Feeding weaner pigs without in-feed antibiotics

With the EU ban on the use of four antibiotic feed supplements and the phasing out of the quinoxaline derivatives carbadox and olaquindox in 1999, a substitute for the so-called growth promoters must be found for the entire field of animal husbandry. The situation is made all the more important in Germany by the continuing decline in prices on the pig market. In part as a consequence of this, many commercial piggeries want to move to a shorter three-week suckling period in order to produce pigs more efficiently and more economically. This pressure favours the larger pig producers and requires a diet that enables smaller piglets to be reared in a healthy, efficient and economic way without the use of antibiotics. It must be stated that at present animal nutrition research is not prepared for this challenge and must now rapidly develop alternatives to antibiotic feed supplements.

Current wisdom holds that the usual weaning procedures are accompanied by a general weakening of the immune system. From this point of view, development of the segregated early weaning and medicated early weaning systems in the US are, therefore, both timely and extremely valuable. The positive effect of reducing outside stress on the immune system (especially stress arising from infection) is understood from developments in poultry farming over the last 40 years. Nevertheless, the improvement in performance that can be achieved in pigs remains highly impressive.

These new methods of production are understandably of interest to the German pig breeders, and variations that are better suited to the smaller local production units are spreading rapidly. One could say that ‘the battle is half won’ if, in response to the discontinued use of antibiotics, breeders were to switch to this type of scheme. Whatever happens, nutritional physiologists will remain concerned with the problem of how to supply nutrients to the intestine such that the natural flora predominate and that any possible ‘derailing’ of the major intestinal immune function is recognized and dealt with locally without burdening the general immune system. The weaner diet must protect the integrity of the intestinal wall as well as continuously inhibit the growth of possibly pathogenic microorganisms. Failure to do so can result in proliferation of pathogens. As local cases have demonstrated, endotoxins of pathogenic bacteria can penetrate the intestinal barrier causing 15% mortality rates in weaners; though these cases involved the particularly pathogenic O:139 strain of E. coli (oedematous form of colienterotoxaemia). The treatment and cure of such diseases by veterinary practitioners, who are themselves often at a loss in such circumstances, is very laborious and certainly costly.


NUTRITIONAL AND PHYSIOLOGICAL PRINCIPLES OF THE WEANER DIET

In the first week post-weaning, the piglet must become accustomed to a totally new diet. At first the piglet eats very little and maintenance requirements are not met. Fat, protein and energy reserves are mobilized, with the result that the regulatory systems switch over to ‘hunger mode’. At this stage the feed conversion ratio (kg feed:kg gain) is typically between 3 and 4. In the second week, after the piglet has adapted to the new diet, feed efficiency improves rapidly. Body weight gain jumps to over 300 g per day. It is predominantly protein that is accumulated and food intake per kg of body weight gain falls to 1.5 kg. This highly compensatory and very intensive period of growth lasts for weeks, with individual piglets of the modern meat breeds gaining 1000 g per day at a body weight of 25 kg.

This short period of low intake (relative to gain) is not dangerous to the weaner’s metabolism. All organisms are provided with adequate regulatory mechanisms and storage capacity to be able to cope with such situations.

The one danger that does exist concerns the intestinal flora. The intermittent passage of food during the hunger period and the subsequent hyperphagia generate excellent conditions for microbial multiplication. Moreover, a potentially fatal shift in the intestinal bacterial population can result from the change from milk to solid feed and incorrect feeding (strongly buffering, high-nutrient food, based solely on nutrient requirements).

The favourable lactobacilli disappear and conditions encourage the growth of acid-intolerant coliform bacteria with strong pathogenic potential. Unfortunately, the pig’s defences against the full force of such an attack often prove too weak. The few defence measures such as stomach acidity, pancreatic capacity, or establishment of a resistant flora in the colon are still underdeveloped.

The success of the nutritional program will depend largely on how these physiological changes are dealt with. In the two to three weeks after weaning, the feed must meet the following three requirements:

1. The diet must have a functional ability to inhibit certain bacterial populations. Of importance are a low buffering capacity and the ability to encourage material passage through the intestine.
2. Diet components must support the rapid establishment of a stable colon microflora. A certain fraction of dietary fibre from long-chain hydrocarbons should be incorporated.
3. The diet ingredients should act as a substrate intervening in the reorganization of the intestinal microflora. Eubiosis can be effectively promoted by encouraging lactic acid-producing flora or blocking the attachment of pathogenic bacteria onto the intestinal wall.

These requirements cannot be met by simply making changes to the mineral fraction of the diet to reduce buffering capacity. In our studies, a basic feed mix of wheat-barley (approximately 1:1), soya (44% crude protein), and 3% each of fishmeal and soyabean oil has proved useful. Relevant reference values are for example an energy value of 13.2 MJ ME/kg, a crude protein content of 17.5-18% and a crude fibre content of 3.5-4%. Premixes are used containing amino acid supplements (12-13 g lysine/kg feed), minerals and vitamins to achieve typically 7 g calcium, 5 g phosphorus and 15,000 IU vitamin A/kg feed. This feed mixture is capable of meeting important physiological functions (low acid-binding capacity, ease of passage due to the dietary fibre content) and is also able to generate increases in body weight of 400-450 g per day in four-week-old weaners in the rearing section through 25 kg liveweight. However, the frequency of diarrhoea in such feeding groups can be 10% or higher, as was reported from Sweden following the ban on the use of antibiotics in 1986. The question raised is thus whether further, special feed additives can improve performance and reduce diarrhoea to the same extent that was achieved using antibiotics (additional weight gains of 15% and a reduction in diarrhoea of 50-66%).


THE EFFECTS OF DIETARY ADDITIVES

Feed components that may be considered useful in gaining the three objectives of weaner diet formulation mentioned above are carbohydrates, oligosaccharides, organic acids, metals, minerals, enzymes, probiotics and herbs. This chapter gives the results of our investigations involving acids and oligosaccharides together with investigations using phytase. Earlier work involving zinc and copper and absorbent materials such as diatomaceous earth and bentonite produced favourable results in the treatment of diarrhoea. However, for ecological reasons in the case of zinc, and for energetic/metabolic reasons in the case of bentonite, these additives should not be used prophylactically for diarrhoea.


ORGANIC ACIDS

Of the available alternatives to performance-enhancing drugs, the most important dietary components are the organic acids. The highly reproducible positive effects of organic acids on growth, feed utilization and alleviation of diarrhoea are indisputable. Indeed organic acids are in widespread use at present, being administered in addition to antibiotics.

In addition to the twomethods of lowering buffering capacity mentioned earlier (calcium and crude protein reduction), acid supplements can also be used to reduce feed pH to 4.8-5. Apart from promoting stomach function (maintenance of the bacterial barrier in the stomach, optimum pepsin activity, more rapid evacuation), a lower buffering capacity also increases the rate of absorption of trace elements and the pre-caecal digestibility of organic materials (Blank et al., 1988; Decuypere et al., 1997).

In fourteen investigations using different acids, we observed an average 11% increase in body weight, an inhibition of stomach fermentation by a factor of one third and an 18 % increase in the gastric emptying time (Bolduan, 1988). The blood urea levels also appeared to be lower. Recent evaluation of 144 experiments in the pig rearing sector have shown that formic acid caused a 15% additional increase in bodyweight and a 7% improvement in the feed conversion ratio (Freitag, 1998; Table 1). These data showing benefits of dietary acids confirmed earlier results with sorbic acid and potassium formate (Kirchgessner et al., 1997). Acids are now a recognized dietary supplement used to support stomach function in weaner pigs. Volatile acids are to be preferred as they also act to control microbial contamination of feeds.


Table 1. Improvements in performance of piglets receiving acid supplements compared with a control group (piglets reared from 8 to 25 kg).





OLIGOSACCHARIDES AND PHYTASE

A normal diet contains over 10% sugar polymers of various chain lengths. They are of little energetic value and since they cannot be digested enzymatically by the host; and they pass through the intestine to become a substrate for fermentation by colon bacteria. By virtue of their fermentability these sugar polymers sustain important functions of the colon such as material transport and waste excretion. When considering applications for weaner pigs, both the great variety of this class of substances and the predicament of the piglet should be considered. In addition to crude fibre detected by proximate analysis (lignin, cellulose and hemicellulose, which together account for about 5% of the ration), developments over the last few years have focused increasingly on short chain compounds appropriately named non-starch polysaccharides (NSPs). These compounds make up a further 5-8% of the ration. To improve utilisation of dietary gross energy, the biotechnology industry has developed suitable enzyme complements (pentosanases, glucanases, etc.) used as feed additives in the pig production sector to improve feed utilization and weight gains by 3-4%.

From a dietary standpoint, this is only of significance in that the enzyme supplements reduce digesta viscosity, which is typically determined by the swelling and gelling capacity of most polymers from glucan to pectin. The reduction in viscosity due to enzyme supplementation has had beneficial effects in the poultry industry, in particular for chick starter diets. Feed viscosity is not as important when rearing piglets as the glucans are hydrolzed in the pre-caecal region by the lactic acid-producing bacteria. In additon, we continue to detect diarrhoea when enzymes of this type are administered, as well as a significant hyper-proliferation of the intestinal flora in the frontal region of the jejunum (Bolduan, 1995). Obviously sugar molecules are a welcome substrate for the flora of the small intestine.

With regard to the piglet, oligosaccharides can be assessed as follows:

• The NSP fraction is retained in the ration as valuable dietary fibre.
• Search for a specific enzyme that does not degrade NSP but does break down other polysaccharide compounds thereby lowering viscosity.
• Search for oligosaccharides from natural sources that help the piglet control the negative shift in intestinal flora toward pathogens.

Our recent developmental work with piglets has indicated that phytase and the mannanoligosaccharides and fructo-oligosaccharides (MOS and FOS) are substances that are able to meet these high demands. MOS and FOS pass through the large intestine and act as a bacterial substrate specific to the bifidobacteria and lactobacilli (Spring, 1996). In our investigations, phytase proved able to enhance performance on its own and proved useful in combination with FOS and organic acids.


FRUCTO-OLIGOSACCHARIDES

For the investigations with FOS we used inulin, which is present in Jerusalem artichoke (Helianthus tuberosus). The extract was a solution containing 40% inulin. Inulin, with a molecular weight of 5000, is comprised of about thirty fructose molecules joined by 1,2 glycosidic linkages. Bolduan et al. (1993) demonstrated that a 0.2% FOS feed supplement reduced blood urea by 24%, increased gastric emptying rate by some 11%, and increased the concentration of lactic acid in the colon five-fold.

In the rearing trials, FOS was administered as a syrup concentrate of Jerusalem artichoke juice containing 30% inulin. In six experiments performance of piglets receiving FOS was compared with that of piglets given in-feed antibiotic additives (50 ppm zinc bacitracin). Average weight gain was 96% of that in the control group and the average feed conversion ratio was 98% of the group receiving antibiotics. Adjusting the inclusion rate resulted in performance equal to the group given antibiotics. Average values from three experiments clearly demonstrate the effect of changing use rate in response to need (data refer to weaners on a four week feeding regime, Table 2).


Table 2. Effects of inulin1 (FOS) dosage on bodyweight gain and feed efficiency of piglets².





The decreasing dosage scheme also allowed a 25-30% saving in the quantity of FOS used. This effect underscores the fact that several starter mixtures covering a range of concentrations are beneficial from a dietary point of view because it ensures that the weaners are, in all events, supplied with sufficient additive in the early stages of weaning. This is important as colienterotoxaemia will begin within the first ten days. The additive could be discontinued as early as the fourth week. The use of FOS was not accompanied by diarrhoea though faeces were somewhat softer due to the stimulation of the colon.


MANNANOLIGOSACCHARIDES

Linked mannose polymers are present in the walls of yeast cells (Saccharomyces cerevisiae). They also act as a substrate for lactic acid bacteria and in addition possess the ability to block bacterial attachment by occupying bacterial fimbria specific for mannose lectins in several strains of salmonella and E. coli. This essentially lowers pathogenicity of these coliforms and allows the potential pathogens in the lumen to be washed through the gastrointestinal tract (Spring, 1996).This should result in better growth performance. In an investigation of this, Bio-Mos mannan added to a pig starter feed gave a 10% improvement in growth rate of weaner pigs compared with an untreated control. An established growth promoter (olaquindox) gave only a 6%improvement (Bolduan et al., 1997). In both cases the treatments were applied with 0.65% formic acid.

In our experiments we used washed yeast cell walls from brewing yeast strains including, amongst others, Bio-Mos from Alltech Inc. with a mannan content of between 21 and 30%. Weaner pigs at four weeks of age were subjected to four-week rearing tests in which the feed contained no antibiotics. It follows from these results that Bio-Mos represents an excellent alternative to in-feed antibiotics with an added advantage when used in combination with organic acids. The preferred approach utilizes graduated doses and administration in combination with formic acid where growth rate improved by 11 % and no diarrhoea was reported.


Table 3. Effects of yeast cell wall, Bio-Mos and formic acid treatments on piglet performance weeks 1-4 post-weaning.





SUMMARY

Diets designed to respond to the phasing out of feed antibiotics should exhibit a low buffering capacity to promote the proper function of the stomach and an optimized crude fibre content to ensure the passage rate through the intestine. Organic acid supplements are clearly able to improve performance, with weight gain increases of between 11 and 25% and a reduction in diarrhoea observed. Of the various enzyme additives, only phytase can be recommended for use. Within the oligosaccharide group of substances, it is the polymers of mannose and fructose which, in specific doses and in combination with organic acids, result in improvements in performance of between 4 and 20%.


REFERENCES

Blank, R., R. Mosenthin and W.C. Sauer. 1988. Effect of fumaric acid supplementation and dietary buffering capacity on ileal and fecal nutrient and energy digestibilities in early weaned pigs. Vortr. Jahrestagung GfE , Go¨ ttingen.

Bolduan, G. 1988. Die Steuerung der Darm-Flora bei Ferkeln und Sauen. Chemie und Erna¨hrung. (Controlling the intestinal flora of piglets and sows. Chemical and nutritional studies.) 3. BASF - Forum Tiererna¨hrung, Ausg. 23, Nr. 11.

Bolduan, G. 1995. Carbohydrasen in der Schweineerna¨hrung. (Carbohydrases in the diet of pigs) Lohmann - Informat. Sept.-Dez. Nr. 4:15.

Bolduan, G., M. Beck and C. Schubert. 1993. Zur Wirkung von Oligosacchariden in der Ferkelfu¨ tterung. (On the effects of oligosaccharides in pig feeds) Arch Anim. Nutr. Berlin 44:21.

Bolduan, G.A., Schuldt andW. Hackl. 1997. Diet feeding in weaner pigs. (Arch. Tierz., Dummerstorf, Sonderheft 95-100.

Decuypere, J., M. De Brun and N. Dierick. 1997. Influence of buffering capacity of the feed on the pre-cecal digestibility in pigs. Proceed. 7. Internat. Symp. Nutr. Physiol. Pigs. Saint Malo.

Freitag, N. 1998. Wirkungen von Futterzusa¨tzen zur Ablo¨ sung der Leistungsfo¨ rderer in der Schweineproduktion. (The effects of feed additives as substitutes for performance enhancers in pig production) Forschungsber. FH Soest.

Kirchgessner, M., B.R. Paulicks and F.X. Roth. 1997. Effects of supplementation of diformate complexes on the growth and carcass performances of piglets and fattening pigs in response to application time. Agribiol. Res. 50:1

Spring, P. 1996. Effects of mannanoligosaccharide on different cecal parameters and on cecal concentrations of enteric pathogens in poultry. Diss. ETH Zurich, Nr. 11 897.

Author: G. BOLDUAN
Institute for Applied Agricultural Ecology, University of Rostock, Germany