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Optimization of swine production by use of acidifiers


Weaning exposes piglets to nutritional, environmental and social stress that usually results in a postweaning lag phase manifested by slow growth and scouring. This postweaning lag is a complex phenomenon and evidence suggests that it may be related in part to a limited capacity to maintain proper gastric pH (Cranwell and Moughan, 1989; Ravindran and Kornegay, 1993). Insufficient hydrochloric acid (HCl) secretion impairs the enzyme inactivation and together with the stress of weaning and sudden change in feed consistency, may also disturb the balance of intestinal flora and allow the proliferation of coliforms resulting in scours and poor performance. The failure to maintain a low gastric pH has major implications for the performance of early weaned pigs. Dietary supplementation with acidifiers showed to decrease the occurrence of pathogenic bacteria in the gastrointestinal (GI) tract thus improving animals' growth performance and health status. Additionally dietary acidification with organic acids has been shown to contribute to environmental hygiene preventing feed raw materials, compound feed and water from bacterial and fungal deterioration and reducing the transmission of disease to animal and human populations.

The extent to which acidifiers affect production performance of animal depends on the type and inclusion level of acid, as well as diet and animal factors. Various studies have been carried out to determine the efficacy of organic acids on performance in weaned pigs (Giesting and Easter, 1991; Ravindran and Kornegay, 1993; Partanen and Mroz, 1999). It was confirmed that individual organic acids are effective growth promoters, however, their efficacy might be improved by blending them together. In the present study performance improvements through supplementation of diet with a blend of formic (FO) and propionic (PR) acids were determined in weaned pigs.

Materials and methods

Sixty weaned pigs were randomly allocated into two groups with 5 replicates in each group and 6 piglets in each replicate according to genetics, sex and body weight (BW) (7.58±0.15). The piglets were kept in the cages, equipped with feeders and nipple drinkers. Feed and water was provided ad libitum. The basal diet was calculated to reach nutrient requirements for piglets 5 to 10 kg BW (NRC, 1998). The diet composition and nutrient analyses of the diets is shown in Table 1. The basal diet of control group contained no acidifier, whereas the basal diet of the trial group was supplemented with a blend of FO and PR acids (Biotronic® SE, BIOMIN, Austria) at inclusion level of 4 kg per ton of feed. The animals were weighed at the beginning and at the end of the trial. The trial was carried out in a period of 30 days. Feed intake (FI) was recorded daily.

At the end of the trial six piglets from each group were slaughtered by electrocutation followed by exsanguinations. The viscera were exposed via a midline incision and stomach, duodenum, jejunum, ileum, colon were aseptically isolated, double ligated and removed. The content of stomach and different intestinal compartments was collected and kept at -20 °C. The contents of stomach and duodenum were pooled and the activity of digestive enzymes pepsin, amylase and lipase were measured. Enzyme activity was measured by diluting the stomach and duodenum chyme with deionized water within ratio 1:5 w/v and centrifuged at 10 000 RPM for 10 min. The pepsin activity in the supernatant was determined by a detection kit (Nanjing Jiancheng Bioengineering Institute). Amylase activity was determined by the method of Rick and Stegbauer (1974). Lipase content was determined titrimetrically by the method of Erlanson-Albertsson et al. (1987).

The pH was determined in the diets and digesta of the control and trial group. The pH of the diet was measured according to the Radecki (1988) method. The 20 g of the diet was taken and diluted with 40 ml of deionized water. The mixture was blended for 10 min and afterwards the pH was measured (pH-meter 537, WTW, Germany). The digesta pH was measured according to Burnell (1998). Digesta were mixed with deionized water in the ratio 1:8 w/v and blended for 5 min prior to pH measurement (pH-meter 537, WTW, Germany).

Table 1. The composition of the experimental diets?.

Normal Physiologic Discharge Control Diet Trial Diet
Corn 56.80 56.80
Soybean meal 14.00 14.00
Expended soybean 6.00 6.00
Soy protein concentrate 4.00 4.00
Wheat middling 2.00 2.00
Corn protein powder 3.00 3.00
Fish meal 3.00 3.00
Whey powder 3.00 3.00
Glucose 2.00 2.00
Soybean oil 1.20 1.20
DL-Methionine 0.05 0.05
L-Lysine-HCl 0.25 0.25
Choline 0.16 0.16
Dicalcium phosphate 1.20 1.20
Limestone 1.00 1.00
NaCl 0.30 0.30
Premix* 1.00 1.00
Sweetener 0.10 0.10
Zeolite Powder 0.94 0.54
Acidifier - 0.40
Total 100 100

*Premix contains per kg: vitamin A, 10350 IU; vitamin D3, 2300 IU; vitamin E, 23 IU; vitamin K3, 2.3 mg; vitamin B1, 1.15 mg; vitamin B2, 6.9 mg; vitamin B6, 0.46 mg; vitamin B12, 29 ?g; pantothetic acid, 115 mg; niacinamide, 23 mg; biotin, 23 ?g; folacin, 0.46 mg; choline, 800 mg; aureomycin, 75 mg; Fe, 150 mg; Cu, 250 mg; Zn, 150 mg; Mn, 40 mg; I, 1 mg; Se, 0.35 mg. ?Calculated nutrient composition of the diet: DE, 3.36 Mcal/kg; crude protein, 20.34%; Ca, 0.88%; total P, 0.64%; available P, 0.46%; Lysine, 1.19%; Methionine, 0.41%; Threonine, 0.81%.

Acid binding capacity of the diet was measured according to Bolduan et al. (1988). The 100 g air-dry diet was mixed with 200 ml of deionized water, heated in a thermostatic water bath up to 37 °C and blended with a magnetic stirrer. The initial pH value of the feed slurry was determined (pH-meter 537, WTW, Germany) and then the feed slurry was titrated with 1M HCl acid to pH 4.0. The acid binding capacity was represented as the amount of 1M HCl acid (ml) needed to reach pH value 4.0.

The data were analyzed using one way analyses of variance program of Statistica 7.0. The Student t-test was used to determine the effect of the diet between two different groups. The data are expressed as means±standard deviation.

Results and discussion

Generally performance response to organic acid supplementation is more pronounced in piglets than in fattening pigs due to immature digestive physiology of the younger animal (Metzler and Mosenthin, 2007). In the present study the dietary supplementation with the blend of FO and PR acids showed the slight improvement in growth performance compared with those in the control group. The growth performance data are shown in Table 2. The supplementation of the blend of FO and PR acids did not have significant effect on average daily weight gain (ADWG) and final BW. The FI in the trial group was numerically decreased by 3.6 percentage units compared to that of the control group (p > 0.05). The decrease in FI did not have a negative impact on ADWG, which was slightly numerically higher compared with that in the control group.

Table 2. Effect of the blend of formic and propionic acids on the growth performance.

Item Control Group Trial Group
No. animals/group n = 30 n = 30
Initial weight, kg 7.61±0.12 7.56±0.18
Final weight, kg 19.47±1.31 19.49±1.06
Feed intake, kg 19.13±1.80 18.44±1.45
Average daily weight gain, g; 395±0.04 398±0.03
Feed conversion rate 1.62±0.11 1.55±0.03

Feed conversion rate (FCR) was improved by 4.3 percentage units in the trial group compared to the control group. The available reports have shown the growth and feed efficiency improvements adding formic or propionic acids in weaned pigs' diets (Bolduan et al. 1988; Mathew et al. 1991). The improvement in growth performance correlated directly with inclusion level of the acid. In the present study the improvement in FCR might be attributed to the optimization of feed efficiency by the reduction of the pH and buffer capacity in the diets, and due to the pH decrease in GI tract, which stimulated the secretion of pepsin and pancreatic enzymes (Tables 3 and 4).

The observed differences in performance responses to dietary organic acids may also be due to differences in dietary buffer capacity (B-value). Buffer capacity is lowest in cereal and cereal by-products, intermediate or high in protein feedstuffs and very high in mineral sources (Partanen and Mroz, 1999). 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 (Jung and Bolduan, 1986; Lawlor et al. 1994; Blank et al., 1999). Lowering dietary buffering capacity, via acidification with organic acids, has been shown to inhibit luminal growth of enterotoxigenic microflora and to enhance swine performance (Ravindran and Kornegay, 1993; Gabert and Sauer, 1994). In the present study it was shown that dietary supplementation with a blend of FO and PR acids decreased the buffer capacity by 11 percentage units in the trial group compared with the control group. This is in good agreement with the study carried out by Bolduan et al. (1988) where dietary supplementation with the blend of FO and PR acids at inclusion rate of 1% reduced the weaned piglet diet by 11 percentage units.

Table 3. Effect of the blend of formic and propionic acids on buffer capacity and pH of the diet and on pH of the intestinal content.

Item Control Group Trial Group Delta ?
No. animals/group n = 6 n = 6  
Buffer value 33.1 29.4 3.70
pH 5.63 5.58 0.05
Chyme samples
Stomach 4.02±0.59 3.56±0.85 0.46
Duodenum 5.87±0.94 5.42±0.47 0.45
Jejunum 6.42±0.36 6.23±0.30 0.19
Ileum 7.04±0.26 6.87±0.33 0.17
Colon 6.38±0.33 6.36±0.36 0.06

Various studies have reported pH levels of swine diets ranging from 4.36 to 5.79 (Kluge et al., 2006; Partanen et al. 2007; Mroz, 2008), which is in a good agreement with the pH values determined in the present study. Due to acidification of the diet the pH value was decreased by 0.05 pH units in the trial group. The decrease in the pH value in weaned pigs' diets supplemented by various organic acids and their salts was determined in the studies by Bolduan et al. (1988), Blank et al. (1999), Partanen et al. (2007).

Dietary acidification is important to create unfavorable conditions for microorganisms and for reduction of pH and stimulation of GI tract enzymes. In the present study the lowest pH was determined in the stomach, followed by the duodenum, jejunum, colon and ileum. The dietary supplementation with the blend of FO and PR acids decreased the pH value from 4.02 to 3.56 in the stomach (p > 0.05). Due to the diet acidification the pH values were decreased in the duodenum, jejunum, ileum and colon ranging from 0.02 to 0.46 pH units difference (p > 0.05). The smallest decrease in pH value in the trial group was noticed in the colon compared to the control group. On average the decrease in pH values supplemented with different organic acids in the stomach by 0.34, in the jejunum by 0.21, in the ileum by 0.09 and cecum by 0.19 pH units was reported in various studies (Risley et al., 1992; Kim et al., 2005). Only few studies documented that dietary acidification significantly decreased GI tract pH, whereas most of the studies have failed to show any significant effect despite large numerical decrease in pH. High variations in the GI tract pH measurements indicate that it is difficult to obtain the representative sample, as the proportion of feed and endogenous excretions can vary from sample to sample (Partanen and Mroz, 1999).

According to the other studies carried out in weaned pigs the reduction of pH in GI tract lead to decrease in pathogenic bacteria counts along the GI tract, decreasing scouring of piglets (Bolduan et al., 1988, Mathew et al., 1991). It has been shown that acidic 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. In the present study the counts of E. coli was not determined, however it might be assumed that the number of pathogenic bacteria was decreased in the GI tract of the trial group compared to the control group.

It is known, that 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. In the present study it was shown that the dietary supplementation with the blend of FO and PR acids stimulated secretion of pepsin, amylase and lipase by 57, 18 and 32 percentage units, respectively, compared to the control (Table 4).

Table 4. Effect of the blend of formic and propionic acids on the enzyme activity in the intestinal tract.

Item Control Group Trial Group
No. animals/group n = 6 n = 6
Pepsin (IU*/ml) 1660.4±520.7 2608±173.9
Amylase (IU /ml) 10.3±7.18 12.2±16.29
Lipase (IU /ml) 15.5±5.32 20.5±12.11

*International Units per ml.

The highest difference in enzymes content was for pepsin, which might be related to optimum pH needed for this enzyme activation. Inactive form of pepsin, pepsinogen, is rapidly activated at pH 2, but very slow at pH 4, and it remains inactive at pH 6 (Kidder and Manners, 1978). Moreover, the end products of pepsin digestion and the low pH of digesta entering the duodenum are involved in the stimulation of pancreatic secretion (Partanen and Mroz, 1999). It might be assumed that due to the higher induced secretion of pancreatic enzymes, the digestibility of nutrients might be improved leading to better FCR. This is in a good agreement with studies carried on weaned piglets with various organic acids, where the dry matter, nitrogen and amino acids digestibility were improved (Kirchgessner and Roth, 1982; Mosenthin et al., 1992).


The data of the present study showed that dietary supplementation with the blend of formic and propionic acids enhanced growth performance by optimizing feed efficiency in weaned pigs. Due to acidification the pH value in the diet and GI tract, and buffer capacity in the diet were reduced leading to improved enzyme activity and improved nutrient utilization.


The dietary acidifiers maintaining sufficient low gastric pH at weaning could be a key to the successful rearing of piglets. The extent to which organic acids affect growth performance and digestibility depends on the type and inclusion level of the acid used, as well as on diet and animal factor. The organic acid effect is more pronounced in younger animals, as well as in the diets high in cereal feedstuffs and low in high-protein feedstuffs. Moreover, the potential of acidification in protecting weaned pigs against enteropathogenic bacteria has the research support. Additional research is needed to determine the effect among individual organic acids and the mode of action of their blends on reduction of pH, buffer capacity and enhancement of growth performance.


Bolduan G et al. 1988. J Anim Physiol Anim Nutr. 59: 72-79.
Partanen K and Mroz Z. 1999. Nutr Res Rev. 12: 117-145.
Ravindran V and Kornegay ET. 1993. J Sc Food Agric. 62: 313-322.
Risley CR et al. 1992. J Anim Sci. 70: 196-206.

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