Brazilian Journal of Veterinary Research and Animal Science; Vol. 43 Núm. 5 (2006); 581-587 Brazilian Journal of Veterinary Research and Animal Science; Vol. 43 No. 5 (2006); 581-587 Brazilian Journal of Veterinary Research and Animal Science; v. 43 n. 5 (2006); 581-587 Brazilian Journal of Veterinary Research and Animal Science; V. 43 N. 5 (2006); 581-587 Brazilian Journal of Veterinary Research and Animal Science Faculdade de Medicina Veterinária e Zootecnia da Universidade de São Paulo (FMVZ-USP) instacron:USP