Insulin-like growth factor-I, passive immunity transfer, and stereological characteristics of small intestine of newborn calves

This study evaluated the concentration of insulin-like growth factor (IGF)-I present in the mammary secretions, its relation with changes in serum IGF-I and immunoglobulin (Ig)G, and intestinal mucosa alterations of 42 calves during the first week of life. Cows were randomly assigned to two groups, treated and control, with 21 animals in each. The treated group was injected with 500 mg recombinant bovine somatotropin (rbST) at day -35 relative to predicted calving date. Newborn calves were randomly assigned to a 2 x 3 factorial scheme: dams group and slaughter date (at birth, 2 and 7 days of life). IGF-I concentration was higher in the colostrum of treated cows (P < 0.05), but did not differ in the subsequent mammary secretions. Immunoglobulin G concentration in colostrum and subsequent mammary secretions did not differ between groups (P > 0.05). No differences were found in calf serum IGF-I levels from birth to the seventh day or serum immunoglobulin G concentration after 24 h of life (P > 0.05). IGF-I colostrum levels observed in this study did not affect the small intestine morphometry. The segment from the middle jejunum showed higher mucosa partial volume (Vv) at birth and 7 days old compared to other segments, and at just 2 days of age this segment reduced its Vv, not differing from other segments of the same date.