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1737
Effects of dietary energy on muscle growth of low birth weight neonatal pigs
Increasing the efficiency of nutrient utilization in farm animals remains one of the most important means to increase profitability. It is well documented that increasing energy intake increases insulin-like growth factor I (IGF-I) concentration in animals. In addition, our previous data suggest that IGF-I signaling is compromised in muscle of low birth weight (LBWT) compared to normal birth weight (NBWT) neonatal pigs. We hypothesized that LBWT pigs have a higher energy requirement compared to their NBWT siblings. Twelve pairs of 7-d old, sex matched LBWT (1.73 ± 0.24 kg) and NBWT (2.42 ± 0.29 kg) pigs from the same litters were used. Pigs were fed either a low (LE) or high energy (HE) isonitrogenous diets, that contained 80 or 100% of NRC metabolizable energy requirement for 14 d. Body composition was determined by dual energy x-ray absorptiometry before and 13 d after initiation of feeding. On the last day of the study, pigs were euthanized to collect blood, and weigh and sample muscles. Plasma IGF-I concentration was measured using a commercial ELISA kit, and muscle mRNA expression by real-time PCR. Body weight was lower for LBWT than NBWT pigs throughout the study (P ≤ 0.05). Lean and fat deposition increased with feeding in both LBWT and NBWT pigs, but was lower in LBWT compared with their NBWT littermates (P ≤ 0.05). Longissimus dorsi (LD), gastrocnemius, semitendinosus and soleus muscle weights were lower in LBWT compared to NBWT pigs (P ≤ 0.05). However, there was no effect of diet energy content on body composition and muscle weights. Plasma IGF-I concentration in LBWT pigs was lower than NBWT when pigs were fed LE diet, but increased to similar level as the NBWT group when pigs were fed the HE diet (P ≤ 0.05). Gene expression of IGF-I, IGF-I receptor, and IGF binding protein 3 and 5 were lower in the LD muscle of LBWT compared with NBWT pigs fed the LE diet, while the mRNA abundance of these proteins was similar in LBWT and NBWT pigs fed the HE diet (P ≤ 0.05). These results suggest that although increasing dietary energy content increased plasma IGF-I concentration and muscle mRNA expression of IGF-I and IGF binding protein 3 and 5 in LBWT pigs, the increase in growth was only modest indicating that other macronutrients may be limiting growth.
Keywords:
LBWT; Dietary energy; Muscle growth