The Leptin R84Q Mutation Is Present in Charollais Sheep Increasing Fat Deposition of Carrier Crossbred Lambs

This study investigated the presence of Single Nucleotide Polymorphisms (SNPs) in exon 3 of the ovine Leptin gene (oLEP) in Mexican sheep and their potential phenotypic effects. For that purpose, PCR-SSCP analyses and sequencing of genomic DNA were performed for a set of experimental crossbred lambs. A G251A SNP was detected, which results in a R84Q change in the deduced protein sequence. The G251A mutation was then investigated through real time PCR allelic discrimination analyses. The results showed that the genotype frequencies (n=45) for wild type (WT), heterozygous and mutant homozygotes were 95.6, 4.4 and 0%, respectively. The presence of the G251A SNP in another set of F₁ lambs sired by Suffolk, Hampshire, Charollais, Texel and Dorper rams was determined. Among other phenotypes, average daily feed intake (FI56d) and average daily weight gain (ADG56d) on the first 56 d of a performance test were quantified. In addition, back fat thickness (BFT), kidney fat (KF) and percentage of carcass fat tissue (CFT) at slaughter (target BW of 40 and 42 kg for females and males, respectively) were assessed. Five out of 64 lambs were carriers; interestingly, all of them were sired by Charollais rams and represented 20.8 % (n=24) of that breed group. Even though no differences (P > 0.05) were observed between levels of sex or genotype for FI56d and KF, heterozygous males were located between the 85 to 95 percentiles for FI56d. The ADG56d was higher (P<0.01) for males (0.303 ± 0.01kg) than for females (0.253 kg ± 0.01), but no differences (P > 0.05) were found by genotype; although the data for heterozygous lambs were in the lower half of the percentiles. In females, BFT (4.66 ± 0.88 and 3.55 ± 0.24 mm) and CTF (32.0 ± 1.96 and 23.7 ± 2.35 %) were higher (P < 0.05) in carriers than in WT animals. Finally, 172 registered full blood Charollais from four different flocks in Mexico were genotyped for the G251A SNP.The frequency of carriers was only 1.2 %. We concluded that the R84Q mutation in exon 3 of the oLEP gene in Charollais is related to fat deposition in feeder lambs; however, its frequency is low.