Distributions and associations of single nucleotide polymorphisms in the leptin gene of Bos taurus and Bos indicus cattle
In recent years, the use of genetic markers has become more and more prevalent in beef breeding programs. This research focused on four previously identified single nucleotide polymorphisms in a leptin gene on chromosome 4 of beef cows. The SNP were E2FB, T945M, UA1, and UA2. Beef cows used in this research were maintained at the Louisiana State University AgCenter Central Research Station. Cows consisted of purebred Bos tauras and Bos indicus cattle as well as crossbreds. The objectives were to estimate genotypic and allelic frequencies for each SNP and to determine the influence of cow breed type, cow age, and SNP genotypes on cow calving rate and date of calving in 2006, cow plasma leptin concentration, body condition score, and pregnancy status in September of 2006, and cow weight change from April to September in 2006. Over all cows, each of the genetic markers showed polymorphism. Allelic frequency for T in these SNP was greater than 0.10. Within cow breed groups the trend for lower or higher frequencies of homozygous genotypes tended to be consistent. Genotypes TT in E2FB, TT in T945M, CC in UA1, and TT in UA2 had lower frequencies. Brahman cows were missing both CT and TT genotypes in UA2 and the UA2‐TT genotype was not present in Braford, Romosinuano F1 and Brahman F1 breed groups. Neither of the genetic marker genotypes influenced variation in plasma leptin level (P > 0.05). Several genetic markers had effects associated with cow traits that were of interest to this research. UA1 genotypes tended (P=0.07) to have an effect on calving rate. UA2 genotypes were associated (P<0.05) with calving date as well as weight loss. Cow breed group influenced (P < 0.05) calving rate, Julian calving date, weight change, and palpation status. Six year and older cows had a larger plasma leptin level and two year old cows had lower body condition scores than other ages of cows. These results indicate that after adjusting for cow breed group and cow age, genetic markers UA1 and UA2 appear to be associated with several reproductive and weight change traits of beef cows.