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 m any species, and their effects are influenced by their association wit h IGF-binding proteins (IGFBP). The objectives of this study were to c haracterize the ontogeny of the blood plasma IGFBP in calves and to de termine the effect of dietary IGF-I on neonatal plasma IGFBP. Plasma f rom 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 m ilk replacer was analyzed for IGFBP by ligand blot analysis. In additi on, plasma samples from 1-, 12-, 24-, and 45-wk-old male calves were a nalyzed 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 af fected 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 we re detected from birth to 7 d of age. The 34-kDa was confirmed to be b ovine IGFBP-2 by immunoblot and the 42- to 48-kDa is likely IGFBP-3. T he 29-,31-, and 42- to 48-kDa IGFBP increased between 1 and 45 wk of a ge. 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 decrea sed from 12 to 45 wk. whereas the 26-kDa IGFBP did not change. In conc lusion, IGFBP profiles in calves from birth to puberty have changes th at seem to be similar to those observed in other species. Dietary rhIG F-I did not alter plasma IGFBP profiles of neonatal calves.