Effects of varying levels of dietary protein and net energy on growth performance, nitrogen balance and faecal characteristics of growing-finishing pigs

ABSTRACT This experiment was conducted to evaluate the effects of dietary protein and net energy (NE) levels on growth performance, nutrient digestibility, nitrogen metabolism, and faecal microbiota of growing-finishing pigs. Eighteen crossed barrows were randomly allocated into one of three dietary treatments: high protein + high NE diet, low protein + high NE diet, and low protein + low NE diet. The whole experiment lasted 90 days and was divided into three phases (phase I: 25-50 kg; phase II: 50-75 kg; phase III: 75-105 kg). All pigs were individually housed in a metabolism cage and subjected to four-day total faeces and urine collection period at the end of each phase. There was no significant difference in growth performance, nutrient digestibility, serum total protein, and albumin concentrations of pigs among the dietary treatments. Compared with the high protein + high NE diet, pigs fed low protein + high NE and low protein + low NE diets had lower N intake, urine N, and total N excretion in each phase. At the end of the experiment, pigs fed the low protein + high NE and low protein + low NE diets had lower blood urea nitrogen, serum NH3-N concentrations, faecal pH value, faecal NH3-N concentration, and faecal Escherichia coli count than those fed the high protein + high NE diet. However, there was no significant difference in all of the above indexes between low protein + high NE and low protein + low NE diets. Decreasing the dietary protein content by 3.5 percentage units has no adverse effects on growth performance and nutrient digestibility of pigs while significantly reduces N excretion and faecal Escherichia coli count. Moreover, further decreasing dietary NE level in the low-protein diet by 0.35-0.5 MJ/kg does not affect growth performance, nutrient digestibility, N excretion, blood profiles, and faecal Escherichia coli count of pigs.

摘要 本试验旨在评估日粮蛋白质与净能（net energy, NE）水平对生长育肥猪生长性能、养分消化率、氮代谢以及粪便微生物群的影响。将18头杂交阉公猪随机分为3个日粮处理组：高蛋白+高净能日粮组、低蛋白+高净能日粮组以及低蛋白+低净能日粮组。整个试验周期为90天，分为三个阶段：阶段I（25~50 kg体重阶段）、阶段II（50~75 kg体重阶段）、阶段III（75~105 kg体重阶段）。所有试验猪均单笼饲养于代谢笼中，于每个阶段结束时开展为期4天的全收粪尿试验。各日粮处理组间试验猪的生长性能、养分消化率、血清总蛋白及白蛋白浓度均无显著差异。相较于高蛋白+高净能日粮组，饲喂低蛋白+高净能日粮和低蛋白+低净能日粮的试验猪在各阶段的氮摄入量、尿氮及总氮排泄量均更低。试验结束时，相较于高蛋白+高净能日粮组，饲喂低蛋白+高净能日粮和低蛋白+低净能日粮的试验猪的血尿素氮、血清氨态氮（NH3-N）浓度、粪便pH值、粪便氨态氮浓度以及粪便大肠杆菌计数均更低。但低蛋白+高净能日粮组与低蛋白+低净能日粮组间上述各项指标均无显著差异。将日粮蛋白质含量降低3.5个百分点不会对试验猪的生长性能和养分消化率产生不良影响，却可显著降低氮排泄量与粪便大肠杆菌计数。此外，在低蛋白日粮基础上进一步将净能水平降低0.35~0.5 MJ/kg，不会对试验猪的生长性能、养分消化率、氮排泄量、血液指标以及粪便大肠杆菌计数产生影响。