L. Ramírez Iglesia, E. Soto Belloso, C. González Stagnaro, G. Soto Castillo, and E. Rivero Urdaneta, “Postpartum ovarian activity and anovulatory estrus in primiparous crossbred cows in the venezuelan tropics”, Rev. Cient. FCV-LUZ, vol. 6, no. 3, Jul. 2010.