Digestibility of dry matter, nitrogen and minerals in biosolids

ANIMAL FEED SCIENCE AND TECHNOLOGY

ELSEVIER

Animal Feed Science and Technology 52 ( 1995 ) 299-3 12

Digestibility of dry matter, nitrogen and minerals in biosolids* I.E. Browna, V. Fellner”, R.L. Belyea”>*,M.R. Ellersieckb “Department ofAnimal Sciences, University of Missouri, Columbia, OH 6521 I, USA bDepartment of Math and Statistics, University of Missouri, Columbia, OH 65211, USA

Received 22 October 1993; accepted 2 August 1994

Abstract Digestibility of dry matter (DM), nitrogen (N) and minerals in food processing biosolids (BS) was determined. In Experiment 1, three diets (9% protein) were formulated from corn silage, ground corn, starch, and either dried BS (D), soybean meal (S) or soybean meal plus additional Ca and P (M). These diets plus a control (C, 6% protein) were fed to ktulated cows. Apparent digestibility of DM was lower for Diets C (74%) and D

(72%) than for Diets S (83%) and M (79%). Effects of diets upon digestibilities of fiber and N were similar to effects upon DM digestibility. Digestibilities of minerals were not different among diets. The in situ digestibility of DM in BS was about 50%, compared to about 70% and 90% for alfalfa and soybean meal, respectively. In Experiment 2, chopped corn forage was ensiled with urea (U), soybean meal (S), dried BS (D) or wet BS (W) and fed to sheep. DM digestibility of Diets U (62%), S (64%) and D (64%) was greater than for Diet W (54%). Digestibility of N in Diet D (48O/k)was lower than in Diets S ( 52%) and U (54%); digestibility of N in Diet W (42%) was lower than in Diet D. Low digestiblity of N in BS resulted in low ruminal ammonia, which reduced ruminal DM and energy digestibility and decreased volatile fatty acid concentrations. Dried BS were more digestible than native (wet) BS; BS could be added to silage as means of feeding and probably are best suited for maintenance diets. Bioprocessing methods are needed to increase the digestibility of DM and N in BS. Keywords: Biosolids; Calcium; Dry matter degradation; Nitrogen; Phosphorus

*Corresponding author. *Missouri Agricultural Experiment Station, Journal Series Number 12232. 0377-8401/95/$09.50 0 1995 Elsevier Science B.V. All rights reserved SSDZO377-8401(94)00713-6

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1. Introduction Aerobic treatment of wash water from the cleaning of food processing facilities results in biosolids (BS ). A typical milk processing plant will produce about 2000 kg of dry BS daily (Belyea et al., 1990). Traditionally, BS are applied to land or put into landfills; however, these disposal options may become limited because of the potential of the nitrogen (N) and phosphorus (P) in BS for polluting ground water and because of increased user costs. Because BS have nutritional value and do not contain Environmental Protection Agency (EPA) priority pollutants (Clevenger, 1990), they could be fed to animals (Belyea et al., 1990; Caton et al., 199 1) . Diets containing 10 and 20% BS were fed to sows for 3 years, resulting in live parities of pigs (Zinn et al., 1992). Feeding BS did not have adverse effects upon health or reproductive functions in sows or health or growth of pigs, but relatively high proportions of fat had to be added to the diets to maintain body weight (Zinn et al., 1992). We also found digestibilities of DM and N to be reduced when diets containing BS were fed to cattle and sheep (Caton et al., 1989; Belyea et al., 1990). However, we had no direct measurements on the digestibility of dry matter (DM), N and minerals of BS. One objective of this study was to determine digestibility of the DM and N of BS directly (in situ) and to determine the apparent digestibility of DM, N and minerals in diets containing BS. In previous studies, BS were dried and fed as ingredients in dry diets. In some situations, it might be advantageous to add BS to silage-based diets. The second objective was to determine digestibility of corn silage-based diets containing BS when fed to cattle and sheep.

2. Materials and methods 2. I. Biosolids preparation BS were obtained from a milk processing plant, the eftluent of which was treated in an aeration basin. After flocculation and setting, they were concentrated with a vertical screw press to about 8% DM. Most of the BS used in the studies to be described were dried on site in a forced-air oven ( 55 ‘C) for 48 h, shipped to the University of Missouri campus and ground finely; a portion was transported immediately (by plane) to campus and refrigerated. On a dry basis, BS contained 35% protein, 35% ash, 1% ether extract and 29% neutral detergent fiber (NDF) (Zinn et al., 1992.). Most of the protein was in amino acid form; amino acid profile and trace mineral concentrations have been reported (Clevenger, 1990; Zinn et al., 1992). 2.2. Experiment 1

Four ruminally tistulated, mature beef cows (455 kg body weight (BW) ) were fed four diets (4 x 4 Latin square), formulated from corn silage, ground corn,

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soybean meal, dried BS, starch, molasses and mineral supplement (Table 1) to meet National Research Council (NRC, 1989) guidelines. The control diet (C, 6% protein) contained no protein supplement. Diet D (9% protein) contained 9% dried BS as a protein supplement, while Diet S (9% protein) contained 5% soybean meal. Diet M contained soybean meal plus additional mineral supplement to result in calcium (Ca) and P concentrations similar to those of Diet D. Diets were designed so that Diets C and S would have different protein concentrations but similar Ca and P concentrations. Diets S, M and D contained similar levels of protein but Ca and P content of Diet M was higher than for Diet S and similar to Diet D. For Diet M the increased Ca and P were from an inorganic supplement, whereas for Diet D increased Ca and P were from BS. Diets were mixed in a portable mix wagon in quantities that would last 7- 10 days. Propionic acid ( 1.5%, wt./v&) was added to prevent deterioration. Periods were 2 1 days for adjustment and 5 days for balance and ruminal measurements. Diets were fed at 1.75% of BW in equal portions at 06:OOand 1800 h. Samples of diets were taken daily and dried at 55 ’C.Uneaten feed was weighed daily; samples were taken daily and dried at 55 ‘C. Cows were weighed prior to the study and at the end of each period; weighing was done about 4 h after the 0600 h meal. During collection, feces were accumulated in gutter pans and weighed daily; a 10% (wt./wt. ) sample was taken and dried at 55 ‘C. Dried feed and fecal samples were ground coarsely and composited; composites were ground through a screen with 1.0 mm diameter openings. Urine was collected using urine cups (Fellner et al., 1988) and weighed daily; a 1% (wt./wt.) sample was taken, acidified and frozen. During Days 2 and 4 of collection, samples (approx. 60 ml) of fluid were taken from ventral, middle and dorsal areas of the rumen just prior to (0 h ) and at 1, Table 1 Formulation

of diets (Experiment

Ingredient’

Corn silage Ground corn3 Starch Soybean meal Dried BS4 Molasses Limestone Dicalcium phosphate

1) Diet’ C

s

M

D

45.0 22.2 18.0

46.0 23.2 12.0 5.0

44.0 22.9 13.0 4.0

43.0 17.1 17.0

13.0 0.9 0.9

12.0 0.9 0.9

13.0 1.3 1.8

9.0 13.0 0.9 _

‘Supplemented with soybean meal (S), soybean+mineral (M), dried biosolids (D) or no protein supplement (C ) . ‘Percent on air-dry basis. 31ncluded vitamin ADE premix. 4BS, dried biosolids (35% protein, 34% ash, 3OWNDF, 6.0% Ca, 5.00/oP, 0.5% Mg, dry basis; Zinn et al., 1992).

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2, 4, 6 and 8 h after each meal. The three samples were cornposited and filtered through six layers of cheesecloth. Four aliquots (5.0 ml each) were transferred to vials. Two vials were acidified with 1.Oml metaphosphoric acid for volatile fatty acid (VFA) analysis and frozen. Two were acidified with two drops of 36 N H2S04 for ammonia determination and frozen. Absolute DM of diet and fecal samples was determined as weight loss at 105 ‘C for 24 h. NDF and acid detergent fiber (ADF) were determined according to Goering and Van Soest ( 1970). Filter paper (No. 541) was used instead of crucibles to isolate residues; decahydronaphthalene and sodium sulfite were omitted from the NDF procedure. N in feed, feces and urine samples was determined according to Watkins et al. ( 1987 ). The Ca and magnesium (Mg) concentrations of feeds, feces and urine samples were determined by atomic absorption spectrophotometry (Association of Official Analytical Chemists, 1984); P was determined calorimetrically (Koenig and Johnson, 1942) using a double beam spectrophotometer. Citrus leaves (NBS No. 15 12) were analyzed as external standards. For VFA analyses, vials of acidified ruminal fluid were thawed and centrifuged at 6000 rpm for 15 min; supernatant was filtered (0.45 pm pore size) to remove debris. Samples were injected into a gas chromatograph (Perkin Elmer Model 8500) (Supelco, 1975) equipped with a glass column ( 180 cm longx2.0 mm i.d. ) which was packed with 10% SP- 1200/ 1% H3P04 on 80/ 100 chromosorb. Conditions were: column temperature, 135 ‘C; injector temperature, 190’C; detector temperature, 175°C; flow rate, 35 ml min-I; sample size, 2.0 ~1; carrier gas, N2. For ammonia analyses, vials of ruminal fluid were thawed and NH3 was measured by the known addition method using an ion selective electrode (Sievers et al., 1984; Orion, 1986). Intake and digestion data were analyzed statistically as a Latin square using a general linear model (Statistical Analysis Systems Institute Inc. (MS), 1985), which included effects of diet, cow and period. Means of diets were separated by least significant difference (SAS, 1985) when effects of diet were significant. Ruminal pH, VFA and NH3 data were analyzed statistically as a repeated measurement design (Gill and Hafs, 197 1) using a general linear model (SAS, 1985 ) . Periods were main plots; within main plot, effects were diet and cow; Error A (cow within period x diet) was used to test main plot effects. Subplot effects included time and all possible interactions of time with main plot effects. Subplot effects were tested with Error B (random error). Means were separated by least significant difference (SAS, 1985). An in situ digestion study was carried out in conjunction with the in vivo digestion trial. Digestion bags were constructed from polyester cloth (52 pm pore size; Tetko, Briarcliff Manor, NY); nominal dimensions were 12 cmx 7 cm. Seams along one end and side were double-sewn with polyester thread and sealed with resin. Four loops (one per cow) were made from plastic tubing; holes were pierced in each loop so that seven metal rings (one per digestion time) could be attached. Batches (approx. 500 g) of alfalfa hay, soybean meal and dried BS were ground through a screen with 1.O mm diameter openings. Substrate ( 1.Og alfalfa or soy-

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air dried and mixed with ground corn grain, mineral supplement and wet BS (equal to 4% on a dry basis). Water was added to each treatment, increasing moisture content 35-400/o and improving packing and anaerobiosis. Ingredients were blended and placed in drums lined with plastic bags. Thermocouples were inserted into the center of the ensiled material for temperature measurement (Omega 450 TT thermocouple and Type T digital thermometer; Omega Engineering, Norwalk, CT) and bags were sealed. Temperatures were recorded daily for 60 days. Wethers were placed in stainless steel metabolism crates equipped with fecal and urine collection hoppers and were fed a standardization diet of corn silage (2.3% SW). They were then switched to assigned diets and were fed at 90% of DM intake attained during standardization. Feeds were weighed and offered twice daily. Vitamins A and D (in a corn-based premix) were added to meals (0.25 kg per meal) at feeding time. The study lasted 34 days; balance measurements were made during Days 13- 17 and Days 30-34. Feed samples (about 50 g ) were taken daily during the study and frozen. Refusals were weighed daily; samples were dried at 55°C for 48 h. Feces were collected and weighed daily; a 20% sample (wt. /wt. ) was dried for 48 h at 55 ’C. Urine also was collected and weighed daily. A 10% (wt./wt. ) sample was taken, acidified with 36 N HCl and frozen. Wethers were weighed at the start of the study and at the end of the collection periods. Fecal samples were composited by animal within collection period and ground through a screen with 1.0 mm diameter openings. Urine samples were thawed, subsampled and composited by animal within collection period. Feed samples were thawed and mixed thoroughly; a portion (about 20%) of each sample was composited by diet and collection period. Half of each composite was dried at 55°C and ground through a screen with 1.O mm diameter openings. The other half was freeze-ground with dry ice through a screen with 1.0 mm diameter openings. Dried feed and feces were analyzed for NDF, ADF and N by methods described earlier. The N content of urine samples was determined but data were aberrant (for reasons unknown) and not presented. The VFA and NH3 concentrations of the ground, wet feed samples were determined by procedures outlined by Supelco ( 1975 ). Lactic acid concentration was measured by gas chromatography as butyl ester derivative. Conditions were similar to those for VFA, except that 23% JXR on 100/200 mesh chromosorb column was used (Iannotti et al., 1979). Intake and digestibility data were analyzed as a repeated measurement study (Gill and Hafs, 197 1) using a general linear model (SAS, 1985 ). Main plots effected were diet and animal; animal within diet (Error A) was used to test main plot effects. Subplots were periods; within subplots, effects were diet, period and diet xperiod. Random error (Error B) was used to test subplot effects. Means were separated by least significant difference (SAS, 1985 ) . Silage pH, NH3 and VFA data were analyzed as a simple block design; means were separated by least significant difference (SAS, 1985 ), when main effects were significant.

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bean meal, 1.5 g BS) was added to bags (duplicate); bags were folded, sealed with rubber bands and tightly attached to rings on the loops. Forty-eight bags were used per cow per period. There were 12 bags of alfalfa (six digestion endpoints x two duplicates), 14 bags of soybean meal, 14 bags of BS and eight blank (empty) bags (one per endpoint). Forty-one bags were attached to a loop. There were ten bags containing alfalfa (removed at 6, 12, 24, 48 and 72 h), 24 bags containing BS or soybean meal (removed at 2,4,6, 12,24 and 48 h) and seven blanks (no substrate). Bags to be removed at a particular digestion endpoint were attached to the same ring. Six bags with substrate (two per feed) plus a blank were tied together (but not to the loop) and put into the rumen at the same time as the loop; these were the 0 h samples. They were allowed to soak for 5 min and were removed. After removal, all bags were rinsed thoroughly with tap water to remove external debris and purged until rinse water was clear. They were dried at 60°C for 24 h and weighed. A sample (0.25 g) of residue was removed from each bag and analyzed for N content by methods described previously. The amount of DM or N remaining was expressed as percent of original weight. Potentially digestible DM (PDDM) was calculated as 0 h DM residue minus 48 h DM residue (Waldo et al., 1972 ) A repeated measurements design (Gill and Hafs, 197 1) was used for analyzing in situ digestion data; the model was the same as the one used to analyze ruminal VFA and NH, data. 2.3. Experiment 2 Twenty-four growing wethers (approx. 39 kg) were grouped by weight and randomly assigned within weight group to one of four diets (Table 2). Three diets were created to meet requirements (NRC, 1985 ) by ensiling freshly chopped corn plant with ground corn, mineral supplement and either 1%urea (U ), 3% soybean meal (S) or 4% dried BS (D). For the fourth diet (W), chopped corn plant was Table 2 Formulation Ingredient*

Corn silage Corn Limestone Urea Soybean meal Dry BS’ Wet BS

of diets (Experiment

2)

Diet’ LJ

s

D

W

97.6 2.0 0.3 0.1

94.7 2.0 0.3

93.1 2.0 0.3

93.7 2.0 0.3 _ __ _

3.0 4.0

‘N supplements: U, urea; S, soybean meal; D, dried biosolids; W, wet biosolids. ‘Percent on an air-dry basis. ‘BS, biosolids (composition in Table 1).

4.0

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Table 4 Intake, digestibility, and balance data (Experiment 1) Diet

SE

C

DM intake (kg day-’ ) Digestibility (%) DM ADF NDF N Ca P Mg Balance (g day-’ ) N Ca P Mg Body weight (kg)

S

M

D

4.3

4.3

4.1

4.4

73.6b 35.4b 38.6b 33.3b 14.9 50.3 31.4

82.7” 58.9” 65.8” 59.7” 32.8 51.0 46.7

78.7” 57.78 63.3” 52.9” 17.4 39.2 31.7

72.0b 35.4b 43.4b 39.lb 13.5 45.1 25.1

+ 1.0 15.1 9.5 0.92 480

-18.0 7.2 4.5 -0.17 462

-8.7 11.0 1.7 -0.99 448

-9.8 10.6 5.5 -0.05 421

0.09

1.6 4.3 3.2 3.7 14.0 5.7 5.4 5.7 8.4 2.4 0.62 5.5

For diet descriptions, see Table 1. “sbMeansin same row and having different letters differ (PcO.05). SE, standard error. Table 5 Ruminal measurements (Experiment 1) Diet C

PH NH3 (mg 1-r) VFA (mEq 1-l) Total Acetate Propionate Butyrate

SE2 S

M

D

6.5”

6.2b

6.3b

6.4”

0.05

4.4b

23.4”

16.5”

6.4b

3.5

73.4” 48.6b 12.4 9.6

87.1b 61.4” 14.1 7.9

86.7b 62.7” 12.6 8.5

77JY 53.lb 13.1 8.0

2.0 1.2 0.77 1.2

For diet descriptions, see Table 1. ‘sbMeans in same row with unlike letters differ (PC 0.05 ) . SE, standard error.

(PxO.05) for Diets C (4.4 mg 1-l) and D (6.4 mg 1-l) than for Diets S and M (23.4 and 16.5 mg l-r, respectively). There were significant interactions of ruminal NH3 with sampling time (Fig. 1). Ruminal NH3 was significantly higher prior to feeding (0 h) and at 1.Oh postfeeding for cows fed Diets S and M, compared to those fed Diets C and D. At 2.0 h postfeeding, NH3 concentrations decreased for Diets S and M but still were significantly higher than for Diets C and D. By 4.0 h, ruminal NH3 concentrations were similar among dietary treatments.

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301

15 -~ 10

-~ \p-11::::::1

5

k

-3

Oc-1

0

2

6

4

6

Sample time (hl

Fig. 1. Ruminal ammonia concentrations (Experiment 1). 0 , Diet C, control; ? ,?Diet S, soybean meal; +, Diet M, soybean meal plus minerals; 0, Diet D, dried biosolids.

40 ac 20

-s

-!A

-D

I

0. 0

1

2

4

6

8

Sample timelh)

Fig. 2. Ruminal total VFA concentrations (Experiment 1). 0 , Diet C, control; ? ,?Diet S, soybean meal; +, Diet M, soybean meal plus minerals; 0, Diet D, dried biosolids.

Total ruminal VFA concentrations increased following eating (Fig. 2 ) , but there were no significant interactions of diet with sampling time. Cows fed Diets C and D had lower mean total ruminal VFA than Diets S and M (Table 5 ). Lower acetate concentration accounted for most of the decrease in total VFA and presumably reflected lower fiber digestibility. Alfalfa and soybean meal had more PDDM (42% and 6 1%, respectively) than BS ( 30%) and were digested more completely (Table 6 and Fig. 3 ) . The proportion of PDDM in BS (0.90) that was digested in 24 h exceeded that of alfalfa and soybean meal but, because the latter two had more PDDM, absolute quantities

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Table 6 In situ dry matter disappearance data

0 h residue’ 24 h residue’ 48 h residue’ PDDM2 PDDM at 24 h3

Soybean meal

Alfalfa

Biosolids

64 21 3 61 0.70

71 39 29 42 0.76

76 49 46 30 0.90

‘Percent of sample DM remaining. 2Potentially digestible DM (0 h residue minus 48 h residue), 3Proportion of PDDM disappeared at 24 h.

0

2

4

6

12

24

46

72

Dbeatim time Ihl

Fig. 3. Dry matter disappearance (Experiment 1) . SBM, soybean meal; ALF, alfalfa; BS, biosolids.

of digested PDDM were similar. The data for N disappearance are not presented, but responses were similar to DM disappearance. 3.2. Experiment 2 Temperatures of silage containing BS (Diets D and W) increased 2-4°C during the first 2-3 days of ensiling and gradually decreased (Fig. 4). By Day 6, temperatures of all diets were similar; remaining temperatures were omitted. Diets were similar in DM, protein and fiber concentrations (Table 7)) but protein content was 1.O- 1.5% units lower than expected because protein content of the corn forage (7.5% DM) was lower than in previous years (8.5-9.0% DM). Silage pHs were 3.8-4.0 and lactic acidacetic acid was > 3: 1, which suggests that the ingredients ensiled effectively (McCullough, 1978 ) . Diets S, D and W had higher NH3 concentrations than Diet U; Diets D and W

I.E. Brown et al. /Animal Feed Science and Technology 52 (1995) 299-312

G

25

3

20

309

% 5 c

15 10 5 i OJ

/ 1

2

3

4

5

6

Day of Ensiling

Fig. 4. Temperatures of ensiled diets (Experiment Diet D, dried biosolids; 0, Diet W, wet biosolids. Table 7 Composition

of silage diets (Experiment

2 ) 0 , Diet U, uear; 0, Diet S, soybean meal; +,

2) SE

Diet

DM (%) ADF (W DM) NDF (96 DM) Protein (% DM) PH NH, (mgl-‘) Fermentation acids mEq 1-l Acetate Propionate Lactate Total

U

s

D

W

37.1 29.9 49.3 1.7 3.8 59.7b

37.8 25.8 42.3 8.4 3.9 66.4”

35.4 21.4 47.2 1.9 4.0 63.3”

31.9 21.8 48.1 8.4 4.0 64.8”

0.05 5.2

11.2 0.22 32.4” 44.4s

12.0 0.19 33.2’ 43.gb

13.3 0.30 44.gb 58.9”

12.9 0.36 42.0b 55.1”

2.4 0.09 13.2 14.4

For diet descriptions, see Table 2. 4bMeans in the same row with unlike letters differ (PiO.05). SE, standard error.

had higher lactic acid concentrations than Diets U and S, which resulted in higher total silage fermentation acids (Table 7 ) . Diets in Experiment 1 had a soil-like odor; there was no apparent odor in the the ensiled diets in Experiment 2. Sheep readily ate Diets D and W, suggesting that palatability was not a concern. Digestibility of DM was lower for Diet W than the other three diets (Table 8 ); digestibilities of NDF and ADF were lower for Diets S and W than for Diets U and D. Digestibility of N was lower (P~0.05) for Diets D and W than for Diets U and S and lower for Diet W than for Diet D. Digestibility of N was generally

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Table 8 Intake and apparent digestibility data (Experiment 2) SE

Diet

DMI intake (g day-‘) Digestibility (%) DM ADF NDF N Weight Initial (kg) Gain (g day-‘)

U

S

D

W

798

880

166

731

61.88 54.78 53.4O 53.5* 38.1 29b

63.1” 48.0b 41.9b 51.8” 37.6 107”

56

64.0” 51.1” 49.5” 48.4b

54.3b 43.3b 41.1s 42.8”

1.3 1.7 2.1 2.1

37.8 70”

37.5 61”

1.9 25

For diet descriptions, see Table 2. B*b*cMeans in same row with unlike letters differ (RO.05). SE, standard error.

lower than on Experiment 1, apparently because of low N concentration in diets. Weight gains for all four treatments were small but positive.

4. Discussion

These data demonstrate that DM and N of BS and of diets containing BS are not as digestible as DM and N of many common feeds. In Experiment 1, low N digestibility resulted in low ruminal N and low DM and energy digestibility (VFA). In Experiment 2, DM and N in the BS diets were less digestible than in the other two diets. However, the DM of Diet D was more digestible than that of Diet W, suggesting that drying increased digestibility of BS. The availability of major minerals in BS is relatively high; BS could be used as a practical mineral supplement. Because of low energy and low available N content, BS probably should not exceed 1O-20% of diet DM and probably should be restricted to mature animals fed at maintenance or low production levels. Fat could be added to increase energy concentration; fat would also improve physical form, as ground BS contain a considerable amount of fine particles. Diets containing BS are palatable to sheep and cattle. Ensiling could be a means for incorporating BS into diets. Dried BS would be preferred, because of higher digestibility and ease of handling and mixing. Adding 10% dried BS to corn silage will increase total protein by 2-3 percentage units, complement the mineral profile and add value. Corn forage ensiled with BS will have increased lactic acid concentration, which could increase storage and bunk life.

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5. Conclusion Biosolids can be fed to animals as a means of disposal; palatability is not a problem but low digestibility limits opportunities for feeding. Bioprocessing methods are needed to increase the digestibility and feed value of BS.

Acknowledgements This project was partially funded by USDA Special Grant No. 85CRSR-22548. The authors appreciate the help of Shirley Ireland in VFA analyses. This paper is dedicated to the memory of Ted Sedgwick, who was responsible for much of the animal care and analytical work.

References Association of Official Analytical Chemists, 1984. Oflicial Methods of Analysis, 19th edn. Association of Official Analytical Chemists, Arlington, VA, pp. 164-165. Belyea, R.L., Williams, J.E., Gieseke, L., Clevenger, T.E., Brown, J.R. and Tumbleson, M.E., 1990. Evaluation of dairy wastewater solids as a feed ingredient. J. Dairy Sci., 73: 1864-l 87 1. Caton, J.S., Williams, J.E., Beaver, E.E., May, T. and Belyea, R.L., 1989. Effects of dairy biomass protein on ruminal fermentation and site and extent of nutrient digestion by lambs. J. Anim. Sci., 67: 2762-2771. Caton, J.S., Williams, J.E., May, T., Beaver, E.E. and Belyea, R.L., 199 1. Evaluation of dairy food processing, washwater solids as a protein source. I. Forage intake, animal performance, ruminal fermentation and site of digestion in heifers fed medium quality hay. J. Anim. Sci., 69: 3406-3415. Clevenger, T.E., 1990. Safety and efficacy of food processing sludges: chemical characterization. Res. Water Pollut. Control Fed., 62: 820-827. Fellner, V., Weiss, M.F., Belo, A.T., Belyea, R.L., Martz, F.A. and Ormz, A.H., 1988. Urine cup for collection of urine from cows. J. Dairy Sci., 71: 2250-2255. Gill, J.L. and Hafs, H.D., 1971. Analysis of repeated measurements of animals. J. Anim. Sci., 33: 331-336. Goering, H.K. and van Soest, P.J., 1970. Forage fiber analyses (apparatus, reagents, procedures, and some applications). ARS, USDA Agriculture Handbook No. 379, pp. 1-9. Holter, J.A. and Reid, J.T., 1967. Relationship between the concentrations of crude protein and apparently digestible protein in forages. J. Anim. Sci., 18: 1339-l 349. Iannotti, E.C., Porter, J.H., Fischer, J.R. and Sievers, D.M., 1979. Changes in swine manure during anaerobic digestion. Dev. Ind. Microbial., 20: 5 19-529. Koenig, R.A. and Johnson, C.R., 1942. Calorimetric determination of phosphorus in biological materials. Anal. Chem., 14: 155-160. McCullough, M.E., 1978. Fermentation of Silage-A Review. NFIA, Des Moines, IA, pp. 3-25. National Research Coucil, 1985. Nutrient Requirements of Sheep, 6th edn. National Academy Press, Washington, DC, pp. 45-53. National Research Council, 1989. Nutrient Requirements of Dairy Cattle, 6th edn. National Academy Press, Washington, DC, p. 147. Orion, 1986. Model 45-12 Ammonium Electrode Instruction Manual. Orion Research, Boston, MA, pp. l-36. Sievers, D.M., Doyle, K. and Porter, J.H., 1984. Ammonia measurement in high organic wastes. Trans. Am. Sot. Agric. Eng., 27: 182-l 84.

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Statistical Analysis Systems Institute Inc., 1985. SAS User’s Guide: Statistics, 5th edn. Statistical Analysis Systems Institute Inc., Cary, NC, pp. 433-506. Supelco, 1975. GC Separation of VFA C2-C5. Bull. 749B. Supelco, Bellefonte, PA, pp. 1-31. Waldo, D.R., Smith, L.W. and Cox, E.L., 1972. Model of cellulose disappearance from the rumen. J. Anim. Sci., 55: 125-129. Watkins, K.L., Veum, T.L. and Krause, G.F., 1987. Total N determination of various sample types: a comparison of the Hach, Kjeltec and Kjeldahl methods. J. Assoc. Offtc. Anal. Chem., 70: 410412. Zinn, G.M., Belyea, R.L., Williams, J.E., Tumbleson, M.E., Clevenger, T.E. and Brown, J.R., 1992. Feeding washwater solids to swine during gestation and lactation: sow productivity, pig performance and tissue concentrations. J. Anim. Sci., 70: 3 112-3 124.