Comparative study on Insulin-Like Growth Factor I (IGF-I) plasma concentrations in new-born horse foals, donkey foals and calves

During the postnatal period, the most important growth regulator is represented by the insulin-like growth factor-I (IGF-I). Horses, donkeys, and cattle are monotocous species with considerable gestational lengths. The birth of a live, viable new born at the end of a healthy pregnancy, and the survival of the single newborn, represent essential prerequisites for a successful reproductive success. Therefore, the full knowledge about neonatal biology of these species is mandatory. The aim of this study was to investigate the IGF-I plasma profiles in the neonates of these three species during the first 14 days of life. Six horse foals, 6 donkey foals and 6 calves, healthy and mature, were enrolled, and blood samples collected at 30 minutes, 3, 12, 24 hours, and 3, 7, 10, 14 days after birth. IGF-I plasma concentrations were analysed by RIA. Horse foals showed higher (p<0.05) IGF-I plasma concentrations at 10 and 14 days of age in comparison to the values observed at 24 hours of age, while higher (p<0.05) IGF-I plasma concentrations were detected at 14 days of age in comparison to all the previous sampling times Donkey foals showed a significantly higher (p<0.05) value at 10 days compared to the first 24 hours. Calves showed the highest value at 30 minutes, followed by a significant (p<0.05) decrease at 3 hours and a further significant (p<0.05) decrease at 7 days of age. Comparing the profiles of the three species, no differences between horse and donkey foals were observed, while calves showed significant (p<0.05) lower levels compared to donkeys at 7,10 and 14 days and to horse foals at 14 days. This study confirm the important role of IGF-I n the early postnatal life in these three species, but also underlines the need of additional species-specific studies for a better understanding of the possible different role played by IGF-I in the different species neonatal physiology.