| Stereotypies are repeated, relatively invariable sequence of movements, which have no obvious purpose and function, often occur in intense husbandry systems. Stereotypies are considered by many scientists as a chronic stress symptom and criteria for measurement of good or poor welfare. Previous studies suggest that stereotypy is a result of interaction between genetic predisposition and environmental effects. Up to the present, the many researches have been focused on the environmental conditions eliciting the Stereotypies of sows, but genetic factors have been rarely studied. The purpose of this study is to investigate the possible influence of genetic factors on the stereotypic behavior of sows .Opioid receptors are the members of G protein-coupled receptor superfamily, widely distributed in the center nervous system (CNS). The opioid receptors play an important role in maintaining threshold value of pain perception and stress-induced analgesia, mediating emotion state under normal and stressed conditions, and involving in reward behavior and self-stimulation behavior. Stereotypies as quantitative trait that are affected by both multiple genetic loci and non-genetic factors may be controlled by the possible presence of one or more major genes. In the present study, the mu and kappa opioid gene were chosen as the candidate genes that affect the stereotyped behavior in sows, through behavioral observed experiment and molecular marker techniques-single nucleotide polymorphism detected, and combined with quantitative genetics method to calculate and deduce the effect of opioid receptor genes mutation on stereotyped behaviors. The possibility of the mu and kappa opioid receptor gene as major gene affecting the stereotyped behavior in sows was discussed. The expression pattern of mu and kappa opioid receptor gene in different breeds was analyzed with half-quantitative RT-PCR and Nest PCR. The following are the results:1) Sows in farrowing crate conditions showed different types of stereotypic behaviors. Some Stereotypies, sitting, manipulating trough, bar-biting and vacuum chewing showed an increased tendency during observed periods.2) Different parities of sows had significant effect on performance of behavioral Stereotypies. The stereotypic behaviors of multiparous sows including sitting, manipulating trough, bar-biting and vacuum-chewing were significantly higher than that of parity 1.3) Different breeds had significant effect on performance of behavior. The stereotypic behaviors of Duroc including lying, manipulating trough, bar-biting and vacuum chewing were significantly lower than that of Yorkshire and Landrace, while other behaviors includingsitting and standing were significantly higher than that of Yorkshire and Landrace. Vacuum chewing of Yorkshire was significantly higher than that of Landrace. The results showed the predisposition of stereotypies possess genetic background.4) The frequencies of genotypes distribution in mu opioid receptor gene and kappa opioid receptor gene were found to be related with breeds. The 8 pairs of primers for mu opioid receptor gene were designed to analyze single nucleotide polymorphisms in 5' untranslate region, coden region and 3' untranslate region by PCR-SSCP. Five SNPs were identified in mu opioid receptor gene (GenBank: AF521309). The 3 pairs of primers for kappa opioid receptor gene were designed to analyze single nucleotide polymorphisms in partial coden region by PCR-SSCP. One SNP was identified in kappa opioid receptor gene (GenBank: AY130756). The results of population genetic analysis indicated that the frequencies of genotypes distribution among the breeds were significantly different (P< 0.01). Mu opioid receptor gene of the Duroc breed tended to be homozygous and conservative, while the Landrace showed small diversity, but the Yorkshire were more polymorohic. Kappa opioid receptor gene of the Duroc breed was more polymorohic, while Yorkshire showed small diversity.5) The opioid receptor genes polymorphisms we...
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