Nutritional quality of mulberry cultivated for ruminant feeding

Carlos F. Boschini
Experimental Station Alfredo Volio Mata
University of Costa Rica, Tres Ríos, Costa Rica

INTRODUCTION

Dairy husbandry phases the challenge of improving production and feeding systems. It is hoped that future models have as their basis a sustainable focus and a rational use of natural resources (Castro and Benavides, 1994). Mulberry, although originally from Asia, has adapted excellently to the tropics of Central America (Benavides, Lachaux and Fuentes, 1994; Rodriguez, Arias and Quiñones, 1994; Boschini, Dormond and Castro, 1998) and gives very high yields. For forage production, mulberry has shown excellent characteristics of palatability and, consequently, high intakes by cattle (Benavides, Lachaux and Fuentes, 1994; Ortiz, 1992; Castro, 1989). The literature reports that the whole plant contains between 14-22 percent crude protein on DM basis (Piccioni, 1970) and in vitro digestibility between 70 to 80 percent (Ortiz, 1992). The mulberry samples analysed by the UFAG Laboratories in Switzerland, from the high zone of Cartago in the Central Plateau of Costa Rica, gave on a DM basis, 22 percent of crude protein (CP), 19 percent of crude fibre (CF), 2.3 percent of ether extract, 50 percent of by-pass protein and an estimated 1.48 Mcal/kg of net energy for lactation. Eswara and Reddy (1992) when evaluating the nutritive value of mulberry leaves, reported DM intakes of 2.74 and 3.55 percent of liveweight in goats and sheep, respectively, with 12 percent CP and 71 percent TDN.

The nutritional value of mulberry is in its leaves. However, being a shrub, biomass supply is considered an important aspect when used in animal feeding. Boschini, Dormond and Castro (1998) reported leaf:stem ratios above 1, before 100 days of growth. Leaf:stem proportion varies with cultivation and management conditions, plant density and cutting frequency. The whole mulberry plant, once chopped, is offered to cattle. This represents a mixture of leaf and stem which the animal selects during consumption. For this reason it is necessary to know precisely chemical composition of leaves and stems. The results of the influence of plant density, cutting height and frequency on the chemical composition throughout the year in a high tropical environment are presented here.

ENVIRONMENTAL CONDITIONS, MANAGEMENT AND HARVEST

Research was conducted at the Dairy Cattle Experimental Station "Alfredo Volio Mata" at the University of Costa Rica. The station is located at 1 542 m above sea level, and has a mean rainfall of 2 050 mm, distributed during the months of May to November. From December to mid-May, there is no rainfall. Mean temperature is 19.5ºC and relative humidity 84 percent. The soil is volcanic, classified as Typic Distrandepts (Vásquez, 1982). It is characterized by its medium depth, good natural drainage and medium fertility (7.7 of Ca, 3.0 of Mg, 1.54 cmol/l of K, 10.0 of P, 28.8 of Cu, 234 of Fe, 6.3 of Mn and 2.6 mg/l of Zn). The pH is 5.9. Ecologically, the zone typifies as low mountain humid forest (Tosi, 1970, cited by Vásquez, 1982).

Agricultural practices, seeding conditions and management were described by Boschini, Dormond and Castro (1998). The plantation was left to grow for one year, during which weeding was practised and fertilization with ammonium nitrate was applied at the rate of 150 kg of N/ha/year in two equal doses (July and October). The following year in May, the three plots received a standardization cut, with scissors, half of the plot at 30 cm and half at 60 cm from the ground. From that date, cuts were given every 56 days (6 cuts), 84 days (4 cuts) or 112 days (3 cuts), during the experimental period of 336 days. After each cut, the plots were weeded, leaving the needs between rows. When the shoots reached 3-5 cm (approximately two weeks after harvest) they were fertilized with ammonium nitrate at a dose equivalent to 150 kg of N/ha/year.

Mulberry samples were collected at each spacing, cutting height and frequency. The branches were weighed fresh in the field, and then the leaves and stems were separated and weighed. Each sample was dried in the oven at 60 ^ºC for 48 hours until weight was constant. The samples were then milled and subjected to DM (at 105ºC), crude protein (Kjeldall) and total ash (AOAC, 1980) determinations. NDF), ADF and lignin were analysed by the method described by Goering and Van Soest (1970). Hemicellulose and cellulose values were obtained by difference. DM and chemical fractions were analysed with PROC GLM of the statistical package SAS (1985). Variation sources with statistical significance were subjected to the Duncan test to differentiate the significance among means.

BROMATOLOGICAL COMPOSITION OF HARVESTED FORAGE

The chemical composition of leaves and stem as affected by planting density, cutting height and frequency are presented in Table 1. DM percentage in the fresh forage was very constant (P >0.05) in leaves for the different planting densities. Cutting height and frequency did not influence DM percentage (P >0.05). However, the difference in DM content between 30 and 60 cm in cutting height was less than 1 percent. There were no differences in DM percentage between 56 and 84 days, and only 2.3-3 percent between them and 112 days. Crude protein content showed very little differences (P <0.05) between spacings and cutting heights. These variations were accentuated (P <0.01) between cutting frequencies, decreasing two to three percent for every 28 days from eight weeks growth. Planting densities did not influence (P >0.05) cell walls, ADF, hemicellulose, cellulose, lignin and total ash. Cell wall and total ash showed very small differences between cutting heights. Hemicellulose, ADF, cellulose and lignin showed not significant differences (P >0.05) between cutting heights. Cutting height influenced cell wall and total ash (P <0.01), ADF and cellulose (P <0.05). Changes in hemicellulose and lignin were not significant (P>0.05) with height.

The interaction planting density and cutting frequency was significant (P <0.01) for leaf DM content and its content of protein and minerals. The structural fractions were not affected (P <0.01) by the group effect (Table 2). In Table 3, the chemical composition of leaves and stems planted at different spacing and harvested at different heights are presented. DM, CP, cell walls, hemicellulose and total ash all had an interaction effect (P <0.05) due to these variables. ADF and its components were not affected. The associated effects of cutting height and frequency (Table 4) on chemical composition were significant for CP, cell wall (P <0.01) and total ash (P <0.01). Contents of DM, NDF components and hemicellulose did not show important variations.

Table 5 presents the values of leaf chemical components detailed by cutting number within each frequency. The effect was highly significant (P<0.01) for all chemical fractions studied. The highest level interaction, density by cutting height, influenced DM, CP and total ash (P <0.01). None of the structural carbohydrates showed important variations.

TABLE 1

Leaf and stem chemical composition (% DM) of mulberry at three spacings, two cutting heights and three frequencies

Factor	DM	CP	NDF	Hem.	ADF	Cel.	Lignin	Ash
				Leaf
Spacing
60 cm	24.5	23.7a	33.5a	9.2a	24.4a	18.5a	5.8a	16.7a
90 cm	24.5	23.5a	32.4a	8.3a	24.1a	19.1a	5.1a	24.5a
120 cm	24.8	23.2b	32.6a	8.6a	24.1a	18.7a	5.4a	24.8a
Height
30 cm	24.1	23.8a	33.5a	9.4a	24.1a	18.9a	5.3a	17.0a
60 cm	25.1	23.1b	32.1b	7.9b	24.2a	18.7a	5.6a	16.5b
Frequency
56 days	24.1	25.6a	34.3a	9.1a	25.2a	19.5a	5.7a	16.1a
84 days	23.7	22.2b	32.3b	8.8a	23.5b	18.6a	4.9a	16.9b
112 days	26.8	20.8c	30.7c	7.6a	23.1b	17.4b	5.7a	18.1c
				Stem
Spacing
60 cm	23.2a	8.7a	63.2a	14.5a	48.7a	40.0a	8.7a	8.2a
90 cm	23.4a	8.8a	63.2a	14.5a	48.8a	40.5a	8.3a	8.3a
120 cm	24.9b	8.8a	64.4a	16.3b	48.1a	39.6a	8.5a	7.7b
Height
30 cm	23.4a	8.8a	63.6b	14.8a	48.8a	40.2a	8.6a	8.0a
60 cm	24.2b	8.8a	63.6a	15.4a	48.2a	39.8a	8.4a	8.1a
Frequency
56 days	20.9a	10.7a	59.0a	15.7a	36.6a	43.3a	6.7a	10.0a
84 days	23.6b	7.8b	65.9b	12.7b	43.2a	53.2b	10.0b	7.1b
112 days	30.0c	6.3c	69.8c	17.0c	42.7b	52.7b	10.1b	5.5c

¹ On a DM basis; a,b,c = significant differences (P <0.05)

TABLE 2

Leaf and stem chemical composition (% dry matter) of mulberry cultivated at three planting distances and harvested at three cutting frequencies.

Spacing (cm)	Frequency (days)	DM	CP	NDF	Hem.	ADF	Cel.	Lignin	Ash
					Leaf
60	56	24.4	25.9	35.0	10.1	24.8	19.3	5.5	16.3
60	84	23.2	22.5	33.5	9.6	23.9	18.4	5.4	16.6
60	112	26.3	20.9	30.6	6.5	24.1	16.8	7.2	17.6
90	56	24.8	25.8	33.4	8.6	24.9	19.3	5.5	16.1
90	84	23.2	22.0	31.3	7.3	24.1	18.6	4.4	17.0
90	112	25.6	21.0	31.6	8.9	22.6	17.7	4.9	18.0
120	56	23.1	25.1	34.5	8.6	25.9	19.9	6.0	15.9
120	84	24.6	22.3	31.9	9.5	22.5	17.8	4.8	16.9
120	112	28.5	20.6	29.8	7.3	22.5	17.6	4.9	18.6
					Stem
60	56	21.4	10.6	58.5	15.7	42.8	36.4	6.4	9.9
60	84	21.2	7.8	64.9	11.4	53.4	42.9	10.5	7.6
60	122	29.6	6.3	70.3	16.1	54.3	43.4	10.9	5.5
90	56	21.2	10.7	58.6	14.9	43.7	37.1	6.7	10.2
90	84	23.0	7.8	66.1	12.3	53.8	44.3	9.4	7.2
90	112	28.2	6.3	68.7	16.6	52.1	42.2	9.9	5.7
120	56	20.1	10.8	59.8	16.5	43.3	36.2	7.1	9.7
120	84	26.6	7.6	66.7	14.4	52.4	42.4	10.0	6.5
120	112	32.1	6.3	70.2	18.3	51.9	42.4	9.5	5.3

TABLE 3

Leaf and stem chemical composition (percent of DM) of mulberry cultivated at three planting distances and harvested at two cutting heights

Spacing (cm)	Height (cm)	DM	CP	NDF	Hem.	ADF	Cel.	Lignin	Ash
					Leaf
60	30	24.6	33.9	33.9	9.6	24.2	18.8	5.4	17.3
60	60	24.4	23.4	33.2	8.6	24.5	18.3	6.3	16.1
90	30	23.5	23.7	32.0	8.2	23.8	18.7	5.1	17.2
90	60	25.6	23.3	32.8	8.3	24.4	19.4	5.0	16.4
120	30	24.3	23.5	34.8	10.4	24.4	19.1	5.4	16.5
120	60	25.3	22.9	30.5	6.8	23.7	18.3	5.4	17.2
					Stem
60	30	23.0	8.8	62.7	13.7	49.0	40.3	8.7	8.3
60	60	23.5	8.7	63.7	15.2	48.4	39.8	8.6	8.0
90	30	23.3	9.0	63.2	15.2	48.0	39.6	8.4	8.2
90	60	23.5	8.7	63.3	13.8	49.5	41.3	8.1	8.3
120	30	24.0	8.7	64.9	15.5	49.4	40.7	8.6	7.5
120	60	25.8	8.9	63.8	17.1	46.8	38.4	8.4	7.9

TABLE 4

Leaf and stem chemical composition (percent of DM) of mulberry harvested at two cutting heights and three cutting frequencies

Height (cm)	Freq. (days)	DM	CP	NDF	Hem.	ADF	Cel.	Lignin	Ash
					Stem
30	56	23.6	25.8	35.0	10.0	25.0	19.7	5.4	16.5
30	84	23.0	22.8	34.0	10.2	23.8	18.5	5.4	17.0
30	112	26.8	21.0	29.9	7.2	22.8	17.7	5.2	18.1
60	56	24.6	25.4	33.6	8.3	25.4	19.3	6.0	15.7
60	84	24.4	21.7	30.5	7.4	23.1	18.7	4.4	16.7
60	112	26.9	20.6	31.4	8.0	23.4	17.2	6.2	18.0
					Stem
30	56	21.5	10.7	58.9	15.2	43.7	37.0	6.7	9.9
30	84	22.0	7.9	66.0	12.3	53.7	43.4	10.2	7.2
30	112	29.2	6.2	69.7	17.2	52.6	42.4	10.2	5.4
60	56	20.3	10.7	59.1	16.2	42.9	36.2	6.7	10.0
60	84	25.2	7.6	65.8	13.1	52.7	43.0	9.7	7.0
60	112	30.7	6.4	69.8	16.9	52.9	42.9	10.0	5.6

The interaction between density and cutting frequency (Table 2) was significant (P <0.01) for stem DM but CP, ash and structural carbohydrates were not. Table 3 shows the chemical composition of the stem of plants at different densities and cutting heights. Hemicellulose, ADF and cellulose were affected by the associated action of these factors significantly (P <0.01). Other components were not affected. When analysing the interaction of cutting height and frequency on stem chemical composition (Table 4), only DM was affected (P <0.01). Table 5 presents stem chemical composition by harvest number at each cutting frequency. The analysis showed that harvest numbers within each frequency had a significant effect (P<0.01) on all chemical components studied. The interaction between density and cutting frequency only affected stem DM content (P <0.05).

The general chemical composition (mean and standard deviation) of the experiment was: DM 24.6 percent (±2.24); CP 23.5 percent (±0.59); NDF 32.8 percent (±3.87); hemicellulose 8.7 percent (±3.85); ADF 24.2 percent (±2.76); cellulose 18.8 percent (±2.46); lignin 5.4 percent (±2.21) and total ash 16.8 percent (±0.75) in leaves and DM 23.8 percent (±2.01); CP 8.8 percent (±0.66); NDF 63.6 percent (±2.8); hemicellulose 15.1 percent (±2.8); ADF 48.5 percent (±2.99); cellulose 40.0 percent (±2.78); lignin 8.5 percent (±1.13) and total ash 8.0 percent (±0.88) in the stems.

TABLE 5

Leaf and stem chemical composition (percent of DM) of mulberry harvested at three cutting frequencies by cut number

Freq. (days)	Cut #	DM	CP	NDF	Hem.	ADF	Cel.	Lignin	Ash
					Leaf
56	1	22.0	27.9	37.4	15.3	22.0	17.8	4.2	15.4
56	2	22.0	27.6	46.0	10.2	35.8	28.6	7.2	16.7
56	3	26.6	23.9	33.9	9.8	24.1	17.9	6.3	16.0
56	4	25.6	24.5	27.8	5.4	22.4	16.5	5.9	16.6
56	5	24.0	24.1	30.6	7.4	23.2	17.5	5.6	16.8
56	6	24.4	25.7	30.2	6.5	23.6	18.7	4.9	15.0
84	1	15.8	24.7	34.5	10.4	24.1	18.7	5.4	15.8
84	2	25.0	21.1	35.7	12.7	23.0	18.1	5.1	17.9
84	3	26.2	22.1	26.9	4.1	22.9	18.5	4.4	17.3
84	4	27.8	21.0	31.8	8.0	23.8	19.2	4.6	16.5
112	1	26.3	22.1	32.8	8.9	23.9	16.9	7.0	17.3
112	2	26.9	20.6	28.3	6.3	22.0	16.7	5.4	19.6
112	3	27.2	19.8	30.9	7.6	23.3	18.7	4.6	17.4
					Stem
56	1	17.3	13.4	63.2	18.1	45.2	38.3	6.9	9.7
56	2	17.1	11.3	60.1	35.1	25.1	19.4	5.7	10.1
56	3	21.1	10.3	57.6	11.5	46.1	38.5	7.6	10.3
56	4	23.6	9.8	57.9	10.5	47.4	41.0	6.4	10.5
56	5	22.4	9.44	58.5	9.3	49.2	42.5	6.7	9.7
56	6	24.0	10.0	56.7	9.8	46.9	39.8	7.1	9.4
84	1	13.8	8.9	68.9	14.5	54.3	44.2	10.1	6.9
84	2	22.3	8.6	62.7	12.0	50.7	41.5	9.2	8.2
84	3	25.7	7.0	65.6	11.0	54.6	43.7	10.9	6.8
84	4	32.6	6.5	66.4	13.3	53.2	43.5	9.7	6.6
112	1	27.3	6.9	70.4	19.3	51.1	41.9	9.2	5.2
112	2	28.2	6.9	69.2	14.9	54.3	43.7	10.6	6.0
112	3	33.9	5.2	69.6	16.8	52.8	42.4	10.4	5.2

EXPECTED QUALITY VARIATIONS AND OTHER FORAGE COMPARISONS

The chemical composition of leaf and stem and their variations have been indicated previously. Planting density produced significant variations on leaf CP and stem DM, hemicellulose and total ash. However, differences were slight from the biological point of view. The rest of the components showed very narrow variation from the mean. In general, spacing did not influence the nutrients present in leaf and stem. Cutting height statistically also affected leaf DM, CP, cell wall, ADF and total ash, but only stem DM. These differences were less than 1 percent, which are not biologically important to favour a certain cutting height. Contrary to what had been found for planting density and cutting height, cutting frequency had a significant effect on nutrient accumulation, except for leaf hemicellulose and lignin. At frequent cuttings, leaf and stem CP and leaf cell wall were high. At longer cutting, stem NDF and all cell wall components increased. Total ash in leaves increased with cutting interval, whereas the opposite occurred with the stem.

Chemical composition was very different between leaf and stem, except for the percentage of DM. Leaf CP was three times that of the stem, and leaf cell wall and ADF were half. Cellulose was 75 percent of ADF in leaf and 80 percent in stem. Lignin was 25 percent of ADF in the leaf and 20 percent in the stem. Mulberry had two to three times more ash in leaves than in stem. Piccioni (1970) reports, on DM basis, mulberry leaf CP of 16 percent, ether extract 4.1 percent, cellulose 6.9 percent and ash 11 percent. Rodríguez, Arias and Quiñones (1994) found CP concentrations of 21 percent without fertilizer and 24 percent with 80 kg of N/ha after each 6-week harvest. Increasing cutting frequency to 12 weeks, leaf CP decreased to 18 percent without fertiliser and to 16 percent with fertiliser. Eswara and Reddy (1992) reported DM and CP values of 30 percent and 14.5 percent respectively.

When comparing mulberry with tropical and subtropical grasses, CP is higher than in alfalfa (17 percent), young Orchard grass (15 percent), Pangola grass (1 percent) and Elephant grass (9 percent). Mulberry leaf has 33 percent NDF and the stem 64 percent, whereas alfalfa has 40 percent, Orchard grass 55 percent, Pangola grass 70 percent and Elephant grass 72 percent (Van Soest, 1992), Mulberry stem at 112 days has a cell wall equal to or smaller than any tropical grass. Lignin in subtropical grasses varies between 4-8 percent and in tropical grasses between 7 and 8 percent, whereas mulberry has 5.5 percent in the leaves and 8 percent in the stem. It can be deducted that mulberry leaf is superior to any subtropical forage and that mulberry stem compares to tropical grasses. Considering that net energy for lactation in cattle (Weiss, 1998; Traxler et al., 1998) is calculated from TDN from lignin content in NDF or ADF, the high digestibility of mulberry is confirmed (Rojas and Benavides, 1994; Eswara and Reddy, 1992). Table 6 presents hemicellulose, cellulose and NDF for leaf and stem. Lignin represents between 15 and 18 percent of leaf cell wall and between 11 and 15 percent of stem cell wall, which is used to estimate the high digestibility of both fractions.

The main limitation of the use of mulberry stem as feed is not related to chemical quality per se but to the physical form in which it is offered to animals for their use. Many tropical feeds, rspecially in dry periods, are inferior to mulberry stem in terms of quality. Mulberry leaf, properly dried and ground, is of excellent quality and its characteristics make it most suitable for inclusion in compounded feed for highly producing dairy cattle.

TABLE 6

Hemicellulose, cellulose and lignin in the neutral detergent fibre (NDF) or cell wall of mulberry leaf and stem

Factor	NDF (% DM)	Hemi. (% of NDF)	Cellulose (% of NDF)	Lignin (% of NDF)	Hem. Cellulose
Spacing (cm)
60	33.5	27.3	55.2	17.5	0.50
90	32.4	25.5	58.9	15.6	0.43
120	32.6	26.3	57.4	16.5	0.46
Height (cm)
30	33.5	28.0	56.2	15.9	0.50
60	32.1	24.6	58.0	17.3	0.42
Frequency (d)
56	34.3	26.6	56.9	16.6	0.47
84	32.3	27.2	57.8	15.2	0.47
112	30.7	24.8	56.7	18,5	0.44
Spacing (cm)
60	63.2	22.9	63.3	13.7	0.36
90	63.2	22.9	64.0	13.1	0.36
120	64.4	25.3	61.5	13.3	0.41
Height (cm)
30	63.6	3.2	63.2	13.5	0.37
60	63.6	24.2	62.6	13.2	0.39
Frequency (d)
56	59.0	26.6	73.4	11.4	0.36
84	65.9	19.3	80.7	15.1	0.24
112	69.8	24.4	75.6	14.5	0.32

IMPLICATIONS AND RECOMMENDATIONS

Leaf CP and cell wall contents, together with structural carbohydrates and ash, indicate that mulberry is an excellent feed for high yielding animals, and can be offered fresh or dried in compounded feeds. Stem composition is very similar to tropical grasses. Experimental factors influenced DM chemical composition. Planting density and cutting height produced small variations in leaf and stem composition. Although cutting frequency produced greater variation, the differences in DM, CP, structural carbohydrates and total ash were less than 3 percent between the smallest and the longest interval. In the stem, the largest change was of 9 percent and occurred in DM, cell wall and in structural carbohydrates, such as cellulose. The number of cuts within the yearly cycle produced a variation in chemical composition, which should be considered when feeding mulberry. Under tropical conditions, industrial mulberry production for compounded feeds needs further study.

BIBLIOGRAPHY

AOAC. 1980. Methods of analysis. Ed. 13. Washington DC, Association of Official Analytical Chemists.

Benavides, J., Lachaux, M. & Fuentes, M. 1994. Efecto de la aplicación de estiércol de cabra en el suelo sobre la calidad y producción de biomasa de Morera (Morus sp.). Arboles y arbustos forrajeros en América Central, p. 495-514. Technical Report No. 236. Vol. 2. Turrialba, Costa Rica, CATIE.

Boschini, C., Dormond, H. & Castro, A. 1998. Producción de biomasa de morera (Morus alba) en la Meseta Central de Costa Rica, establecida y cosechada a diferentes distancias de siembra, alturas y frecuencias de poda. Agronomía Mesoamericana, 9(2): 28-39.

Castro, A. 1989. Producción de leche de cabras alimentadas con King grass (Pennisetum purpureum x P. typloides), suplementales con diferentes niveles de follaje de Poró (E. poeppigrama) y de fruto de plátamo va de (Musa sp. var. Pelipita). Turrialba, Costa Rica, University of Costa Rica/CATIE. 58 pp. (thesis).

Castro, A. & Benavides, J. 1994. Evolución de los sistemas de alimentación en explotaciones caprinas de Costa Rica. Arboles y arbustos forrajeros en América Central, p. 245-250. Technical Report No. 236. Vol. 2. Turrialba, Costa Rica, CATIE.

Eswara, P. & Reddy M.R. 1992. Nutritive value of Muberry (Morus alba) leaves in goats and sheep. Indian J. Anim. Sci., 8(4): 295-296.

Goering, H.K. & Van Soest, P.J. 1970. Forage fiber analysis (apparatus, reagents, procedures and some applications). Agricultural Handbook No. 379. Washington, DC, ARS-USDA.

Ortiz, G. 1992. Efecto de la alimentación con pasto King grass (Pennisetum purpureum x P. typhoides), suplementado con diferentes niveles de follaje de morera (Morus alba) y de banano verde (Musa sp.) sobre la producción de leche de cabra. Escuela de Zootecnia. University of Costa Rica. 45pp.

Piccioni, M. 1970, Diccionario de alimentación animal, p. 492-494. Saragossa, Editorial Acribia.

Rodríguez, C. Arias, R. & Quiñones J. 1994. Efecto de la frecuencia de poda y el nivel de fertilización nitrogenada, sobre el rendimiento y calidad de la biomasa de Morera (Morus sp.) en el trópico seco de Guatemala. Árboles y arbustos forrajeros en América Central, p. 515-528. Technical Report No. 236. Vol. 2. Turrialba, Costa Rica, CATIE

Rojas, H. & Benavides, J. 1994. Producción de leche de cabras alimentadas con pasto y suplementadas con altos niveles de morera (Morus sp). Arboles y arbustos forrajeros en América Central, p. 305-319/Technical Report No. 236. Vol. 1. Turrialba, Costa Rica, CATIE.

SAS Cary, NC 1985. SAS User´s Guide: Statistics (Version 5 Ed.) SAS Institute Inc. Cary, NC. Statistical Analysis System.

Traxler, M.J., Fox, D.G., Van Soest, P.J., Pell, A.N., Lascano, C.E., Lanna, D.P.D., Moor, J.E., Lana, R.P., Velez, M. & Flores, A. 1998. Predicting forage indigestible NFD from lignin concentration. J. Anim.Sci. 76 (5): 1469-1480.

Van Soest, P.J. 1982. Nutritional ecology of the ruminant. Dortland, USA, Durham and Downey, Inc.

Vásquez, A. 1982. Estudio detallado de los suelos de la Estación Experimental de Ganado Lechero El Alto. Escuela de Fitotécnia, Facultad de Agronomía, Universidad de Costa Rica. 36 pp.

Weiss, W.P. 1998. Estimating the available energy content of feeds for dairy cattle. J. Dairy Sci., 81(3): 830-839.