Batch Fermentation of Cheese-Whey Supplemented Poultry, Swine and Cattle Waste Filtrates

Biological Wastes 22 (1987) 23-37

Batch Fermentation of Cheese-Whey Supplemented Poultry, Swine and Cattle Waste Filtrates*

M. D. Erdmant & C. A. Reddy

Departments of Animal Science and of Microbiology and Public Health, Michigan State University, East Lansing, Michigan 48824, USA

(Received 2 June 1986; revised version received 25 November 1986; accepted 2 January 1987)

ABSTRACT

The fermentative conversion of poultry, swine and cattle feedlot waste filtrates (PWF, SWF and CWF, respectively) into nitrogen-rich feed supplements for ruminants was investigated. Unsupplemented or cheese-whey supplemented waste filtrates were fermented either individually or in 1:1 combination with each other at 43°C. Indigenous flora served as the inoculum. Ammonium hydroxide was automatically added to the fermentor to maintain pH at 7.0. Ammonium hydroxide addition was a function of organic acid production and was responsible for the increase in total nitrogen content in the fermentation product. The ammonium hydroxide neutralized the ferment- ation acids produced and formed ammonium salts of organic acids, which have been shown to be valuable as nitrogen supplements for ruminant animals. Fermentation of unsupplemented waste filtrates resulted in little change in total nitrogen content but ammonia nitrogen concentration increased 8"3-fold during P WF fermentation, suggesting transformation of urea and uric acid nitrogen to ammonia nitrogen. Fermentation of cheese-whey supplemented PWF, SWF and CWF resulted in products containing 62%, 47"4% and 72% crude protein (total nitrogen x 6.25), respectively, on a dry basis; ammonia nitrogen, respectively, accounted for 63%, 53% and66% of the crude protein. Lactate and acetate were the major acids in fermented PWF ( 73% and20%, respectively), whereas lactate, acetate, and propionate (30%, 29% and26%, respectively) were the predominant acids in fermented SWF. Fermentation of cheese-whey supplemented PWF+ SWF and PWF+ CWF resulted in

* Michigan Agricultural Experiment Station Journal Article No. 9109. t Present address: USDA-ARS, Tifton, Georgia 31794, USA.

23 Biological Wastes 0269-7483/87/$03'50 © Elsevier Applied Science Publishers Ltd, England, 1987. Printed in Great Britain

24 M. D. Erdman, C. A. Reddy

products containing, respectively, 51.6% and 56" 7% crude protein; ammonia nitrogen accounted for 81% and 61% of the crude protein, respectively. Lactate, acetate and propionate were the major acids (54"5%, 24.5% and 15.7%, respectively, o f the total acids produced) in P W F + S W F

fermentation. In the corresponding P W F + C W F fermentation, the same acids accounted for 69%, 21% and 8% of the total acids produced, respectively. In all fermentations, use of the added lactose was > 90% within 8 h and > 90% of the carbon from lactose was recovered in the organic acids produced. These results indicate that ammoniated organic acid fermentation of livestock wastes, combined with a readily metabolizable carbohydrate waste, is a rapid and efficient means o f recycling livestock wastes into nitrogen-rich produets, poten tially useful as feed supplements for ruminants.

INTRODUCTION

Disposal of the large amounts (1.0 x 108 dry metric tons) of livestock wastes produced annually in the United States represents a serious environmental pollution problem and an economic and nutrient loss to the livestock industry (Sloneker et al., 1973; Yeck et aL, 1975; Van Dyne & Gilbertson, 1979). Recycling livestock wastes as animal feeds, after appropriate processing, is an attractive alternative to disposal of wastes (Bhattacharya & Taylor, 1975; Anon., 1977).

Poultry waste has been ensiled (Harmon et al., 1975; Labosky et al., 1977; Syrett, 1977; Caswell et al., 1978) and fermented aerobically and anaerobically (Jackson et al., 1970; Vuori & Nasi, 1977). Several studies are also reported on the fermentative conversion of swine waste (Wilson & Houghton, 1974, 1977; Garrett & Allen, 1976; Henry et al., 1976; Weiner, 1977a,b; Chung et al., 1978), cattle feedlot waste (Weiner & Rhodes, 1974; Prior et al., 1986a) and buffalo waste (Singh et aL, 1985). Overall, these studies showed that fermentative conversion of unsupplemented wastes resulted in little improvement in nutritional value or increased crude protein content when compared to unfermented substrates (Prior et aL, 1986a,b).

In the ammoniated organic acid fermentation, a fermentable substrate is converted to organic acids, and these acids are continuously neutralized by the addition of ammonium hydroxide or ammonia gas to form ammonium salts of the organic acids (Gerhardt & Reddy, 1978). Nitrogen addition to the fermentation results in a ruminant feedstuff rich in crude protein. This approach was successfully used for recycling cheese-whey as a crude protein feed supplement for ruminants (Huber et al., 1976; Reddy et al., 1976; Crickenberger et al., 1981). This crude protein feed supplement has been approved for feeding by the Food and Drug Administration (CFR 573.450) and is being used by several commercial firms. Batch and continuous

Fermentation of cheese-whey supplemented livestock wastes 25

fermentation processes for the conversion of cattle feedlot waste filtrate (CWF) into nitrogen-rich products have been described (Reddy & Erdman, 1977; Erdman & Reddy, 1979, 1986). In these processes, CWF was supplemented with cheese-whey, a complementary carbohydrate-rich waste, and was fermented under controlled conditions. The two wastes (CWF and cheese-whey) were complementary in the sense that the CWF, which was deficient in readily fermentable carbohydrate, primarily provided the inoculum and growth factors whereas the cheese-whey primarily con- tributed lactose to the fermentation (Erdman & Reddy, 1986). Organic acids produced during the fermentation were neutralized with ammonium hydroxide to produce ammonium salts of organic acids, which have been shown to be excellent sources of dietary nitrogen and energy for ruminants (Hungate, 1966; Howes, 1972; Dutrow et al., 1974; Crickenberger et al., 1981).

The objective of this study was to evaluate fermentative conversion of unsupplemented and cheese-whey supplemented poultry, swine and cattle feedlot waste filtrates, and mixtures of these wastes to produce nitrogen-rich products that are potentially utilizable as ruminant feed supplements.

MATERIALS AND METHODS

Fresh poultry waste ( _< 1 day old from 20 to 24 month old leghorn hens) was collected from concrete floors in a 5000 head, caged house. Hens were fed a layer ration described by Flegal et al. (1975). Fresh swine waste was collected from the surface of concrete slotted pens containing growing-finishing pigs (Hampshire and Yorkshire, 59kg body weight) which were fed a corn-soybean ration fortified with lysine (Miller, 1975). Cattle feedlot waste was collected from uncovered pens with concrete floors containing steers (Hereford x Angus, 317 to 362 kg body weight) fed a corn-corn silage ration (Fox & Cook, 1977).

The fractionation and fermentation scheme used for poultry waste, swine waste and cattle feedlot waste is presented in Fig. 1. Total Solids in poultry, swine and feedlot wastes were 27.6, 35.6 and 16.5%, respectively. Each type of waste was collected and processed individually. Wastes were diluted 1 : 1 (w/w) with tap water and mechanically agitated until a homogeneous slurry was obtained (30 min). The slurry was passed through a No. 8 sieve (3 mm 2 mesh) to obtain filtrate and residue fractions. Poultry waste filtrate (PWF) and swine waste filtrate (SWF) contained 90-7% and 100%, respectively, of the Total Solids originally present in unfractionated wastes (Fig. 1). In contrast, cattle waste filtrate (CWF) accounted for only 17.6% of the Total Solids in the starting material. In mixed fermentations, equal volumes of the

26 M. D. Erdman, C. A. Reddy

FILTRATE

Waste % TS recovered

PWF 90.7

SWF I00.0 CWF 17.6

1 FERMENTED

+- Waste carbohydrate

43"C pH controlled with ammonia

indigenous flora

1 PRODUCT

WASTE

PW, 27.6*/. TS

SW, 3 6 . 6 % TS

CW, 16.5% TS

DILUTED I:1 ( w / w )

1 AGITATED

1 FILTERED (SIEVE .NO. 81

RESIDUE

Waste % TS recovered

PWR 10.9 SWR 0.0

CWR 81,4

Fig. 1. Scheme for fractionation and fermentation of poultry waste (PW), swine waste (SW) and cattle feedlot waste (CW). PWF, SWF, and CWF are abbreviations for poultry, swine and cattle feedlot waste filtrates, respectively. PWR, SWR, and CWR represent poultry, swine and

cattle feedlot waste residues, respectively. Total Solids is represented by TS.

specified filtrates were combined. In most fermentations, the individual waste filtrate or mixtures of these filtrates were supplemented with cheese- whey powder (Michigan Milk Producers, Ovid, MI) at 5 g per 100 ml. Cheese whey powder, rather than liquid cheese-whey, was used because it is a convenient and uniform substrate. Also, previous studies showed that cheese-whey powder and liquid cheese-whey were comparable substrates yielding similar data (Erdman & Reddy, 1986). Cheese-whey powder

Fermentation of cheese-whey supplemented livestock wastes 27

supplementation at the 5% level typically contributed per 100ml: 3"83 g of lactose, 0"5 g lactic acid, and 0.05 g total nitrogen (Erdman & Reddy, 1986).

A 28-liter fermentor (model CMF-128S, New Brunswick Scientific, New Brunswick, N J) equipped with automatic temperature, agitation and pH controls, was used throughout the study. The fermentor was operated at the 20-liter level; temperature was maintained at 43°C and pH controlled at 7.0 by the automatic addition of ammonium hydroxide. The increased total nitrogen content in the fermentation product was due to the ammonium hydroxide addition. All other procedures were previously described (Reddy & Erdman, 1977; Erdman & Reddy, 1986).

Samples were collected periodically throughout the fermentation in glass screw-capped vials and immediately stored at -18°C until analyzed. Samples were analyzed for total nitrogen, ammonia nitrogen, organic acids, lactose and total solids as previously described (Erdman & Reddy, 1979). Lactose carbon recovery was estimated by quantitatively accounting for the lactose carbon decrease during fermentation compared with organic acid carbon increase. Crude protein represents total nitrogen × 6"25. The presence of aerobic and anaerobic pathogens was checked at the Michigan State University Animal Health Diagnostic Laboratory. Mean values of samples analyzed in duplicate from two fermentations replicated in time were reported.

A preliminary process cost analysis was performed using the pilot scale, 2270-1itres fermentation system at Michigan State University (Reddy et al.,

1976). Operating costs were $0.10 per kilowatt-hour of electricity, $0"625 per cubic metre of propane gas, $0-34 per kilogram of aqueous ammonia (29% ammonia), $0.033 per litre of acid cheese-whey (which is the current hauling and land disposal cost), formaldehyde solution (37%) stabilization at a final concentration of 0"05%, and $3"50 per hour labor costs. A $5-00 credit was applied to the value of utilizing the livestock waste. Electrical energy and propane fuel requirements were estimated from equipment design specifications while operating at the 2 metric ton per day level. Filtering estimates were calculated using a high speed slurry separator (Gascoigne, Boythorpe Farm Systems Limited, London).

RESULTS

Unsupplemented fermentations

The compositions of unsupplemented PWF, SWF and CWF before and after fermentation are presented in Table 1. The total nitrogen content was low in all three wastes before fermentation, but the unfermented PWF and

28 M. D. Erdman, C. A. Reddy

TABLE 1 Composition of Unsupplemented Poultry (PWF), Swine (SWF) and Cattle (CWF) Waste

Filtrates Before and Following Fermentation °

Component b P WF S WF C WF

Time (h) Time (h) Time (h) 0 24 0 24 0 24

Total nitrogen 1.09 1.11 0.72 0.72 0.26 0.27 Ammonia nitrogen 0.10 0.83 0.19 0.48 0.02 0.04 Lactose 0-03 0.03 0.02 0.02 0.01 0.01 Total acids 121.1 141-0 35.8 91.0 28.8 34.6

Acetic 61-6 107-7 18.7 50.7 22.0 27.6 Propionic 25"2 16'6 10-9 27-1 3'7 5"4 Butyric 20"6 16.7 6"2 13'2 0'4 1'3 Lactic 13.7 0'0 0'0 0"0 2'7 0'3

a Fermentations were conducted anaerobically at 43°C with continuous agitation. b Total nitrogen is expressed as g per 100ml of filtrate. Ammonia nitrogen and lactose concentrations are expressed as g per 100ml of clarified filtrate, whereas organic acids concentration is expressed as micromoles per millilitre of clarified filtrate.

SWF contained several fold more total nitrogen than CWF. Fermentat ion of unsupplemented wastes resulted in no increase in total nitrogen, but ammonia nitrogen concentration greatly increased during fermentation of unsupplemented P W F and SWF and represented 66.7% and 74.8%, respectively, of the total nitrogen content of these products. Organic acids changed qualitatively and quantitatively during fermentation of un- supplemented P W F and SWF although total organic acid concentration was relatively low. In contrast, little change in organic acids occurred during fermentation of CWF.

Cheese-whey supplemented fermentations

Total nitrogen (Fig. 2A) and ammonia nitrogen (Fig. 2B) increased rapidly during the first 6 to 8 h of cheese-whey supplemented PWF, SWF and C W F fermentations and remained relatively constant thereafter, except that ammonia nitrogen in P W F fermentation increased throughout 24 h. Total nitrogen increase due to ammonium hydroxide addition was 164%, 65% and 37%, respectively, during the first 6h of CWF, SWF and P W F fermentations. Ammonia nitrogen accounted for 55%, 66% and 78% of the total nitrogen, respectively, in fermented SWF, C W F and PWF. Most of the added lactose ( > 9 0 % ) was utilized within the first 6 h of fermentation (Fig. 2C).

Fermentation of cheese-whey supplemented livestock wastes 29

1.8 ,.z, .~ , . 5 -

_ 1.2- ~ 0.9-

~0.6- v .

0.3- 1.2

Z A

o.9-

Z

,,~ ~0.6-

A

e

i " i ' i " i •

- F "

O.O- J * i • i , i •

4 c

o • , , • j

o ; ,~ ,s 20 2~ TIME (hours)

Rate of increase in total nitrogen

E 3

0

8 ~ 2 E I E

Fig. 2. (A) and ammonia nitrogen (B) and rate of lactose utilization (C) during fermentation of poultry (O), swine (E]), and cattle (0 ) waste

filtrates supplemented with cheese-whey.

480~ ~A

.u 4°° I

,=, 320- 9= ~ 240-

i ~ 16o- $. 80-

0- i i i a

0 5 10 I 5 20 25

TIME [HOURS) SO

B

"3.5 20- ~ _~ .

O 1%

< 90- -

~ 60- 30-

0- i i i i , i

5 I 0 15 20 25

TIME (HOURS) Fig. 3. Concentrations of acetic (Q), pro- pionic (D), butyric (~), and lactic (A) acids during fermentation of poultry (A) and swine (B) waste filtrates supplemented with cheese-

whey.

The concentration of total organic acids after 8h of cheese-whey supplemented PWF fermentation was 632 ~moles ml- i . Lactic and acetic acids were predominant and accounted for 73% and 20%, respectively, of the total organic acids produced (Fig. 3A). Minor amounts ofpropionic and butyric, and trace amounts (data not shown) of isobutyric, fumaric and succinic acids were also observed. During fermentation of cheese-whey supplemented SWF (Fig. 3B), lactic acid concentration increased initially, but decreased dramatically after 4h. Acetic and propionic acid con- centrations greatly increased during the first 8h, remained relatively constant through 17 to 18 h, and then gradually decreased through 24h of fermentation. The flux of organic acids observed during this fermentation suggests that dynamic changes in microbial populations occur at different

30 M. D. Erdman, C. A. Reddy

stages of the fermentation. The concentrations of total organic acids were 192, 371 and 295/~moles ml - i at 0, 4 and 24 h, respectively, of fermentation. Lactose carbon recovery in the form of organic acids was > 90% after 8 h fermentation for CWF, PWF and SWF. Similar recoveries occurred for mixed, lactose supplemented fermentations.

Lactic and acetic acids were predominant and accounted for 72% and 26%, respectively, of the total acids present at the end of 6h CWF fermentation. Between 6 and 24 h, lactic acid decreased dramatically, propionic and butyric acids increased and acetic acid remained relatively constant. The per cent distributions of lactic, acetic, propionic and butyric acids at the end of 24h of fermentation were 24%, 34%, 14% and 28%, respectively.

Cheese-whey supplemented mixed waste fermentations

Poultry waste filtrate is high in total nitrogen, most of which is urea and uric acid (Bhattacharya & Taylor, 1975). Based on the observation that 66% of the total nitrogen was converted to ammonia nitrogen during fermentation of PWF (see Table 1), we investigated the possibility of reducing exogenous ammonia addition during fermentation of CWF or SWF when supple- mented with poultry waste and cheese whey. These results are presented in Table 2.

The product obtained after 8 h of cheese-whey supplemented PWF + CWF fermentation contained 1-0% total nitrogen on a wet basis (9.1% on a dry basis). Ammonia nitrogen accounted for 81% of the total nitrogen in the product. Most of the added lactose (92%) was metabolized

TABLE 2 Substrate Changes During Fermentation of PWF + CWF and PWF + SWF Mixtures

Supplemented with Cheese-whey a'h Waste Time TN AN Lactose Ac id~" Acetic Propionie Butyric Lactic mixture (h) ( % ) ( % ) ( % ) ( % )

P W F + C W F 0"0 0"59 0"11 2"90 83'9 52'3 13'6 12"4 21.7

4'0 0"91 0"62 1"36 315'2 20"7 9"3 2"0 68'0 8-0 1"02 0"80 0.24 486"5 20-7 8"3 1"9 69" I

24"0 1'01 0"82 0.14 302"7 30"6 15'4 29"7 24"3 P W F + S W F 0-0 078 0"12 3-34 127"9 45"9 18"7 13"7 21"7

4"0 1"22 0"59 1-02 406" I 22-9 15"6 5"6 55"9 8"0 1"26 0"77 0"31 470-0 24'5 1'5"7 5-3 54-5

24"0 1"26 0"82 0"27 307'1 39'0 23.6 25-2 12"2

5g cheese-whey powder per 100ml of waste mixture was employed. Fermentat ions were maintained at 43°C and pH 7"0. Abbreviat ions: TN, Iotal nitrogen; AN, ammonia nitrogen: PWF, poultry waste filtrate; SWF, swine waste filtrate; CWF, cattle waste filtrate.

b Total nitrogen is expressed as g per 100 ml of filtrate. Ammon ia nitrogen and lactose concentrations are expressed as g per 10Oral o f clarified filtrate, whereas acids concentration is expressed in micromoles per millilitre o f clarified filtrate, and per cent of acids.

Fermentation of cheese-whey supplemented livestock wastes 31

within 8 h. Total organic acid concentration was 486 #moles ml- 1 at the end of 8 h; lactic and acetic acids were predominant and accounted for 69% and 21% of the total acids present. Continuing this fermentation for 24h resulted in a slight decrease in total nitrogen, a corresponding increase in ammonia nitrogen and a 38% decrease in total organic acids. These data again suggest that it is desirable to terminate the fermentation at 8 h. Cheese- whey supplemented PWF + CWF mixed, fermentation resulted in higher total nitrogen and ammonia nitrogen than the corresponding CWF fermentation, but lower values than those seen in cheese-whey supplemented PWF. Furthermore, the amount of exogenous ammonia consumed during the fermentation of PWF + CWF mixed fermentation was 14% less than that consumed during the fermentation of corresponding CWF ferment- ation (data not shown).

Fermentation of cheese-whey supplemented PWF + SWF for 8 h resulted in a product containing 1.3% total nitrogen on a wet basis (8"3% on a dry basis); ammonia nitrogen accounted for 61% of the total nitrogen. Total nitrogen and ammonia nitrogen increased 62% and 542%, respectively, during the fermentation. Most of the added lactose (90"7%) was metabolized during fermentation. Total organic acid concentration was 470/~moles ml- at 8 h. The relative proportions of lactic, acetic, propionic and butyric acids were 55: 24:16: 5, respectively. Continuing the fermentation for 24 h resulted in no increase in total nitrogen, only a slight increase in ammonia nitrogen, and about a 35% decrease in concentration of organic acids, indicating that it would be preferable to terminate the fermentation at 8 h. Furthermore, cheese-whey supplemented PWF + SWF fermentation had total nitrogen and total organic acids concentrations comparable to those of cheese-whey

TABLE 3 Process Cost Estimate for Poultry Waste Fermentation"

Item Estimated cost (US dollars)

Livestock waste - 5.00 Waste collection 0.88 Cheese-whey per dilution 57.75 Filtering 14.38 Ammonium hydroxide 4.29 Agitation-pumping 4.80 Temperature control 16-40 Formaldehyde preservation 42"59 Labor 21.00 Cost per metric ton 157.09

Based on 2-metric ton pilot plant.

32 M. D. Erdman, C. A. Reddy

supplemented SWF. The amount of exogenous ammonia consumed during the fermentation of PWF + SWF was similar to that consumed during the corresponding SWF fermentation; thus there appears to be no real advantage of fermenting PWF and SWF together as compared to fermentation of SWF alone.

The estimated processing cost for PWF was $157-09 per metric ton (Table 3). Cheese-whey transportation and formaldehyde preservation costs accounted for 64% of the total processing cost. Similar costs would be expected for the CWF, SWF, and mixed fermentations, except exogenous ammonia addition costs would be expected to change. Exogenous ammonia cost estimates were $5.61, $6-56, $5.13 and $5.73 per metric ton for SWF, CWF, PWF + CWF and PWF + SWF fermentations, respectively. Filtering costs for SWF would not be necessary since all the waste was recovered in the filtrate (Table 1).

DISCUSSION

The results show that ammoniated organic acid fermentation ofPWF, SWF, or mixtures of these wastes supplemented with cheese-whey at the 5 % level, was efficiently conducted batchwise at pH 7.0 and 43°C using indigenous microbial flora as the inoculum. The product obtained had total nitrogen and total organic acid contents higher than the starting material and the fermentation time was several fold shorter than a number of CWF fermentation processes previously described (Jackson et al., 1970; Weiner & Rhodes, 1974; Rhodes & Orton, 1975; Weiner, 1977a,b; Reddy & Erdman, 1977; Morrison et al., 1977) but was comparable to an optimized batch fermentation process for CWF recently described by Erdman & Reddy (1986). The shorter fermentation time and higher total nitrogen content is attributed to the rapid lactose metabolism and subsequent neutralization of the fermentation acids with ammonium hydroxide.

Previous studies have shown that the addition of readily fermentable carbohydrate sources to livestock wastes increased the rate of fermentation, the concentration of organic acids, or single-cell protein content (Weiner & Rhodes, 1974; Vuori & Nasi, 1977; Reddy & Erdman, 1977; Weiner, 1977a,b). Although cheese-whey powder was used in this study for convenience, unprocessed cheese-whey would be a more economical substrate and would also serve as a diluent. Current cheese-whey disposal costs are $0-03 and $0.033 per liter for city sewage or hauling and land disposal, respectively. Utilization of this raw waste resource would reduce dairy manufacturing costs. In areas where cheese-whey is unavailable, other waste carbohydrates such as potato or sugar beet processing wastes may be

Fermentation of cheese-whey supplemented livestock wastes 33

substituted (Reddy & Erdman, 1977). The fermentation characteristics and products obtained, however, may be substantially different from those observed for the cheese-whey supplemented fermentation.

Protein in ruminant rations is generally the most expensive component; therefore, any process designed to recycle a waste should conserve as much of the utilizable nitrogen in the waste as possible. Extensive studies have shown that dried poultry waste is useful as a feed supplement for ruminants and other livestock species (Bhattacharya & Taylor, 1975; Flegal et aL, 1975); however, it has been reported that as much as 15% of the total nitrogen in the fresh poultry waste may be lost by volatilization during the drying process, and energy costs involved in drying are significant. In contrast, during PWF fermentation by the indigenous flora as described here, practically all the nitrogen in the original material was conserved. The results also suggest that urea and uric acids, which were the main nitrogenous components in fresh poultry waste, were being converted to ammonia nitrogen during the fermentation; ammonia nitrogen is known to be the preferential nitrogen source for supporting the growth of a majority of the microbial populations in the rumen.

Maximum amounts of organic acids were produced within 8 h during the fermentation of cheese-whey supplemented SWF and PWF. This was followed by extensive qualitative and quantitative changes in these acids between 8 to 24h indicating the occurrence of dynamic microbial population changes. For example, in CWF fermentation, lactate and acetate were the predominant acids at the end of the first 6 to 8 h of fermentation following which there was a dramatic decline in lactic acid concentration and a corresponding rise in propionate and butyrate concentration between 8 to 24h; acetate levels remained essentially the same during the fermentation (Erdman & Reddy, 1979, 1986). In SWF fermentation, however, lactate, acetate, propionate and butyrate were all predominant in the first 6 to 8 h, but after 8 h, lactate, as in the CWF fermentation, was metabolized rapidly and butyrate concentration increased. In contrast, in cheese-whey supplemented PWF fermentation, lactate and acetate peaked in 8 h and remained relatively constant through 24 h. These results suggest that different microbial populations are active during different ferment- ations and that extending the fermentation beyond 8 h is not desirable since as much as 35% of the organic acids undergo further metabolism between 8 to 24 h.

An important concern in fermentative recycling of agricultural wastes to animals is the effects of pathogenic microbes or toxic residues present in the fermentation products (Fontenot & Webb, 1975; Gilka, 1985). In the study presented here, fermentation samples were routinely submitted to the Bacteriology Section of the Animal Health Diagnostic Laboratory at

34 M. D. Erdman, C. A. Reddy

Michigan State University. All samples were reported to be negative for aerobic, facultative or anaerobic pathogenic bacteria. Nonetheless, stabilization of the product by pasteurization is recommended before feeding to animals unless further investigations show that this precaution is unwarranted. Pasteurization, however, would increase the cost of the process. Other researchers have stabilized the fermentation product with formaldehyde (Kung et al., 1981).

The ammoniated organic acid fermentation process applied to PWF, SWF, CWF, and mixed waste filtrates was an effective means of converting these wastes into potentially useful nitrogenous feed supplements for ruminants. Although extensive feeding trials with the fermentation product have not been performed, hydraulic addition of the fermented product to forage in a completely mixed ration or as a protein replacement appears to be the most suitable method for feeding. In preliminary feeding trials with steers (M. Yokoyama, pers. comm.), corn silage at 35% dry matter content (9"5% CP) was supplemented with sufficient fermented CWF derived from beef cattle to raise the CP content to 12%. The CWF was stabilized with formaldehyde prior to feeding. The steers accepted the diet and no palatability or product storage problems were observed. Lactating Holstein cows fed beef CWF, however, experienced palatability difficulties and decreased dry matter intake and total milk production when compared to similar animals fed conventional corn silage diets (Kung et al., 1981). Additional scale-up and feeding studies are needed to determine more fully the nutritional value of the fermented livestock waste products.

Accurate processing cost estimates are difficult to obtain because of cost differences in various geographic locations and variations in livestock husbandry techniques (Ashrafet aL, 1974; Azevedo & Stout, 1974; Midwest Plan Service, 1975). The estimated processing cost, however, for the fermented livestock product was comparable to retail costs of commercially prepared complete rations. Additional reductions in processing costs may be achieved by livestock producers located near whey production facilities. Further research is needed to determine product stability and potential human and animal health problems related to recycling fermented livestock wastes. If preservation is shown to be unnecessary, a substantial reduction in processing cost could be made.

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Fermentation of cheese-whey supplemented livestock wastes 35

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36 M. D. Erdman, C. A. Reddy

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