Sexual behaviour in female pigs Lene Juul Pedersen ⁎ Danish Institute of Agricultural Sciences, Department of Animal Health, Welfare and Nutrition, Research Centre Foulum, PO Box. 50, DK-8830 Tjele, Denmark Received 27 March 2007; revised 27 March 2007; accepted 28 March 2007 Available online 1 April 2007 Abstract This paper reviews the influence of social mechanisms on oestrus and sexual motivation in pigs. The social relations between the animals and the signals they send out can inhibit as well as encourage their social motivation. Social stimuli from both boars and other sows in oestrus tend to induce and synchronise oestrus and ovulation amongst sows. The courting behaviour of boars is also facilitated by social stimuli from other boars. However, when sows are kept under conditions where the social pressure is high, e.g. due to limited space and/or resources, the social stress experienced by particularly the subordinate individuals may inhibit sexual motivation during oestrus. To a large extent this effect seems to be mediated via specific fear reactions towards dominant individuals of sows that have lost many aggressive encounters. For example, fear reduces the sexual motivation during mating and during sexual interactions amongst sows within a group, and fear may thus inhibit their chances of reproductive success. Similarly, fear of humans caused by innate fearfulness or negative handling procedures reduces sexual motivation in the presence of the human handler even when sows are in standing oestrus. © 2007 Elsevier Inc. All rights reserved. Keywords: Sexual behaviour; Pigs; Sus Scrofa; Social stress; Fear Sexual behaviour in female pigs Free-living domestic pigs and wild boars form matriarchal family groups consisting of 1–4 sows with piglets depending on the supply of resources. Normally a well-established linear hierarchy dominated by the oldest sow is seen (Gundlach, 1968; Kaminski et al., 2005). When the males reach sexual maturity, they leave the group to form small groups of boars and later on they become solitary animals. Only in the mating season, which in wild boars is during the early winter months (Mauget, 1982), will the boars be in contact with the females (Gundlach, 1968). In contrast, domestic pigs have no marked seasonal variation in the occurrence of oestrus and, thus, often have more than one litter a year. When sows approach oestrus, a marked increase in social activities is seen both when the sows are kept under semi-natural conditions (Babu et al., 2004) and when housed in female groups under production conditions (Nath et al., 1983; Pedersen et al., 1993; Pedersen, 1998; Signoret, 1971). These include snout contacts between sows, ano-genital sniffing, flank nosing and female–female mounting. In the same period, the sows will approach the boar more and more often, and during oestrus they will spend much time in standing posture outside the boar pen (Babu et al., 2004; Nath et al., 1983; Pedersen, 1998; Signoret, 1971). Pedersen (1998) made 24 h sampling of the occurrence of all the social activity during the days around pro-oestrus and oestrus in three groups of sows, each of which consisted of 9 sows housed in large straw bedded pens (9 m × 6 m) and with access to one feeding stall per sow (voluntary cubicle). A gradual increase in mounting, nosing and standing close to the boar pen was seen from 2–3 days before standing oestrus (Fig. 1). For several days, some sows were observed to mount other sows more than 40 times per 24-h period. The sow performing the mounting was always in pro-oestrus or in oestrus. The activity was observed throughout the 24 h, thus the normal resting period at night was completely broken (Fig. 2). The function of these behavioural elements is presumably to attract the attention of the boar and to stimulate sexual activity in the male, as demonstrated in goats (Billings and Katz, 1999; Shearer and Katz, 2006). This part of the sexual behaviour is termed the appetitive part (also called the proceptive behaviour), and it differs from the consumatory part of the sexual behaviour that is characterised Hormones and Behavior 52 (2007) 64 – 69 www.elsevier.com/locate/yhbeh ⁎ Fax: +45 89991500. E-mail address: lene.juulpedersen@agrsci.dk. 0018-506X/$ – see front matter © 2007 Elsevier Inc. All rights reserved. doi:10.1016/j.yhbeh.2007.03.019