Transition to diets without zinc oxide (2/2): additives

After the opinions of the Committee for Veterinary Medicinal Products (CVMP) on 9/12/16 and 16/3/17 concerning the refusal to grant marketing authorizations and the withdrawal of the existing ones for veterinary products containing zinc oxide (ZnO), the European Commission has decided to ban ZnO as a medicinal premix in piglet feed, with a maximum moratorium of 5 years. This is, on the whole, good news for the producers, as there is enough time to adapt to the new situation, where using ZnO in post-weaning diets will not be possible.

The first step, in my view, is to focus on eradicating the use of ZnO beyond 14 days post-weaning, since this is a practice that, in addition to being illegal and generating toxicity, only delays the problem of its complete withdrawal. At the same time, we will find another two key elements in the next few years that will affect its use:

1. Closer monitoring of the use of medicated premix, in most cases through electronic prescription, including real-time reporting of the prescriptions issued by the farm, the company and the veterinarian, thus allowing for the completion of comparative studies.
2. The request of compatibility studies between different premixes to be able to combine them, which is complicated for products containing ZnO.

As stated in the previous article, it is crucial to take a holistic approach to this new scenario, improving health, management and nutrition. Regarding management, the most important measure will probably be the increase of the piglets age at weaning, although care must be taken to ensure this does not lead to an increment on the vertical transmission of pathogens. When it comes to nutrition, certain measures will need to be taken, that can be grouped in 5 areas:

1. Modification of the nutritional profile, possibly tapering down the energy and, to a higher extent, also the protein, and increasing the insoluble fibre.

2. Raw materials with protein sources of higher digestibility and the possible introduction of a minimum quantity of barley to increase digestive security.

3. Feed presentation, trying to increase particle size and using meal in the most problematic farms.

4. The use of combinations of additives that regulate the flora and promote digestive health and physiology.

5. Ensuring water quality through purification treatments, as water will be a key element for the administration of drugs and additives as both prevention and curative treatments.

As regards additives, it is very difficult for a single additive to mimic the effect of the addition of antibiotics or ZnO. This is why we need to combine groups of additives in water and feed, so they act both, as prevention and treatment. Amongst the additives, organic acids (OA) are the ones with a larger distribution. OA (mainly formic, propionic, lactic, and benzoic acids) are very efficient controlling pathogens in the feed. They are also very efficient strengthening the antimicrobial barrier of the stomach, preventing infection and /or re-infection by several pathogens. OA can be combined with their salts, which makes them much easier to handle. The main limitation of the OA is that they are pH-dependent, being much more efficient in their non dissociated form (therefore in acid environments) and nearly completely ineffective in neutral pH (the rest of the digestive tract after the stomach).

Medium-chain fatty acids (MCFA) are another emerging group, both as acids or as monoglycerides (MG). This group include fatty acids ranging from butyric acid (C4:0) to lauric acid (C12:0), and are used for both their antimicrobial effects and their physiological ones. MCFA have a very strong regulatory effect on the flora, being efficient against both gram negative bacteria (E. coli, Salmonella), and gram positive bacteria (Clostridium, Staphyloccocus, Streptococcus). Physiologically, butyric acid stands out in its different forms (salts, monobutyrin, tributyrin), as its inclusion enhances gut health by:

1. Direct nutrition for the enterocites.

2. Enhancing the unions between enterocites, preventing the pathogens arrival to the lamina propria and the onset of inflammation.

The differences between MG and free MCFA include:

1. MG-MCFA have a greater antimicrobial power than MCFA.

2. Their activity neither affects nor depends on pH (they maintain their activity throughout all the digestive tract).

   

3. MG-MCFA are dispersible in water (except for monolaurin), allowing their administration in drinking water).

4. MG-MCFA prevent bad taste and smell at the feed mill and for the animal.

The third group of products with an increasing interest are essential oils. These can be administered as a plant extract or as a synthetic pure product. The main limitation of the plant extract is the wide variability between harvests, which limits the options to guarantee a proper concentration of active ingredients. Its advantage, however, is that it provides a group of ingredients with different activities. If added as pure product, a stable content of active ingredients is ensured which is much better suited to livestock practices. The use of essential oils is based equally on their strong wide-spectrum antimicrobial effect and their physiological effects. The most relevant ones include carvacrol, thymol, and cinnamaldehyde.

Due to lack of space, prebiotics, probiotics and enzymes will not be addressed in this article.

A combination between additives must have the following characteristics:

1. Synergistic actions: addressing both flora regulation and digestive physiology aspects.

2. A combination of different modes of action to hinder the appearance of resistance.

3. Presentations both in feed for prophylactic use and in water to be used as a treatment.

This way, combinations of OA and MG-MCFA are one of the possible alternatives that will contribute to the withdrawal of medications from weaner diets. Figure 1 shows the effect of the addition of a combination of OA and MG-MCFA instead of just ZnO in a trial carried out during the starter period (from 38 to 66 days, 28 days trial, from 9 to 21 Kg). In general, the results for the animals that were given ZnO and the ones that received the combination of OA and MG-MCFA were similar, but the animals fed ZnO had a worse FCR (1,629 vs. 1,367), which indicates that ZnO can be removed from this stage without a drop in productivity or increased mortality.