Evaluation of pre-breeding reproductive tract scoring as a predictor of long term reproductive performance in beef heifers

Abstract

In a 7-year longitudinal study 292 Bovelder beef cows in a restricted breeding system in South Africa were observed from 1-2 d before their first breeding season, when reproductive tract scoring (RTS, scored from 1 to 5) was performed, until weaning their 5 th calves. The objective was to determine whether pre-breeding RTS in heifers is a valid tool to predict long-term reproductive performance. Outcomes measured were failure to show oestrus during the first 24 days of the first 50-day AI season (24-day anoestrus), failure to become pregnant during each yearly artificial insemination (AI) season (reproductive failure), number of days from the start of each AI season to calving, and number of years to reproductive failure. The effect of RTS on each outcome was adjusted for year of birth, pre-breeding age, BW and body condition score (BCS), and for 24-day anoestrus, bull, gestation length, previous days to calving and previous cow efficiency index, the latter two in the case of the 2 nd to the 5 th calving season. During their first 1 RTS long-term usefulness and predictive value breeding season, heifers with RTS 1 and 2 combined were more likely to be in anoestrus for the first 24 days (OR = 3.0, 95% CI 1.5, 6.4, P = 0.003), and were also more likely to fail to become pregnant even after adjusting for 24-day anoestrus (OR = 2.1, 95% CI 1.1, 3.9, P = 0.025), compared to those with RTS 4 and 5 combined. Animals with RTS 1 and 2 combined were at increased risk of early reproductive failure compared to those with RTS 4 and 5 combined (HR = 1.4, 95% CI 1.0, 1.9, P = 0.045) although RTS was not associated with calving rate or days to calving after the second calving season. Low RTS at a threshold of 1 had consistent specificity of ≥94% for both 24-day anoestrus and pregnancy failure, however its predictive value was lower in the age cohort with a higher prevalence of anoestrus. We conclude that RTS is a valid management tool for culling decisions intended to improve long-term reproductive success in a seasonal breeding system, by excluding heifers that are likely to fail to become pregnant or likely to calve late during their first calving season.

Ultrasonographic reproductive tract measures and pelvis measures as predictors of pregnancy failure and anestrus in restricted bred beef heifers

“…The farming system, breed and location have been described previously [5,7,20,[23][24][25]. Farm data collected included the following: birth weight and birth date, parity of dam, sire, bull allocated and first to fourth AI day numbered from the mating start date (MSD).…”

“…For the purpose of regression models, BCS was categorised into 2 categories (<6 and ≥6) and RTS into 3 categories (1-2, 3 and 4-5) [30]. Diameter of the largest follicle was used either as a continuous variable or was dichotomized using various cut-offs (7,8,9, 12, 13 and 14 mm). Pelvis area (PA) was calculated as the product of the TD and VD, and rescaled values of PA (RPA) as well as uterus diameter (RUD) were calculated within birth cohort using the following formula:…”

“…Reproductive tract score (RTS) predicts anestrus and pregnancy failure in heifers independently of age, body weight (BW) and body condition score (BCS), and is a valid selection tool to enhance reproductive performance of herds [3][4][5][6][7]. However, estrus cycle stage and proportion of heifers in anestrus affect the accuracy of RTS, the complexity of the RTS system affects its repeatability, and other tests with potential to improve RTS are available [5,[7][8][9].…”

Ultrasonographic evaluation of the reproductive tract as predictors of pregnancy in Girolando heifers submitted to Timed Artificial Insemination

“…In another study, Holm et al (2015) analyzed data from a Bovelder herd (South African crossbred) composed of 12-15-month-old heifers. Although the age is different from the present study, the authors also concluded that an evaluation of the reproductive tract score is a valid management tool to improve reproductive efficiency over the long term, excluding heifers that probably would not breed or could be born late during their first breeding season, and therefore detrimental to the reproductive performance of the subsequent season.…”

Explanation and Elaboration Document for the STROBE‐Vet Statement: Strengthening the Reporting of Observational Studies in Epidemiology—Veterinary Extension

“…… Farm management and staff were blinded to RTS (reproductive tract scoring) data throughout the study.53 …”