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J. Anim. Sci. 2002. 80:1725-1735
© 2002 American Society of Animal Science

Effect of liquid feeding weaned pigs on growth performance to harvest1,2

P. G. Lawlor*,3, P. B. Lynch*, G. E. Gardiner{dagger}, P. J. Caffrey{ddagger} and J. V. O’Doherty{ddagger}

* Pig Production Department and and {dagger} Dairy Quality Department, Teagasc, Moorepark Research Centre, Fermoy, Co. Cork, Ireland and and {ddagger} Department of Animal Science and Production, Faculty of Agriculture, University College, Dublin, Ireland

3 Correspondence:
phone: 353-25-42217; fax: 353-25-42340; E-mail:
plawlor{at}moorepark.teagasc.ie.


   Abstract
Top
 Abstract
Introduction
 Materials and Methods
 Results
 Discussion
 Implications
 Literature Cited
 
Four experiments were undertaken to examine the effect of feeding postweaning diets as dry pelleted feed, fresh liquid feed, acidified liquid feed, and fermented liquid feed on pig performance from weaning (26 d) to harvest. In Exp. 1 (n = 12 replicates) and 2 (n = 10 replicates), the treatments were 1) dry pelleted feed and 2) fresh liquid feed. In Exp. 1, 2 kg of starter diet (16.7 MJ of DE/kg and 1.6% lysine) per pig and 5 kg of transition diet (16.7 MJ of DE/kg and 1.5% lysine) per pig followed by a weaner diet (14.0 MJ of DE/kg and 1.36% lysine) were offered to 27 d after weaning. In Exp. 3 (n = 8 replicates), the treatments were 1) dry pelleted feed, 2) fresh liquid feed, and 3) acidified liquid feed. In Exp. 4 (n = 8 replicates), the treatments were 1) dry pelleted feed, 2) acidified liquid feed, and 3) fermented liquid feed. In Exp. 2, 3, and 4, 3 kg of starter diet (16.1 MJ of DE/kg and 1.74% lysine) per pig and 6 kg of transition diet (15.3 MJ of DE/kg and 1.5% lysine) per pig followed by a weaner diet (14.0 MJ of DE/kg and 1.36% lysine) was offered to 27 d after weaning. All treatments were balanced for boars and gilts and diets were offered for ad libitum consumption. Acidified liquid feed was produced by adding lactic acid to the liquid feed so that its pH was decreased to 4.0. Fermented liquid feed was produced by adding an inoculum of Lactococcus lactis subsp. cremoris 303 (1.3%, vol/wt) to the first mix. In Exp. 1, ADG from weaning to d 27 after weaning was 338 and 286 g/d (SEM = 10; P < 0.01) and DM gain/feed in the same period was 888 and 594 g/kg (SEM = 23.1; P < 0.001) for dry pelleted feed and fresh liquid feed, respectively. In Exp. 2, ADG was 391 and 352 g/d (SEM = 6.4; P < 0.01) and DM gain/feed was 856 and 642 g/kg (SEM = 9.9; P < 0.001) for dry pelleted feed and fresh liquid feed, respectively, during the period from weaning to d 27 after weaning. In Exp. 3, ADG was 408, 416, and 433 g/d (SEM = 12.7; P > 0.05) and DM gain/feed was 865, 755, and 789 g/kg (SEM = 14.5; P < 0.001) for dry pelleted feed, fresh liquid feed, and acidified liquid feed, respectively. In Exp. 4, ADG was 361, 389, and 347 g/d (SEM = 13.2; P = 0.11) and DM gain/feed was 888, 749, and 733 g/kg (SEM = 15.8; P < 0.001) for dry pelleted feed, acidified liquid feed, and fermented liquid feed, respectively, during the period from weaning to d 27 after weaning. It is concluded that although feeding acidified liquid feed may have some merit in the first 27 d after weaning, this benefit is lost in the subsequent period. No benefit arose from feeding fresh liquid feed or fermented liquid feed. Growth performance from d 28 after weaning to harvest was not improved by any liquid feed treatment.

Key Words: Fermentation • Lactic Acid • Pigs • Postweaning Interval


   Introduction
Top
 Abstract
 Introduction
Materials and Methods
 Results
 Discussion
 Implications
 Literature Cited
 
Liquid feeding has been reported to stimulate ADFI after weaning and thus to increase growth rate (Brooks et al., 1996; Jensen and Mikkelsen, 1998). Jensen and Mikkelsen (1998) summarized the results of 10 studies on liquid feeding of newly weaned pigs and found that ADG was increased by 12.3 ± 9.4% compared with dry feeding. They also reported that ADG of pigs offered fermented liquid feed was 13.4 ± 7.1% higher than that found with fresh liquid feeding. Geary et al. (1999) reported that pigs offered liquid feed that was acidified with lactic acid performed similarly to pigs offered fermented liquid feed. Regardless of the type of liquid feed provided to weaned pigs, a reduction in gain/feed is normally found relative to pigs offered dry feed (Jensen and Mikkelsen, 1998).

Any benefit from liquid feeding newly weaned pigs is likely to arise from an increase in ADFI. Increasing ADFI after weaning by liquid feeding has been found to help maintain gut integrity and, in particular, villous height (Deprez et al., 1987; Pluske et al., 1996). This could serve to maintain the digestive capacity of the pig and thus might prevent the "growth lag" often experienced at this time. Fermented liquid feed and acidified liquid feed may offer further advantages to pig performance because the pH of the feed is usually 4.0 to 4.5, which will help eliminate deleterious microbes such as Escherichia coli from the digestive tract (Mikkelsen and Jensen, 1998). A low pH in the feed will also help promote protein digestion in the stomach (Longland, 1991).

The objective of this series of experiments was to examine the effect of liquid feeding on postweaning performance and to examine any residual effects on pig performance up to harvest. Experiments 1 and 2 compared fresh liquid feed with dry pelleted feed. Acidified liquid feed was investigated in Exp. 3 and 4 and fermented liquid feed was also investigated in Exp. 4.


   Materials and Methods
Top
 Abstract
 Introduction
 Materials and Methods
Results
 Discussion
 Implications
 Literature Cited
 
Animal Welfare
All experiments complied with EU Council Directive 91/630/EEC, which lays down minimum standards for the protection of pigs, and EU Council Directive 98/58/EC, which concerns the protection of animals kept for farming purposes.

Procedure
In each of four experiments, pigs were weaned at 26 d of age and formed into single-sex groups of even weight. Groups were formed on consecutive weeks until the desired number of replicates was obtained. These groups were blocked on the basis of sex (boars and gilts) and weaning weight and assigned to treatments in a randomized complete block design. The duration of each experiment was 27 d, after which pigs were offered a common weaner diet (dry pellets) to 35 kg. A common finisher diet was offered as a liquid feed (3:1 water:meal) from 35 kg to harvest at 95 kg. The ingredient composition and nutrient content of the experimental diets are presented in Table 1Go. Daily feed intake, growth rates, and carcass characteristics were recorded to harvest.


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  		Table 1. Composition of experimental diets (on an air-dry basis, %)
 
Experiment 1.
There were 12 replicates of each treatment, and each replicate was composed of a single sex group/pen of 16 pigs. The treatments used were 1) dry pelleted feed and 2) fresh liquid feed. For both treatments, 2 kg of Diet 1 followed by 5 kg of Diet 2 was offered per pig. Thereafter, Diet 5 was offered for ad libitum consumption to 27 d after weaning.

Experiment 2.
There were 10 replicates of each treatment, each replicate composed of a single sex group/pen of 15 pigs. The treatments used were: 1) dry pelleted feed and 2) fresh liquid feed. For each treatment, 3 kg of Diet 3 followed by 6 kg of Diet 4 was offered per pig. Thereafter, Diet 5 was offered for ad libitum consumption to 27 d after weaning.

Experiment 3.
There were eight replicates of each treatment, each replicate composed of a single sex group/pen of 14 pigs. The treatments used were 1) dry pelleted feed, 2) fresh liquid feed, and 3) acidified liquid feed. For each treatment, 3 kg of Diet 3 followed by 6 kg of Diet 4 was offered per pig. Thereafter, Diet 5 was offered for ad libitum consumption to 27 d after weaning.

Experiment 4.
There were eight replicates of each treatment, each replicate composed of a single sex group/pen of 14 pigs. The treatments were 1) dry pelleted feed, 2) acidified liquid feed, and 3) fermented liquid feed. For each treatment, 3 kg of Diet 3 followed by 6 kg of Diet 4 was offered per pig. Thereafter, Diet 5 was offered for ad libitum consumption to 27 d after weaning. The experimental diets used in Exp. 4 did not contain an antibiotic growth promoter; Moran et al. (1998) had previously shown that some antimicrobial products can interfere with the microbial fermentation process.

Feeding
Dry Feeding.
Pigs were given ad libitum access to experimental diets from stainless steel dry meal hoppers (750 mm long with three internal divisions; O’Donovan Engineering, Coachford, Co. Cork, Ireland). Water was available for ad libitum consumption from bowls (BALPI, Charleville-Mezieres, Cedex, France).

Liquid Feeding.
Liquid feed was produced by mixing water with dry pelleted feed at a ratio of 2:1 (wt:wt). Liquid feeds were offered three times daily in the 1st wk after weaning and pigs were given ad libitum access to feed thereafter, with care being taken to avoid wastage. In the case of fresh liquid feed, feed was mixed each day. The acidified liquid feed was prepared daily, and food-grade lactic acid (E207—88%; ADM Ringaskiddy, Co. Cork, Ireland) was added to the feed to decrease feed pH to 4.0. Rates of lactic acid addition for this purpose were predetermined and were 30 mL/kg, 45 mL/kg, and 50 mL/kg for Diets 3, 4, and 5, respectively. Fermented liquid feed was prepared as described for fresh liquid feed but with a 1.3% (vol/wt) inoculum of a Lactococcus lactis subsp. cremoris 303 (C. Hansen’s Laboratories, Little Island, Cork, Ireland) culture containing ~109 cfu/mL added as a starter culture to the first mix. The fermented liquid feed diets were prepared by mixing feed in a container so that the container always contained a reserve at least equal to the quantity of feed required for the next day’s feed. This reserve acted as the inoculum when fresh feed and water were added. Additional fresh water was available from bowls (BALPI).

In Exp. 1 and 2 a simple cube-type design of feeder measuring 1,230 x 155 x 155 mm (length x width x height) with two internal divisions was used. For Exp. 3 and 4, troughs of improved design (to minimize feed wastage) were manufactured (O’Donovan Engineering). These troughs measured 1,250 long x 275 mm wide and had a sloped bottom and seven internal spacers that protruded from the front of the trough. This design also had a step up to the trough 50 mm from floor level and 75 mm wide.

Average daily feed intake was calculated on a DM basis and was expressed in grams per day. Gain/feed was calculated as ADG divided by DMI expressed in grams per kilogram.

Housing
Pigs were housed for 27 d after weaning in a controlled environment facility in pens (2.7 x 1.3 m) with cast-iron slatted floors. Air temperature was controlled at 28°C during wk 1 and decreased by 2°C per week to 22°C.

The experimental groups were maintained throughout the entire feeding period up to harvest. From d 28 after weaning to approximately 35 kg, pigs were penned in weaner pens (3.6 x 1.2 m) and temperature was regulated at 20 to 22°C. Here pigs were given ad libitum access to a common dry pelleted feed (Diet 5). At 35 kg, groups were transferred to finisher pens (4.02 x 2.62 m) with fully slatted floors. Air temperature was controlled at 20 to 22°C and a computerized liquid feeding system (Big Dutchman, Vechta, Germany) was used to feed Diet 6 to all pigs.

Harvest
Pigs were harvested when individual pigs reached 95 kg. They were transported 14 km to the abattoir and killed by bleeding after CO2 stunning. Backfat thickness was measured at 6 cm from the edge of the split back between the 3rd and 4th last rib using a Hennessy Grading Probe (Hennessy and Chong, Auckland, New Zealand). The lean meat percentage was estimated according to the following formula (Department of Agriculture and Food [Ireland], 1994): Estimated lean meat percentage in the carcass = 53.41 - 0.786x + 0.266y, where x = fat depth (mm) and y = muscle depth (mm).

Carcass weight was estimated by multiplying by 0.98 the weight of the hot, eviscerated carcass (minus tongue, bristles, genital organs, kidneys, flare fat, and diaphragm) 45 min after harvest. Dressing percentage was calculated as carcass weight/live BW at harvest x 100.

Laboratory Analysis
Representative samples of each diet were taken before feeding in each experiment. Prior to analysis, samples were ground through a 2-mm screen using a laboratory hammer mill (Christy and Norris, Scunthorpe, U.K). Dry matter was determined by oven drying for 4 h at 103°C (Department of Agriculture and Food [Ireland], 1984). Ash was determined by incineration in a muffle furnace (Gallenkamp, London, U.K.) at 550°C overnight. Crude protein was determined as N x 6.25 by a LECO FP—2000 analyzer (Leco Instruments [UK] Ltd., Stockport, Cheshire, U.K.). Fat was determined according to the method described by Usher et al. (1973) by extraction with perchlorethylene in a Foss Let 15300 (A/S N. Foss Electric, Hillerod, Denmark). Crude fiber was measured by a Fibertec semiautomatic system (Tecator, Hoganas, Sweden).

In Exp. 3 and 4, pH of the liquid feeds was measured. In Exp. 3, feed pH measurements were taken each morning after mixing the feeds. In Exp. 4, pH measurements were taken from the mixing tanks before the first feed each morning and after the last feed each evening following replenishment of the feed tank. The pH meter used (HD 8705, Delta OHM, Caselle di Selvazzano, Italy) was calibrated on a daily basis using buffers of pH 4.01 and 6.86.

In Exp. 4, samples of the liquid mix were taken before addition of the starter culture and after 6, 12, 24, and 168 h of fermentation for microbiological analysis. Fresh feed and chlorinated water were added to the fermentation chamber every 24 h and all microbial counts measured up to 24 h of fermentation were taken from the original feed and water mix. In addition, dry pelleted feed, acidified liquid feed, and fermented liquid feed were examined on a weekly basis. Representative samples (300 mL) of each feed were aseptically taken in the morning prior to replenishment of the mixing tank. Samples were refrigerated immediately and microbial counts were performed within 4 h. Weighed samples of feed were homogenized in maximum recovery diluent (Oxoid Ltd., Basingstoke, Hampshire, U.K.) for 4 min in a stomacher (Stomacher 400, Seward, London, U.K.) and diluted 10-fold in the same medium. Appropriate dilutions were pour-plated on MRS agar (de Man et al., 1960; Difco Laboratories, Detroit, MI) and the plates were incubated at 30°C for 3 d to enumerate lactobacilli. Total lactic acid bacteria (bacteria that synthesize lactate as a major end product of carbohydrate fermentation; LAB) counts were obtained on LM17 agar (Terzaghi and Sandine, 1975; Oxoid Ltd.) after 3 d of incubation at 30°C. Coliform bacteria were enumerated on Violet Red Bile Agar (VRBA; Oxoid Ltd.) following 24 h of incubation at 30°C. Yeast and mold counts were performed on YGC agar (International Dairy Federation, 1990; Merck, Darmstadt, Germany) after incubation for 5 d at 25°C.

Statistical Analysis
Boars or gilts and dry pelleted feed or fresh liquid feed were used in a 2 x 2 factorial arrangement in six randomized complete blocks in Exp. 1 and five randomized complete blocks in Exp. 2. In Exp. 3, boars or gilts and dry pelleted feed, fresh liquid feed, or acidified liquid feed were used in a 2 x 3 factorial arrangement in four randomized complete blocks. In Exp. 4, boars or gilts and dry pelleted feed, acidified liquid feed, or fermented liquid feed were used in a 2 x 3 factorial arrangement in four randomized complete blocks. In all cases, each block consisted of groups of pigs allocated to experiment on the same day. All four experiments were analyzed using the GLM procedures of SAS (SAS Inst. Inc., Cary, NC) for a randomized complete block design. The pen was the experimental unit and the model used for the statistical analysis of pig performance had the effects for block, treatment, and sex and the interaction effect of treatment and sex. Weaning weight was used as a covariate in each of the experiments. No interaction effects were observed and only the effect of treatment is presented here. The results were presented as least squares means ± SEM. Duncan’s multiple range procedure was used for means separation in Exp. 3 and 4.


   Results
Top
 Abstract
 Introduction
 Materials and Methods
 Results
Discussion
 Implications
 Literature Cited
 
Diet Composition and Analysis
The ingredient inclusion rates of the commercial diets offered during the experimental period in Exp. 1 (Diets 1 and 2) were not available. However, these diets contained wheat, corn, full-fat soybean meal, dried milk products, soybean oil, minerals, vitamins, and synthetic amino acids. The chemical composition of these diets is presented in Table 1Go. The ingredient composition and nutrient content of Diets 3, 4, 5, and 6 are given in Table 1Go.

Experiment 1
Pig Performance from d 0 to 27.
The effect of dietary treatment on pig performance is presented in Table 2Go. Pigs offered fresh liquid feed had a higher DMI during the period from d 0 to 13 (P < 0.001) and from d 0 to 27 (+26%; P < 0.001) than pigs offered dry feed. Pigs offered fresh liquid feed had lower body weights at d 13 (P < 0.01) and d 27 (P < 0.001) than pigs offered dry feed. As a consequence, pigs offered fresh liquid feed had lower daily gain during the periods from d 0 to 13 (P < 0.01), d 13 to 27 (P < 0.01) and d 0 to 27 (-15%; P < 0.01) than pigs offered dry feed. Similarly, pigs offered fresh liquid feed had lower DM gain/feed during the periods from d 0 to 13 (P < 0.001) and d 0 to 27 (P < 0.001) than pigs offered dry feed.


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  		Table 2. Effect of liquid feeding on pig performance in Exp. 1 and 2 (LSMa ± SEM)
 
Pig Performance from d 0 to Harvest.
Pigs were harvested at 131.6 and 132.3 (SEM = 0.75) d after weaning for dry pelleted feed and fresh liquid feed treatments, respectively (P > 0.05). Pig live weight at harvest and carcass weight were unaffected by treatment (P > 0.05). Dry matter intake, ADG, and gain/feed were similar for both treatments during the period from d 28 to harvest (P > 0.05). However, from d 0 to harvest, DMI was higher (P < 0.001) and DM gain/feed was lower (P < 0.001) for pigs fed fresh liquid feed than for pigs fed dry pelleted feed. Dressing percentage and lean meat percentage were similar (P > 0.05) for both treatments.

Experiment 2
Pig Performance from d 0 to 27.
The effect of dietary treatment on pig performance is presented in Table 2Go. Dry matter intake increased as a result of liquid feeding during the periods from d 0 to 13 (P < 0.01) and d 0 to 27 (P < 0.001), respectively. There was a 19% increase in DMI during the latter period. Weight at d 13 tended to decrease (P = 0.07) as a result of liquid feeding. At d 27, pigs offered fresh liquid feed were 5% lighter (P < 0.01) than pigs offered dry pelleted feed. Daily gain in the period from d 0 to 13 tended to decrease (P = 0.09) due to feeding fresh liquid feed. During the period from d 0 to 27 this difference was significant (P < 0.01). Fresh liquid feed caused a decrease in gain/feed during the periods from d 0 to 13 (P < 0.001), d 13 to 27 (P < 0.001), and d 0 to 27 (P < 0.001).

Pig Performance from d 0 to Harvest.
Pigs were harvested at 135.0 and 135.5 (SEM = 0.60) d after weaning for dry pelleted feed and fresh liquid feed treatments, respectively (P > 0.05). Pig live weight at harvest was lighter (P < 0.05) and carcass weight tended to be lower (P = 0.07) for pigs offered fresh liquid feed than for pigs offered dry pelleted feed. Dry matter intake was higher for pigs offered dry pelleted feed than for pigs offered fresh liquid feed (P < 0.05) during the period from d 28 to harvest; however, ADG and gain/feed were similar for both treatments (P > 0.05) during this period. In the period from d 0 to harvest, gain/feed tended to be higher (P = 0.07) for pigs offered dry pelleted feed than for pigs offered fresh liquid feed. Lean meat percentage was higher for fresh liquid feed than for dry pelleted feed (P < 0.01), whereas dressing percentage was unaffected (P > 0.05) by treatment.

Experiment 3
Diet pH.
Diet pH, measured following mixing of the liquid feeds, is presented in Table 3Go. The pH of fresh liquid feed was greater than 6.0 for each of the diets offered. The pH of each diet was effectively decreased from greater than 6.0 to approximately 4.0 following acidification with lactic acid.


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  		Table 3. pH of fresh liquid feed and acidified liquid feed in Exp. 3 taken after mixing
 
Pig Performance from d 0 to 27.
The effect of treatment on pig performance is presented in Table 4Go. Dry matter intake was unaffected (P > 0.05) by treatment from d 0 to 13. However, DMI was higher for the pigs offered either fresh liquid feed or acidified liquid feed than for pigs offered dry pelleted feed from d 13 to 27 (P < 0.05) and d 0 to 27 (P < 0.01). Pig weights were unaffected by treatment at d 13 (P > 0.05) and d 27 (P > 0.05). Daily gain was not affected by treatment from d 0 to 13 (P > 0.05) and d 0 to 27 (P > 0.05). However, ADG from d 13 to 27 was higher for pigs that were offered acidified liquid feed than for the other treatments (P < 0.01). Gain/feed from d 0 to 13 was unaffected by treatment (P > 0.05). In the period from d 13 to 27, gain/feed was similar for pigs offered dry pelleted feed and acidified liquid feed, and both were greater than that found for pigs offered fresh liquid feed (P < 0.01). Gain/feed from d 0 to 27 was similar for pigs offered fresh liquid feed and acidified liquid feed, and both treatments were less efficient than when pigs were offered dry pelleted feed (P < 0.01).


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  		Table 4. Effect of treatment on pig performance in Exp. 3 and 4a (LSMb ± SEM)
 
Pig Performance from d 0 to Harvest.
Pigs were harvested at 126.6, 128.1, and 127.7 (SEM = 1.09) d after weaning for pigs offered dry pelleted feed, fresh liquid feed, and acidified liquid feed treatments, respectively (P > 0.05). Pig live weight at harvest and carcass weight were not affected by treatment (P > 0.05). During the periods from d 28 to harvest and d 0 to harvest, treatment had no effect on DMI, ADG, or gain/feed (P > 0.05). Neither lean meat percentage nor dressing percentage was affected by treatment (P > 0.05).

Experiment 4
Pig Performance from d 0 to 27.
The effect of treatment on pig performance is presented in Table 4Go. Dry matter intake from d 0 to 13 was higher for pigs offered acidified liquid feed than for pigs offered either dry pelleted feed or fermented liquid feed (P < 0.01). Pigs offered fermented liquid feed and acidified liquid feed had similar DMI, which was higher from d 13 to 27 (P < 0.001) and d 0 to 27 (P < 0.001) than that found for pigs offered dry pelleted feed. Pig weights were similar among treatments at d 13 (P > 0.05), and at d 27 there was a tendency for pigs offered acidified liquid feed to be heavier (P = 0.10). In the period from d 13 to 27 ADG was similar for pigs offered dry pelleted feed and fermented liquid feed, although both had lower ADG than pigs offered acidified liquid feed (P < 0.05). Gain/feed was greater for pigs offered dry pelleted feed than for either of the two liquid feed treatments from d 0 to 13 (P < 0.01), d 13 to 27 (P < 0.001), and d 0 to 27 (P < 0.001), respectively.

Pig Performance from d 0 to Harvest.
Pigs were harvested at 136.2, 131.9, and 132.6 (SEM = 1.45) d after weaning (P < 0.05) for dry pelleted feed, fresh liquid feed, and acidified liquid feed treatments, respectively. Pig live weight at harvest was not affected by treatment (P > 0.05); however, pigs offered dry pelleted feed tended to have heavier carcass weights than pigs on either of the liquid feed treatments (P = 0.06). Dry matter intake was higher for dry pelleted feed than fermented liquid feed (P < 0.05) from d 28 to harvest, and there was a tendency (P = 0.09) for this to occur from d 0 to harvest. Lean meat percentage and dressing percentage were not affected by treatment (P > 0.05).

Diet pH.
The mean pH values for the liquid diets were measured daily and are presented in Table 5Go.


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  		Table 5. pH and temperature (mean ± SD) of liquid diets used in Exp. 4
 
Microbial Analysis of Fermented Liquid Feed.
The microbial growth curves and trend in pH for fermented liquid feed over the first 168-h period after addition of the starter culture to Diet 3 are presented in Figure 1Go. Means for the microbial counts for the treatment diets, which were taken weekly, are presented in Table 6Go. Counts on LM17 (total LAB) and MRS (lactobacilli) were similar and increased from 4.2 log10 cfu/g prior to addition of the starter culture to concentrations of 9.1 log10 cfu/g after 12 h of fermentation. No further increases were observed for the remainder of the 168-h fermentation period (Figure 1Go) or at any point thereafter (Table 6Go).



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  		Figure 1. Mean microbial counts of lactic acid bacteria (bacteria that synthesize lactate as a major end product of carbohydrate fermentation), {blacksquare}; lactobacilli, {square}; total coliforms, {circ}; yeasts, •; and molds, {blacktriangleup}) and pH (bar) in fermented liquid feed over a 168-h period of fermentation.

 

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  		Table 6. Microbial counts (mean ± SD) of diets used in Exp. 4
 

   Discussion
Top
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
Implications
 Literature Cited
 
Fresh Liquid Feed
Experiments 1, 2, and 3 compared the feeding of fresh liquid feed with conventional dry feeding. In each experiment, DMI was increased as a result of liquid feeding up to d 27 after weaning. Increased DMI has previously been demonstrated to result from feeding fresh liquid feed to newly weaned pigs (Kornegay and Thomas, 1981; Partridge et al., 1992). Daily gain decreased as a result of liquid feeding from d 0 to 27 in Exp. 1 and Exp. 2. In Exp. 3, in which a feeder of improved design was used, no difference in ADG was observed between pigs offered dry pelleted feed and fresh liquid feed. This was contrary to the findings of Partridge et al. (1992), who found that liquid feeding increased ADG in a 3-wk trial period. Dry feeding was also found to result in increased ADG compared to liquid feeding in one experiment reported by Kornegay and Thomas (1981), but when the results of the three reported experiments were compiled, ADG of pigs offered liquid and dry feed were similar. Gain/feed decreased as a result of liquid feeding from d 0 to 27 in all experiments. Brooks et al. (1996) also reported that gain/feed decreased in experiments as a result of liquid feeding and cautioned that the term feed usage should be used rather than feed intake because high levels of feed wastage can occur when liquid feeding newly weaned pigs. Improved feeder design may help decrease this wastage, and Partridge et al. (1992) found that gain/feed was unaffected by liquid feeding when an experimental automated liquid feeder that dispensed feed and water at a ratio of 1:1 was used. Brooks et al. (1996) also found that gain/feed of pigs offered liquid feed was similar to that found for pigs offered dry pelleted feed when the feeder design was improved. In Exp. 1 and 2 of the present study, feeder design probably allowed for feed wastage, and therefore feeders of improved design were used in Exp. 3. However, from the gain/feed values, feed wastage still appears to have been a problem in the latter experiment.

Fresh liquid feed in the present experiments was prepared freshly each morning and then fed throughout the next 24 h. This practice would have allowed for the growth of microorganisms in the feed, and in effect the fresh liquid feed used in the present experiments was a partially fermented material. Mikkelsen and Jensen (2000) reported a rapid growth in the microbial flora in liquid feed during the first 24 h after preparation of liquid feed. High microbial activity in the feed could be responsible for the production of biogenic amines (Fox and Wallace, 1997), a disruption of the amino acid balance in the feed (Scholten et al., 2000), and a reduction in the energy content of the fresh liquid feed (Smith, 1976). This is discussed in more detail below. Microbial counts were not taken in the first three experiments; however, a coliform bloom occurred in the first 24 h of fermentation of fermented liquid feed in Exp. 4 (Figure 1Go).

A search of the literature failed to reveal data relating to the effect that liquid feeding newly weaned pigs has on their performance in subsequent stages up to harvest. In Exp.1 and 2, pig weight at the end of the experimental period (d 27 after weaning) was lower for pigs fed fresh liquid feed than for pigs offered dry pelleted feed. In the subsequent period to harvest, pigs on both treatments were offered common diets. Pig weight at the end of this period was similar for both treatments in Exp. 1, indicating that compensatory growth had occurred (McMurtry et al., 1988; Hornick et al., 1999). However, in Exp. 2, live BW at harvest was heavier (P < 0.05) for pigs offered dry pelleted feed than for those given fresh liquid feed. In Exp. 3 pig weight was not affected by treatment at the end of the experimental period or at any period up to harvest.

Acidified Liquid Feed
Microbial Analysis.
The mean LAB counts for acidified liquid feed ranged from 5.44 to 6.39 log10 cfu/g. These values are much lower than those previously reported for acidified liquid feed (Geary et al., 1999), where LAB exceeded 8.0 log10 cfu/g. This was not surprising considering that Geary et al. (1999) added lactic acid and fresh feed to a tank of continually fermenting acidified liquid feed, whereas in the present study acidified liquid feed was prepared freshly each day. A further consequence of this practice was that yeast counts were also lower in the present study. However, coliform concentrations were higher in the acidified liquid feed in the present experiment than in that fed by Geary et al. (1999), possibly due to the lack of competition from LAB. Mean mold counts in the present study ranged from 2.71 to 5.40 log10 cfu/g.

Pig Performance.
Dry matter intake increased with acidified liquid feed from d 0 to 27 in Exp. 3 and 4. This was associated with a reduction in gain/feed in both experiments over the same period. These increases in DMI are consistent with findings for liquid feed in Exp.1 and 2 of the present study and are similar to those previously reported by Russell et al. (1996). There was no benefit from feeding acidified liquid feed from d 0 to 13 in Exp. 3 and 4. However, acidified liquid feed increased ADG from d 13 to 27, and this tended to increase pig weight at d 27 by approximately 5% in Exp. 3 (P < 0.15) and Exp. 4 (P < 0.10). Organic acids have previously been shown to benefit postweaning pig performance when added to the diet or the drinking water (Lawlor, 1992).

Benefits reported from experiments with fermented liquid feed are thought to arise from microbial production of lactic acid and a reduction in diet pH, which ultimately causes a lowering of gastric pH (Mikkelsen and Jensen, 1998; Geary et al., 1999). This reduction in gastric pH has two main benefits: it decreases the population of deleterious microorganisms such as coliforms in the digestive tract (Mikkelsen and Jensen, 1998) and it helps provide suitable conditions for pepsin activity (Longland, 1991), which is necessary for protein degradation in the stomach. To overcome the difficulties previously encountered in controlling fermentation of liquid feed (Brooks, 1999; Brooks et al., 1999), Exp. 3 and 4 had a liquid feed treatment that was supplemented with lactic acid in order to lower the pH to approximately 4.0. To achieve this, the supplementation rate of lactic acid to dry feed ranged from 30 g/kg for the starter diet to 50 g/kg for the weaner diet. This level of supplementation was much greater than the optimum rate of 16 g/kg for dry feed previously found by Roth et al. (1993) but was necessary to decrease the pH of the feed to 4.0. In Exp. 4, pig weight at d 27 tended to be approximately 7% higher with the acidified liquid feed than with fermented liquid feed. Contrary to this, Geary et al. (1999) showed that liquid feed supplemented with lactic acid at concentrations similar to those used in the present study gave growth performance comparable to that found with fermented liquid feed. The difference between the studies in this regard may be explained by the different methods used to prepare the acidified liquid feed in both, as discussed earlier. The acidified liquid feed produced by Geary et al. (1999) had microbial counts more like those found in fermented liquid feed than like those found in the acidified liquid feed that was prepared daily in the present study.

Fermented Liquid Feed
Microbial Analysis.
Feed can be fermented without the addition of starter culture, whereby under appropriate conditions, the indigenous microflora grow and produce lactic acid. Mikkelsen and Jensen (2000) successfully fermented feed without addition of a starter culture and obtained > 9.5 log10 cfu LAB/g after 24 h of fermentation. However, deliberate addition of a starter culture, as in the present study, ensures a more reliable controlled fermentation (Geary et al., 1999).

In Exp. 4 following addition of a L. lactis starter culture, LAB grew to reach concentrations exceeding 9 log10 cfu/g during the first 24 h of fermentation and remained at this level throughout the feeding trial. These concentrations are similar to those obtained by Mikkelsen and Jensen (2000), who depended on the indigenous microflora of the feed to perform the fermentation process. Geary et al. (1999) also obtained similar LAB counts (> 8.0 log10 cfu/g) when a Pediococcus acidilactici starter culture was employed. However, growth was slower in the latter study, with high concentrations of LAB obtained only after 10 d of fermentation. The LAB are an important component of the fermentation, producing lactic acid and thereby reducing the pH of the feed. The pH of the fermented liquid feed in Exp. 4 had reached 4.10 within the first 24 h and remained relatively stable for the duration of the experiment. Mikkelsen and Jensen (2000) also found that diet pH had reached 4.07 after 24 h of fermentation. However, in another study, pH did not drop below 4.5 at any stage, and this pH was only achieved after a 10-d period of fermentation (Geary et al., 1999). The numbers of LAB in the feed are also likely to be important in their own right; evidence shows that they can decrease intestinal coliform concentrations, perhaps by a competitive exclusion mechanism. Muralidhara et al. (1977) reported that feeding an L. lactis strain to pigs had a suppressive effect on coliform numbers. Other studies have described how LAB and acidophilus milk also decreased coliform numbers in pigs and humans, respectively (Ayebo et al., 1980; Tortuero et al., 1995). Fermented liquid feed has previously been shown to decrease stomach pH and lower the concentrations of E. coli along the digestive tract when offered to weaned pigs (Mikkelsen and Jensen, 1998, 2000; Moran et al., 2000). It has also been found to decrease the incidence of diarrhea in weaned pigs when compared with fresh liquid feed (Mikkelsen and Jensen, 1998).

Total coliforms in the fermented liquid feed increased from 2.75 log10 cfu/g to 5.38 log10 cfu/g during the first 24 h of fermentation. Thereafter, mean coliform concentrations in fermented liquid feed were less than 1.5 log10 cfu/g, which was similar to the level found by Russell et al. (1996).

After 24 h of fermentation yeast had reached 6.39 log10 cfu/g, and concentrations as high as 7.07 log10 cfu/g were obtained during the experiment. Geary et al. (1999) found similar concentrations in fermented liquid feed after approximately 4 d of fermentation, and Mikkelsen and Jensen (2000) found in two experiments that yeast did not reach concentrations greater than 4.8 log10 cfu/g during the first 24 h of fermentation. Molds were detectable at a level of 1.90 log10 cfu/g after 24 h of fermentation, further increased to reach 3.85 log10 cfu/g by 168 h and fluctuated around this level throughout the experiment. The presence of molds in feed may be important due to the possible production of mycotoxins. However, molds were not identified in the present study because even the presence of a mycotoxin-producing mold is a poor indicator of the presence or absence of mycotoxins (Osweiler, 1992; Lawlor et al., 2001).

Pig Performance.
Pig weight at d 27 and ADG from d 0 to 27 was similar for pigs offered fermented liquid feed and those given dry pelleted feed. Other studies have found that feeding fermented liquid feed increased ADG (Nielsen et al., 1983; Russell et al., 1996). In a study by Russell et al. (1996) fermented liquid feed increased ADG by up to 25% and pigs offered control dry feed diets had ADG similar to that found in the present study. However, ADG of pigs offered control dry feed diets in the study by Neilsen et al. (1983) was only 179 g/d. In effect, the study by Russell et al. (1996) is the only published study comparable to the present one; other studies on fermented liquid feed did not use a dry feed control or performance levels were very poor. Brooks (1998) reported that fermented liquid feed tended to increase ADG relative to dry pelleted feed; however, the difference was not significant. In the present study, pig weight at d 27 tended to be higher (7%) for acidified liquid feed than for fermented liquid feed. It is likely that the higher microbial load in the fermented liquid feed was detrimental to pig performance; Jensen and Mikkelsen (1998) found that approximately 3% of the dry matter and energy content of the feed is lost during the fermentation process. Geary et al. (1999) found that ADG was similar for pigs fed fermented liquid feed and acidified liquid feed. However, in their study the microbial load was similar for both treatments because the acidified liquid feed was also allowed to ferment. Thus, these results are not directly comparable to those with the acidified liquid feed used in this study.

Dry matter intake was higher for pigs offered fermented liquid feed than for pigs offered dry pelleted feed from d 0 to 27, in agreement with previous findings (Russell et al., 1996; Brooks, 1998). Gain/feed was also less for fermented liquid feed than for dry pelleted feed in the present experiment. Russell et al. (1996) also found this to be the case but showed that improving feeder design could greatly decrease feed wastage.

There may also be other reasons why growth rate on fermented liquid feed was poorer than that observed on acidified liquid feed. This may be related to the presence of biogenic amines, produced by microbial decarboxylation of free amino acids during fermentation (Fox and Wallace, 1997). Many biogenic amines are toxic in high concentrations and negatively influence animal performance (Keirs and Bennett, 1993; Bakker, 1994). Synthetic amino acids are particularly accessible for decarboxylation (Bakker, 1994), a fact that could possibly affect the amino acid balance of the diet. For this reason, recent work with liquid feeding involves fermentation of only the cereal portion of the diet (Scholten et al., 2000; A. Ø. Pedersen, personal communication). Fermentation of liquid feed also decreases its dry matter and energy content by 3%, as a result of the breakdown of sugars in the diet to form lactic acid (Smith, 1976; Mikkelsen and Jensen, 1998). This could also decrease pig performance when fermented liquid feed is offered.


   Implications
Top
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
 Implications
Literature Cited
 
Feeding liquid feed to weaned pigs does not increase pig growth rate and, in fact, can decrease it. It was also found to be quite wasteful of feed, leading to unacceptable DM gain/feed. There are perhaps some merits to feeding lactic acid-supplemented liquid feed, because feed wastage was decreased and average daily gain increases were seen. However, lactic acid is quite expensive and supplementation levels need to be high to achieve a diet pH of 4.0. In theory, fermented liquid feed should give performance similar to that found with acidified liquid feed; however, uncontrolled fermentation of liquid feed is highly unpredictable and growth of undesirable bacteria, yeasts, and molds can cause problems. Even though a starter culture was deliberately added to produce fermented liquid feed, average daily gain and DM gain/feed were decreased. It is concluded from these experiments that there is no benefit from liquid feeding weaned pigs whether in fresh, acidified, or fermented form.


   Footnotes
 
1 Supported by European Union Structural Funds (EAGFF). Back

2 The technical assistance of Tom Cullinan, Jim Dowling, Dan O’Donovan, Jim O’Reilly, and Joanne Hayes is gratefully acknowledged. Back

Received for publication August 7, 2001. Accepted for publication January 25, 2002.


   Literature Cited
Top
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
 Implications
 Literature Cited
 


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