B. G. Gasperin, G. F. Freling, R. Ferreira, J. F. C. de Oliveira, V. Bordignon, and P. B. D. Gonçalves, “Intravaginal progestagen for estrus and parturition control in sows”, PAB, vol. 46, no. 8, pp. 961–964, Oct. 2011.