Hötzel, M. J., Filho, L. C. P. M. and Costa, O. A. D. (2005) “Behaviour of pre-parturient sows housed in intensive outdoor or indoor systems”, Pesquisa Agropecuaria Brasileira, 40(2), pp. 169–174. doi: 10.1590/S1678-3921.pab2005.v40.6938.