| After birth, neonatal piglets are exposed to a challenging social and physical environment. Littermates share the same 'foraging' territory, i.e. the sow's udder. During the lactation period, piglets experience intense social (including aggressive) interactions with their littermates until they establish a reliable teat order on the mother's udder. We revealed that in the first two weeks after farrowing, when piglets appear randomly distributed on the udder, geometric constraints (suckling space limitations) are an important force, driving the piglets' distribution along the limited udder. An effect of geometric constraint results in the specific hump-shaped distribution, known as the mid-domain effect. In addition, our results show that prior to the establishment of teat order, piglets rely on group suckling cohesion, an order mechanism that refers to the maintenance of significantly similar inter-individual distances on the udder. Although group suckling cohesion is in effect, neonatal piglets still get involved in a direct struggle with their littermates. Despite the possible adaptive function of fighting due to competition for limited colostrum, stimulation of the mammary glands, and thermoregulation, a certain level of suckling orderliness is essential because it reduces exaggerated teat disputes and the risk of missing suckling, which consequently affects survival. Suckling cohesion occurs first, after which the teat order develops (piglets fix their positions at the udder). The mechanism underlying the choice that leads each piglet to the same suckling position is still not clarified. However, our observations indicate that the spatial configuration of the sow's udder, determined by two parallel rows of teats arranged in pairs, can hypothetically be proposed as an important cue for the suckling orientation of piglets. Early life experiences considerably influence the behavioural development and, hence, the expression of acquired behavioural patterns later in life. Our results confirmed this hypothesis. The post-weaning formation of new social structure and agonistic behaviours (aggression) exhibited by individuals are in accordance with their suckling position. Piglets that suckled on the middle part of the mother's udder showed an instable nature in social order formation and exhibited significantly more aggressive behaviour. In conclusion, our studies elucidate some important aspects of suckling behaviour in piglets, revealing complex littermate interactions. These findings provide novel insights into suckling behaviour and behavioural development during lactation. Inasmuch as effective management of litters demands a holistic and detailed knowledge of piglet suckling behaviour, this novel perspective on suckling behaviour increases our understanding of the suckling process. |
