Organic Acids Yield Advantages

Organic acids and acidifiers are powerful tools that can provide one more barrier to disease transmission in large feeding installations.
By Renata Urbaityte | October 06, 2009
Prevention of disease transmission and enhancement of growth and feed efficiency are critical factors in modern animal production. When pathogenic bacteria contaminate feed, it becomes a potential route of transmission of disease to animal and human populations, and is consequently of great concern to producers and consumers. Food-producing animals (e.g., cattle, chickens, pigs, and turkeys) are the main reservoirs for many of these microorganisms, which include non-Typhi serotypes of Salmonella enterica, Campylobacter species, Shiga toxin producing strains of Escherichia coli, and Yersenia enterocolitica.

The microflora found in feed materials comes from a variety of ecological niches such as soil and the animals' gastrointestinal (GI) tract. The GI tract pathogens can be introduced into food chain by animals defecating in the farm environment or by fertilization of crops with manures, consequentially making feed a carrier for animal and human pathogens.

Feed materials may be inoculated with microorganisms, mostly bacteria and fungi, at any time during growing, harvesting, processing and storage. Counts of microorganisms vary depending on the function of materials, location of its origin and climatic conditions. It is known that microfloral growth is dependent on moisture, pH value, temperature and composition of feed materials. For example, the optimal temperature for E. coli O157:H7 is 37 degrees Celsius, with a minimum of 7-8 degrees C and a maximum of 46 degrees C. The optimal pH is between 6 and 7, however it might stand a pH range between 4.4 to 9.0. The E. coli O157:H7 doubles in number approximately every 24 minutes at the optimal temperature and pH value.

Some microorganisms including, E. coli, may adapt to conditions without water and can actively grow in stored feed. Various authors have reported that grains and oilseed crops possess a diverse microflora, with populations ranging from 5x103 to 1.6x108 colony-forming units (CFU)/g that are highly resistant to low moisture conditions.

Experimentally, very low doses of E. coli O157:H7 may result in colonization of some piglets. Once some piglets are colonized, they may amplify E. coli O157:H7 and transmit it to other piglets via contact. Enterotoxigenic E. coli strains are a major cause of diarrhea and death in neonatal and newly weaned pigs. Enterotoxigenic E. coli deliver toxins when it adheres to the small intestinal microvilli and produces enterotoxins that act locally on enterocytes. This action results in hypersecretion of water and electrolytes, and reduced absorption.

Heat treatment, usually during conditioning, pelleting or extrusion of feeds has been shown to be an effective way to reduce microbial loads in feed materials and compound feed. Reduction of the bacterial contamination by heat is dependent on the temperature and treatment time. However, these methods do not prevent a recontamination of feed materials and compound feed afterwards. Dietary acidification with organic acids has been shown to contribute to environmental hygiene preventing feed raw materials and compound feed from microbial and fungal deterioration. Moreover, constant treatment with organic acids has a residual protective effect in feed, which helps to reduce recontamination and also to reduce the contamination of milling and feeding equipment.

Supplementation of organic acids in feed tends to decrease the feed pH, buffer capacity, and to prevent undesirable microbial growth. However, for each acid, its specific inhibiting effect on bacteria, yeast and mold has to be considered when recommendations for feed supplementation are made. For example, some organic acids, such as formic and propionic have broader antimicrobial activities and can be effective against bacteria and fungi, including yeast.

Dietary acidification is important to create unfavorable conditions for microorganisms and for reduction of pH and stimulation of GI tract enzymes. Optimum pH is needed for enzyme activation, for example, pepsinogens are rapidly activated at pH 2, but very slow at pH 4. Pepsin has its optimum between pH 2 and 3.6, and remains inactive at pH 6. Due to insufficient production of HCl and pancreatic enzymes, and sudden changes in feed consistency and intake, piglets have limited digestive capacity and absorption at weaning.

Moreover, the stress associated with weaning is known to disturb the intestinal microflora. Various studies show that acidification of the diets decreased pH-value in feed and consequentially reduced the coliform and E. coli counts along the intestinal tract, decreasing scouring and mortality of piglets. It has been shown that acid conditions favor the growth of lactobacilli in the stomach, which possibly inhibits the proliferation of E. coli and produces lactic acid and other metabolites which lower the pH and inhibit E. coli The reported pH levels of the swine diets in these studies range from 4.36 to 5.79. Dietary acidification by a mixture of organic acids decreased the pH value in swine diets by 0.15 to 0.98 pH units. The decrease in pH values was dependent on the inclusion levels of organic acids, which varied from 0.5 to 3 percent, and composition of the diet. This was in agreement with a recent study, where a blend of formic and propionic acids at an inclusion level of 0.3 percent reduced the pH by 0.11 pH units in starter and grower diets. A higher inclusion level of 0.5 percent of the same acid blend reduced pH of the diet by 0.23 and 0.21 pH units in the starter and grower diets, respectively.

Another factor affecting the response of acidifiers would be the buffering capacity of the diets. By definition, the buffering capacity (B-value) is the change in the pH value of a defined volume or mass after the addition of a strong acid. A more practical definition in the feed industry is that the B-value is the amount of 1 M hydrochloric acid (HCl) solution which needs to be added to a 10 percent slurry of feed or a feed ingredient in 100 ml of water in order to obtain a pH-value of 5, in some cases a pH value of 4 or 3. This definition is the reason why we find different values for the same expression in practical applications. For example, various studies have reported B-values ranging from 380 to 700 mEq per kg feed.

Acid-buffering capacity is lowest in cereals and cereal by-products, intermediate or high in protein feedstuffs and very high in minerals. It might be reasonable to assume that the buffering capacity of pig feed can be considerably influenced by selection of feed ingredients, and it may in part result in differences in the effectiveness of acidifiers. It is recommended that swine diets should not exceed 700 mEq/kg of feed B-value.

High protein and mineral content of feed ensures rapid animal growth, but generates high buffering capacity, thus reducing levels of HCl in the stomach. Results of some studies demonstrated that high B-value of the diet increased gastric pH and resulted in decreased amino acids digestibility.

Lowering dietary buffering capacity, via acidification with organic acids, has been shown to inhibit luminal growth of enterotoxigenic microflora and to enhance swine performance. The results of one in vitro study showed that an acidifier consisting of a blend of formic and propionic acids at an inclusion level of 0.3 percent decreased B-value by 16 and 17 percent in starter and grower pig diets, respectively. Moreover, the inclusion level of 0.5 percent of the same acid blend decreased B-value by 18 and 19 percent in starter and grower pig diets, respectively. The decrease in B-value was directly related to the inclusion level of acidifier and the diet composition.

Acidifiers are powerful tools to maintain animal health and improve their performance, as well as to control feed and environmental hygiene. Consistent beneficial effects on productivity in weaned pigs have been reported in numerous scientific studies with results showing the decreased microbial counts in feed and improved animal growth performance, reduced diarrhoea, morbidity and mortality rates. Furthermore, an overwhelming portion of livestock producers consider acidifiers as an outstanding solution to enhance performance and, therefore, profitability. EP

Renata Urbaityte is technical manager for Biomin. Reach her at