Effect of IGF-I genotype on milk production and the metabolic endocrinology in the transition period in dairy cows in pastoral conditions

The present study investigated the effect of IGF-I AF017143 polymorphism on metabolic and endocrine profiles during the transition period and on milk production in dairy cows under grazing conditions. Blood samples were taken during a period of -20 to +40 days from calving from 32 dairy primiparous cows. Data was analyzed by a repeated measures analysis with a mixed model including IGF-I genotype, days regarding calving and interactions. Allelic frequencies were 0.56 for A and 0.44 for B. Cows with AA genotype produced more milk (P<0.05) than cows with AB or BB genotypes (20.3±0.7 vs 18.2±0.8 y 17.2±1.2 L/day), that did not differ. Protein and fat percentage in milk were not affected by genotype. Insulin, IGF-I, cholesterol, albumin and non-esterified fatty acids (NEFA) concentrations were not affected by genotype, but were affected by days related to calving as low as concentrations of these variables were found around calving, except for NEFA concentrations that decreased throughout the experiment. The genotype affected b-hydroxybutorate (BHB, P<0.01) and total plasmatic proteins (P=0.062) concentrations; AB cows had greater BHB and lower protein concentrations than AA and BB cows (0.88±0.11 vs. 0.57±0.09 and 0.46±0.07 mM; 71.7±0.8 vs. 73.8±1.0 and 74.6±0.9 g/L, respectively). This study shows that IGF-I AF017143 polymorphism may affect milk production and metabolism in primiparous cows under grazing conditions.