Conclusions
For the intron 5 polymorphism, no significant associations between the genotypes and growth traits were found. However, moderate associations of genotypes with weight at day 56 (P = 0.08) and IGF-I concentration at day 56 (P = 0.09) were observed. Animals with genotype AB had higher weight at day 56 and higher IGF-I concentration at day 56. For the exon 6 polymorphism, significant associations were found between the HinfI genotypes and birth weight (P = 0.03) and preweaning gain (P = 0.01). Therefore, this Pit-1 polymorphism appears to affect preweaning growth traits in Angus beef cattle and may be a candidate for use in MAS. Finally, the newly identified MspI polymorphism was related to day 56 IGF-I concentration in the high IGF-I selection line. Genotype EE was associated with higher day 56 IGF-I concentration and also had a higher frequency. For most of the growth traits, EE animals also tended to have higher performance than animals with the other two genotypes based on the 80 cattle that were typed. A larger sample is needed to verify these discoveries.
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