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Sweet thorn (Acacia karroo)

Datasheet

Description
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Common names 

Sweet thorn, cape gum, cape thorn tree, cockspur thorn, deo babool, karroo thorn, karrothorn, mimosa thorn, white-thorn [English], mimosa à longues épines, mimosa hérissé, mimosa odorant, cassie, piquants blancs [French]; Akazie, Süssdorn-, Akazie, Weissdorn [German]; acacia orrida, mimosa karroo [Italian]; doorn boom, doringboom, karoodoring, mookana, soetdoring; witdoring, umuNga [Afrikaans]; aromo de Sudáfrica [Spanish]; isinga [Ndebele]; mookana, mooka [Tswana]; umNga [Xhosa]; umNga, isiKhombe [Zulu]; سنط كارو [Arabic]; آکاکیا کارو  [Farsi]

Synonyms 

Acacia campbellii Arn., Acacia dekindtiana A. Chev., Acacia eburnea sensu auct., Acacia horrida sensu auct., Acacia inconflagrabilis Gerstner, Acacia karoo Hayne, Acacia minutifolia Ragup., Acacia natalitia E. Mey., Acacia pseudowightii Thoth., Acacia roxburghii Wight & Arn., Mimosa eburnea L. f., Vachellia karroo (Hayne) Banfi & Galasso

Taxonomic information 

In the 2000s, molecular phylogenetic studies resulted in the controversial transfer of many Acacia species into the genera Vachellia, Senegalia, Mariosousa and Acaciella, with only Australian species remaining the Acacia genus (Kyalangalilwa et al., 2013). The current accepted taxon of Acacia karroo is thus Vachellia karroo. However, since most of the scientific literature refers to Acacia karroo, this latter taxon is used is the datasheet.

Related feed(s) 
Description 

Sweet thorn (Acacia karroo Hayne or Vachellia karroo (Hayne) Banfi & Galasso) is a very variable and very thorny tree species that is widespread in Africa and grows to a height of 5-12 m. It is a multipurpose tree providing food, feed, commercial products, and environmental services. Livestock and wild animals relish on its foliage, pods and seeds, which do not contain antinutritional factors.

Morphology

Acacia karroo is a very variable, thorny, evergreen or almost evergreen tree that grows to a height of 2-20 (-25) m. It has a rounded crown. The branches emerge rather low on the trunk. The bark is smooth and dark red on young branches, becoming rough or fissured and blackish on the trunk and on old branches. The leaves are alternate, pedunculated, bipinnate, bearing 2-7 pairs of primary pinnae each bearing 5-15 (-27) pairs of leaflets. Very long (up to 17 cm), straight, and conspicuous white spines are borne at the base of the leaf-stalk. The leaflets are 4-7 mm long x 1-3 mm broad. The flower-heads are axillary borne on young shoots and grouped in pompons. They are deep or golden yellow in colour. The flowers are ball-shaped. The fruit is a 18 cm long dehiscent pod, green to brown when mature. It is flat and has a crescent shape, constricted between the seeds. Pods split open at maturity. The seeds are small, 5-8 mm x 3-5 mm long, oblong-elliptic in shape, olive green to brown in colour (CABI, 2018; Aubrey, 2002; US Forest Service, 2018).

Uses

Acacia karroo is a multipurpose tree that can be used for food and feed, and yields useful products. The foliage and the pods are readily eaten by livestock and wildlife. They can be browsed or cut, and are reported to be deprived of antinutritional substances. The tree yields an edible gum similar to arabic gum and useful for candy production. The seeds can be roasted to make a coffee substitute. The flowers are attractive to bees and the long flowering period allows to produce pleasant honey from the nectar. Sweet thorn is a valuable source of fuelwood and charcoal. The timber is used to make posts and pens. The bark yields tannins used for dyeing leather to a reddish colour but also providing an unpleasant odour. The inner bark is used to make ropes. Sweet thorn provides environmental services (see Environmental impact) (Ecocrop, 2019; Fern, 2014; Orwa et al., 2009; Aubrey, 2002).

Distribution 

Acacia karroo is native to South Africa, where it is the most common Acacia (sensu largo) species. It is found from South Africa to Angola, Zambia, Malawi and Mozambique, and in Australia, where it is considered as a weed. Acacia karroo occurs in a wide range of habitats like dry thornveld, river valley scrub, bushveld, woodland, grassland, banks of dry watercourses, riverbanks, coastal dunes and coastal scrub (Ecocrop, 2019. Sweet thorn is found from sea level up to 1000 m altitude. It grows where mean annual temperature is 12-40°C and annual rainfall is ranging from 200 - 1500 mm (Orwa et al., 2009). Acacia karroo grows on most soil types, though it does better on soils with a relatively high fertility such as clay, loam, black hydromorphic vertisols with high pH or deep alluvial soils along the banks of rivers and streams (Ecocrop, 2019; Orwa et al., 2009). It does well in arid environments provided that it can find supply of groundwater. Sweet thorn is very tolerant of cold and resistant to frost down to -10°C, which may cause defoliation but does not kill the trees. Young plants are frost sensitive. Sweet thorn is tolerant to wind, fire and salt spray (Ecocrop, 2019). It is an aggressive pioneer, readily invading degraded or overgrazed areas.It competes for space, water and nutrients with pasture grasses, and may replace them (Orwa et al., 2009).

Processes 

Leaf meal

The making of Acacia karro leaf meal can be a way to limit the proportion of thorns in the feed. This implies cutting small trees or branches, 15 and 30cm above the ground, stacking then up to 1.5 m high on polythene sheets, letting them dry to reach to reach a DM content above 80%, collecting dried leaves by shaking the branches above the propylene sheets and sieving then though a 2-4 mm sieve to discard the thorns. This preparation of leaf meal is labour intensive and less laborious leaf meal harvesting technologies are still sought (Mapiye et al., 2011).

Tannin reduction

Due to the presence of condensed tannins that may have adverse effects on livestock, practical and cost-effective methods to reduce these effects in smallholder farms have been studied (Brown et al., 2016). Sudies based on other tannin-rich legume trees show that while promise, sun-drying techniques may cause losses of water soluble carbohydrates due to plant respiration and Maillard reactions. The storage of leaf meal in bags in well-ventilated shade or storeroom until fed may improve the nutritive value of the forage but this has not been tested for Acacia karroo (Mapiye et al., 2011).

Environmental impact 

Pioneering species

Acacia karroo is a fast growing species that establishes readily in full sunlight and does not need shelter or protection from grass fires. Seed germination might be promoted by fires. Sweet thorn is resistant to heavy grazing, to fire and to frost. Grazing by goats has been suggested for the alleviation of bush encroachment (Dingaan et al., 2018).

Soil improver, erosion control and reclamation

A N-fixing tree, Acacia karroo)improves soil N status. Its roots system improves soil structure, making it more susceptible to infiltration by water (Orwa et al., 2009). In communal areas of Zimbabwe, it is believed that dryland crop yields increase where sweet thorn has grown and been cleared (Orwa et al., 2009). Sweet thorn extracts water from deep underground, and is thus an indicator for underground water (CABI, 2018; Orwa et al., 2009). The development of its canopy benefits to the grass growing under it, as it reduces the temperatures of the soil and provides shade (Dingaan et al., 2018; Orwa et al., 2009). However, while a low tree density improves grass production, high density (>300 trees/ha) is detrimental to it (Stuart-Hill et al., 1987). Sweet thorn is reported to stabilize sand dunes and disturbed areas (CABI, 2018).

Live fence

A very thorny species, sweet thorn can be used as a living hedge (CABI, 2018).

Bush encroachment and invasiveness

Acacia karroo is a pioneering species prone to be responsible for bush encroachment in grasslands and farming land in South Africa. It may thus be detrimental to grass production because of the competition for soil moisture between grass and trees, decreasing the livestock carrying capacity of grassland. In the Molopo area of South Africa, sweet thorn encroachment may have reduced grass production by 30% (Dingaan et al., 2018).

In Australia, sweet thorn is referred to as a noxious weed, requiring notification and destruction in New South Wales, Western Australia and Queensland (US Forest Service, 2018).

Nutritional aspects
Nutritional attributes 

The protein content of Acacia karroo foliage range between 10% and 23% DM (Brown et al., 2016), which meets the N requirements of growing cattle or goats. These values compare favorably with those of other indigenous Acacia species (Mapiye et al., 2011; Mokoboki et al., 2005; Ngwa et al., 2002; Aganga et al., 2000), and is quite high when compared to the 2-5% range observed in most tropical grasses during dry season (Brown et al., 2016). Acacia karroo is thus a valuable a protein supplement for livestock fed low quality forage (Brown et al., 2016; Mapiye et al., 2011).

The fibre content of Acacia karroo leaves is consistent with the fibre contents of leaves from other acacias (Brown et al., 2016; Mapiye et al., 2011; Mokoboki et al., 2005). Acacia karroo leaves contain high proportions of unsaturated fatty acids, and more particularly linolenic acid, compared to other acacias (Mapiye et al., 2011). The mineral content of Acacia karroo leaves is high, with favourable mineral profile (Brown et al., 2016; Mapiye et al., 2011; Halimani et al., 2005Aganga et al., 1998). Contents in Ca, P and Mg are relatively higher than those observed for other Acacias species and they increase during the dry periods (Mapiye et al., 2011; Aganga et al., 2000). Contents of Ca, Mg , Fe and Zn are above the recommended diet contents for beef cattle (Mapiye et al., 2011). Acacia karroo foliage and pods contain reasonably high levels of essential amino acids (Mapiye et al., 2011; Halimani et al., 2005; Ngwa et al., 2002).

Variations in the composition Acacia karroo foliage are caused by differences in populations, soil, climate, season, stage of growth, and browsing pressure. Its nutritive value is higher in young plants in the growing season with fertile soil (Brown et al., 2016; Mapiye et al., 2011; Scogings et al., 2008; Aganga et al., 2000).

Potential constraints 

Thorns

The presence of thorns in Acacia karroo can be a problem for the ingestion of leaves by livestock, which may be alleviated by cutting and sieving it to produce a leaf meal (Mapiye et al., 2011).

Tannins

Acacia karroo contains high levels of condensed tannins, with values between 5.5% and 10% DM (Brown et al., 2016; Mapiye et al., 2011; Mokoboki et al., 2005; Dube et al., 2001), when a 2-8% range is expected to be beneficial to ruminants (Mueller-Harvey, 2006); Mapiye et al., 2011). Condensed tannins of Acacia karroo have been reported to increasing fecal N excretion and decrease N retention in goats, which should be the result of the complexation between tannins and endogenous proteins (Mapiye et al., 2011). The condensed tannins contents of Acacia karroo is expected to be higher in old plants, during the dry season, on low quality soils (Scogings et al., 2008).

Ruminants 

Acacia karroo, like many Acacia species in Southern Africa, is a valuable source of forage for ruminants, particularly during dry periods, when it can provided a significant supply of protein compared to other available forages (Brown et al., 2016; Ngambu et al., 2013; Mapiye et al., 2011; Aganga et al., 2000). However, the presence of thorns and tannins limits its consumption and their adverse effect can be alleviated by feeding young sprouts or leaf meal (Brown et al., 2016; Mapiye et al., 2011).

Digestibility

The DM digestibility and particularly the protein digestibility of Acacia karroo are relatively low compared to those reported for similar browse plants, which may be explained by the presence of phenolic compounds and more specifically condensed tannins (Mapiye et al., 2011; Aganga et al., 1998)..

Beef cattle

For beef production, Acacia karroo leaf meal can be mixed with locally available feed energy sources such as rangeland hay or chopped crop residues, before being distributed into troughs in pens or distributed in the rangeland. It can also be fed to steers each morning before they graze poor quality forages. Alternatively, dried leaves can be ground and used in home based or commercial rations (Mapiye et al., 2011).

Grazing steers (3 to 19 months old) supplemented with Acacia karoo leaf meal, in such a way to insure a supply of 150 g of protein, showed higher body condition score, average daily gain, slaughter weight, cold and warm carcass weights than those that were not supplemented. They also showed increased blood concentrations of total protein, albumin, urea, non-esterified fatty acids, P, Ca, Mg and Fe. Supplementing steers with Acacia karroo leaf meal, rather than supplementing them with sunflower cake or not supplementing them, increased meat protein content, and proportions of α-linolenic acid and its derivative docosapentaenoic acid in meat. In these studies, the growth performance of steers supplemented with Acacia karoo leaf meal remained lower than those of steers supplemented with sunflower cake ( (Mapiye et al., 2009a; Mapiye et al., 2009b).

Goats

Acacia karroo leaves are used to supplement grazing goats, or goats fed with low quality forage (Brown et al., 2016). Goats fed alfalfa hay and supplemented with fresh Acacia karroo leaves included at 40% showed higher growth rates, lower meat pH, higher meat tenderness and higher meat juiciness than goats not supplemented with Acacia karroo (Ngambu et al., 2013; Ngambu et al., 2012). Goats fed a mixture of fresh Acacia karroo sprouts and alfalfa showed a higher average daily gain than goats fed a mixture of lucerne hay and commercial pellets at a feeding level of 3% of body weight. The protein content of fresh Acacia karroo sprouts was higher than that of commercial pellets and the composition of the diets was calculated to meet the metabolizable energy requirements of goats (Nyamukanza et al., 2008).

Control of gastro-intestinal parasites

Acacia karroo foliage has anthelmintic properties in ruminants when fed with at an inclusion rate around 40-50% (Brown et al., 2016; Marume et al., 2012, Mapiye et al., 2011; Xhomfulana et al., 2009; Kahiya et al., 2003). Total fecal egg counts and Haemonchus contortus or Oesophagostomum colombianum worm burdens decreased in grazing steers supplemented with Acacia karroo leaf meal compared with non-supplemented steers or steers supplemented with sunflower cake diet (Xhomfulana et al., 2009). A decrease in fecal egg counts and worm counts was observed in kids infected with Haemonchus contortus larvae and given Acacia karroo whereas the infection progressed in kids not fed Acacia karroo (Marume et al., 2012). The anthelmintic properties of Acacia karroo have been attributed to its high content in condensed tannins and not to other polyphenols. For instance, though it contains less polyphenols than Acacia nilotica, Acacia karoo had higher anthelmintic properties in goats than Acacia nilotica and most of its polyphenols are in the form of condensed tannins (Kahiya et al., 2003).

Pigs 

Feeding Acacia karroo leaf meal at low (10%) inclusion level in the diet of pigs depressed nutrient digestibility, increased endogenous protein secretion and increased the activity of liver enzymes but did not reduce growth rate and was therefore considered as potentially feasible (Halimani et al., 2005; Halimani et al., 2007).

Rabbits 

Feeding a diet containing 4% of Acacia karroo leaf meal to growing rabbits did not result in differences in intake and digestibility. It was concluded that the amount of tannins in the diet was not high enough to have negative effects and that an inclusion rate of 4% was ideal for supplementation (Mashamaite et al., 2009).

Nutritional tables
Tables of chemical composition and nutritional value 

Avg: average or predicted value; SD: standard deviation; Min: minimum value; Max: maximum value; Nb: number of values (samples) used

Main analysis Unit Avg SD Min Max Nb  
Dry matter % as fed 87.3 7.4 72.9 94.5 8  
Crude protein % DM 13.4 3.1 10.6 23.2 15  
Crude fibre % DM 18.2   11.9 25.9 3  
Neutral detergent fibre % DM 46.2 10.5 26.8 56.8 10  
Acid detergent fibre % DM 27.8 9.4 14.6 46.5 10  
Lignin % DM 12.3   7.1 20 4  
Ether extract % DM 2.8   2 3.6 2  
Ash % DM 8.2 3 5.1 15.3 9  
Gross energy MJ/kg DM 18.1       1 *
               
Fatty acids Unit Avg SD Min Max Nb  
Myristic acid C14:0 % fatty acids 3.9       1  
Palmitic acid C16:0 % fatty acids 28.7       1  
Stearic acid C18:0 % fatty acids 9.2       1  
Oleic acid C18:1 % fatty acids 5.8       1  
Linoleic acid C18:2 % fatty acids 16.9       1  
Linolenic acid C18:3 % fatty acids 34.4       1  
               
Minerals Unit Avg SD Min Max Nb  
Calcium g/kg DM 16.3 8.1 3.8 27 7  
Phosphorus g/kg DM 1.3 1 0.08 3.3 7  
Potassium g/kg DM 6.9 4 1.9 12 5  
Sodium g/kg DM 1.49   0.1 3.2 4  
Magnesium g/kg DM 3.3 1.9 0.4 5.3 5  
Manganese mg/kg DM 23   13 32 2  
Zinc mg/kg DM 34 25 2 66 5  
Copper mg/kg DM 12   9 14 3  
Iron mg/kg DM 204 174 15 424 5  
               
Secondary metabolites Unit Avg SD Min Max Nb  
Tannins (eq. tannic acid) g/kg DM 20   10 20 3  
Tanins, condensed (eq. catechin) g/kg DM 40 30 4 80 8  
               
In vitro digestibility and solubility Unit Avg SD Min Max Nb  
In vitro DM digestibility (pepsin) % 49   45 53 2  
In vitro OM digestibility (pepsin) % 45   40 49 2  
In vitro DM digestibility (pepsin-cellulase) % 47   44 48 4  
In vitro OM digestibility (pepsin-cellulase) % 53   48 59 4  
               
Ruminants nutritive values Unit Avg SD Min Max Nb  
OM digestibility, ruminants % 53          
Energy digestibility, ruminants % 50.7         *
DE ruminants MJ/kg DM 9.2         *
ME ruminants MJ/kg DM 7.5         *

The asterisk * indicates that the average value was obtained by an equation.

References

AFZ, 2017; Aganga et al., 2000; Aganga et al., 2008; Groenewald et al., 1967; Halimani et al., 2005; Mapiye et al., 2009; Marume et al., 2012; Matlebyane et al., 2009; Mokoboki et al., 2005; Mokoboki et al., 2011; Mokoboki et al., 2011

Last updated on 09/11/2019 01:31:33

References
References 
Datasheet citation 

Heuzé V., Tran G., Boudon A., Lebas F., 2019. Sweet thorn (Acacia karroo). Feedipedia, a programme by INRA, CIRAD, AFZ and FAO. https://www.feedipedia.org/node/349 Last updated on November 9, 2019, 1:34