The composition of the milk and colostrum diets may have also contributed to the observed
differences in the immune response of SF-pCD and FARM pigs. Colostrum is rich in
immunoglobulin, but mature bovine and porcine milk contains much lower immunoglobulin
concentration [17,18]. In addition to immunoglobulin, a large number of bioactive substances
have been identified in bovine colostrum, such as insulin-like growth factors (IGF)-I and –II,
epidermal growth factor (EGF), lactoferrin, and others [19]. By consuming bovine colostrum
throughout the entire preweaning phase, SF-pCD pigs consumed more of these bioactive
factors than FARM pigs. Although bovine and porcine colostrum contain similar levels of
IGF-I, the mature milk of both species has about 10-fold less. Thus, SF-pCD pigs would have
consumed more IGF-I throughout the suckling phase than FARM pigs that may have
contributed to differences in the immune responses of SF-pCD relative to FARM pigs.