Bitter compound quinine hydrochloride improved post-weaning pig performance in the absence of zinc oxide

Context Dietary zinc oxide (ZnO) (a bitter antimicrobial chemical) in pigs is being gradually phased out due to pollution and antibiotic resistance. Bitter compounds like quinine hydrochloride (HCl) have shown potential to enhance growth and feed efficiency by slowing gastric emptying and intestinal passage rates in pigs. Aims This study aimed to evaluate quinine’s ability to improve performance in weanling pigs without ZnO. Methods Two experiments were conducted. Experiment 1: 120 Landrace (LD) × Large White (LW) weaned piglets (initial BW 6.8 ± 0.1 kg) were randomly assigned to one of four diets in a 2 × 2 factorial design: with/without ZnO and copper sulfate (CuSO4) (3000 and 250 ppm, respectively) and two quinine levels (0 and 500 ppm). Parameters measured included average daily feed intake (ADFI), average daily gain (ADG), gain to feed ratio (G:F), and faecal score. Experiment 2: 1440 LD × LW piglets (initial BW 7.4 ± 0.2 kg) were housed in groups of 18 per pen and assigned the same four dietary treatments as in Experiment 1. Key results Growth performance parameters were recorded and analysed, showing that ZnO/CuSO4 supplement improved growth and feed efficiency (P < 0.05) compared to the ZnO/CuSO4-free diet group. In Experiment 1, pigs supplemented with quinine in non-ZnO/CuSO4 diets showed similar (P > 0.05) performance levels to the ZnO/CuSO4 fed group. In addition, an interaction (P < 0.05) was found, indicating that adding quinine improved or worsened ADG and G:F depending on the absence or presence of ZnO/CuSO4 in the diet, respectively. In Experiment 2, quinine inclusions in non-ZnO diets improved (P < 0.05) ADG but did not affect (P > 0.05) ADFI and G:F. Conclusion Our findings suggest that the anticipated deleterious effects of phasing out the use of dietary ZnO can be partially compensated by includingquinine in the diet of post-weaning pigs. The negative effect of quinine when provided together with ZnO is compatible with a competitive exclusion mechanism linked to both stimulating bitterness, a mechanism that warrants further investigation. Implications Quinine shows potential as a partial replacement for ZnO in post-weaning pig diets, providing a promising alternative to maintain piglet health and growth while transitioning away from ZnO.