LAUSR

Accelerated skeletal maturity is prevalent in modern commercial heifers harvested under 30 months of age. It is hypothesized that selection for increased growth and earlier reproductive maturity over several decades, unintentionally co-selected for precocious skeletal ossification in heifers. This study examines the relationship of single nucleotide polymorphisms (SNPs) in beef heifers with developmental maturity (A-, B-, C- Maturity) assessed at harvest, and evaluates specific genotype and production implant potency interactions. Two SNPs within Estrogen Receptor 1 (ESR1) and one SNP within Alkaline Phosphatase (ALPL) genes that have been previously associated with carcass skeletal maturity were examined. USDA inspected beef heifer carcasses (< 30 months) that were A- (n = 318), B- (n = 296), or C- (n = 251) skeletal maturity were sampled. DNA was extracted and SNP genotypes were ascertained using custom designed allelic discrimination assays (Taqman® Custom SNP Assays). Dominant and basic association tests were performed, and the impact of implants were evaluated as co-variates against genotypes using a linear regression model in the SNP and Variation Suite (SVS) software (Golden Helix, Inc.). A significant association with skeletal maturity was detected with ESR1 SNP 1 (P < 0.05) and a trend observed with ALPL (P < 0.1), but there was no significance identified in ESR1 SNP 2. A highly significant interaction with genotype and incidence of skeletal maturity was identified for ESR1 SNP 1 (P < 0.01) and ALPL (P < 0.01) when estrogenic implant concentration was included. There exists a strong relationship for these genotypes and advanced skeletal maturity in commercial heifers which is influenced by estrogenic potency of the commercial implant used. This study confirms the association of previously identified genotypes with advanced skeletal maturity and provides evidence that genetic variations in ESR1 play an important role in the regulation of bone mineralization in heifers.