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

Abstract

Previous reports have shown that reproductive tract score (RTS) can predict reproduction outcomes in seasonally bred beef heifers, although the accuracy can vary.Some ultrasonographic measures of the female reproductive tract and pelvis area have also been associated with reproductive outcome in young heifers. The objectives of this study were to determine which transrectal ultrasound or pelvis measures taken at a single examination are independent predictors of reproductive failure, and if the RTS system can be optimised with this information. In this observational study 488 year-old beef heifers in 2 birth cohorts were followed from prior to first breeding until confirmation of pregnancy. A single pre-breeding examination included BCS, RTS, ultrasound measures 2 of the reproductive tract (length and diameter of the left and right ovaries, presence and diameter of a CL, largest follicle diameter and left uterus horn diameter) and transverse and vertical diameters of the pelvis. Additional farm records including dam parity, sire, birth weight and birth date, weaning weight, weaning date, pre-breeding BW, AI dates and semen used were available. Breeding consisted of 50 d of AI, followed 5 to 7 d later by a 42 d bull breeding period. Pregnancy failure was defined as the failure to become pregnant after the AI and bull breeding periods while anestrus was defined as the failure to be detected in estrus during the 50 d AI period. From the pre-breeding data and farm records independent predictors of pregnancy failure and anestrus were identified using step-wise reduction in multiple logistic regression models. Age at the onset of breeding was the only consistent independent predictor of pregnancy failure and anestrus in both cohorts of this study (P < 0.05). BCS, uterus horn diameter, absence of a CL, largest follicle of less than 13 mm and pelvis area (PA) were the pre-breeding examination variables that remained in prognostic models (P < 0.1). Combining either the model based on the three remaining ultrasound measures or RTS with PA provided more accurate prognostic models for pregnancy failure and anestrus than using RTS alone (P < 0.05). It is concluded that ultrasound measures have prognostic value for pregnancy failure in restricted bred yearling heifers as a result of their association with anestrus, and that smaller pelvis area has additional prognostic value for poor performing heifers.

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

“…Also, in terms of ovarian development, the results of the present study are in agreement with the findings by Holm et al (2016) who did observe that the ovary length variables were independently associated with reproductive outcomes in this study (pregnancy failure). These authors also point out that one of the possible explanations for not finding a difference between ovary size and pregnancy failure may be due to a measurement error in ovary length at the time of data collection, thus making this analysis difficult.…”

“…These physical conditions of the heifers could mean that they have already reached sexual maturity, and thus, the uterine development is complete, implying in an absence of interference of this variable on pregnancy rate. This fact was confirmed by Holm et al (2016) who, when evaluating genital development in heifers using ultrasonography, concluded that the development of the reproductive system is influenced both by age and live weight, and animals that have reached sexual maturity are not influenced anymore by the uterine diameter on conception or the pregnancy rate.…”

“…The diameters of the right and left horns were measured using ultrasonography, after the transverse cut at the bifurcation (Figure 1), when the two uterine horns could be observed separately, as described by Holm et al (2016). Three uterine horn measurements were taken from each individual, subsequently, based on the calculated mean, classified into scores from 1 to 3, as following: score 1: Ø <1.4cm; score 2: 1.4 ≤ Ø <1.7cm; score 3: Ø ≥ 1.7cm.…”

A comprehensive assessment of automatic logistic regression model selection methods

“…Logistic regression is an integral part of data analysis focused on exploring the strength and direction of associations between a dichotomous response variable and a set of potential predictors, and is widely used by researchers [1], [2], [3], [4], [5], [6]. In general, the goal of these research studies is to identify the set of true predictors that are incorporated in the final model which is used for classification, prediction or interpretation.…”

Application of longitudinal data analysis allows to detect differences in pre‐breeding growing curves of 24‐month calving Angus heifers under two pasture‐based systems with differential puberty onset

“…Indeed, it has been proposed that puberty should be reached 45 days before the breeding season. [11][12][13] This developmental reproductive milestone would be influenced by the productive system, female physiology and genetics, 9,14,15 but the main factor that can be handled is nutrition under rearing.…”