Association between leptin single nucleotide polymorphism and reproductive performance of lactating Holstein cows.

The objectives of the current study were to evaluate the associations among reproductive performance of Holstein cows, single nucleotide polymorphism (SNP) in the R4C locus of the Exon-2 region of the leptin gene and health disorders. Lactating dairy cows (n=814) had their DNA sequenced at the Exon-2 region of the leptin gene to determine the presence of SNP in the R4C locus. Cows had the stage of estrous cycle synchronized with two injections of PGF(2α) 14d apart, with or without a progesterone insert. After the second PGF(2α), cows were either inseminated on detected estrus and, if not inseminated within 13d, cows were submitted to a timed artificial insemination (AI) protocol 13d after the second PGF(2α). Blood was sampled at 35±3, 49±3, and 62±3d in milk (DIM) and cows with progesterone <1.0ng/mL in the first two samples were considered to be anovular, whereas those with at least one of the first two samples with progesterone ≥1.0ng/mL were considered to have initiated estrous cyclicity. Anovular cows with progesterone ≥1.0ng/mL at 62±3DIM were considered to have resumed estrous cyclicity. Pregnancy was diagnosed at 31 and 60d after first postpartum AI and at 42d after subsequent inseminations. Resulting genotypes were CC (34.6%), CT (48.2%), and TT (17.2%). Leptin genotype was associated (P=0.03) with increased prevalence of estrous cyclic cows at 49±3DIM, as TT cows were and tended to be less likely to be estrous cyclic than CC and CT cows, respectively. Other measures of reproductive performance in the first 305DIM were not associated with leptin genotype. Cows diagnosed with at least one postparturient disease were less likely to become pregnant after first (P<0.01) and second (P=0.02) AI and to be pregnant at 305DIM (P<0.01). Furthermore, cows diagnosed with a disease event had a 36% reduction (P<0.001) in the rate of pregnancy, which extended the median interval to pregnancy by 60d. Estrous cyclic cows had a 35% increased rate of pregnancy, which reduced the interval to pregnancy by 34d. Cows homozygous for the T allele were less likely to be cyclic early postpartum, but leptin genotype was not associated with other reproductive responses when cows were subjected to a controlled breeding program.