Effect of Dietary Energy Level on Nutrient Utilization, Insulin-like Growth Factor-I and Insulin-like Growth Factor Binding Protein-3 in Plasma, Liver and Longissimus dorsi Muscle in Growing-finishing Pigs Using Soybean Oil as an Energy Source*

Two experiments were carried out to study the effects of dietary energy level on nutrient digestion, nitrogen (N) utilization, growth performance, insulin-like growth factor-I (IGF-I), and insulin-like growth factor binding protein-3 (IGFBP-3) in plasma, liver and longissimus dorsi muscle in growing-finishing pigs. In experiment 1 (Exp 1), 15 castrated male pigs (Duroc×Landrace ×Large White) (Body weight, BW, 55.6±1.8 kg) were divided into three groups and fed rations containing 13.33, 14.87 and 17.35 MJ digestible energy (DE)/kg as treatments I, II and III, respectively, using soybean oil as an energy source. The experiment lasted 8 days and faecal and urinary samples were collected during the last 3 days. The results showed that the digestibility of dry matter (DM), energy and N was increased from treatments I to III (p<0.01). N-retention and N-retention rate were not influenced by dietary DE level (p>0.05). In experiment 2 (Exp 2), 36 female pigs (Duroc×Landrace×Large White) (BW 41.5±3.8 kg) were divided into three groups. The pigs were fed with the same three rations used in Exp 1 for 60 days. At the end of Exp 2, eight pigs were selected from each group for blood sampling and 4 pigs for slaughter trial. The results indicated that average daily feed intake (ADFI) and N-intake were significantly decreased (p<0.01), and DE intake (p<0.01) and average daily gain (ADG) (p<0.05) were increased. IGF-I and IGFBP-3 in plasma were increased (p<0.05). No significant differences in IGF-I and IGFBP-3 in liver and longissimus dorsi muscle were found between different treatments. It was concluded that higher dietary DE level improved nutrient digestibility, ADG and feed/gain ratio when soybean oil was used as an energy source in the ration of growing-finishing pigs. No significant differences were found in Nretention and IGF-I and IGFBP-3 in liver and longissimus dorsi muscle between different treatments. (