Insulin-like growth factor-I and piglet intestinal development

Porcine milk contains hormones and growth factors that stimulate piglet intestinal growth and development. Milk-borne insulin-like growth-factor-I (IGF-I) has received considerable attention. In swine, IGF-I concentrations range from 0.10 to 0.4. mg/L in colostrum and approximately 0.01 to 0.04. mg/L in mature milk. Two experimental approaches have been utilized to investigate the role of orally administered IGF-I in neonatal intestinal development. In the first approach, piglets were reared on sow milk replacer formulas containing recombinant human IGF-I (rhIGF-I) at concentrations of 0.1 to 12. mg/L. The advantage of this approach is that specific effects of IGF-I can be assessed in the absence of other bioactive components, changes in milk composition, and other environmental factors. However, the applicability to swine production is limited. A second approach has been to develop transgenic mice or swine that overexpress IGF-I in milk under the direction of promoter regulatory elements of milk proteins to result in animals experiencing mammary specific overexpression of IGF-I during lactation. Herein, the effect of orally administered IGF-I on neonatal intestinal development in artificial rearing studies, as well as studies utilizing transgenic overexpression of IGF-I in milk, was reviewed. Both rhIGF-I in formula or transgenic IGF-I overexpression increased villus growth and disaccharidase activity; however, these effects were primarily observed late in the suckling period (d 21 postpartum) in piglets suckling IGF-I transgenic sows. We speculate that piglets suckling IGF-I transgenic sows may have improved intestinal health during the weaning transition.