Rumen digestion of ensiled apple pomace in sheep: effect of proportion in diet and source of nitrogen supplementation

Animal Feed Science and Technology, 39 ( 1992 ) 193-207

193

Elsevier Science Publishers B.V., Amsterdam

J. Gasa, C. Castrillo$J.A. Guada and J. Balcells Dpto. de Producei& Animal y Ciencia de losAlimentos, Universidadde Zaragoza, Zaragoza, Spain

(Received 18 July 1991; accepted 22 May 1992)

ABSTRACT Gasa, J., Castrillo, C., Guada, J.A. and Balcells, J., 1992. Rumen digestion of ensiled apple pomace in sheep: effect of proportion in diet and source of nitrogen supplementation. Anim. Feed Sci. Technol., 39: 193-207. Three diets composed of alfalfa hay and 40% (A), 7O?h(B) or 1OOI (C) of ensiled apple pomace

(EAP) were each given to three rumen cannulated sheep at intakes of 45 g DM kg-’ ?VO.”and 63 g DM kg-’ W”.‘§in Experiments 1 and 2, respectively. Diet C in Experiment 1 and Diets B and C in Experiment 2 were supplemented with urea to a minimum crude protein content of 100 g kg- ’ DM or 130 g kg-t DM, respectively. In the third experiment, three diets containing 60% EAP plus alfalfa hay or ammonia-treated straw supplemented with urea or sunflower meal and urea were formuiated to a similar protein content and offered ‘ad libitum’. Degradation kinetics of main dietary ingredients were studied using the nylon bag technique, and rumen pH, ammonia and volatile fatty acids (VFAs) concentrations were periodically determined during an 8 h period after feeding. In Eperiment 1, when the dietary level of EAP was increased above 4096, DM degradability of alfalfa hay and EAP were significantly (PcO.05) reduced. Total VFAs concentration decreased and rumen ammonia concentrations lower than 50 mg NH,N 1-l were recorded. This effect was eliminated by the higher level of urea supplementation in Experiment 2 which increased ammonia concentrations above 70 mg NHaN 1-t but EAP degradability still tended to be lower in Diet B. This effect was associated with low rumen pH caused by higher cumulative intake of EAP after feeding. In Experiment 3 voluntary dry matter intake decreased (PcO.05) from 83.1 L 3.12 to 76.7 f 1.46 when alfalfa hay was replaced by ammonia-treated straw and urea was the only source of supplementary nitrogen but no other measured parameter was significantly affected by diet.

INTRODWCTION

Apple pomace is a by-product generated by milling and pressing fresh apples for juice production, although this description also applies to fermenCorrespondence to: C. Castrillo, Dpto. de Produceion Animal y Ciencia de 10s Alimentos, Universidad de Zaragoza, Miguel Servet, 177, Zaragoza, Spain.

0 1992 Elsevier Science Publishers B.V. All rights reserved 0377-840 l/92/$05.00

194

J. GASAET 4k.

tation residue of cider making. The chemical composition of fresh apple psmace (see Boucque and Fiems, 1988) is characterised by high contents of moisture (greater than 750 g kg” ), soluble carbohydrates and pectins together with a low level of crude protein (less than 80 g kg-’ ) which is only about 50% rumen degradable (Gasa et al., 1988). When ensiled, fermentation induces a high alcohol content; 190 and 166 g kg- ’ dry matter were reported by Alibes et al. ( 1984) and Gasa et al. ( 1988), respectively. Apple pomace can supply up to 50% of the total diet dry matter without adverse effects on intake and performance of pregnant ewes (Rumsey and Lindahl, 1982) when mixed with a diet including dehydrated alfalfa (20%), wheat straw (44%) and corn meal (36%) and supplemented with natural protein or non-protein nitrogen. Higher levels of inclusion have also been reported, in sheep (Alibes et al., 1979) and cattle (Thonney et al., 1986), when supplemented with soya bean meal or hay. In contrast, several reports (e.g. Fontenot et al., 1977) indicate that non-protein nitrogen is less satisfactory. Urea supplementation reduces intake and acceptability (Oltjen et al., 1977) and causes serious reproductive problems in pregnant beef cattle (Fontenot et al., 1977) and ewes (Rumsey, 1979). While this by-product has potential as an energy source for ruminants, further information is required on the maximum level of inclusion and the need for non-protein nitrogen supplementation. This paper reports three experiments to evaluate the effect of feeding high levels of ensiled apple pomace (EAP). Two experiments studied the effect of the dietary level of EAP and urea supplementation when given with alfalfa hay, and the third was designed to investigate the substitution of alfalfa hay with ammonia-treated barley straw (ATS) fortified with urea or sunflower meal. MATERIALS AND METHODS

Animals and diets Nine mature, non-breeding Rasa Aragnonesa ewes fitted with rumen cannula were used in each experiment. Their mean body weights (W) were 44.8 + 5.08 kg, 43.3 2 5.76 kg and 59.8 + 7.8 1 kg in Experiments 1,2 and 3, respectively. Ewes were distributed, according to weight, in three blocks and the animals from each block randomly assigned to the following treatments. In Experiment 1 EAP was fed together with chopped alfalfa hay at three rates of inclusion in the diet: 0.4 (Diet A), 0.7 (Diet B) and 1.0 (Diet C). Diet C was supplemented with urea to reach a minimum crude protein content of 100 g kg- *. In Experiment 2 the same diets were used but the crude protein content of Diets B and C was increased to 130 g kg-‘, similar to Diet A, by urea supplementation. In Experiment 3 a diet containing 0.6 EAP and 0.4 chopped alfalfa hay (Diet AH) was compared with two diets in which the hay

RUMEN DIGESTION OF ENSILEDAPPLE POMACE IN SHEEP

195

was substituted by chopped ATS plus urea ( opped ATS plus iet SS). The ingredient composition of the diets proximate analysis of main ingredients is given in Table 2. Urea and sodium sulphate (0.13 g g-l of urea) were added to EA water solution ( 50 ml day- ’ ) which was thoroughly mixed by hand w diet immediately before feeding. Diets were given in two equal meals at 09:OO and 17:OOh. All diets were offered at d level of intake: in Experiments 1 of 45 g DM kg-’ Vp75 and 2 of 63 kg- ’ w”*7s,to avoid.selection. In both experiments the level was restricted to the consumption recorded the week before on Treatment B. In Experiment 3 all offered ‘ad libiturn’. Fresh water, limestone, disodium phosphate rnercial mineral block (0.98 g Mg, 0.80 g n, 0.80 g Zn, 0.40 g Cu, 0.04 g Co, 0.04 g I and ClNa up to 1 kg) were continuously available. TABLE 1 Ingredient composition (%) of Diets A, B, C in Trials 1 and 2 and Diets AH, SU and SS in Trial 3 Ingredients (%)

Ensiled apple pomace Alfalfa hay Ammonia-treated straw Sunflower meal Urea: Experiments l/2

Experiments 1 and 2

Experiment 3

A

B

C

AH

SU

ss

40 60 -

70 30

100

60 40

60 40

60 30 10 0.5

-

0.0/1.4

2.013.0

-

1.5

TABLE 2 Proximate composition (g kg’ dry matter) of dietary ingredients Ammonia

Dry matter (g kg-‘) Organic matter Crude protein Ether extract Crude fibre Neutral: detergent fibre Acid detergent fibre Permanganate lignin

Experiments 1 and 2

Experiment 3

Ensiled apple pomice

Alfalfa hay

Ensiled apple pomice

Alfalfa hay

Treated straw

189’ 966 67 66 254 491 358 83

837 900 175 28 332 490 393 115

166’ 894 90 72 271 512 361 86

888 875 210 23 282 446 368 101

903

‘Corrected for volatile compounds following Gasa et al. ( 1988).

930

101 12 446 753 479 72

196

J. GASA ET AL.

Experimentaiprocedure Each experimental period comprised 2 1,14 and 35 days (Experiments 1,2 and 3, respectively) of adaptation to the diets followed by an 8 day measurement period. Fed intake was recorded (Experiments 2 and 3 only) and studies on dry matter disappearance from nylon bags of dietary main ingredients and rumen parameters (pH, NHJH and volatile fatty acids concentrations (VFAs) ) were carried out. During rumen sampling days, in Experiments 2 and 3, refusals were collected, at each sampling time, weighed and returned to the feeder. The rate and extent of rumen dry matter disappearance of all main dietary ingredients were studied using the nylon bag technique as described by @rskov et al. ( 1980). Ground samples (2 mm screen) of each ingredient (4-5 g) were incubated in nylon bags suspended in the rumen of each animal for 6, 12,24 and 48 h beginning 0.5 h after the morning feeding. The bags were tied to nylon cords (25 cm long) and anchored to the rumen cannula. Immediately after withdrawal, each bag was thoroughly washed in cold running tap water and dried to a constant weight at 60°C for 48 h. One bag for each time was incubated in each animal and the degradation rate was calculated assuming that DM disappearance from the bags between 6 and 48 h followed a firstorder kinetics model. Rumen liquor samples were taken, just before morning feeding (0 h) and at 1,2,4,6 and 8 h after feeding, on the last day of the experimental period. After being strained througn cheesecloth, liquor pH was measured and two acidified (H$O, 0.2 N) subsamples were collected for ammonia and VFAs analysis. Analyticalmethods

Dry matter was determined by oven drying to constant weight at 100105”C, organic matter by ashing at 55O”C,and crude protein by the Kjeldahl method with Se as catalyst. Crude fibre and ether extract were determined according to the procedure of the Association of Official Analytical Chemists ( 1980) procedures and neutral detergent fibre, acid detergent fibre and permanganate lignin following Goering and Van Soest ( 1970). EAP dry matter was corrected for volatile losses as ammonia, alcohol and VFAs content ( Gasa et al., 1988). Ammonia was analysed as reported by McMeniman and Armstrong ( 1979). VFAs were determined by gas-liquid chromatography using a Packard Model 5890a gas chromatograph (Jouany, 1982).

RUMEN DIGESTIOY OF ENSILEDAPPLE POMACE IN SHEEP

197

Statistical analysis Data from all experiments were subjected to analysis of variance as a randomised block design (Steel and Torrie, 1960) and treatment means were compared by the Duncan test. RESULTS

Experiment I Daily intake was not recorded but refusals wer C. Dry matter degradability of both alfalfa hay an nificantly depressed by increasing the dietary level of A). This effect was markedly lower and not significant levelled off for the al Figure 1 shows vari d amm.onia and total VFAs concentrations let except just before feeding and 8 h later wever ammonia concentration was co sampling period. of Diet C during the first hours after feeding and remained below or near to 50 mg NH3N 1-l during the whole period. Total VFAs concentration inTABLE 3 Dry matter disappearance (g per 100 g) and degradation rate (96, h’ *) of alfalfa hay (AH) and ensiled apple pomace (EAP) in the rumen of sheep consuming diets with 40% (A), 70% (B) or 100% (C j of ensiled apple pomace plus alfalfa hay and urea SuppIementation to provide a minimum crude protein content of 100 g kg-’ Material incubated

Diet

Degradation rate

Incubation period (h ) (6)

(12)

(24)

(48)

AH

A B V SED’ Sign, level

51.8” 38Sb 41.2b 1.51 **+

57.78 50.0b 47.gb 2.13 4

66.Y 62Jb 61.gb 1.11 *

68.2 68.8 66.7 1.69 NS

11.0 7.1 6.8 1.15 0.07

EAP

A B C SED Sign. level

23.0 23.0 26.0 2.00 NS

47.8a 29.2b 39.3s 3.61 0

69.00 45.5b 57.8’ 4.73 +

84.4” 64.5b 78.1a 2.75 +**

5.9 2.1 3.5 0.70 0.06

Means in the same row with different superscripts differ. * 3-z 0.05; * +* PC 0.001; NS, not significant. ‘SED, standard error of the difference between means.

J, GASA ET AL.

17.5 -

12.5 -

7.5 -

2.5 -

0

100

2

1

4

3

7

6

5

8

1

Ii

;

-

I

2

-

1

3

.

I

4

-

I

.

5

6

7

8

Time after feeding Fig. 1. Time course variation of ruminal pH, ammonia and volatile fatty acid (VFAs) concentrations in sheep consuming diets made up of 40O51 ( alfalfa hay and urea to provide a minimum crude protein content of 100 g kg-’ DM in Experiment 1. Vertical bars: standard error of the means.

RUhlEN DIGESTIONOF ENSILED APPLE POh4ACEIN SHEEP

199

creased after feedin.g; iet A had the highest values although significant differences (PC 0.05 ) were only detected 1 and 4 h after feeding. The mean concentration of total VFAs and molar proportions are given in Table 4 which also includes the results from Experiments 2 and 3. The proportions of major VFAs (acetic, propionic and butyric) were unaffected but proportions of branched VFAs, isobutyric and isovaleric were ~0.05) and those of valeric acid lower (P< 0.0 1) in Diet A. While DM degradability figures were poorly correlated with both p ues and VFAs concentrations, significant correlations (P< 0.05 ) were between mean or minimum ammonia concentrations a adation rates of both, alfalfa hay (r=0.74 and 0.71, respectively) a ( t= 0.72 and 0.76). Experiment 2

Since intake was very low in one of the sheep on iet C, all its measurements were deleted fro the statistical analysis. The average daily dry matter TABLE 4 Mean total concentration (mm01 I-’ ) and molar proportions (U) of ruminal volatile fatty acids following morning feeding of sheep fed 40% (A), 70% (B) and IOOOA (C) of ensiled apple pomace in Trials 1 and 2 or 60% of ensiled apple pomace supplemented with lucema hay (LH), ammoniatreated straw plus urea (SW) and ammonia-treated straw plus sunflower meal and urea (SS) in Experiment 3 Trial

Diet

A

Mean

Volatile fatty acids’ c-2

c-3

c-4

IC-4

c-5

IC-5

73.95

B C SED Sign. level

74.p 54.gb 52.2b 4.98 +

74.10 74.98 1.505 NS

15.27 15.84 13.62 1.234 NS

8.44 7.69 8.27 0.826 NS

0.64” 0.4Ob 0.20’ 0.032 *++

1.17c 2.05b 2.92a 0.236 +*

0.52 0.35 0.34 0.075 NS

2

A B C SED Sign. level

50.28b 57.7a 38.7b 3.95 < 0.10

77.16 77.23 79.78 1.046 NS

15.50 14.73 13.48 0.624 NS

5.63 6.29 4.77 0.505 NS

0.578 o.34b 0.20b 0.055 *

0.76b 1.27’ l.65a 0.105 *

0.42 0.25 0.27 0.052 NS

3

AH su ss SED Sign. level

65.9 59.7

70.02 71.74 72.92 1.119 NS

17.71 16.98 17.11 1.027 NS

7.10 7.62 7.13 0.631 NS

0.52 0.44 0.52 0.045 NS

1.89 2.68 1.83 0.348 NS

0.44 0.47 0.60 0.048 NS

1

57.4 6.72 NS

Means in the same row with different superscripts differ. ‘C-2, acetic acid; C-3, propionic acid; C-4, butyric acid; C-5, vale& acid; IC-4, isobutyric acid; IC-5, isovaleric acid. ‘P< 0.05; **PC 0.01; ***P< 0.00 1; NS, not significant.

J. GASA ET AL.

200

intake was 63.0 g, 56.1If:6.7 g and 48.2 2 I .7 g kg’ ’ W”-75 on Diets A, B and C, respectively.Cumulative intake (Fig. 2 ) of total dry matter was higher for Diets A and B compared with Diet C (PC 0.05) at 4,6 and 8 h after feeding and, consequently,EAP consumptionwas higher for Diet B during the first 6 h after feeding (P= 0.085) . Most of the differencesin rumen degradabilitywere eliminated by supplementing with urea (Table 5), although EAP degradability still tended (P
Time after feeding (II) Fig. 2. Cumuiative total (closed symbols} or EAP (open symbols) dry matter intake of diets made up of 40% ( ) of EAP plus alfalfa hay and urea in Experiment 2. Vertical bars: standard error of the means.

RUMEN DIGESTION OF ENSILED APPLE POMACE IN SHEEP

201

TABLE 5 Dry matter disappearance (g per 100 g) and degradation rate (%, h-r) of alfalfa hay (AH) and et&led apple pomace (EAP) in the rumen of sheep consuming diets with 40% (A), 70% (B) or 100% (C) ensiled apple pomace plus alfalfa hay and urea supplementation to provide a minimum crude protein content of 130 g kg-’ Material incubated

Diet

Incubation period (h )

Degradation rate

(6)

(12)

(24)

(48)

AH

A B C SED’ Sign. Ievel

45.6 43.4 47.2 3.34 NS

59.2 55.6 59.2 1.85 NS

69.7 68.3 67.1 1.70 NS

73.2 72.7 72.6 1.26 NS

10.7 9.0 9.7 1.05 NS

EAP

A B c SED Sign. level

26.1 23.5 26.1 2.23 NS

42.2 34.2 43.5 4.26 NS

63.8 57.4 64.0 7.54 NS

85.3 77.3 84.0 4.20 NS

4.1 4.4 5.4 1.00 NS

‘SED standard error of the difference between means. NS, not significant.

EAP dry matter degradability and intake were significantly (P< 0.05 ) correlated with pH values. he higher correlations were achieved between minimum pH and D disappearance at 48 h or EAP intake at 6 h after feeding (Fig. 4). Experiment 3

Dry matter intake was lower (F~0.05) on Diet SU (76.7 t 1.46 g kg-’ W’S’~)than on Diets AH and SS (82.9 + 2.95 g and 83.2 2 3.23 g kg-’ W”-75, respectively) and the cumulative dry matter intake during the rumen sampling period did not differ (P> 0.05 ) among diets. The degradability and degradation rates of alfalfa hay and EAB were not modified by diet (Table 6 ) . Only the degradation of ammonia-treated straw at 12 and 48 h was significantly lower on Diet AH. Mean pH values were unaffected by diet with minimum values after feeding consistently greater than 6.0. can ammonia concentrations measured lower values were after feeding ranged fro to 267 mg NH3N 1-l an s or molar proporalways found with Die Total concentrations of tions were unaffected by diet (Table 4).

J. GASA ET AL.

202 8.0 7.5 -

7.0 -

SC

6.5 -

6.0 -

5-5 -

I I III I - I - 1 - I - 8 - ’ * ‘.

I

0

1

2

3

4

5

6

’ 7

0

1

2

3

4

5

6

7

”

8

30 25 20 2

15-

.z 6

10 -

z Q

sO-

8

80 -

60 -

III t 0

-

1 I

1

-

I

2

-

I

3

-

I

4

1

I -

I

5

’

I

6

’

1

7

‘1 8

Time after feeding Fig. 3. Time course variation of ruminal pH, ammonia and volatile fatty acid (VFAs) concentrations in sheep consuming diets made up of 40O,41 ( ), 70% (+) and 100% (A) EAP plus alfalfa hay and two rates of urea supplementation to provide a crude protein content of 130 g kg” DM in Experiment 2. Vertical bars: standard error ofthe means.

RUMEN DIGESTION OF ENSILED APPLE POMACE IN SHEEP

203

90 -

85 -

g % .Y a

SO-

Q

75 -

r=0.82 (~10.01) 70 -

65 -

Iv

I

5.5

-

I

5.6

-

5.7

I

-,

5.8

(

-

6.0

5.9

.,

-

6.1

,.,

.

6.2

6.3

1

6.4

Minimum pH

6.4

6.2 X ’ z ‘2 ’

e

r=O.95 (plO.00 1)

A

60 ’ 5.8

8

5.6

I

I

12

14

-

I

=

16

EAPIntakc

(g

a

I

I

18

20

22

DM

kg-’ W’.”

-

1

24

]

Fig. 4. Relationship betwee.n rimen dry matter disappearance of EAP from nylon bags at 48 h (Dis 48, %) and minimum pH and between the later and EAP dry matter intake (g kg-’ ~7s) after 6 h from morning feeding in Experiment 2.

J. GASA ET AL.

204

TABLE 6 Dry matter disappearance (g per 100 g ) and degradation rate (%, h- ’ ) of alfalfa hay, ensiled apple pomace (EAP) and ammonia-treated straw (ATS) in the rumen of sheep fed mixed diets containing 60% of EAP plus alfalfa hay (AH) or ammonia-treated straw supplemented with urea (SU) or sunflower meal and urea (SS) , in Experiment 3 Material incubated

Diet

Degradation rate

Incubation period (h) (6)

(12)

(24)

(48)

AH su ss SED Sign. level

40.5 41.4 37.4 1.54 NS

56.8 54.6 so.2 3.19 NS

69.3

68.0 67.9 1.23 NS

71.8 74.3 72.3 1.42 NS

13.0 8.8 10.1 2.5 NS

EAP

AH su ss SED Sign. level

30.2 28.5 28.2 2.33 NS

37.7 41.4 39.5 3.53 NS

63.1 62.1 58.9 4.09 NS

74.8 77.7 73.4 1.54 NS

4.7 4.9 4.6 1.16 NS

ATS

AH su ss SED Sign. level

14.4 16.7 14.5 1.11 NS

19.8b 27.8” 26.08 1.93 +

39.3

58.gb

44.6 38.7 3.19 NS

65.48 62.5”b 0.95 *

3.1 3.8 3.7 0.66 NS

Alfalfa

VcO.05, NS, not significant. Means in the same row with different superscripts differ. DISCUSSION

Rumen ammonia concentrations were insufficient to achieve the optimal degradation rate of diets containing more than 700 g kg-’ EAP. ‘In vitro’ (Satter and Slyter, 1974) and ‘in vivo’ studies (Hume, 1970) suggest that a minimum ammonia nitrogen concentration of 50 mg NHsN l- ’ is required to promote optimum microbial growth, although higher concentrations have been reported to maximise substrate degradation (Hume, 1970; 0rskov, 1982). In Diets B and C an equivalent crude protein content of 100 g kg- ’ was insufficient to maintain rumen ammonia concentration above this critical level probably due to both the low nitrogen content of EAP and its moderate rumen degradability ( 5 1.7% reported by Gasa et al., 1988 ). Rumen ammonia concentration remained above 70 mg NH3N 1-l and differences in DM degradability were removed by increasing the level of urea supplementation in Experiment 2. Nevertheless, EAP dry matter degradability was apparently lower for Diet B (Table 5 ). Two of the three ewes in Diet B presented a higher cumulative intake of EAP following morning feeding

RUMEN DIGESTION OF ENSILED APPLE POMACE IN SHEEP

205

( scxzFigs. 2 and 4) which could have a detrimental effect on degradability through a reduction in the rumen (see Figs. 3 and 4). A decrease of rumen pH below 6.0 has been suggested bourn et al., 1970; Stewarth, 19’77)as a cause of a reduction in number and activity of the microbial population especially when cellulolytic bacteria are involved. The minimum rumen p higher with Diet C, in part due to the alkaline effect of the’ammoniu (Oltjen et al., 1977) and also because less EAP was ingested (see Fig. 2 ). Fontenot et al. ( 1977) also noticed low rates of intake when feeding cows apple pomace plus a small amount of corn meal including urea, biuret or ureabiuret, probably as a consequence of the urea taste. The lower mean pH values recorded just before feeding on Diet C in Experiments 1 and 2 (Figs. 1 and 3) also agrees with a slower pattern of intake with When mixed diets ( 600 g EAP kg- ’ ) were fed ‘ad li m’, in Experiment 3, total dry matter intake increased, but EAP consumption was similar tc that of Diet C (all EAP) in 1.7 versus 49.7 + l&45.9 -+0.9 (4 and 49.8 + 2.0 g DM kg ets , SU and SS, respectively). When urea was the only source of nitrogen supplementation, daily dry matter intake was reduced (Diet SU), but no othe measured parameter was modified by diet, except for the decrease in ATS egradability with not include ATS. In steers consumin in an hour, equal kg-’ ~*75) of diets containing 70-75% of apple pomace supplemented with and the ammonia and VFAs concencotton-seed meal or urea, the rume with a control diet of corn silage and trations were similar to those recor cotton-seed meal ( msey, 1978). Furthermore, rumen acteria numbers le pomace were supplemented wilh were similar when n urea was the main nitrogen supcotton-seed meal, ncbed VFG (T&le 4 ) 5 ir, agreement with previous findings by msey ( 1978) comparing apple pomace plus urea with corn silage as the main dietary ingredients (0.58 20.15 and 0.46 20.21 versus 1.02-+0.04 and 1.31+0.18 for isobutyric and isovaleric acids, respectively), may reduce amino id synthesis in cellul ryant and Robinson, 1962; hority et al., 1967). from pectin ferment in silo or in the rumen (mainly ethanol) does not seem to disturb rumen fermentation ey, 1978) aIthough it may be detrimental TVliver function in the lo In conclusion EAP can be safely incorporated at up to 60% in mixed ro age diets properly supplemented with degradable nitrogen. Higher lev inclusion may depress rumen pH with a subsequent reduction in rumen fermentation in response to an increase in cumulative alfalfa hay or ammonia-treated straw-based diets an content of 130 g kg- Lwas ecough to maintain rumen ammonia concentration I- l and offset detrimental effects on above the critical level of 50 mg N

206

J. GASAET AL.

rumen digestion, Although urea can be effticiently used as a source of degradable nitrogen, roughages which are poor in preformed protein, such as ammonia-treated straw, will require a vegetable protein supplementation to avoid reductions in voluntary intake as a result of the poor taste produced by the urea itself. Other factors, such as inadequate supply of branched VFAs to the rumen, may also be involved. ACKNOWLEDGEMENTS

We are grateful to Dr. 1.1. Bonafonte for undertaking the surgical preparation of the animals and to J.A. Ruiz and A. Barcelo for the skilled technical support at the animal house and laboratory, respectively. This work was financed by D.G.A. as research project Al-26.

REFERENCES Alibes, X., Rodriguez, J., Mufioz, F. and Geria, R., 1979. Valor alimenticio de1ensilado de pulpade manzana: suplementaci6n con distintas fuentes de nitrogeno. IV Jomadas Cientiiicas de la Sociedad Espafiola de Ovinotecnia. pp. 2 13-223. Alibes, X., Muiioz, F. and Rodriguez, J., 1984. Feeding value of apple pomace silage for sheep. Anim. Feed Sci. Technol., 11: 186-l 97. Associationof OfficialAnalytical Chemists, 1980.Official Methodsof Analysis. 13thEdn. AOAC, Washington, DC. Boucque, Ch.V. and Fiems, L.O., 1988. Vegetableby-products of agroindustrial origin. Livestock Prod. Sci., 19: 97- 135. Bryant, M.P. and Robinson, I.M., 1962.Some nutritional characteristics of predominant culturable ruminal bacteria. J. Bacterial., 84: 605-614. Dehority, B.A.,Scott, H.W. and Kowaluk,P., 1967. Volatile fatty acid requirements of cellulolytic rumen bacteria. J. Bacterial., 94: 537-543. Fontenot, J.P., Bovard, K.P., Oltjen, R.R., Rumsey, T.S. and Priode, B.M., 1977. Supplementation of apple pomace with non protein nitrogen for gestatingbeef cows. I-Feed intake and performances. J. Anim. Sci., 46: 5 13-522. Gasa, J., Castrillo, C. and Guada, J.A., 1988.Valor nutritivo para 10srumiantes de 10sprincipales subproductos de la industria conservera de hortalizas y frutas. 3-Pulpa de manzana. Invest. Agraria: Production y Sanidad Animal, 3: 93-108. Goering, M.K. and van Soest, P.J., 1970. Forage Fibre Analysis. Agricultural Handbook No. 397. Agric. Res. Serv. USDA, Washington, DC, 20 pp. Hume, J.D., 1970.Synthesis of microbial protein in the rumen. III The effect of dietary protein. Aust. J. Agric.Res., 21: 305-314. Jouany, J.P., 1982. Volatile fatty acid and alcohol determination in digestive contents, silage juices, bacterial cultures and anaerobic fermentor contents. Sciences des Aliments, 2: 13l144. McMeniman, N.P. and Armstrong, D.G., 1979.The flow of aminoacids into the small intestine of cattle when fed heated and unheated beans (Vicia faba). J. Agric. Sci., Cambridge, 93: 181-188. Gltjen, RR., Rumsey, T.S.,Fontenot, J.P., Bovard, K.P. and Priode, B.M., 1977.Supplemen-

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