Silva, Antônio Emidio Dias Feliciano, et al. “Seasonal Sexual Activity of Nellore Breed Bulls and Their Crosses With Fleckvieh and Chianina: Spermatic Characteristics”. Pesquisa Agropecuaria Brasileira, vol. 26, no. 10, Oct. 1991, pp. 1751-60, doi:10.1590/S1678-3921.pab1991.v26.3522.