The importance of post-weaning feeding to reach market weight in an adequate time frame

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 5% increase in average daily gain in the 20 days post-weaning made it possible to achieve an by 1kg increased slaughter weight. Furthermore, it has been reported, that a 1kg increase in weight after the grower period leads to a 2 to 4kg increase in slaughter weight.  In general, it was reported, that the industry equates a 1kg increase in weight at the end of the grower period to a 2.5kg increase in slaughter weight or a 2.5 to 3.5 days reduced period to reach the slaughter weight. Thus, even if the more complex diets fed after weaning are more expensive per kg compared to the diets fed to finisher pigs, the average daily feed intake of a finisher pig is significantly higher compared to the daily feed intake of a pig in the early post-weaning period, so that a 2.5 to 3.5 reduction in days 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 lot of stressors 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 effectively combat possibly harmful bacteria 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 synergisms to more powerfully combat pathogenic bacteria. Essential oils in general serve as antioxidants, stimulate the immune system, suppress harmful microorganisms on one side 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. However, the mode of action of different phytochemicals varies a lot. 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 dividison 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 gastro-intestinal tract.

Weakening the outher 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 permeabilizers. All the permeabilizing substances act quite differently. Some of them remove stabilizing 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 permeabilizing substances it is of high importance, that the membrane permeability is increased, which is the case only for a couple of permeabilizing substances. When permeabilizing 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 permeabilizing substance is added to a mixture of organic acids. However, if a synergism can be found highly depends on the right combination of organic acids and permeabilising substances, as not with each combination a synergism will be found.

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 five was twice as high compared to phytochemicals 1 and 2, while the inclusion level of phytochemicals 7 and 8 were even eight times higher compared to 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 persistently good inhibition on all bacterial stains and represented therefore 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, testing 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 Per4izer^®. 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 Per4izer^® 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 Per4izer^® in the higher inclusion levels. So in clear words, the research done overall 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 Per4izer^®. However, to which extent the effectiveness can be improved strongly depends on which phytochemical and which permeabilising substance is used as well as at which inclusion level the permeabilising substance is used.

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 at 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 Per4izer^® 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 x Large White) x Pietrain]. Pigs were assigned to 2 treatments with 3 replicate pens per treatment and 10 pigs per pen. Pigs were fed a cereal based starter diet between day 1 to 14 (13.7 MJ ME, 17.27% crude protein, 1.37% lysine) and a cereal based grower diet (13.0 MJ ME, 19.7% crude protein, 1.18% 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 by 6 % (P<0.05) higher in the trial group compared to the control group. Average daily gain was improved by 8% in the Biotronic^® group compared to the group with no NGP added  and also feed conversion ratio was improved by 3% (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’ gastro-intestinal 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 5% increase in daily gain in the first 20days post-weaning made it possible to achieve an by 1kg increased slaughter weight and in the study described above resulted in a 8% 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. The company has launched the NGP as Biotronic^® Top3.