Concentrations of nonnutritional factors, such as insulin-like growth factor-I (IGF-I), in bovine colostrum are high and can modulate neonatal gastrointestinal tract development and function. In neonatal calves, we have investigated effects on intestinal epithelial cell morphology, proliferation, and absorption of feeding milk-born human IGF-I (hIGF-I) or a bovine colostrum extract. Calves were fed a milk-based formula containing amounts of nutrients comparable to colostrum for the first 3 d and a milk replacer from d 4 on. Formula and milk replacer contained only traces of nonnutritional factors. In experiment 1, supraphysiological amounts of hIGF-I (3.8 mg/L formula; secreted by transgenic rabbits with their milk) were added to the formula. Xylose appearance in blood (after feeding xylose on d 5) and intestinal traits (after euthanasia on d 8) did not differ between groups. In experiment 2, an extract of first-milked bovine colostrum that provided physiological amounts of IGF-I (0.50, 0.15, and 0.09 mg of IGF-I/L formula on d 1, 2, and 3, respectively, and 0.09 mg of IGF-I/L milk replacer on d 4) was added to formula or milk replacer. Plasma xylose concentration in the control group was transiently higher than in calves fed the colostrum extract. On d 5 (after euthanasia), villus circumferences and heights in small intestine, and epithelial cell proliferation rate in intestine were higher in calves fed the colostrum extract than in controls. In conclusion, orally administered hIGF-I from transgenic rabbits had no effect on the intestinal tract. However, feeding a bovine colostrum extract enhanced intestinal villus size, although it appeared to transiently decrease the absorptive capacity.

The neonatal development of the gastrointestinal tract around parturition in precocious mammals is greatly affected by endocrine factors like glucocorticoids as well as by nutritional factors. We have studied the effects of glucocorticoids and colostrum supply on intestinal morphology, cell proliferation, digestive enzyme activities, and xylose absorption in neonatal calves to test the hypothesis that the intestinal development in neonatal calves is influenced by glucocorticoids, dependent on colostrum feeding. Calves designated GrFD^– and GrFD⁺ were fed a milk-based formula, whereas those designated GrCD^– and GrCD⁺ received colostrum. Dexamethasone (DEXA; 30 µg/kg/day) was injected at feeding times to calves of GrFD⁺ and GrCD⁺. On day 3, the D-xylose absorption was measured. The calves were euthanized on day 5 of life. Colostrum feeding increased villus sizes in jejunum and ileum, enhanced xylose absorption capacity, and increased peptidase activities in the ileum. DEXA treatment diminished sizes and cell proliferation rates of Peyer’s patches in the ileum, yet increased proliferation of crypt cells in the ileum of formula-fed calves. DEXA reduced aminopeptidase N activities in the jejunum of formula-fed calves, but increased the peptidase activities mainly of colostrum-fed calves in the ileum. Thus, DEXA effects depended on intestinal segment and on different feeding, resulting in stimulation of crypt cell proliferation in the less mature ileum (of formula-fed calves) and in stimulation of peptidase activities in the more mature ileum (of colostrum-fed calves). We conclude that the effects of DEXA were related to the developmental stage of the neonatal intestine and promoted the intestinal development, depending on the developmental stage.

Glucocorticoids and colostrum feeding influence postnatal maturation of the somatotropic axis. We have tested the hypothesis that dexamethasone (Dexa) affects the somatotropic axis in neonatal calves dependent on colostrum intake. Calves were fed either with colostrum or with a milk-based formula ( n = 14/group), and, in each feeding group, one-half of the calves were treated with Dexa (30 μg · kg body wt-1 · day-1). Pre- and postprandial blood samples were taken on days 1, 2, 4, and 5, and liver samples were taken on day 5 of life. Dexa increased insulin-like growth factor (IGF)-I, but decreased growth hormone (GH) and IGF-binding protein (IGFBP)-1 and -2 plasma concentrations and increased GH receptor (GHR) mRNA levels in liver. Dexa increased IGF-I mRNA levels only in formula-fed calves and increased hepatic GHR binding capacity, but only in colostrum-fed calves. Colostrum feeding decreased IGFBP-1 and -2 plasma concentrations and hepatic IGFBP-2 and -3 mRNA levels. In conclusion, Dexa and colostrum feeding promoted maturation of the somatotropic axis. Dexa effects partly depended on whether colostrum was fed or not.