Association of polymorphisms in leptin and leptin receptor genes with circulating leptin concentrations, production and efficiency traits in sheep

• Novel polymorphisms were identified in the ovine leptin gene and its receptor.
• Circulating leptin concentrations vary at different reproductive stages in ewes.
• Polymorphisms in the ovine leptin gene were significantly associated with circulating leptin concentrations.
• Polymorphisms in the ovine leptin receptor gene were significantly associated with residual feed intake at defined times of gestation and lactation.

The relationships among nucleotide sequence polymorphisms in the genes for leptin (LEP) and leptin receptor (LEPR) and circulating concentrations of leptin and variables related to energy turnover were investigated in a Awassi-Merino crossbred sheep population. Blood sampled at several times during gestation and lactation was used for the assay of circulating leptin and for DNA extraction. Parts of the ovine LEP and LEPR genes were sequenced and, of a total of seven polymorphisms identified, two for each gene were used for genotyping. Feed intake and body weight were recorded for 199 ewes (age 2.9–9.4 years) daily and milk yield and composition were measured. The data were used for association studies between single nucleotide polymorphisms (SNPs), circulating leptin concentration and production traits. Both polymorphisms identified in the ovine LEP gene were associated with circulating leptin concentration (P < 0.05) and one SNP was associated with feed intake per unit milk production (P < 0.05). For the SNPs in the LEPR gene, there were significant effects for residual feed intake during lactation (P < 0.05) and for feed intake and residual feed intake at defined times during gestation (P < 0.05). We conclude that polymorphisms in the LEP and LEPR genes are associated with production and efficiency traits. The interaction between body condition, milk production, energy efficiency and leptin concentrations should be investigated in detail in future studies. Further studies are also needed to identify the specific roles played by LEP and LEPR in the regulation of circulating leptin concentrations and energy metabolism.