Effects of Replacing Medical Zinc Oxide with Different Ratios of Inorganic: Organic Zinc or Reducing Crude Protein Diet with Mixed Feed Additives in Weaned Piglet Diets

SIMPLE SUMMARY: Piglets frequently experience post-weaning diarrhea (PWD) due to various stress factors at the weaning stage. PWD affects the growth performance and mortality of piglets, and they face various diseases due to reduced immunity response. A high dose of zinc oxide (ZnO) is used as a feed additive to prevent diarrhea occurrence and to promote immune system development. However, most of ZnO is discharged as manure, causing soil heavy metalization, accumulation in pork, increased and antimicrobial resistance. For this reason, research to reduce zinc excretion and prevent PWD through the supplementation of low-dose zinc in feed is essential; moreover, it is essential to develop alternatives to ZnO addition. Therefore, we hypothesized that different ratios of inorganic zinc and organic zinc at 1000 mg/kg or a low-protein diet with commercial feed additives containing either essential oils, protease, and xylanase (MFA) could replace high-dose ZnO by preventing diarrhea and improving growth performance, nutrient digestibility, and gut health. We found that inorganic and organic zinc at a ratio of 500:500 mg/kg and a low-protein diet with essential oil, protease, and xylanase can be used to replace medical ZnO in weaned piglet diets. ABSTRACT: One hundred twenty weaned piglets (9.34 ± 0.74 kg) were used in a four-week experiment to investigate the effects of replacing medical ZnO with a different ratio of inorganic and organic zinc (IZ:OZ) or a low-crude-protein diet (LP) with mixed feed additives (MFAs) in the weaned piglets’ diet. The dietary treatments included a control (CON), T1 (T1; ZnO 1000 mg/kg), T2 (IZ:OZ 850:150), T3 (IZ:OZ 700:300), T4 (IZ:OZ, 500:500), and T5 (LP with MFAs (0.1% essential oils + 0.08% protease + 0.02% xylanase)). The growth performance was decreased (p < 0.05) in the CON treatment compared with the T4 treatment. The diarrhea incidence was decreased (p < 0.05) in the T4 and the T5 treatment compared with the CON and the T1 treatments. The apparent total tract digestibility (ATTD) of nutrients were increased (p < 0.05) in the T4 and T5 treatments compared with the CON, T1, and T2 treatments. The T4 treatment had a higher (p < 0.05) ATTD of zinc than the T1, T2, and T3 treatments. The fecal microflora was improved (p < 0.05) in the T5 treatment compared with the CON and T3 treatments. In conclusion, IZ:OZ 500:500 could improve growth performance, nutrient digestibility, and zinc utilization while reducing diarrhea incidence in weaned piglets. Moreover, LP with MFA could replace medical ZnO.