Viana, C. H. C., Silveira, P. R. S. da, Moretti, A. S., & Rodrigues, P. H. M. (1999). Relationships between the characteristics weaning-to-estrus interval, estrus duration and moment of ovulation by ultrasonography in sows. Brazilian Journal of Veterinary Research and Animal Science, 36(4), 212-218. https://doi.org/10.1590/S1413-95961999000400008