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Formulating antibiotic-free diets

When formulating a diet all nutritionists have to pay attention to cost, ingredients and nutrients. This is even more so the case when it has to be an antibiotic-free diet.

It is best to lean towards less feed rather than 'less quality' when choosing piglet nutrition

By Dr Ioannis Mavromichalis, Ariston Nutrition, Spain

Discussions regarding antibiotic-free diets always focus on replacements or alternatives. Yet, research and empirical evidence have clearly identified the lack of any single ‘additive’ in offering the same degree of protection and level of performance as enjoyed by traditional feed-grade growth promoting agents. Indeed, there is general consensus regarding the need for two more areas that need to be addressed if such additives are to work as efficiently as possible: Hygiene and feed formulation (Figure 1).

When faced with a computer screen looking at the main interface of any feed formulation programme, a nutritionist has to keep his eye on three aspects: cost, ingredients, and nutrients. Quite often, the cost, which is rather important if the feed is to be sold, is neglected with subsequent reformulation attempts to bring it down to more ‘reasonable’ levels. So, these three areas shall be addressed in the mentioned order (Table 1).

Antibiotics (and such other antimicrobial agents, which are all referred here simply as antibiotics) were, without the slightest doubt, very cheap. So cheap, that they became universal. But, since they are gone, at least in many parts of the world, any alternative options are unlikely to be as inexpensive. In fact, the more efficacious such an alternative is, the more expensive it will be, until similar products become competitively produced and marketed. But, given the fact that such single product or combination of additives has yet to be proven to be as effective as most antibiotics were, alternatives will remain rather expensive for the foreseeable future.

Thus, manufacturers and users of antibiotic-free diets should be prepared to buy and sell such diets at higher prices than they were used to before. It might be that in a market where antibiotics are still allowed, antibiotic-free diets may have to be sold at a lower margin in order to establish a viable market. In other cases, such as in most EU countries, antibiotic-free piglet diets are kept less expensive to what they should have been because of fierce competition, reluctance to buy expensive piglet feeds, and a general preference for less complex diets due to widespread economic crisis. But, quality also suffers when such diets are offered at reduced prices as margins are quite often inelastic.

It is always better to use a more expensive, and correct, antibiotic free diet for a reduced period of time, rather than a less expensive diet for a longer period. For example, if a medicated pre-starter was to be used say, at 2 kg per piglet and cost of a non-medicated similar feed is deemed excessive, it is better to reduce allowance of such diet to perhaps, 1 kg per piglet rather than buy a diet that is less expensive and still feed it at 2 kg per piglet. Although a less expensive feed would be suitable towards the end of the period in question, it will cause nevertheless more damage than it will do good in the first stage, especially if this is immediately post-weaning. So, it is best to feed less rather than provide ‘less quality’.

This is the area that requires most attention as cost savings are often sought after in ingredient quality and/ or quantity. Assuming ingredient quality will not change and remains high as it should be for any respectable piglet feed, let’s discuss what ingredients should be used when the feed contains no growth promoting antibiotics.

First, cereals need to be of a mixture that offers both enough energy and functional fibres, without too much in terms of anti-nutritional factors. To this effect, a blend of maize (or wheat of good quality) with some barley, works very effectively. Adding to this blend some oats, especially steam flaked oat groats have been shown to support a more balanced gut microflora due to reduced digesta passage time and the presence of functional fibres that feed the beneficial bacteria. In some cases, some diets will even benefit from the addition of a suitable carbohydrase.

Second, milk products need to be reevaluated. Lactose is a natural laxative and the same is true for sucrose. Thus, simple sugar levels must be reduced, but this will invariably depress feed intake - for which other means must be used to bring it back to normal. In most EU diets, especially those used in Northern and Eastern Europe, lactose levels are about 10% in the first diet post-weaning and no more than 5% in the second diet post-weaning, these are considered diets rather high in lactose.

Third, functional fibres must be used. Such fibres are derived from ingredients such as chicory pulp, carob meal, sugar beet pulp, apple pomace, etc. The exact balance and level of each of these ingredients is today perhaps the best kept commercial secret among feed manufacturers, each owning to their choice being of course the best.

Fourth, protein sources need to be very refined in antibiotic-free diets. This means they need to be even more digestible and without much in terms of anti-nutritional factors. This largely excludes standard soybean meal, and such similar protein sources as canola meal, rapeseed meal, sunflower meal, peas, fababeans, etc. Here, soy protein can still be used in the form of well extruded full-fat soybeans or concentrated soy protein. Fish meal is nowadays of limited value because good quality fish meal has been priced out of most formulas, whilst less expensive fish meal is rather unsuitable for high quality piglet feeds. Numerous other protein sources exist in the market, all competing against soy protein concentrate, which is deemed the reference protein for piglet feeds.

Fifth, immunoglobulins need to be increased. This is perhaps the best ingredient to be used in antibiotic-free diets, be either animal plasma or eggderived antibodies. The latter is likely to be better as it is a very specific product designed to counteract piglet diseases, whereas animal plasma is more aspecific and depends on what pathogens the animals from which it is derived were exposed to. Needless to say, animal plasma is so expensive that it requires substantial sacrifices in terms of quality if it is to be used in meaningful concentrations and still produce a marketable finished feed.

Undoubtedly, it is widely known that bacteria, and especially most pathogens, require protein to thrive. Thus, not only all protein sources used in quality piglet feeds should be of the highest possible digestibility, but overall (crude) protein in the feed must be limited to about 18-19% or even less, in all diets from creep feed to the last one up to 20-30 kg body weight. Achieving this target frequently requires the use of crystalline amino acids, but always taking care not to use more than 0.5% L-Lysine HCL. Fibre, as eluded above, must be increased. In the past, piglet feeds with as little as 2% crude fibre were considered ideal, but in antibiotic-free diets this is actually the opposite.

Such diets, assuming they contain the right blend of functional fibres, should contain about 3% crude fibre, with a bit more as pig age advances, but never exceeding 4% (again depending on age, and feed quality versus cost considerations).

Sodium levels should be reduced to about 0.3%, given that salt is also a laxative, and also avoiding excessive levels of whey, fish meal, and animal plasma will help greatly. In contrast, if sodium levels cannot be reduced, any ingredient with a high water absorbing capacity can be used, but again which one is the best remains the exclusive secret of most feed companies, with each one using of course a different product.

Energy is discussed last, only because after having worked on the above issues the feed will invariably contain less energy, unless a large inclusion level of fat/ oil is used, which is unlikely considering the current price of most quality sources of lipids for animal feed. Thus, an energy level of 10 MJ/kg in terms of Net Energy is deemed satisfactory for antibiotic-free diets.

Further considerations
It would be unfair to conclude that everything needed to make an ideal antibiotic- free diet is mentioned in the above brief remarks. Indeed, books have been written on this subject, and countless hours have been spent in seminars and conferences worldwide in search of the best feed formulation practices in the absence of antibiotics. Similarly, scientific literature is full of research projects on this topic. Nevertheless, the above notes can be used as a guideline in designing or buying antibiotic-free diets. Invariably, each nutritionist will have his or her own preferred practices to serve their own needs.