The effect of wattle tannin on intake, digestibility, nitrogen retention and growth performance of goats in South Africa

K Bengaly, S Mhlongo* and I V Nsahlai*

Institut d' Economie Rurale (IER), BP 258, Bamako,
konis6@yahoo.com
*School of Agricultural Science and Agribusiness, University of KwaZulu- Natal,
 P/Bag X01 Scottsville, Pietermaritzburg 3209, South Africa
 

Abstract

This study was conducted to determine the effect of wattle tannin extract (WTE) on protein utilisation by goats in a metabolism and a growth trial. Iso-nitrogenous diets (18% CP) with the following ingredients: filler, sunflower cake, molasses, hominy chop, vitamin-mineral mix and lucerne hay were formulated and mixed with 0, 7.5, 15, 22.5 and 30 g WTE/kg dry matter (DM). The diets were fed to goats supplemented with 20% (w/w) native pasture hay.

In the metabolism trial eighteen male (5 Nguni and 13 Boer) goats, within a live weight range of 21.5 to 37.5 kg (with a mean of 28.6, S.D. = 4.88), were blocked by weight and randomly assigned to the five treatment rations. Incremental levels of WTE in the diet resulted to small and non-significant increases (P>0.05) of total intake (g/day) of dry matter (DM) (mean 1089 ± 58.6), organic matter (OM) (mean 902 ± 48.3), and nitrogen (N) (mean 32 ± 1.8) but the intake of neutral detergent fibre (NDF) (mean 351± 17.6) significantly increased linearly (P<0.05) with increasing WTE dosage. The apparent digestibility (g/kg) of DM (mean (661± 17.9) did not change (P>0.05)across treatments. Microbial N supply (g/day) and its efficiency of synthesis were similar across dietary treatments. N digestibility was adversely (P<0.05) affected by the levels of WTE. In response to supplementation with WTE, faecal N (mean 8 ± 0.4 g/day) rose while urinary N excretion (mean 13 ± 1.0 g/day) was not affected, and neither was N retention (mean 10± 0.7 g/day).

In the growth trial, South African indigenous Nguni and Boer goats (n = 26) were used. Goats were about at 8-24 months of age with live weights ranging from 11 to 28 kg (mean 17.8, S.D. = 3.80 kg). Boer goats converted feed significantly more efficiently than Nguni goats (0.21 vs. 0.17 g gain/g feed, P<0.001). These results indicate that WTE given as dietary supplement is unlikely to improve the protein status and therefore growth performance of goats to a considerable degree.

Keywords: Condensed tannin, goat, growth, nutrient digestibility, protein, wattle

Introduction

Two alien wattle species, Acacia dealbata (Silver Wattle) and Acacia mearnsii (Black Wattle) are widely distributed in the Eastern Cape and KwaZulu-Natal provinces of South Africa. The trees are used for the production of timber and tannins, as well as for medicinal purposes (De Neergaard et al 2005). Another alternative use of the wattle, though limited, is as green manure.

Recently, the role of condensed tannins (CT) either directly from forages or as plant extracts has received considerable attention in ruminants nutrition because CT have anti-nutritional effects in addition to their potential ability for improving the supply of protein post-ruminally (Mangan 1988; Reed 1995). In vitro investigations (Bengaly et al 2006) indicated that wattle tannin extract (WTE) could be used to protect protein from degradation in the rumen. But the benefits would depend on the size of the rumen-escape protein pool and the likelihood of tannins during passage in the lower gut.

Tannins have a harsh astringent taste and they can cause a feeling of constriction, dryness and roughness in the oral cavity (Haslam 1979). Because of this property, the presence of tannins in ruminant feeds can negatively affect voluntary food intake. Indeed, an inverse relationship has been found between tannin concentrations in browse sources and voluntary feed intake by herbivores (Kumar and Vaithiyanathan 1990). On the other hand, tannins have been shown to be beneficial at low concentrations, between 20 and 40 g/kg. Such benefits include bloat prevention (Jones and Mangan 1977; Salunke et al 1990; Lees 1992), enhanced rumen-escape protein due to the ability of tannins to bind proteins under the neutral pH conditions but later release these proteins at the acidic pH of the abomasums for subsequent digestion and in the small intestine (Perez-Maldonado and Norton 1996; Waghorn and Shelton 1992). As a result, nitrogen (N) retention and live weight gain may increase in ruminants fed tannin-containing feeds (Nsahlai et al 1999). However, post-ruminal availability of proteins may be hindered if the released CT rebind to those proteins such that N retention may not change or be reduced (Komolong et al 2001).

The objective of this study was to investigate the effect of adding a commercial CT extracted from wattle bark to goat diets on intake, digestibility, nitrogen balance and growth performance.
 

Material and methods

Study site

This study, comprising a metabolism and a growth trial, was conducted at the Ukulinga Research Farm, University of KwaZulu-Natal outside Pietermaritzburg in the subtropical hinterland of KwaZulu-Natal province. It lies at 30^o24'S, 29^o24'E, and approximately 700 m above sea level. The mean annual rainfall is 735 mm, falling mostly in summer, between October and April, and the maximum and minimum mean annual temperatures are 25.7 and 8.9°C, respectively. Light to moderate frost occurs occasionally in winter.

Experimental diets

Five iso-nitrogenous (about 18% crude protein (CP)) dietary treatments (Diets 1, 2, 3, 4 and 5) were formulated to contain 0%, 0.75%, 1.5%, 2.25% and 3% tannin, respectively. Dietary tannin consisted of a commercial condensed tannin (Wattle Bark Industry, South Africa) extracted from wattle bark. Ingredients (except hay) included in these diets (see Table 1) were purchased from NCD, Pietermaritzburg. Hay was obtained from the Ukulinga Research Farm. Mixing of diets was done at the farm. Diet 1 containing 0% CT was mixed first, followed by Diet 5 containing 3% CT. These two diets were then blended in equal portions to constitute Diet 3, which was blended in equal portion in turn with each of Diets 1 and 5 to produce Diets 2 and 4, respectively.

Metabolism trial

Eighteen male (5 Nguni and 13 Boer) goats, aged between 2 to 3 years within a live weight (LW) range of 21.5 to 37.5 kg (with a mean of 28.6, S.D. = 4.88 kg), were used. The animals were purchased from a local farm near Pietermaritzburg. Prior to the start of the experiment goats were drenched against gastro-intestinal parasites. Goats were housed individually in pens. They were blocked on weight and randomly assigned to the 5 dietary treatments. The basal diet consisting of a natural pasture hay was provided at 20%, and the remaining part of the diet (80%) was the treatment rations. The initial feeding level was at 45 g/kg LW (as fed) and the daily feed allowance was proportionately 0.20 in excess of the previous day's consumption in two equal portions at 09:00 and 16:00 h.

The animals were weighed before and at the end of the experiment. The experimental period consisted of a 14-d adjustment period followed by a 7-d collection period. Goats were allowed to adjust to metabolism crates 3 days before data collection. The second batch of goats was moved into the crates after collection of data from the first batch. Goats had free access to water. Food intake was recorded throughout the experiment but only the intake recorded during the 7-d collection period is reported here. Orts were collected every day before the morning meal, weighed and pooled for each animal. For total collection of faeces, goats were fitted with faecal collection bags using harnesses. Urine was collected into plastic buckets over 100 mL of 10% H₂SO₄ to prevent ammonia-N loss. The daily output of faeces from each goat was recorded and 10% sub-sampled, pooled on animal basis and frozen pending chemical analysis. Daily urine for each goat was diluted to 3 L, sub-sampled (150 mL), pooled in a 1-L collection bottle during the 7-d collection period and kept refrigerated. At the end of the collection period urine was thoroughly mixed, sub-sampled (150 mL) and kept frozen until required for analysis.

Urinary excretion of allantoin (Y, mmol/day) was used to calculate microbial purines absorbed (X, mmol/day) from the equation:

Y = 0.84X + (0.150 x W^0.75 x e^-0.25)

where W is animal live weight (kg).

Microbial N supply (g/day) was calculated was calculated using the relationship:

70X/(0.83 x 0.116 x 1000)

Where:

70 is the N content of purines (mg N/mmol),

X is as defined above,

0.83 is the assumed digestibility of microbial purines,

0.116 is the ratio of purine N/total N in mixed rumen microbes and

1000 converts mg to g (Chen and Gomes 1992).

Data were analysed according to a randomized complete block design. They were adjusted for initial live weight by covariance analysis and are presented as adjusted least-square means. Model sums of squares were further partitioned to test linear and quadratic effects of tannins.

Growth trial

This study also took place at the Ukulinga Research Farm for seventy-seven days.

Twenty-six goats (13 Nguni and 13 Boer) between 8 and 24 months of age within a LW range of 11 to 28 kg (with a mean of 17.8, S.D. = 3.80 kg) were used. Goats were purchased from a local farm in Pietermaritzburg. They were drenched against gastro-intestinal parasites prior to starting the experiment.

The experiment was a 5 (Diets) x 2 (goat breeds) factorial arrangement according to a randomised complete block design. Within each breed animals were blocked by weight and randomly assigned to the five dietary treatments. The feeding management was the same as described above.

Data for intake were recorded every week. The average daily intake was calculated for each goat and its average daily feed allowance for the following week was re-calculated as 1.2 times its average intake. Animals were weighed on Friday every week after withholding food for 14 hours.

Chemical analysis

Feeds, faeces and urine were analysed for DM, organic matter (OM) and nitrogen (N) following the standard procedures of AOAC (1990). Urine was also analysed for allantoin (Chen and Gomes 1992). Neutral detergent fibre (NDF), acid detergent fibre (ADF) were analysed according to Van Soest et al (1991). Diets were analysed for tannin (Hagerman and Butler 1982; Martin and Martin 1982; Wisdom et al 1987).

Calculation and statistical analysis

All analyses were done using procedures in SAS (2001). For the growth study average intake was calculated by subtracting refusal per week from feed offered per week. Average weight gain was derived by regressing the weekly live weight on time, in days (the regression coefficient representing the live weight gain (LWG)). Feed conversion efficiency (FCE) was calculated by regressing the weekly live weights on cumulatively weekly intake and intake by time. All variables were adjusted for initial LW before testing for effects of tannin level, breed and tannin x breed interaction.
 

Results

Chemical composition

The dietary range for OM, CP and ADF was narrow but NDF contents increased by 31 g/kg DM in the diets containing the highest levels of tannin (Diet 4 and Diet 5) when compared to Diet1 without tannin (Table 1).

Metabolism trial

Data on intake, digestibility and nitrogen balance are presented in Table 2.

The WTE-fed goats consumed more DM (P<0.05), OM (P<0.05), NDF (P<0.01) and ADF (P=0.08) than the control goats. Increasing levels of WTE did not affect intake of DM but intake tended to increase in a linear fashion for OM, N (P=0.10), and NDF (P<0.05). Incremental feeding of WTE did not cause any changes in the digestibilities of DM, NDF and ADF but resulted to linear decreases in the digestibilities of OM (P=0.07) and N (P<0.05).

Averagely, the tannin-supplemented goats excreted (g/day) more N (P<0.01) via faeces than the control goats but urinary N excretion did not differ (P>0.05) between dietary treatments as neither did N retention. However, when faecal and urinary N were expressed as percentages of N intake, the differences only tended to approach significance (P=0.06) in faecal N output while urinary N excretion linearly declined (P<0.05) with increasing levels of tannin. Urinary allantoin excretion, microbial N (MN) supply from allantoin and efficiency of MN supply were similar (P>0.05) across dietary treatments. Incremental feeding of WTE did not affect any of the above parameters.

Growth trial

Results for the growth trial are presented in Table 3.

Overall, initial live weights were similar for the two breeds of goats (Nguni 15.4 kg; Boer 16.6 kg) final live weights were lower (P<0.05) for Nguni (27.5 kg) compared to Boer goats (32.1 kg). Dietary treatments had no significant (P>0.05) effect on daily total DMI, live weight gain and feed conversion efficiency. There was no significant (P>0.05) breed x treatment interaction for the above parameters. The tendency for live weight gain to decrease with increasing level of tannin supplementation was more pronounced in Nguni goats compared to Boer goats. Consequently, Boer goats had higher weight gains (214 vs. 162 g/day, P<0.01) and converted feed significantly more efficiently than Nguni goats (0.21 vs. 0.17 g gain/g feed, P<0.001)
 

Discussion

Fibre, especially NDF contents increased in the tannin-treated samples compared to the non-treated ones (Table 1). Makkar et al (1995) indicated that the major difficulty encountered in fibre analysis of tannin-containing feeds using the detergent method is the presence of tannin-protein complexes. These complexes are insoluble and can appear in the fibre fraction during analysis (Van Soest et al1987), which taken together with the observation by Makkar et al (1995) could explain why added WTE inconsistently increased the NDF content.

It has been suggested that condensed tannins may have a detrimental effect on animal's appetite when present in the diet at concentrations more than 3% (Provenza 1995). In the present study, WTE was added in the diet at a maximum level of 3%, and voluntary intake of food was not altered. In contrast, Mbatha (2001) observed reduced voluntary intake when goat diets contained more than 5% of WTE. The increased intake of WTE-supplemented diet (Table 2) is also in agreement with the hypothesis promoted by previous reports (Nsahlai and Umunna 1997; Nsahlai et al 1999) that when the diet is non-limiting in protein, an advantageous interaction between free condensed tannins and protein would result in higher intakes of nutrients, hence, higher performance. Our diet contained 19% CP (Table 1). Similarly, in the study reported by Athanasiadou et al (2001) sheep given a high protein diet (18.8% CP) supplemented with Quebracho tannin extract consumed more food than the control animals. The authors suggested that the increased intake in the tannin-supplemented sheep could be a mechanism to compensate for dietary or endogenous protein loss caused by tannins. However, the similarity between dietary treatments in voluntary food intake observed in the growth trial (Table 3) of this study, in contrast to results of the metabolism trial (Table 2), does not seem to support this theory. Probably goats used in the growth trial which had a low initial weight (mean = 15.6 kg), thus, a higher responsiveness to the feeding regimen, could not "cope" to a greater extent with the endogenous loss of protein compared to goats of the metabolism trial with a high initial weight (mean = 28.6 kg). Further studies are required to determine unequivocally the impact of WTE on goat response.

Higher intakes of NDF were associated with lower digestibility values for N and increased faecal N output in goats given the tannin-containing diets compared to the control animals. Although tannins may have increased the residue determined as fibre, as discussed above, it is a well-known fact that increased intake can elicit increased passage and greater escape will depress digestibility. Since intake of N tended to increase among the levels of WTE, faecal and urinary losses were expressed as percentages of N intake (Nunez-Hernandez et al 1989). The data showed slightly increased faecal and reduced urinary N losses with increasing levels of tannin. These results accord with several studies on the influence of tannin on nutrient utilization by ruminants. Nunez-Hernandez et al (1989), Kaitho et al (1998), Dawson et al (1999), Komolong et al (2001) all pointed out that condensed tannins from foliage or of exogenous origin undoubtedly reduced apparent N digestibility, increased faecal N and reduced urinary N excretion. Mbatha (2001) reported similar results in goats using WTE.

Tannins are well-known for their ability to protect protein from degradation in the rumen either by forming complexes with dietary protein or by reducing the activities of microbial proteases. Urinary allantoin excretion was used to estimate microbial protein supply (Chen et al 1992). The values obtained in this study are similar to those reported by Ngwa et al (2002) in sheep given veld hay supplemented with dry meal or silage from pods of Acacia sieberiana with or without wheat bran. Although the levels of WTE had no significant effects on urinary excretion of allantoin and hence microbial protein synthesis, the yields of 14-18 g MN per kg of organic matter apparently digested in the rumen (DOMR) fall within the desired range of 14-49 g/kg DOMR reported by ARC (1984). The efficiency of microbial N supply should have increased with increased DM intake (Chen et al 1992) in the WTE-containing diets compared to the control but it was not the case in this study. Nevertheless, the positive values and the tendency for the retained N to increase with increasing levels of WTE indicate that tannin supplementation met the animals' needs for maintenance.
 

Conclusion

• Dietary inclusion of wattle tannin did not adversely affect palatability, as intake by goats was comparable to or actually exceeded that of untreated diet. Feeding wattle tannin resulted in higher faecal N excretion and lower N digestibility.

• There was no effect on live weight gain and South African Indigenous Nguni goats appear to be affected the same way by condensed tannins as Boer goats which grew faster.

• More research is required that evaluates goat breed and/or age differences, and wattle tannin under different feeding strategies (e.g. restricted versus ad libitum feeding).
   

Acknowledgments

The first author was a Postdoctoral Fellow at the University of KwaZulu-Natal. Financial support from the National Research Foundation (NRF), GUN 2054055, South Africa is acknowldged. We also acknowledge the assistance from the staff of the Animal Science Department Laboratory and from the Livestock Section at Ukulinga Research Farm.
 

References

AOAC 1990 Official Methods of Analyses, 15^th edition. Association of Official Analytical Chemists, Washington, DC

ARC 1984 The Nutrient Requirements of Ruminant Livestock: Supplement 1. Commonwealth Agricultural Bureaux, Slough, UK.

Athanasiadou S, KyriazakisI, Jackson F and Coop R L 2001 The effects of condensed tannins supplementation of foods with different protein content on parasitism, food intake and performance of sheep infected with Trichostrongylus colubriformis. British Journal of Nutrition 86, 697-706

Bengaly K, Mhlongo S and Nsahlai I V 2006 Influence of wattle tannin on nitrogen utilization by goats. 41^st Congress of South African Society for Animal Science (SASAS), 3-6 April 2006, Bloemfontein, Odeion, University of the Free State, South Africa.

Chen X B and Gomes M J 1992 Estimation of microbial protein supply to sheep and cattle based on urinary excretion of purine derivatives- an overview of the technical details. International Feed Resource Unit, Rowett Research Institute, Bucksburn, Aberdeen, UK. Occasional Publication.

Chen X B, ChenY K, Franklin M F, Brskov E R andShand W J 1992 The effect of feed intake and body weight on purine derivative excretion and microbial protein supply in sheep. Journal of Animal Science 70, 1534-1542 http://jas.fass.org/cgi/reprint/70/5/1534

Dawson J M, Buttery P J, Jenkins D, Wood C D and Gill M 1999 Effects of dietary quebracho tannin on nutrient utilisation and tissue metabolism in sheep and rats. Journal of Science Food and Agriculture 79, 1423-1430

De Neergaard A, Saarnak C, Hill T, Khanyile M, Martinez Berzosa A and Birch-ThomsenT 2005 Australian wattle species in the Drakensberg region of South Africa-An invasive alien or a natural resource? Agricultural Systems 85, 216-233

Hagerman A E and Butler L G 1982 Condensed tannin purification and characterization of tannin-association protein. Journal of Agriculture Food Chemistry 28, 947-952

Haslam E 1979 Vegetable tannins. In Biochemistry of plant phenolics (editors: T Swain, J B Harborne and C Van Sumere), pp. 475-523. Plenum London

Jones W T and Mangan J L 1977 Complexes of the condensed tannins of sainfoin (Onobrychis vicifolia scop) with fraction of leaf protein with submaxillary mucoprotein and their reversal by polyethylene glycol and pH. Journal of Science Food and Agriculture 28, 126-136

Kaitho R J, Umunna N N, Nsahlai I V, Tamminga S and van Bruchem J 1998 Utilization by sheep of browse supplements with varying tannin levels Utilization of browse supplements with varying tannin levels by Ethiopian Menz sheep: 2. Nitrogen metabolism. Agroforestry Systems. 39, 161-173

Komolong M K, Barber D G and McNeill D M 2001 Post-ruminal protein supply and N retention of weaner sheep fed on a basal diet of Lucerne hay (Medicago sativa ) with increasing levels of quebracho tannins. Animal Feed Science and Technology 92, 59-72

Kumar R and Vaithiyanathan S 1990 Occurrence, nutritional significance and effect on animal productivity of tannins in tree leaves. Animal Feed Science and Technology 30, 21-38

Lees G L 1992 Condensed tannins in some forage legumes: Their role in the prevention of ruminant pasture bloat. In Plant polyphenols (editors: R W Hemingway and P E Laks), pp. 915-934. plenum, New York

Makkar H P S, Blummel M and Becker K 1995 Formation of complexes between polyninylp pyrrolidone or polyethylene glycol and tannins, and their implication in gas production and true digestibility in in vitro techniques. British Journal of Nutrition 73, 897-913

Mangan J L 1988 Nutritional effects of tannins in animal feeds. Nutrition Research Reviews 1, 209-231

Martin J S and Martin M M 1982 Tannin assays in ecological studies: lack of correlation between phenolics, proanthocyanidins and protein-precipitating constituents in mature forages of six oak species. Oecologia 54, 205-211

Mbatha K R 2001 The effects of tannin ingestion on the physiology of Boer goats. MSc thesis, University of Natal.

Ngwa A T, Nsahlai I V and Iji P A 2002 Effect of supplementing veld hay with a dry meal or silage from pods of Acacia sieberiana with or without wheat bran on voluntary intake, digestibility, excretion of purine derivatives, nitrogen utilization, and weight gain in South African Merino sheep. Livestock Production Science 77, 253-264

Nsahlai I V, Umunna N N and Osuji P O 1999 Influence of feeding sheep on oilseed cake following the consumption of tanniferous feeds. Livestock Production Science 60, 59-69.

Nsahlai I V and Umunna N N 1997 Is it beneficial to sequence the intake of oilseed cake following that of tanniferous feeds? South African Society of Animal Science-KwaZulu-Natal Branch Symposium: Animal Science Research in KwaZulu-Natal, 14 August 1997. Cedara p.37

Nunez-Hernandez G,Holechek J L, Wallace J D, Galyean M L, Tembo A, Valdez R and Cardenas M 1989 Influence of native shrubs on nutritional status of goats: nitrogen retention. Journal of Range Management 42, 228-232

Perez-Maldonado R A and Norton B W 1996 The effects of condensed tannins from Desmodium intortum and Calliandra calothyrsus on protein and carbohydrate digestion in sheep and goats. British Journal of Nutrition 76, 515-533

Provenza F D 1995 Postingestive feedback as an elementary determinant of food selection and intake in ruminants. Journal of Range Management 48, 2-17

Reed J D 1995 Nutritional toxicology of tannins and related polyphenols in forage legumes. Journal of Animal Science 93, 1516-1528 http://jas.fass.org/cgi/reprint/73/5/1516

Salunke D K, Chavan J K and Kadam S S 1990 Dietary tannins: Consequenses and Remedies. CRC Press, Boca. Raton, F.L.

SAS 2001 Procedures Guide: version 9.1. Statistical Analysis Systems Institute, Cary, NC.

Van Soest P J, Conklin N L and Horvalt P J  1987 Tannins in foods and feeds. In: Cornell Nutrition Conference for Feed Manufacturers. Departments of Animal Science and Avian Science, Cornell University, New York, pp.115-122

Van Soest P J, Robertson J B and Lewis B A 1991 Methods of dietary fibre, neutral detergent fibre and non-starch monosaccharides in relation to animal nutrition. Journal of Dairy Science 74, 3583-3597 http://jds.fass.org/cgi/reprint/74/10/3583

Waghorn G C and Shelton I D 1992 The nutritive value of Lotus for sheep. Proc. New Zealand Society of Animal Production 52, 89-92

Wisdom C S, Gonzalez-Coloma A and Rundel P W 1987 Ecological tannin assays. Evaluation of proanthocyanidins, protein binding assays and protein precipitating potential. Oecologia 72, 395-401

Received 19 November 2006; Accepted 23 February 2007; Published 2 April 2007

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