SESSION 3
(a) RESOURCES - FEEDS

THE IMPACT OF CLIMATE ON VELD (NATURAL PASTURE OR RANGELAND) AND ANIMAL PRODUCTION

H.O. de Waal¹, W.J. Combrinck¹, M.D. Howard² and H.J. Fouché^3
1 Department of Animal Science, University of the Orange Free State, PO Box 339, Bloemfontein 9300, Republic of South Africa
² Department of Agrometeorology, University of the Orange Free State, PO Box 339, Bloemfontein 9300, Republic of South Africa
³ ARC - Range and Forage Institute, PO Box 339, Bloemfontein 9300, Republic of South Africa

Introduction

The countries participating in this Joint Workshop of the Zimbabwe Society for Animal Production (ZSAP) and the Food and Agricultural Organization (FAO) of the United Nations, are all situated on the Southern African subcontinent. The climate of most of these countries is tropical and subtropical with wet summers and dry winters. i.e. typical of summer rainfall regions. However, as reflected by conditions in the arid zone of the Kalahari desert, this does not always imply a good and steady rainfall and an abundance of grazing material for livestock. The southern tip of Africa and a substantial part of South Africa extend beyond the southern limit often arbitrarily set for the subtropics, i.e. 30°S (Mannetje, 1984). This part of South Africa also includes the Western Cape with wet winters and dry summers, i.e. a winter rainfall or Mediterranean climate.

Several aspects of natural pasture (veld) are addressed by other presentations at this Workshop. Therefore, this paper focuses on the nutrition of ruminants on veld in the subtropics of South Africa, with special emphasis on the effects of the climate, especially variation in rainfall, on seasonal variation in dry matter (DM) yield and the quality of the veld. De Waal (1990) provided some results from a long-term research programme in the Free State and Northern Cape. More information obtained in this programme, conducted jointly by animal and pasture scientists over a period of more than three decades, is presented with a view to promote a more informed perspective of the grazing ruminant and veld.

Rainfall and dry matter (DM) production of the veld

South Africa is primarily a pastoral country. Many of the problems faced by livestock producers in the more arid grazing zones of South Africa can be related to the effects of rainfall, both the inconsistency in distribution and variation in different years, and especially, the inability of producers to take adequate precautions to lessen the adverse effects on their production enterprises (De Waal, 1994). According to Mannetje (1984), a knowledge of the edible DM yield and the energy and protein status of a pasture, as well as the seasonal changes in these attributes, is of paramount importance for good pasture management and enables a manager to determine (i) the carrying capacity of the pasture, (ii) the expected animal production, (iii) the periods of the year when nutritional deficiencies occur, (iv) the type and amount of fodder or concentrates required to correct these deficiencies and (v) the best way to match the animal's needs to the pasture's ability to provide nutrition through the year.

An estimated 68.4 million ha of veld, or 80 percent of the land available for agricultural purposes in South Africa, can only be effectively utilized by grazing ruminants (De Waal, 1990). The South African veld types are extremely diverse in terms of botanical composition (Acocks, 1988), DM production potential and therefore nutritive value, i.e. the ability to sustain animal production.

Variation in DM yield of veld, primarily due to variation in rainfall, occurs between years at any specific site and is reflected in animal performance. Negative aspects of continuous overstocking and overgrazing on the DM production potential and stability of veld and, inevitably, on animal production, must also be considered.

The development of effective strategies for dry season feeding of animals, i.e. during winter, requires a basic knowledge of the nutrition of animals from veld through the year. This includes an understanding of the profound effect which rainfall has on DM yield and quality of veld and thus animal production (De Waal, 1990, 1994).

The long-term annual rainfall of Glen (26° 20' E and 28° 51' S; north of Bloemfontein in the central grass veld of South Africa) for the period 1929/30 to 1991/92, is presented in Figure 1.

Figure 1. The long-term annual rainfall (mm per year) of Glen for the period 1929/30 to 1991/92

Considerable variation in annual rainfall is evident in Figure 1. Calculated over the 63-year period, the long-term mean annual rainfall for Glen is 551.9 mm with a median of 530.2 mm. During this period, the lowest rainfall of 274 mm was recorded in 1973 and the highest rainfall of 1175 mm was recorded in 1988. Arguably it may be nice to have such statistics, but the main interest that livestock producers have in rainfall should lie in the resultant DM production of the veld, or simply, food for their animals. However, very little quantitative data is available on DM yields of veld, because until fairly recently, the only method available to determine DM yields of veld was the conventional and labourious way of cutting, drying and weighing large numbers of herbage samples (De Waal, 1994). Major advances were made in this regard by Fouché (1992) in developing a deterministic micro-computer-based model (PUTU 11) which, based on climatological (rainfall, maximum/minimum temperature, evaporation, sunshine hours, soil water balance), plant physiological and soil variables, simulates DM production of veld on a daily basis. The annual yield (kg DM/ha) of veld at Glen for the 63-year period (1929/30 to 1991/92), as simulated with PUTU 11 (De Waal, 1994), is presented in Figure 2.

Figure 2. The annual dry matter yield (kg DM per ha) of veld at Glen, as simulated with PUTU 11 over a period of 63 years (1929/30 to 1991/92)

Very similar to the situation for annual rainfall depicted in Figure 1, considerable variation in the annual DM yield of the veld at Glen is evident in Figure 2. However, a comparison of the two graphic presentations (Figures 1 and 2) suggests that the relationship between annual rainfall and DM yield is not very strong. Calculation of this relationship (r = 0.6) indicated that, in addition to annual rainfall, other factors play a role in determining DM yield of veld. Without negating the possible role of the other factors, De Waal (1994) suggested that the distribution of rainfall within the growing season is probably one of the more important factors in determining DM yield of veld.

The long-term average monthly rainfall at Glen and the resulting average monthly DM production of veld (as simulated with PUTU 11; De Waal, 1994), are presented in Figures 3 and 4 respectively.

Figure 3. The long-term average monthly rainfall at Glen (1929/30 to 1991/92)

Figure 4. The average monthly dry matter (DM) production (kg DM per ha) of veld at Glen, as simulated with PUTU 11

The typical bell-shaped (normal distribution) monthly rainfall pattern for summer rainfall regions is clearly evident in Figure 3. It is also evident that, for Glen, the bulk of the rainfall in summer is received from October to April (Figure 3), while the bulk of the DM yield of the veld is produced from December to March (Figure 4). Therefore, De Waal (1990) suggested that these periods of high rainfall and DM production of the veld should be the focus for high levels of animal production from veld, especially where grass predominates. However, it is very important to note that the specific time frame for these periods of optimum veld production may change somewhat between sites, depending on specific rainfall patterns and veld type, especially those with substantial shrub, bush and tree components.

De Waal (1994) also emphasized the importance of three general aspects of rainfall which are often, if not mostly, ignored. Firstly, the large and unpredictable variation in annual rainfall, and secondly, the incidence of years with below-average rainfall, which tends to exceed those with higher-than-average rainfall. Thirdly, another very important feature of rainfall and one which is mostly disregarded, is the distribution of rainfall in a specific year. Some of this data for Glen, analysed over a period of 47 years (H.J. Fouché, 1992; unpublished data as cited by De Waal, 1994), is shown in Table 1.

Table 1. Rainfall and production variables for the respective months during a 47-year period (1940–1987) at Glen

Source: H.J. Fouché (1992; unpublished data as cited by De Waal, 1994)
¹ Average monthly rainfall
² Probability of rainfall
³ Coefficient of variation
⁴ Growth rate per month

During this period of 47 years (1940–1987; Table 1), about 80 percent of the annual rainfall at Glen was received between October and April, i.e. during the active growing season (De Waal, 1994). Although the probability (P) of receiving consistent rainfall during this time is better than during the rest of the year, it still only varies between 51.4 and 61.1 percent. Furthermore, the coefficient of variation (CV) in veld production during the early part of the growing season (October - December), is markedly higher than later in the growing season. If DM production at Glen takes place during the period January to March (70.4%), and more than half (55.9%) of the DM is produced during February and March. Grazing livestock are depending all year round on veld for nutrition. Therefore, among other management strategies and procedures that may be considered and applied, this clearly calls for adequate DM reserves to be carried over annually from the previous season.

Grazing capacity of veld

The results presented in Table 1 corroborate those of De Waal (1990), who showed a threefold difference in annual DM yield of veld at Glen between successive years (1614 kg vs 1243 kg vs 527 kg vs 572 kg). Variations in rainfall and DM yield of this magnitude are typical for most of the summer rainfall areas of South Africa, therefore, the resulting effects on animal production should be major considerations in determining realistic long-term grazing capacities and stocking rates (De Waal, 1990). For example, the grazing capacities for veld proposed by the Department of Agriculture at five research centres, situated in a vast area of South Africa (covering about 21.7 million ha), namely Glen, Armoedsvlakte (near Vryburg), Vaalharts (near Jan Kempdorp), Koopmansfontein (near Barkly West on the Ghaap plateau) and Massakloutjie (near Upington in the Kalahari), are respectively 6, 7, 9, 10 and 18 ha/Large Stock Unit (LSU; Meissner et al., 1983) per annum (De Waal, 1990).

In a long-term trial with beef cattle grazing veld at Armoedsvlakte, Fourie (1983) studied the relationships between stocking rate (ha/LSU), production per ha and production per animal, clearly demonstrating the need for adopting and adhering to the concept of optimum and not maximum animal production per unit area. Moreover, if stocked correctly (7 ha/LSU for Armoedsvlakte), sufficient herbage was available at the beginning of September to last the cattle for 300 days, without having to rely on any new regrowth of the veld. Conversely, if overstocked at four ha/LSU, the available herbage would only be sufficient for 70 days (Fourie, 1983).

Considering the low and inconsistent DM yield during the first part of the growing season (Figure 4 and Table 1), the consequences for stable animal production are obvious. However, according to De Waal (1990) many producers, as well as other supposedly better informed operators, apparently do not yet realise the importance of these basic facts. In the long run, optimal animal production can only be achieved and stability of veld maintained if realistic stocking rates are applied according to the grazing capacity of the veld. According to Fourie et al., (1985), even under normal rainfall conditions, overgrazing limits the available grazing and affects animal production more than the quality of the diet selected by livestock. Furthermore, the suggested grazing capacities should not be regarded as constants, but, ideally, stocking rates should be judiciously adjusted in the short term according to rainfall (both annual and distribution), DM yield and veld condition (De Waal, 1990). In addition to the natural occurrence of drought, injudicious grazing practices and especially high stocking rates, which ultimately cause veld deterioration, increase the frequency and intensity of droughts and create so-called man-made droughts (De Waal, 1994). According to Fouché et al., (1985) the incidence of feed droughts at Glen is very low at a stocking rate of 6.2 ha per LSU, while the probability of a feed drought increases markedly to about 70 percent at a stocking rate of 3 ha per LSU.

Among others, many of these principles have been incorporated by Meissner et al., (1983) in the guidelines provided regarding substitution rates for different classes of livestock in South Africa. The general confusion created by the myriad of definitions which were in use for different classes and/or species of livestock were greatly overcome in this approach by defining all livestock in terms of a standardised livestock unit, namely a Large Stock Unit (LSU). An excerpt from a table in Meissner et al., (1983), is presented in Table 2.

Table 2. Large Stock Unit (LSU) equivalents for grazing beef cattle

Source: after Meissner et al., (1983; Table 5.1)

It should be noted that an LSU is not equal to one head of cattle, because per definition an LSU is based on the daily energy requirement (food intake per day) by animals (Meissner et al., 1983). Furthermore, the energy requirement of animals varies according to their body mass and production function (maintenance, growth, gestation and lactation). For example, it can be calculated from the information provided by Meissner et al., (1983) that 100 small mature size cattle are equivalent to 90 medium mature size cattle (see Table 2) and equivalent to 79 large mature size cattle. Furthermore, calculations along the same lines show that 100 of the non-lactating medium mature size cows are equivalent to only 78 lactating cows of similar body size or mass. Regardless of the long-term negative consequences for veld condition, many producers are still relying on numbers of livestock only.

The usefulness and application of the micro-computer-based models referred to earlier (Fouché, 1992), have since been increased markedly (De Jager et al., 1999). Some of the output produced by this technology, namely the long-term grazing capacities for veld in the Free State Province (H.J. Fouché and M.D. Howard, 1999 unpublished data), is presented in Figure 5.

Figure 5. The long-term grazing capacity for veld (rangeland) in the Free State Province

Recently, Fouché and Howard (1999, unpublished data) also demonstrated the ability of the current generation of PUTU models to forecast or predict the available DM on the veld. This information can assist livestock producers in their decision making and also to act timely to changing veld conditions by deciding when to reduce stock numbers and/or to provide strategic supplementary feeding. Unfortunately the general role, application and value of these micro-computer-based models as inexpensive risk management tools, are poorly understood by policy makers and, therefore, also grossly underutilised. Thus, the rapid further development of these simulation models, especially with a view to increase their usefulness as risk management tools, are seriously impede.

Quality of veld and diet selection

Grazing ruminants exist in highly dynamic situations where animal performance in terms of growth, milk and wool production, is determined by changes in nutrient requirements, but also by the physical environment as well as quantity and quality of available pasture (De Waal. 1994). Ruminants have a primary requirement for dietary energy and a minimum crude protein (CP) requirement for the microbial breakdown of ingested food in the rumen. When the dietary CP is below this estimated level of six to 8.5 percent, intake will be reduced (Mannetje, 1984). However, at a low intake of available energy the animal has a very low requirement for nitrogen (N) and will respond to extra N only when N is given in a form that itself provides energy or that enables the animal to obtain more energy from the herbage (Balch and Moir, 1984). Naturally, there are also minimum mineral and vitamin requirements for normal metabolism (McDowell et al., 1984).

The nutritive value of a feed depends largely on its chemical composition, digestibility of the ingested nutrients and the voluntary intake per unit of time by the animal (Blaxter, 1964). Thus, the rate of animal production is a function of the daily digestible nutrient intake. It presupposes that animals must be able to walk long distances to select plant material and ingest sufficient nutrients, often on sparse veld and in very hot climates. Animals must also be able to select and ingest sufficient nutrients from a wide range of pastures, commensurate with the various animal production functions during the cyclical seasonal production year of the plant populations in different veld types.

Seasonal trends in CP and digestible organic matter (DOM) content of the diet selected by oesophageally fistulated (OF) cattle and sheep are well documented, especially for veld at various sites in the Free State and Northern Cape (De Waal, 1990). Typical CP and DOM contents of the diet selected by sheep at Glen (De Waal, 1979; De Waal, 1990) and at Koopmansfontein Research Station on the Ghaap Plateau in the Northern Cape (H.O. de Waal and C.B. van Zyl, 1986; unpublished data), are shown in Figures 6 and 7 respectively.

Figure 6. The crude protein (CP) and digestible organic matter (DOM) content of the diet selected by oesophageally fistulated (OF) wethers at Glen

Figure 7. The crude protein (CP) and digestible organic matter (DOM) content of the diet selected by oesophageally fistulated (OF) wethers at Koopmansfontein

Although the results at Koopmansfontein (Figure 7) are slightly different from that for Glen (Figure 6), it also shows a typical seasonal trend for CP content and DOM, reaching highs during the active growing wet season in summer and lows during the dry dormant winter. On the Ghaap Plateau sheep browse the bush component (such as Tarchonanthus camphoratus, Grewia flava and Acacia spp) extensively during certain times of the year, thus accounting for the higher CP values during winter and very low DOM of the selected herbage, especially during July 1986 (Figure 7).

The long-term monthly rainfall for Vaalharts Research Station (near Jan Kempdorp) is presented in Figure 8. The bell-shaped pattern of monthly rainfall in the summer rainfall regions referred to earlier (in Figure 3), is again clearly evident. The seasonal variations in CP and DOM content of the veld at Vaalharts, as sampled manually (cut by hand with sheep shears) or selected by OF cattle (adapted from Engels, 1983 as cited by De Waal, 1990), are shown in Figures 9 and 10 respectively.

Figure 8. The long-term monthly rainfall for Vaalharts Research Station (1938 to 1991)

Figure 9. The crude protein (CP) content of veld samples at Vaalharts, collected manually or selected by oesophageally fistulated (OF) cattle

Figure 10. The digestible organic matter (DOM) content of veld samples at Vaalharts, collected manually or selected by oesophageally fistulated (OF) cattle

It is well known that sheep are more selective grazers than cattle (Engels et al., 1981; Read, 1984). Despite the usual decline in CP and DOM content of the veld during winter, cattle, and especially sheep, are still able to select herbage with a fairly high quality (De Waal, 1990). Furthermore, these values are much higher than those usually cited for South African veld which is a discrepancy originating from the differences in techniques used for sampling of the pastures for analysis. For example, the large differences in DOM and CP content of samples collected manually or by OF cattle on the veld at Vaalharts Research Station, are clearly shown in Figures 9 and 10. Engels and Malan (1978) concluded that chemical analysis based on herbage samples collected manually, can by no means serve as an indication of the nutritive value of mixed veld. Ruminants have the ability to select plants and parts of plants in their search for quality food but, nevertheless, many individuals erroneously persist in quoting the absurdly low values from analysis of manually collected veld samples, especially with a view to justify the need for supplementation (De Waal and Combrink, 1999). In this regard, De Waal (1990) concluded that a basic premise in the evolution of, and justification for supplementary feeding strategies, namely that grazing animals ingest herbage which is mostly of an inferior quality and deficient in several nutrients, is evidently erroneous.

Results from several studies (Aucamp, 1980; Engels et al., 1981, Read, 1984; Du Toit et al., 1995; Du Toit and Blom, 1995) suggest that the different livestock species (i.e. cattle, sheep and goats) differ substantially in their selective grazing behaviour and ability to select a diet of a higher quality, while the differences in diet selection within species such as between sheep breeds are considered negligible (Langlands, 1969; Engels et al., 1974a; De Waal et al., 1980). The lack of breed differences regarding selective grazing behaviour, as reflected in the CP content and DOM of samples collected by Dorper and Merino wethers (De Waal et al., 1980), is especially important because it refutes the common belief that the two most populous sheep breeds in South Africa select different diets when having access to the same pasture (De Waal and Combrink, 1999).

Herbage intake from veld

The selective grazing behaviour of ruminants, i.e. diet selection from the available herbage, and their ability to ingest sufficient quantities of herbage and thus nutrients on veld, i.e. voluntary feed intake per day, are confounded in the minds of many (De Waal and Combrink, 1999). Although the quality of the diet that is selected is important, levels of production by grazing ruminants are more dependent on the total daily intake of digestible nutrients. Relative to the number of studies conducted on the selective grazing behaviour of ruminants, fewer studies concentrated on the voluntary herbage intake of grazing livestock. This may be attributed to several factors, which may include the additional input in labour, facilities and cost needed when applying the sophisticated techniques to estimate indirectly the voluntary feed intake by grazing ruminants. However, considering the quality of herbage selected by cattle and sheep, reasonable levels of animal production may be expected even during winter, provided intake is not impaired nor that the nutrient requirements imposed by physiological status (growth, lactation) are too high (De Waal, 1990).

Several studies showed that cattle may occasionally have difficulty in satisfying their nutrient requirements from veld (Engels et al., 1974b; Read, 1984; Du Pisani et al., 1987). However, these shortfalls between daily requirements and intake are neither as frequent nor as severe as with sheep, especially with woolled breeds like the Merino (De Waal, 1979; De Waal and Biel, 1989a,b,c; De Waal et al., 1981; Engels, 1972; Engels and Malan, 1979; De Waal and Combrinck, 1999).

Voluntary feed intake from veld is influenced by specie, breed and physiological status or production stage (Engels et al., 1974a,b; De Waal and Biel, 1989a,b,c). However, it should be noted that some of the differences in voluntary feed intake often observed between breeds may merely be the result of differences in body size or mass.

It is generally observed that dry and non-reproducing cattle and sheep experience little difficulty in ingesting enough edible material to meet their nutrient requirements, even during winter (De Waal, 1990). However, owing to their higher nutrient requirements, lactating ewes are more likely to be affected by an inadequate nutrient intake, resulting in a severe loss of body condition. This is especially true during winter, as demonstrated with lactating Merino and S.A. Mutton Merino ewes (Engels and Malan, 1979) and Merino and Dorper ewes (De Waal and Biel, 1989a,b,c) at Glen and lactating Dorper ewes at Koopmansfontein (De Waal et al., 1987 unpublished data). De Waal (1986) calculated from published data that lactating ewes at pasture require at least 55 g DOM/Wkg^0.75 day^-1 to achieve and maintain satisfactory levels of production (i.e. good growth rates by the lambs and a minimum loss of body condition by the ewes). In the trials by De Waal and Biel (1989a,b,c), lactating Dorper and Merino ewes consumed only 20 to 30 percent more herbage from veld during winter than non-lactating ewes. The lactating ewes suffered severe losses in body mass and the performance of their lambs was poor, while non-lactating ewes were able to maintain body condition. Although herbage was abundantly available, the lactating ewes were evidently unable to increase intake from the veld sufficiently during winter. In the trials that were conducted during the summer (De Waal and Biel, 1989a,b,c), lactating ewes could more easily satisfy their nutrient requirements from veld and the lambs also benefited directly from the better grazing conditions during spring and summer.

Engels et al., (1974b) determined the voluntary feed intake of two beef cattle breeds on veld at Glen. The feed intake of Simmental and Afrikaner cows, both lactating and dry females, were estimated monthly from November to April. The lactating Simmental and Afrikaner cows consumed respectively 46.7 percent and 52.1 percent more herbage per day than dry females of the same breeds (Engels et al., 1974b). Furthermore, lactating and dry Simmental cows consumed 11 percent and 15 percent more herbage per day respectively than comparable Afrikaner cows. The impact of differences of this magnitude in daily feed intake on stable animal production from veld is quite obvious.

Animal production

Body mass changes of grazing sheep and cattle generally follow seasonal trends in DM yield, CP and DOM content of the veld during specific years, but differ between years (De Waal, 1990; De Waal and Combrinck, 1999).

Considering the effects of climate, especially rainfall, on DM yield and quality of veld, animal production systems should first and foremost be planned according to the ability of veld to satisfy the specific nutrient requirement for reproduction. Niemann and Heydenrych (1965) showed that the weaning mass of calves decreased by 2.86 kg per week for calves born after 1 October, suggesting that the calving season for beef cattle should commence as early as possible in spring. This is corroborated by the results obtained with two large beef cattle herds at Armoedsvlakte and Vaalharts (De Waal, 1990). It is also true for Bonsmara beef cattle (H.O de Waal and W.J. Combrinck, 1999 unpublished data) and Dorper sheep at Glen (De Waal and Combrinck, 1999). In all these references, the animals were mated such that birth coincided with the emergence of the pasture's spring growth. At Armoedsvlakte and Vaalharts the cattle had ad lib access to a salt/phosphorus lick only all year round, while at Glen the Bonsmaras and Dorpers only received a salt lick all year round at restricted levels.

The monthly body mass of the reproducing Bonsmara cow herd at Glen, is shown in Figure 11.

Figure 11. The monthly body mass of the reproducing Bonsmara beef cows at Glen, relative to weaning, calving and mating

The annual post-partum body mass of the Dorper ewes at Glen, as affected by variation in climate and veld conditions, is shown in Figure 12

Figure 12. The annual post-partum body mass of the Dorper ewes at Glen over a period of 16 years

The Dorper flock at Glen was established in 1982 (De Waal and Combrinck, 1999). The flock have access only to veld and to a salt (NaCl) lick all year round. After being exposed to teaser rams for 14 days, the ewes are mated annually for a period of 34 days during April/May (autumn) to lamb during October/November (spring/early summer).

Practical application

De Waal (1990) concluded that most livestock producers in the Free State can attain similar levels of animal production by applying sound pasture and animal management practices. Although many livestock producers are achieving good results, this is sadly not yet the general norm.

In South Africa, concerted efforts should be aimed at a better understanding of drought and especially long-term drought management strategies and short-term tactics in livestock production (De Waal, 1994). Livestock producers cannot change the climate, therefore, the impact of climate (i.e. variation in DM yield and quality) can only be managed through skilful manipulation of the animal production system, i.e. reduction in numbers and/or provision of strategic supplementary feeding.

A next logical step in the development of decision support systems is to quantify the risk attached to different scenarios in terms of animal production systems. The ability to manage drought, be it of a short (seasonal) or longer duration, should become an integral part of livestock production, beginning with an awareness campaign for and the training of producers, advisers and policy makers.

Acknowledgements

The authors acknowledge the contribution of all those involved in this research programme, spanning several decades in the erstwhile Free State Region, especially Dr Elias Engels, Mrs Heila Terblanché, Dr Marion Read, Mr Chris Biel, Mr Johan Smith, Mr Skapie Basson and the late Dr Daan Els, Mr Alfonso Malan and Dr Jan Fouri.

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Engels, E.A.N. De Waal, H.O., Biel, L.C. and Malan, A. 1981. Practical implications of the effect of drying and treatment on nitrogen content and in vitro digestibility of samples collected by oesophageally fistulated animals. South African Journal Animal Science. 11: 247.

Engels, E.A.N. and Malan, A. 1978. Die involved van twee veebeladings op die samestelling van die dieet en inname van skape in >n driekampstelsel in die sentrale Oranje-Vrystaat. South African Journal Animal Science. 8: 19.

Engels, E.A.N. and Malan, A. 1979. Feed intake of non-pregnant, pregnant and lactating ewes on native pasture and lucerne hay. South African Journal Animal Science. 9: 27.

Engels, E.A.N., Malan, A. and Baard, Margarietha A. 1974a. The voluntary feed intake of three breeds of sheep on natural pasture. South African Journal Animal Science. 4: 27.

Engels, E.A.N., Malan, A. and Baard, Margarietha A. 1974b. The voluntary feed intake of dry and lactating cows on natural pasture. South African Journal Animal Science. 4: 113–116.

Fouche, H.J., 1992. Simulering van die produksiepotensiaal van veld en die kwantifisering van droogte in die sentrale Oranje-Vrystaat. Ph.D. (Agric.) proefskrif. Universiteit van die Oranje-Vrystaat, Bloemfontein.

Fouche, H.J., De Jager, J.M. and Opperman, D.P.J. 1985. A mathematical model for assessing the influence of stocking rate on the incidence of droughts and for estimating the optimal stocking rates. Journal of the Grassland Society of South Africa. 2:3:4.

Fourie, J.H., 1983. Karakterisering van die weidingskapasiteit van natuurlike weiding in Noord-Kaapland. Ph.D.(Agric.)-proefskrif, Universiteit van die Oranje-Vrystaat, Bloemfontein.

Fourie, J.H., Opperman, D.P.J. and Roberts, B.R. 1985. Influence of stocking rate and grazing systems on available grazing in the northern Cape. Journal of the Grassland Society of South Africa. 2:3:24.

Langlands, 1969. Studies on the nutritive value of the diet selected by grazing sheep. IV. Variation in the diet selected by sheep differing in age, breed, sex, strain and previous history. Animal Production. 11:369.

Mannetje, L. =t, 1984. Nutritive value of tropical and subtropical pastures, with special reference to protein and energy deficiency in relation to animal production. In: Herbivore Nutrition in the Subtropics and Tropics. Eds. F.M.C. Gilchrist and R.I. Mackie. The Science Press, Craighall, South Africa. p 51.

McDowell, L.R., Conrad, J.H. & Ellis, G.L., 1984. Mineral deficiencies and imbalances, and their diagnosis. In: Herbivore Nutrition in the Subtropics and Tropics. Eds. F.M.C. Gilchrist and R.I. Mackie. The Science Press, Craighall, South Africa. p 67.

Meissner, H.H., Hofmeyr, H.S., Van Rensburg, W.J.J. and Pienaar, J.P. 1983. Classification of livestock for realistic prediction of substitution values in terms of a biologically defined Large Stock Unit. Tech. Comm. No. 175. Department of Agriculture, Pretoria.

Niemann, P.J. and Heydenrych, H.J. 1965. Some environmental and physiological factors affecting birth and weaning weights of beef calves. Technical Communication No 41. Department of Agricultural Technical Services. Government Printer, Pretoria.

Read, Marion V.P. 1984. Animal performance from natural pastures and the effects of phosphorus supplementation. M.Sc. (Agric.) thesis. University of Stellenbosch

ANTI NUTRIENT FACTORS IN NATURALLY OCCURRING VEGETATION

I.M. Duncan
Agricura (Pvt) Ltd, P O Box 2742, Harare, Zimbabwe

Introduction

Domestic livestock, as we know it, is exotic to the African environment. Wild animals, by contrast, have evolved in this region over an extended period of evolutionary time. They have evolved, among other things, mechanisms which enable them to utilize the available food source. Introduced domesticated livestock, on the other hand, have not and at best may be seen to be in a transitional state of adaptation. Consequently domestic livestock are at a distinct disadvantage in dry periods. Addressing this problem has challenged the attention of animal nutritionists for many years. Meeting adequately the nutritional needs of domestic livestock in dry periods is still one of the major priorities in domestic animal husbandry.

Clarification of terms

It is necessary at the outset to clarify certain terms used in the title of this workshop. With your permission therefore, I would like to paraphrase the title to read: Strategies for the provision of adequate nutrition for domestic livestock in the dry season period. In respect of the subject assigned I would suggest Anti nutrient factors in naturally occurring vegetation would be appropriate.

Along with this I submit the following points to sharpen our focus further:

By “animals” it is presumed we mean domesticated, introduced livestock such as cattle, sheep and goats. It would not be surprising if cattle claimed the major share of our attention.

By “dry season” we obviously mean the period between two rainy seasons, when the nutritive value of the food base deteriorates.

It is stating the obvious to point out that this workshop is taking place because it is generally recognized that, in most situations, the domestic livestock we have in mind are unable to utilize enough of the naturally occurring food source to maintain condition through this dry period. It would suggest that after many years of research and activity in this field an entirely satisfactory solution to the problem still evades us.

Reasons why domestic introduced animals are nutritionally disadvantaged in the dry season environment.

Most introduced livestock, particularly cattle, evolved in other ecological settings as green-grass grazers. In such environments there was no need for such animals as cattle to exploit other facets of the food source such as browse. What they had evolved to utilize, namely grass, was totally, nutritionally adequate.

The wild animal populations in Africa have, by contrast, adapted to the dry season environment over long periods of evolutionary time. Important also, is the fact that the diverse species composition of African wildlife, ensures wide use of all the facets of the food source. For example eland (Tauratragus oryx) are heavy browsers of certain types of vegetation, while kudu (Tregalaphus strepsiceros) also browsers, utilize different types of vegetation. Buffalo are known to select sporobolus (Sporobolus pyramidalis) grass while other animals do not. Zebra and wildbeest are able to process large quantities of dry grass.

It is important to recognize therefore, that domestic livestock in our environment is in a transitional state and it is likely to remain so as long as current management practices persist. I have read that, so far as is known, the first bovines crossed into north Africa somewhere between the seventh and second centuries BC. There was a steady migration of these Sanga type animals both down the west and east coasts of Africa. In comparatively recent times European type breeds were introduced. This is an important fact since this repeated introduction has been instrumental in maintaining the transitional status of cattle in general. In other words, instead of having a situation where the original Zebu types could adapt to and evolve in the African environment, such adaptation and evolution has been retarded by the repeated introduction of exotic European type cattle which were not adapted to the environment.

The role of anti nutrients

The main purpose of this presentation is to review the work of various researchers in identifying anti nutrient factors and their effects on livestock.

What are anti nutrients? Anti nutrients are described as secondary metabolities produced by plants which inhibit, by a variety of mechanisms, normal digestion and assimilation of a nutrient.

A number of chemical groups, found naturally occurring in vegetation, have been identified. It is not within the scope of this presentation to discuss all of these. A review of the literature on the subject identifies three main associated groups. These are tannins, terpenes and saponins. The group which would appear to receive the most attention is without a doubt the tannins.

McKey describes tannins as “A group of complex phenolic polymers widely distributed in plants”. (McKey, 1978) There is good news and bad news regarding tannins. According to Barry levels of up to 40 g per kg of dry matter are beneficial in that they delay the rapid degradation of dietary proteins. However, levels above this depresses protein digestion. (Barry, 1989; Robbins et al., 1987).

Broadly speaking tannins are categorized as condensed tannins and hydrolysable tannins. In most recent times certain tannins within these two groups have been identified further as protein precipitating tannins. This is important since not all tannins precipitate nutrients, and some are even considered to be beneficial.

Condensed tannins

Condensed tannins are referred to as proanthocyanidins, polymeric flavonols, and leucoanthocyanidins. They have a molecular weight of between 1000 and 28000. (Barry, 1988).

Hydrolysable tannins

Hydrolysable tannins are also secondary plant metabolities. They undergo hydrolysis in the stomach to gallic acid and related compounds. These are considered toxic and can be absorbed causing toxicity. The metabolities pyrogallol and pyrocatechin are considered particularly toxic (Singleton and Kratzer, 1969).

The effects of tannins

Effects of condensed tannins.

• They form indigestible, stable complexes with dietary protein. (Barry and Manley, 1984; Robins et al., 1987).

• They bond with digestive enzymes, retarding digestion. (Price and Butler, 1980)

• They are capable of destroying useful rumen micro organisms. (Barry, 1988)

• They cause raw lesions on the rumen lining through which hydrolysable tannins may gain entry. (McCleod, 1974; Hoff and Singleton, 1977).

In practical terms these effects result in serious digestive problems for the browsing animal. It is speculated that these complex anti nutrient substances developed as plant defense mechanisms to discourage browsing. Furthermore, increased browsing results in further elevation of the anti-nutrient level in browsed plants (Benz, 1977; Haukioja, 1980; Van Hoven, 1991). Certain wild animals such as eland have powerful muco proteins which neutralize the effects of tannins. Domestic livestock have no such mechanism.

The effects of hydrolysable tannins

Hydrolysable tannins and their metabolities are toxic. Excessive intake of these substances can result in liver and renal failure. (Singleton and Kratzer, 1969).

Relatively small amounts of hydrolysable tannin reaching the abomasum of animals are capable of precipitating large amounts of pepsin (Hill, 1961).

In a personal discussion with Professor Wouter Van Hoven, of the University of Pretoria, it was pointed out that in dry periods there is a sharp distinction in the way that C tannin and H tannin toxicity is manifested in affected cattle. C tannins result in nutrient deprivation and consequent loss of condition and often emaciation. H tannins on the other hand, result in acute toxicity with the animal often dying while in relatively good condition. (Van Hoven, - personal communication).

What are the options?

Animal husbandry management practices show little sign of changing in the near future. We will go down the same road we have trodden for many years. Part of this scenario includes the utilization of a type of animal which is not only foreign to the environment but has little chance, given current management practices, of adapting to it.

In the meantime we have to consider the following options:

• Modify the environment to accommodate the animal. This includes the planting of pastures and forage vegetation, usually exotic varieties.

• Continue with the tried and tested policy of supplementary feeding.

• Modify the animal by manipulating its digestive processes through the use of digestive modifiers, which enable it to utilize the “naturally occurring nutrient” in the “naturally occurring” vegetation.

In Zimbabwe work has been carried out which has resulted in the commercial introduction of a digestive modifier to neutralize the effect of anti nutrients in browse. This was reported initially by Duncan and McKenzie (1993). Positive results have also been reported by Mhlanga and Mutisi (1997), Topps (1997), and Halimani et al., (1994), in Zimbabwe. Salawu et al., (1997), have reported on work from the United Kingdom, and McSweeney and Palmer (personal communication) have reported on positive results from Australia. Varied results have been reported by Matopos Research Station in Zimbabwe.

Conclusion

An abundant, low cost food source lies untapped in the naturally occurring vegetation in large parts of Africa. It is imperative that ways and means be devised to exploit this source. Along with this must be a holistic approach to management systems which accommodate a variety of strategies in producing an animal that is ecologically compatible with the environment which supports it.

References

Barry, T.N. 1989. Condensed tannins their role in ruminant protein and carbohydrate digestion and possible effects upon the rumen ecosystem. In “The Roles of Protozoa and Fungi in Ruminant Digestion.

Barry, T.N. and Manley T.R. 1984, The role of condensed tannins in the nutritional value of Lotus predunculatus for sheep. British Journal of Nutrition. 51:493–504

Benz, G. 1977, Eucarpia/IOBC working group breeding for resistance to insects and mites. Bull. SCROP 1977/3 (Report from 1^st, meeting held at Wageningen, The Netherlands, 7–9 Dec 1976). 155–159.

Duncan, I. M. 1993. A review of the development and use of polyethylene glycol and Browse Plus as digestive modifiers in domestic livestock and their application during the Zimbabwe dry season. Journal of the Zimbabwe Society for Animal Production. 6: 31–36.

Halimani, E. T., Mutisi C. and Kusina, N. T. 1994. Effects of a digestive modifier, Browse Plus, on ruminal and intestinal breakdown of forages containing high tannin levels. Department of Animal Sciences, University of Zimbabwe.

Haukioja, E. 1980. On the role of plant defences in the fluctuation of herbivore populations. Oikos. 35: 202–213.

Hill, K.J. 1961. Digestive secretions in the ruminant. In Digestive Physiology and Nutrition of the Ruminant. Ed: D. Lewis, pp. 48–58. Butterworth, London.

Hoff, J. E. and Singleton, K.I. 1977. A method for determination of tannins in foods by means of immobilized protein. Journal of Food Science. 42: 1566–1569.

McCleod, M. N. 1974. Plant tannins and their role in forage quality. Commonwealth Bureau of Nutrition. Nutrition Abstracts and Reviews. 44: 803–815

McKey, D. 1978. Phenolic content of vegetation in two African rainforests. Ecological implications. Science. 20: 611–63

Mhlanga, F. N. and Mutisi, C. 1997. Effect of Browse Plus on weight gains of Hereford steers. Department of Animal Science Report, University of Zimbabwe.

Price, M. L. and Butler, L. G. 1980, Tannins and nutrition. Purdue University Agriculture Experimental Station Bulletin. 272: 12–15.

Robins C. T., Mole S., Hagerman A. E. and Hanley T. H. Role of tannins in defending plants against ruminants: Reduction in protein availability Ecology. 68: 1606–1615.

Singleton, V. L. and Kratzer, F. H. 1969. Toxicity and related physiological activity of phenolic substances of plant origin. Journal of Agriculture, Food and Chemistry. 17: 497–512.

Solawu, M. B., Acamovic T., Stewart C. S. and Hovell F. D. DeB. 1997. Quebracho tannins with or without Browse Plus (a commercial preparation of polyethylene glycol) in sheep diets: effect of digestibility of nutrients in vivo and degradation of grass hay in sacco and in vitro. Animal Feed Science and Technology. 10: 84–101.

Topps, J.H. 1997, Nutritive value of indigenous browse in Africa in relation to the needs of wild ungulates. Animal Feed Science and Technology. 10: 1–11.

Van Hoven, W. 1991, Mortalities in kudu (Tragelaphus strepsiceros) populations related to chemical defence in trees. Journal of African Zoology. 105: 141–145.

CROP RESIDUES AS A DRY SEASON FEED RESOURCE FOR RUMINANT LIVESTOCK IN SOUTHERN AFRICA

B Manyuchi¹, C Chakoma² and A Tigere^2
1 Africa University, Mutare, Zimbabwe
² Grasslands Research Station, Marondera, Zimbabwe

Introduction

The Communal areas of Zimbabwe occupy 16.4 million hectares and are currently inhabited by 7.5 million people and about 2.5 million LSUs (consisting of 89% cattle, 6 % goats, 3.5 % donkeys and 1.5 % sheep) (Central Statistical Office, 1998; GFA, 1987). Over the years the expansion of the human and livestock population has put enormous pressure on natural resources. A study in Masvingo province shows that the ratio of arable to grazing land has increased from 1:4 to 4:1 during the past 30 years (CARD, 1989).

Livestock is a major source of livelihoods in communal lands, not only measured in their intrinsic value, but because crop production is largely dependent on livestock e.g. supply of draught power and manure (Shumba, 1984). Productivity of livestock in Communal areas is however very low (Clatworthy, 1987). Under-nutrition, especially during the dry season, is one of the most important limiting factors to livestock production in the communal areas. Overgrazing of the rangeland during the wet season leaves very little fodder for livestock during the dry season. Thus, although dry season forage is of poor quality due to low nitrogen and high fibre content (Elliott and Topps, 1963), shortage of forage remains the primary limiting factor to ruminant productivity (GFA, 1987).

Crop residues, available during the dry season, have the potential to increase availability of fodder to ruminants (Mache, 1995; Smith et al., 1987). The annual production of cereal crop residues (maize, sorghum, millets) was estimated to be 2.1 million m/t (Sibanda, 1993) and enough to meet between 70 and 80 percent of food requirements of ruminants during the dry season, if all the residues are utilized as livestock feed.

Improving the contribution of crop residues to livestock feed

If farmers leave stover in the field to be grazed in situ by cattle during the dry season they save on labour and transport costs, and any uneaten stover is incorporated into the soil as livestock trample the crop residues. If stover is grazed in situ, fodder losses of up to 40 percent occur due to trampling and soiling (Manyuchi et al., 1992). Besides these losses, grazing stover in situ does not allow the farmer to control the rate, timing and prioritization of feeding.

Increasingly, farmers are adopting the practice of harvesting crop residues to stall feed livestock due to increasing shortage of livestock fodder resulting from overstocking. If stover is harvested prior to feeding, the farmer has a much greater control on the utilization of the resource. Under normal farming conditions, the contribution of crop residues to livestock feeding maybe less than optimum due to inefficiencies associated with harvesting, transportation, storage and feeding. In communal areas, stover is usually thrown into the kraal during feeding resulting in high rates of spoilage. Stover is commonly stored in open stakes and may be subject to losses due to spoilage from occasional rains that fall during the dry season. Management strategies to minimize losses of stover via the routes outlined above will increase contribution of stover to livestock feeding, which in turn increases animal productivity.

Effect of rate of offer

Although stover can generally be described as a poor quality feed, some components of stover such as leaves are of high nutritive value. Studies in Zimbabwe (Smith et al., 1989; Manyuchi et al., 1990) and elsewhere (Wahed and Owen, 1986; Wahed and Owen, 1987) have shown that increasing rate of offer of crop residues will increase feed intake. Animals offered stover at high rates of offer, are able to select dietary fractions of high nutritive value and this is reflected in higher intakes and better performance (Manyuchi et al, 1990; Table la). In a study by Manyuchi et al., (1990), changing rate of offer was achieved by changing stocking rate when stover was grazed in situ.

Table 1(a). Effects of rate of offer on intake of maize stover

Source: Smith et al., (1989)

Table 1. (b). Effects of stocking rate on weight gain and stover selection in grazing steers (90 days grazing period)

Source: Manyuchi et al., (1992)

Supplementation of crop residues

Urea supplementation

Crop residues, especially from cereal crops, have high fibre and low nitrogen content (Greenhalgh, 1984), factors that contribute to their low consumption and digestibility by ruminants. The feeding value of cereal crop residues can be improved by supplementation with nitrogen (Elliott and Topps, 1963). The benefits of supplementing maize stover with urea are illustrated in Table 2. When stover is supplemented with molasses its intake is depressed probably due to negative associative effects (Table 3). The depressive effects of molasses are reversed when urea is added. These results confirm that nitrogen is the major limitating factor when animals consume poor quality forages.

Table 2. Effects of supplementing maize stover with one or three percent urea on intake and digestibility

Source: Manyuchi et al., (1994)

Table 3. Effect of molasses + urea supplements

Molasses added at 27% DM
Source: Manyuchi et al., (1994)

Supplementation with legume stover

Studies show that stover from leguminous crops such as groundnut and cowpea can be used as supplements to cereal crop residues (Mosi and Butterworth, 1985; Smith, et al., 1989). However, if legume supplements constitute more than 30 percent of the diet, inefficiency results from the substitution of the basal diet by the legume supplement (Manyuchi et al, 1997; Table 4). The use of legume forage supplements may be cost effective and maximizes the use of feeds available on farms. The benefits of supplementation have been confirmed by improved weight gains as shown in Table 5.

Table 4. Intake and digestibility of veld hay supplemented with groundnut stover (sheep)

Source: Manyuchi et al., (1997)

Table 5. Effects of legume supplements on animal performance

Source: Manyuchi et al., (1994)

Chemical treatment of crop residues

Treatment of crop residues with alkali has been shown to improve feeding value of crop residues (Sundstol, 1981; Owen, 1981; Greenhalgh, 1984; Smith et al., 1987, Manyuchi et al., 1994). The alkali hydrolyses ligno-cellulose bonds and makes the cell wall more digestible and enables animals to achieve greater intake compared to untreated roughage. Early studies where carried out using sodium hydroxide and ammonium hydroxide. It become evident that treatment with ammonia gave a much better product because in addition to the alkali effect, the treated roughage is enriched with nitrogen. In the tropics urea can be used as a source of ammonia because it is easily hydrolysed by urease enzymes present in plant materials to yield ammonia. Stover to be treated requires to be incubated in a completely sealed environment for a period of upto five weeks in order to allow for the hydrolysis of urea and sufficient contact time between the ammonia and the roughage. In Zimbabwe, optimum treatment is normally achieved by using five percent urea (w/w) dissolved in 20 percent water to the weight of roughage and incubating for five weeks.

Some of the advantages of treating stover with urea are shown in Table 6. Treated stover is enriched with nitrogen and fibre content is reduced. Treatment increases intake and digestibility of the forage. The superiority of urea treatment compared to urea supplementation is shown in Figure 1 (Manyuchi et al., 1994). Treated stover was degraded in the rumen to a much greater extent than urea supplemented stover. A study carried out on a smallholder farm showed that feeding treated stover increased milk yield (Chakoma et al., 1997). (Table 7)

Table 6. Effect of treating maize stover with urea on chemical composition, intake and digestibility.

Table 7. Effect of feeding urea treated stover on milk yield

Source: Chakoma et al., (1997)

Figure 1. DM degradation of urea treated stover and stover supplemented with one or three percent urea

Conclusions

Crop residues constitute a vital feed resource for livestock during the dry season. A variety of options are available to improve feeding value of crop residues. The appropriateness of each method will depend on the farming conditions and resources available to the farmer. The economics of each choice will probably be the most important overriding factor to the farmer's choice.

References

CARD, 1987. Coordinated Agriculture and Rural Development: Analysis of its results, strategy and sustainability. A review three years after its inception. GTZ, Zimbabwe.

Clatworthy, J N. 1987. Feed resources for small-scale livestock producers in Zimbabwe. In: Feed Resources for Small-Scale Livestock Producers. Eds: J A Kategile, A. N Said and B H Dzowela, International Development Research Centre, IDRC-MR 165e, Nairobi, Kenya. pp 44–60

Chakoma, C., Tigere, A and Mugweni, A. 1997. On-farm studies on feeding urea treated stover to dairy cows. Grasslands Research Station, Unpublished

Elliott, R. C. and Topps, J. H. 1963. Voluntary intake of low protein diets by sheep. Animal Production. 5: 269–276.

GFA, 1987. Study of the economic and social determinants of livestock production in communal areas of Zimbabwe. Final Report. Department of Veterinary Services, Government of Zimbabwe.

Greenhalgh, J. F. D. 1984. Upgrading crop and agricultural by-products for animal production. In: Herbivore Nutrition in the Sub-tropics and Tropics. Science Press, Pretoria, South Africa.

Mache, B. 1995. Use of crop residues for ruminant feeding. Journal of the Zimbabwe Society for Animal Production. 7: 71–74

Manyuchi, B., Mikayiri, S. and Smith, T. 1992. The effect of stocking rate on live weight change and utilisation of maize stover grazed in situ by Mashona steers. Proceedings of the Research Council of Zimbabwe Third Symposium on Science and Technology, Harare, 6–8 Oct. 1992.

Manyuchi, B., 1995. Improving the feeding value of poor quality forages by urea supplementation or urea treatment. Journal of the Zimbabwe Society for Animal Production. 8: 169–173.

Manyuchi, B., Mikayiri, S. and Smith, T 1994. Effect of treating or supplementing maize stover with urea on its utilisation as feed for cattle and sheep. Animal Feed Science and Technology. 49: 11–23

Manyuchi, B., Hovell, F. D. DeB., Ndlovu, L. R., Topps, J. H. and Tigere, A. 1997. Napier or groundnut hay as supplements in diets of sheep consuming poor quality natural pasture hay. 1. Effect on intake and rumen digesta kinetics. Livestock Production Science. 49: 43–52

McIntyre, J., Bourzat, D. and Pingali, P. 1992 Crop-livestock interaction in sub-Saharan Africa. World Bank.

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Owen, E. 1981. Use of Alkali-treated low quality roughages for sheep and goats. In: Utilization of Low Quality Roughages in Africa. Eds: J. Kategile, A. N. Said and F. Sundstol. Royal Agricultural University of Norway, AAS, Norway.

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Smith, T, Chakanyuka, C. Sibanda, S and Manyuchi, B. 1989 Maize stover as feed for ruminants. In: Overcoming Constraints to the Efficient Utilization of Agricultural By-Products as Animal Feed. Eds: A N Said and B H Dzowela, ILCA, Addis Ababa, Ethiopia. pp 218–231

Smith, T., Manyuchi, B. and Mikayiri, S. 1989. Legume supplementation of maize stover. In: Utilization of Research Results on Forage and Agricultural By-Product Materials as Animal Feed. Eds: B H Dzowela, A N Said, A Wadem-Agenehu and J A Kategile, ILCA, Addis Ababa, Ethiopia.

Sundstol, F. 1981. Methods of treatment of low quality roughages. In: Utilization of Low Quality Roughages in Africa. Eds: J A Kategile, A N Said and F Sundstol. Royal Agricultural University of Norway, AAS, Norway.

Wahed, R. A. and Owen, E. 1986. The effects of amount offered on selection and intake of barley straw by goats. Animal Production. 42: 89–95

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