Influence of ad libitum milk replacer feeding and butyrate supplementation on the systemic and hepatic insulin-like growth factor I and its binding proteins in Holstein calves.

Ad libitum milk feeding and butyrate (B) supplementation have the potential to stimulate postnatal growth and development in calves. The somatotropic axis is the main endocrine regulator of postnatal growth and may be affected by both ad libitum milk replacer (MR) feeding and B supplementation in calves. We hypothesized that ad libitum MR feeding and B supplementation stimulate systemic and hepatic insulin-like growth factor (IGF)-I and IGF binding proteins (IGFBP) in preweaning calves. Sixty-four (32 male, 32 female) Holstein calves were examined from birth until wk 11 of life. Calves received MR either ad libitum (Adl) or restrictively (6 L/d; Res). In each feeding group half of the calves received a MR with 0.24% butyrate and the other half received same MR without butyrate. Ad libitum MR feeding was performed from d 4 until wk 8 of age. From wk 9 to 10, Adl and Res calves were gradually weaned and were fed 2 L/d until the end of the trial. Concentrate, hay, and water were freely available. Feed intake was measured daily and body weight weekly. Blood samples for analyzing plasma concentrations of glucose, insulin, IGF-I, and IGFBP-2, -3, and -4 were taken on d 1, 2, 4, and 7, then weekly or every other week (IGFBP) until wk 11 of life. Liver samples were taken on d 50 and at the end of the study (d 80) to measure gene expression of the growth hormone receptor 1A (GHR1A), IGF1, IGFBP1 to 4, and of the IGF Type 1 and insulin receptor in the liver. Intake of MR and body weight were greater, but concentrate intake was lower in Adl than in Res. Plasma concentrations of IGF-I and IGFBP-3 were greater and plasma concentration of IGFBP-2 was lower in Adl than in Res during the ad libitum milk feeding period. After reduction of MR in both groups to 2 L/d plasma concentrations of IGF-I and IGFBP-4 were lower and plasma concentration of IGFBP-2 was higher in Adl than in Res. Supplementation of B depressed plasma IGF-I from wk 1 to 4 and in wk 9. On d 50, mRNA abundance of the GHR1A and IGF1 was greater and of IGFBP2 mRNA was lower in Adl than in Res. At d 80, IGFBP2 mRNA was greater in Adl than in Res, and IGFBP2 mRNA increased with B supplementation. Ad libitum MR feeding stimulated the systemic and hepatic IGF system and mirrored the greater growth rate during the ad libitum MR feeding, whereas butyrate supplementation partly reduced the systemic and hepatic IGF system.