there is a management tool available that can be very helpful in determining if heifers are ready for breeding. Reproductive Tract Scoring (RTS) is the management tool. RTS is a subjective measurement which involves the rectal palpation of the heifer reproductive tract (uterine horns and ovarian structures) and the subsequent assignment of a reproductive tract score, ranging from 1 to 5 (1 = immature; 5 = presence of a corpus luteum), to assist the producer in making replacement heifer decisions. Since age at puberty is difficult to measure directly, RTS can estimate pubertal status, and if performed before the onset of the breeding season, can be a predictor of heifer reproductive performance allowing for heifers with a poor breeding potential to be removed from the breeding group before any further costs are incurred. The RTS system has been shown to be a repeatable measure between and within practitioners and to be moderately heritable.
A RTS of 1 is refers to a prepubertal heifer, a RTS of 2 or 3 is refers to a peripubertal heifer (transitional stage), and a RTS of 4 or 5 is refers to a pubertal (cycling) heifer. The reproductive performance of heifers with an RTS of 1 or 2 is less than that of heifers with an RTS of 3 or greater. Heifers with a RTS of 1 or 2 are less likely to be cycling at the beginning of the breeding season and therefore are less likely to become pregnant or if they do become pregnant, do so later in the breeding season suggesting that heifers with a RTS of 1 should possibly be eliminated from the breeding group. It is worth mentioning, that some heifers do not exactly fit a particular RTS score and it is up to the producer and/or practitioner to decide on which of the measures are to be given the most emphasis.
RTS should be done about 1 month or less prior to breeding if the score is to be used as a culling tool as an indicator of a heifer’s ability to conceive early during the first breeding season. If RTS is to be used as a selection tool to place pressure on age at puberty, the best time to evaluate the heifers is when approximately 50% of the heifers are thought to be cycling based on age, weight, and occasional observations for estrus.
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