Context: There are contradictory results concerning the relationship between antral follicle count (AFC) and reproductive traits for different breeds of cattle. Understanding this relationship could be useful to selecting animals for breeding. Aims: We evaluated the effects of AFC on parameters related to in vitro embryo production (IVP), and the influence of AFC on sexual precocity and conception rate at first fixed timed artificial insemination (FTAI) of Senepol females. Methods: Ovarian ultrasound was performed to count antral follicles, and females were classified as low AFC (≤22 follicles), intermediate AFC (23–36 follicles) or high AFC (>36 follicles). Expt 1 evaluated the influence of AFC on IVP, with data from 146 adult cows that were submitted to follicular aspiration. Expt 2 evaluated the influence of AFC on heifer sexual precocity, determined by the presence of a corpus luteum (n = 608), and on conception rate at first FTAI (n = 143). Key results: High AFC cows had a greater (P < 0.0001) number of viable oocytes and cleaved embryos and a higher average number of embryos than low AFC cows (38.28 vs 9.92, 38.28 vs 7.75 and 9.34 vs 2.41, respectively). However, the conversion rate (total viable embryos per oocytes) was not affected (P = 0.46) by AFC category. High AFC heifers tended (P = 0.07) to be more sexually precocious than low AFC heifers (16.73% vs 9.47%). An influence of AFC or of AFC category on conception rate at first FTAI was not detected (P = 0.35 and 0.19, respectively). Conclusions: Despite greater IVP in high AFC cows, the conversion rate of viable oocytes to IVP was not affected by AFC category. High AFC heifers tended to be more sexually precocious, although AFC did not influence the conception rate at first FTAI. Implications: Oocyte quality is probably not influenced by AFC, but selection of animals according to AFC may improve the sexual precocity of the herd.

Growth and carcass traits are essential selection criteria for beef cattle breeding programs. However, it is necessary to combine these measurements with body composition traits to meet the demand of the consumer market. This study aimed to estimate the genetic parameters for visual scores, growth (pre and post-weaning weights), and carcass (rib eye area (REA), back and rump fat thickness) traits in Nellore cattle using Bayesian inference. Data from 12,060 animals belonging to the HoRa Hofig Ramos herd were used. Morphological traits were evaluated by the MERCOS methodology. The heritability estimates obtained ranged from low to high magnitude, from 0.15 to 0.28 for visual scores, 0.13 to 0.44 for growth, and from 0.42 to 0.46 for carcass traits. Genetic correlations between visual scores and growth traits were generally of moderate to high magnitudes, however, visual scores showed low correlations with carcass traits, except between sacral bone and structure and REA. Selection for visual score traits can lead to favorable responses in body weight and vice versa, but the same is not true for carcass traits. Morphological categorical traits can be used as complementary tools that add value to selection.

This study aimed to estimate the variance components, heritabilities and genetic correlations between four new different categories of stayability (STAY48‐2, STAY48‐3, STAY54‐2, STAY54‐3) with weight at 240 days of age (W240), weight at 450 days of age (W450), scrotal circumference at 365 days of age (SC365), age at puberty in males (APM), traditional stayability (STAY72), probability of precocious calving at 30 months of age (PPC30), ribeye area (REA), rump fat thickness (RFT), residual feed intake (RFI), dry‐matter intake (DMI), residual live weight gain (RG) and frame score (FRAME). Records from 80,958 females born between 2000 and 2019, exposed to mating starting at 10 months of age, raised on pasture from 508 farms in the central‐west, southeast, northeast and northern regions of Brazil that participate in the National Association of Breeders and Researchers (ANCP), were analysed. The (co)variance components were estimated by Bayesian inference in a two‐trait animal model. The posterior means of heritability estimates for STAY48‐2, STAY48‐3, STAY54‐2 and STAY54‐3 were moderate to low, 0.20, 0.20, 0.22 and 0.22 respectively. The traits related to different categories of stayability showed low genetic correlations with male reproductive traits (−0.22 to 0.19), feed efficiency (−0.03 to 0.13), carcass (0.11 to 0.18) and body composition (−0.09 to −0.6), moderate with growth (0.04 to 0.29) and high with sexual precocity (0.88 to 0.93) and fertility (0.65 to 0.73). The heritability estimates of the different categories of stayability indicate genetic improvement for longevity in early challenged females. The genetic correlations with sexual precocity showed that its use as selection criteria is recommended for production systems of younger females challenged in the reproductive season rather than traditional stayability to increase the probability of stayability in the herd.

Studies on reproductive tract score (RTS) and antral follicle count (AFC) in Senepol cattle are limited. These traits are essential as they are linked to the reproductive ability and reproductive performance of animals. Understanding the heritability and genetic correlation of these traits is crucial for guiding selection programs and selecting animals with greater reproductive efficiency and higher production potential. Therefore, this study aimed to estimate the genetic parameters of weight, RTS, and AFC in Senepol cattle using transrectal ultrasonography. Reproductive data were collected from 850 female Senepol cattle aged 10-16 months. At the time of evaluation, the following were measured: RTS traits (scores from 1 to 5), AFC (0 to 100), and female weight (kg). Variance and covariance components, genetic heritability, and correlations were estimated by univariate and bivariate analyses using the bull model. Heritability estimates were moderate for AFC (0.52) and weight (0.46), and low for RTS (0.12). The genetic correlation between RTS and AFC was almost zero (-0.05). The estimated genetic correlation between weight and AFC was -0.41, while the correlation between weight and RTS was 0.48. Selective breeding of AFC and RTS can enhance the reproductive efficiency of the herd and result in animals with earlier pubertal age and increased fertility. Estudos sobre o escore do trato reprodutivo (ETR) e a população folicular em bovinos da raça Senepol são limitados. Essas características são essenciais, pois estão ligadas à capacidade reprodutiva e ao desempenho reprodutivo dos animais. Compreender a herdabilidade e a correlação genética dessas características é crucial para orientar os programas de seleção, permitindo a escolha de animais com maior eficiência reprodutiva e potencial de produção. Portanto, este estudo teve como objetivo estimar os parâmetros genéticos para características de peso, ETR e CFA usando ultrassonografia transretal em bovinos da raça Senepol. Dados reprodutivos foram coletados de 850 fêmeas Senepol com idades entre 10 e 16 meses. As características de ETR (pontuações de 1 a 5), CFA (0 a 100) e o peso das fêmeas (em kg) no momento da avaliação foram analisados. Componentes de variância e covariância, juntamente com herdabilidade genética e correlações, foram estimados por meio de análises univariadas e bivariadas usando o modelo de touro. As estimativas de herdabilidade foram moderadas para CFA (0,52) e peso (0,46) e baixas para ETR (0,12). A correlação genética entre ETR e CFA foi próximo de zero (-0,05). A correlação genética estimada entre peso e contagem de folículos foi de -0,41, enquanto a correlação entre peso e RTS foi de 0,48. A seleção genética para CFA e ETR pode aprimorar a eficiência reprodutiva do rebanho, resultando em animais com idades puberais mais precoces e maior fertilidade.