| dc.description.abstract | The first study investigated American Aberdeen (AD) cattle's genetic structure and its genetic relationships with five American taurine beef breeds and the genetic population structure of a related admixed cattle herd for improved statistical modeling. The last two studies investigated the role of leptin (LEP) c.73C>T polymorphism, leptin diplotype (LEPD), and leptin hormone (LEPH) concentration on reproductive, growth, size, feeding, and carcass ultrasound traits in beef cows and heifers. High levels of polymorphism were observed in admixed, Red Angus, and Gelbvieh (GV) populations. The lowest level of polymorphism was found in AD followed by undetermined parentage. Pairwise fixation index displayed the largest genetic differentiation between AD and GV, Simmental, and Shorthorn breeds. Even though founder animals originated from the Angus breed, the AD breed exhibited unique genomic characteristics. Mixed animal models with or without pedigree that included the primary ancestral breed group (ABG) for admixed individuals developed from diversity analyses performed better than models without the ABG. With these improved models, novel relationships between LEP genotype and number of follicles and ovary size were identified. Similar relationships of the LEP genotype in multiple growth and weight traits that have been published before have been confirmed. However, reverse relationships were observed for feed efficiency. The LEPD showed associations for feed efficiency, weight traits, and body size traits. Novel relationships between LEPH categories (high vs. low) were reported on two feeding behavior traits, including number of meals per day and feed intake per meal. However, no relationship was observed between LEP genotype and plasma LEPH concentration in this population. Literature indicates the increased productivity of the T allele for growth and carcass attributes, so it was expected that the same increased productivity would be found for reproductive traits. Therefore, the T allele of LEP c.73C>T marker could be used as a valuable marker for selecting for improved growth, body size, and reproductive performance in commercial beef heifers. Also, circulatory LEPH before the breeding season may serve as a predictor for feeding behavior, body size, and reproductive traits. Even so, not all comparisons could be statistically proven; therefore, additional investigations may be warranted. | en_US |
