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.