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Effect of jackfruit leaves on feed utilization and ruminal fermentation of growing goats

Lam Phuoc Thanh, Pham Truong Thoai Kha, Pham Van Trong Tinh1 and Tran Thi Thuy Hang1

Department of Animal Sciences, College of Agriculture, Can Tho University, Viet Nam
phuocthanh@ctu.edu.vn
1 Department of Agricultural Technology, College of Rural Development, Can Tho University, Viet Nam

Abstract

This study aimed to evaluate effect of jackfruit leaves (JF) replacing for Para grass (PG) on intake, digestibility, nitrogen balance and ruminal fermentation in growing meat goats. Four male Boer goats, 4 months old, were used in a 4×4 Latin square design. A basal diet consisted of pelleted concentrate and PG (C:F 30:70). The treatments were 4 levels of JL (0, 50, 75 and 100%) replacing PG on a DM basis (equivalent to: 0, 36.9, 52.7 and 70.3% of diet DM on basis of actual intakes during the experiment). Result showed that replacement of JL for PG in the diets increased (p<0.01) DM intake (DMI), accounting for 27.8, 54.9, 54.2% increase in diet containing 36.9, 52.7 and 70.3% JL compared with diet contained only PG. Goats fed 70.3% JL in the diet decreased (p<0.05) NDF digestibility by 41.3% compared with those fed only PG. Nitrogen retention showed the greater values (p=0.06) in goats fed JL diets (8.77-9.76 g/d) compared with goats fed only PG (4.31 g/d). A greater live weight gain (p=0.08) of goats consumed JL-diets, accounting for 87.8-131 g/d increase compared to goats fed only PG. Total VFA and NH3-N concentrations were not affected, but blood urea nitrogen decreased linearly (p<0.01) by increasing levels of JL in the diets. Overall, combined data suggest that substitution of JL for PG at 75 and 100% in the diets of growing meat goats reduces nutrient digestibility, but improves nutrient intake, nitrogen retention and live weight gain without affecting ruminal fermentation. Thus, feeding JL instead of PG in growing meat goats would get positive efficiency of feed local resources and animal performance.

Key words: digestibility, jackfruit leaves, meat goats, nitrogen balance, ruminal fermentation


Introduction

Domesticated ruminants, including meat and dairy goats contribute immensely to sustainable food and nutrition systems because these ruminants can convert low-value human-inedible feed input into high-value human-edible protein output in the form of meat and milk (Ben Salem and Smith, 2008; Enahoro et al 2019; Salami et al 2019). In recent years, livestock population has been driven rapidly by increasing demand for animal proteins due to a concomitant rise in population, urbanization and household income. Livestock production systems demand high energy inputs, land, chemicals and water – all of which are becoming increasingly scarce (Preston, 2009). Meanwhile, some tropical regions (e.g., Viet Nam) are characterized by long dry season with inconsistent rainfall patterns, which makes challenging to get enough forage for the maintenance of small ruminants. Distel et al (2020) suggested that replacement of simple traditional forage by complementary forage species that enable ruminants to select a diet in benefit of their nutrition, health, whilst reducing the negative environmental impacts caused by agricultural systems. Therefore, an approach promoting to improve efficient use of feed local resources is very necessary. In this regard, jackfruit (Artocarpus heterophyllus) leaves (JL), a fodder tree leaves, can be used as an alternative forage source for traditional grasses in goat production. This foliage characterized by great contents of dry matter (33.2%), crude protein (16.6%) and neutral detergent fiber (52.6%) (Mui et al 2002) compared to more common forage crops for ruminant feed such as Para grass (Brachiaria mutica) (Mui et al 2002), Napier grass (Maleko et al 2019) and Guinea grass (Oliveira et al 2020). Moreover, JL also has high content of insoluble protein (Kouch et al 2003) and phenolic compounds, e.g. tannins (Pal et al 2015).

Goats can feed more types of grass compared with other ruminant species (Shaheen et al 2020). Van et al (2005) concluded that goat diet containing many kinds of foliage potential resulted in higher intake compared to feeding the foliage alone. In Viet Nam, 38% jackfruit trees (approximate 30,000 hectares) are cultivated in Mekong delta, a down south region. To our knowledge, no reports have been published on the replacement of traditional forage in goat diets by JL which is more specifically forage in tropical countries, particularly Mekong Delta – Viet Nam, where this forage material is readily available with large amount and can be a very low-cost and viable alternative for goat feeding. Thus, this study aimed to evaluate effect of replacement of JL for Para grass (PG) on intake, digestibility, nitrogen (N) balance, and ruminal fermentation in growing goats. The hypothesis was that increasing supplement of by-pass protein from JL, digestibility would not be an index of nutritive value, which is generally believed.


Materials and methods

Study site

The studies were conducted in Vietnam at Can Tho University Farm (Hoa An campus), Phung Hiep district, Hau Giang province, 40 km south-west of Can Tho city, a center of Mekong Delta in Viet Nam. The experimental site is between the coordinates 9°47′ N latitude and 105°28′ E longitude, and at an elevation of 2 m below sea level. The area receives about 1,800 mm of rainfall per year. The climate is tropical monsoon, with a wet season between May and November and a dry season from December to April. The mean daily temperature ranges from 20°C to 35°C.

Animal, experimental design and diet

Four male Boer goats (Photo 1), 4 months old, and 15.1 ± 1.41 kg body weight were housed in individual cages (1.2m × 0.6m × 1.2m, L×W×H) and fed a basal diet of Para grass and concentrate. Animals were allocated to 4 treatments in a 4×4 Latin square design. The treatments were 4 levels of JL (0, 50, 75 and 100%) replacing PG on a DM basis (equivalent to: 0, 36.9, 52.7 and 70% of diet DM on basis of actual intakes during the experiment). Each experimental period was lasted for 14 days including 7 days for adjustment and 7 days for sampling. Diets were offered in equal amounts twice daily at 07:30 and 17:30 h. The concentrate used in the experiment was mixed and pelleted from ingredients including 29.6% soybean meal, 37.7% ground corn, 30% rice bran, 0.6% limestone, 0.3% DCP, 0.5% NaCl, and 1.4% premix of mineral and vitamin (as DM basis). The foliage of jackfruit was pruned from 3-5 years old trees (Photo 2) ensuring that some branches were left for continued growth. The leaves were separated from the branches (Photo 3) and offered to the goats. Para grass was cut daily at 30-40 days regrowth and chopped before feeding. Both JL and PG were collected from the areas around Can Tho University Farm.

Photo 1. Goats in the study Photo 2. Jackfruit trees
Photo 3. Jackfruit leaves
Sampling and measurements

From d8 to d12, data on feed offered and refused as well as total fecal and urine outputs were recorded daily for each goat during a 5-d period. Feces were collected in wire-screen baskets placed under the floor of the cages, and urine was collected through a funnel into plastic buckets containing 50 mL of 10% H2SO4. The acidification to keep the final pH of urine below 3 was necessary to prevent loss of volatile ammonium and microbial degradation. Representative samples (10%) of feeds, feces, and urine were collected over 5 consecutive days, stored at −20°C, and pooled for chemical analysis. On d13, blood samples were collected before the morning meal for analysis of blood urea nitrogen (BUN) concentration. Briefly, blood was withdrawn from the jugular vein into evacuated tubes containing lithium heparin, immediately placed on ice, and centrifuged at 4,500×g for 5 min. On d14, rumen fluid samples were collected at 0, 3 and 6 h post morning feeding using a 100-mL syringe. The rumen fluid was immediately determined pH value. The subsample was then filtrated through a clean double layer of cotton cloth, and the liquid fraction was acidified with 1M H2SO4 (9:1 w/w), centrifuged at 10,000×g for 15 minutes and stored at −20°C for analyses of VFA and NH3-N concentrations. Body weight at the beginning and end of the experimental period was also recorded.

Chemical analysis

Feed, feed refusal, and feces samples were first dried in a forced-air oven at 60°C for 48 h and then ground to pass a 1-mm screen (Cutting Mill SM 100, Retsch, Haan, Germany) before analysis. Chemical analyses of the diet, refusals, and feces were determined according to standard methods of AOAC (1991) for dry matter (DM), organic matter (OM), total mineral (Ash), crude protein (CP) and ether extract (EE). The solubility of the protein was determined by method of Whitelaw and Preston (1963). Neutral detergent fiber (NDF), acid detergent fiber (ADF) and acid detergent lignin (ADL) were analyzed following the methods of Van Soest et al (1991). Determination of tannins in the feeds was done following the method of AOAC (1995). Concentration of BUN in plasma samples were determined using a biochemical analyzer (XL 200, Erba, India). Ruminal pH was determined by a pH meter (HI5222, Hana Instruments, US). Ruminal NH3-N concentration was analyzed using the Kjeldahl methods (AOAC, 1991).

Concentrations of individual VFA were analyzed using a Thermo Trace 1310 GC system (Thermo Scientific, Waltham, MA, USA) equipped with a flame ionization detector. The inlet and detector temperature were maintained at 220°C. Aliquots (1 μL) were injected with a split ratio of 10:1 into a 30m × 0.25mm × 0.25μm Nukol fused-silica capillary column (Cat. No: 24107, Supelco, Sigma-Aldrich, St. Louis, MO, USA) with nitrogen carrier gas set to a flow rate of 1 mL/min and initial oven temperature of 80°C. The oven temperature was held constant at the initial temperature for 1 min, and thereafter increased at 20°C/min to a temperature of 180°C and held for 1 min, and increased at 10°C/min to a final temperature of 200°C, and a final run time of 14 min (Bharanidharan et al 2018). Individual VFA peaks were identified based on their retention times, compared with external acid standards including acetic, propionic, butyric, valeric, iso-butyric and iso-valeric (Sigma-Aldrich, USA).

Statistical analysis

Statistical tests were performed using SAS University Edition 2019 (SAS Institute Inc., Cary, NC, USA). Data were statistical analyzed using the General Linear Model procedure. The statistical model was Yijk = µ + Ai + Dj + Pk + εijkl, where Yijk = the dependent variable, Ai = the effect of animal (i = 1-4), Dj = the effect of diet (j = 1-4), Pk = the effect of period (k = 1-4), and εijk = the residual effect. Data on ruminal fermentation patterns were analyzed using a Mixed model with the repeated measures (hours). The statistical model was Yijklm =μ + Ai + Pj +Dk + Tl + (D ×T)kl + εijklm, where Yijklm = the dependent variable, μ = the overall of mean, Ai = the random effect of animal, Pj = the fixed effect of period, Dk = the fixed effect of diet, Tl = the fixed effect of time (hour), (D×T)kl = the fixed effect of interaction between diet and time, and εijklm = the random residual error. Significant differences among diet means were statistically compared using Tukey. Differences were declared significant at p<0.05, and tendency was declared at 0.05≤p<0.1.


Results and discussion

Composition of diet ingredients and of the diets

The CP level (% in DM) was low for both PG (11.8%) and JL (12.9%) thus about 50% of the dietary CP was supplied by the concentrate (Table 1). Jackfruit leaves had lowest protein solubility (27.6%) while this was 42.0 and 66.3% in PG and concentrate, respectively. Kouch et al (2003) showed that protein solubility in JL was 33.7%. Lignin content in JL was 19.1% while this was only 14.2 vs. 8.32% in concentrate and PG, respectively. Moreover, total tannins were 11.6% in JL, remarkably higher than those in concentrate and PG (0.88 vs. 3.47%).

Table 1. Chemical composition of feeds and diets

Item

Feed

Jackfruit leaves in diet DM#, %

Conc

PG

JL

0

36.9

52.7

70.3

DM

88.6

17.7

38.3

41.0

47.6

51.1

53.4

As % of DM

OM

90.1

88.1

84.0

88.8

87.2

87.0

86.0

Ash

9.89

11.9

16.0

11.2

12.8

13.0

14.0

CP

21.1

11.8

12.9

15.3

15.4

15.6

15.7

Protein solubility (PS)

14.0

4.96

3.55

7.92

7.27

7.06

6.66

PS/CP, %

66.3

42.0

27.6

51.8

47.1

45.1

42.5

EE

4.02

1.73

2.71

2.51

2.82

2.99

3.12

NDF

44.2

61.3

34.9

55.1

45.8

42.3

37.9

ADF

18.7

33.9

28.5

28.9

27.4

26.6

26.1

ADL

14.2

8.32

19.1

10.2

14.1

15.8

17.7

Total tannins

0.88

3.47

11.6

2.62

5.67

6.95

8.43

Conc: concentrate, PG: Para grass, JL: Jackfruit leaves #According to recorded intakes during the experiment

Intake

Replacement of JL for PG in the diets increased (p<0.01) DM intake (DMI), accounting for 27.8, 54.9, 54.2% increase in diet containing 36.9, 52.7 and 70.3% JL compared with diet contained only PG (Table 2). There was a quadratic regression between level of JL in diet and DMI with y = − 0.0227x2 + 6.3341x + 566.33 and R² = 0.94 (Figure 1). That increased nutrient intake in goats fed JL diets in this study was similar to the result in goats of Das and Ghosh (2007), but was different from the result of Mui et al (2002), where increasing JL replaced for concentration caused a linear reduction of DM and CP intakes in goats. Malik et al (2017) found no change in DMI of sheep fed JL replaced for wheat bran. Kibria et al (1994) showed that JL are highly palatable and thus goats consumed higher amount of feeds offered. Other factors affecting feed intake in this study may also include other substances such as volatile oils or phenolic compounds in JL. Pal et al (2015) showed that JL contained 40.1% total phenolics comprised of 12.9% non-tannin phenolics.

Table 2. Mean values for feed intake (DM, g/d) in goats fed jackfruit leaves as replacement for Para grass

Item

Jackfruit leaves in diet DM, %

SEM

p

0

36.9

52.7

70.3

Concentrate

182b

228ab

269a

264a

24.7

<0.01

Para grass

389a

234b

143b

0c

49.7

<0.01

Jackfruit leaves

0c

270b

474b

618a

81.5

<0.01

Total DM

572b

732ab

886a

882a

79.3

<0.01



Figure 1. Curvilinear trend in DM intake as Jackfruit leaves place Para grass in the diet of goats
Total-tract digestibility and nitrogen balance

There was a negative linear regression between level of JL in diet and DM digestibility (y = − 0.1213x + 64.73; R² = 0.98; Figure 2). Goats fed 70.3% JL in the diet decreased (p<0.05) NDF digestibility by 41.3% compared with those fed only PG (Table 3). The NDF digestibility showed a negative linear trend as increased JL in the diets (y = − 0.3494x + 62.713; R² = 0.97; Figure 3). Nitrogen (N) intake increased (p<0.01) by 58.8% in diet containing 70.3% JL compared with only PG-contained diet. Feeding increased amounts of JL in the diet increased linearly (p <0.01) fecal N, and the extent of the increase was greater for 70.3% JL in diet (10.2 g/d) compared without JL in diet (3.96 g/d); however, N excretion via urine was linearly lower (p<0.01) in JL diets (3.10-3.42 g/d) compared with PG diet (5.75 g/d). Nitrogen retention showed the greater values (p=0.06) in goats fed JL diets (8.77-9.76 g/d) compared with goats fed only PG (4.31 g/d). With only a 14-day duration of each period, we could also detect a greater live weight gain (p =0.08) of goats consumed JL-diets, accounting for 87.8-131 g/d increase compared with goats fed only PG. Figures 4 shows a very close relationship between level of JL in the diet and nitrogen retention (y = − 0.0017x 2 + 0.1911x + 4.284; R² = 0.99), whereas a close relationship between level of JL in the diet and live weight gain is presented in Figure 5 (y = − 0.0575x2 + 5.3508x + 44.116; R² = 0.98).

Table 3. Mean values for digestibility, N balance and live weight change in goats fed jackfruit leaves as replacement for Para grass

Item

Jackfruit leaves in diet DM, %

SEM

p

0

36.9

52.7

70.3

Digestibility, %

DM

64.5

60.9

58.2

56.0

5.84

0.29

OM

67.0

63.7

61.8

60.4

5.35

0.40

CP

70.0

67.0

58.6

53.4

8.51

0.11

NDF

62.0a

50.2ab

46.5ab

36.6b

7.43

0.02

Nitrogen (N) balance, g/d

Intake

14.0b

18.1ab

21.9a

22.3a

2.27

<0.01

Feces

3.96b

6.04ab

8.68a

10.2a

1.69

<0.01

Urine

5.75a

3.28b

3.42b

3.10b

0.47

<0.01

Retention

4.31

8.77

9.76

9.00

2.23

0.06

Live weight (LW)

Initial LW, kg

19.8

18.1

18.8

18.6

0.68

0.06

Final LW, kg

20.6

20.7

21.7

21.0

0.88

0.36

LW change

45.2

156

176

133

59.1

0.08



Figure 2. Negative linear trend in DM digestibility as Jackfruit
leaves replace Para grass in the diet of goats
Figure 3. Negative linear trend in NDF digestibility as Jackfruit
leaves replace Para grass in the diet of goats


Figure 4. Curvilinear trend in N retention as Jackfruit
leaves replace Para grass in the diet of goats
Figure 5. Curvilinear trend in live weight gain as Jackfruit
leaves replace Para grass in the diet of goats

That decreased NDF digestibility with increasing levels of JF in the diet was supported by Das and Ghosh (2007). For this reason, JL contained high insoluble protein which escaped from the rumen took with its particles of fiber which would be digested with lesser efficiency than if they had been digested in the rumen. A remarkable decrease in NDF observed in JL diets could be also a result of higher intakes of ADF and ADL. Moreover, the higher tannin content in JL (11.6%) compared with that in PG (3.47%) was also a factor to reduce nutrient digestibility. High dietary CT had been showed to decrease extremely in vitro DM degradability in four ruminant species (Bueno et al 2020). Similar result was found in the study of Pal et al (2015). Tannins depress fiber digestion by forming complexes with lignocellulose and hence prevent microbial digestion (Piñeiro-Vázquez et al 2015). Moreover, tannins have been implicated for their inhibitory effects on nutrient digestion because tannins have high ability to bind protein at- and post-rumen which led to decrease apparent protein digestibility and increase excretion of N via feces (Patra and Saxena, 2011). In the current study, shifting pattern of nitrogen excretion from urine to feces is beneficial environmentally. In fact, urinary nitrogen is mainly in the form of urea, which is more rapidly hydrolyzed to ammonia and nitrified to nitrate, whereas fecal nitrogen is largely in the organic form, which is less volatile. Therefore, decreased nitrogen excretion via urine could reduce ammonia and nitrous oxide emissions into the atmosphere. The greater fecal N excretion with increasing rates of JL (high contains of tannins) in the current study was similar to previous studies in meat goats and dairy cows (Animut et al 2008; Grainger et al 2009).

Ruminal fermentation patterns

Interactions between diet and sampling time (h) for rumen fermentation characteristics were not significant. Therefore, only averages of VFA measurements at the different sampling times are presented in Table 4. Total VFA and NH3-N concentrations were not affected by feeding JL in the diets. Concentration of BUN reduced linearly (p<0.01) by 1.76 and 2.05-folds in goats fed 52.7 and 70.3% relative to goats fed PG alone. There was a negative linear trend in BUN when increasing level of JL in goat diets (y = − 0.0002x2 − 0.051x + 8.3146;
R² = 0.97; Figure 6).

Table 4. Mean values for rumen fermentation parameters in goats fed jackfruit leaves as replacement for Para grass

Item

Jackfruit leaves in diet DM, %

SEM

p

0

36.9

52.7

70.3

pH

6.76

6.72

6.75

6.72

0.06

0.94

NH3-N, mg/dL

23.1

24.6

25.6

25.3

1.96

0.81

VFA

Total, mM

74.5

77.6

78.3

74.5

2.02

0.43

Acetate, %

55.5

57.0

55.9

56.8

0.67

0.37

Propionate, %

20.2

20.0

19.8

20.4

0.25

0.38

Butyrate, %

11.2b

11.5b

11.0b

12.3a

0.17

<0.01

Valerate, %

3.52

3.24

3.58

3.45

0.17

0.55

Iso-butyrate, %

3.92

2.99

4.40

2.51

0.47

0.07

Iso-valerate, %

5.59

5.25

5.32

4.44

0.35

0.18

BUN, mmol/L

8.27a

6.53ab

4.70b

4.03b

1.22

<0.01



Figure 6. Negative linear trend in BUN as Jackfruit leaves replace Para grass in the diet of goats

Das and Ghosh (2007) found no effect on ruminal VFA concentration of growing goats when JL was used at 50% in the diet. Similar result was observed in a study of Dschaak et al (2011), where dairy cows supplemented with 3% condensed tannin extract had no change on total VFA and NH 3-N concentrations. However, Roca-Fernández et al (2020) reported that feeding condensed tannins at 3.80-7.56% in the diets reduced strongly ruminal VFA concentration. That reduced BUN concentration in goats fed 52.7 and 70.3% JL in the diet is negative effects of insoluble protein and tannins on goat health in these diets. High insoluble protein in JL reduced ruminal protein degradation and therefore ruminal NH3-N concentration. The complexes formed between tannins and proteins render them inaccessible to rumen degradation and favor post-rumen release, thereby reducing ammonia concentration in the rumen (Ningrat et al 2016) and urea concentration in blood. However, no reduction of ruminal NH 3-N concentration was found in this study. It was explained partially that the greater ingested nutrients in JL could compensate for low rumen degradability of this feed, which led to maintain concentrations of VFA and NH3-N in the rumen. Moreover, it is probably that phenolic compounds in JL might stimulate protein synthesis of rumen microbes. Jayanegara et al (2011) found that concentrations of total tannins and condensed tannins in leaves had positively correlate with bacterial populations. With the higher nutrient ingest, the greater number of ruminal microbes could help to increase total nutrient fermentability in the rumen.


Conclusion


Acknowledgement

This study was supported in part by the Can Tho University Improvement Project VN14-P6 supported by a Japanese ODA Loan under Grant No. A9.


References

Animut G, Puchala R, Goetsch A L, Patra A K, Sahlu T, Varel V H and Wells J 2008 Methane emission by goats consuming diets with different levels of condensed tannins from lespedeza. Animal Feed Science and Technology, 144(3), 212-227.

AOAC 1991 Official Method of Analysis, 15th ed. Association of Official Analytical Chemists, Washington D.C.

AOAC 1995 Official Methods of Analysis, 16th ed. Association of Official Analytical Chemists, Washington, DC.

Ben Salem H and Smith T 2008 Feeding strategies to increase small ruminant production in dry environments. Small Ruminant Research, 77(2), 174-194.

Bharanidharan R, Arokiyaraj S, Kim E B, Lee C H, Woo Y W, Na Y, Kim D and Kim K H 2018 Ruminal methane emissions, metabolic, and microbial profile of Holstein steers fed forage and concentrate, separately or as a total mixed ration. PloS One, 13(8), e0202446.

Bueno I C S, Brandi R A, Fagundes G M, Benetel G and Muir J P 2020 The role of condensed tannins in the in vitro rumen fermentation kinetics in ruminant species: Feeding type involved? Animals, 10(4), 635.

Das A and Ghosh S K 2007 Effect of partial replacement of concentrates with jackfruit (Artocarpus heterophyllus) leaves on growth performance of kids grazing on native pasture of Tripura, India. Small Ruminant Research, 67(1), 36-44.

Distel R A, Arroquy J I, Lagrange S and Villalba J J 2020 Designing diverse agricultural pastures for improving ruminant production systems. Frontiers in Sustainable Food Systems, 4, 215.

Dschaak C M, Williams C M, Holt M S, Eun J S, Young A J and Min B R 2011 Effects of supplementing condensed tannin extract on intake, digestion, ruminal fermentation, and milk production of lactating dairy cows. Journal of Dairy Science, 94(5), 2508-2519.

Enahoro D, Mason-D’Croz D, Mul M, Rich K M, Robinson T P, Thornton P and Staal S S 2019 Supporting sustainable expansion of livestock production in South Asia and Sub-Saharan Africa: Scenario analysis of investment options. Global Food Security, 20, 114-121.

Grainger C, Clarke T, Auldist M J, Beauchemin K A, McGinn S M, Waghorn G C and Eckard R J 2009 Potential use of Acacia mearnsii condensed tannins to reduce methane emissions and nitrogen excretion from grazing dairy cows. Canadian Journal of Animal Science, 89(2), 241-251.

Jayanegara A, Wina E, Soliva C R, Marquardt S, Kreuzer M and Leiber F 2011 Dependence of forage quality and methanogenic potential of tropical plants on their phenolic fractions as determined by principal component analysis. Animal Feed Science and Technology, 163(2), 231-243.

Kibria S S, Nahar T N and Mia M M 1994 Tree leaves as alternative feed responses for black Bengal kids under stall fed conditions. Small Ruminant Research, 13, 217-222.

Kouch T, Preston T R and Ly J 2003 Studies on utilization of trees and shrubs as the sole feedstuff by growing goats; foliage preferences and nutrient utilization. Livestock Research for Rural Development. 15, #50. http://www.lrrd.org/lrrd15/7/kouc157.htm

Maleko D, Mwilawa A, Msalya G, Pasape L and Mtei K 2019 Forage growth, yield and nutritional characteristics of four varieties of napier grass (Pennisetum purpureum Schumach) in the west Usambara highlands, Tanzania. Scientific African. 6, e00214.

Malik P K, Kolte A P, Baruah L, Saravanan M, Bakshi B and Bhatta R 2017 Enteric methane mitigation in sheep through leaves of selected tanniniferous tropical tree species. Livestock Science, 200, 29-34.

Mui N T, Ledin I, Udén P and Binh D V 2002 The foliage of flemingia (Flemingia macrophylla) or jackfruit (Artocarpus heterophyllus) as a substitute for a rice bran - soya bean concentrate in the diet of lactating goats. Asian-Australasian Journal of Animal Sciences, 15(1), 45-54.

Ningrat R W S, Mardiati Z and Heny S 2016 Effects of doses and different sources of tannins on in vitro ruminal methane, volatile fatty acids production and on bacteria and protozoa populations. Asian Journal of Animal Sciences, 11, 47-53.

Oliveira J K S D, Corrêa D C D C, Cunha A M Q, Rêgo A C D, Faturi C, Silva W L D and Domingues F N 2020 Effect of nitrogen fertilization on production, chemical composition and morphogenesis of Guinea grass in the humid tropics. Agronomy, 10(11), 1840.

Pal K, Patra A K, Sahoo A and Kumawat P K 2015 Evaluation of several tropical tree leaves for methane production potential, degradability and rumen fermentation in vitro. Livestock Science, 180, 98-105.

Patra A K and Saxena J 2011 Exploitation of dietary tannins to improve rumen metabolism and ruminant nutrition. Journal of the Science of Food and Agriculture, 91(1), 24-37.

Piñeiro-Vázquez A, Canul-Solís J, Alayón-Gamboa J, Chay-Canul A, Ayala-Burgos A, Aguilar-Pérez C, Solorio-Sánchez F Ku-Vera J J A D M V 2015 Potential of condensed tannins for the reduction of emissions of enteric methane and their effect on ruminant productivity. Archivos de Medicina Veterinaria, 47(3):263-272.

Preston T R 2009 Environmentally sustainable production of food, feed and fuel from natural resources in the tropics. Tropical Animal Health and Production, 41(7), 1071.

Roca-Fernández A I, Dillard S L and Soder K J 2020 Ruminal fermentation and enteric methane production of legumes containing condensed tannins fed in continuous culture. Journal of Dairy Science, 103(8), 7028-7038.

Salami S A, Luciano G, O'Grady M N, Biondi L, Newbold C J, Kerry J P and Priolo A 2019 Sustainability of feeding plant by-products: A review of the implications for ruminant meat production. Animal Feed Science and Technology, 251, 37-55.

Shaheen H, Qureshi R, Qaseem M F and Bruschi P 2020 The fodder grass resources for ruminants: A indigenous treasure of local communities of Thal desert Punjab, Pakistan. PloS One, 15(3), e0224061.

Van D T T, Mui N T and Ledin I 2005 Tropical foliages: effect of presentation method and species on intake by goats. Animal Feed Science and Technology, 118(1), 1-17.

Van Soest P J, Robertson J B and Lewis B A 1991 Methods for dietary fiber, neutral detergent fiber, and nonstarch polysaccharides in relation to animal nutrition. J Journal of Dairy Science, 74(10), 3583-3597.

Whitelaw F G and Preston T R 1963 The nutrition of the early-weaned calf. III. Protein solubility and amino acid composition as factors affecting protein utilization. Animal Science, 5, 131-145.