Nutritional And Physiological Effects Of Whole-Body Protein Turnover In Neonatal Pigs

Two experiments were designed in this study to investigate nutritional and physiological effects of whole-body protein turnover, utilization of protein and energy as well as growth performance of neonatal pigs artificially reared with liquid diet from 4 to 21 d of age. Whole-body protein turnover was measured with the [?N]glycine single-dose urea end-product method. In Experiment I, twenty-four Landrace X Meishan crossbred neonatal pigs(averagely weighed 2.01 ?0.05Kg) at 4 d of age from eight litters were used and allotted to six treatments consisting of 4 pigs each: killed for the determination of intial body composition, remained suckled, or artificially fed liquid diet (DMI9.48%,CP6.70%, GE4.43Ki/g) at 4-hr intervals with four different intake levels in individual metabolism cages.The experiment ended when the neonatal pigs were 2 weeks old to evaluate utilization of ingested protein and energy by neonatal pigs and effects of nutrient intake on whole-body protein dynamic metabolism. The results were as follows: I.The neonatal pigs artificially fed liquid diet gained significantly with increasing intake (P<0.05). The growth performance of neonatal pigs artificially fed ad libitum excelled significantly than that of sow-suckled pigs (ADG were 252.25 and 200.05g/d, respectively). 2.The efficiencies with which protein and energy used by neonatal pigs were far higher than those of growing-finishing pigs reported in the literature. The digestibilities of ingested nitrogen were greater than 97%, and the efficiencies of the conversion of apparently absorbed nitrogen into retained nitrogen were greater than 83%. Metabolic efficiencies of ingested energy were greater than 93%, and the retention efficiencies of ingested energy were greater than 81%. The efficiencies of metabolizable energy used for protein and fat deposition were 0.7308 and 0.8809, respectively. The proportion of ingested metabolizable energy above maintenance used for protein deposition was about 61.8 1%. 73 3 .N itrogen fl ux,protei n fractional synthesis rate( FSR) and fractional breakdown rate(FBR) in the whole-body of neonatal pigs at 12-14 d of age varied significantly (P<0.05) depending on nutrient intake(the ranges were 5.0 1-10.1 lgN/Kg075/d, 16.74-25.95%/d, 9.74-15.56%/d, respectively), and the ratios of protein synthesis to protein accretion(PS/PA values) averaged 2.46 ?0.04 which were lower than those of growing-finishing pigs significantly. 4.The significant power function curvilinear relationship between ADG and FSR showed that FSR was an important factor stimulating growth of neonatal pigs. From the power function curvilinear relationship between ADG and FSR as well as FBR, it was inferred that net protein deposition still occurred when no changes in body weight took place,i.e.,constant body weight didn't mean no changes in body composition. 5.Whole-body protein synthetic potential of neonatal pigs exceeded their ingestive capacity. The significant exponential curvilinear relationship between whole-body protein FSR and nitrogen intake showed that the maximal potential of whole-body protein synthesis in neonatal pigs at 12-14 d of age was 28.99720/01d of which FSR only reached 89.49% when fed ad libitum. 6.Path analysis showed that increases in whole-body protein synthetic activity and capacity were the root cause of increase in whole-body protein FSR, however, increase in plasma insulin level caused by increased nutrie...