In Oklahoma, the selection of replacement heifers from yearling females on wheat pasture is a typical practice during the spring. Producers usually choose heifers based on their specific criteria and breeding objectives, ensuring that the heifers have achieved around 65% of their mature weight by 14-15 months of age. In a normal year, over 90% of these heifers would be fully pubertal and ready for breeding. However, recent years have brought abnormal precipitation and challenges with wheat pasture grazing, resulting in replacement heifers that may be lagging behind in target weights and body condition.
To address this issue and determine the readiness of heifers for breeding, a valuable management tool called Reproductive Tract Scoring (RTS) is available. RTS involves the rectal palpation of the heifer's reproductive tract, assessing the uterine horns and ovarian structures. A reproductive tract score ranging from 1 to 5 is assigned (1 = immature; 5 = presence of a corpus luteum) to aid producers in making decisions about replacement heifers. By estimating pubertal status, RTS can predict heifer reproductive performance, allowing heifers with poor breeding potential to be identified and removed from the breeding group before incurring further costs.
The RTS system has demonstrated repeatability between practitioners and within practitioners, showing moderate heritability. An RTS score of 1 indicates a prepubertal heifer, while scores of 2 or 3 represent peripubertal heifers in the transitional stage. Scores of 4 or 5 signify pubertal (cycling) heifers. Heifers with RTS scores of 1 or 2 exhibit lower reproductive performance compared to those with scores of 3 or higher. They are less likely to be cycling at the beginning of the breeding season, resulting in decreased pregnancy rates or delayed pregnancies. Considering this, heifers with RTS scores of 1 may be considered for removal from the breeding group. It's important to note that some heifers may not fit precisely into a specific RTS score, and the producer or practitioner must determine the most significant factors.
To use RTS as a culling tool and assess a heifer's ability to conceive early in the breeding season, it should be conducted about one month or less before breeding. Alternatively, if RTS is used as a selection tool to encourage early puberty, heifers should be evaluated when approximately 50% of them are expected to be cycling based on age, weight, and occasional observations of estrus.
Another application of the RTS system is to assess the effectiveness of the nutritional program implemented by the producer. By performing RTS within an appropriate timeframe before the breeding season (around 30 to 60 days), producers can adjust the ration based on the scores to help heifers meet developmental goals before breeding begins. Additionally, the start of the breeding season can be modified accordingly.
RTS serves as a valuable tool for evaluating the readiness of replacement heifers for breeding, allowing producers to make informed decisions, optimize reproductive performance, and adjust management strategies to ensure successful outcomes.