Sheep of different temperament (calm or nervous) have different physiological (cortisol secretion) and behavioural responses (motor activity) following exposure to stressors such as novelty and isolation (the method for temperament assessment). The genetic basis of these individual differences is not understood, but include two possibilities: i) dopaminergic pathways – polymorphism of the dopamine receptor and catabolic enzymes are associated with mood characteristics and emotional reactivity; ii) enzymatic regulation of the activity of the hypothalamo-pituitary-adrenal axis (HPA) – polymorphisms have been associated with differences in cortisol response in goats. We therefore investigated the polymorphisms of three specific genes, one responsible for cortisol production (CYP17) and two associated with personality and behavioural traits, dopamine receptor 2 (DRD2) and monoamine oxidase A (MAOA). The degree of polymorphism in CYP17, DRD2 and MAOA was measured in sheep of nervous (n = 58) or calm (n = 59) temperament and also in sheep of unknown temperament (n = 57) using a real-time PCR genotyping method. A total of 5 polymorphisms (CYP17: SNP628 (A/G), DRD2: SNP483 (C/T) and SNP939 (T/C), MAOA: SNP189 (C/T) and SNP219 (C/T)) were identified. The frequencies of the CYP17 SNP628 (A/A: Nervous 31.0% vs Calm 10.2%, P < 0.01; G/G: Nervous 27.6% vs Calm 47.5%, P < 0.05) and DRD2 SNP939 (T/T: Nervous 25.9% vs Calm 59.3%, P < 0.01; T/C: Nervous 55.7% vs Calm 33.9%, P < 0.05; C/C: Nervous 19.0% vs Calm 6.8%, P < 0.05) genotypes differed between the two temperaments, but those for DRD2 SNP483 and the 2 MAOA SNP genotypes did not. The two putative genetic markers for temperament in sheep needed to be validated, but it sees likely that temperament is based on genetic differences at two levels – brain integration and HPA activation.
Key words: Merino sheep; temperament; HPA axis; CYP17; DRD2; MAOA; genotype