In different species the insulin-like growth factor I (IGF-I) is an important regulatory factor in fetal and neonatal growth, especially in skeletal and gut development. This study was carried out to assess plasma IGF-I profile in newborn healthy donkey and horse foals during the first 2 weeks of age. The study was conducted on 32 horse and 19 donkey foals, born at term, after spontaneous parturition, mature and viable. Blood samples were collected from the jugular vein at 10, 20 and 30 min, 3 and 12 h and at day 3, 7, 10, 14 of life. IGF-I levels were evaluated by RIA. IGF-I showed an increasing profile in both species, with lower levels (p < 0.05) during the first 3 days of life.
Plasma IGF-I levels were found to vary widely between subjects both in donkey and horse foals. Mean plasma levels were higher (p < 0.001) in horses than in donkeys during the first week. However donkey foals showed a greater mean percentage increase (681%) than horse foals (114%). These results evidenced increase of IGF-I concentrations during the first 2 weeks of life that could be associated with a number of physiological challenges in adapting to extrauterine life. Moreover, although horses and donkeys belong to the same genus, these results seem to indicate the presence of some differences in their somatotropic axis activation.
