Intake and digestion by Holstein steer calves consuming grass hay supplemented with broiler litter

Animal Feed Science and Technology, 44 ( 1993 ) 251-263

251

0377-8401/93/$06.00 © 1993 - Elsevier Science Publishers B.V. All fights reserved

Intake and digestion by Holstein steer calves consuming grass hay supplemented with broiler litter A.R. Patil, A.L. Goetsch*, D.L. Galloway, Sr., L.A. Forster, Jr. Department of Animal Sciences, Universityof Arkansas, Fayetteville, AR 72701, USA (Received 2 December 1992; accepted 28 May 1993 )

Abstract

Effects of substituting broiler litter for supplemental corn on feed intake and digestion by Holstein steer calves consuming low-quality grass hay were determined. In Experiment 1, eight steer calves (176 + 3.4 kg average trial body weight (BW)) in two simultaneous 4 × 4 Latin squares consumed vegetative bermudagrass (BER) or mature bromegrass (BRO) hay ad libitum without an energy supplement (control) or with (dry matter basis) 0.75% BW of ground corn (C), 0.56% BW of corn plus 0.26% BW of deep-stacked broiler litter (LL), or 0.38% BW of corn plus 0.52% BW of litter (HL). Litter was 24% ash, 5.0% nitrogen, 40% neutral detergent fiber (NDF) and 6.3% acid detergent lignin (ADL). Total organic matter ( OM ) intake was 4.32, 5.10, 5.16, 5.12, 4.89, 5.66, 5.90 and 5.58 kg day -1 (SE 0.084), and digestible OM intake was 2.57, 3.35, 3.21, 3.01, 2.72, 3.39, 3.42 and 3.06 kg day -1 (SE 0.055) for BER, BER-C, BER-LL, BER-HL, BRO, BRO-C, BRO-LL and BRO-HL, respectively. In Experiment 2, six Holstein steer calves (189 + 15.6 kg average trial BW) in a 6 X 6 Latin square consumed BROad libiturn without an energy supplement (control) or with 0.75% BW of corn (C), 0.75% BW of corn plus 0.13% BW of peanut skins (CS), 0.5% BW of corn plus 0.35% BW of broiler litter (CL), or 0.5% BW of corn plus 0.13% BW of peanut skins mixed with 0.35% BW of litter at feeding (CLS-F) or before deep-stacking (CLS-ST). Litter contained 22% ash, 4.0% N, 49% NDF and 5.5% acid detergent lignin. Total tract NDF digestibility was similar among treatments. Total and digestible OM intake (2.28, 3.01, 2.93, 3.21, 3.14 and 3.04 kg day- 1for control, C, CL, CS, CLS-F and CLS-ST, respectively) were increased (P< 0.05 ) by supplementation and similar among supplement treatments. In conclusion, mixed broiler litter-corn supplements decreased consumption by Holstein steer calves of low-quality grass hay less than all-corn supplements, that partially or completely compensated for low digestibility of litter.

Introduction Broiler litter is of greatest value as a feedstuff for ruminants when given in a limited amount as a source of supplemental nitrogen (Fontenot and Jurubescu, 1980). However, the digestible energy concentration of litter is similar *Corresponding author.

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to that of medium to high quality roughage (Fontenot and Jurubescu, 1980; Ruffin and McCaskey, 1990). Use of litter as an ingredient in energy supplements would increase feeding of the byproduct to ruminants. Sources of energy in litter include undigested dietary constituents, nitrogen-containing waste products of poultry metabolism, microbial cells and bedding, proportions of which vary with production conditions (Ruffin and McCaskey, 1990). Therefore, the pattern of ruminal degradation of litter should differ from that of more homogeneous and common energy supplements, and effects on feed intake and digestion may depend on characteristics of forage and level of litter in mixed supplements. One attribute of litter possibly hindering use by livestock producers and amounts voluntarily consumed by ruminants is the presence of ammonia that may impair smell and (or) palatability. Because ammonia constitutes an important source of nitrogen in litter (Fontenot and Jurubescu, 1980), means to minimize adverse effects without loss of ammonia would be useful. This might be achieved by mixing litter with feedstuffs that adsorb ammonia. Condensed tannins can bind ammonia (Kumar and Singh, 1984; Robbins et al., 1987 ) and ammonia also deactivates condensed tannins (Hill et al., 1986a,b). Peanut skins typically contain 16-20% condensed tannins (McBrayer et al., 1983). Objectives of the first experiment were to determine the effects of substituting broiler litter for different levels of supplemental corn on feed intake and digestion by Holstein steer calves consuming vegetative bermudagrass or mature bromegrass hay. The second experiment was conducted to determine the effects of substituting broiler litter for supplemental corn and mixing litter with peanut skins at deep-stacking on feed intake and digestion by Holstein steer calves consuming bromegrass hay. Materials and methods

Experiment I Eight Holstein steer calves (155+2.4 and 204+4.1 kg mean initial and final body weights, respectively), housed in tie stalls, were used in an experiment with two simultaneous 4 × 4 Latin squares and 14-day periods. Steers were assigned to squares for similar mean body weight (BW) and variation in BW. Free access to water was given in a partially enclosed bam. Steers were dewormed and received a vitamin A (500 000 IU) and D 3 (75 000 IU) injection 7 days before the start of the trial. Body weight was determined at the beginning of the trial and on Day 14 of each period at 13: 00 h. Steers in one square consumed bermudagrass (BER; Cynodon dactylon) hay ad libitum (offered at 105-110% of consumption on previous days ), and the other steers received mature bromegrass (BRO; Bromus inermis) hay (Table 1 ). Bermudagrass hay was cut at a vegetative growth stage (no flow-

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Table 1 Feed composition (% dry matter; Experiment 1) Item

Bermudagrass

Bromegrass

Corn

Broiler litter

Ash Nitrogen Neutral detergent fiber Acid detergent fiber Acid detergent lignin Cellulose Hemicellulose

7.5 1.78 72.7 32.7 5.2 26.6 40.0

8.1 1.10 66.5 40.2 6.2 30.8 26.3

1.7 1.66 12.7

24.2 5.01 40.3 28.0 6.3 14.1 12.3

ering stems and most tillers at stages 15-17; West, 1990); bromegrass hay was mature. Steers were not offered an energy supplement (control) or were given (dry matter basis) ground corn (C; 0.75% BW) or mixes of corn and litter (low litter, LL: 0.56% BW of corn plus 0.26% BW of litter; high litter, HL: 0.38% BW of corn plus 0.51% BW of litter; Table 1 ). Immediately before the experiment, steers were adapted gradually to consumption of broiler litter. Litter was obtained from a commercial broiler house using rice hulls and pine shavings as bedding, and deep-stacked (Ruffin and McCaskey, 1990) at a height of approximately 1.4 m for 1 month before the experiment. All steers were fed a high-protein, basal supplement at 0.28% BW to avoid insufficiencies of nitrogenous compounds (60% soybean meal, 15% feather meal, 14% corn gluten meal and 11% blood meal); 12 g (air-dry) of dicalcium phosphate and 9 g of a 3:1 mix of NaC1 and trace mineral mix (containing > 12.0% Zn, 10.0% Mn, 5.0% K, 2.5% Mg, 1.5% Cu, 0.3% I, 0.1% Co and 0.02% Se) were top-dressed on hay at 08:00 h. Litter was substituted for 25% or 50% of digestible energy provided by corn (National Research Council, 1984) for LL and HL treatments, respectively. Supplements were fed once daily at 08:00 h, with corn and litter for LL and HL hand-mixed immediately prior to feeding. Hay was given in equal meals at 08:00 and 16.00 h after supplement consumption; orts were removed and weighed at 08: 00 h. Hay samples taken on Days 9-14 were composited and ground to pass a 1 m m screen. On Day 9, 100 g of ytterbium (Yb)-labelled hay (Goetsch and Galyean, 1983; 24 h soak) were mixed with 127 g of unlabelled hay of the 08:00 h meal, and the remaining hay was offered thereafter. Fecal grab samples were taken on Days 11-14 at 12 h intervals, advancing 3 h daily, and frozen. Later, samples were dried at 55 °C for 48 h and ground to pass a 2 m m screen. Composite samples formed within steer and period were ground to pass a 1 mm screen. Supplement samples were collected on Day 14 and ground to pass a 1 m m screen. Feed and fecal composites were analyzed for dry matter (DM), ash, Kjeldahl nitrogen (N; Association of Official Analytical Chemists, 1984 ), neutral detergent fiber (NDF; Goering and Van Soest, 1970)

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and acid-insoluble ash (2 N HC1; Van Keulen and Young, 1977); hay and litter were analyzed for acid detergent fiber (ADF) and acid detergent lignin (ADL; Goering and Van Soest, 1970). Cellulose was determined as the loss in weight upon sulfuric acid treatment; ADF subtracted from NDF yielded hemiceUulose. For grain NDF analysis, samples were ground to pass a 0.6 mm screen and treated with amylase (Cherney et al., 1989). Litter was analyzed for ammonia as described by Broderick and Kang (1980). Acid-insoluble ash was used as an internal marker to estimate digestion of organic matter (OM), NDF and N. Individual fecal samples were ashed, solubilized with acid (3 N HCI: 3 N HNO3; Ellis et al., 1982) and analyzed for Yb by atomic absorption spectrophotometry with a nitrous oxide plus acetylene flame. Particulate passage rate (PPR) was estimated by regressing the natural logarithm of Yb concentration against time post-dosing. Composites of corn and basal supplements from the entire experiment were analyzed for in vitro DM disappearance at 3, 6, 9, 12, 18, 24, 48 and 96 h of incubation. In vitro NDF disappearance at 3, 6, 9, 12, 18, 24, 36, 48 and 96 h was determined for hay and litter composites as well. A 4:1 mix of buffer (McDougall, 1948; 1 g 1-1 of urea) and ruminal fluid was used. Ruminal fluid was obtained 3 h post-feeding from two beef steers fed 47.5% BER, 47.5% BRO and 5% soybean meal at 90% of ad libitum intake. Hay intake on Days 10-14 was analyzed as a split-plot in time; because effects of day and the treatment × day interaction were not significant, intake was averaged for digestion measures. Data were analyzed with the following sources of variation: forage source or square, steer within square, period within square, supplement and forage by supplement interaction. Steer within square variation was used to test the effect of forage source. Independent contrasts were made for effects of supplementation (controls vs. other treatments), litter inclusion (C vs. LL and HL), litter level (LL vs. HL) and interactions between forage source and supplementation, litter inclusion and litter level. All analyses were conducted with Statistical Analysis System (1985).

Experiment 2 Six Holstein steer calves (149 _+13.5 and 223 + 18.0 kg mean initial and final BW, respectively) housed in tie stalls were used in a 6 × 6 Latin square experiment with 14-day periods. Free access to water was given in a partially enclosed building. Steers were weighed at the beginning of the trial and on Day 14 of each period at 13:00 h. Bromegrass hay (used in Experiment 1; Table 2 ) was consumed ad libitum (offered at 105-110% of consumption on previous days) with equal meals at 08:00 and 16:00 h; orts were removed and weighed at 08 : 00 h. Supplement treatments were, no energy supplement (control) or supplementation with (DM basis) 0.75% BW of ground corn (C; used in Experiment 1; Table 1 ), or 0.75% BW of corn mixed with 0.13%

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Table 2 Feed composition (% dry matter; Experiment 2) Item

Bromegrass

Broiler litter

Peanut skins

Litter-peanut skins mix

Ash Nitrogen Neutral detergent fiber Acid detergent fiber Acid detergent lignin Cellulose Hemicellulose Condensed tannins

7.6 1.12 67.6 40.7 6.5 31.9 26.9

22.3 4.01 49.4 28.1 5.5 17.8 21.3 1.2

2.7 2.88 41.1

18.1 4.24 52.2 32.3 10.1 19.5 19.9 1.8

13.4

BW of peanut skins (CS), 0.5% BW of corn plus 0.35% BW of broiler litter (CL) or 0.5% BW of corn plus 0.13% BW peanut skins mixed with 0.35% BW of litter at feeding (CLS-F) or before deep-stacking (CLS-ST; Table 2). In addition, all steers received 0.28% BW of the basal protein supplement and mineral sources used in Experiment 1. Immediately preceding the experiment, steers were gradually adapted to consumption of litter and peanut skins; however, during the study incomplete supplement consumption occasionally occurred. Litter was substituted for corn on an assumed digestible energy basis (National Research Council, 1984). Litter was obtained from a commercial broiler house with pine shavings as bedding, and deep-stacked for approximately 1 month either alone or after thorough mixing with peanut skins (73% litter: 27% peanut skins; DM basis). Feed and feces were sampled and analyzed as in Experiment 1. Peanut skins, litter and the litter-peanut skins mix were analyzed for condensed tannins (modified vanillin-HC1 method; Price et al., 1978). Samples from deepstacked litter and the litter-peanut skins mix were stored in 0.1 N HC1 until ammonia analysis. Other procedures were the same as those in Experiment 1. Data were analyzed by analysis of variance with steer, period and treatment in the statistical model. Individual treatment means were compared by least significant difference when the treatment F-test was significant ( P < 0.05 ). Results

Experiment I The N concentration of BER was considerably higher than that of BRO (Table 1 ). Bermudagrass was higher in NDF than was BRO, but because of a higher stage of maturity, ADL:NDF was higher for BRO. Acid detergent lignin comprised 16% of litter NDF, and 24% of total N in litter was from ammonia.

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A.R. Patil et al./Animal Feed Science and Technology 44 (1993) 251-263

In vitro DM disappearance for the basal protein supplement was greater than that of corn at early incubation times and lower later (Fig. 1 ). In vitro digestion ofBRO NDF at 3 and 6 h was negligible; NDF digestion was greater for BER than BRO until 24 h, after which time digestion was similar (Fig. 2 ). Differences in the extent of early digestion appeared solely through disappearance from 0 to 3 h. At 3 h, approximately 9% of litter NDF had disaplO0 9O 8O ®

c

70

m

60

Q. O.

ta ~D

m E ~ Q

50 4O 30 20 -~ Corn

10

Basal supplement

0 0

10

20

30

40

50

60

70

80

90

80

90

T i m e (h)

Fig. 1. In vitro disappearance of dry matter, Experiment 1. 7O A

® 60 50

•~ 40 ,,Q

~ 30 ~

2o

0

0

10

20

30

40

50

60

70

Time (h)

Fig. 2. In vitro disappearance of neutral detergent fiber, Experiment 1.

Table 3 Feed intake, digestion and particulate passage rate for Holstein steer calves fed bermudagrass or bromegrass hay supplemented with corn and (or) broiler litter (Experiment 1 )

.~ .~ e~

Item

Bermudagrass Control a

Bromegrass C

LL

HL

Control

C

LL

SE

Effectb

HL

Organic matter Intake (kg day- 1 ) Basal supplement Corn Litter Hay Total Digestion % kg day- 1

0.49 0.00 0.00 3.84 4.32

0.49 1.35 0.00 3.26 5.10

0.49 1.00 0.38 3.29 5.16

0.43 0.59 0.67 3.43 5.12

0.48 0.00 0.00 4.41 4.89

0.50 1.36 0.00 3.80 5.66

0.48 1.00 0.38 4.04 5.90

0.46 0.63 0.72 3.77 5.58

0.115 0.084

f,S,f×l F,S,L

59.5 2.57

65.8 3.35

62.3 3.21

59.1 3.01

55.5 2.72

60.1 3.39

58.4 3.42

55.0 3.06

0.88 0.055

F,S,I,L S,I,L

3.09

2.82

3.00

3.20

3.27

3.01

3.33

3.27

0.081

I

62.0 1.92

60.1 1.69

57.6 1.72

56.1 1.79

53.1 1.74

52.0 1.56

49.4 1.62

50.7 1.66

0.79 0.061

F,S,I,f×I S

1.7

F,S,I,L,F × S

1.15 2.1

F,S F,S,I,L

0.129

I,f×i

Neutral detergentfiber Intake (kg) Digestion % kgday -~

Nitrogen Intake (g day- ~) Digestion % g day- l Particulate passage rate ( % h -~ )

128 68.8 88 3.44

140 65.9 92 3.60

160

168

65.8 104

65.3 110

3.21

3.21

107 57.3 61 3.46

124 54.4 67 3.64

145 54.2 77 3.64

155 56.9 88 3.51

aControl, no energy supplement; C, corn; LL, low level of litter; HL, high level of litter. bEffect: F and f, forage type ( P < 0.05 and 0.10, respectively); S, supplementation (P< 0.05); I, litter inclusion ( P < 0.05); L, litter level ( P < 0.05); F × S, forage source by supplementation interaction (P < 0.05 ); f × i, forage source by litter inclusion interaction (P < 0.10); f × 1, forage source by litter level interaction ( P < 0.10 ).

t~

A.R. Patil et al. / Animal Feed Science and Technology 44 (1993) 251-263

258

peared. Thereafter, essentially no digestion occurred up to 48 h; 48% of litter NDF had disappeared at 96 h. Corn with the C supplement comprised 25% and 23% of DM intake with BER and BRO, respectively (Table 3); corn was 18% and 16% of total DM intake for LL and 16% and 15% for HL with BRO and BER, respectively. Litter comprised 33-34% and 60% of supplemental DM for LL and HL supplement treatments, respectively. Supplementation decreased hay intake but to an extent less than supplement consumption; thus, supplementation increased total OM intake ( P < 0.05 ). Total OM intake was lower ( P < 0.05 ) for the high rather than the low level of litter; substituting litter for corn increased N D F intake. Supplementation, litter inclusion and level, and the forage source × supplementation interaction affected N intake ( P < 0.05 ). Organic matter digestion rose with supplementation and was lower for HL than for LL ( P < 0.05; Table 2 ). Digestible OM intake was increased by supTable 4 Feed intake, digestion and particulate passage rate for Holstein steer calves fed bromegrass hay supplemented with corn, broiler litter and (or) peanut skins (Experiment 2) Item

Diet a Control

Organic matter Intake (kg day -1 ) Basal supplement Corn

Litter Peanut skins Hay Total Digestion % k g d a y -1

Neutral detergent fiber Intake (kg day -1 ) Digestion % k g d a y -~

Nitrogen Intake ( g d a y -~) Digestion % g day- l

C

CL

CS

CLS-F

CLS-ST

0.51 0.00 0.00 0.00 3.76 4.27 ~

0.50 1.38 0.00 0.00 3.26 5.14 b

0.43 0.79 0.44 0.00 3.62 5.28 b

0.50 1.34 0.00 0.24 3.41 5.48 b

0.49 0.90 0.51 0.25 3.37 5.52 b

0.46 0.84 0.46 0.21 3.42 5.38 b

0.247 0.289

53.3 ~ 2.28 a

58.4 b 3.01 b

54.9 a 2.93 b

58.4 b 3.21 b

56.3 ~b 3.14 b

56.2 ab 3.04 b

0.168

2.81

2.55

3.02

2.75

3.00

3.02

0.187

48.2 1.37

48.1 1.23

47.7 1.45

49.1 1.35

47.4 1.44

48.2 1.47

1.22 0.104

104 a 59.2 b 62 a

123 b 53.7 ~b 67 a

133 ~ 53.0 a 72 ab

130 TM 50.5 ~ 66 a

150 d 51.8 a 80 b

146 cd 54.7 ab 80 b

1.00

5.6 1.97 4.0

aControl, no energy supplement; C, corn; L, litter; S, peanut skins; F, peanut skins and litter mixed at feeding; ST, peanut skins and litter mixed at deep-stacking. Means in a row without a common superscript differ ( P < 0.05).

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259

plementation, declined with inclusion of litter, and was lower for HL than LL (P< 0.05 ). Neutral detergent fiber digestion declined with supplementation and with inclusion of litter in the supplement (P< 0.05; Table 3). Nitrogen digestibility was decreased by supplementation but did not decline further when level of litter substitution rose. Particulate passage rate was depressed by litter inclusion in supplements of BER, whereas little change occurred with BRO (forage source × litter inclusion; P< 0.10).

Experiment 2 Bromegrass hay was similar in composition (Table 2) to BRO in Experiment 1. Litter was higher in NDF, but a lower ADL: NDF ratio suggests higher NDF digestibility. The N content of litter was less than that of litter in Experiment 1. Differences in management practices between the commercial broiler houses from which the litter originated are unknown, apart from different bedding and removal after a greater number of batches of birds for Experiment 2 than for Experiment 1. Assuming additivity in condensed tannin concentration of litter and peanut skins when mixed, the expected concentration was 4.5% as compared with the actual level of 1.8%. Ammonia-N constituted 29% of total N in litter. The expected N concentration of the mix was 3.7%; whereas, the actual level was 4.2%. Corn comprised 26, 14, 23, 15 and 14% of total DM intake for C, CL, CS, CLS-F and CLS-ST, respectively. Litter was 10-11% of total DM intake for CL, CLS-F and CLS-ST, and 41% of supplemental DM for CL was litter. Hay OM intake was not affected by treatment; supplementation increased (P< 0.05 ) total OM intake. Organic matter digestion was increased (P< 0.05 ) by C and CS; whereas, OM digestibility for supplements containing litter did not differ from that of control (Table 4). Digestible OM intake was increased (P< 0.05 ) similarly by all supplement treatments. Total tract digestibility of NDF was similar among treatments. Nitrogen digestibility was similar among treatments with supplements; digestible N intake was greater (P< 0.05 ) for CLS-F and CLSST than for control, C and CS. Discussion

Experiment 1 The depression in hay OM intake per unit of supplement intake (substitution ratio ) for C was 0.42 and 0.43 with BER and BRO, respectively. Assuming that the effects of corn in LL and HL supplements on hay OM intake were similar to that with C relative to the level of corn, the substitution ratio for litter was 0.33, 0.32 and 0.53 for BER-LL, BER-HL and BRO-HL, respec-

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tively. Conversely, hay OM intake for BRO-LL was slightly higher (0.06 kg) than expected. Likewise, dietary inclusion of poultry litter either has not affected or has increased total feed intake in other instances (Harmon et al., 1975; Cross et al., 1978; Arave et al., 1990; Arieli et al., 1991 ). To assess the effects of supplemental litter on digestibility of hay (plus basal supplement), it was assumed that total tract digestibility of corn NDF was 88% (Hsu et al., 1987 ) and that effects of corn in LL and HL supplements on hay digestibility were similar to that of corn in the C supplement relative to corn level. Predicted hay NDF digestibility was 58.1%, 59.1% and 60.3% with BER and 49.4%, 50.4% and 51.4% with BRO for C, LL and HL, respectively. Furthermore, if total tract digestibility of litter NDF approximated in vitro disappearance at 48 h (11%), hay NDF digestibility was 59.6%, 61.0%, 49.6% and 55.0% for BER-LL, BER-HL, BRO-LL and BRO-HL, respectively. A similarity in predicted values for LL with both forages sources, and for HL with BER, suggests that effects of litter on hay fiber digestibility were minimal. The spread between values for HL with BRO indicates that litter may have enhanced BRO NDF digestibility, or that substitution with litter lessened the effects of corn remaining in the supplement. By assuming that total tract corn OM digestibility was similar to total digestible nutrients (90%; National Research Council, 1984) and that effects of corn in LL and HL supplements on hay OM digestibility were similar to that of corn in the C supplement relative to corn level, predicted litter OM digestibility was 34% and 33% with BER and 25% and 27% with BRO for LL and HL, respectively. Thus, total tract digestibility of litter OM did not appear to vary with level of litter but may have differed with forage source. Particulate passage rate of litter was not measured. However, because PPR with Yb-labelled hay was decreased by substituting litter for corn with BER, perhaps time for ruminal digestion of litter was greater with BER than with BRO. This might have contributed to the difference between forage sources in digestibility of litter OM.

Experiment 2 The substitution ratio for the C supplement was 0.37. Similar to results with the low level of supplemental litter and BRO in Experiment 1, hay OM intake for the CL treatment was higher (0.15 kg) than expected. With the assumptions of Experiment 1, hay (plus basal supplement) NDF digestibility was 44% for C and 46% for CL (without considering litter NDF digestibility) as compared with 48% in vivo digestibility of total dietary NDF for CL. Litter NDF digestibility may have been higher in Experiment 2 than in Experiment 1, based on differences in ADL:NDF, but it is doubtful that litter NDF digestibility was high enough to have caused the apparent increase in hay NDF digestibility. Predicted litter OM digestibility, as derived in Ex-

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261

periment 1, was 47% for CL. Hence, litter apparently stimulated hay NDF digestibility, or substitution with litter lowered the adverse effects of corn relative to the level in the CL supplement. Similar total tract NDF digestibilities for C and CS and for CL and CLS-F indicate that the NDF of peanut skins was similar to hay in digestibility. Offering litter with peanut skins did not modify the increase in hay NDF digestibility by substituting litter for corn. Reasons for positive effects on hay intake of litter in the CL supplement in this experiment and of a litter-containing supplement in Experiment l, and for lower substitution ratios for two supplements with litter in Experiment l, are unknown. It is doubtful that effects of litter substitution for corn on forage digestibility were accompanied by changes in the physical nature of forage which were sufficient to affect the ruminal outflow rate of undigested forage. Though the high concentration of minerals in litter conceivably might have elevated the ruminal fluid dilution rate, estimates of PPR in Experiment 1 do not indicate more rapid ruminal outflow of forage digesta. Nonstructural carbohydrates in litter could have stimulated microbial protein production, but this also seems doubtful considering the high level of starch in supplemental corn which the litter replaced. Reasons for increased forage fiber digestibility when litter was substituted for supplemental corn are unknown. In vitro DM disappearance suggests that most protein in the basal protein supplement becoming available to ruminal microbes did so rapidly after consumption. The true protein fraction of total N in litter is approximately 40-50% of total N (Bhattacharya and Fontenot, 1966 ), including protein in microbial cells in poultry excreta (Parsons et al., 1982) and formed during deep-stacking (Loehr, 1977; Merkel, 1981 ). Therefore, slow liberation of nitrogenous compounds from litter may have occurred with high availability to fibrolytic microbes (Slyter et al., 1968; Varga et al., 1981; Akbar et al., 1987). Low digestibility of litter NDF does not indicate that positive effects of litter on forage fiber digestibility occurred via means such as an increased rate or extensiveness of attachment of fibrolytic bacteria to newly ingested forage fiber (Orskov and Ryle, 1990). Alternatively, nonstructural carbohydrates (e.g. starch; Akbar et al., 1987 ) or minerals in litter (Ruffin and McCaskey, 1990) may have affected fiber digestion favorably. The greater than expected N concentration of the peanut skins-litter mix combined at the time of deep-stacking, based on additivity in feedstuff N concentration, suggests that peanut skins increased retention of litter N during deep-stacking, increasing the value of the byproduct as a N supplement. Presumably, this occurred by binding of ammonia by condensed tannins in peanut skins (Kumar and Singh, 1984). Likewise, the lower than expected condensed tannin concentration of the litter-peanut skins mix was probably due to cleavage of tannins by ammonia liberated from litter (Hill et al., 1986a).

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Conclusion In both experiments, the major factor restricting digestible OM intake when litter was substituted for corn appeared to be low digestibility of litter itself rather than negative influences of litter on hay intake or digestibility. In the first experiment, fully or partially compensatory factors when litter was substituted for corn were improvements in hay intake or digestibility. Characteristics of the forage source appeared to alter effects of level of litter substituted for corn on hay intake and fiber digestibility, although the specific forage properties responsible are unknown. In Experiment 2, broiler litter substitution for supplemental corn did not alter digestible OM intake, apparently because of higher forage intake and digestibility which fully compensated for lower digestibility of litter than corn. Feedstuff costs and composition and nutrient requirements by particular classes of ruminants would determine the potential for effective use of litter as an inexpensive substitute for portions of grain in energy supplements. Mixing litter with a feedstuff high in condensed tannins improved the feeding value of litter by increasing N retention during deep-stacking; the condensed tannin concentration of the mixture was depressed as well.

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