Measurement of the acid-binding capacity of ingredients used in pig diets

Abstract

: Some feed ingredients bind more acid in the stomach than others and for this reason may be best omitted from pig starter foods if gastric acidity is to be promoted. The objective of this study was to measure the acid-binding capacity (ABC) of ingredients commonly used in pig starter foods. Ingredients were categorised as follows: (i) milk products (n = 6), (ii) cereals (n = 10), (iii) root and pulp products (n = 5), (iv) vegetable proteins (n = 11), (v) meat and fish meal (n = 2), (vi) medication (n = 3), (vii) amino acids (n = 4), (viii) minerals (n = 16), (ix) acid salts (n = 4), (x) acids (n = 10). A 0.5 g sample of food was suspended in 50 ml distilled de-ionised water with continuous stirring. This suspension was titrated with 0.1 mol/L HCl or 0.1 mol/L NaOH so that approximately 10 additions of titrant was required to reach pH 3.0. The pH readings after each addition were recorded following equilibration for three minutes. ABC was calculated as the amount of acid in milliequivalents (meq) required to lower the pH of 1 kg food to (a) pH 4.0 (ABC-4) and (b) pH 3.0 (ABC-3). Categories of food had significantly different (P < 0.01) ABC values. Mean ABC-4 and ABC-3 values of the ten categories were: (i) 623 (s.d. 367.0) and 936 (s.d. 460.2), (ii) 142 (s.d. 79.2) and 324 (s.d. 146.4), (iii) 368 (s.d. 65.3) and 804 (s.d. 126.7), (iv) 381 (s.d. 186.1) and 746 (s.d. 227.0), (v) 749 (s.d. 211.6) and 1508 (s.d. 360.8), (vi) 120 (s.d. 95.6) and 261 (s.d. 163.2), (vii) 177 (s.d. 60.7) and 1078 (s.d. 359.0), (viii) 5064 (s.d. 5525.1) and 7051 (s.d. 5911.6), (ix) 5057 (s.d. 1336.6) and 8945 (s.d. 2654.1) and (x) -5883 (s.d. 4220.5) and -2591 (s.d. 2245.4) meq HCl per kg, respectively. Within category, ABC-3 and ABC- 4 values were highly correlated: R2 values of 0.80 and greater for food categories i, iv, v, vi, vii and viii. The correlation between predicted and observed ABC values of 34 mixed diets was 0.83 for ABC-4 and 0.71 for ABC-3. It was concluded that complete diets with low ABC values may be formulated through careful selection of ingredients. The final pH to which ABC is measured should matter little as ABC-3 and ABC-4 are highly correlated.

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Introduction
In the pig, protein digestion begins in the stomach with the action
of pepsins, secreted as the enzyme precursors – pepsinogens – by
stomach mucosa. Conversion of pepsinogen to pepsin occurs rapidly
at pH 2.0 but only slowly at pH 5.0 to 6.0. In turn, pepsins work best
in an acidic environment, pH 2.0 to 3.5, and activity declines rapidly
above this pH. Carbohydrate hydrolysis in the stomach occurs by the
action of salivary amylase, which, in contrast to pepsin, is inactivated
once pH falls to 3.5 (Kidder and Manners, 1978; Longland, 1991; Yen
2001).
In the suckling pig, acid secretion is low and the principal source
of acidity is bacterial fermentation of lactose from sows milk to
lactic acid (Cranwell et al., 1968, 1976; Kidder and Manners, 1978).
A high level of lactate in the stomach tends to inhibit HCl secretion
(Cranwell et al., 1976; Yen, 2001). Ingestion of solid feed reduces the
level of lactic acid in the stomach (Yen, 2001) and stimulates HCl
production (Cranwell et al., 1976; Cranwell, 1985) but, in practice,
creep feed consumption is low and variable at least up to four weeks
of age (Lawlor et al., 2002).
At weaning, a combination of low acid secretion, lack of lactose
substrate, and consumption of large meals at infrequent intervals
can result in elevated pH, often to over 5.0 and it may remain high
for several days (Kidder and Manners, 1978). The high acid-binding/
buffering capacity of the feed (its ability to neutralise feed acid) helps
to further raise the stomach pH (Prohaszka and Baron, 1980; Jasaitis
et al., 1987; Bolduan et al., 1988). Inclusion of whey or lactose in
the starter diet ensures continuation of bacterial fermentation and
some, though reduced, lactic acid production (Kidder and Manners,
1978; Easter, 1988). Development of HCl secretory capacity occurs
more rapidly in the weaned pig than in the suckling pig (Cranwell and
Moughan, 1989).
peer reviewed
Measurements of the acid-binding capacity of ingredients used in
pig diets
Peadar G. Lawlor1, P. Brendan Lynch1, Patrick J. Caffrey2, James J. O’Reilly1 and M. Karen O’Connell1
1 Pig Production Department, Teagasc, Moorepark Research Centre, Fermoy, Co. Cork, Ireland
2 Department of Animal Science and Production, Faculty of Agriculture, University College, Dublin, Ireland.
Some feed ingredients bind more acid in the stomach than others and for this reason may be best omitted
from pig starter foods if gastric acidity is to be promoted. The objective of this study was to measure the
acid-binding capacity (ABC) of ingredients commonly used in pig starter foods. Ingredients were categorised
as follows: (i) milk products (n = 6), (ii) cereals (n = 10), (iii) root and pulp products (n = 5), (iv) vegetable
proteins (n = 11), (v) meat and fish meal (n = 2), (vi) medication (n = 3), (vii) amino acids (n = 4), (viii)
minerals (n = 16), (ix) acid salts (n = 4), (x) acids (n = 10). A 0.5g sample of food was suspended in 50ml
distilled de-ionised water with continuous stirring. This suspension was titrated with 0.1mol/L HCl or 0.1
mol/L NaOH so that approximately 10 additions of titrant was required to reach pH 3.0. The pH readings
after each addition were recorded following equilibration for three minutes. ABC was calculated as the
amount of acid in milliequivalents (meq) required to lower the pH of 1kg food to (a) pH 4.0 (ABC-4) and
(b) pH 3.0 (ABC-3). Categories of food had significantly different (P<0.01) ABC values. Mean ABC-4 and
ABC-3 values of the ten categories were: (i) 623 (s.d. 367.0) and 936 (s.d. 460.2), (ii) 142 (s.d. 79.2) and
324 (s.d. 146.4), (iii) 368 (s.d. 65.3) and 804 (s.d. 126.7), (iv) 381 (s.d. 186.1) and 746 (s.d. 227.0), (v) 749
(s.d. 211.6) and 1508 (s.d. 360.8), (vi) 120 (s.d. 95.6) and 261 (s.d. 163.2), (vii) 177 (s.d. 60.7) and 1078 (s.d.
359.0), (viii) 5064 (s.d. 5525.1) and 7051 (s.d. 5911.6), (ix) 5057 (s.d. 1336.6) and 8945 (s.d. 2654.1) and (x)
-5883 (s.d. 4220.5) and -2591 (s.d. 2245.4) meq HCl per kg, respectively. Within category, ABC-3 and ABC-
4 values were highly correlated: R2 values of 0.80 and greater for food categories i, iv, v, vi, vii and viii. The
correlation between predicted and observed ABC values of 34 mixed diets was 0.83 for ABC-4 and 0.71
for ABC-3. It was concluded that complete diets with low ABC values may be formulated through careful
selection of ingredients. The final pH to which ABC is measured should matter little as ABC-3 and ABC-4
are highly correlated.
Key words:
Pig,
Diet,
Ingredients,
Acid-binding capacity.
Corresponding author:
P.G. Lawlor
Pig Production Department,
Teagasc, Moorepark Research Centre,
Fermoy, Co. Cork, Ireland
Tel: + 353 25 42217
Fax: + 353 25 42340
E-mail: plawlor@moorepark.teagasc.ie
Technical update from Intervet
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Raised stomach pH after weaning results in reduced digestion of
feed which will then be fermented in the hind gut and may provoke
diarrhoea. A high gastric pH will also allow pathogens to survive
and allow them greater opportunity to colonise the digestive tract
(Bolduan et al., 1988; Yen, 2001).
The concept of manipulating stomach acidity by adding acid to feeds
or using feeds of low acid-binding or buffering capacity (Prohaszka
and Baron, 1980; Jasaitis et al., 1987; Bolduan et al., 1988; Lawlor et
al., 2005a; Lawlor et al., 2005b) has been around for a long time and
addition of organic acids to piglet starter feeds is a common practice.
However, there is little information on the acid-binding capacity
(ABC) of ingredients that are used in formulation of complete feeds.
The limited published sets of data have been compiled using methods
with different titration-end points (e.g., pH = 3.0 or pH = 4.0) so that
values are not comparable (Prohaszka and Baron, 1980; Jasaitis et al.,
1987; Bolduan et al., 1988; Giger-Reverdin et al., 2002).
The objective of this study was to find the ABC and buffering capacity
values of individual feed ingredients and ingredient categories and to
find if a correlation exists between ABC-3 and ABC-4 values. A further
objective was to investigate the possibility of formulating complete
diets of low ABC for weaned pigs by using the ABC values of each
ingredient in the formulation matrix.
Materials and methods
Procedures
Ingredients commonly used in pig rations were obtained over a
number of years from various commercial sources in Ireland. All
ingredients (as received) were ground through a 2mm screen using
a laboratory hammer mill (Christy and Norris, Scunthorpe, UK),
and were stored in air-tight jars at room temperature until analysis.
Measurements were completed within one month of receiving each
sample. Ingredients were grouped under the following headings
for ease of analysis: (i) milk products, (ii) cereals, (iii) root and
pulp products, (iv) vegetable proteins, (v) meat and fish meal, (vi)
medication, (vii) amino acids, (viii) minerals, (ix) acid salts, and (x)
acids. A modification of the procedure of Jasaitis et al. (1987) was
used to determine pH and acid-binding capacity (ABC). The latter
procedure used only pH = 4.0 as the titration endpoint whereas the
present study used pH = 3.0 as well as pH = 4.0 as titration endpoints
in an effort to provide measures of greater relevance to pig nutrition.
All pH measurements were made using a laboratory pH meter (PHM
220, Radiometer, Copenhagen) which was calibrated using certified
pH = 4.0 and pH = 7.0 buffer solutions (Radiometer, Copenhagen).
A 0.5g sample of ingredient/feed was suspended in 50ml of distilled
and de-ionised water and continuously stirred with a magnetic stirrer.
Titrations were performed by addition of acid (0.1N HCl) in variable
increments (0.1 to 10ml depending on the ingredient type and the
stage of titration). Acid was added so that it would take approximately
10 separate additions of acid to reach pH 3.0. Initial pH and all further
readings taken during the titration were recorded after equilibration
for three minutes. ABC was calculated as the amount of acid in
milliequivalents (meq) required to lower the pH of 1kg of sample to
(a) pH 4.0 (ABC-4) and (b) pH 3.0 (ABC-3). The buffering capacity
(BUF) was calculated by dividing the ABC by the total change in pH
units [from initial pH to the final pH of (a) 4.0 (BUF-4) and (b) 3.0
(BUF-3)]. BUF expresses the amount of acid required to produce a
unit change in the pH of a feed ingredient / feed sample.
Feeds/ingredients with a pH less than 3 or 4 were titrated as above
but against 0.1 N NaOH until pH 4.0 and/or pH 3.0 was reached. ABC
and BUF values in these cases were given negative values.
Statistical analysis
The means and standard deviation for each ingredient were calculated
for pH, ABC-4, ABC-3, BUF-4 and BUF-3. Regression equations (Proc
Reg of Sas Inc., Cary, North Carolina) were established relating ABC-
3 to ABC-4 for the ingredients within each category. This procedure
was also used to establish the relationship between the predicted and
observed ABC-4 and ABC-3 values for 34 mixed pig diets. Predicted
values were obtained by including the ABC-4 and ABC-3 values of
each individual ingredient in the formulation matrix for the mixed diet.
Results
The mean ABC and BUF values for each ingredient are shown
in Table 1. The mean ABC of each category and the correlation
between ABC-3 and ABC-4 values for each category are shown in
Table 2. The correlation between predicted and observed ABC values
for 34 post-weaning diets is presented in Table 3.
Initial pH, ABC-4 and ABC-3 varied greatly between individual
ingredients. Categories of ingredients were statistically different
(P<0.01) with regard to ABC and BUF values but great variation was
also found within ingredient categories for initial pH, ABC and BUF.
Acid salts and minerals were the categories that had the highest
ABC and BUF values. Great variation occurred between the different
mineral types. Zinc oxide, limestone flour and sodium bicarbonate
had the highest ABC values. Of the phosphorus sources, defluorinated
phosphate had the highest ABC values, dicalcium phosphate and mono
dicalcium phosphate had intermediate values, while monammonium
phosphate had the lowest values. Meat and fish meal, milk products,
amino acids, root and pulp products and vegetable proteins were
the categories of organic ingredients with the highest ABC and
BUF values. Cereals had the lowest values of the organic ingredient
Lowering the acid-binding capacity of diets for newly-weaned pigs can help ease
the transition from milk to solid food at weaning.
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TABLE 1: pH, acid-binding capacity (ABC) and buffering capacity (BUF) of some commonly used feed ingredients (mean ±s.d.)
Ingredient N1 pH2 ABC-43 ABC-34 BUF-45 BUF-36
Milk
Acid casein 1 3.9 0 200 0 222
Sows milk 2 8.1±0.04 481±1.0 650±70.7 118±0.8 128±14.8
Whey powder 9 6.6±0.31 434±99.9 714±149.3 168±36.5 199±39.9
Milk replacer 4 6.7±0.22 579±54.6 892±97.8 214±38.1 240±40.6
Skim milk 3 7.1±0.20 756±59.6 1105±108.7 242±29.4 268±35.4
Rennet casein 3 8.1±0.06 1423±35.5 1929±76.9 348±4.0 379±11.1
Cereals
Oat flakes 1 6.7 72 180 27 49
Wheat 12 6.9±0.12 108±14.9 194±15.8 37±5.0 50±3.7
Pin head oats 1 5.5 81 239 56 97
Barley screenings 1 6.7 104 240 39 65
Maize starch 6 7.0±0.78 91±45.6 202±58.5 29±11.4 51±13.5
Maize 8 6.7±0.24 111±35.8 254±53.1 41±10.6 68±11.1
Barley 14 6.6±0.18 113±14.3 266±43.1 43±3.6 73±10.5
Flaked maize 1 7.6 240 424 67 92
Corn distillers 8 4.4±0.17 96±38.6 438±42.9 262±75.4 317±56.3
Pollard 12 6.9±0.29 292±20.6 572±24.0 100±12.1 146±14.7
Root and pulp products
Sugar 2 5.8±0.06 23±8.4 98±11.8 13±5.2 36±3.5
Cassava 1 5.5 167 393 110 156
Beet pulp 1 6.0 191 480 98 163
Molasses 10 6.1±0.08 399±37.6 790±45.5 190±19.1 255±16.9
Citrus pulp 13 6.8±0.08 373±25.4 873±49.9 135±8.1 232±12.2
Vegetable protein
Milo distillers 1 4.1 14 276 174 256
Beans 1 6.8 275 473 98 125
Palm kernal 9 5.9±0.10 250±38.2 485±51.5 132±23.2 167±20.2
Peas 10 6.8±0.11 278±24.0 515±43.1 98±9.8 134±12.7
Lupins 1 6.2 337 645 156 204
Maize gluten 15 4.4±0.07 114±19.7 571±79.4 334±73.1 424±71.4
Full fat soya 10 6.9±0.28 480±43.5 823±62.2 166±13.9 212±16.8
Sunflower meal 11 6.7±0.19 482±52.7 852±91.4 180±14.7 231±16.4
Sycomil 1 7.5 622 959 180 216
Rapeseed meal 12 6.3±0.11 498±49.3 945±65.2 215±20.5 284±21.2
Soybean meal 12 7.1±0.06 642±51.1 1068±74.0 210±18.0 263±20.2
Meat and fishmeal
Meat and bone meal 1 6.6 595 920 214 243
Fishmeal 10 6.7±0.37 738±219.3 1457±334.5 285±96.8 404±105.9
Fat
Fat 1 4.9 16 137 17 72
Fat blend 1 6.6 363 609 138 168
Medication
Spiratet 1 5.6 114 340 73 133
Choline chloride 12 6.7±0.52 101±68.6 226±136.0 37±23.5 61±35.8
Tylamix 1 7.0 370 610 123 152
Microbial protein
Yeast 1 3.4 150 130 -250 325
Amino acids
Lysine 11 6.5±0.38 123±23.3 695±124.3 50±6.0 200±22.5
Tryptophan 8 7.0±0.23 179±17.1 1024±90.8 60±4.6 258±25.4
Methionine 9 6.5±0.34 192±75.9 1219±267.0 77±23.0 349±52.5
Threonine 11 6.5±0.22 218±57.6 1386±354.2 86±17.2 391±83.4
Minerals
Ferrous sulphate 3 3.2±0.09 -655±18.1 93±53.2 -821±77.3 456±96.2
Salt 6 7.5±0.18 83±21.5 162±37.5 24±6.8 36±9.1
Copper sulphate 3 5.1±0.06 92±3.3 269±9.2 80±7.1 125±0.6
Cobalt sulphate 3 7.4±0.04 329±6.5 516±9.7 97±3.0 117±1.5
Monammonium phosphate 3 4.2±0.05 46±10.5 815±40.1 247±13.2 687±33.8
Ferrous oxide 3 8.7±0.16 549±78.5 986±78.6 117±15.8 173±12.5
Mould curb 1 5.3 2517 3460 2014 1538
Finisher minerals and vitamins 3 5.2±0.04 3357±305.5 5123±303.9 2772±194.7 2317±104.8
Weaner minerals and vitamins 3 5.2±0.03 4292±1008.9 6302±1054.0 3472±765.1 2819±448.8
Dicalcium phosphate 5 7.6±0.19 3098±1028.5 5666±1852.4 857±293.7 1234±431.2
Sow minerals and vitamins 3 5.3±0.05 5413±216.4 7503±132.3 4182±300.5 3268±117.1
Potassium citrate 3 8.6±0.07 5703±1.6 7851±13.6 1251±19.0 1412±19.1
Mono dicalcium phosphate 9 4.4±0.26 291±159.5 5494±2574.3 1302±980.8 4400±2564.3
Sodium citrate 3 8.4±0.19 6334±13.6 8745±20.5 1449±66.9 1628±58.6
Defluorinated phosphate 3 9.9±0.09 6412±1032.9 10436±337.5 1085±161.0 1511±28.9
Calcium formate 3 7.4±0.15 3983±97.9 12069±409.7 1182±29.6 2760±18.3
Manganese oxide 3 8.8±0.07 6678±1045.7 10887±2264.6 1400±210.9 1887±381.9
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categories. Of the ingredients, both inorganic and organic, the acids
category had the lowest ABC and BUF values. Most ABC values for
the individual acids were negative with orthophosphoric, fumaric,
formic, malic and citric acids having the most negative values.
The mean ABC-3 and ABC-4 values for ingredients within categories
are well correlated. R2 values of 0.90 or greater were found for milk
products and medication. R2 values of between 0.85 and 0.90 were
found for amino acids and minerals. Both vegetable proteins and meat
and fishmeal had R2 values of between 0.80 and 0.85.
The ABC values for mixed pig starter diets were predicted from the
mean ABC value (Table 1) of each ingredient in their formulation and
their composition in the diet. The correlation between predicted and
observed ABC values was relatively good. For ABC-4, R2 was 0.83 and
for ABC-3 the R2 was 0.71.
Discussion
Some ingredients bind more acid in the stomach than others and for
this reason their use in pig starter diets might result in a high gastric
pH. A high gastric pH is detrimental to the pig because it allows the
proliferation of deleterious micro-organisms (Bolduan et al., 1988) and
inhibits protein digestion (Kidder and Manners, 1978; Longland, 1991;
Yen, 2001).
In the present study, a range of ingredients that are commonly used
in pig diets was examined. It was thought that ingredients of low ABC
would be identified which could then be used to formulate a starter
diet in such a way that gastric acidity would be promoted. Jasaitis et
al. (1987) found that mineral additives had higher ABC-4 and BUF-4
values than organic ingredients. In the present experiment, minerals
as an ingredient category had the second highest ABC and BUF values
of all categories examined. Acid salts were found to have the highest
values. Jasaitis et al. (1987) found that carbonates and dibasic or
tribasic mineral additives had the highest ABC and BUF values. With
the exception of the trace minerals zinc oxide and manganese oxide,
the present experiment agrees with this finding. Limestone flour and
Sodium bicarbonate 3 8.7±0.44 12566±554.1 12870±399.1 2706±147.4 2280±110.3
Limestone flour 13 8.9±0.46 12932±21883 15044±2125.4 2661±479.8 2565±380.6
Zinc oxide 3 8.3±0.19 16321±11701 17908±1100.9 3768±193.0 3363±238.0
Acid
Orthophosphoric acid 3 1.6±0.02 -8858±168.2 -7957±204.5 -3665±54.5 -5616±97.4
Fumaric acid 3 2.3±0.06 -10862±469.6 -4093±669.7 -6314±54.6 -5659±478.7
Formic acid 3 2.3±0.03 -13550±765.0 -3473±110.3 -7824±572.9 -4745±344.7
Citric acid 5 2.2±0.03 -5605±202.2 -2349±164.3 -3156±89.9 -3024±97.5
Ascorbic acid 3 2.8±0.03 -217±28.6 -2249±77.0 -177±19.4 -10159±1048.2
Malic acid 3 2.2±0.15 -7214±694.6 -2550±769.0 -4084±575.8 -3242±333.0
Lactic acid 3 2.4±0.02 -5079±53.9 -1498±23.7 -3129±63.0 -2405±111.3
Acetic acid 3 2.9±0.02 -2283±104.1 -141±24.9 -2011±133.1 -1031±33.6
Propionic acid 3 3.0±0.01 -1358±276.5 -5±8.2 -1348±259.6 -238±412.4
Sorbic acid 1 3.5 -220 120 -400 267
1Number of samples. 2Initial pH of sample. 3Acid binding capacity to pH 4.0. 4Acid binding capacity to pH 3.0. 5Buffering capacity to pH 4.0. 6Buffering capacity to pH 3.0
Table 2: Models for predicting acid-binding capacity to pH 3.0 (ABC-3) from acid-binding capacity to pH 4.0 (ABC-4) for different feed types
Feed type N1 ABC-4 ABC-3 Y2 A3 B4 (R2)5 (Adj. R2)6 RSD7
Milk 22 623±367.0 936±460.2 ABC-4 -118.45*** 0.79*** 0.99 0.99 39.55
Cereals 64 142±79.2 324±146.4 ABC-4 -2.34 0.45*** 0.68 0.67 45.41
Root and pulp products 27 368±65.3 804.7±126.7 ABC-4 14.50 0.44*** 0.73 0.72 34.75
Vegetable proteins 84 380.7±186.1 746±227.0 ABC-4 -177.57*** 0.75*** 0.83 0.83 76.49
Meat and fishmeal 11 749±211.6 1508±360.8 ABC-4 -56.66 0.53*** 0.83 0.81 91.75
Medication 14 120±95.6 261±163.2 ABC-4 -26.55+ 0.56*** 0.92 0.91 27.52
Amino acids 39 177±60.7 1078±359.0 ABC-4 7.40 0.16*** 0.87 0.86 22.51
Minerals 73 5064±5525.1 7051±5911.6 ABC-4 -1157.30*** 0.88*** 0.89 0.89 1833.53
Acid salt 10 5057±1336.6 8945±2654 ABC-4 4909.16* 0.02 0.01 -0.12 1416.90
Acid 30 -5883±4220.5 -2591±2245.4 ABC-4 -2771.41** 1.20*** 0.41 0.39 3304.56
1Number of samples. 2Dependent variable. 3Regression constant. 4Regression coefficient for regression on ABC-3. 5Coefficient of determination. 6Adjusted R2. 7Residual standard
deviation.
Table 3: Models for predicting observed acid-binding capacity to pH 4.0 (ABC-4) and observed acid-binding capacity to pH 3.0 (ABC-3) from their respective
predicted ABC values
Measure N1 Observed Predicted Y2 A3 B4 (R2)5 (Adj. R2)6 RSD7
value value
ABC-4 34 259±93.3 294±124.8 Observed ABC-4 59.50** 0.68*** 0.83 0.82 39.11
ABC-3 34 608±88.8 640±77.6 Observed ABC-3 -9.32 0.97*** 0.71 0.70 48.28
1Number of samples. 2Dependent variable. 3Regression constant. 4Regression coefficient for regression on predicted ABC-4 or ABC-3 value. 5Coefficient of determination. 6Adjusted R2.
7Residual standard deviation.
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sodium bicarbonate had the highest ABC values with defluorinated
phosphate, dicalcium phosphate and mono dicalcium phosphate being
the minerals with the next highest values. Bolduan (1988) found that
increasing the mineral supplementation of a diet from 0 to 4% tripled
the ABC-4 value. For this reason, Bolduan et al. (1988) and Bolduan
(1988) suggested limiting the mineral content of a starter diet for
a short period postweaning. It was hypothesised that this practice
would benefit the pigs in health terms. However, growth may be
retarded to some extent by this practice as the mineral requirement
for bone formation will not be supplied (Bolduan, 1988) especially if
the period of restricted feeding of minerals is prolonged.
With regard to organic ingredients, their ABC values are positively
correlated with their ash and protein contents (Jasaitis et al., 1987;
Bolduan et al., 1988; Bolduan, 1988). Prohaszka and Baron (1980) also
found the ABC-3 of a feed to increase as its protein content increased.
In the present experiment, meat and fishmeal had the highest ABC
and BUF values of all the organic ingredients. This was thought to be
because of their high ash and protein contents. Jasaitis et al. (1987)
also found these ingredients to have the highest ABC-4 values of all
organic ingredients. The milk products category (in particular, rennet
casein and spray dried skim) also had high ABC values. However,
the other ingredients in this category had lower values. Again, this is
believed to be related to the ash and protein contents.
Of the vegetable proteins, soyabean meal, Soycomil, rapeseed, and
sunflower meal had the highest ABC values. Jasaitis et al. (1987)
found that the geographic origin of an ingredient can affect its ABC
because it influences the ion concentration of the ingredient and this
may help to explain the variation in ABC values found for individual
ingredients. Maize gluten and milo distillers meal were uncharacteristic
of the vegetable protein group of ingredients in that they both had pH
values less than 4.5 and their ABC values were low relative to the
other ingredients in this group. Jasaitis et al. (1987) also found such
fermented products to have some of the lowest ABC-4 values of the
organic ingredients examined.
Cereals and some root and pulp products had low ABC and BUF
values in the present experiment. This was in agreement with previous
findings (Jasaitis et al., 1987; Bolduan, 1988; Bolduan et al., 1988 and
BASF, 1989).
Acids were found to have negative ABC values. The use of organic
acids in starter diets offers the opportunity of lowering diet ABC
without having to reduce dietary protein or mineral content. However,
the beneficial effects of organic acids on pig health are strongly
dependent on the initial BUF value of the diet (Blank et al., 2001). The
organic acids of choice would be orthophosphoric, fumaric, formic
or malic if the prime mode of action of these acids was deemed to
be the lowering of diet ABC and increasing gastric acidity. However,
acids for use in pig diets are often selected for other qualities also
such as: antimicrobial effects on pathogenic bacteria, promotion of
beneficial or probiotic bacteria, nutritional value, improved non-
specific immunity (Pratt et al., 1996), stimulatory effect on pancreatic
secretion (e.g., lactic acid: Thaela et al., 1998), physical form (dry or
liquid), corrosive nature and safety.
In the literature, ABC-3 values were used by some researchers
(Prohaszka and Baron, 1980) while ABC-4 values were used by others
(Jasaitis et al., 1987; Bolduan et al., 1988). The present study found
that these values for ingredients are well correlated within ingredient
categories with the exception of acids and acid salts. For this reason, it
should matter little which measure is used. Great variation occurred
within ingredient categories with regard to ABC and BUF values.
The ABC values of complete diets can be predicted if the ABC of
each ingredient in the diet is known. The observed and predicted ABC
values were well correlated. Jasaitis et al. (1987) also found this to
be the case. The result is that diets can be formulated using the ABC
values for ingredients presented here so that complete diets with low
ABC values are produced. Such diets can be used when a high gastric
pH is likely to be a problem (e.g., at weaning). These diets could also
be employed as part of a strategy to reduce E. coli or Salmonella in
older pigs. This is particularly important now due to recent EU bans
on feed antibiotics in response to human fears of antibiotic resistant
bacteria originating in animals (Barton, 2000; Bager et al., 2000).
Acknowledgements
The authors acknowledge the assistance of graduate students and
work study students in performing the titrations recorded here. The
provision of ingredient samples by Glanbia, Portlaoise and Dairygold,
Mitchelstown is gratefully acknowledged.
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