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Effect of urea on the ensiling process of orange pulp
Animal Feed Science and Technology, 12 (1985) 233--238
233
Elsevier Science Publishers B.V., Amsterdam -- Printed in The Netherlands
EFFECT OF U R E A ON THE ENSILING PROCESS OF O R A N G E PULP
CONCHA CERVERA, J U L I O F E R N A N D E Z - C A R M O N A and JU LI A MARTI
E.T.S. Ingenieros Agronomos, Universidad Politecnica, Apdo 2012, Valencia (Spain) (Received 4 October 1983; accepted for publication 16 January 1985)
ABSTRACT Cervera, C., Fernandez-Carmona, J. and Marti, J., 1985. Effect of urea on ensiling process of orange pulp. Anita. Feed Sci. Technol., 12: 233--238. Orange pulp was ensiled fresh or after adding 18 g urea kg -1 pulp dry matter and the ensiling process was studied over a period of 90 days, in laboratory silos. Fermentation was very intense for the first 10 days; at the end of the experiment both silages were stable and well-preserved. Average figures at this stage were, respectively: pH 3.5 and 3.6; ammonia nitrogen 1.2 and 1.7% of the total nitrogen; acetic acid 3.0 and 2.5% DM; lactic acid 2.2 and 2% DM and butyric acid 0.05 and 0.05% DM. High losses of dry matter (32.4 and 32.1%) were registered, those in the effluent accounting for about 15% of the total. Addition o f urea delayed fermentation slightly and increased production o f gases, but did not affect either the quality or the stability of the silage.
INTRODUCTION
Citrus pulp has been studied for animal feeding in both citrus- and noncitrus-producing countries, but most of the work published has been carried out on either fresh or dried pulp. There are few studies on citrus pulp silage (Bondi, 1941; Becker et a l 1946; Gohl, 1973) none of which have followed its evolution, and only data relating to the final stage are available. Citrus pulp is a by-product of the juice industry, with a high content of water, carbohydrates and minerals, b u t low in protein. Non-protein nitrogen has sometimes been incorporated in citrus pulp (Volcani and Roderig, 1953; Volcani and Schindler, 1953), b u t this addition has been studied from the nutritional point of view, not that of silage quality. The objective of the present experiment was to determine the chemical changes and losses in citrus pulp silage when urea was added. M AT ER I ALS AND METHODS
Two series of 18 laboratory silos were filled with 1.4 kg of fresh orange pulp alone (OP series) or after addition of 18 g urea kg -1 pulp dry matter (UOP series). 0377-8401/85/$03.30
© 1985 Elsevier Science Publishers B.V.
234
Three silos from each series were opened at time intervals of 3, 10, 20, 35, 60 and 90 days and analysed for: Physical characteristics, odour and taste. -- Dry matter by oven-drying to constant weight. - - T o t a l nitrogen by macro-Kjeldahl (Association of Official Analytical Chemists, 1975). - pH (Jean-Blain and Urtinette, 1957). --Ammonia-nitrogen (NH3-N) by a modification of Conway's method (Caja, 1975). -- Water-soluble carbohydrates (WSC) by the anthrone reagent technique (Ministry of Agriculture, Fisheries and Food, 1976). -- Volatile fatty acids (VFA) (Annison, 1954). --Alcohol, individual volatile fatty acids and lactic acid by the gas chromatograph techniques of Gouet and Girardeau (1974). An analysis of variance was carried out with the results, following a balanced design of two factors of variation (treatment and days after ensiling) and their interaction. -
-
RESUL TS AND DISCUSSION
Composition of fresh pulp was: dry matter, 18.2%; crude protein, 8.7% DM; water-soluble carbohydrates 15.0% DM; ammonia nitrogen 0.5% of total N; and pH 3.7. White colonies of bacteria appeared on the surface of the silage after 10 days, being present in UOP silos in greater number. Physical characteristics indicated good preservation of the silage and were similar for both series. Dry matter content decreased significantly (P<0.01) during the first 10 days, with no variation afterwards (Table I); there were no significant differences between treatments, but the interaction between treatment and period was significant (P<:0.05), probably because of the irregular changes found in UOP silos. Dry matter losses were also similar for both series of silos and increased until 20 days after ensiling (Table I). Losses through the effluent in the OP series were only 11--31% of the total, and 7--19% in the UOP series. Fermentation of WSC and organic acids, which produces a high proportion of gases, must be the reason for the high dry matter losses registered in the present experiment, and in fact Bondi (1941) working with citrus pulp silage found that the whole amount of citric acid had fermented. Water-soluble carbohydrates disappeared quickly during the first 10-day period (P<0.01) and there were no significant differences between OP and UOP silos {Table I). More than 90% of the losses were due to fermentation, the amount found in the effluent varying from 3 to 10%. Becket et al. (1946) studied citrus pulp silage and considered that most losses were due to carbohydrates, but gave no figures.
235 TABLE I Dry m a t t e r c o n t e n t , loss o f dry m a t t e r and loss o f w a t e r soluble c a r b o h y d r a t e s o f silages ~ Days after ensiling
DM c o n t e n t (%)
DM loss (%)
WSC loss (%)
OP
UOP
OP
UOP
OP
UOP
0 3 10 20 35 60 90 Means
18.20 17.71 16.37 15.87 15.56 15.70 15.44 16.41
18.70 17.08 16.01 15.56 15.95 16.00 16.12 16.49
. 13.08 22.22 27.76 31.08 30.86 32.41 26.23
. 14.53 24.26 29.67 30.08 28.89 32.10 26.59
. 54.35 83.65 83.49 85.17 85.02 87.56 79.87
63.44 81.90 85.26 86.51 84.13 82.26 80.58
S t a n d a r d errors o f m e a n s 2 Treatment Period Treatment × period
0.086 0.161 0.228
NS ** *
0.521 0.903 1.277
NS ** NS
0.773 1,340 1,895
NS ** NS
.
1Each value is t h e m e a n o f t h r e e samples. 2Significance o f d i f f e r e n c e s : NS = n o t significant; * P < 0 . 0 5 ; * * P < 0 . 0 1 .
Addition of urea significantly (P<0.01) increased the concentration of nitrogen in the UOP series (Table II). The N content increased (P<0.01) in both series, because other constituents, especially carbohydrates, disappeared faster. During the first 10 days, the nitrogen content of the UOP silos increased more than that in OP silos, showing a lesser proportion of total T A B L E II N i t r o g e n (as c r u d e p r o t e i n ) , a m m o n i a n i t r o g e n a n d loss o f n i t r o g e n (as c r u d e p r o t e i n ) o f silages 1
Days afterensiling
CP (% DM)
N H : N (% totalN)
CP loss(%)
OP
UOP
0P
OP
UOP
0 3 10 20 35 60 90 Means
8.72 9.03 10.22 10.22 12.52 11.40 10.89 10.43
13.91 16.23 17.51 17.49 19.61 18.02 18.23 17.29
-9.91 8.78 15.30 2.46 9.58 15.62 10.27
-1.62 5.18 11.59 1.45 6.59 11.05 6.25
S t a n d a r d errors o f m e a n s 1 Treatment Period Treatment × period
0.130 0.244 0.345
** ** **
1.057 1.831 2.590
* ** NS
1See f o o t n o t e s in Table I.
0.46 0.41 0.33 0.86 1.13 1.29 1.22 0.81
0.022 0.042 0.059
UOP 0.48 0.48 0.54 1.25 1.23 1.64 1.69 1.04
** ** **
236 nitrogen lost, and consequently a significant (P<0.01) treatment X period interaction was registered. Losses of nitrogen, although smaller in the UOP series (P<0.05), were irregular and low for both series, indicating that nitrogen was mainly retained in the silage. Volcani and Schindler {1953) reported that the ammonia incorporated in citrus pulp was retained in the silo, with a 100% increase in crude protein. Although urea can be hydrolysed, free ammonia is trapped by the acids and pectic substances of the silage (Loosli and McDonald, 1969). Orange pulp is therefore a good subject for urea addition and little free ammonia should be found. Between 65 and 90% of the N losses were due to the effluent, this being 100% in some particular silos. These figures are similar to the standards given by Murdoch (1954) and normal for traditional silages with a high water content. Ammonia-nitrogen values {Table II) were higher in the UOP silos (P< 0.01), increased for both series throughout the experiment (P<0.01), and also there was a significant interaction between t r e a t m e n t and period (P<0.01), but figures were very low, suggesting a reduced clostridial activity and a high retention o f urea in the silage. The pH values of fresh orange pulp are very low (3.7 in our experiment) because of citric and other organic acids. After ensiling there was a small decrease (P<0.01) in pH values. Although a little higher for UOP silos, no significant difference in pH was found between the two series. During the first few days, a great production of gases was observed, suggesting a rapid and substantial fermentation of the material. Final pH values, indicating that the material was well preserved, were similar to those given elsewere, although Volcani and Roderig (1953) and Volcani and Schindler (1953) reported higher figures when a m m o n i u m sulphate or ammonia was added to citrus pulp. The pH, alcohol and individual volatile fatty acid analyses are shown in Table III. Fermentation during the first 35 days gave significant increases (P<0.01) in acetic acid, lactic acid and ethanol; little propionic acid and practically no butyric acid was produced. This pattern of fermentation agrees with the decrease of pH and disappearance of WSC already mentioned. T h e OP silos had more acetic acid than the UOP series (P<0.01) and their acetic acid appeared earlier, the data for UOP silos showing an irregular trend. Lactic acid figures were similar to those reported by N. Lodge (personal communication, 1980) and lower than those of Bondi (1941). We m a y conclude, therefore, that addition of urea to orange pulp had no significant effect on the fermentation process, and no sign of deterioration in the ensiled material was detected over a period of 90 days.
0.01 0.02 0.03
3.7 3.4 3.4 3.4 3.5 3.5 3.5 3.5
NS ** NS
3.7 3.5 3.5 3.5 3.5 3.5 3.6 3.5
7.043 13.176 18.633
** ** **
24.00 22.40 25.07 20.80 32.80 28.53 68.26 55.47 110.67 94.40 155.60 110.93 161.06 108.53 82.49 63.01
UOP
OP
OP
UOP
V F A ( m e q 1-')
pH
1See f o o t n o t e s in T a b l e I.
Standard errors of means Treatment Period Treatment x period
0 3 10 20 35 60 90 Means
Days a f t e r ensiling
0.021 0.039 0.055
0.33 0.49 0.96 1.54 2.99 3.03 2.98 1.76
OP
** ** **
0.32 0.20 0.48 1.01 2.44 2.45 2.45 1.34
UOP
A c e t i c acid (% DM)
0.006 0.011 0.015
0.11 0.12 0.12 0.29 0.38 0.48 0.29 0.26
NS NS NS
0.10 0.10 0.11 0.19 0.29 0.28 0.29 0.19
0.001 0.002 0.003
0.02 0.02 0.01 0.05 0.05 0.05 0.05 0.04
NS NS NS
0.01 0.03 0.03 0.02 0.01 0.05 0.05 0.03
UOP
OP
OP
UOP
B u t y r i c acid (% DM)
P r o p i o n i c acid (% DM)
Values for pH, t o t a l volatile f a t t y acids, o r g a n i c acids a n d e t h a n o l o f silages'
T A B L E III
0.014 0.026 0.037
0.11 0.48 1.48 1.52 2.02 2.15 2.19 1.42
NS ** NS
0.10 0.51 1.41 1.51 1.93 2.52 2.03 1.43
0.004 0.008 0.012
0.19 0.67 0.93 0.90 0.79 0.63 0.65 0.68
0P
OP
UOP
Ethanol (% D M )
Lactic acid (% DM)
NS ** NS
0.18 0.59 0.89 0.92 0.72 0.74 0.63 0.67
UOP
b~ ¢,D -O
238 REFERENCES Annison, E.F., 1954. Studies on the volatile fatty acids o f sheep blood with special reference to formic acid. Biochem. J., 58: 670. Association o f Official Analytical Chemists, 1975. Official Methods o f Analysis. 12th edn. A.O.A.C., Washington, DC, pp. 15--16. Becker, R.B°, Davis, G.K., Kirk, W.G., Dix Arnold, P.T. and Hayman, W.P., 1946. Citrus pulp silage. Fla. Agric. Exp. Stn. Bull., 423: 5--16. Bondi, A., 1941. The ensilage o f citrus fruit pulp. Agric. Res. Stn. Rehovot, December, pp. 89--92. Caja, G., 1975. Efectos metabSlicos 'in vitro' e 'in vivo' de la utilizaciSn del formaldehido como protector de las proteinas en la alimentaciSn de ruminantes. Tesis Doctoral E.T.S.I.A., Madrid, pp. 183--185. Gohl, B.I., 1973. Citrus by-products for animal feed. World Anita. Rev., 6: 24--27. Gouet, Ph. and Girardeau, J.P., 1974. Recommendations pour l'analyse biochimique et bact~riologique des ensilages. Bull. Tech. Inf., 292: 537--548. Jean-Blain, M. and Urtinette, A., 1957. L'analyse physico-chimique des ensilages. Bull. Tech. Inf., 125: 677--699. Loosli, J.K. and McDonald, I.W., 1969. E1 nitr6geno no prot~ico en la alimentaci6n de los rumiantes. F A O : Estud. Agropecu., 75: 71. Ministry o f Agriculture, Fisheries and F o o d , 1976. The analysis of agricultural materials. Tech. Bull. No. 27, H.M.S.O., London. Murdoch~ J.C., 1954. Seepage from silos. Agriculture (London), 61 : 224--225. Volcani, R. and Roderig, Ch., 1953. The enrichment o f citrus peel silage with nitrogen b y application of ammonia and ammonium sulphate. Ktavin, 4: 15--19. Volcani, R. and Schindler, H., 1953. The enrichment of fresh and dried orange and lemon peel with ammonia on laboratory and pilot plant scale. Ktavin, 4: 9--13.
233
Elsevier Science Publishers B.V., Amsterdam -- Printed in The Netherlands
EFFECT OF U R E A ON THE ENSILING PROCESS OF O R A N G E PULP
CONCHA CERVERA, J U L I O F E R N A N D E Z - C A R M O N A and JU LI A MARTI
E.T.S. Ingenieros Agronomos, Universidad Politecnica, Apdo 2012, Valencia (Spain) (Received 4 October 1983; accepted for publication 16 January 1985)
ABSTRACT Cervera, C., Fernandez-Carmona, J. and Marti, J., 1985. Effect of urea on ensiling process of orange pulp. Anita. Feed Sci. Technol., 12: 233--238. Orange pulp was ensiled fresh or after adding 18 g urea kg -1 pulp dry matter and the ensiling process was studied over a period of 90 days, in laboratory silos. Fermentation was very intense for the first 10 days; at the end of the experiment both silages were stable and well-preserved. Average figures at this stage were, respectively: pH 3.5 and 3.6; ammonia nitrogen 1.2 and 1.7% of the total nitrogen; acetic acid 3.0 and 2.5% DM; lactic acid 2.2 and 2% DM and butyric acid 0.05 and 0.05% DM. High losses of dry matter (32.4 and 32.1%) were registered, those in the effluent accounting for about 15% of the total. Addition o f urea delayed fermentation slightly and increased production o f gases, but did not affect either the quality or the stability of the silage.
INTRODUCTION
Citrus pulp has been studied for animal feeding in both citrus- and noncitrus-producing countries, but most of the work published has been carried out on either fresh or dried pulp. There are few studies on citrus pulp silage (Bondi, 1941; Becker et a l 1946; Gohl, 1973) none of which have followed its evolution, and only data relating to the final stage are available. Citrus pulp is a by-product of the juice industry, with a high content of water, carbohydrates and minerals, b u t low in protein. Non-protein nitrogen has sometimes been incorporated in citrus pulp (Volcani and Roderig, 1953; Volcani and Schindler, 1953), b u t this addition has been studied from the nutritional point of view, not that of silage quality. The objective of the present experiment was to determine the chemical changes and losses in citrus pulp silage when urea was added. M AT ER I ALS AND METHODS
Two series of 18 laboratory silos were filled with 1.4 kg of fresh orange pulp alone (OP series) or after addition of 18 g urea kg -1 pulp dry matter (UOP series). 0377-8401/85/$03.30
© 1985 Elsevier Science Publishers B.V.
234
Three silos from each series were opened at time intervals of 3, 10, 20, 35, 60 and 90 days and analysed for: Physical characteristics, odour and taste. -- Dry matter by oven-drying to constant weight. - - T o t a l nitrogen by macro-Kjeldahl (Association of Official Analytical Chemists, 1975). - pH (Jean-Blain and Urtinette, 1957). --Ammonia-nitrogen (NH3-N) by a modification of Conway's method (Caja, 1975). -- Water-soluble carbohydrates (WSC) by the anthrone reagent technique (Ministry of Agriculture, Fisheries and Food, 1976). -- Volatile fatty acids (VFA) (Annison, 1954). --Alcohol, individual volatile fatty acids and lactic acid by the gas chromatograph techniques of Gouet and Girardeau (1974). An analysis of variance was carried out with the results, following a balanced design of two factors of variation (treatment and days after ensiling) and their interaction. -
-
RESUL TS AND DISCUSSION
Composition of fresh pulp was: dry matter, 18.2%; crude protein, 8.7% DM; water-soluble carbohydrates 15.0% DM; ammonia nitrogen 0.5% of total N; and pH 3.7. White colonies of bacteria appeared on the surface of the silage after 10 days, being present in UOP silos in greater number. Physical characteristics indicated good preservation of the silage and were similar for both series. Dry matter content decreased significantly (P<0.01) during the first 10 days, with no variation afterwards (Table I); there were no significant differences between treatments, but the interaction between treatment and period was significant (P<:0.05), probably because of the irregular changes found in UOP silos. Dry matter losses were also similar for both series of silos and increased until 20 days after ensiling (Table I). Losses through the effluent in the OP series were only 11--31% of the total, and 7--19% in the UOP series. Fermentation of WSC and organic acids, which produces a high proportion of gases, must be the reason for the high dry matter losses registered in the present experiment, and in fact Bondi (1941) working with citrus pulp silage found that the whole amount of citric acid had fermented. Water-soluble carbohydrates disappeared quickly during the first 10-day period (P<0.01) and there were no significant differences between OP and UOP silos {Table I). More than 90% of the losses were due to fermentation, the amount found in the effluent varying from 3 to 10%. Becket et al. (1946) studied citrus pulp silage and considered that most losses were due to carbohydrates, but gave no figures.
235 TABLE I Dry m a t t e r c o n t e n t , loss o f dry m a t t e r and loss o f w a t e r soluble c a r b o h y d r a t e s o f silages ~ Days after ensiling
DM c o n t e n t (%)
DM loss (%)
WSC loss (%)
OP
UOP
OP
UOP
OP
UOP
0 3 10 20 35 60 90 Means
18.20 17.71 16.37 15.87 15.56 15.70 15.44 16.41
18.70 17.08 16.01 15.56 15.95 16.00 16.12 16.49
. 13.08 22.22 27.76 31.08 30.86 32.41 26.23
. 14.53 24.26 29.67 30.08 28.89 32.10 26.59
. 54.35 83.65 83.49 85.17 85.02 87.56 79.87
63.44 81.90 85.26 86.51 84.13 82.26 80.58
S t a n d a r d errors o f m e a n s 2 Treatment Period Treatment × period
0.086 0.161 0.228
NS ** *
0.521 0.903 1.277
NS ** NS
0.773 1,340 1,895
NS ** NS
.
1Each value is t h e m e a n o f t h r e e samples. 2Significance o f d i f f e r e n c e s : NS = n o t significant; * P < 0 . 0 5 ; * * P < 0 . 0 1 .
Addition of urea significantly (P<0.01) increased the concentration of nitrogen in the UOP series (Table II). The N content increased (P<0.01) in both series, because other constituents, especially carbohydrates, disappeared faster. During the first 10 days, the nitrogen content of the UOP silos increased more than that in OP silos, showing a lesser proportion of total T A B L E II N i t r o g e n (as c r u d e p r o t e i n ) , a m m o n i a n i t r o g e n a n d loss o f n i t r o g e n (as c r u d e p r o t e i n ) o f silages 1
Days afterensiling
CP (% DM)
N H : N (% totalN)
CP loss(%)
OP
UOP
0P
OP
UOP
0 3 10 20 35 60 90 Means
8.72 9.03 10.22 10.22 12.52 11.40 10.89 10.43
13.91 16.23 17.51 17.49 19.61 18.02 18.23 17.29
-9.91 8.78 15.30 2.46 9.58 15.62 10.27
-1.62 5.18 11.59 1.45 6.59 11.05 6.25
S t a n d a r d errors o f m e a n s 1 Treatment Period Treatment × period
0.130 0.244 0.345
** ** **
1.057 1.831 2.590
* ** NS
1See f o o t n o t e s in Table I.
0.46 0.41 0.33 0.86 1.13 1.29 1.22 0.81
0.022 0.042 0.059
UOP 0.48 0.48 0.54 1.25 1.23 1.64 1.69 1.04
** ** **
236 nitrogen lost, and consequently a significant (P<0.01) treatment X period interaction was registered. Losses of nitrogen, although smaller in the UOP series (P<0.05), were irregular and low for both series, indicating that nitrogen was mainly retained in the silage. Volcani and Schindler {1953) reported that the ammonia incorporated in citrus pulp was retained in the silo, with a 100% increase in crude protein. Although urea can be hydrolysed, free ammonia is trapped by the acids and pectic substances of the silage (Loosli and McDonald, 1969). Orange pulp is therefore a good subject for urea addition and little free ammonia should be found. Between 65 and 90% of the N losses were due to the effluent, this being 100% in some particular silos. These figures are similar to the standards given by Murdoch (1954) and normal for traditional silages with a high water content. Ammonia-nitrogen values {Table II) were higher in the UOP silos (P< 0.01), increased for both series throughout the experiment (P<0.01), and also there was a significant interaction between t r e a t m e n t and period (P<0.01), but figures were very low, suggesting a reduced clostridial activity and a high retention o f urea in the silage. The pH values of fresh orange pulp are very low (3.7 in our experiment) because of citric and other organic acids. After ensiling there was a small decrease (P<0.01) in pH values. Although a little higher for UOP silos, no significant difference in pH was found between the two series. During the first few days, a great production of gases was observed, suggesting a rapid and substantial fermentation of the material. Final pH values, indicating that the material was well preserved, were similar to those given elsewere, although Volcani and Roderig (1953) and Volcani and Schindler (1953) reported higher figures when a m m o n i u m sulphate or ammonia was added to citrus pulp. The pH, alcohol and individual volatile fatty acid analyses are shown in Table III. Fermentation during the first 35 days gave significant increases (P<0.01) in acetic acid, lactic acid and ethanol; little propionic acid and practically no butyric acid was produced. This pattern of fermentation agrees with the decrease of pH and disappearance of WSC already mentioned. T h e OP silos had more acetic acid than the UOP series (P<0.01) and their acetic acid appeared earlier, the data for UOP silos showing an irregular trend. Lactic acid figures were similar to those reported by N. Lodge (personal communication, 1980) and lower than those of Bondi (1941). We m a y conclude, therefore, that addition of urea to orange pulp had no significant effect on the fermentation process, and no sign of deterioration in the ensiled material was detected over a period of 90 days.
0.01 0.02 0.03
3.7 3.4 3.4 3.4 3.5 3.5 3.5 3.5
NS ** NS
3.7 3.5 3.5 3.5 3.5 3.5 3.6 3.5
7.043 13.176 18.633
** ** **
24.00 22.40 25.07 20.80 32.80 28.53 68.26 55.47 110.67 94.40 155.60 110.93 161.06 108.53 82.49 63.01
UOP
OP
OP
UOP
V F A ( m e q 1-')
pH
1See f o o t n o t e s in T a b l e I.
Standard errors of means Treatment Period Treatment x period
0 3 10 20 35 60 90 Means
Days a f t e r ensiling
0.021 0.039 0.055
0.33 0.49 0.96 1.54 2.99 3.03 2.98 1.76
OP
** ** **
0.32 0.20 0.48 1.01 2.44 2.45 2.45 1.34
UOP
A c e t i c acid (% DM)
0.006 0.011 0.015
0.11 0.12 0.12 0.29 0.38 0.48 0.29 0.26
NS NS NS
0.10 0.10 0.11 0.19 0.29 0.28 0.29 0.19
0.001 0.002 0.003
0.02 0.02 0.01 0.05 0.05 0.05 0.05 0.04
NS NS NS
0.01 0.03 0.03 0.02 0.01 0.05 0.05 0.03
UOP
OP
OP
UOP
B u t y r i c acid (% DM)
P r o p i o n i c acid (% DM)
Values for pH, t o t a l volatile f a t t y acids, o r g a n i c acids a n d e t h a n o l o f silages'
T A B L E III
0.014 0.026 0.037
0.11 0.48 1.48 1.52 2.02 2.15 2.19 1.42
NS ** NS
0.10 0.51 1.41 1.51 1.93 2.52 2.03 1.43
0.004 0.008 0.012
0.19 0.67 0.93 0.90 0.79 0.63 0.65 0.68
0P
OP
UOP
Ethanol (% D M )
Lactic acid (% DM)
NS ** NS
0.18 0.59 0.89 0.92 0.72 0.74 0.63 0.67
UOP
b~ ¢,D -O
238 REFERENCES Annison, E.F., 1954. Studies on the volatile fatty acids o f sheep blood with special reference to formic acid. Biochem. J., 58: 670. Association o f Official Analytical Chemists, 1975. Official Methods o f Analysis. 12th edn. A.O.A.C., Washington, DC, pp. 15--16. Becker, R.B°, Davis, G.K., Kirk, W.G., Dix Arnold, P.T. and Hayman, W.P., 1946. Citrus pulp silage. Fla. Agric. Exp. Stn. Bull., 423: 5--16. Bondi, A., 1941. The ensilage o f citrus fruit pulp. Agric. Res. Stn. Rehovot, December, pp. 89--92. Caja, G., 1975. Efectos metabSlicos 'in vitro' e 'in vivo' de la utilizaciSn del formaldehido como protector de las proteinas en la alimentaciSn de ruminantes. Tesis Doctoral E.T.S.I.A., Madrid, pp. 183--185. Gohl, B.I., 1973. Citrus by-products for animal feed. World Anita. Rev., 6: 24--27. Gouet, Ph. and Girardeau, J.P., 1974. Recommendations pour l'analyse biochimique et bact~riologique des ensilages. Bull. Tech. Inf., 292: 537--548. Jean-Blain, M. and Urtinette, A., 1957. L'analyse physico-chimique des ensilages. Bull. Tech. Inf., 125: 677--699. Loosli, J.K. and McDonald, I.W., 1969. E1 nitr6geno no prot~ico en la alimentaci6n de los rumiantes. F A O : Estud. Agropecu., 75: 71. Ministry o f Agriculture, Fisheries and F o o d , 1976. The analysis of agricultural materials. Tech. Bull. No. 27, H.M.S.O., London. Murdoch~ J.C., 1954. Seepage from silos. Agriculture (London), 61 : 224--225. Volcani, R. and Roderig, Ch., 1953. The enrichment o f citrus peel silage with nitrogen b y application of ammonia and ammonium sulphate. Ktavin, 4: 15--19. Volcani, R. and Schindler, H., 1953. The enrichment of fresh and dried orange and lemon peel with ammonia on laboratory and pilot plant scale. Ktavin, 4: 9--13.