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Department of Animal Science and Interdepartmental Nutrition Program, North Carolina State University, Raleigh 27695
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Abstract |
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 Top Abstract INTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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Key Words: ammonium formate • formic acid • growth performance • pig
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INTRODUCTION |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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). Although they are effective in promoting health and productivity, a current focus in animal agriculture is to reduce use of antibiotic growth-promoting compounds. Weaning is a time of nutritional and environmental stress. Inclusion of dietary organic acids as an alternative to antibiotic addition was evaluated in several studies using weaned pigs and in growing and finishing swine. In general, inclusion of organic acids increased ADG, ADFI, and improved the efficiency of gain (Partanen and Mroz, 1999; Partanen, 2001).
In current production systems, the typical weaning age of pigs is around 3 wk of age. The acid and pepsin secretory capacity of the stomach is still developing at this age. Provision of creep feed during the suckling period and weaning to dry diets were both associated with increased stomach weight relative to BW. During the period from 3 to 5 wk of age, acid secretory capacity increased, in association with increased stomach weight, whereas pepsin secretion increased per unit of stomach weight in pigs (Cranwell, 1985).
The objective of this experiment was to determine the effective dose of formic acid-ammonium formate in feed for enhancing growth performance of pigs fed diets currently used in production systems. Formic acid-ammonium formate was tested in pigs receiving the treated diets throughout the nursery and grower-finisher periods and also in pigs fed the control diet during the nursery phases and then fed the treated diets during the grower-finisher phases. Because the postweaning period is a time of elevated stress, and gastric secretion in weaned pigs is still developing, a higher inclusion rate of formic acid-ammonium formate was used during the nursery phases than during the grower-finisher phases.
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MATERIALS AND METHODS |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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A randomized complete block design was used. A total of 224 pigs were included in the experiment. The experiment was conducted in 2 groups separated by 28 d. Each group had 112 pigs (56 gilts and 56 barrows). All pigs used in the experiment were crossbred pigs from litters farrowed at the NCSU Swine Educational Unit. The boars were Duroc x Hampshire crossbreds, and females were Landrace x Yorkshire crossbreds. Pigs were weaned at approximately 3 wk of age (21 ± 2 d old) and weighed. Electronic data were sorted by sex, and pig weights within sex were ranked from high to low. Within each sex, 2 BW blocks (28 pigs per BW block, 4 pigs per pen) were assigned using the criteria that the initial BW for each block should be within the range of the average BW for the block plus or minus 5% or less.
There were 7 pens per sex-weight block, which corresponded to the 7 treatments. Within each sex-weight block, littermates were balanced across treatments. For each sex-weight block, the 7 pens were contiguous on 1 side of a nursery room. Treatments were assigned randomly to pens, with 8 pens total per treatment.
Animal Management and Housing
The study was conducted in 4 nursery rooms and in the south finishing barn at the NCSU Swine Educational Unit. The nursery rooms had overhead fluorescent lighting on a 14L:10D cycle and were heated with a forced-air gas heater and ventilated with a negative pressure ventilation system. Each pen had a 2-holed, stainless steel feeder, 2 nipple waterers, and triangular steel flooring (Tri-Bar, Nooyen Manufacturing Inc., Mt. Sterling, KY). The nursery pen size was 1.52 x 1.83 m.
The finishing barn was curtain-sided to provide natural ventilation. The building used natural lighting conditions. There were also overhead incandescent lights and supplemental kerosene heaters that were used as needed. The barn had fans plus misters for cooling. Each pen had a 2-holed stainless steel feeder, 2 adjustable nipple waterers, and a concrete slatted floor. The pen size was 1.83 x 2.44 m.
Pigs were observed daily, and a fecal score was assigned for each pig. A fecal score of 1 indicated normal, solid feces; a score of 2 indicated soft feces; and a score of 3 indicated liquid diarrhea.
Feed and Treatments
There were 6 diet formulation phases or periods throughout the experiment. The initial nursery diet (NR1) was fed from d 1 to 13, and a second nursery diet (NR2) was fed from d 14 to 35 of the experiment (Table 1). Pigs were moved to the finishing barn at the end of the nursery period, and a grower 1 diet (GR1) was fed during wk 6 to 9, a grower 2 diet (GR2) was fed during wk 10 to 13, a finisher 1 diet (F1) was fed during wk 14 to 17, and a finisher 2 diet (F2) for the remainder of the study.
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The 7 treatments (Table 2) included either formic acid-ammonium formate only, formic acid-ammonium formate plus water, or water only, such that the total weight added was 1.2% of the mixed diet for the nursery diets (NR1 and NR2). For the grower and finisher diets, the total weight added was 1.0%. A feed sample was taken from all batches of feed during the bagging process. Every other bag was sampled to produce a composite sample for each batch.
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Feed Analysis
Feed samples were prepared for analysis by mixing well and using a riffle divider to partition the feed sample from each batch of a given treatment into a small, homogenous subsample. The subsamples for all batches of a treatment diet for a given diet phase were combined on an equal weight basis to produce a single mixed sample.
For analysis of formate concentration and pH, a 10.0-g sample of feed was added to a 600-mL beaker. Distilled deionized water was added to a final weight of 300.0 g. The solution was homogenized using a polytron homogenizer. Beakers containing samples were covered with parafilm and placed in the freezer at –20°C for 30 min. Beakers were removed from the freezer, the solution was stirred, and a subsample was taken for centrifugation. Samples were centrifuged at 20,900 x g for 1 h at 4°C. The supernatant fraction was removed to a separate tube. The supernatant fraction was diluted, and the pH was adjusted before analysis of formate concentration using a kit (Boehringer Mannheim, Darmstadt, Germany). Standard samples of both formate and the formic acid-ammonium formate product were included with each set of feed samples that was analyzed. The formate concentration measured was converted to formic acid-ammonium formate concentration in the feed. The pH of the homogenate was determined using a pH meter (Accumet, Fisher Scientific, Atlanta, GA) after removal of the subsample for centrifugation.
Statistical Analysis
The data were analyzed as a randomized complete block design using the MIXED procedure (SAS Inst. Inc., Cary, NC). Pen was the experimental unit. The model used was:
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where Yijklm = the ith pig in the jth block in the kth start group in the lth treatment in the mth sex; µ = the overall mean; Sk = the effect of the kth start group; B(S
)jkm = the effect of the jth block in the mth sex in the kth start group; 
l = the effect of the lth dietary level of formic acid-ammonium formate; m = the effect of the mth sex; ()lm = the effect of the interaction of the lth treatment with the mth sex; Skl = the effect of the interaction of the kth group with the lth treatment; Skm = the effect of the interaction of the kth group with the mth sex; Sklm = the effect of the interaction of the kth group with the lth treatment and the mth sex; and 
ijklm = the residual error. The Sk, B(S)jkm, Skl, Skm, Sklm, and ijklm were random effects.
The Kenward-Roger approximation method (Kenward and Roger, 1997) was used to calculate the denominator df and to identify the appropriate error terms for testing the significance of the treatment effects. Planned contrasts were done regardless of the significance of the overall treatment effect. Pen data were analyzed separately for each phase of the experiment. Contrasts in the nursery phases were as follows: C1, control treatments compared with those containing formic acid-ammonium formate; C2, linear response to inclusion of formic acid-ammonium formate; and C3, quadratic response to inclusion of formic acid-ammonium formate. Contrasts in the grower-finisher periods were as follows: C4, control treatment compared with those containing formic acid-ammonium formate; C5, response for treatments including formic acid-ammonium formate in the nursery and grower-finisher compared with treatments that included formic acid-ammonium formate in the grower-finisher periods only; C6, linear response to inclusion of formic acid-ammonium formate; C7, contrast to evaluate whether the linear response to formic acid-ammonium formate differed between pigs supplied with formic acid-ammonium formate in the nursery and grower-finisher periods or grower-finisher periods only; C8, quadratic response to inclusion of formic acid-ammonium formate; C9, contrast to evaluate whether the quadratic response to formic acid-ammonium formate differed between pigs supplied with formic acid-ammonium formate in the nursery and grower-finisher periods or grower-finisher periods only.
Pen data were also analyzed for the nursery phases combined, the grower-finisher phases combined, and for all phases of the experiment combined from the NR1 through the F2 phase. For the combined nursery-grower-finisher phases, the contrasts were as described above for the grower-finisher phases.
Effects were considered significant at P < 0.05. Probability values that were greater than 0.05 and less than 0.10 are listed in the tables and discussed as trends.
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RESULTS |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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Fecal scores were used to highlight major changes in gastrointestinal function that could be related to treatment. Throughout the experiment, fecal scores were relatively consistent across treatments. In most cases, they fluctuated from a score of 1 (normal, solid) to 2 (soft). Observation of a fecal score of 3 (liquid, diarrhea) was uncommon and sporadic (data not shown).
Feed Analysis
Average recoveries of formic acid-ammonium formate added to the feed, based on measured concentration, were approximately 95% or greater for most of the feed that was mixed (Tables 3 and 4). The measured pH of diets decreased as the percentage of added formic acid-ammonium formate increased. In the nursery diets, the lowest inclusion rate of formic acid-ammonium formate (0.8%) resulted in a decrease in feed pH of approximately 1 pH unit. In the grower and finisher diets, the lowest inclusion rate of formic acid-ammonium formate (0.6%) resulted in a decrease in feed pH of approximately 0.8 pH units. This was a greater pH decline than reported in a study in which 1.8% K-diformate was added (Paulicks et al., 2000).
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). During the GR2 period, pigs fed treatments containing formic acid-ammonium formate in nursery diets (TRT 2, TRT 4, and TRT 6) gained at a greater rate (P = 0.02) than pigs fed diets containing formic acid-ammonium formate in the grower-finisher periods only (TRT 3, TRT 5, and TRT 7). The linear response to level of formic acid-ammonium formate differed (P = 0.004) between pigs supplied with formic acid-ammonium formate in the nursery and grower finisher periods or grower-finisher periods only. Gain decreased as dose increased for pigs that had received formic acid-ammonium formate in the nursery, whereas gain increased with increasing dose for pigs that had not received formic acid-ammonium formate in the nursery periods. There was no effect of formic acid-ammonium formate on ADG during the F1 or F2 phases.
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) tended to decrease (P = 0.07) for pigs fed formic acid-ammonium formate treatments in the NR1 period and decreased (P < 0.05) for pigs fed formic acid-ammonium formate during the NR2, GR1 and GR2 periods compared with pigs fed control in each period. Intake tended (P = 0.10) to decrease as dose increased for pigs that had received formic acid-ammonium formate in the nursery, whereas intake tended to increase with increasing dose for pigs that had not received formic acid-ammonium formate in the nursery periods. There was no effect of formic acid-ammonium formate inclusion on feed intake in the finisher periods.
The G:F (Table 5) was not affected by formic acid-ammonium formate in the nursery or F1 periods. During the GR1 period, there was a trend (P = 0.10) toward improved G:F for pigs fed treatments containing formic acid-ammonium formate compared with pigs fed control (TRT 1). During the GR2 period, G:F increased (P = 0.01) for pigs fed treatments containing formic acid-ammonium formate compared with pigs fed control. The response was greater (P = 0.03) for pigs that had been fed ammonium formate-formic acid during the nursery periods (TRT 2, TRT 4, and TRT 6). During the F2 period, there was a trend (P = 0.08) for the quadratic response to inclusion of formic acid-ammonium formate to differ depending on whether pigs were fed the formic acid-ammonium formate during the nursery periods. Pigs fed the intermediate dose of formic acid-ammonium formate in both the nursery and grower-finisher periods (TRT 4, 1.0 and 0.8%) tended to have the greatest G:F, whereas pigs that were fed treatments containing formic acid-ammonium formate in the grower-finisher periods only tended to have greater response to both the low (TRT 7, 0.0 and 0.6%) and high (TRT 3, 0.0 and 1.0%) dose compared with the intermediate dose.
Data were then combined for both nursery periods and grower-finisher periods (Table 6). In the nursery, there was no effect of formic acid-ammonium formate on ADG. Pigs fed diets containing formic acid-ammonium formate ate less feed (P = 0.04) and had improved G:F (P = 0.04) compared with pigs fed the control treatments (TRT 1, TRT 3, TRT 5, TRT 7). On average, G:F was improved 1.9% for pigs on diets containing formic acid-ammonium formate. Combining the grower and finisher periods, the linear response to dose differed (P = 0.04) for pigs fed the formic acid-ammonium formate in the nursery and those that were not fed the supplement. Pigs fed formic acid-ammonium formate in the nursery (TRT 2, TRT 4, TRT 6) had the greatest gain on the lowest dose, whereas pigs fed formic acid-ammonium formate in the grower-finisher only had the greatest gain on the highest dose level. The only treatment not receiving formic acid-ammonium formate in the nursery with a mean value greater numerically than that of the control (TRT 1) was the highest dose level (TRT 3, 0.0 and 1.0%). Average daily feed intake was not affected by treatment during grower-finisher periods; however, G:F for pigs fed diets containing formic acid-ammonium formate was greater (P = 0.05) than for pigs fed the control feed (TRT 1). The efficiency of gain was improved 3.5% for pigs fed all formic acid-ammonium formate treatments, ranging from 2.3 (TRT 7) to 5.9% (TRT 4), compared with pigs fed control (TRT 1).
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), there was a difference (P = 0.03) in the linear response of ADG to dose between pigs fed formic acid-ammonium formate in the nursery and those that did not receive the supplement similar to that observed for the combined grower-finisher periods. The only treatment not receiving formic acid-ammonium formate in the nursery with a mean value greater numerically than that of the control (TRT 1) was the highest dose level (TRT 3, 0.0 and 1.0%), whereas the only treatment that did receive formic acid-ammonium formate in the nursery with a mean value greater numerically than that of the control (TRT 1) was the lowest dose level (TRT 6, 0.8 and 0.6%). There was no effect of formic acid-ammonium formate inclusion on ADFI. The G:F tended (P = 0.08) to be greater for pigs fed formic acid-ammonium formate compared with pigs fed control (TRT 1). There was a tendency for a 3.0% improvement in G:F for pigs fed all formic acid-ammonium formate treatments, ranging from 1.8 (TRT 7) to 5.2% (TRT 4), compared with pigs fed control (TRT 1). Sex effects were also present throughout the study. Overall, barrows gained at a faster rate (P < 0.001) and consumed more feed (P < 0.005) than gilts. The G:F was not different for barrows and gilts. Sex x treatment interactions were present for the overall experiment for ADG and ADFI but not G:F. Where present, the interactions were not consistent across dose level or variable (data not shown).
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DISCUSSION |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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). Each acid has unique properties, including its pKa, and therefore, results cannot be generalized from one acid to another. In addition, differing salts of formate also affect animal response. Overland et al. (2000) reported that K-diformate was more effective to improve ADG and feed conversion efficiency than Na-Ca-formate. The K-diformate provided both formate and formic acid, whereas the Na-Ca-formate provided formate only. Thus, K-diformate would have greater potential antimicrobial activity.
Previous studies using formic acid or formates have shown positive trends in performance variables. Using a meta-analysis approach to combine results from several studies in which formic acid-formates were used showed that addition of formates improved ADG and feed conversion efficiency in weaned pigs with inclusion rates from 46 to 444 mEq of formate per kilogram of diet and in fattening pigs with inclusion rates from 77 to 231 mEq of formate per kilogram of diet (Partanen and Mroz, 1999; Partanen, 2001). Feed intake was also greater on the acidified diets in weaned pigs (Partanen, 2001). Inclusion rates in the current experiment were from 154 to 232 mEq of formate per kilogram of diet in the nursery phase and from 116 to 193 mEq/kg of diet in the grower-finisher phases. These levels are within the range evaluated by Partanen and Mroz (1999).
Justifications for the greater dose of formic acid-ammonium formate in the nursery phase included the possibility of insufficient secretion of HCl within the stomach; stress from weaning, changing diets, and regrouping; use of feed ingredients (such as plant or animal protein meals and minerals), which are high in acid-binding capacity; and lower feed intake compared with that of grower-finisher pigs. Despite the greater inclusion rate in the nursery phase, there was no increase in gain in response to formic acid-ammonium formate in the current study. However, feed intake decreased (P = 0.04) and G:F was improved (P = 0.04) in pigs fed the formic acid-ammonium formate-treated feed in the combined nursery periods compared with those fed the control feed. Lack of a response on ADG was observed also in a 4-wk nursery study in which K-diformate was used (Canibe et al., 2001) and a 5-wk study with formic acid (Baustad, 1993).
Pigs receiving diets containing formic acid-ammonium formate in the nursery and grower phases consumed less feed or tended to consume less feed in each phase than animals fed the control diet. This is in contrast to results of analysis of previous studies in pigs (Partanen, 2001), in which feed intake was greater on acidified diets. Pigs given a choice of diets showed no preference for an unacidified diet vs. a diet acidified with 1.2 or 2.4% K-diformate. In a second study by Ettle et al. (2004), pigs were given a choice between an unsupplemented diet and a diet supplemented with 1.2% formic or 1.2% sorbic acid. In both cases, preference was greater for the unsupplemented than the supplemented diet. For the choice of unsupplemented or 1.2% formic acid, preference for the unsupplemented diet increased over the 6-wk experimental period. It is possible that palatability had some role in the lower feed intake of pigs fed the treated feed.
Performance response to inclusion of formic acid or formates in individual experiments was variable and increased with time on feed in some experiments. A trend for improved efficiency of gain was observed in pigs fed a diet containing formic acid (Canibe et al., 2005) or formic acid-ammonium formate (Partanen et al., 2002) when the entire grower-finisher period was included in the analysis rather than the grower period only. In contrast, improved ADG and feed conversion ratio in response to dietary formic acid (Siljander-Rasi et al., 1998) or K-diformate (Overland et al., 2000) was observed in the grower but not the finisher period. In the current study, most of the treatment effects on ADG and G:F were observed in the GR2 phase. When data were combined for the different phases (Table 6), G:F was improved for the nursery and grower-finisher phases and tended to be improved for the entire nursery-grower-finisher for pigs fed diets containing formic acid-ammonium formate compared with control feed. In the nursery phase, ADG was not improved. In the grower-finisher phases, the linear response of ADG to dose differed depending on treatment in the nursery and showed a decreasing response to formic acid-ammonium formate as dose increased for pigs that had been fed the additive in the nursery period. The treatment values for pigs in the grower-finisher phases, which received the additive in the nursery, tended to be greater values than the control treatment and suggest a benefit to inclusion during the nursery phases. Only the high dose (TRT 3) mean, for pigs not receiving the additive in the nursery, tended to be greater arithmetically than the control (TRT 1).
One of the potential confounding factors in comparing results across studies is the basal diet used in each experiment. Nursery pigs fed diets containing different grains had improved feed conversion in response to K-diformate on barley and wheat-based diets but not on corn-based diets (Paulicks et al., 2000). Many previous experiments used diets that were barley-, oat-, or wheat-based (Baustad, 1993; Siljander-Rasi et al., 1998; Partanen et al., 1998, 2002; and Canibe et al., 2001, 2005). Diets in the current experiment were corn-based.
Dietary factors, in addition to type of grain, include energy density and fiber concentration. Paulicks et al. (2000) found that ADG increased and feed conversion improved in response to K-diformate on lower-energy diets compared with diets approximately 5% greater in energy density. Improved apparent ileal digestibility of Lys, due to decreased endogenous Lys flow, was observed in growing pigs on by-product-based diets (219 g of NDF/kg of DM) but not on barley-based diets (188 g of NDF/kg of DM; Partanen et al., 1998). The differing fiber content of the diets could be a factor; however, the difference was small. A later study by Partanen et al. (2002) using high- (240 g of NDF/kg of DM) or medium-(188 g of NDF/kg of DM) fiber diets in growing-finishing pigs showed no effect of dietary fiber on performance response to additives. In this study, feed conversion ratio was improved in the growing and finishing period for pigs on formic acid-ammonium formate-treated diets.
Many mechanisms could be responsible for improved performance with formic acid or formate salts. A trend toward improved DM digestibility was observed by Franco et al. (2005) in nursery pigs fed diets containing formic acid as well as diets containing other acids. Increased apparent ileal digestibility and N retention were observed in growing-finishing pigs fed diets varying in content of organic acids, including formic (Mroz et al., 2000). Total anaerobic bacteria and lactic acid bacteria decreased along the gastrointestinal tract in weaned pigs after 7 d of feeding wheat-based diets containing K-diformate. By 28 d of treatment, total anaerobes decreased in the stomach and small intestine, whereas lactic acid bacteria and yeast decreased throughout the tract. Formic acid concentration increased in the stomach and small intestine in response to dietary inclusion. Decreased microbial populations could result in improved digestibility of feed (Canibe et al., 2001). In growing-finishing pigs, feeding a diet containing formic acid decreased total anaerobes in the proximal gastrointestinal tract and decreased lactic acid bacteria, enterobacteria, and yeasts throughout the gastrointestinal tract compared with control diets (Canibe et al., 2005). In weaned pigs, diets containing formic acid tended to reduce coliforms in the small intestine, although formic acid was more effective in conjunction with lactic acid (Franco et al., 2005). The pKa of formic acid is 3.75; thus, it will exist in the ionized form predominantly in the intestine. However, the free acid would still be available to cross the cell wall of bacterial cells, dissociate intracellularly, acidify the cell, and suppress cellular metabolism (Partanen and Mroz, 1999). Such effects may decrease coliforms or enterobacteria and result in improved animal health.
Results of the current study demonstrated that the main response to inclusion of formic acid-ammonium formate in the diet was improved G:F in conjunction with decreased feed intake in the combined nursery and grower periods. Evaluating the individual periods of the experiment, the improvement in G:F was most pronounced in the GR2 period. During the GR2 period, pigs fed treatments containing formic acid-ammonium formate in nursery diets (TRT 2, TRT 4, and TRT 6) had greater (P < 0.05) ADG and G:F than pigs fed diets containing formic acid-ammonium formate in the grower-finisher periods only (TRT 3, TRT 5, and TRT 7). In the combined grower-finisher periods, G:F was improved (P = 0.05) 3.5% for pigs fed all formic acid-ammonium formate treatments, ranging from 2.3% for pigs fed the low dose in the grower-finisher only (TRT 7) to 5.9% in pigs fed the intermediate dose in both the nursery and grower-finisher (TRT 4) compared with pigs fed control (TRT 1). For the entire study, nursery through grower-finisher, there was a tendency (P < 0.08) for a 3.0% improvement in G:F for pigs fed all formic acid-ammonium formate treatments, ranging from 1.8% for pigs fed the low dose in grower-finisher only (TRT 7) to 5.2% in pigs fed the intermediate dose throughout the trial (TRT 4) compared with pigs fed control (TRT 1).
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Footnotes |
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2 We thank G. Huntington, C. Powell, S. Beasley, C. Salmon, J. Plummer, E. Fritts, K. McCaughey, C. Fogal, K. Frick, L. Roberson, D. McLaurin, H. Settlemyre, L.Tancredi, J. Asbill, J. Hamilton, D. St. Hilaire, J. Rogerson, K. Magee, and N. Muley for their assistance in conducting the experiment and R. Condon for his assistance with the statistical analysis.
3 Corresponding author: Joan_Eisemann{at}ncsu.edu
Received for publication July 13, 2006. Accepted for publication February 18, 2007.
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LITERATURE CITED |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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