Master of Science (MS)
Animal Science (Animal, Dairy, and Poultry Sciences)
The first objective of these two studies was to evaluate genetic trends for bulls that have comprised the LSU AgCenter Dean Lee performance bull test for the past 55 years. Data included birth weight (BW), initial weight, 112-day weight, average daily gain (ADG), adjusted yearling weight, and scrotal circumference (SC), on 7,488 yearling bulls of 34 breeds on 112d of test for the last 55 years. The top 4 represented bull breeds with greater than 500 animals (Angus, Charolais, Hereford, and Simmental) were included in this analysis. Analyses revealed that growth traits for all bulls regardless of breed demonstrated a linear increase across the years with BW and SC being the lone exceptions. Birth weight demonstrated a decrease over the years. Hereford and Simmental breeds displayed the greatest decrease in birth weight. For start weight and 112-day weight, Simmental and Angus exhibited the greatest increase in weight over the years. Adjusted yearling weight had the greatest increase in the Simmental breed. Simmental breed exhibited the greatest decrease for SC over the years. The second objective was to test the association of single nucleotide polymorphisms (SNPs) on three candidate genes calpastatin (CAST), somatotropin (GH1), and insulin-like growth factor 1 (IGF-1) with growth and performance traits in bulls participating in a forage based performance bull test. Of the 49 SNP genotyped, 20 were chosen for CAST, 9 for GH1, and 20 for IGF-1. These SNP were genotyped on 47 purebred Angus, Braford, and Brahman bulls against traits including average daily gain, birth weight, weaning weight, initial weight, final weight, hip height, backfat (BF), intramuscular fat %, ribeye area (REA), and scrotal circumference (SC). The mixed model procedure of SAS was utilized to evaluate associations of the 49 SNPs and measured traits. Insulin-like growth factor 1 markers (rs133980322, rs137651874, rs132665612, rs132951819, rs110959643, rs109022910, rs110266103, rs109199979 and rs109327701) were determined to be associated with growth and performance traits, including weaning weight, initial weight, final weight, average daily gain, backfat, intramuscular fat %, hip height and scrotal circumference. GH1 marker rs10927590 was significantly associated with weaning weight, initial weight, and final weight.
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Howard, Tabitha, "Evaluation of 54 years of Louisiana bull testing, and SNP affecting growth and performance of yearling bulls on a forage performance bull test" (2013). LSU Master's Theses. 2521.