Developmental Histology, Segmental Expression, and Nutritional Regulation of Somatotropic Axis Genes in Small Intestine of Preweaned Dairy Heifers

Schematic illustration showing histological measurements. Villus height (VH), villus circumference (VC), and crypt depth (CD) were completed using ImagePro Plus 6.2.0 software (Media Cybernetics, Silver Spring, MD). The VH was measured from the tip to the base of the villus; CD was measured from the tip of the crypt to the point where it meets the muscularis mucosa; VC was measured by encircling the entire surface of the villus. A minimum of 5 full villi were chosen randomly per animal and the average measurement per animal was used for statistical analyses for each variable.

Fold difference in expression of mRNA of somatotropic axis components in different locations of the small intestine of preweaned dairy heifers relative to the endogenous reference gene ß-actin. Abundance of IGF-IR mRNA was lowest (A, P=0.005) in the duodenum, greatest in the ileum, and intermediate in jejunum. Insulin-like growth factor-I mRNA (B, P=0.003) was lower in duodenum than jejunum or ileum. Relative expression of IGFBP-6 was lower (C, P=0.016) in the duodenum. Bars with different superscripts differ, P<0.05. Data presented as least squares means±SE.

Mean villus height (A), crypt depth (B), and villus circumference (C) in different locations of small intestine of preweaned dairy heifers. Villus height was lowest (P=0.035) in the ileum, whereas crypt depth was not different (P=0.242) between different locations. There was no difference (P=0.976) in the villus circumference measured between the different intestinal locations. Bars with different superscripts differ, P<0.05. Data presented as least squares means±SE.