DNA polymorphism of insulin-like growth factor-binding protein-3 gene and its association with birth weight and body weight in cattle.

Insulin-like growth factor-binding protein-3 (IGFBP-3) is a protein that binds the majority of insulin-like growth factors in circulation for regulation of its action on growth and metabolism of the animals. Animals belonging to Hariana, Holstein-Friesian (HF) and their crossbreds (HF x Hariana) were studied using polymerase chain reaction-restriction fragment length polymorphism and nucleotide sequencing of the IGFBP-3 gene. A 651-bp fragment of the IGFBP-3 gene spanning over a part of exon 2, complete intron 2, exon 3 and a part of intron 3 was amplified and digested with HaeIII restriction enzyme. Three patterns of restriction fragments were observed in HF and crossbred cattle revealing polymorphism in both the populations. The frequency of AA, AB and BB genotypes was 0.65, 0.32 and 0.03 in crossbreds and 0.29, 0.65 and 0.06 in HF respectively. The allelic frequency of the A and B allele was 0.81 and 0.19 in crossbreds and 0.62 and 0.38 in HF cattle respectively. Only one restriction pattern (AA genotype) was observed in all the animals of Hariana breed of Bos indicus showing the absence of polymorphism. Nucleotide sequencing revealed a C --> A mutation in the intron 2 region of the IGFBP-3 gene as the cause of the polymorphism. Least squares analysis revealed a significant effect (p < 0.05) of genotypes on birth weight and body weight (weight at 12, 18 and 24 months of age) of the animals. Animals of AB genotype showed higher birth weight and body weight than the animals possessing AA genotype.

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