Association of insulin-like growth factor I gene polymorphisms (IGF1/TasI and IGF1/SnaBI) with the growth and subsequent milk yield of Polish Holstein-Friesian heifers

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The aim of this study was to estimate potential relationships between insulin-like growth factor I gene polymorphisms (IGF1/TasI and IGF1/SnaBI) and the growth parameters of calves as well as their subsequent milk performance. The study involved a total of 191 Polish Holstein-Friesian var. Black-and-White calves. Both polymorphic sites were determined with Amplification Created Restriction Sites-Polymerase Chain Reaction (ACRS-PCR). In the case of the IGF1/SnaBI polymorphism, the genotype and allele frequencies were as follows: TT – 0.27, CT – 0.55, CC – 0.18, T – 0.54, and C – 0.46. The CC genotype was favourable and associated with higher body weight at the 2<sup>nd</sup> month of age of calves (WT60) and their daily body weight gains from the 1<sup>st</sup> to the 2<sup>nd</sup> month (P ≤ 0.05) as well as subsequent milk, fat, and protein yield (P ≤ 0.01). For the IGF1/TasI polymorphism, the highest frequency of the AA genotype (0.69) was found. Allele frequencies were 0.75 and 0.25 for the A and C alleles, respectively. In the association study, the AC genotype was significantly associated with higher WT60 and average daily gains in the periods from the 2<sup>nd</sup> to the 3<sup>rd</sup> month of age and for the whole rearing period (P ≤ 0.05) as well as subsequent milk, fat, and protein yield (P ≤ 0.01). Combined genotypes were also included into the analysis. The highest yields of milk as well as fat and protein were found in cows with the CC/AA combination. No clear relationships between body weight and genotype combination were found.