Studies have shown that, besides birth and weaning weight, especially the daily gain early post-weaning is not only a predictor for weight at slaughter but also for the days needed to reach the required slaughter weight. Out of one of the studies mentioned before it was shown, that a five per cent increase in average daily gain in the 20 days post-weaning made it possible to achieve an increase in slaughter weight of 1kg. Furthermore, it has been reported that a 1-kg increase in weight after the grower period leads to a 2- to 4-kg increase in slaughter weight. In general, it was reported that the industry equates a 1-kg increase in weight at the end of the grower period to a 2.5-kg increase in slaughter weight or a reduction of 2.5 to 3.5 days in the time to reach slaughter weight. Thus, even if the more complex diets fed after weaning are more expensive per kilo than diets fed to finisher pigs, the average daily feed intake of a finisher pig is significantly higher than the daily feed intake of a pig in the early post-weaning period, so that a 2.5- to 3.5-day reduction in time to reach slaughter weight represents an economical benefit to the producer.

However, what producers often experience in the period is a decrease in feed intake and therefore a reduced average daily gain. Pigs undergo a great deal of stress after weaning. They change from liquid to solid feed, suffering from being relocated and being mixed with unfamiliar pen mates. This leads to the effects described and results in a greater susceptibility to diarrhoea. In this regard and keeping the importance of the post-weaning daily gain to reach market weight in an adequate time in mind, producers should make sure to combat bacteria especially in the time post-weaning to avoid economical losses.

To combat possibly harmful bacteria effectively, structural differences of gram-positive and gram-negative bacteria have to be taken into account. The cytoplasm of the cell is surrounded by the cytoplasmic membrane, which is covered by a thick cell wall layer. This layer is significantly thinner in gram-negative bacteria compared to gram-positive bacteria. However, gram-negative bacteria are surrounded by an additional outer membrane. This outer membrane provides the bacteria with an inherent resistance to hydrophobic antibiotics and detergents due to the presence and features of lipopolysaccharides in the outer membrane.

Organic Acids in Combination with Other Naturally Derived Products

Organic acids have already for a long time been known to have antimicrobial effects. Often, organic acids were combined with other naturally derived products such as essential oils in an attempt to use possible synergies to combat pathogenic bacteria more powerfully. Essential oils in general serve as antioxidants, stimulate the immune system, suppress harmful microorganisms on one hand but stimulate beneficial microbes on the other, they regulate the activity of enzymes, especially lipase, are known to protect the gut villi and to interfere with the DNA replication of bacterial cells and therefore have anti-bacterial effects.

The mode of action of different phytochemicals varies widely. So, for example, cinnamaldehyde, which is a phytochemical derived from cinnamon bark oil, has an even more complex mode of action as it targets the FtsZ protein, which is playing a major role in the cell division of potentially harmful bacteria. FtsZ polymerizes into filaments, which assemble at the place within the cell, where the cell division takes place. There they form into a polymeric structure known as the Z-ring on the inner membrane in the mid of the cell, which is responsible for the division of the cell. Cinnamaldehyde inhibits not only the formation of FtsZ into filaments, but also inhibits essential processes involved in the Z-ring formation and its function and thus the cell division. This results in a reduction of the bacterial load, within the gastrointestinal tract.

Weakening the Outer Membrane of Gram-Negative Bacteria

Even if the outer membrane of the gram-negative cell is acting as a protective barrier for external agents it is possible to weaken the outer membrane by agents commonly characterised as permeabilisers. All the permeabilising substances act quite differently: some of them remove stabilising cations from the outer membrane, while others bind to the outer membrane resulting in the loss of barrier function; others destabilise or disintegrate the outer membrane or displace cations from the outer membrane causing membrane damage.

However, when it comes to combining organic acids and permeabilising substances, it is important that membrane permeability is increased, which is the case only for a couple of permeabilising substances. When permeabilising substances weaken the outer membrane of gram-negative bacteria, the activity of other antimicrobials is increased by facilitating external substances capable of inhibiting or destroying cellular functions when entering into the cells. This leads to synergistic effects when a permeabilising substance is added to a mixture of organic acids. However, whether a synergism can be found depends on the right combination of organic acids and permeabilising substances, as the synergy will not be found with each combination.

In–Vitro Inhibition of Bacteria

Figure 1 shows the effects of an acid blend and an acid blend combined with different phytochemicals on the inhibition of different bacteria. In general, the combination of an acid blend with a phytochemical seemed to improve the inhibition of bacteria. However, the inclusion level of phytochemicals 3 to 5 was twice as high as phytochemicals 1 and 2, while the inclusion level of phytochemicals 7 and 8 were even eight times higher than phytochemicals 1 and 2. As a higher inclusion level is always associated with an increase in cost, the combination of the acid blend with phytochemicals 1 and 2 turn out to be the most attractive, keeping costs in mind. Phytochemical 2, which was cinnamaldehyde combined with the acid blend, showed consistently good inhibition on all bacterial stains and, therefore, represented the most attractive combination to further work on more effectively combating possibly harmful bacteria.

Figure 1. Effect of an acid blend and phytochemicals on the inhibition of bacteria

As it was hypothesised that the permeabilisation of the outer membrane of gram-negative bacteria would boost the effects of an antimicrobial mixture combining an acid blend and a phytochemical, further in vitro tests using different permeabilising substances were carried out. In Figure 2, the inhibition of an antimicrobial mixture alone and in combination with different permeabilising substances is shown. This figure clearly shows the synergism between an antimicrobial mixture of organic acids and an essential oil and most of the tested permeabilising substances. However, the most persistent effect on the inhibition of the tested bacteria was seen by combining the antimicrobial mixture with the Biomin perforizing substance.

This was also shown in in-vitro tests done with a Scandinavian research centre, in which the susceptibility of a gram-negative bacterium to an antimicrobial mixture consisting of an organic acid blend and a phytochemical, the Biomin perforising substance alone, and at different inclusion levels combined with the antimicrobial mixture was tested. This research clearly indicates that the growth of a gram-negative bacterium was only diminished when the antimicrobial mixture was combined with the Biomin perforising substance in the higher inclusion levels.

In summary, the research on more effectively combating pathogens showed that the effectiveness with which bacteria are inhibited can be improved by combining an acid blend, a phytochemical and the Biomin perforising substance. However, the improvement in efficacy depends on the combination of phytochemical and permeabilising substance used as well as the inclusion level the permeabilising substance.

Figure 2. Effect of an antimicrobial mixture (acid blend and phytochemical) combined with different permeabilising substances on the inhibition of bacteria

Effects on Animal Performance

In pigs, body weight on day 56 post-weaning, average daily gain and also feed conversion ratio was improved if fed a cereal-based starter diet supplemented with 1kg of an organic acid blend, phytochemical and Biomin perforising substance mixture per ton of feed compared to pigs fed the same diet without any supplementation.

The trial was carried out at the Centre of Applied Animal Nutrition (Mank, Austria), using 60 weaning pigs [(Landrace × Large White) × Pietrain]. Pigs were assigned to two treatments with three replicate pens per treatment and 10 pigs per pen. Pigs were fed a cereal-based starter diet between days 1 and 14 (13.7MJ ME, 17.27 per cent crude protein, 1.37 per cent lysine) and a cereal-based grower diet (13.0MJ ME, 19.7 per cent crude protein, 1.18 per cent lysine) from day 15 until the end of the trial.

Growth performance was improved due to the supplementation of the diets with the natural growth promoter (NGP) Biotronic® Top3. Body weight at day 56 was six per cent higher (P<0.05) in the trial group than the control group. Average daily gain was improved by eight per cent in the Biotronic group compared to the group with no NGP added and also feed conversion ratio was improved by three per cent (P>0.05) in the Biotronic Top3 group compared to the control group.

Thus, results clearly indicate that the presence of bacteria within the animals' gastrointestinal tract highly influences their growth performance, as less energy is lost to immune responses and less nutrients are lost to bacteria. This may also lead to beneficial effects regarding the time to reach market weight. As research has shown, it can be expected that a five per cent increase in daily gain in the first 20 days post-weaning made it possible to achieve a 1-kg increase in slaughter weight and the study described above resulted in an eight per cent increase in average daily gain.

However, the synergy caused by the inclusion of the permeabilising substance allows a reduction in inclusion level, resulting in economical benefits for the end user. Therefore, it presents a different strategy to act against bacteria. Biomin has launched the NGP as Biotronic Top3.

October 2011