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${\times}$Landrace${\times}$Large White) (Body weight, BW, 55.6${\pm}$1.8 kg) were divided into three groups and fed rations containing 13.33, 14.87 and 17.35 MJ digestible energy (DE)/kg as treatments I, II and III, respectively, using soybean oil as an energy source. The experiment lasted 8 days and faecal and urinary samples were collected during the last 3 days. The results showed that the digestibility of dry matter (DM), energy and N was increased from treatments I to III (p<0.01). N-retention and N-retention rate were not influenced by dietary DE level (p>0.05). In experiment 2 (Exp 2), 36 female pigs (Duroc${\times}$Landrace${\times}$Large White) (BW 41.5${\pm}$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.