Reduced Dietary Protein Levels Improved Growth Performance, Promoted Efficient Nutrient Utilization, Increased Fecal Lactobacillus, and Reduced Fecal Malodorous Compounds in Late-Fattening Barrows

The objective of this study was to evaluate the effect of reducing dietary protein levels on barrows during the late fattening period. Fifty Duroc × Landrace × Yorkshire barrows with body weights averaging 76.30 ± 6.57 kg were randomly divided into normal protein (NP) and low protein (LP) groups. The feeding experiment lasted for 55 days. Dietary crude protein (CP) contents were 13.5% in the NP and 11.5% in the LP during days 1–28 and 12.5% and 10.5% during days 29–55, respectively. Results showed that compared with the NP, the LP increased the average daily gain (ADG) of barrows during days 29–55 (p < 0.05); enhanced the digestibility of nutrients, including dry matter (p < 0.01), CP (p < 0.01), calcium (p < 0.01), and phosphorus (p < 0.05); and decreased serum blood urea nitrogen (p < 0.01), total cholesterol (p < 0.05), and free fatty acids (p < 0.05). Lowering dietary CP increased fecal Lactobacillus abundance (p < 0.01); reduced concentrations of fecal ammonia nitrogen, histamine, butylamine, putrescine, 1,2-heptaenediamine, p-cresol, and indole-3-acetic acid (p < 0.01); and had no negative effects on meat quality (p > 0.05). These results suggested that reducing dietary CP by 2% could improve growth, promote efficient nutrient utilization, increase beneficial fecal microbiota abundance, and reduce the emission of fecal malodorous compounds in late-fattening barrows.