ORIGINAL ARTICLE Evaluation of Obturator Foramen Suggests No Differences Between Sexes in Young Bovines P. M. Pare ´ s-Casanova* Address of author: Department of Animal Production, University of Lleida, Av. Alcalde Rovira Roure, 191, E-25198, Lleida, Catalunya, Spain *Correspondence: Tel.: +34 973 70 64 60; Fax: + 973 70 28 74; e-mail: peremiquelp@prodan.udl.cat With 3 figures and 3 tables Received January 2012; accepted for publication June 2012 doi: 10.1111/j.1439-0264.2012.01175.x Summary Among the numerous bovine pelvic traits displaying sex differences, no detailed studies of bovine obturator foramen are available in the veterinary lit- erature. The purpose of this work was to study quantitatively this structure using lineal biometrics, shape indexes and Fourier analysis. The material con- sisted of 60 hemicoxae belonging to young bovines of approximately 1 year of age. Although significant differences were found in area, perimeter and length of obturator foramen, none of the analyses used were able to differentiate between sexes and thus cannot be used as a natural trait for determining sex, at least in young bovines. Introduction Sexual size dimorphism has been studied intensively in mammals (Schutz et al., 2009). Generally, males are larger than females (‘male-dominant’), although a small number of ‘female dominant’ cases also exist (Ralls, 1977; Leute- negger, 1978; Abouheif and Fairbairn, 1997; Weckerly, 1998; Loison et al., 1999). Rensch (1960) observed that in male-dominated species, the magnitude of sexual size dimorphism is greater in larger versus smaller species. This allometric pattern by which sexual dimorphism is greater among larger species if males are the larger sex has become known as Rensch’s rule (Fairbairn and Prezi- osi, 1994). Studies of Rensh’s rule are common in both mammals and the broader animal literature, and exam- ples of Rensch’s rule include primates, pinnipeds and art- iodactyls (Sutter et al., 2008). Primarily, studies to measure size are based on univari- ate proxies such as skull length, or directly as body length or body mass. Although these descriptors of size are use- ful when discussing overall body size dimorphism, they do not represent shape and therefore do not fully describe differences between males and females, nor do they typi- cally address sexual differences occurring in specific body regions (Schutz et al., 2009). The anatomical morphology of bone is used as an important tool for archaeologists to identify animal spe- cies, as well as to distinguish human from animals (Saj- jarengpong et al., 2003). Several specific bones can be also used for determining the sex of animals, one being the pelvic bones (Sajjarengpong et al., 2003; Bierry et al., 2010). The pelvis is considered to be a part of the skele- ton, which presents a large sexual dimorphism (De Pana- fieu, 2011). Many parts of the human pelvic bones have been studied, such as the great sciatic notch (Jovanovic and Zivanovic, 1965; Jovanovic et al., 1973; Singh and Potturi, 1978; Hager, 1996), the cranial border (Gomez and Ferna ˜ndez, 1992), the obturator foramen (Bierry et al., 2010) and the entire bone (Milne, 1990). Pelvic studies have been also carried out in non-human anthro- poids (Gingerich, 1972; Hager, 1996) and also in species such as the dog (Sajjarengpong et al., 2003), grey foxes (Schutz et al., 2009), the northern water vole (Ventura et al., 1991), the mouse (Uesugi et al., 1992a,b, 1993), whales (Bejder and Hall, 2002) and the bat (Nwoha, 2000), but no detailed studies of bovine obturator fora- men are available in the veterinary literature. The obturator foramen (foramen obturatum) is a large opening in the pelvis, between the ischium and the pubis, that gives passage to vessels and nerves and is partly closed by a fibrous obturator membrane. This large fora- men lies below, and slightly cranial to, the acetabulum, between the pubis and ischium. It is bordered by: (1) the caudal border of the pubis (cranial margin), (2) the © 2012 Blackwell Verlag GmbH Anat. Histol. Embryol. 1 Anatomia, Histologia, Embryologia