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Effects of 'browse plus' on the utilisation of Colophospermum mopane (mopane) browse by sheep

L. Hove1 and D. Mpofu

Department of Research and Specialist Services
Matopos Research Station, P Bag K5137, Bulawayo, Zimbabwe

1. Present address: Makoholi Research Station, P. Bag 9182, Masvingo, Zimbabwe.


Abstract
Introduction
Materials and methods
Results
Discussion
Conclusion
References

Abstract

In two experiments using indigenous sheep the effects of 'browse plus' (mixture of polyethylene glycol [PEG], polyvinylpyrrolidone [PVP] and a mineral and vitamin mix) on intake and digestibility of bushmeal (BM) was determined. In the first experiment bushmeal special (BMS) (BM plus 'browse plus') intake was higher (P<0.05) than BM when both diets were offered ad libitum. At similar levels of intake, dry-matter and organic-matter digestibilities were higher (P<0.05) for BMS than for BM. There was no apparent difference in N metabolism between animals receiving the two diets. In the second experiment BM and BMS did not increase (P>0.05) hay intake and nutrient digestibility when fed as supplements to grass hay. Total dry matter intake and N retention were increased (P<0.05). No lesions were observed on the gastro-intestinal tract, liver and kidneys of the animals receiving BM or BMS. It was concluded that BM and BMS could serve as feed resources for ruminants.

Introduction

Drought feeding strategies have included the intensive use of browse because trees are less susceptible to climatic fluctuations than herbaceous plants. Browse usually has higher crude protein content than grasses (Dube and Ncube 1993). However, the presence of secondary compounds, mainly polyphenolics/tannins, limits the feeding value of the browse through depression of intake and digestibility (McLeod 1974). Tannins bind with dietary, enzymatic and microbial protein to form insoluble complexes that are not degraded in the rumen, resulting in reduced digestibility and intake. Information on fate of tannin-protein complexes post-rumen has been variable. Kidney, liver and gastro-intestinal tract damage in animals consuming tanniferous forage has been reported (Bailey 1978).

Polyethylene glycol (PEG) and polyvinylpyrrolidone (PVP) preferentially bind with tannins, resulting in the reversal of tannin effects on forage utilisation Response to PEG depends on the type of tannin and the tannin: PEG ratio (Strachan et al 1988).

Drought tolerant Colophospermum mopane (mopane) is prevalent in the southern and western lowveld regions of Zimbabwe where fallen dry leaves and pods are an important feed resource for both domestic and wild ungulates. Fresh leaves are rarely browsed probably due to the presence of secondary compounds. During the severe drought of 1992 mopane browse (leaf and fine stem) was fed to cattle as bushmeal (BM; mopane browse comprising leaf and fine stem) by crushing and mixing with maize bran, molasses and coarse salt in the ratio 53.8:30:15:1.2 (Triangle Limited). 'Browse plus' (Agricura Zimbabwe) crystals were added at a rate of 100 g/t of BM to make bushmeal special (BMS). 'Browse plus' contains PEG, PVP and a vitamin and mineral mix. Animal responses to feeding of both BM and BMS have not been studied. The current study was undertaken to determine the effect of feeding BM and BMS as sole feeds or as supplements to poor quality hay on nutrient utilisation and clinical status of the kidneys, liver and gastrointestinal tract of sheep.

Materials and methods

Preparation of feeds

BM and BMS were obtained wet from Triangle Limited. On arrival at the station they were sun-dried before feeding. Natural pasture hay was cut during the dry season and was of poor quality.

Animals and feeding

Ten 2-year old indigenous wethers (average weight 41.1±1.0 kg) were used in the first experiment. Animals were drenched with an anthelminthic (Ranide, Agricura, Zimbabwe) before being housed in metabolism crates which allowed separate collection of faeces and urine. The animals were blocked on the basis of live weight and randomly allocated to either BM or BMS within each block. Feed was offered ad libitum in two equal meals at 0800 and 1600 h and the amount offered was 115% of the previous day's intake. Water was offered three times a day.

A 21-day adjustment period was followed by a seven-day collection period. At the end of the first collection period animals receiving BMS remained in the experiment for another 14 days divided equally into adjustment and collection periods. Their dry-matter (DM) intake was, however, restricted to the same level as those on BM.

In the second experiment 14 two-year old wethers (average weight 40.0±1.0 kg) were used. The animals were blocked on the basis of live weight and the diets were randomly allocated to the animals within the blocks. Hay alone was fed to four animals while each of the supplements was fed to five animals. Animals received 200 g/head per day of the supplement. The supplement was offered during the first 30 minutes of feeding. Hay was then offered at 115% of the previous day's intake. A 21-day adjustment period followed by seven days of sampling was used.

During the collection periods refusals and urinary and faecal output were recorded. Refusals were pooled over the collection period for each animal and stored at room temperature awaiting analysis. Ten per cent of the faeces were oven-dried at 55°C to determine dry matter content. Urine was collected in vessels containing 25 ml of 1N H2SO4 to reduce loss of ammonia. Ten per cent of the urine was stored at 20°C for subsequent chemical analysis. At the end of the feeding period three animals from each treatment were slaughtered for visual detection of lesions on the liver, kidneys and the gastro-intestinal tract.

Laboratory methods

Feed, refusals and faecal samples were ground to pass through a 1 mm screen for determination of organic matter (OM) and nitrogen using standard procedures (AOAC 1984). Neutral-detergent fibre (NDF) was determined using the method described by Goering and Van Soest (1970). Urine was analysed for nitrogen content using the Kjeldahl method.

Statistical analysis

Analysis of variance on all data was carried out using a model that included the effect of diet (Genstat 1988).

Results

The chemical composition of the hay, BM and BMS is shown in Table 1. The N contents of BM and BMS were similar but were higher (P<0.05) than those of the hay. However, the hay had higher (P<0.05) NDF content. There was no apparent damage to the liver, kidneys and the gastro-intestinal tract of the animals from the two experiments.

Table 1. Chemical composition of bushmeal (BM), bushmeal special (BMS) and grass hay (GH) used in the study.

Chemical components

BM

BMS

GH

Dry matter

9.1

90.4

94.2

Organic matter

90.2

906.5

940.8

Nitrogen

15.0

15.0

4.3

Neutral-detergent fibre

547.4

555.9

841.1

Acid-detergent fibre

307.1

311.9

nd

Dry matter as % of wet weight, other constituents as g/kg dry matter.
nd = not determined.

Intake

Animals readily ate both BM and BMS. When offered ad libitum DM intake from BMS (1.4 kg/head per day) was higher (P<0.05) than that from BM (1.3 kg/head per day) (Table 2). Table 3 shows intake of various nutrients when grass hay was supplemented with BM and BMS. Supplementation did not reflect grass hay intake (P>0.05). However, animals receiving supplements ate more total DM and OM than those fed grass hay alone (P<0.05). Supplementing with BM did not increase (P>0.05) NDF intake while supplementation with BMS resulted in higher (P<0.05) NDF intake than the control.

Nutrient intake, dry-matter and organic-matter digestibility and N retention by sheep fed bushmeal (BM) and bushmeal special (BMS).

Parameters

BM

BMS1

BMS2

SED

Intake (g/head per day)


Dry matter

1268.5a

1242.7a

1404.0b

61.8


Organic matter

1158.2

1156.2

nd

23.8


NDF

690.3

631.5

nd

18.0

Apparent digestibility (%)


Dry matter

58.8a

68.2b

60.1a

1.5


Organic matter

59.9a

70.3b

nd

1.6

N balance (g/head per day)


N eaten

20.6b

18.6a

nd

0.2


N in faeces

8.0

6.9

nd

1.0


N in urine

1.7

2.1

nd

0.3


N balance

10.9

9.7

nd

1.0


N faeces/N urine

5.0

3.5

nd

1.2

1. BMS = BMS dry matter intake restricted to that of BM ad libitum.
2 BMS = BMS fed ad libitum.
Values are means of five observations;
SED = standard error of differences of means.
NDF = neutral-detergent fibre;
nd = not determined.
Within row means with different superscripts differ significantly (P<0.05)

Dry matter and OM digestibility

In the first experiment, when BM and BMS intakes were similar, DM and OM digestibilities were higher (P<0.05) in animals receiving BMS (Table 2). However, when BMS was fed ad libitum, DM digestibility was similar for the two diets. In the second experiment DM and OM in the three diets were digested to a similar (P>0.05) extent (Table 3).

Nitrogen balance

In Experiment 1 nitrogen balance was measured in animals consuming similar amounts of BM and BMS. Animals receiving BM ate more N (P<0.05) than those receiving BMS (Table 2). However, faecal and urinary N output and the relation between the two was not affected by diet (P>0.05). Nitrogen retained by the animals on the two diets was similar (P>0.05). In Experiment 2, supplementation of veld hay increased (P<0.05) N intake although N intake by the groups receiving supplements was similar (P>0.05) (Table 3). Faecal and urinary N output were similar (P<0.05) for all three diets and N retention was higher (P<0.05) in the groups receiving supplements than in those fed hay alone.

Table 3. Nutrient intake, dry-matter and organic-matter digestibility and nitrogen retention by sheep fed grass hay C supplemented with 200 g/head per day of bushmeal (BM) or bushmeal special (BMS).

Parameters

GH alone

GH+BM

GH+BMS

SED1

SED2

No. of animals/treatment

4

5

5



Intake (g/head per day)


GH

626.3

602.2

675.2

51.4

48.4


Total dry matter

626.3a

713.6b

752.5b

27.2

25.6


Organic matter

588.0a

655.0b

707.6b

25.4

23.9

Neutral-detergent fibre

513.8a

544.5a

589.8b

18.3

17.3

Apparent digestibility (%)


Dry matter

48.4

49.2

51.0

3.2

3.0


Organic matter

51.3

49.5

53.4

3.1

2.9

Nitrogen balance (g/head, per day)


N intake

3.1a

5.1b

5.1b

0.1

0.1


N in faeces

3.1

3.3

3.8

0.3

0.3


N in urine

1.1

1.1

0.7

0.2

0.3


N balance

-1.1a

0.7b

0.6b

0.8

0.7


N faeces/N intake

1.0b

0.7a

0.7a

0.1

0.1

SED1 = standard error of differences of means of unequally replicated treatments.
SED2 = standard error of differences of means of equally replicated treatments.
Within row means with different superscripts differ significantly (P<0.05)

Discussion

Although no tannin assay was carried out on BM or BMS, Walker (1980) stated that mopane browse has high levels of tannins. These are implicated in the reluctance of livestock to eat fresh mopane browse. In the current study animals readily consumed both BM and BMS indicating the improved palatability due to maize bran, molasses and salt. It is generally accepted that polyphenolics/tannins interfere with forage nutrient utilisation by animals through their protein-precipitating ability which causes reduced intake and digestibility of most nutrients (McLeod 1974; Barry and Duncan 1984; Woodward and Reed 1989).

Reversal of tannin effects on nutrient utilisation by PEG observed in this study has been reported by other workers. Barry and Manley (1984) reported increased OM digestibility when they sprayed tanniferous Lotus pedunculatus (lotus) fresh herbage with PEG. In another study Strachan et al (1988) observed increased DM intake and unchanged digestibility by sheep consuming a mulga (Acacia aneura) diet with PEG inclusion. However, Nunez-Hernandez et al (1991) observed no effects of PEG on OM intake and digestibility by goats and sheep fed mountain mahogany (Cercocarpus montanus).

The similarity in N metabolism between animals consuming BM and BMS was not expected. Despite higher N intake by animals receiving BM, faecal and urinary N and N retention were not different. This is contrary to the findings of Nunez-Hernandez et al (1991) who observed reduced faecal N and increased urinary N when animals consuming mountain mahogany were given PEG. Increased excretion of N through faeces by animals fed high tannin forage was also observed by Barry and Duncan (1984) when they fed lotus to sheep. The increase in faecal N is due to the formation of indigestible protein-tannin complexes (Woodward and Reed 1989).

Total DM intake increased with BM and BMS feeding with no effect on basal diet intake and DM and OM digestibilities. Strachan et al (1988) and Nunez-Hernandez et al (1991) observed increased DM and OM intake with no effect on digestibility. Strachan et al (1988) postulated that rate of rumen turnover is increased by PEG inclusion. The level of PEG used in this study (±0.1 g/head per day) is not expected to have had profound effects on digesta flow kinetics. The higher N retention on supplementation was due to higher N intake.

The comparison of published results with the current study needs to be viewed with caution. Tannin-PEG-protein interactions are affected by many factors such as tannin molecular weight and structure, protein type (Scalbert 1991) and PEG molecular weight. In the studies reviewed different forages were used with different levels of PEG, complicating the interpretation of results. It is likely that polyphenolics present in mopane browse are different to those in the forages used by the other workers.

Conclusion

This study confirms other research findings that PEG reverses the effects of polyphenolics/tannins on nutrient utilisation largely through improved nutrient digestibility. Both BM and BMS could serve as dry season feed resources although longer feeding periods are required to have conclusive results on physiologic effects. Research into methods of encouraging in situ feeding of mopane browse warrant investigation in view of the costs of making bushmeal.

Acknowledgements

The assistance of Agricura and Mr J. Stambolie of Triangle Limited in providing the feeds, and the Nutrition Section staff at Matopos Research Station in looking after the animals is acknowledged. Thanks to Drs T. Smith and S. Sibanda for comments on the draft of this paper.

References

AOAC (Association of Official Analytical Chemists). 1984. Official Methods of Analysis. AOAC, Washington, DC, USA. 1141 pp.

Bailey E.M. 1978. Physiologic response of livestock to toxic plants. Journal of Range Management 31:343-347.

Barry T.N. and Duncan S.J. 1984. The role of condensed tannins in the nutritional value of Lotus pedunculatus for sheep. 1. Voluntary intake. British Journal of Nutrition 51:485-491.

Barry T.N. and Manley T.R. 1984. The role of condensed tannins in the nutritional value of Lotus pedunculatus for sheep. 2. Quantitative digestion of carbohydrates and proteins. British Journal of Nutrition 51:493-504.

Dube J.S. and Ncube S.1993. The potential of Matopos browse species in livestock production. In: Dzowela B.H. and Shumba E.M. (eds), Agroforestry Research and Development in Zimbabwe. Proceedings of the National Seminar held at the University of Zimbabwe, 3-5 March 1992. National Agroforestry Steering Committee, Zimbabwe. pp. 39-46.

Genstat 5 Release 1.3. 1988. Lawes Agricultural Trust, Rothamsted Experimental Station, UK.

Goering H.K. and Van Soest P.J. 1970. Forage Fiber Analysis (Apparatus, Reagents, Procedures and Some Applications). Agriculture Handbook 379. ARS (Agriculture Research Service), USDA (United States Department of Agriculture), Washington, DC, USA. 20 pp

McLeod M.N. 1974. Plant tannins - their role in forage quality. Nutrition Abstracts and Reviews 44:803-815.

Nunez-Hernandez G., Wallace J.D., Holechek J.L., Galyean M.L. and Cardenas M. 1991. Condensed tannins and nutrient utilization by lambs and goats fed low-quality diets. Journal of Animal Science 69:1167-1177.

Scalbert A. 1991. Antimicrobial properties of tannins. Phytochemistry 30:3875-3883.

Strachan D.B., Pritchard D.A., Clarke M.R. and O'Rourke P.K. 1988. The Efect of Polyethylene Glycol: Tannin Ratio on Dry Matter Intake and Digestibility of Nulga Leaf by Steers. Queensland Department of Primary Industries, Queensland, Australia.

Walker B.H. 1980. A review of browse and its role in livestock production in southern Africa. In: Le Houerou H.N. (ed), Browse in Africa: Current State of Knowledge. ILCA (International Livestock Centre for Africa), Addis Ababa, Ethiopia. pp. 7-24.

Woodward A. and Reed J.D. 1989. The influence of polyphenolics on the nutritive value of browse: A summary of research conducted at ILCA. ILCA Bulletin 35:2-11. ILCA (International Livestock Centre for Africa), Addis Ababa, Ethiopia.


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