For decades and especially since the world-wide ban of antibiotics growth promoters had begun, zinc oxide at pharmacological dosages has been widely in use to effectively control diarrhoea in post-weaning piglets. But much like AGP, zinc oxide is a double-edged sword. It promotes the selection of antimicrobial resistant pathogens like E. coli in the intestine and is a co-factor in the development of resistance in Gram positive bacteria. Since there is also concern about possible contamination of the environment, the use in therapeutic dosages has been under scrutiny in several countries, not only in the EU (Satessa et al., 2020). The decision to ban zinc oxide from piglet feed has long been taken, yet the search for effective alternative control measures is still ongoing. With the ban finally in place, concerns are growing that post-weaning diarrhoea in piglets will increase.
The problem of post-weaning diarrhoea
Post-weaning diarrhoea syndrome, a multifactorial disease with a high incidence in many European countries, is a threat to both animal welfare and production profitability. If it occurs right after weaning, it has a negative impact on lifetime performance. Furthermore, the needed treatments against diarrhoea will drive up the cost of production and possibly the use of antibiotics.
What happens at weaning? In general, piglets are weaned at a very young age and the animals are exposed to numerous stressful situations. At that time, the gastro-intestinal tract of the piglets is still immature and has to adapt to the transition to solid food. Coupled with the stress of rehousing and fighting among the newly mixed litters, piglets sometimes require up to 48 hours to take their first feed. This low feed intake directly after weaning is largely responsible for changes in the epithelial structure of the gut. Weaned pigs show an increased intestinal permeability and at the same time pro-inflammatory cytokines are upregulated, indicating a strong immune response (Moeser, et al., 2017). Add the possible contamination with pathogens transferred from one group of piglets to the other, and the risk of intestinal infections and diarrhoea increases dramatically.
What made zinc so successful?
With the ban of antibiotic growth promoters in the EU, pharmacological dosages of zinc oxide were one of the preferred means used to control post-weaning diarrhoea (PWD) in piglets. The exact mode of action for the observed beneficial effects is still not quite clear. There are various explanations, one of which is the ability of zinc oxide to improve intestinal barrier function by supporting the integrity of the gut wall’s tight junctions during the weaning phase. The influence on immunological response by reducing pro-inflammatory cells within the intestine has been mentioned, as has a moderate antimicrobial effect and modulation of the intestinal flora (Bonetti et al., 2021).
So where to look for an alternative?
There is no miracle drug to simply replace medicinal zinc oxide in the diets of weaning pigs. However, this does not mean that we do not have promising alternatives which may even turn out to be a better solution for all concerned in the end. It is the same methods recommended to reduce the use of antibiotics which are likely to have a positive outcome (figure 1).
Figure 1: Management tools to reduce post-weaning diarrhoea without zinc oxide and antibiotics
Factors influencing the incidence of PWD include housing conditions, stocking density, the feeding regime as well as pre- and post-weaning management. Weaning heavier piglets and an older age, reducing environmental stress, avoiding the mixing of litters, good sanitation and a strict in-and-out system will improve on these contributing factors.
Dietary intervention will not be able to solve all problems. Nevertheless, nutrition plays a key role in keeping the piglets healthy. Here, the early feed intake of piglets is of utmost importance. There are several factors that affect feed intake, for instance the availability of solid feed before weaning, the environment, the palatability of the feed and its physical form. High quality of the used ingredients and an optimal nutrient balance will favourably impact feed intake as will a high digestibility of the diet (Dong & Pluske, 2007).
What can feed additives do?
There is probably no feed additive that can replace zinc oxide single-handedly. Looking at the described mechanisms of zinc oxide – and also antibiotics –, the modes of action imparting the beneficial effects cover a range of activities. Since the ban of antibiotic growth promoters in the EU and in other countries around the world, the search for the same or similar actions in feed additives other than zinc oxide has led to the development of innovative solutions to increase resilience and welfare in animals and especially in young piglets.
Organic acids have long been established as one of the most successful groups of feed additives in piglet nutrition. Since they are able to reduce gastric pH and lower the acid binding capacity of the feed, they support a proper protein digestion in young animals. The direct antimicrobial effect, moreover, reduces coliform bacteria in the intestine and lowers the incidence of diarrhoea (Suiryanrayna & Ramana, 2015). Therefore, it makes sense not only from an economic point of view to use effective feed acidifiers such as CaPlus (Dr. Eckel Animal Nutrition GmbH & Co. KG) to prevent diarrhoea. The acid blend, based on formic, lactic and citric acid and their salts reduce the diarrhoea incidence in weaned piglets significantly as has been demonstrated in a number of trials (figure 2).
Figure 2: Influence of acidification of the diet with CaPlus on diarrhoea incidence of piglets after weaning
An exciting new and innovative group of alternative feed additives are phytogenic formulations since they offer very promising solutions for the challenges faced in modern animal production. For instance, they contain plant metabolites to improve health and performance of weaned piglets. Modes of action include alleviating stress-related problems, reducing inflammation, supporting the immune system and improving feed intake.
The phytogenic formulation Anta®Phyt is a case in point. Specific selected hop components and other plant-based ingredients in Anta®Phyt are designed to support a healthy microflora in the digestive tract. Numerous studies have shown that Anta®Phyt positively influences performance parameters such as daily weight gain and feed conversion as well as animal welfare indicators.
To test its impact especially during the sensitive time of weaning, a feeding trial was conducted during the rearing period with piglets weaned after 23 days (fig. 3).
Figure 3: Anta®Phyt improves feed intake and weight gain the first week after weaning and the total rearing period
Compared to the positive control group receiving an antibiotic growth promoter, Anta®Phyt improved feed intake and weight gain over the whole rearing period. In the first week after weaning, the piglets supplemented with Anta®Phyt had a markedly better daily weight gain than the control piglets, showing that the phytogenic formulation was able to support the animals during this critical time in life.
Conclusions
PWD still is one of the major welfare concerns in pig production. Antibiotics and pharmacological levels of zinc oxide used to be the most effective way to prevent PWD. There is a chance that with the ban we will see an increase in antibiotic use for necessary treatment of nursery pigs. However, optimising pre- and post-weaning management, using all the existing knowledge of diet formulation and feed additives gained during the search for antibiotic alternatives, will help to mitigate the negative impact on health and welfare of young piglets. All in all, the situation also presents an opportunity because by using all known tools in the management box, we are most likely to improve overall profitability and sustainability of the operation.
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