IGF-I is not a useful marker for nutritional status in the growing pig under commercial conditions

Abstract

Plasma hormone concentrations were measured in gilts after fasting, long-term protein restriction, or supplementation. In 11-week-old pigs fasted overnight, plasma insulin, glucagon, gastrin, urea, and glucose were increased 30 min after re-feeding (P < 0.05), whereas IGF-I did not change. In 16-week-old gilts fed a standard commercial diet [14.6% crude protein (CP)], or a high-protein diet (16.7% CP) for 4 weeks, the high-protein diet increased weight gain (13%; P < 0.05) and carcass weight (4%; P < 0.05), but did not alter plasma IGF-I, insulin, or glucagon. In 10-week-old gilts fed high-protein diets (19.4% and 18.3% CP), or low-protein diets (15.5% and 13.3% CP) for 12 weeks during the grower and finisher phases, respectively, the low-protein diet decreased weight gain (18%; P < 0.001) and carcass weight (11%; P < 0.01), with a marked increase in plasma glucagon (P < 0.05), no change in insulin, and only a trend towards decreased IGF-I (P = 0.1). The pigs were more sensitive to altered dietary protein at 10 weeks of age than at 16 weeks. Plasma IGF-I was not responsive to the short-term effects of feeding or the long-term effects of dietary protein. Glucagon could provide a useful marker for nutritional status in young pigs, provided that time of feeding is taken into account.