EFFECTS OF DIETARY RECOMBINANT HUMAN INSULIN-LIKE GROWTH FACTOR-I ON CONCENTRATIONS OF HORMONES AND GROWTH-FACTORS IN THE BLOOD OF NEWBORN CALVES

Colostrum is rich in insulin-like growth factor-I (IGF-I) and IGF-II and the dietary effects of recombinant human IGF-I (rhIGF-I) on the newborn are of interest. The objective of this study was to examine the effects of dietary rhIGF-I upon selected hormones and growth factors in the blood. Calves were fed for the first 2 days of life with one of three experimental diets: (1) milk replacer plus isolated colostrum-derived globulin (MR(-)), (2) as (1) plus 98 mu mol rhIGF-I/1 (MR(+)) or (3) pooled cow colostrum. Thereafter, all animals received only milk replacer at 5% of body weight/feeding twice a day with only treatment 2 having the continued addition of 98 mu mol rhIGF-I/1 until completion of the experiment 7 days after birth. Radioimmunoassays for insulin, prolactin, IGF-I, IGF-II, GH, L-thyroxlne, 3,5,3'-L-triiodothyroline and cortisol were conducted. With the exception of GH, all hormones and growth factors examined showed some form of dietary effect, but many were transient, changing only with the first feeding. Both insulin and prolactin concentrations exhibited a transient increase in blood at the first feeding, but insulin increased with the MR(-) treatment whereas prolactin increased with the MR(+) treatment. Total IGF-I concentration in blood did not show any diet-induced changes for the first 4 days, but thereafter a rise in blood concentrations of IGF-I was observed. These data indirectly support the hypothesis that dietary IGF-I may be absorbed and causes transient systemic effects in the newborn calf.