This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. Highlights We estimated genetic parameters for male and female reproductive traits. Our focus was on genetic correlations with scrotal circumference at different ages. Age at first calving correlated strongly with earlier scrotal circumference measurements. In turn, adult scrotal circumference was poorly correlated with age at first calving. We conclude scrotal circumference should be recorded earlier in breeding programs.
Los toros de 15 meses resultan una alternativa efectiva para reducir los costos de cría. Conocer sus características reproductivas y su evolución a lo largo del tiempo permite hacer un uso racional de esta herramienta. Los objetivos de esta tesis fueron: a) describir el evento madurez sexual (MS); b) establecer un esquema diagnóstico que permita detectar de forma fácil y económica a los toros maduros sexualmente; c) estudiar la asociación entre marcadores genéticos y caracteres fenotípicos relacionados con la MS; d) evaluar el efecto del servicio en toros jóvenes. Se trabajó con toros Angus, a partir de los 10 meses de edad, pertenecientes a establecimientos de la provincia de Buenos Aires. Se evaluó la calidad seminal y se registró: peso (P), alzada y circunferencia escrotal (CE). Los animales que tuvieron una concentración espermática de 50 x106/ml con un 10% de motilidad, fueron clasificados como púberes. Para ser considerados maduros debían presentar al menos un 30 % de motilidad y un 70 % de espermatozoides morfológicamente normales. Se determinaron los genotipos para SNPs seleccionados en los genes PRM1, SERPINA7 e IGF1. Finalmente, se evaluó el efecto del servicio precoz sobre el crecimiento, desarrollo testicular y calidad seminal de un grupo de toros de 15 meses que fueron enviados a servicio, contrastándolo con un grupo de contemporáneos que permanecieron en recría, en un ambiente similar. Se concluye que en estas condiciones los toros alcanzan la MS alrededor de los 16,5 meses de edad, que el P y la CE son buenos predictores del momento de presentación de la MS y que el servicio precoz parece no afectar la aptitud reproductiva futura de los toros.
BACKGROUND Longitudinal data analysis contributes to detect differences in the growing curve by exploiting all the information involved in repeated measurements, allowing to distinguish changes over time within individuals, from differences in the baseline levels among groups. In this research, longitudinal and cross‐sectional analysis were compared to evaluate differences in growth in Angus heifers under two different grazing conditions, ad libitum (AG) and controlled (CG) to gain 0.5 kg day−1. RESULTS Longitudinal mixed models show differences in growing curve parameters between grazing conditions, that were not detected by cross‐sectional analysis. Differences (P < 0.05) in first derivative of growth curves (daily gain) until 289 days were observed between treatments, AG being higher than CG. Correspondingly, pubertal heifer proportion was also higher in AG at the end of rearing (AG, 0.94; CG, 0.67). CONCLUSION In longitudinal studies, the power to detect differences between groups increases by exploiting the whole information of repeated measures, modelling the relation between measurements performed on the same individual. Under a proper analysis, valid conclusion can be drawn with fewer animals in the trial, improving animal welfare and reducing investigation costs. © 2019 Society of Chemical Industry
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