SEXUAL DIFFERENCES IN CNS EXCITABILITY AN D HABITUATION OF PIGS (SUS-SCROFA F-DOMESTICA)

Large-capacity facilities bring about stresses to which the animals re spond in keeping with their individual behavioral characteristics. In this context many authors draw attention to inadequate social behavior of pigs, to their aggressiveness, caudophagy and canibalism. Such beh avior results from stresses in some excitable individuals which were p referentially used for their commercial traits in hybridization progra ms. In the papers published until now individual characteristics of an imals were investigated by habituation tests. The results of observati ons of age differences in habituation indicated a possibility of predi cting individual behavioral characteristics at early age (Novacky, Lid ay, 1994). In the present paper individual CNS excitability and proces s of habituation of pigs are evaluated with respect to differences bet ween the males and females which are of the same importance as age dif ferences in practical farming conditions. In four 30-minute habituatio n tests locomotor activity and voice signs, which are characteristic a ctivities of habituation of orientation-exploratory behavior in a new environment, were investigated in 78 pigs (39 young boars and 39 gilts ) of the Landrace, Hampshire and Duroc breeds and different cross comb inations. The animals were individually tested in morning and afternoo n tests at the age of three (37 kg) and six (85 kg) months. The result s make it possible to describe: a) individual excitation level of CNS given by the values of indicator reactions; b) dynamics of habituation process with respect to sexual differences between the young boars an d gilts at the age of 3 and 6 months. Excitability level. Frequency of reactions in gilts prevailed (Fig. 2 - solid curves). It is to note t hat frequency of reactions in gilts was more expressive at the age of 6 months than at 3 months of age, and it was higher in the indicator o f locomotor activity than in voice (acoustic) signs. There was a signi ficant sexual difference in locomotor activity in the animals 6 months old. While 3-month boars and gilts had the same values, a large sexua l difference was observed in 6-month animals since the activity of you ng boars decreased in comparison with the gilts (P < 0.001) Habituatio n speed. Locomotor activity and voice sings were adopted more quickly by young boars than by gilts in morning tests. This difference was sig nificant in the indicator of voice signs in 6-month animals (Fig. 1). Dishabituation was observed in gilts, accompanied by an increasing tre nd of the frequency of reactions described by positive regression coef ficients while the young boars had their characteristic process of hab ituation. It was also found out that 3-month animals were more mobile and the frequency of their voice sings was higher than in the 6-month ones. The activity is in general decreasing with the growing weight. T he decrease is larger in the young boars than in the gilts and it is l ikely to be due to castration at early age. There are other sexual dif ferences in the dynamics of locomotor activity and voice signs. While the average habituation curves of locomotor activity have their peaks at the beginning of tests, habituation curves of voice signs have the peaks 6 to 8 minutes after the beginning of tests and the habituation process starts at that moment. The weakening of the frequency of voice signs in gilts is due to the fact that the 6-month gilts are more exc itable than the young boars of equal age in the period of maturation, therefore their habituation to an experimental chamber is slower. The frequency of voice signs was found to increase in the 6-month gilts (F ig. 2B). The increase is related to the need of acoustic communication with the males in the housing space. These are so called informative acoustic signals which are changing from low-pitch sounds to wailing a coustic signs as the excitation of animals is increasing. The trend of dishabituation of acoustic signs in the gilts is conditioned by their instinctive characteristics with regard to the innate need for the ca re of the young. The sows communicate with the young through acoustic communication, like e.g. in the wild boar (Sus scrofa), the ancestor o f pigs. The high frequency of voice signs in gilts in comparison with boars ensues from inborn characteristics of domesticated swine.