2
While the piglet suckles, the dominant bacteria in the stomach and small intestine are usually Lactobacillus and Streptococcus, adapted to the lactal substrate. After weaning the lactobacilic bacteria are reduced and there is a proliferation of gram- bacteria such as E. coli, Salmonella and Brachyspira. This alteration in the composition and stability of the microbial population increases the susceptibility of the piglets to diarrheas of nutritional etiology provoked by the supply of food that is strange and dry such as carbon hydrates and complex non-dairy proteins.
The protein from milk, casein, needs the piglet’s stomach to have a pH of 4 in order to coagulate, precipitate and reach a digestibility of 98%. However, the vegetable and fish proteins need pepsin in order to hydrolyze and get ready for the posterior enzymatic digestion in the intestine. This protease presents its maximum activity at pH 2 – 3.5, and this level of acidity can be achieved by including organic acids in the feed.
Due to their multiple effects at a physiologic and cellular level organic acids function as antimicrobials, modifiers of the intestinal flora, pH reducers, stimulants of pancreatic secretion and of the growth of intestinal microvilli, improvers of the gastric and intestinal flora, inhibitors of ammoniac production and of other metabolic depressors of growth, as well as energetic.
The antimicrobial organic acids are the short-chain monocarboxilic acids such as formic, acetic, propionic, butyric, sorbic and fumaric, and those that have a hydroxyl group such as lactic, malic, tartaric and citric. In the diets of pigs we use the acids that maintain 50% without dissociating at a pH between 3 and 5, because their antimicrobial effect is dependent on the pH, and it increases with the presence of non-dissociated forms, in such a way that each acid has its spectrum of antimicrobial activity. The acidity of the digestion increases the concentration of lypophilic non-dissociated forms of the organic acid, and they spread through the bacterial cell membrane where they dissociate. The result is the reduction in the pH of the cellular content, the alteration of its enzymatic system and of the nutrient transport system.
The quantity of organic acid that must be added in order to acidify the digestion depends on the blocking capacity of the food. Protein sources such as soy flour have a greater blocking capacity than cereals. Minerals, especially calcium carbonate, play an important role, so that 5% of the mineral intake in the diet blocks all the gastric acid above all in young and stressed pigs.
At the levels that are usually used we can observe improvements in the feed conversion rate:
|
Formic
|
Propionic
|
Fumaric
|
Citric
|
|
| Range of acid levels (% in feed) |
0.3 - 1.8
|
0.5 - 2.5
|
0.6 - 2.5
|
0.5 - 2.5
|
| Improvement in the conversion rate (%) | ||||
|
4
|
12
|
-
|
11
|
|
6
|
8
|
7
|
-
|
Acid salts have been commercialized with a partially neutralized acid that can be liberated in water solution. In this way the benefits of the free acids is combined with the security of the salts. The calcium citrate salts are especially interesting as they can substitute part of the diet’s calcium, they are easily digested and they do not have the undesirable blocking capacity of normal calcium sources. However, if the industry wants to supplement the diet with an antimicrobial that also functions in the intestine, that stimulates pancreatic secretions, that is active after pelleting and whose presentation is powdery, the best would be a mix of formic, acetic and propionic on a base of calcium citrate that would improve the weight increase and the feed conversion rate.
Recent experiments (A. van Dijk, 2009) recommend the combination of essential oils, such as thymol and carvacrol, with organic acids to take advantage of their synergic effects. The essential oils damage the bacterial cell wall which permits the entrance of organic acid and its bactericidal action on E. coli and Salmonella, even in intestinal conditions of neutral pH.
In conclusion, we need to find solutions that lessen the derived risks of the prohibition of antibiotic growth promoters with regard to productive performance and to the increase in subclinical infections caused by E. coli, Salmonella and Brachyspira. Organic acids are a good alternative for the development of a new concept of better balanced diets and alimentation.
