Effective application of enzymes and microbes to enhance the nutritional value of pig feed ingredients: a case for liquid feeding

The increase in feed energy costs and increased availability of co-products from the bio-fuel and food industry represent both challenges and opportunities for the pork industry. An approach that is explored in swine nutrition research at the University of Guelph is to treat co-products with enzymes and microbes at source, and to feed (condensed) liquid co-product directly to pigs using computerized liquid feeding systems.

In general and when used at 15% or less of diet dry matter content, the use of corn steep water and partly fermented corn distillers solubles does not result in major changes in pig growth performance and carcass quality, but can reduce feeding costs. When steeping high moisture corn and corn steep water with phytase, 85% or more of phytate phosphorus is released quickly.

Moreover, through controlled fermentation the lactic acid content of liquid swine feeds can be increased easily to levels required to control feed and food pathogens. There is substantial potential to enhance the feeding value of liquid pig feed ingredients by steeping with enzymes and controlled fermentation. Some of these concepts may apply to dry pig feeding systems as well, but the effects of exogenous feed enzymes and microbes appear larger in swine liquid feeding systems.


Introduction

The increase in feed energy costs and increased availability of co-products from the bio-fuel and food industry represent both challenges and opportunities for the pork industry. At the University of Guelph research is conducted to explore treatment of coproducts with enzymes and microbes at source, and to use computerized liquid feeding systems for feeding (condensed) liquid co-products directly to pigs. This is to enhance the nutritional value of co-products, and to reduce feeding costs and energy costs of processing co-products.

Some of these concepts may apply to dry pig feeding systems as well, but the effectiveness of exogenous feed enzymes and microbes appears substantially larger in liquid feeding systems. In this contribution, the value of liquid feeding corn-based diets to growing-finishing pigs and the use of enzymes and microbes to enhance the nutritional value of co-products are explored.

The value of liquid feeding corn-based diets to growing-finishing pigs Liquid feeding of swine is a relatively new and emerging technology in North America. In Ontario, Canada, more than 20% of growing-finishing pigs are now raised on liquid feeding systems (SLFA, 2006).

Liquid feeding has many potential benefits over conventional dry feeding, such as improved gut health, use of inexpensive co-products from the food and bio-fuel industries, flexibility and ease of diet delivery, and manipulation of feeding value of ingredients with enzymes and bacteria.

Swine liquid feeding research has been conducted largely in Western Europe with barley and wheat-based diets. In recent experiments at the University of Guelph, we have demonstrated that there is no real benefit of liquid feeding conventional corn and soybean meal-based diets to growing-finishing pigs in terms of growth performance and carcass quality (Table 1; de Lange et al., 2006).

Apparently, fibrous ingredients, such as barley and wheat, benefit more from soaking than corn (MLC, 2005). Soaking is also likely to benefit ingredients with endogenous phytase activity; unlike corn and soybean meal, wheat and barley have substantial endogenous phytase activity. In the University of Guelph studies, no concerns were observed with gut health or pathogens, such as salmonella.

However, in a survey of commercial swine farms in Ontario with liquid and dry feeding systems, the prevalence of salmonella was lower on farms with liquid feeding systems, which was a confirmation of European findings (van der Wolf et al., 2001).

Table 1. Impact of feeding corn-based diets in different forms on growth performance aspects of carcass and meat quality of growing-finishing pigs1.

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1de Lange et al. (2006). Liquid-fed pigs received four equal meals daily, and the water:feed dry matter ratio was 2.5:1, while additional water was available from nipple drinkers. In the conventional dry feeding system, pigs were fed ad libitum from single space feeders. SEM represents standard error of treatment means. 2Dry matter basis 3Canadian carcass grading system abTreatment means differ (P<0.05)

For further information on the value and limitations of swine liquid feeding the reader is referred to various reviews (Brooks et al., 2001; van Winsen et al., 2001; MLC, 2005; de Lange et al., 2006).


Feeding value of some co-products and its manipulation

A survey of swine liquid feeding practices and swine feed ingredients that are used in Ontario was conducted (Braun and de Lange, 2004) and is posted on the website of the Swine Liquid Feeding Association (SLFA, 2006). For various co-products, the feeding value – and means to enhance it – were then explored in studies conducted at the University of Guelph.


CORN DISTILLERS SOLUBLES

Corn distillers solubles (CDS) is a liquid co-product from fuel alcohol production, and is generally blended with the distillers grains, prior to drying to generate dried distillers grains plus solubles (DGGS). Condensed CDS contains typically 30% dry matter and, on a dry matter basis, 22% protein, 19% fat, 8.4% ash (1.4% phosphorus), 10% starch, and about 6% soluble sugars.

The feeding value of CDS may be captured more fully and drying costs reduced when condensed CDS is fed in a liquid form to pigs. However, initial on-farm experiences with liquid CDS were not positive, largely because of poor palatability. The latter may be attributed to soluble sugars and mycotoxins that can accumulate in liquid corn co-products.

In a simple and small-scale fermentation unit, fermentation conditions were explored to enhance the nutritional value of CDS (Squire et al., 2004). Standardizing the initial pH to 6 and inoculation with both Lactobacillus acidophilus and Bacillus subtilus bacteria resulted in the most effective fermentation.

This is based on decline of pH, appearance of beneficial lactic acid and volatile fatty acids, and on microbial evaluation of the fermented material. These practices were also effective on a larger scale and when feed was prepared for a pig performance study (Figure 1).

In a preliminary study in which growing pigs were fed diets that contained 0, 7.5, 15.0 and 22.5% CDS, it was established that feed palatability was reduced when the dietary inclusion level exceeded 15.0% (Squire, 2005). In a full-scale grower pig performance study, feeding non-fermented CDS resulted in significant reduction in growth performance, while growth performance of pigs fed the fermented product was not different from the control (Table 2; Squire et al., 2004).

Fermenting CDS apparently provided more beneficial lactic acid and lactic acid producing bacteria (LAB) to the pigs, which enhanced feed and nutrient utilization. The digestibility of energy and protein was slightly reduced in pigs fed fermented CDS (Table 2), apparently due to the generation of volatile organic acids that are largely lost while drying liquid samples for nutrient analyses. The digestibility of fat was increased in pigs fed CDS-containing diets, indicating that fat in CDS is highly digestible.

Only pigs fed the control diet and the non-fermented CDS were raised all the way up to slaughter weight. Feeding CDS did not impact routine carcass measurements that determine carcass value (Table 2; Squire et al., 2005).

However, among the various measurements that were taken to evaluate carcass and loin meat quality (subjective color scores, NPPC and Japanese colour score, firmness and wetness score, subjective marbling score, actual fat depths at grading site, loin eye area, Minolta fat and lean colour, drip loss, 24 hr pH), only the pH at 24 hr post-mortem differed between the two treatments (Table 2). The higher pH in the pigs fed fresh CDS coincided with a trend (P<0.10) towards reduced drip loss from loin samples. This reduced drip loss is a benefit to meat processors.

Figure 1. Lactic acid content and acidity (pH) of fermented and non-fermented (Control) corn distillers solubles used in a pig performance study.

In this study we did not observe a positive effect of fermented feed on gut microflora, in terms of LAB bacteria count in the gut or balance between beneficial LAB and potentially harmful coliform bacteria. We hypothesize that it is more difficult to influence microflora in the lower gut when feeding fermented feed to pigs with a mature digestive system – especially with low stomach pH. Alternatively, fresh CDS may have some prebiotic properties that are lost during fermentation.


CORN STEEP WATER

Untreated corn steep water (CSW) is used to feed cattle, but pigs may utilize nutrients in this product more efficiently. Samples of CSW (n=8) were analyzed to have a pH of 4.3, contain 45% DM and, on a DM basis, 50% crude protein, 2% lysine, 18.0% ash, 5% potassium, 3.3% phosphorus (about 80% of which is bound in phytate), 1.5% magnesium, 0.5% crude fat and 20% lactic acid (Niven et al., 2006b). The high lactic acid content may reduce pathogen load and stimulate gut development in pigs.

In a preliminary finishing pig performance trial, the inclusion of 5% CSW (DM basis) in the diet numerically enhanced live body weight gain and gain:feed (1.10 vs 1.17 kg/day, SE 0.03, and 2.46 vs 2.30 kg/kg, SE 0.05), while the inclusion of 10% CSW in the diet numerically reduced pig performance (1.06 kg/day and 2.45 kg/kg; Niven et al., 2006b).

Studies were then conducted to explore means to enhance the nutritional value of CSW.

Table 2. Growth performance, apparent fecal nutrient digestibility and carcass quality of pigs fed a corn and soybean meal-based control diet, or corn and soybean meal-based diets with either non-fermented or fermented CDS at 15% of diet dry matter1.

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1Squire et al. (2005) and Squire (2005). All diets were fed in a liquid form. 2Dry matter basis 3Canadian carcass grading system abValues within rows followed by different superscripts differ (P<0.05)

In controlled small-scale fermentation studies we were unable to ferment the product, most likely because of the antimicrobial properties of the high lactic acid content. In an attempt to release phytate-bound phosphorus, 200 mL samples of CSW were steeped with a commercially available phytase at four inclusion levels (125, 250, 500 and 750 FTU/kg DM) and at two temperatures (40 ºC and 50 ºC; typical temperatures during initial storage of CSW at the processing plant).

The rate of phytate phosphorus release was increased (P<0.05) with increased temperature and phytase inclusion level. At 50 ºC and with 750 FTU/kg appearance of soluble phosphorus was maximized at 27.17 g P/kg DM (SE 0.28) of total phosphorus after 24 hrs. For all treatment combinations, there was no further increase (P>0.10) in soluble phosphorus after 48 hrs of steeping.

In a subsequent and larger scale finishing pig study, the impact of feeding phytase treated CSW at different dietary inclusion levels was then evaluated (Table 3; de Lange et al., 2006). These findings show a linear negative effect of dietary inclusion level of phytase treated CSW on growth performance, but the drop in performance was most apparent when the dietary inclusion level of CSW exceeded 15%. Carcass value was not influenced by dietary CSW inclusion level, indicating that this product can be used effectively in pig diets, provided that ingredient costs offset the changes in feed efficiency and body weight gain.

Table 3. Pig performance and carcass characteristics of pigs fed liquid diets containing varying inclusion levels of phytase-treated corn steep water (CSW)1.

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1de Lange et al. (2006) 2Pen is the experimental unit with 4 pens per treatment and 8 pigs per pen 3Dry matter basis 4Canadian carcass grading system abValues followed by different superscripts differ (P<0.05)

HIGH MOISTURE CORN

High-moisture corn (HMCorn) undergoes partial fermentation during storage that may enhance its nutritional value for pigs. For example, stored HMCorn contains more soluble phosphorus (an approximation of non-phytate and available phosphorus) than fresh HMCorn (0.13% vs 0.03% in DM; total phosphorus was 0.29%) and contains 19 mM lactic acid and 19 mM acetic acid (Niven et al., 2006a).

However, the lactic acid content in stored HMCorn is below the critical level of 75 mM at which level it reduced the pathogen load of feeds (Beal et al., 2002). At the same time the acetic acid levels should be controlled; levels exceeding 20 mM have been associated with reduced diet palatability (Brooks et al., 2001). Based on these considerations further studies were conducted to enhance the nutritional value of HMCorn.

Simply mixing HMCorn with water (1:2 ratio) and storing it in 1 L bottles at 37 ºC increased soluble phosphorus content in the first 6 hrs by 0.05%, and then remained constant thereafter, indicating little endogenous phytase activity. Steeping of HMCorn with a commercial phytase product was examined at four inclusion levels (0, 500, 750, 1000 FTU/kg) and at either 21ºC or 37ºC.

At 37ºC added phytase released virtually all phytate phosphorus within 6 hrs irrespective of the level (soluble phosphorus levels increased by 0.15%); at 21ºC, the increase in soluble phosphorus was maximized at 0.12% after 24 hrs (Niven et al., 2006a). Apparently, the release of the last phosphorus atom from the phytate molecule requires higher temperatures. This demonstrates, however, that the use of phytase in liquid swine feeding, and when the feed is allowed to steep, is more effective than in dry feeding systems.

When phytase is added to dry pig feeds, about 60% or less of phytate phosphorus is released (Kornegay and Verstegen, 2001; Rapp et al., 2001). Given the anti-nutritional effects of phytate, phytase will not only increase availability of phosphorus, but also that of other nutrients that may be bound to the phytate complex, such as amino acids, microminerals and energy yielding nutrients (Kornegay and Verstegen, 2001).

In our studies, lactic acid content increased to between 147 and 179 mM and was not affected (P>0.05) by inoculation with exogenous Lactobacillus and Bacillus bacteria.

The endogenous LAB in HMCorn appear capable of generating substantial amounts of lactic acid during steeping HMCorn with water. We are now exploring potential beneficial effects of feeding HMCorn steeped with phytase on phosphorus utilization and measures of gut health in newly weaned piglets.

Acknowledgement

The swine liquid feeding research program at the University of Guelph is supported by a number of organizations, including: Swine Liquid Feeding Association, Natural Sciences and Engineering Research Council, Ontario Pork, OMAFRA Food Safety Research Program, OMAFRA & University of Guelph Research Partnership Program, Big Dutchman, Daco Laboratories Inc., Grand Valley Fortifiers, B.S.C. Nutrition, Great Lakes Nutrition, Furst McNess, Chris Hanssen Laboratories, Kenpall, Dwyer Manufacturing Ltd., Farmix/Ridley Inc., Corn Products International.


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