In the commentary entitled ‘Fighting by Kittens and Piglets During Suckling: What Does it Mean?’ published in this journal (Vol. 119, Issue 5, 353–359), Hudson and Distel (2013) suggested that the aggressive behaviour (fighting) of piglets/kittens during suckling may be an epiphenomenon of developmental processes, anticipating the use of these behaviours in later functional contexts. The fact that there are normally more teats than young, with glands being of equal quality per se (reviewed by Hudson & Distel 2013), strongly supports the authors’ assertion that there is little reason for littermates to fight. Hence, this behaviour appears to lack adaptive value in the momentary functional context. However, here, possible adaptive explanations for fighting during suckling have been suggested, which are primarily based on extensive studies of domestic piglets. It is important to note that none of the discussed adaptive explanations can be simply generalised for all mammals. This is because of differences in the colostrum and mature milk composition (in some mammals, there is almost no difference between colostrum and mature milk), mechanisms of transferring immunoglobulin that supply passive immunity to
neonates (prenatal vs. post-natal transfer), strategies used to compete for teats (e.g. tenacious nipple attachment in many rodents) and litter size (uniparous vs. multiparous mammals).