IGF-I and its role in dairy animals: investigations on Holstein Friesian cows and Sarda sheep

The aim of this thesis was to investigate the roles of IGF-I in dairy animals, in order to improve their production considering the importance of the dairy sector. In study 1, 98 primiparous and 234 multiparous Holstein Friesian cows were chosen to measure plasma IGF-I concentration by ELISA and to determine how IGF-I changes during days 0-27 post-partum, based on their parity, calving to conception interval, number of insemination needed to conception and positive or negative pregnancy diagnosis. The mean of IGF-I concentration was higher in primiparous than in multiparous cows but no difference was found with their reproductive activity. Moreover, from the above animals 40 cows were selected to evaluate the expression of candidate immune genes, 1-8 days after calving and its connection with IGF-I concentration and health status. Despite the role that IGF-I has on reproduction and immunity system, any interesting connection was observed in this research. In study 2, 214 multiparous Sarda sheep were selected to detect polymorphisms within the 5’UTR sequence of the IGF-I gene and to investigate possible association with milk yield and reproduction traits. A SNP (G855C) and a nucleotide variation (G857A) in linkage disequilibrium were found and the animals that carried the G allele produced a significantly higher milk yield compared to the others. In addition, a visible effect, despite not statistically significant, of the G allele on the shortening of the lambing to conception interval was found. It would be interesting to conduct further analysis comprising a higher number of animals to confirm the real frequency and effect that the found SNP has to confirm the strength of the IGF-I as candidate gene in animal performances.