DIET EFFECTS AND ONTOGENY OF ALTERATIONS OF CIRCULATING INSULIN-LIKE GROWTH-FACTOR BINDING-PROTEINS IN NEWBORN DAIRY CALVES

Insulin-like growth factors (IGF) are important growth regulators in many species, and their effects are influenced by their association with IGF-binding proteins (IGFBP). The objectives of this study were to characterize the ontogeny of the blood plasma IGFBP in calves and to determine the effect of dietary IGF-I on neonatal plasma IGFBP. Plasma from newborn and 7-d-old male calves fed milk replacer, milk replacer + recombinant human IGF-I (rhIGF-I), or colostrum for 2 d followed by milk replacer was analyzed for IGFBP by ligand blot analysis. In addition, plasma samples from 1-, 12-, 24-, and 45-wk-old male calves were analyzed for IGFBP and IGF-I. Newborn and 7-d-old calf plasma contained IGFBP with M, of 26, 34, and 42 to 48 kDa. These profiles were not affected by the dietary treatments; however, a slight increase in the 34-kDa IGFBP and a slight decrease in the 26- and 42- to 48-kDa IGFBP were detected from birth to 7 d of age. The 34-kDa was confirmed to be bovine IGFBP-2 by immunoblot and the 42- to 48-kDa is likely IGFBP-3. The 29-,31-, and 42- to 48-kDa IGFBP increased between 1 and 45 wk of age. Similarly, plasma IGF-I concentrations were increased from 49.7 to 449.7 ng/mL in plasma from calves from 1 to 45 wk of age. In contrast, the 34-kDa IGFBP increased from 1 to 12 wk but then gradually decreased from 12 to 45 wk. whereas the 26-kDa IGFBP did not change. In conclusion, IGFBP profiles in calves from birth to puberty have changes that seem to be similar to those observed in other species. Dietary rhIGF-I did not alter plasma IGFBP profiles of neonatal calves.