Studies on utilization of trees and shrubs as the sole feedstuff by growing goats; foliage preferences and nutrient utilization 

The chemical characteristics of the foliages  (leaves and petioles attached to green stems), and  leaves plus petioles, from plant terminal branches of approximately 25 to 40 cm length, are shown in Table 3. 

Animals and housing

Three male crossbred goats averaging 20 ± 1.5 kg live body weight were used for the evaluation of every plant species. The goats were housed in metabolism cages (1.0x0.8 m), elevated 0.8 m and allowing the separate collection of faeces and urine. The cages were made of wood, bamboo and rattan and were situated in a shed with roof and open sides  (Photo1: Him Aun 2002) .

 Photo 1: The locally made bamboo cage for measuring digestibility and N retention

Feeding management

The feeds were offered ad libitum. The mulberry and cassava materials were offered fresh, immediately after harvesting, whereas jackfruit foliage was obtained every two days. The feed was offered in three methods comprising either leaves, or leaves and stems offered in the trough, or leaves and stems offered hanging after tying to a bamboo pole over the cage. Before preparing the feeds, the ratio of leaves plus petioles and old stems, was determined by sampling 3 times (1 kg per time) the foliage. The leaves plus petioles were separated from the old stems then weighed (Table 2). The goats were offered the feed three times per day (8:00 AM, 11:00 AM and 2:00 PM).

Measurements

Intake, digestibility and N retention

Feed offered and refused, output of  faeces and urine, was recorded daily during the last 5 days of each period. Samples of feed offered and refusals were taken daily and analysed for DM and N. Faeces were put in plastic bags in the freezer (-20 °C). Urine was collected in a bucket containing enough H₂SO₄ solution to maintain a pH of 4 or lower. Nutrient digestibility and N balance were calculated by standard procedures outlined for the direct estimation of animal digestibility (Crampton and Harris 1969). 

Feeding behaviour

Eating and ruminating time was continuously monitored by two people during periods of 24 hours on days 5, 10 and 15 in each experimental period. The time spent eating and ruminating was recorded.

The intake rate and ruminating rate were calculated by:

• Intake rate (g/min) = Total DM intake (g) /eating time (min)
• Ruminating rate (g/min) = Total DM intake (g) / ruminating time (min)

Rumen environment

Rumen fluid samples were collected by stomach tube two hours after feeding on day 16, at the end of each experimental period, to measure rumen ammonia, pH and protozoa population. About 15 ml of rumen fluid collected from each goat were transferred into individual containers, filtered through two layers of cotton cloth and thereafter two drops of concentrated H₂SO₄ were added to inactivate rumen microbial activity. Ten ml of acidified rumen liquor were mixed with 4 ml of saline formaldehyde solution and the treated samples were stored in refrigeration until counting. Protozoa counting was conducted by placing one drop of sample onto a slide and then covering with a cover-slip. The protozoa number was counted 20 times under a 10x magnification in a microscope. This procedure was repeated 2 to 3 times per sample. 

Calculation of the number of protozoa:

The counting of 20 times for each slide was recorded and then the average of the slides for one sample was calculated. This represented the number of protozoa in the microscope field (P1, protozoa count). In this counting, the protozoa were divided into large which were roughly 80 µm and small which were roughly 20 µm.

­       Use A as the area of the microscope field at 10x magnification, A=2.66 mm², and B as the area of rumen liquor under the cover-slip, B=144 mm².  B/A=54.2.

­       P2 the number of protozoa per B. P2 = P1*B/A  = P1* 54.2

­       The volume of rumen liquor in one drop under the cover slip (C) was calculated by adding 100 drops to a weighing bottle. The volume of liquor under the cover slip can then be estimated; i.e. one drop= Wt/ 100. In this case C = 0.043 ml.

­       P3 the number of protozoa per 1 ml of dilute sample. P3 =  P2/C = [P1*(B/A)]/C = (P1*54.2/ 0.043)

­       Knowing the counts of each field (P1), the volume of liquor under the cover slip, area of microscope field A and area of cover slip B, the density of protozoa  (P3) was estimated in the diluted sample.

  ­       Use D as the volume of rumen fluid per ml of diluted sample, 10ml of rumen fluid plus 4 ml of diluent. D = 10/14

­       Protozoa count per ml of rumen fluid (P4) was then:

P4 = P3/D = P3 * 1.4 = protozoa count x 1.4 x 54.2/ 0.0556 

Chemical analysis

Feed and faecal samples were dried by microwave radiation to measure the DM content (Undersander et al 1993). Total N of feed, faeces and urine was measured by the Kjeldahl procedure as outlined by the AOAC (1990). The ash content of feed and faeces was determined following the AOAC (1990) recommendations and therefore, the organic matter was assumed to be the result of subtracting the percentage of ash from 100. The water soluble DM and N were determined according to Ly and Preston (2001).

Rumen pH was determined by glass electrode measurements in a digital pH meter and NH₃ was estimated by steam distillation according toi AOAC (1990).  

Biometrical analysis

The data were analyzed according to the analysis of variance technique and means separation was conducted by the Duncan’s multiple range and multiple F test (Steel and Torrie 1980) using the general linear model (GLM) procedure in the software of  MINITAB (release 13.31).

The mathematical model used was:

Y_ijk = M + A_i + B_j + C_(i,j),k + e_ijk

where:

Y_ijk      =   Independent variable (Intake, apparent digestibility, etc)

 M       =   Overall mean

A_i        =   Effect of period

B_j         =   Effect of goats

C_k        =   Effect of treatment

eijk      =   Effect of random error 

Results

Feed composition

During the experiment all animals were in good health and in positive live weight balance. In all the plant species examined, leaves had higher contents of  DM, ash and crude protein than the foliage (Table 3).

There were no marked difference in DM solubility between leaves and foliage within every type of plant sample analyzed. However, jackfruit had a relatively low DM solubility as compared to mulberry and cassava. N solubility was variable, according to the type of sample evaluated. Overall, N solubility was high and with no remarkable differences between leaves and leaves plus stems. On the contrary, N solubility in jackfruit was relatively low, as contrasted to that of mulberry, with higher values for leaves and stems as compared to leaves alone. On the other hand, cassava leaves showed fairly high values for N solubility, although lower than that of mulberry. However, the inclusion in the feed of cassava stems (foliage) resulted in a slight decrease in N solubility. 

Voluntary feed intake

There were remarkable differences in feed intake in response to the method of offering the feed (Table 4).  DM intake was highest in the three plant species when the foliage was presented hanging in the cage, and was lowest when the leaves were offered separately in the feed trough.

There were apparent differences in the rate of adaptation to the foliages and leaves of each plant species. It was observed that the goats avidly consumed the fresh leaves and the young stems of mulberry and Jackfruit, immediately the feeds were offered. In contrast, the rate of adaptation to the cassava was much slower and required some 7 days before the maximum intake was achieved.

For all plant species, the time spent eating was shortest for foliage hanging in the cage and longest for leaves offered in the trough (Table 5).  The effect of offer method on rumination time varied with plant species. In the case of cassava, it was shorter for foliage hanging in the cage compared with leaves in the trough. For mulberry and jackfruit there were no differences due to offer method.  The ratio of time spent eating to time ruminating also varied according to plant species. The ratio was least for hanging foliage and highest for leaves in the case of mulberry and jackfruit, with the opposite response in the case of cassava.

 Figure 1: Dry matter intake by goats of foliage / leaves of three plant species,
according to the method of offering the feed

For all the plant species, the rate of eating,  expressed as g of feed DM consumed per minute, was highest when the foliage was hung in the cage and lowest when the leaves were offered separately (Table 6; Figure 2). The rumination rate (g feed DM intake per minute of time spent ruminating) was highest for hanging the foliage, and lowest for the separated leaves, in the case of jackfruit and cassava, with no apparent differences due to offer level for the mulberry. The fastest rate of eating was on the mulberry hanging foliage (about 4 g/minute), followed by the jackfruit (3.5 g/minute) and the cassava (2.8 g/minute).

Figure 2: Intake rate of three plant species by goats according to method of offering the feed

Figure 3: Rumination rate of three plant species by goats according to method of offering the feed

Digestibility indices

There were differences in the dry matter content of the faeces between plant species but not between the methods of offering the feed (Table 6), with the lowest value for mulberry (45 to 46%) and much higher values (64 to 70%) for jackfruit and cassava. There was no effect of the offer method nor the plant species on the pH of the faeces which was alkaline in all cases.

Both feeding method and plant species affected the digestibility of dry matter and organic matter (Figure 4). For all species the apparent digestibility coefficients were highest for foliage hanging in the cage and lowest for leaves fed in the trough. Digestibility coefficients were high for Mulberry (70 to 79%) and cassava (69 to 80%) and considerably lower for jackfruit (48 to 63%).

Figure 4: Digestibility of three plant species by goats according to method of offering the feed

For all plant species daily N retention was highest for hanging foliage in the cage and lowest for leaves fed in the trough (Tables 7 to 9; Figure 5), with differences being more marked for jackfruit (P=0.001) and cassava (P=0.04) than for mulberry (P=0.35). Although not strictly comparable, it was apparent that daily N retention was higher on mulberry (8.4 to 12.0 g/day) than on jackfruit and cassava (3.6 to 7.9 and 3.6 to 8.5, respectively).

Figure 5: N retention of three plant species by goats according to method of offering the feed

There was no effect of method of feeding on pH, ammonia and protozoa numbers in rumen fluid (Table 10). Rumen ammonia levels and pH appeared to be higher, and protozoa numbers lower, for goats fed cassava as compared with the other plant species. Ammonia levels were extremely high in all cases.

Discussion

Feed characteristics

In general the chemical composition data for the three plant species in the current experiment are within the range of values reported by other researchers, with the exception of the protein in the jackfruit leaves which was lower than other reported values (Table 11).

The high DM and N water solubility values in the Mulberry are in agreement with other previous reports from this laboratory (Ly et al 2001). DM and N solubility of jackfruit leaves and foliage  were relatively low as compared to similar indices for mulberry and cassava foliage. These observations are in accordance with previous findings of Ly and Preston (2001). Variations in chemical composition of leaves reported by us and other workers could be attributed to differences in climatic conditions between the study areas. Another factor contributing to this difference could be the harvesting season and time, because leaves develop their structure and morphology according to their age and management (Audru et al 1991).

Eating, ruminating time and intake

The data on feed intake show quite clearly that goats eat more dry matter when offered foliages with the leaves attached to the stems than when the leaves are offered separately, and that foliages suspended from the roof of the cage support higher intakes than when they are offered in the feed trough. Foliage suspended in the cage most closely simulates the natural condition when goats browse trees and shrubs. It appears that the goats find it easier to bite the leaves when they are attached to stems offering some resistance to the action of eating, as is the case for hanging foliage compared with the foliage placed loosely in the feed trough. The higher eating rate by hanging the foliages compared with foliages offered loose (in the feed trough) confirms this supposition.  It was also apparent from observing the eating habits of the goats that they found it easier to bite the leaves of the mulberry and more difficult to bite those of the cassava, which was reflected in the higher rate of eating in the former.  The bunches of mulberry and jackfruit foliages hanging in the pen were more open than the bunches of cassava, which could have been another factor facilitating consumption. of the two former species.

The high voluntary intakes of the goats fed hanging mulberry foliage (4.6% of body weight) is supported by the findings of Rojas and Benavides (1994 cited by Sánchez 2000) that dry matter intake and milk production of goats offered a mixture of King grass and mulberry foliage increased to 5.5% of body weight as the level of mulberry was increased. The high DM intake of hanging jackfruit foliage (4.87% of body weight), despite its low digestibility,  agrees with the report of Keir et al (2997) that this foliage was much superior  to that from Trichanthera gigantea, even though in vitro and in vivo digestibility were lower than for the Trichanthera. 

There was no apparent toxicity effect due to feeding cassava foliage as the sole diet. However, the fact that the goats took longer to adapt to this foliage could be interpreted as being due to the time required for the rumen flora to become adapted to metabolizing the HCN presumably liberated in the rumen.  

Apparent digestibility and N retention

The high value for DM digestibility of the Mulberry foliage (79.2%) is similar to the findings of Jegou et al (1994 cited by Sánchez 2000), who reported DM digestibility values for leaves in the range of 78.4 to 80.8%. Benavides (1995 cited by Trujillo 2002) reported that digestibility of mulberry leaves can be in the range 80 to 93% and that of stems to be as high as 50%. These values are higher than those reported by Yao et al (2000), who claimed that in vitro organic matter digestibility in goats varied from 66 to 72% and from 56 to 61% for spring and autumn mulberry leaves, respectively. This latter value is similar to that reported by Singh et al (2000) for digestibility of the organic matter fraction (58%).

DM digestibility of the hanging jackfruit foliage (63.3%) was 14.8 units higher than for the separated leaves, an increase of some 30%. Keir et al (1997) reported a higher value of  66% but the leaves in this case were supplemented with a block of molasses-urea. Nguyen Thi Mui (2001) reported that the digestibility of jackfruit foliage was 52.6%, which is in agreement with the values for foliage fed in the trough in our experiment. The DM digestibility of hanging cassava foliage was very high (80.1%) and similar to that reported by Him Aun (2002) for cassava foliage hung in the cage and offered as the sole diet (83.5%). Wanapat et al (1997) reported a DM digestibility of 71% in cattle fed cassava foliage hay as the sole diet.

Nitrogen retention was highest for the hanging foliage and lowest when separated leaves were fed.  These trends mirrored the trends in voluntary DM intake although the relationship was not strong (r = 0.55). A closer relationship was observed  between N intake and N retention (r = 0.76).

Rumen ecology

The concentrations of ammonia in rumen fluid (in the range of 467 to 1076 mg/litre) were higher than has been reported in other studies with goats fed tree foliages. Thus Tran Quoc Viet (1997) encountered  199 mg/litre in growing goats fed jackfruit leaves while Nguyen Thi Hong Nhan (1997) reported levels of 180 mg/litre in lactating goats fed jackfruit leaves as the basal diet.

The concentrations encountered in our experiment are much higher than the suggested optimum levels (200 to 300 mg/litre) proposed by Perdok (1987) and almost certainly reflect the high intakes of the protein-rich leaves of all three plant species. While there is an energy cost associated with the urinary excretion of excess nitrogen, this is not necessarily a disadvantage if the goats are managed in an integrated farming system where both manure and urine are recycled as fertilizer or as substrate for earth worms. Nguyen Quang Suc et al (2000) reported that goat excreta supported faster growth of earth worms and produced a superior “ worm”  compost than excreta from cattle or buffalo.

Protozoal numbers were not influenced by the method of offering the feeds. There was an indication that populations were lower on the cassava than on mulberry or jackfruit, which may be related with the presence of condensed tannins in the leaves of the cassava (Wanapat et al 1997). There are reports that feeding of cassava foliage is associated with reduced numbers of intestinal nematodes in buffaloes (Netpana et al 2001) and in goats (Seng Sokerya and Rodriguez 2001). 

The most difficult finding to explain is the higher digestibility of the DM and organic matter of all the plant species when offered as hanging foliage as compared with loose leaves and petioles in the feed trough. The differences for DM digestibility were 8.5, 14.8 and 11.3 units for Mulberry, Jackfruit and Cassava, respectively. It has to be assumed that these differences were related to the method of consuming the leaves. Eating time was shortest when the forages were suspended in the cage and longest when separated leaves were offered; and eating time was closely and negatively related  (R² = 0.75) with N retention (Figure 6).

Figure 6: Relationship between eating time and N retention in goats fed foliages
or leaves from three plant species

It can be assumed that greater salivary secretion would occur when eating time was increased, from which it could be inferred that some compounds excreted in saliva were responsible for the depression in digestibility of the organic matter in the leaves.  This is an area meriting research. 

Conclusions

• The method of feeding by hanging the foliages is the best way to improve feed intake of goats and also increases performance. It can be accept easily by farmers, because less inputs (feed troughs not required; no need to chop or process the foliage) but high production..

• The foliage of mulberry, jackfruit and cassava is of nigh nutritive value and can be fed as the sole component of the diet to goats.

• There appear to be no problems of toxicity with any of the three foliages when fed in the fresh state as the sole component of the diet, but a period (3 to 5 days) of gradual adaptation to cassava foliage is recommended.

• Nutrient digestibility of tree foliage for goats can be improved by hanging the foliage as compared to the same feed offered in the feed trough.

Acknowledgments

This paper formed part of the MSc thesis (MEKARN-SLU, Uppsala, May 2003), of the senior author, who wishes to express his gratitude to the MEKARN project, supported by  SIDA/SAREC of Sweden for financing this study; to Dr. T.R Preston, Director of the University of Tropical Agriculture (UTA), for advice and allowing the use of the research farm and laboratory facilities of UTA; to Dr J Ly for advising on analysis of data and the first correction of the draft paper. Thanks are also given to Mr. Roath for technical assistance throughout the experiment.

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Received  1 June 2003; Accepted 30 July 2003

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