Lactational variation and relationship to postnatal growth of insulin-like growth factor-I in mammary secretions from genetically diverse sows

Abstract

Mammary secretions obtained from four groups of sows at parturition and on days 7, 14 and 21 of lactation were defatted and assayed for total protein and insulin-like growth factor-I (IGF-I). Sows (n = 57) represented two breeds (Landrace and Duroc) and two genetic lines (selected for differences in sow productivity index, SPI) within each breed. Colostrum of Duroc sows was 4–6 fold and 30–60 fold greater in protein (P < .001) and IGF-I (P < .001) concentrations, respectively, than the corresponding day 7 milk from these sows. In contrast, the colostrum of Landrace sows was 2–3 fold and 30–50 fold greater in protein (P < .001) and IGF-I (P < .001) concentrations, respectively, than the corresponding day 7 milk. The IGF-I content in milk from Duroc sows did not differ among days 7, 14 and 21 of lactation, whereas the IGF-I content of day 7 milk from Landrace sows exceeded those for the corresponding 14 day and 21 day secretion (P < .05). IGF-I concentration in days 14 and 21 milk was higher in Duroc (P < .001 respectively) than Landrace sows. No significant differences in total protein or IGF-I content of mammary secretions were observed between the selected and control lines within each breed. Concentration of IGF-I in colostrum and milk was negatively correlated with: a) SPI (6.5 × number of pigs born alive + adjusted litter weight at day 21 (P < .05)), b) newborn pig survival to day 21 (P < .10) and c) adjusted litter weight at day 21 (P < .05). However, total protein concentration was not associated with any of these parameters. The data demonstrate significant differences in secretory concentrations of IGF-I among pig breeds and may indicate a physiological association between milk IGF-I and growth and survival of neonatal pigs.