J Macala 1, B. Sebolai 1 and R R Majinda 2
1 Department of Agricultural Research
Animal Production Research Unit
Private Bag 0033, Gaborone, Botswana2 Department of Chemistry
University of Botswana
Private Bag 0022, Gaborone, Botswana
ABSTRACT
Livestock in Botswana depend on natural rangelands for feed during both wet and dry seasons. Indigenous browse plants providing feed for livestock include leguminous types such as Acacia nilotica and nonleguminous types such as Colophospermum mopane. The mopane tree has long roots which enable it to extract moisture at great depth: because of this ability the plant breaks dormancy and produces fresh green leaves before the rainy season. During the dry season and drought years, mopane trees bear pods with seeds and these, together with the dry mopane leaves, are consumed by livestock.
Cereal stovers are used to feed livestock during the dry season in certain areas of Botswana. Because cereal stovers are low in crude protein, digestible energy and mineral content, livestock farmers grow lablab (Lablab purpureus), a legume fodder crop, to feed in association with crop residues in the dry season.
A dietary selection study on goats showed that the crude-protein content of the plant material browsed in May, June and July was about 11.5%, compared with about 9% in August. The average dry matter of the plant material browsed in June, July and August was 93% compared with 84% in May. Liveweights of animals dependent on browse plants during the dry season remained constant.
Differences in the apparent digestibilities of dry matter, crude protein and organic matter found in a nutrient digestibility study with goats were highly significant (P<0.001). There was a wide variation in the feed value of the dry mopane leaves offered to the animals.
Fresh green mopane leaves contain more polyphenolic compounds and condensed tannins than dry mopane leaves.
Average liveweight change and daily gain for steers fed sorghum stover with lablab hay were higher (P<0.001) than those of steers fed sorghum stover alone or with dry mopane leaves. The average cold dressed weight for Bonsmara steers fed stover with lablab hay was higher (P<0.05) than for Bonsmara steers fed stover alone or stover with mopane leaves. The poor performance of steers fed stover with dry mopane leaves could be due to poor condition of the plant material and/or to using steers that were not used to browsing the mopane plant.
RESUME
Utilisation de fourrage de Colophospermum mopane et de paille de sorgho dans l'alimentation des ruminants au cours de la saison sèche au Botswana
Que ce soit au cours de l'hivernage ou pendant la saison sèche, l'essentiel des aliments du bétail utilisés au Botswana proviennent des ressources pastorales naturelles. Les espèces ligneuses locales qui entrent dans l'alimentation du bétail sont, entre autres, des légumineuses (exemple: Acacia albida) et d'autres espèces végétales comme Colophospermum mopane. Avec ses longues racines, ce ligneux peut aller chercher l'eau à des profondeurs insoupçonnées, ce qui lui permet d'éviter le phénomène de dormance et de produire des feuilles vertes avant le début de la saison des pluies. Au cours de la saison sèche, Colophospermum mopane porte des gousses avec des graines, lesquelles sont consommées par les animaux au même titre que les feuilles mortes.
La paille de céréales entre également dans l'alimentation des animaux d'élevage dans certaines régions du Botswana Etant donné que la paille est pauvre en protéines brutes, en énergie digestible et en matières minérales, elle est complémentée en saison sèche par du foin de Lablab purpureus, une légumineuse cultivée sur place par les éleveurs.
Des analyses ont révélé que le taux de protéines brutes des ligneux broutés par les caprins était d'environ 11,5% en mai, juin et juillet contre 9% en août. Quant à leur teneur en matière sèche, elle était en moyenne de 93% en juin, juillet et août contre 84% en mai Les animaux se nourrissant de ces ligneux au cours de la saison sèche parvenaient à maintenir un poids relativement constant.
Une étude de digestibilité des éléments nutritifs effectuée sur des caprins a permis de mettre en évidence des différences hautement significatives (P<0,001) entre les taux de digestibilité apparente de la matière sèche, les teneurs en protéines brutes ou les taux de matière organique. Par ailleurs, d'importantes différences ont été enregistrées dans la valeur nutritive des feuilles sèches de Colophospermum mopane.
De même, les feuilles vertes contenaient plus de composés polyphénoliques et de tanins que les feuilles sèches.
Les variations et les gains moyens de poids des boeufs soumis à un régime composé de paille de sorgho complémentée avec du foin de Lablab purpureus étaient plus élevés (P<0,001) que ceux des animaux recevant de la paille de sorgho associée ou non à du fourrage de Colophospermum mopane. Chez les boeufs Bonsmara, un régime composé de paille complémentée avec du foin de Lablab purpureus se traduisait par un poids moyen de la carcasse refroidie supérieur (P<0,05) à celui associé à un régime constitué de paille complémentée ou non avec des feuilles de Colophospermum mopane. Les performances médiocres liées à la complémentation avec des feuilles sèches de Colophospermum mopane pourraient s'expliquer par le piètre état du matériel végétal utilisé et/ou le fait que les boeufs de cette expérience n'avaient guère l'habitude du fourrage de Colophospermum mopane.
INTRODUCTION
There are several species of indigenous trees in Botswana which provide feed for both game and livestock, especially during dry seasons and drought years. Browse plants provide the bulk of the protein, vitamins and mineral elements which are normally lacking in grasses during the dry season (le Houérou, 1980).
Colophospermum mopane trees, which have formed a distinctive vegetation in the mopane veld area, provide feed for livestock during dry seasons and drought years. Livestock browse mopane leaves when they turn reddish-brown in colour, at which time their crude-protein content averages about 11%. Fresh green mopane leaves have higher crude-protein content (almost 13%) but they are not eaten as readily by livestock as the reddish-brown leaves. Fresh mopane has low pH (4.83-5.05) and a bitter taste, which might contribute to its low acceptability by livestock (Ernst and Sekhwela, 1987). Furthermore, during the time when the mopane leaves are still green, natural grasses are abundant, and livestock prefer to graze rather than browse. Also, antinutritional factors such as tannins and polyphenolics may be present in high concentration in fresh mopane and may reduce its intake by livestock. Polyphenolic compounds and tannins in browse affect intake, digestibility and animal performance by reducing degradation of fibre and protein by rumen micro-organisms.
During the dry season C. mopane plants bear pods with seeds which contain 15-16% crude protein and are readily eaten by livestock. The mopane plant has long roots which enable it to extract moisture at great depths. Because of this ability, the mopane plant breaks dormancy and produces fresh green leaves before the rainy season, and therefore provides fodder for ruminants during the periods of grass shortage.
The importance of goats and cattle to Botswana's economy, and of browse plants to these animals during the dry season and drought years, justifies conducting studies to determine the nutritive value and goats' selection patterns of browse plants. Utilisation of dry mopane leaves and lablab (Lablab purpureus) hay as dry-season supplementary feeds for beef steers fed sorghum stover was investigated. The objectives of the studies were to:
· assess antinutritional factors in fresh and dry mopane leaves· determine the nutritive value of goats diets
· evaluate the effect of feeding dry mopane leaves with sorghum stover on nutrient digestibility by goats
· evaluate the performance of beef steers fed sorghum stover with mopane dry leaves or lablab hay as supplementary feeds during the dry season.
MATERIALS AND METHODS
The sorghum (Sorghum bicolor) stover used in the goat nutrient digestibility and steer performance studies was obtained from Sebele Agricultural Research Station fields: it was chopped through a 10-cm size screen using a forage harvester, left on the fields for two weeks to dry, and then piled together to prevent loss of nutrients through leaching. Fresh and dry mopane leaves were hand picked from Lesego Government Research Ranch in north-east Botswana. Lablab hay was grown and harvested from Sunnyside Research Station farm.
Experiment 1
A study of goat diet selection patterns was conducted at Lesego Government Ranch The ranch covers an area of about 3990 ha, of which two 200-ha paddocks, each with a similar vegetation cover, were used for the experiment. There are several varieties of browse plants on Lesego ranch, but its vegetation is classified as mopane mixed tree and shrubland. Four castrated male Tswana goats (average initial liveweight 62 kg), fitted with an oesophageal fistula, were used in the study. One day before sampling, animals were kraaled at 1200 hours to starve them so as to increase their intake of the browse plants during the sampling period. At 0800 hours on the day of sampling, the fistula plugs were removed and each animal was fitted with a collection bag around its neck. Sampling was done monthly for four months during the dry season (May to August). At least two samples for each goat were collected each month. Sampling time was about 30-40 minutes and this was preceded by removal of the sampled plant material from the collection bag into plastic bags kept on dry ice to prevent further changes by plant enzymes. After sampling the fistula plugs were refitted and the goats were transferred to the paddock not used for sampling. The browsed samples for each individual goat were freeze-dried, the ratio of browse plants/pods with seeds of the dried browsed plants was determined, and the dried plant material was then ground through a 1-mm screen for chemical analysis.
Experiment 2
A second study with goats was conducted to investigate nutrient digestibility. Three groups of four Tswana goats (average initial liveweight 55 kg) were randomly assigned to one of three diets:
· 540 g sorghum stover per day (diet 1)
· 407 g sorghum stover + 133 g mopane dry leaves per day (diet 2)
· 280 g sorghum stover + 260 g mopane dry leaves per day (diet 3).
The experimental regimen consisted of an ad libitum intake period of 18 days, followed by a five-day adjustment period to the feeding levels of the three experimental diets.
Each animal also received (at 0800 hours each day) 260 g of concentrate supplement containing 50% lablab leaves, 45% sorghum bran and 5% mineral mix (dicalcium phosphate and salt (1:2)). The chemical composition of the supplement was:
· dry matter: 94.04%
· crude protein: 1335% of dry matter
· organic matter: 79.97% of dry matter
· ash: 20.03% of dry matter
· crude fibre: 11.23% of dry matter
· ether extract: 11.81% of dry matter
· nitrogen-free extract: 358% of dry matter
All animals were kept in metabolic crates during both the voluntary feed intake and nutrient digestibility periods and were weighed at the start and end of the experiment.
Weights and samples of feed offered and refused were taken daily during the last seven days of the voluntary intake and nutrient digestibility period. Urine and faeces were also collected daily from each animal during the digestibility study. Samples of feeds offered and refused and of faeces were ground through a 1-mm screen and analysed for dry matter and nitrogen by standard methodology (AOAC, 1980). Crude fibre was determined using a Fibertec System M (#1020 Hot Extrator). Ether extract was determined using the Soxtec System HT6 (#1043 Extraction Unit). Neutral and acid detergent fibre were determined on the browsed plant material using the method of Goering and Van Soest (1970). Lignin was determined using the 72% suphuric acid procedure (Goering and Van Soest, 1970). A quantitative analysis for polyphenolic compounds and condensed tannins was done on both the fresh and dry mopane leaves using the procedure outlined by Marini-Bettolo (1980).
Experiment 3
The effect of dry mopane leaves and lablab hay as supplementary feeds for beef steers fed sorghum stover during the dry season is being evaluated in an on-going study.
Three groups of three Tswana and three Bonsmara steers (average initial liveweight 385 kg) were randomly assigned to one of three diets:
· 50% sorghum stover + 50% mopane dry leaves (diet 1)
· 70% sorghum stover + 30% lablab hay (diet 2)
· sorghum stover alone (diet 3)
All animals were also offered dicalcium phosphate and salt (1:2) ad libitum. The amount of feed offered to the animals was calculated based on the average body size of the animals.
Animals were dipped every two weeks to control external parasites and were weighed monthly. At the end of the experimental period (90 days) animals were sent to the Botswana Meat Commission (BMC) for slaughter and the carcasses were graded according to standard procedures.
Samples of feeds offered and refused were taken daily during the first seven days of each month for a period of 90 days. The feeds were analysed for dry matter and nitrogen by standard methods (AOAC, 1980). Neutral and acid detergent fibre were analysed using the method described by Goering and Van Soest (1970). Lignin was determined using the 72% suphuric acid procedure (Goering and Van Soest, 1970). In vitro organic matter digestibility was measured using the Tilley and Terry (1963) procedure. The rumen fluid used in the in vitro procedure was collected from two steers fed lablab and grass hay.
RESULTS
Experiment 1
The ratio of browsed plant material and pods with seeds found in the collection bags of goats during the months of June and July was equal. The pods with seeds were mainly of Dichrostachys cinera (Moselesele) and small quantities of Acacia nilotica (Moka). Monthly chemical analyses of the browsed plant material are presented in Table 1. Average dry-matter content of goats' extrusa samples was lowest in May, while crude-protein content and in vitro organic matter digestibility were lowest in August.
Table 1. Monthly chemical analysis of plant material browsed by goats at Lesego Ranch
|
|
Chemical composition (% DM) |
|||
|
May |
June |
July |
August |
|
|
Dry matter |
84.00 |
93.00 |
93.00 |
93.77 |
|
Crude protein |
12.00 |
10.98 |
11.49 |
9.07 |
|
Neutral detergent fibre |
38.41 |
39.96 |
38.24 |
38.27 |
|
Acid detergent fibre |
27.21 |
29.97 |
26.58 |
27.52 |
|
Lignin |
12.03 |
12.45 |
11.09 |
11.99 |
|
Calcium |
1.57 |
1.11 |
1.62 |
1.48 |
|
Phosphorus |
0.18 |
0.27 |
0.18 |
0.20 |
|
In vitro organic-matter digestibility |
- |
- |
58.25 |
45.23 |
Experiment 2
In the digestibility trial, substituting dry mopane leaves for stover increased the crude-protein content and the total digestible nutrients of diets 2 and 3 over the control diet (Table 2). The digestibilities of nutrients in goats fed diet 3 were higher (P<0.001) than those in goats fed diet 1 or 2 (Figure 1).
The concentration of condensed tannins was higher in fresh than in dry mopane leaves.
Average liveweights of the goats were 68 kg in May, 70 kg in June and July and 67 kg in August.
Table 2. Chemical composition and total digestible nutrients of diets fed to goats in the nutrient digestibility trial
|
Ingredients |
Chemical composition (% DM) |
||
|
Diet 1 |
Diet 2 |
Diet 3 |
|
|
Dry matter |
95.02 |
95.07 |
95.07 |
|
Crude protein |
6.48 |
8.55 |
10.62 |
|
Organic matter |
82.87 |
85.25 |
86.78 |
|
Ash |
17.13 |
14.75 |
13.22 |
|
Ether extract |
9.28 |
14.25 |
14.25 |
|
Crude fibre |
22.52 |
21.78 |
21.09 |
|
Neutral detergent fibre |
44.59 |
40.67 |
40.82 |
|
Total digestible nutrients |
43.69 |
66.15 |
67.41 |
Experiment 3
The chemical analysis of the diets given to the animals is presented in Table 3.
Average daily dry-matter intakes were 31.17, 49.17 and 43.80 kg for animals fed stover + mopane, stover + lablab hay and stover alone, respectively. There were differences (P<0.001) in the liveweight changes and average daily gains of the animals offered the experimental diets, and in the cold dressed carcass weights of Bonsmara steers (P<0.05) (Table 4).
Two carcasses of steers that were fed stover alone and one carcass of a steer fed stover and dry mopane leaves were condemned at BMC because of cysticercus bovis.
DISCUSSION
The lower crude-protein and higher DM content obtained in browsed plants sampled in August confirms that plant material deteriorates in quality as the dry season progresses. Subsequently, the performance of animals dependent on this plant material is affected. In the tropics, animals need a diet of 7% crude protein and 45% dry matter digestibility to maintain their liveweight. Animals fed a diet with the 10-11% crude protein and 55% DMD are expected to gain weight (McDowell, 1972). In this experiment, the average liveweights of the goats remained constant in May, June and July and dropped slightly in August. The decrease in liveweight of the goats in August may be attributed to the decrease in crude protein and increase in DM of the plant material eaten by the goats. The lignin content of the sampled plants during the dry season was similar and high. Previous studies comparing the digestive efficiency of goats, sheep and other ruminants have shown that goats are more efficient in digesting crude fibre (Devendra, 1986; ILCA, 1988). The greater efficiency for goats to digest fibre is associated with the intake of poor quality roughages, the feeding behaviour, concentration of celluotic bacteria and rate of feed movement along the alimentary tract (Devendra, 1986).
Figure 1. Nutrient digestibility by diet
Table 3. Ingredients and chemical composition of the diets fed to steers
|
Ingredient |
Chemical composition (% DM) |
||
|
Diet 1 |
Diet 2 |
Diet 3 |
|
|
Dry matter |
93.76 |
93.44 |
93.52 |
|
Crude protein |
7.86 |
10.06 |
5.57 |
|
Neutral detergent fibre |
52.16 |
65.54 |
69.90 |
|
Acid detergent fibre |
33.31 |
41.98 |
41.35 |
|
Lignin |
6.38 |
6.00 |
4.80 |
|
In vitro dry-matter digestibility |
45.1 |
59.46 |
49.15 |
Table 4. Liveweight changes, daily gains and cold dressed carcass weights of beef steers fed sorghum stover + mopane leaves, stover + lablab hay and sorghum stover alone during the dry season
|
Parameters |
Diet 1 |
Diet 2 |
Diet 3 |
SE | |
|
Initial mean liveweight (kg) |
384 |
385 |
385 |
ns | |
|
Final mean liveweight (kg) |
404 |
436 |
402 |
22.0 | |
|
Change in liveweight (kg) |
18 |
51 |
17 |
6.66 | |
|
Average daily gain (g) |
200 |
566.7 |
188.2 |
52.65 | |
|
Cold dressed weight (kg) |
|
|
|
| |
|
|
Tswana |
166 |
168 |
158 |
ns |
|
|
Bonsmara |
168 |
191 |
168 |
|
Even though a significant increase in the digestibility of nutrients was found in goats fed diet 3, this increase was due mainly to the high proportion of concentrate supplement fed with the stover. There was a high degree of variation in the crude-protein, calcium and phosphorus content in the dry mopane leaves offered to the goats during the nutrient digestibility study (Table 5): this variation may be due to picking mopane leaves that may be low in feed value even though still attached to the plant. Mopane and other browse plants selected by the goats during the dietary selection study had crude-protein contents higher than the 7% suggested for liveweight maintenance (McDowell, 1972). This therefore indicates that goats are able to select nutritious plant material. However, the overall productivity of these animals dependent on browse plant during the dry season can be improved by providing them with locally available supplementary feeds such as sorghum bran, sorghum chaff and a mineral supplement. The higher concentration of condensed tannins in fresh than in dry mopane leaves suggests that these antinutritional factors have a contributory effect on the intake of fresh mopane leaves by animals. Research work on the quantitative and qualitative analysis of both the fresh and dry mopane leaves is necessary in order to make any recommendations on the efficient utilisation of the mopane plant for livestock feeding during the dry season and drought periods.
Table 5. Percentage crude protein, calcium and phosphorus of Colophospermum mopane plant offered to goats at Lesego Government Ranch during the dry season
|
Nutrient |
Content (% DM) |
|||
|
May |
June |
July |
August |
|
|
Crude protein |
10.53 |
9.01 |
9.23 |
8.97 |
|
Calcium |
1.74 |
1.42 |
1.45 |
1.40 |
|
Phosphorus |
0.19 |
0.15 |
0.14 |
0.14 |
The average daily gain of 0.566 kg obtained for steers supplemented with lablab hay was due to the high intake of lablab hay and agrees with the results of McDowell (1972) that animals given a diet with 10% crude protein and 55% DMD can gain 0.5-0.6 kg per day. The high average liveweight change, daily gain and cold dressed weight obtained with steers supplemented with lablab hay was mainly due to the better performance of the Bonsmara animals; these increased their liveweight by 21% compared to 12% for Tswana steers fed the same diet. The better performance of Bonsmara cattle indicates that animals with a high genetic potential can perform better under improved management. Utilisation of cereal crop stovers with lablab hay for cattle feeding in the dry season is a new intervention which has been adopted by a number of livestock farmers in Botswana, especially dairy producers. However, appropriate technology for harvesting, conservation and utilisation of the lablab crop is needed if it is to be used efficiently as a livestock feed.
It is generally accepted that tree forage improves livestock performance when fed in combination with cereal residues (Agishi, 1988). However, in this experiment, dry mopane leaves were poorly accepted compared with lablab hay. The poor acceptance of the dry mopane leaves could have been due to poor condition of the plant material and/or to using steers that were not used to browsing the mopane plant. More research work is being planned with the mopane plant and with other browse plants that provide fodder for livestock during the dry season and drought years when there is no grass available for livestock feeding.
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