In the framework of the current antibiotic-free, low-zinc farming system, having a healthy gut is important. Studies from China have shown that using mannan-rich fractions combined with organic acid/zinc proteinate can reduce incidence of diarrhoea, promote growth and improve gut health in piglets.
Weaning is a critical period in pig production. During weaning, piglets’ gastrointestinal tract and immune system are not fully developed, and the piglets are also facing multiple stressors, such as separation from sows, feed changes (from milk to solid feed) and pathogen threats, which often cause diarrhoea, low feed utilisation and stunted growth and can lead to significant losses in pig production.
Antibiotics and zinc oxide (ZnO) are 2 common methods that producers use to help their pigs cope with weaning stress. With the widespread ban on antibiotic growth promoters in feed, producers are widely using pharmacological doses of ZnO (e.g., 2,000 mg/kg or higher) in their piglet diets to help maintain growth and mitigate incidence of diarrhoea during the weaning period.
However, when provided at high doses or used over a long period, ZnO can be harmful both to pigs and the environment. In addition, at high levels, zinc interacts with other nutrients and may impact the absorption of other trace elements, such as iron, and can also reduce the activity of phytase.
Excessive zinc that is excreted in the faeces accumulates in the soil and water and can lead to environmental pollution. High levels of zinc have also been reported to cause negative changes to the gut microbial composition of piglets and can increase their antimicrobial resistance.
Restrictions on ZnO in weaning diets
Due to the negative impacts incurred by high levels of ZnO, the governments of various countries around the world have introduced policies to its use in weaning diets. The European Union has banned the use of pharmacological doses of zinc in piglet feed at levels greater than 150 mg/kg since June 2022. China also restricts zinc in the diets of nursery pigs (less than 25 kg) to no more than 110 mg/kg, and ZnO is only allowed to be used in the first 2 weeks after weaning at levels of no more than 1,600 mg/kg. Fortunately, pig producers are finding effective alternatives to high doses of ZnO.
To replace ZnO, focus on gut health
Pig producers widely understand that the goal is not only to find effective replacement products or solutions for ZnO but, more importantly, to foster a healthy gut and a strong immune system in their piglets. Focusing on gut health is particularly important in the current antibiotic-free, low-zinc system of production.
Pigs with healthy guts can better withstand the multiple stressors they face during the weaning period, allowing them to grow more successfully and experience less diarrhoea. Finally, fostering a healthy gut early on will have a positive impact on the health and performance of pigs for the rest of their lives.
Research support from China
Both organic acid and mannan-rich fractions (MRF) from the cell wall of Saccharomyces cerevisiae are recognised as beneficial for the gut health of pigs. One unpublished study in China by Alltech-Northwest A&F University Research Alliance evaluated the effect of replacing ZnO with a combination of MRF and organic acid (benzoic acid) on the growth performance and faecal scores of weaned piglets. The results of the study showed that the combination of MRF and organic acid could replace 1,600 mg/kg of ZnO in weaning pig diets. The advantages of the MRF and organic acid diet were even more pronounced in the second week after weaning, with improvements in the average daily gain at greater levels than those seen with the ZnO treatment.
In 2022, a team of researchers led by Gang Zhang from China Agricultural University published a study evaluating the potential of using organic zinc with MRF to replace ZnO. Compared with ZnO, zinc proteinate (an organic form of zinc) was shown to offer higher bioavailability, fewer negative interactions with other nutrients (e.g., iron, phytase) and less zinc excretion into the environment.
As mentioned previously, MRF has been demonstrated to improve the intestinal health of piglets, strengthen the function of the intestinal barrier and improve piglet immunity. As such, it was hypothesised that a combination of MRF and zinc proteinate could be used as an alternative to ZnO.
In the study, a low-protein, corn/soybean-meal basal diet was used as a control group, and the treatment groups were basal diets supplemented with 1,600 mg zinc/kg from ZnO or 60 mg zinc/kg from zinc proteinate plus 800 mg/kg MRF (MRP). The effects of each treatment on growth performance, incidence of diarrhoea and intestinal health in piglets were evaluated.
The study indicated that the MRP diet could be used as an alternative to 1,600 mg/kg of ZnO in piglet diets. The main takeaways of that study included:
1. Improvement of intestinal morphology
The MRP diet could improve intestinal morphology and microbial structure, thereby reducing incidence of diarrhoea. In the experiment, MRP reduced incidence of diarrhoea to a level comparable to that of the ZnO group (see Figure 1). Villus height and villus height/crypt depth measurements were the highest in the MRP group, indicating an improvement in the intestinal morphology. The colonic microbiota of piglets in the MRP group tended to have a higher relative abundance of Prevotellaceae/Prevotella than those in the control and ZnO groups, which are positively correlated with volatile fatty acid production and anti-inflammation functions. Considering these results altogether, it is clear that the combined use of MRF with zinc proteinate (MRP) could benefit gut functions and enhance anti-inflammatory functions in pigs, thereby reducing the risk of diarrhoea.
2. Benefits to growth performance
The improved gut morphology and gut function in the MRP group promoted the digestibility of nutrients (e.g., dry matter, organic matter, crude protein) in piglets. In both the second period (days 15 to 28) and for the overall post-weaning period (days 1 to 28), the average daily gain of the pigs was greater on the MRP diet. The final body weight also tended to be higher in this group than in the other groups.
3. Decrease of faecal zinc excretion
The concentration of zinc in the faeces of the pigs decreased significantly (p < 0.05) in the MRP group compared to the ZnO group (-94.5%), which means less pollution into the environment.