Endocrine and metabolic aspects in milk-fed calves

In neonatal calves besides adaptations in organ function there are marked m etabolic and endocrine changes. The growth hormone (GH)-insulin-like growth factor (IGF) axis is basically functioning, but needs maturation. Various metabolic and endocrine traits do not exhibit marked ontogenetic changes af ter the first week of life, but others remain different from the adult stag e. Thus, plasma oxytocin or an oxytocin-like substance and nitrate concentr ations are elevated for months. The ability to digest colostrum (C) and mil k involves great alterations in structure and function of the gastrointesti nal (GI) tract. C intake is important for passive immunity, provision of nu trients, minerals and vitamins, and contains biologically active substances . IGF-I, present in C in high amounts, appears to enhance GI tract developm ent and function. For sufficient absorption not only of immunoglobulins, bu t also of fatty acids and fat-soluble vitamins, C should be ingested immedi ately after birth. The amino acid pattern and the glutamine/glutamate ratio depends greatly on whether C is fed or not. Effects on insulin, IGF-I, and IGF binding proteins depend on time-point and amounts of C fed. After the colostral period calves are almost exclusively fed milk and milk substitute s or weaned. Low iron intake, required for the production of pale meat, bes ides anemia causes metabolic and endocrine adaptations, such as enhanced in sulin-dependent glucose utilization and appears to reduce IGF-I responses t o GH. Metabolic and endocrine changes, such as insulin resistance and distu rbed glucose metabolism, can be observed in part in association with high f eeding intensity in veal calves. (C) 1999 Elsevier Science Inc. All rights reserved.