Efficacy of Three Doses of Halquinol on Growth Performance, Diarrhea Incidence, Nutrient Digestibility, and Fecal Microbiome of Weaned Pigs

The weaning period is a critical phase for nursery pigs that is characterized by rapid growth and alterations in the intestinal microbiome associated with nutrient utilization. The present study aimed to investigate the efficacy of halquinol, when used as an antibiotic (ABO), on the growth performance, diarrhea incidence, coefficient of apparent total tract digestibility (CATTD), fecal volatile fatty acids (VFAs), and microbiota in pigs. A total of 210 healthy weaned pigs with an average initial weight of 6.9 kg and aged 28 ± 2 days were assigned to five treatments (six pens/treatment) in a complete randomized design, including a control group (T1, CON; feed with no ABO), a colistin group (T2, CLT; feed containing 120 ppm colistin), and three halquinol groups (T3 to T5, HAL; feed containing 180, 240, and 360 ppm halquinol, respectively). The experiment period lasted for 10 days. Field recordings, observation, and feces collection were performed on D1, D5, and D10. CATTD and VFA assessments were conducted on D10. The composition of the fecal microbiota was analyzed via 16S rRNA gene sequencing using the Illumina Miseq platform. The results demonstrated that the in-feed ABO groups exhibited a significantly lower ADFI (<i>p</i> < 0.01). Pigs fed the T3 and T4 diets had the lowest FCR (<i>p</i> < 0.01) on D5 and D10 and, thus, had reduced ADFI (<i>p</i> < 0.01). A quadratic contrast was found in ADFI and FCR on D5 and D10, indicating a negative correlation with HAL concentration (<i>p</i> < 0.01). Pigs fed CLT and HAL had significantly reduced levels of coliform (<i>p</i> < 0.01) and <i>E. coli</i> (<i>p</i> < 0.01). Moreover, pigs receiving ABO also had a lower fecal score compared to those on the CON diet (<i>p</i> < 0.01). Dietary in-feed ABO had no effect on all the parameters of the CATTD on D10 (<i>p</i> > 0.05), except for fat digestibility in pigs that received T4 (<i>p</i> < 0.01). Pigs fed the T4 and T5 diets had higher propionate concentrations and lower A/P ratios than pigs fed T1, T2, and T3 (<i>p</i> < 0.01). The microbial diversity shifted quickly through the early weaning period. The relative abundance of beneficial <i>Enterococcus</i> microbes increased in pigs fed in-feed ABO, whereas the relative prevalence of pathogenic bacteria, such as <i>Escherichia</i> and <i>Klebsiella</i>, decreased. <i>Escherichia</i> and <i>Bacteroides</i> were negatively correlated with carbohydrate digestibility and butyric and valeric acid production (<i>p</i> < 0.05). Overall, the appropriate HAL dosage was 240 ppm (T4), and this antimicrobial can potentially be characterized as an in-feed colistin replacer that improves feed efficiency and fat digestion, enhancing VFA production, alleviating post-weaning diarrhea, and protecting ABO-resistant piglets.