Effects of Protein-Chelated Zinc Combined with Mannan-Rich Fraction to Replace High-Dose Zinc Oxide on Growth Performance, Nutrient Digestibility, and Intestinal Health in Weaned Piglets

Simple Summary The early weaning of piglets is a key strategy for the modern pig industry. However, the digestive system of early-weaned piglets is not well developed, and weaned piglets suffering from psychological, nutritional and environmental stresses, cause significant losses to the pig industry. In order to mitigate the challenges of weaning, adding zinc oxide to the diet of weaned piglets has become standard in the industry. However, the excessive output of zinc from pigs' feces to the water and soil will produce toxicity to crops and threaten animal and human health. Mannan-rich fraction, derived from Saccharomyces cerevisiae, can improve gut health and the immune system. In addition, protein-chelated zinc has stable chemical properties, a higher absorption rate and biological potency. Therefore, we speculate that the combination of protein-chelated zinc and mannan-rich fraction will be an alternative to high-dose zinc oxide to relieve weaning stress. Our study showed that the combined addition of protein-chelated zinc and mannan-rich fraction is an alternative for zinc oxide in beneficially supporting the growth performance and intestinal health of weaned piglets, as well as contributing to a lower diarrhea rate and environmental pollution from fecal zinc excretion. A total of 168 weaned piglets (average initial body weight of 7.70 +/- 0.75 kg) were used in a 4-week feeding trial to investigate the effects of dietary supplementation with protein-chelated zinc (Zn-Pro) alone or combined with a mannan-rich fraction (MRF) to replace high-dose zinc oxide (ZnO) for weaned piglets. The dietary treatments included a basal diet as control (CON), a ZnO diet (basal diet + 1600 mg Zn/kg from ZnO), a Zn-Pro diet (basal diet + 60 mg Zn/kg from Zn-Pro), and a MRF plus Zn-Pro diet (MRP, basal diet + 800 mg/kg MRF + 60 mg Zn/kg from Zn-Pro). The average daily gain of piglets in the MRP group was higher (p <= 0.05) than that in CON and Zn-Pro groups during d 15-28 and d 1-28 of experiment. The apparent total tract digestibility of dry matter, organic matter, and crude protein in the MRP group was higher (p <= 0.05) than that in the CON group. The serum insulin-like growth factor-1 level in the MRP group was markedly higher (p <= 0.05) than that of piglets in the other three treatment groups. Piglets fed the Zn-Pro and ZnO diets had greater (p <= 0.05) acetic acid in cecal digesta than those fed the CON diet, while the MRP diet had higher (p <= 0.05) cecal propionate concentration than those that were fed the CON diet on d 28 of experiment. Moreover, the villus height of ileum in the MRP group tended to be greater than the CON group (p = 0.09). Compared with the CON and MRP groups, the relative abundance of Lactobacillaceae (p = 0.08) and Lachnospiraceae (p = 0.09) in the Zn-Pro group showed an increasing trend. The relative abundance of Prevotellaceae in the Zn-Pro group was significantly lower (p <= 0.05) than that in the MRP group. In conclusion, the combined addition of MRF and Zn-Pro acted as a suitable alternative to ZnO to beneficially support the growth performance and intestinal health of weaned piglets, as well as contribute to a lower diarrhea rate and environmental pollution from fecal zinc excretion.