| Summary: | Dietary energy is the largest single cost in pork production. Accurate and current understanding of energy metabolism is crucial to production efficiency. The overall objective of this thesis was to evaluate the effects of dietary energy concentration and energy intake on growth, nutrient deposition rates and energy utilization in weaned pigs. In experiment 1, the optimum total lysine:DE ratio for weaned pigs was estimated at 4.27 and 4.46 g/Mcal for pigs growing from 7.5 to 12.8 kg and 7.5 to 22.5 kg BW, respectively. Experiment 2 determined if a more predictable growth, nutrient deposition and energy utilization in the weaned pig is achieved with NE or with DE. ADG either remained similar or was depressed with increased NE compared to the control (P < 0.05). Empty body protein content and deposition (PD) declined relative to the control (P < 0.05) and lipid content and deposition (LD) tended to increase (P < 0.10). Body composition and nutrient deposition rates were more correlated with determined NE concentration and intake compared with DE. The results of Experiment 3 indicated that amino acid intake impaired the growth of pigs when an energy intake restriction greater than 30% occurred. Experiment 4 investigated the interaction of dietary NE concentration and feeding levels (FL) on body weight gain, tissue (protein, lipid, ash, water) accretion rates and ratios. Growth performance was not affected by NE (P > 0.05) but increased with feeding level (P < 0.001). Energy intake increased with NE and FL (P < 0.001), but the efficiency of energy utilization for growth declined (P < 0.05). Empty body protein content declined (P < 0.05) while lipid content increased with NE (interaction, P < 0.05). Empty body PD was not affected by NE (P > 0.05) but both LD and LD:PD ratio increased (interaction, P < 0.001). These data suggest that when amino acid:energy ratio is optimal, increasing dietary energy concentration increased energy intake but does not improve PD and overall body weight gain of weaned pigs. However, body lipid content and LD were increased. Finally, NE offers an advantage over the DE in predicting the body composition and nutrient deposition rates rather than in overall BW gain.
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