Agricultural and Food Science in Finland, Vol. 11 (2002): 107–119 107 A G R I C U L T U R A L A N D F O O D S C I E N C E I N F I N L A N D Vol. 11 (2002): 107–119. © Agricultural and Food Science in Finland Manuscript received February 2002 A G R I C U L T U R A L A N D F O O D S C I E N C E I N F I N L A N D Vol. 11 (2002): 107–119. Dietary preferences of weaned piglets offered diets containing organic acids Kirsi Partanen, Hilkka Siljander-Rasi and Kaija Suomi MTT Agrifood Research Finland, Animal Production Research, Pigs, Tervamäentie 179, FIN-05840 Hyvinkää, Finland, e-mail: kirsi.partanen@mtt.fi A preference test and a performance trial were carried out to examine weaned piglets’ feed intake response to diets containing either lactic acid, formic acid, calcium formate, or sodium benzoate (8 g kg-1 feed). In Experiment 1, throughout a 21-d post-weaning period, 30 entire litters (306 piglets) weaned at the age of 30 d were allowed to choose between two organic-acid-supplemented diets. All of the four different organic-acid-supplemented diets were tested in pairs against each other, and the six possible combinations were lactic acid + formic acid, lactic acid + calcium formate, lactic acid + sodium benzoate, formic acid + calcium formate, formic acid + sodium benzoate, and calcium for- mate + sodium benzoate. Piglets preferred diets supplemented with sodium benzoate to ones supple- mented with formic acid or calcium formate. The acceptability of diets supplemented with lactic acid, formic acid, or calcium formate was similar. In Experiment 2, until the age of 58 d, 60 piglets from 10 litters weaned at the age of 28 or 38 d were fed non-acidified diets or ones supplemented with lactic acid, formic acid, calcium formate, or sodium benzoate. Feed consumption did not differ between piglets fed non-acidified and those fed organic-acid-supplemented diets. Growth perform- ance was reduced by dietary calcium formate supplementation, while the performance of piglets fed other organic-acid-supplemented diets did not differ significantly from those fed the non-acidified control diet. The frequency of post-weaning diarrhoea was highest in piglets fed diets supplemented with calcium formate and lowest in piglets fed diets supplemented with formic acid. Key words: calcium formate, diarrhoea, formic acid, lactic acid, palatability, sodium benzoate Introduction Considerable research has addressed the topic of including organic acids in diets for weaned piglets to improve their performance. In gener- al, dietary organic acids appear to improve the growth and feed-to-gain ratio of weaned piglets, but these responses can vary greatly depending on the type and amount of acid used, diet com- position, weaning age, and the animals’ health status (Ravindran and Kornegay 1993). In data consisting of 46 published performance trials, the growth response of weaned piglets to die- tary organic acids was closely associated with these acids’ influence on feed intake (r = 0.77, P mailto:kirsi.partanen@mtt.fi 108 A G R I C U L T U R A L A N D F O O D S C I E N C E I N F I N L A N D Partanen, K. et al. Weaned piglets offered diets containing organic acids < 0.001) (Partanen 2001). The feed intake of weaned piglets was enhanced by dietary formic acid and potassium diformate supplementations, whereas citric and fumaric acid supplementa- tions had no effect compared to the non-acidi- fied control diet (Partanen 2001). Other organic acids, e.g. lactic and sorbic acid, have also been reported to enhance the feed intake of weaned piglets (Roth et al. 1993, Kirchgessner et al. 1995), whereas tartaric acid, which has a strong odour and flavour, decreases feed intake com- pared to the non-acidified control diet (Kirch- gessner et al. 1993). According to Pluske et al. (1995), the level of voluntary feed intake during the immediate post-weaning period is crucial for the subsequent performance. Although the choice of organic acid appears to affect the palatability of organic-acid-supplemented diets, the prefer- ence of weaned piglets for different organic ac- ids has not been much investigated. In the study of Henry et al. (1985), piglets preferred non-acid- ified diets when they were able to choose freely between non-acidified diets and diets supple- mented with citric acid (30 g kg-1) or fumaric acid (15 g kg-1). When only a single diet was offered, piglets ate most citric-acid-supplement- ed diets. The first aim of this study was to investigate whether weaned piglets are able to differentiate or demonstrate a preference for a specific organic acid when given a free choice of two acidified weaner diets containing either lactic acid, for- mic acid, calcium formate, or sodium benzoate. The second objective was to investigate the per- formance response of weaned piglets to diets supplemented with the aforementioned organic acids. Material and methods Experiment 1 Thirty entire litters (306 piglets) were used in a choice-feeding trial to determine the relative consumption of diets containing lactic acid, for- mic acid, calcium formate, or sodium benzoate. The experiment was begun at weaning and was continued for 21 days. All of the four different acid supplements were tested in pairs against each other in order to test all six possible com- binations: 1) lactic acid + formic acid, 2) lactic acid + calcium formate, 3) lactic acid + sodium benzoate, 4) formic acid + calcium formate, 5) formic acid + sodium benzoate, and 6) calcium formate + sodium benzoate. Each combination was tested with five entire litters with a mini- mum of eight piglets at weaning. At the age of 30 days, piglets were weaned to farrowing pens, where they were housed throughout the trial. Wood shavings were used as bedding material. There was a heating lamp, which was removed when the piglets were six weeks old. When the piglets were 14 days old, two identical gravity flow feeders were placed into the pen that both provided a non-acidified basal diet ad libitum. The composition of the basal diet is presented in Table 1. At weaning, two different acidified diets were placed into the feeders depending on the combination of diets to be tested. The location of the acidified diets varied from pen to pen but was kept constant within the pen. The acidified diets were prepared by supplementing the basal diet with 8 g kg-1 of lactic acid (80–85%), formic acid (80–90%), calcium formate, or sodium benzoate. All feeds were cold pelleted (Amandus Kahl Labour- presse, 4 mm die). Feed disappearance from both feeders was determined separately on days 1, 2, 3, 4, 5, 6, 7, 9, 11, 13, 15, 18, and 21 after wean- ing. No determination of feed wastage was pos- sible. Piglets were weighed at birth, weaning, and 7 and 21 days after weaning. Experiment 2 A total of 60 weaned piglets from 10 litters were used in the trial. The litters were divided into two replicates according to the weaning age (28 or 38 days). Within these replicates, six piglets from each litter were randomly allotted to three 109 A G R I C U L T U R A L A N D F O O D S C I E N C E I N F I N L A N D Vol. 11 (2002): 107–119. pairs, and these were assigned to five dietary treatments: 1) non-acidified basal diet and diets containing 2) lactic acid, 3) formic acid, 4) cal- cium formate, or 5) sodium benzoate according to an incomplete block design (Plan 11.2; Co- chran and Cox 1957). Piglet pairs were housed in pens measuring 0.78 × 1.68 m (0.68 m2 of solid concrete floor and 0.63 m2 of plastic slatted floor) throughout the trial, which started at wean- ing and was continued until the piglets were 58 days old. Wood shavings were used as bedding material. The composition of the basal diet is present- ed in Table 1. The acidified diets were prepared by supplementing the basal diet with 8 g kg-1 of lactic acid (80–85%), formic acid (80–90%), calcium formate, or sodium benzoate. Experi- mental diets were available ad libitum from grav- ity flow feeders. Before weaning, piglets were offered the basal diet ad libitum starting from the age of 14 days. Feed disappearance was de- termined 7 days after weaning and at the age of 51 and 58 days. Piglets were weighed at birth, weaning, and at the age of 51 and 58 days. Chemical analyses Feed samples were ground to pass through a 1- mm sieve before analysis. Dry matter content was determined by drying at 103°C for 16 h. Nitrogen was determined with the Dumas meth- od using a Leco FP-428 N analyser (Leco Corp., St Joseph, USA). Dietary pH was measured in a mixture of 20 g feed and 100 ml water 15 min- utes after having been mixed with a whirl mixer for 20 sec. Dietary buffering capacity was de- termined as the amounts of 0.1 M HCl required Table 1. Ingredients and calculated composition of basal diets in Experiments 1 and 2. Experiment 1 Experiment 2 Ingredients, g kg-1 feed Barley 378.6 350.0 Wheat 400.0 343.0 Oat meal – 100.0 Soya bean meal 106.1 80.0 Low lactose whey powder (CP 250 g kg-1, lactose 380 g kg-1) 30.0 – Whey protein concentrate (CP 730 g kg-1, lactose 120 g kg-1) 76.0 Fish meal 60.0 20.0 Limestone 9.7 11.4 Monocalcium phosphate 1.6 6.9 L-Lysine HCl 1.7 – Mineral and vitamin premix1 12.4 13.0 Calculated composition Net energy, MJ kg-1 9.2 9.5 Crude protein, g kg-1 186 195 Ileal digestible lysine, g kg-1 9.3 9.7 Ileal digestible threonine, g kg-1 5.6 7.2 Ileal digestible methionine and cystine, g kg-1 5.6 6.5 Calcium, g kg-1 9.0 9.2 Phosphorus, g kg-1 5.5 5.9 CP = crude protein. 1 Ten grams of premix contained the following minerals and vitamins: 1.8 g Ca, 0.6 g P, 0.4 g Mg, 2.5 g NaCl, 79 mg Fe, 17 mg Cu, 70 mg Zn, 18 mg Mn, 0.21 mg Se, 0.17 mg I, 3980 IU vitamin A, 398 IU vitamin D 3 , 38 mg vitamin E, 1.5 mg thiamin, 3.6 mg riboflavin, 2.1 mg pyridoxine, 15 mg vitamin B 12 , 0.15 mg biotin, 11 mg pantothenic acid, 15 mg niacin, 1.5 mg folic acid, and 1.5 mg vitamin K. 110 A G R I C U L T U R A L A N D F O O D S C I E N C E I N F I N L A N D Partanen, K. et al. Weaned piglets offered diets containing organic acids to lower the pH of a mixture of 5 g feed and 50 ml water to 4 and 3. Lactic acid was analysed according to Haacker et al. (1983) and benzoic acid according to a modified method of Plasser and Klostermeyer (1988). Formic acid was meas- ured by spectrophotometry using a commercial kit and according to the manufacturer’s instruc- tions (Cat. No. 979 732, Boehringer Mannheim GmbH, Mannheim, Germany). Calculations and statistical analyses In Experiment 1, each individual test diet’s rel- ative preference (%) was calculated by dividing the feed intake in that diet (kg per piglet) by the total ingested in the two test diets (kg per pig- let) offered simultaneously in the pair combina- tion. The differences in feed intake and relative preference (the arcsin(X) value of the relative preference) between the study’s diet pairs were tested by means of a t-test (Snedecor and Co- chran 1989). The diet selection paths of each lit- ter were described by plotting the cumulative differences between the feed intakes (a–b) against the cumulative total feed intake (a + b) as described by Kyriazakis et al. (1990). Per- formance data were analysed using the GLM- procedure of SAS (SAS 1998) and the follow- ing model (Snedecor and Cochran 1989): Yij = µ + ti + εij where ti is the fixed effect of treatment i (i = 1,…6) and εij is the normally distributed error with a mean of 0 and the variance σ2. The litter was the experimental unit. In Experiment 2, feed intake and perform- ance data were analysed with the MIXED pro- cedure of SAS (SAS 1998) using REML estima- tion and the following model (Snedecor and Cochran 1989): Yijk = µ + ai + l(a)ij + tk + (a × t)ik + εijk where ai is the fixed effect of weaning age, l(a)j is the random effect of litter within wean- ing age, tk is the fixed effect of dietary treatment, (a × t)ik is the interaction between weaning age and dietary treatment, and εijk is the normally distributed error with a mean of 0 and the vari- ance σ2. To test the effect of weaning age, l(a)j was used as an error term. The pen with two pigs was the experimental unit. Organic-acid-supple- mented diets were compared to the non-acidi- fied control diet with the Dunnett test. Results and discussion The analysed chemical composition of the ex- perimental diets is shown in Table 2. Dietary formic acid supplementation resulted in the greatest decrease in dietary pH, followed by lac- tic acid and calcium formate supplementation, whereas sodium benzoate supplementation slightly increased dietary pH. Dietary lactic and formic acid supplementations resulted in simi- lar decreases in dietary buffering capacity, whereas calcium formate and sodium benzoate supplementations increased dietary buffering capacity. This is in accordance with the results of Roth and Kirchgessner (1989), who reported that dietary pH was decreased more by lactic and formic acid than calcium formate and that calci- um formate supplementation increased the die- tary buffering capacity. In Experiment 1, the average consumption of creep feed from day 14 to weaning at day 30 was small, 94 g per piglet (s.d. 96.5), but highly var- iable, ranging from 0 to 458 g per piglet. Sever- al studies have reported enormous variation in creep feed consumption before weaning. Barnett et al. (1989) found that total creep feed consump- tion varied from 13 to 194 g per piglet from day 10 to weaning at day 28, while Pajor et al. (1991) found a range in individual intake from 13 to 1911 g per piglet in the 14-day period before weaning. In this study, no correlation was found between creep feed consumption and birth or weaning weight of piglets (Table 3), which is in accordance with the results of Appleby et al. (1991). According to Pluske et al. (1995), the potential contribution of creep feed is from 1 to 111 A G R I C U L T U R A L A N D F O O D S C I E N C E I N F I N L A N D Vol. 11 (2002): 107–119. 17% of the daily energy intake of nursing pig- lets. There may be some benefit from feeding creep feed to nursing piglets, but evidence for its effect on weaning weight or post-weaning performance is limited. One reason for the equiv- ocal performance results could be the high vari- ability in creep feed consumption both among and within litters (Pajor et al. 1991). In the study of Bruininx et al. (2001b), piglets that ate creep feed during the suckling period ate more and performed better during the post-weaning peri- od than those that had consumed no creep feed. The development of feed consumption dur- ing the 21-d experimental period is shown in Figure 1. The increase in daily feed consump- tion was small (less than 30 g d-1) during the days 3 to 6 after weaning, and feed consumption did not start to increase substantially until 9 days after weaning. This plateau in the development of daily feed consumption coincided with post- weaning diarrhoea, which was observed in the majority of litters. Feed consumption during the first post-weaning week correlated positively with creep feed consumption before weaning (r = 0.62, P < 0.001), which is in accordance with the results of Appleby et al. (1991) and Brui- ninx et al. (2001b). However, when three litters in which the creep feed consumption was over 160 g per piglet were excluded from the data, no correlation was found between pre- and post- weaning feed consumption. No correlation was found between weaning weight and feed con- sumption during the first week after weaning. In the study of Bruininx et al. (2001a), piglets weaned at an average body weight of 6.7 kg had higher initial feed intakes than their counterparts weaned at an average body weight of 7.9 and 9.3 kg, but the daily increase in feed intake and total post-weaning feed consumption was simi- lar in these groups. There was a strong positive Table 2. Analysed composition, pH, and buffering capacity of basal and organic-acid-supplemented diets in Experiments 1 and 2. Diet BD L F CaF NaB Experiment 1 Dry matter, g kg-1 887 882 882 884 880 Ash, g kg-1 DM 54 54 55 57 56 Crude protein, g kg-1 DM 204 203 211 208 203 Lactic acid, g kg-1 DM – 8.33 – – – Formic acid, g kg-1 DM – – 7.41 6.11 – Benzoic acid, g kg-1 DM – – – – 7.19 pH 5.82 5.31 4.90 5.51 5.85 Buffering capacity, meq kg-1 DM pH 4 252 209 202 254 412 pH 3 545 495 493 623 642 Experiment 2 Dry matter, g kg-1 880 841 868 846 846 Ash, g kg-1 DM 51 57 57 60 63 Crude protein, g kg-1 DM 212 217 210 216 216 Lactic acid, g kg-1 DM – 8.42 – – – Formic acid, g kg-1 DM – – 7.50 5.40 – Benzoic acid, g kg-1 DM – – – – 8.13 pH 5.48 5.14 4.89 5.32 5.53 Buffering capacity, meq kg-1 DM pH 4 166 80 84 144 154 pH 3 331 254 293 361 287 BD = basal diet, L = lactic acid, F = formic acid, CaF = calcium formate, NaB = sodium benzoate, DM = dry matter. 112 A G R I C U L T U R A L A N D F O O D S C I E N C E I N F I N L A N D Partanen, K. et al. Weaned piglets offered diets containing organic acids correlation between feed consumption and weight gain during the first post-weaning week and during the whole experiment (Table 3). Pig- lets that learn to eat immediately after weaning and gain weight during the first post-weaning week perform better during the subsequent peri- ods, which translates to a several day lead in reaching slaughter weight (Pluske et al. 1995). It can take quite a long time before piglets start to eat after weaning. In the study of Bruininx et al. (2001a), 47% of piglets had not started to eat during the first 4 h after weaning, and 11% of piglets had not consumed any feed yet even 28 h after weaning. No significant differences were found in the performance results of piglets given a choice of different organic-acid-supplemented diets (Ta- ble 4). In general, the average growth rate re- mained relatively low, less than 300 g d-1. This probably resulted from the high incidence of post-weaning diarrhoea; 21 out of 30 litters were medicated for post-weaning diarrhoea, which lasted on average for 6 days. There was no dif- ference between the treatments in the incidence of post-weaning diarrhoea. The total consump- tion and relative preferences of the organic-acid- supplemented diets offered in free-choice set- tings are presented in Table 5. The consumption of feeds or their relative preferences did not dif- fer between feeders in any of the experimental treatments or in the whole trial (P > 0.05, results not shown). No significant differences were ob- served in total consumption or relative prefer- ences between diets supplemented with lactic acid and formic acid, lactic acid and calcium formate, lactic acid and sodium benzoate, and formic acid and calcium formate. Piglets offered diets supplemented with formic acid and sodi- um benzoate or calcium formate and sodium benzoate preferred diets with sodium benzoate to those with formic acid (P < 0.10) or calcium formate (P < 0.05). Table 3. Correlations among variables based on litter means (n = 30 litters). Pre-weaning Birth feed Pre-weaning Weaning First week after weaning weight intake weight gain weight Feed intake Weight gain Pre-weaning feed intake –0.01 Pre-weaning weight gain 0.23 0.08 Weaning weight 0.43* 0.08 0.97*** First week after weaning Feed intake 0.20 0.62*** –0.23 –0.17 Weight gain 0.09 0.39* –0.30 –0.26 0.85*** Whole post-weaning period Feed intake 0.40* 0.43* –0.04 0.06 0.81*** 0.63*** Weight gain 0.32 0.36* –0.17 –0.10 0.79*** 0.87*** Significance: * (P < 0.05) and *** (P < 0.001). Fig. 1. Daily feed consumption of weaned piglets during the 21-d post-weaning period based on the means of the 30 litters used in Experiment 1. 113 A G R I C U L T U R A L A N D F O O D S C I E N C E I N F I N L A N D Vol. 11 (2002): 107–119. Diet selection paths of individual litters (Fig. 2) show that when piglets were offered diets sup- plemented with lactic acid or formic acid, none of the litters developed a preference for either of the diets, and the cumulative difference was less than 2 kg of feed by the end of the trial. When diets supplemented with either lactic acid or calcium formate were offered, two litters out of five seemed to develop a slight preference for the lactic acid (cumulative difference over 2 kg). When diets supplemented with either lactic acid or sodium benzoate were tested, one litter had a Table 4. Performance and feed consumption of weaning piglets offered organic-acid-supplemented diets in a free-choice setting in Experiment 1. Free choice L / F L / CaF L / NaB F / CaF F / NaB CaF / NaB Treatment1 1 2 3 4 5 6 SEM2 Piglets per litter At weaning 10.0 9.8 10.2 10.2 10.0 11.0 7 d after weaning 10.0 9.6 10.2 10.0 9.8 10.6 21 d after weaning 9.8 9.4 10.0 9.8 9.4 10.6 Weight, kg At weaning 9.2 8.7 8.4 8.3 8.9 8.7 0.47 7 d after weaning 10.0 9.0 9.1 9.1 9.7 9.9 0.48 21 d after weaning 15.0 13.8 13.8 14.1 15.0 14.8 0.72 Weight gain, g d-1 0–7 d after weaning 121 41 105 116 114 171 46.3 0–21 d after weaning 278 246 258 276 291 291 29.0 Feed consumption, g d-1 0–7 d after weaning 253 191 235 265 206 261 40.1 0–21 d after weaning 513 473 513 560 496 514 31.1 Kg feed per kg gain 0–21 d after weaning 1.87 2.02 2.06 2.04 1.71 1.77 0.158 L = lactic acid, F = formic acid, CaF = calcium formate, NaB = sodium benzoate, SEM = standard error of the mean. 1 Five entire litters per treatment. 2 F-test for treatment effects was not significant (P > 0.05). Table 5. Consumption and relative preference of the experimental diets offered in a free-choice setting to weaned piglets during 21-d post-weaning period in Experiment 1. Free Feed consumption Relative preference choice kg/piglet % Treatment1 a / b a b t Signif.2 a b s.d. t Signif.2 1 L / F 5.62 ± 1.24 5.62 ± 1.04 0.660 52.3 47.7 7.9 0.655 2 L / CaF 5.37 ± 1.38 4.50 ± 1.42 0.915 55.6 44.4 14.5 0.868 3 L / NaB 5.03 ± 2.71 5.70 ± 3.30 0.256 48.0 52.0 29.5 0.129 4 F / CaF 5.44 ± 2.51 6.03 ± 2.74 0.266 47.6 52.4 24.3 0.225 5 F / NaB 3.22 ± 1.48 6.69 ± 1.91 2.635 o 32.6 67.4 15.7 2.455 o 6 CaF / NaB 2.73 ± 1.42 7.67 ± 2.44 3.161 * 27.0 73.0 15.5 3.300 * L = lactic acid, F = formic acid, CaF = calcium formate, NaB = sodium benzoate. 1 Five entire litters per treatment. 2 t 0.10(4) = 2.132, and t 0.05(4) = 2.776. Significance: o (P < 0.10) and * (P < 0.05). 114 A G R I C U L T U R A L A N D F O O D S C I E N C E I N F I N L A N D Partanen, K. et al. Weaned piglets offered diets containing organic acids strong preference for the former, and three lit- ters for the sodium benzoate. Diets supplement- ed with formic acid or calcium formate were equally acceptable for two litters, while the former diet was preferred by two litters, and the latter by one. When the diet supplemented with sodium benzoate was offered together with di- ets supplemented with formic acid or calcium formate, three and four litters, respectively, out of five developed a strong preference for the sodium benzoate supplemented diet. Previous studies have shown that weaned piglets are able to discriminate between differ- ent cereals and protein sources as well as diets of different lysine content (Ermer et al. 1994, Bruneau and Chavez 1995, Kirchgessner et al. 1999). In our study, weaned piglets preferred sodium benzoate to formic acid and calcium for- mate, which indicates that weaned piglets are able to differentiate between diets supplement- ed with different organic acids. This is not sur- prising since the pig tongue is known to possess a large number of taste buds, three to four times more than the human tongue (Chamorro et al. 1993, Danilova et al. 1999). Among the various taste stimuli tested in the study of Danilova et al. (1999), citric acid elicited the largest response in the chorda tympani proper nerve, which con- veys the information from the fungiform taste buds. This indicates that citric acid creates a dis- tinct taste quality in pigs. In the study of Henry et al. (1985), piglets preferred non-acidified diets to those supplemented with citric or for- mic acid, but no difference was observed in the palatability of the organic-acid-supplemented di- ets. Of the investigated acids, formic acid has a strong pungent odour, while its calcium salt is odourless or has a sweet caramel-like odour (Kirchgessner and Roth 1987). However, no dif- ference was found in the palatability of diets supplemented with formic acid or calcium for- mate. Lactic acid has a pleasant sour odour, and diets with naturally high lactic acid content have been shown to be palatable to piglets (Mikkelsen and Jensen 1997). The reason for the preference for sodium benzoate remains unknown. In hu- man panels, benzoic acid was found to be pun- gent (prickling) and slight sour, while sodium benzoate has been reported as sweet, salty, and bitter (Otero-Losada 1999). Weaned piglets have been shown to prefer diets with high salt con- tent (Falkowski et al. 1998). The performance response of weaned piglets offered single non-acidified or organic-acid-sup- plemented diets in Experiment 2 is presented in Table 6. No significant weaning age × dietary treatment interactions were observed, and thus only the main effects are shown. Despite of a 10-day difference in the weaning age, no signif- icant difference was found in the weight of pig- lets at weaning or at the age of 58 days. Birth weight was higher in litters weaned at 28 days of age than in those weaned at 38 days of age (1.9 vs. 1.5 kg, P < 0.01), which could be the major reason that there was a small difference in weaning weight. Although piglets weaned at the age of 38 days consumed more feed per day during the first week of and throughout the whole trial than those weaned at the age of 28 days (P < 0.001), no significant difference was observed in the growth performance or feed conversion ratio of the piglets. There was no difference in daily feed consumption between piglets receiv- ing non-acidified and organic-acid-supplement- ed diets (P > 0.05). The growth rate of piglets fed diets supplemented with calcium formate was slower than that of piglets fed a non-acidified control diet. In addition, the feed conversion ra- tio and the incidence of post-weaning diarrhoea tended (P = 0.06) to be higher than in the con- trol treatment. The performance of piglets of- fered other organic-acid-supplemented diets did not differ from that of piglets fed the non-acidi- fied control diet (P > 0.05). The considerably higher feed consumption and conversion ratio compared to Experiment 1 indicates that there was some feed wastage due to feeders. It is pos- sible that some acids may increase feed wast- age. However, because feed consumption was equally high in the control group, it seems more likely that the feeders used in Experiment 2 were responsible for high feed wastage. Furthermore, the piglets were housed in pairs, and the amount 115 A G R I C U L T U R A L A N D F O O D S C I E N C E I N F I N L A N D Vol. 11 (2002): 107–119. Fig. 2. The paths of diet selection of weaned piglets given a choice between weaner diets supplemented with a) lactic acid or formic acid, b) lactic acid or calcium formate, c) lactic acid or sodium benzoate, d) formic acid or calcium formate, e) formic acid or sodium benzoate, and f) calcium formate or sodium benzoate. Each line refers to a litter. L = lactic acid, F = formic acid, CaF = calcium formate, and NaB = sodium benzoate. 6.0 4.0 2.0 0.0 -2.0 -4.0 -6.0 -8.0 6.0 4.0 2.0 0.0 -2.0 -4.0 -6.0 -8.0 6.0 4.0 2.0 0.0 -2.0 -4.0 -6.0 -8.0 6.0 4.0 2.0 0.0 -2.0 -4.0 -6.0 -8.0 6.0 4.0 2.0 0.0 -2.0 -4.0 -6.0 -8.0 6.0 4.0 2.0 0.0 -2.0 -4.0 -6.0 -8.0 116 A G R I C U L T U R A L A N D F O O D S C I E N C E I N F I N L A N D Partanen, K. et al. Weaned piglets offered diets containing organic acids T ab le 6 . E ff ec t of w ea ni ng a ge a nd d ie ta ry o rg an ic a ci ds o n th e pe rf or m an ce a nd f ee d co ns um pt io n of w ea ne d pi gl et s in E xp er im en t 2. W ea ni ng a ge D ie ta ry t re at m en t1 28 d 38 d S E M S ig ni f. 2 B D L F C aF N aB S E M S ig ni f. 2 W ei gh t, k g A t w ea ni ng 10 .0 10 .9 0. 65 10 .0 10 .1 10 .8 10 .0 11 .2 0. 49 * A t th e ag e of 5 1 d 15 .4 15 .7 1. 39 15 .9 15 .0 16 .0 13 .8 17 .0 0. 98 ** A t th e ag e of 5 8 d 18 .9 19 .5 1. 68 19 .7 18 .8 19 .7 16 .6 21 .3 1. 18 ** * F ee d co ns um pt io n, g p er p ig le t pe r d 0- 7 d af te r w ea ni ng 42 7 68 9 69 .6 * 50 4 50 9 62 7 48 0 66 9 65 .7 o W ea ni ng t o th e ag e of 5 1 d 64 2 87 3 48 .9 ** 69 2 82 5 78 8 69 7 78 8 58 .1 W ea ni ng t o th e ag e of 5 8 d 72 6 10 07 48 .5 ** 80 9 94 9 89 3 80 4 87 6 59 .8 W ei gh t ga in , g W ea ni ng t o th e ag e of 5 1 d 25 9 32 6 46 .5 33 0 27 1 30 6 21 4 34 4 40 .3 o W ea ni ng t o th e ag e of 5 8 d 32 0 39 9 50 .6 38 9 34 8 37 3 27 1 41 8 38 .4 ** K g fe ed p er k g ga in W ea ni ng t o th e ag e of 5 8 d 2. 43 2. 77 0. 34 8 2. 08 3. 07 2. 36 3. 29 2. 20 0. 43 4 D ay s in d ia rr ho ea 3. 8 3. 8 0. 90 2. 8 3. 9 1. 5 6. 3 4. 4 1. 34 D ia rr ho ea i nd ex 3 5. 0 4. 9 1. 33 4. 1 4. 5 1. 5 8. 3 6. 1 1. 99 B D = b as al d ie t, L = l ac ti c ac id , F = f or m ic a ci d, C aF = c al ci um f or m at e, N aB = s od iu m b en zo at e, S E M = s ta nd ar d er ro r of t he m ea n. 1 S ix p ig le t pa ir s pe r tr ea tm en t. 2 S ig ni fi ca nc e: o ( P < 0 .1 0) , * ( P < 0 .0 5) , * * (P < 0 .0 1) a nd * ** ( P < 0 .0 01 ). U nd er li ne d tr ea tm en ts d if fe r si gn if ic an tl y fr om t he n on -a ci di fi ed c on tr ol d ie t (P < 0 .0 5) . 3 D ia rr ho ea i nd ex = d ay s in d ia rr ho ea × s ev er it y of d ia rr ho ea . 117 A G R I C U L T U R A L A N D F O O D S C I E N C E I N F I N L A N D Vol. 11 (2002): 107–119. of feed wastage per piglet probably becomes greater than in trials with entire litters. According to Partanen (2001), several stud- ies have shown that dietary formic acid supple- mentation enhances the performance of weaned piglets. Dietary levels of 6-12 g kg-1 have in- creased post-weaning feed consumption, where- as higher levels (18–24 g kg-1) have resulted in reduced feed intake compared to a non-acidified control diet (Eckel et al. 1992). In the study of Kirchgessner and Roth (1987), ad libitum feed consumption of weaned piglets was decreased by 3–5% in diets supplemented with calcium formate (9–27 g kg-1). Dietary calcium formate had no significant influence on the growth per- formance of piglets, but it improved their feed conversion ratio (P < 0.05) and reduced the fre- quency of diarrhoea compared to that of piglets fed the non-acidified control diet. The negative effect of dietary calcium formate supplementa- tion on the performance of weaned piglets could be related to the increased dietary calcium con- tent. Calcium formate contains about 330 g kg-1 of calcium, and the supplementation of 8 g kg-1 feed increased the dietary calcium content from 9 to 11 g kg-1 feed. According to Pallauf et al. (1993), calcium formate supplementation of di- ets already meeting the calcium requirement of piglets had a negative effect on feed intake, weight gain, and feed conversion ratio. Particu- larly the digestibility of fat was decreased. There- fore, the total dietary calcium level should not exceed the optimum when diets are supplement- ed with calcium formate. Dietary lactic acid supplementation (8–24 g kg-1) increased feed consumption of weaned piglets by 6% compared to a non-acidified control diet (Roth et al. 1993). Information about the effect of dietary sodium benzoate supplementation on weaned piglet per- formance is scarce. Sodium benzoate supplemen- tation has been shown to enhance the perform- ance of growing-finishing pigs, for which the main interest in dietary benzoate supplementa- tion is to lower urinary pH and to thus reduce ammonia emission (van der Peet-Schwering et al. 1999). Conclusions The results showed that there may be some dif- ferences in the palatability of different organic- acid-supplemented diets. When allowed to choose, piglets preferred diets supplemented with sodium benzoate to diets supplemented with formic acid or calcium formate. The acceptabil- ity of diets supplemented with lactic acid, for- mic acid, or calcium formate was similar for weaned piglets. Growth performance was re- duced by dietary calcium formate supplementa- tion, while the results of diets supplemented with other acids did not differ significantly from those of the non-acidified control diet. The frequency of post-weaning diarrhoea was highest in diets supplemented with calcium formate and lowest in diets with formic acid. Acknowledgements. The authors wish to thank Kemira Chemicals, Ltd., Formics, Finland for financial support for this study. References Appleby, M.C., Pajor, E.A. & Fraser, D. 1991. Effects of management options on creep feeding by piglets. Animal Production 53: 361–366. Barnett, K.L., Kornegay, E.T., Risley, C.R., Lindemann, M.D. & Schurig, G.G. 1989. Characterization of creep feed consumption and its subsequent effects on im- mune response, scouring index and performance of weanling pigs. Journal of Animal Science 67: 2698– 2708. 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SELOSTUS Orgaanisten happojen vaikutus porsasrehun maittavuuteen Kirsi Partanen, Hilkka Siljander-Rasi ja Kaija Suomi MTT (Maa- ja elintarviketalouden tutkimuskeskus) Valinta- ja kasvatuskokeissa selvitettiin porsasrehun maitohappo-, muurahaishappo-, kalsiumformiaatti- ja natriumbentsoaattilisäysten (8 g/kg rehua) vaikutus- ta vieroitettujen porsaiden rehun syöntiin. Valintako- keessa oli 30 pahnuetta (306 porsasta), jotka vieroi- tettiin 30 päivän iässä. Orgaanista happoa sisältäviä rehuja testattiin pareittain ja tutkitut kuusi yhdistel- mää olivat maitohappo/muurahaishappo, maitohappo/ kalsiumformiaatti, maitohappo/natriumbentsoaatti, muurahaishappo/kalsiumformiaatti, muurahaishappo/ natriumbentsoaatti ja kalsiumformiaatti/natriumbent- soaatti. Vieroituksesta 21 päivän ajan porsailla oli mahdollisuus syödä vapaasti automaatista jompaa kumpaa tarjolla ollutta orgaanista happoa sisältävää rehua. Porsaat söivät mieluummin natriumbentsoaat- tia kuin muurahaishappoa tai kalsiumformiaattia si- sältävää rehua. Maitohappoa, muurahaishappoa tai kalsiumformiaattia sisältäneiden rehujen maittavuu- dessa ei ollut eroja. Kasvatuskokeessa oli 60 porsas- ta 10 pahnueesta, jotka oli vieroitettu 28 tai 38 päi- vän iässä. Porsaat saivat syödä vapaasti lisäaineetonta tai maitohappoa, muurahaishappoa, kalsiumformiaat- tia tai natriumbentsoaattia sisältävää rehua vieroituk- sesta 58 päivän ikään. Lisäaineettoman ja orgaanisia happoja sisältäneiden rehujen kulutuksessa ei ollut eroja. Rehun kalsiumformiaattilisäys heikensi porsai- den kasvua lisäaineettomaan ruokintaan verrattuna. Muut happolisäykset eivät vaikuttaneet porsaiden kasvuun. Ripulia esiintyi eniten porsailla, joiden re- huun lisättiin kalsiumformiaattia, ja vähiten niillä, joiden rehuun lisättiin muurahaishappoa. Title Introduction Material and methods Results and discussion Conclusions References SELOSTUS