Association of single nucleotide polymorphisms in the leptin gene with body weight and backfat growth curve parameters for beef cattle

¹ Department of Agricultural Economics, Oklahoma State University, Stillwater 74078

^* To whom correspondence should be addressed. E-mail: jayson.lusk{at}okstate.edu.

	Abstract

Previous research has identified differences in carcass characteristics across SNP in the bovine leptin gene at slaughter, but before feedlot operators implement selection and sorting strategies, more information is needed to determine how carcass characteristics change over time. The objective of this study was to investigate the effect of two leptin SNP on growth curve parameters for body weight and backfat. Two SNP (UASMS2 and R25C) were genotyped on 1,653 crossbred steers and heifers in a commercial feedlot. Up to four serial measures of live weight and ultrasound estimates of backfat thickness were taken for each animal from the time of placement on feed to slaughter. The measures were used to estimate growth models that describe changes in weight and backfat thickness as a function of days on feed. Data analysis was carried out by estimating non-linear mixed models to determine the individual and joint effect of each SNP on growth curve parameters. Brody growth curves were fit to the weight data. Variations in the R25C SNP did not significantly affect growth parameters, either individually or in combination with the UASMS2 SNP. Variations in the UASMS2 SNP were significant in Brody growth curve parameters for weight growth (P < 0.001). The genotype UASMS2-CC was the heaviest at the beginning of the feeding period and exhibited the largest asymptotic mature weight, but UASMS2-TT cattle exhibited the fastest rate of weight growth. A modified power function was fit to the serial ultrasound backfat measures. Models that included the combined effect of the R25C and UASMS2 SNP provided the best fit to the data. Genotypes differed significantly in power function parameters for backfat growth (P < 0.001). The R25C-CC/UASMS2-TT cattle had the smallest backfat thickness at placement. The genotype R25C-CC/UASMS2-TT exhibited the fastest backfat growth rate, while backfat in R25C-CC/UASMS2-CC cattle grew at the slowest rate. The association between leptin genotype and growth in weight and backfat present opportunities to identify genetically distinct animals and differentially optimize feeding times accordingly.

Key Words: backfat, beef cattle, growth curves, leptin gene, single nucleotide polymorphisms