Livestock Research for Rural Development 22 (1) 2010 Guide for preparation of papers LRRD News

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A note on the effect of supplementing rangeland grazing with Acacia angustissima mixed with pearl millet on growth performance of goats in a smallholder farming area in Zimbabwe

L Mukandiwa, P H Mugabe*, T E Halimani and H Hamudikuwanda

Department of Animal Science, Faculty of Agriculture, University of Zimbabwe, Box MP167, Mt Pleasant, Harare, Zimbabwe
* Institute of Environmental Studies, University of Zimbabwe, Box MP167, Mt Pleasant, Harare, Zimbabwe


Numerous research efforts have been directed at finding ways to improve feed supply to goats and these have entailed the use of tree legumes as supplementary feeds. However most of the research has been done on stations managed by researchers and the technologies developed have not been adapted to suit farmers in the semi-arid areas. The objective of this study was to test the effect of supplementary feeding Acacia angustissima mixed with pearl millet on goat growth performance on-farm during the dry season in Bubi smallholder farming area, Matabeleland North Province, Zimbabwe. Twenty goats were supplemented with 200 g of a 37.5% Acacia angustissima mixed with 62.5% pearl millet diet in the morning and later released on to the rangeland. A group of twenty goats that solely subsisted on the rangeland was also observed as the control. The goats were weighed every 14 days for 16 weeks to evaluate their response to treatments and discussions were held with farmers to get their comments and suggestions as well as their observations from the experiment.


The average daily weight gain of goats supplemented with Acacia angustissima was 36g/d and significantly higher (P < 0.05) than that of the control goats which was 7g/d. Treatment and time had an interaction (P < 0.05) on the average daily weight gain.


Supplementary feeding improved the growth performance of goats grazing on the rangeland during the dry season.

Keywords: dry season feeding, on-farm, tree legumes, weight gain


Goat production has long been and continues to be of major importance to farmers in the semi-arid areas of Zimbabwe (Ndlovu and Sibanda 1991; Kusina N and Kusina J 1999; Sikosana et al 2002). However, goat production in most of these areas is constrained by the poor quality of the feed consumed (Sikosana et al 2001), particularly during the dry season when the protein content of the pasture falls below 7%. In view of this, numerous research efforts have been directed at finding ways to improve feed supply to goats and these have entailed the use of tree legumes as supplementary feeds (Norton 1994; Dzowela et al 1994; Nherera et al 1998; Hove et al 2001), which have proved to be valuable sources of protein, vitamins and minerals.


Most chemical analyses and feeding trials with ruminants have ranked Leucaena leucocephala and Acacia angustissima as high in crude protein content, and adaptability to local conditions (Devendra 1992; Hove et al 1999; Murungweni 2000; Chakoma et al 2004). Acacia angustissima is a fodder tree with a high potential as a leguminous supplement. It is fast growing and retains green leaf during long dry seasons (Gutteridge 1994). It prefers free draining acidic soils and adapts well to infertile soils. It shows excellent drought tolerance due to its substantial tap root (Fact Net 1999). Acacia angustissima has high nitrogen content (33.2 to 40.8 g/kg Dry Matter) (Dzowela et al 1997; Odenyo et al 1997) and it contains minerals such as sulphur (1.4 g/kg Dry Matter) and phosphorous (1.3 g/kg Dry Matter) (Norton 1994). The agronomic requirements of Acacia angustissima make it highly suitable for the smallholder farming areas which are prone to droughts and are characterized by poor soils. The high mineral nutritional value of Acacia angustissima in terms of nitrogen (N), phosphorous (P) and potassium (K) makes it a potential tool to improve goat performance in the smallholder farming area where it is limited by poor nutrition. However there is not much information on the use of Acacia angustissima in combination with energy sources that are locally and abundantly available in the smallholder farming sector.


Supplying additional protein during the dry season will increase the microbial growth and rate of fibre digestion leading to increased forage intake, thereby improving nutrient absorption for enhanced animal productivity (Norton 1994).  There is also a need to supply additional energy that will allow for the utilization of the additional protein. Traditionally maize has been used as an energy source for livestock (Tewe 2004); however in semi-arid areas the farmers barely have maize to feed themselves let alone animals. Most of the research on supplementary feeding of livestock with tree legumes has been done on stations managed by researchers and the technologies developed have not been adapted to suit farmers in the semi-arid areas.


Under the traditional system of management of livestock in Zimbabwe, goats are allowed to browse around the village during the dry season. During the rainy season when most of the land is under crop production; goats depend on browse found along the roadsides or where they are usually tethered. While this system entails little or no cost to the producer, it has adverse implications on the animals. Inadequate feeding leads to, among other limitations, poor growth rates, late sexual maturity, abortions, long post-partum anoestrus and high kid mortalities. In light of this, Sikhosana and Maphosa (1995) reported that there is an imperative need to improve feed supply. This could entail adoption of the on-station developed, tree legume-based feeding systems.


From the diagnostic surveys conducted in the area of study as a preliminary to this study it was established that most of the farmers were unaware of the tree legume-based feeding technologies, and hence there was poor adoption of the technologies. The few farmers that were aware of the technologies were not convinced that tree legume-based leaf meals could improve the performance of their livestock. Therefore, the objective of this study was to test the effect of Acacia angustissima mixed with pearl millet on bodyweight changes in goats when given as a supplement to natural grazing on-farm and under farmer management.


Materials and methods 

Study site


The survey was conducted in Mbembeswana 1 Ward in Bubi district, a smallholder farming area of Zimbabwe. Bubi District is in Matabeleland North province and is approximately 160 km North of Bulawayo. It lies 19 46' 30" South and 28 46' 30" East. This site is in Agro-ecological Zone IV of Zimbabwe and receives a mean annual rainfall ranging between 450 and 650 mm. It experiences mean minimum and maximum temperatures of 20C and 40C, respectively (Rukuni and Eicher 1994). In Agro-ecological Zone IV the rains are erratic and normally insufficient for crop production (Rukuni and Eicher 1994) and; as a result, the region has a low crop production potential but high livestock production potential, particularly for goat production (Ndlovu and Sibanda 1991).


The vegetation type in these villages is savanna comprising of semi-open woodlands and a mixture of grassland and shrubland. The dominant tree species are Brachystegia spiciformis, Brachystegia boehmii, Terminalia spp., Acacia spp. and Colophospermum mopane. The common grass species are Heteropogon contortus, Panicum maximum and Cynodon dactylon.


Animals and management


Twenty Small East African goats (Matebele type), aged between 1 and 2 years of age and weighing 25.2 0.5kg, distributed equally among ten farmers were used in the feeding trial. Based on information obtained from the farmers in a baseline study in the study area, goats in the age range of 1 to 2 years are nutritionally challenged during the dry season and the farmers find it difficult to feed them. Ten control groups of 2 animals each were also observed during the trial period. The goats were dosed against internal parasites using VALBAZEN (Pfizer Animal Health) and vaccinated against Pulpy Kidney (Enterotoxaemia) a week before the feeding trial. The goats were dipped a week before the feeding trial and once every two weeks during the experiment. They were under farmer management during the entire study period. They were kept in pens and then released onto the rangeland at 1200 hours after they had been fed with the supplementary feed and were brought back into their pens after 1700 hours in the evening.




The study started with a 21-day period during which the animals were adapted to their feed. The goats were given a longer adaptation period than the normal 14 days (AOAC 1990) because they were untrained and it was their first time to be subjected to experiments. They were given rations of 37.5% Acacia angustissima air-dried leaves mixed with 62.5% pearl millet. Acacia angustissima was harvested in January 2006 from the Southern African Development Community- International Centre for Research in Agroforestry (SADC-ICRAF) research plots at Dombosahava Training centre, 25 km northeast of Harare. Dombosahava lies 31 13' E and 17 30' S at an altitude of 1530m. The Acacia angustissima leaves and petioles were harvested at mature stage, air dried in a shed for five days, and stored in polyethylene sacks. Before diet formulations, the leaves and petioles were milled to pass through a 3.5 mm screen. The chemical composition of the diet is shown in Table 1.

Table  1.   Chemical composition of Acacia angustissima, pearl millet and formulated supplementary feed used in the on-farm feeding trial

Proximate constituent, %

Dry matter

Crude protein

Organic matter

Neutral detergent fibre

Acid detergent fibre


Total tannins

Acacia angustissima








Pearl millet








Formulated feed








nd = not determined

Each animal was given 200 g of the supplementary feed and then released onto the rangeland at 1200h after they had been fed with the supplementary feed. Since the farmers did not have scales a practical way of measuring the 200 g was devised. After the researcher had weighed a 200 g ration the farmers found cups of equivalent volume (Figure 1) and thereafter they used the cup in feeding their goats.

Figure 1.  Photograph of cup used by Bubi communal farmers to measure 200 g of the Acacia angustissima + pearl millet supplement

The control group was maintained under the typical management of goats in the study area. They were kept in their pens in the mornings with no feed available and then released onto the rangeland at 1200h.


Data collection


The feeding trial lasted 16 weeks from August to December 2006 and goats were weighed once every two weeks using a spring balance. Discussions were held with farmers to get their comments and suggestions regarding the feeding trial, as well as their observations from the experiment.


Laboratory analysis


Samples of Acacia angustissima, pearl millet and the formulated supplementary diet were analysed for proximate chemical composition of Dry Matter, Crude Protein, Acid Detergent Fibre, Neutral Detergent Fibre and Ash (AOAC 1990). Table 1 shows the chemical compositions of the Acacia angustissima and pearl millet.


Statistical analysis


Repeated measures ANOVA was conducted using the PROC MIXED procedure of SAS (2000) to determine the effect of supplementary feeding with Acacia angustissima mixed with pearl millet on bodyweight changes. The initial bodyweight of the animal was used as a covariate. The statistical model used was:

Yijkl= μ + Ti + Wj + β 1Ik + (T xW)ij +eijkl

Yijkl      = two-weekly bodyweight;

μ          = overall mean common to all observations;

Ti            = fixed effect of diet (I = 1, 2);

Wj          = fixed effect of time (j = 1,…16);

β1            = linear regression coefficient of initial weight on response variable;

Ik            = initial bodyweight (covariate);

(T xW) ij = interaction of diet and time;

eijkl       = random error distributed as N (0, 1σ2E).



Farmers reported that the goats did not readily consume the supplementary feed at the beginning of the adaptation period. They observed that the goats tended to select the pearl millet in the supplementary feed leaving Acacia angustissima. As the adaptation period progressed, the farmers reported improved intake of supplementary feed and by the end of this period the goats were consuming the entire supplementary feed given. The bodyweight gains over time of goats in the supplemented group were numerically higher than those in the control group (Table 2).

Table 2.  Live weights of goats on a rangeland grazing basal diet supplemented with Acacia angustissima mixed with pearl millet as an energy source


1Treatment LS mean

2Control LS mean


P value

Initial weight, kg





Final weight, kg





Average daily gain, g/d





1Treatment =200g of (Acacia angustissima +pearl millet) + rangeland grazing

2Control = Rangeland grazing only

Goats in both the supplemented and control groups gained bodyweight during the study period. However a notable decrease in average daily gain was observed between weeks 10 and 12 for the goats under treatment and between weeks 10 and 14 for goats in the control group (Figure 2).

Figure 2.  LS mean weights of Matebele goats fed to Acacia angustissima mixed
with pearl millet as an energy source during different periods in the dry season

The average daily gains of goats under Acacia angustissima supplementation remained almost constant after week 12 whilst of those in the control continued to decrease. There was a treatment and time interaction (P< 0.05) with the treatment being superior over time.


Farmers commented that providing their goats with supplementary feeding in the morning whilst they were still tethered at home was convenient. It gave the farmers comfort that their goats were not starving or straying into neighbours’ gardens. Farmers reported that the technology was easy for them to adopt, as it required trees, which they could grow, and pearl millet that they had in abundance. The farmers also established small Acacia angustissima nurseries in their gardens with the assistance of the researcher.



The observed interaction of treatment and time could be attributed to changes in rangeland conditions with time as the goats made up for the rest of their feed requirements from the rangeland forage resources. The goat feed calendar for Bubi District (Kindness et al 1999) may be used to account for the decline in magnitudes of average daily gains observed in both groups. According to this calendar feed shortage starts in June and in this month the goats have access to fallen leaves and pods from Acacia tortilis, Acacia nilotica and Dichrostachys cinerea, crop residues in the fields and dry leaves and grass. In July and August fallen leaves and pods are the only sources of feed available. In September and October there is barely any feed available to goats if there are no stored feeds. In November new tree shoots and green grass begin to grow but there is still feed shortage. From December to May there is no feed shortage. Since the goats were released into the rangeland to make up for their feed requirements, it means that as the trial progressed from August to December there was a decline in the feed resource available hence the decline in average daily gain. The observed pronounced decline in growth rate between weeks 10 and 12 coincided with the onset of the flush in grass at the onset of the rains in the study area. Therefore, this decline could be due to consumption of grass low in dry matter. The observed higher growth rates in goats supplemented with Acacia angustissima and pearl millet compared to the goats in the control group support findings of Prasad et al (1995) and Sikosana and Maphosa (1995) who reported that supplementary feeding of goats on rangeland in the semi-arid areas during the dry season supports high growth rates.


The variability observed in this study is too great to be attributed to feed only. It is important to note that this study was undertaken under field conditions which tend to lead to serious variability. Since the goats selected for the study were of more or less the same weight, the observed variation could be attributed to farmer differences.


In this study the utilization of Acacia angustissima mixed with pearl millet as a protein and an energy source was evaluated under farmer management, resources and environment. From the comments and observations of the farmers, this allowed for the assessment of other factors that are likely to influence the acceptability of the technology to the farmer. The farmers’ comments on pearl millet gave an indication of the likelihood of continuity of the technology amongst the farmers based on their resources. The fact that the farmers went on to establish Acacia angustissima nurseries after the feeding trial gives an indication of the appreciation of technology by farmers, the farmers had witnessed the benefits of supplementary feeding with Acacia angustissima. This supports the observations by Shelton (2000) that to improve the uptake of tree-legume based technologies by smallholder farmers, there is need to take the technology to the farmers for them to experience and appreciate the trees.





This project was funded by World Agroforestry Centre (ICRAF) and the Canadian International Development Agency (CIDA). The authors would like to acknowledge the Bubi community and Catholic Relief Services-Bulawayo who made this work possible.



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Received 17 September 2008; Accepted 2 November 2009; Published 1 January 2010

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