Effects of Multi-Strain Probiotic Supplementation in Low–Crude Protein Diets on Growth Performance, Apparent Nutrient Digestibility, Fecal Microbial Indicators, and Nitrogen Utilization in Weaned Piglets

This study evaluated the effects of supplementing a multi-strain probiotic (MSP) in low-crude protein (LP) diets on growth performance, apparent nutrient digestibility, selected fecal microbial populations, and nitrogen (N) utilization in weaned piglets. A 7-week feeding trial was conducted using 105 weaned crossbred piglets (Duroc × [Landrace × Yorkshire]) with an initial body weight of 6.55 ± 1.09 kg. Based on initial body weight and sex, piglets were randomly assigned to three dietary treatments using a randomized complete block design, with seven replicates per treatment and five pigs per pen (two gilts and three barrows). The dietary treatments included CON: normal crude protein (CP) diet; TRT1: LP diet; and TRT2: LP diet supplemented with 0.01% MSP. At week 7, the final body weight (BW) was higher in CON and TRT2 than in TRT1 (<i>p</i> < 0.05). During weeks 1-3, the feed conversion ratio (FCR) was lower in CON than in TRT1 (<i>p</i> < 0.05). In weeks 5-7, average daily gain (ADG) was higher in CON and TRT2 than in TRT1 (<i>p</i> < 0.05), while only CON showed a reduced FCR (<i>p</i> < 0.05). Over the entire trial, ADG was highest in TRT2 (<i>p</i> < 0.05), and FCR was lower in both CON and TRT2 compared with TRT1 (<i>p</i> < 0.01). At the end of the experiment, apparent nitrogen digestibility was significantly improved in CON and TRT2 relative to TRT1 (<i>p</i> < 0.05). Fecal <i>Lactobacillus</i> counts were elevated, and <i>Escherichia coli</i> abundance decreased in TRT2 (<i>p</i> < 0.05), indicating a more favorable profile of selected fecal bacterial indicators. In the N balance trial, six healthy piglets (three barrows and three gilts) per treatment were randomly selected and housed individually in metabolism cages. After a 3-day adaptation, total feces and urine were collected for four days to determine N intake, fecal and urinary N excretion, and N retention. At week 7, DM and N intake were unaffected by dietary treatment, whereas fecal N excretion was lower in TRT2 and CON relative to TRT1 (<i>p</i> < 0.05). Overall, supplementation of MSP in LP diets partially mitigated the adverse effects associated with reduced dietary protein by enhancing feed efficiency and nitrogen utilization, resulting in growth performance comparable to that of piglets fed a normal CP diet.