Ensiling of tropical forages with Particular
Reference to African Livestock Systems.
TITTERTON M.,1 MHERE O.,2 MAASDORP B.,3
KIPNIS T.,4 ASHBELL G.,5 SMITH T.6
[Paper presented at the XIIIth International Silage Conference, 11-13th September, 2002]
The ensilage of adapted forages and legumes in the semi-arid regions of Southern Africa can play an essential role in providing the opportunity for smallholder dairy farmers to maintain milk production and fertility in spite of poor and erratic rainfall and long dry seasons. Production of intercropped pennisetums and forage sorghums with legumes, on small plots with the use of low-cost and appropriate technology, has been developed and adopted after participatory farm trials in a dairy cooperative in a communal farming area.
However the use of agro-forestry, strategic irrigation, harvesting management for maximum digestibility, feeding strategy and farming system are important areas requiring further research and development before silage can assume full significance in smallholder dairy cow nutrition in this region.
Livestock is recognized as being an integral component of the mixed farming systems that predominate in developing countries in the tropics, of which many are in Africa. Animal manure and traction make the land more productive than would be the case in their absence. Yet it has been recognized with equal force that livestock owned in the semi-arid regions, which predominate in much of Africa, are forced to barely subsist on poor and sparse vegetation in the dry season, leading to severe loss of body condition, productivity and fertility and on the land, the threat of desertification. In the smallholder farming system, the production of forage and fodder is often a sideline activity that is integrated with other areas of agricultural production (Nitis, 1999).Technologies aimed at achieving a balance, whereby livestock can increase in productivity, so enhancing wealth for the livestock owner, while resource degradation is minimized, must be developed (Steinfield, 1998). In the semi-arid regions of Africa, smallholder dairying generates a more regular income than any other rural enterprise and can lead to improved human nutrition and health, poverty alleviation and improvement of household food security (International Livestock Research Institute, 1997).
During the rainy season in Zimbabwe, despite erratic rains lasting in general from November through March (five months) the supply and quality of forage (normally as grazing on natural pasture or veld) are usually adequate for milk production from the indigenous and cross-bred cow (Nyoni et al., 2000). The remaining seven months, however, leave a large deficit in adequate nutrient supply for the productive animal. Small ruminants (goats, sheep and donkeys) are able to subsist on the poor winter grazing, crop residues (sorghum and maize stover) and browse, as are cattle herd "followers", such as weaners and young oxen. The dairy cow, the traction animal and the finishing steer, however, which are more productive, and which represent opportunity for wealth for the livestock owner, require a much higher plane of nutrition (Zerbini and Alemu, 1999).
Traditional smallholder dairy production is characterized by low levels of milk production, long calving intervals, of two years or more, and short lactations. Hence the availability of milk for local markets is erratic, as is income for the farmer. There are three major reasons for this: the high cost of commercially produced stockfeed, putting this source of feed beyond the reach of smallholders; the lack of adequate, good quality forage in the dry season; and the breed of cow (Dube, 1995; Henning, 1995; Gandiya, 1999).
Extensive research has been carried out to find technologies which would enable the farmer to plan ahead and strategically manage the feeding of their livestock.
One such technology is the conservation of forage produced during the wet season, for feeding to stallfed or partially zero-grazed livestock during the dry season. Other technologies include improving the nutritional value of crop residues through physical and chemical treatment, improved management of grazing and the use of by -products by the peri-urban farmer, all of which can contribute to the forage bank (Smith, 2001) The conservation of high quality forages, however, may be the only such technology that would satisfy the high demand for nutrients for such livestock operations as small-scale dairy farms in the semi-arid regions of the tropics (Dube, 1995) and for traction which commences in the dry season (Smith, 2001).
CURRENT ROLE AND IMPORTANCE OF SILAGE
In the semi-arid regions of the tropics, the conditions are harsh for conserved forage. High temperatures combine with short rainy seasons on largely poor soils to produce grasses and legumes which, while able to produce high yields under good management, still deteriorate rapidly in nutritional quality after only three months of growth, as lignification proceeds (Skerman, 1988).
The two ways of conserving forage are by hay making and by ensiling. Hay making of forages in Southern Africa is difficult because to conserve forage at its optimum yield, protein levels and digestibility, it should be cut in February or early March and this usually coincides with the wettest part of the rainy season (Topps and Oliver, 1993). It requires the use of mower-conditioners for rapid drying, hay balers and large sheds for protection from the rain, all suited to the commercial type of farming operation and not to the smallholder. For the smallholder, rain damage results in a loss of dry matter and quality due to leaching of nutrients by rotting. Thin -stemmed forages such as legumes can dry within two or three days (Cameron, 1988) but bulky forages such as napier, hybrid pennisetums and forage sorghum take too long to dry even when left out on racks (Mhere, 1997). If cutting is delayed to later in the season, there is a severe reduction in quality and excessive leaf shattering and loss, especially in legume forages (Maclaurin and Wood, 1987).
On the other hand, ensiling of adapted forage crops or grasses in March has a good chance of success because the procedure relies on a high moisture content of the crop and after sealing, protection from leaching, rodents and insect damage. However, successful ensilage of forage depends on a number of principles, creating a major challenge to the smallholder:
Even with a high yield of good quality forage, the quantity conserved would not be sufficient to feed dairy cows through both the dry season and during the rains, when the cow is lactating and may require higher levels of nutrition than can be supplied by grazing alone. This is of particular concern with regard to cross bred cows. Feeding strategy to maximize returns in the form of both milk yield and fertility from a limited amount of silage needs to be determined.
Our research was aimed at addressing all five of these constraints. However, participatory research on-farm, where there are one or two animals per farm and a wide range of soils and farmer attitudes, inherently produces large variation and experimental error, hence both formal and on-farm participatory experimentation have been undertaken concurrently.
1. PRODUCTION OF HIGH YIELDING, HIGH QUALITY FORAGE
In the high rainfall areas of Southern Africa, maize is the crop of choice for silage, because of its high yield, fermentation quality and energy content. It is suitable for intercropping with legumes (Maasdorp and Titterton, 1997) or can be mixed with legume tree leaf forage (Mugweni et al., 2000) to improve protein content of the silage. However, maize is susceptible to moisture stress and consequently cannot be considered as a reliable crop for silage in the marginal and semi-arid areas, where dairy production offers the best means of improving livelihood for the smallholder livestock owner. In these areas, grain sorghum, forage sorghums and Pennisetum are more drought tolerant than maize and have a high yield potential as silage crops (Titterton and Bareeba, 1999; Mhere et al., 1999). However, it was concluded after an evaluation of grain and forage sorghums in semi-arid areas that sweet forage sorghums offer better potential as silage crops than grain sorghums (Cole et al., 1996). As with maize, however, these crops have a low crude protein content (7 and 9% for grain and forage sorghums respectively) and in order to produce a high quality ration to meet the nutrient requirements of dairy cows, protein-rich crops need to be introduced into the silage, either by growing them as sole crops and mixing them at ensilage with the forage crops, or intercropping them with the forage crops. A three-year study was carried out, using both formal trials and participatory trials on-farm, to determine the feasibility of intercropping forage sorghum and Pennisetum with legumes. Both cowpea (Vigna ungiculata) and dolichos bean (Lablab purpureus) were undersown using differing planting patterns and on two types of soil. Total biomass yields and protein content of silages from the mixed crops was significantly improved over that of the sole cereal crops. Pennisetum/legume crops produced between 5 and 10 tons dry matter on sandy and clay soils respectively while forage sorghum/legume crops produced between 8 and 13 tons dry matter (Table 2). Mhere et al. (1999) found, however, that soil type, planting pattern and weather had significant effects on the proportions of legume in both forage sorghum and forage pennisetum crops.
Table 1. Crude protein and dry matter digestibility (g/kg) of hybrid Pennisetum and forage Sorghum intercrops with cowpeas and dolichos beans,grown over three seasons (1996-96, 1996-97, 1997-98) at Matopos Research Station (extracted from Mhere, 1999, Mhere et al., 1999).
Table 2. Dry matter yields (t/ha) on station and
on-farm (Gulathi communal area)
Elsewhere in Africa, high biomass yields from intercroppping forage sorghum with cowpea (Enyi, 1973), forage sorghum with dolichos bean (Kusekwa et al., 1992), hybrid Pennisetum with cowpeas (Maiti et al., 1988) and hybrid Pennisetum with Leucaena leucocephala (Gill and Tripathi, 1991) have also been reported.
Multi purpose leguminous trees are a good potential source of protein in conserved forages in the semi-arid areas. Fodder trees produce protein-rich forage and, being deep rooted, they generally withstand water stress well, possibly better than adapted annual legumes. The addition of wilted Amaranthus hybridus to maize (1:1) at the time of ensiling resulted in good fermentation and raised the crude protein content of the silage from 6.9% to 11.6%, while reducing the crude fibre content (Bareeba, 1977). In a study of four silages made from maize and forage legumes, Acacia boliviana, Calliandra calothyrsus, Gliricidia sepium and L.leucocephala, (mixed 1:1 on a w/w basis and ensiled in fertilizer bags) maize and tree fodder was shown to ensile well and to have high levels of crude protein (Table 3) but digestibility decreased substantially with the addition of A. boliviana and C. calothyrsus. Of interest was the effect of ensilage on protein binding by phenolic compounds (tannins) in which it was found that protein precipitation activity was reduced in ensiled tree fodder. However, the degree of reduction varied with type of tree (Mugweni, 2000; Mugweni, 2001). Milk yields were the same from Holstein cows on the mixed silages as those from cows on maize silage and protein concentrate (Mugweni, 2001), suggesting that it would be worthwhile carrying out a similar study with forage sorghum and Pennisetums with tree fodder fed to cross-bred cows.
Table 3. Fermentation and nutritional quality of silages made from
maize and legume forage trees.
1 Acidity of < pH5 needed for good preservation
DETERMINATION OF APPROPRIATE HARVESTING STAGE USING NUTRIENT PROFILES ON THE CEREALS.
Nutrient profiles of cowpea and lablab showed that optimum protein and digestibility levels were reached at 12 to 14 weeks after planting, around mid February to mid- March in Zimbabwe, while forage sorghum has reached the soft dough stage of maturity by this time(Mhere, 2002). However, with other farming activities limiting the farm labour available for harvesting, cutting was mostly delayed to early April. The nutrient analysis of the two cereal crops at this stage showed a reasonable water soluble carbohydrate content in the dry matter but an unacceptably low digestibility (Table 4).
Table 4. Quality parameters of forage crops at 18 weeks post establishment.
Clearly more attention needs to be paid to achieving a better digestibility through earlier harvesting. Some farmers have tried cutting their hybrid pennisetums in January at one metre high and fed them fresh or, after wilting, ensiled them. The second cutting was then carried out in the last two weeks of March of both the Pennisetum and legume. These informal trials showed that by the time of the third cutting this strategy had allowed better growth of the legume and greater yields of total ensiled forage. With less forage to handle on each occasion, labour was less of a constraint. Formal experimentation needs to be carried out to verify these results, which look promising. Clearly the advantage with the use of wilting in semi-arid Southern Africa, is the dry, hot climate which facilitates rapid drying. Wilting was not found to be of any benefit in crops that were between 25 and 30% dry matter (Mhere, 1999), but when cut in January and February, the crops are less than 25% dry matter and should benefit from wilting. Wilting studies are recommended for this reason.
Either maize or a commercial additive (Sil-all) enhanced fermentation and quality of Pennisetum/legume silage, while it was not found to be of any benefit in forage sorghum/legume silage (Mhere, 1999). However, most perennial tropical grasses require some form of additive at ensiling and, where it is available, molasses is suitable (Humphreys, 1999). Molasses in Zimbabwe is often scarce, but home grown additives (sweet-stem Sorghum stems) give similar fermentation patterns to maize meal and Sil-all (Alltech), but higher total nitrogen content when added at 10% fresh weight to hybrid Pennisetum/legume silage (Mhere, 1999). This is probably due to the reduction in proteolysis.
3 AND 4. THE USE OF LOW-COST TECHNOLOGY TO PRODUCE SILAGE
The objectives of this study were to examine ways of overcoming the major constraints to smallholder farmers when ensiling forages, the use of high-cost machinery traditionally used in chopping and compressing forage on large-scale farms and unsuitable silos. Labour and gender issues were addressed as both are important in the smallholder dairy farming system.
The treatments consisted of:
Summary of results
There were differences in fermentation and nutritional quality of silages due to grass crop variety but none due to chop length, compression treatment or type of bag (Table 4). Therefore, on-farm silage can be made in non-permeable plastic bags with coarsely chopped crop material, which is compressed by hand if there is no mechanization available. Notwithstanding that, labour and time constraints led to the accepted use of the petrol-driven chopper on -farm. This type of chopper is available on hire to dairy farmers, whose cooperatives are members of the dairy development programme in Zimbabwe. Collaborative studies carried out in Israel (Ashbell et al., 1999; Kipnis et al., 2001) suggested that success of ensilage, despite the lack of fine chopping and partial compression, is due to effective sealing of the bags, preventing the loss of effluent containing lactic and volatile fatty acids, compared with pit or bunker silages, where loss of effluent is high, necessitating fine chopping and effective compression.
The technology is found to be ideal for smallholder farmers as losses are minimal, compared with silage pits, which have been used in smallholder dairy farms in the higher rainfall areas, where silage losses amount to as much as 30% of the dry matter due to poor compression and exposure losses in the remainder during removal for feeding. The bag technology has also been found to benefit women and children, as the bags can easily be stored and carried to the cows for feeding, thus there is minimum labour in feeding compared with daily digging out from pits. The nutrient requirements of a cross-bred Tuli/Jersey cow producing 8 litres a day are met from 5 kg silage dry matter per day, which equates to one bag of 15 kg of air-fresh silage per day (Nyoni et al., 2000).
The fertilizer bags, being thicker, could be used over two seasons. This makes their present cost (2002, Zim$9.00) equivalent, when used over two seasons, to the cheaper bags (present cost around Zim$4.50). When no longer usable, the bags can be used for the manufacturing of wax for floor polish, a traditional practice in most smallholdings. Some losses (5%) in the cheaper bags were experienced due to poor packing of bags in the silage storeroom, a problem requiring attention.
Table 5. Fermentation quality of forage crops ensiled under differing conditions. (From Kipnis et al., 2001)
STRATEGIC FEEDING OF SILAGE
During a severe drought in Gulathi communal area, it was found that cows fed on half a bag of silage a day (3 kg dry matter ) for the months of August and September during the dry season, were in reasonable body condition at calving ( mean body condition score 2.0 on a scale of 0-5 (Mulvaney, 1978), compared with those cows not supplemented (mean body condition score 1.0) (Titterton, 1999). In a good year, cows fed on a bag of silage (6 kg dry matter) a day achieved body condition scores of 3.5 and 3.0 for indigenous and Tuli-Jersey cross-bred breeds respectively (Nyoni, 2000). While feeding in the dry season improved fertility, through reduced delay to conception and higher conception rates, there was no effect on milk yields in the following lactation (Nyoni, 2000). However, supplementation of a small amount of concentrate in the lactation period alone improved both yields and fertility (Garwe et al., 2000).
CONCLUSIONS AND RECOMMENDATIONS
The authors and collaborators of the studies in producing and conserving forages for smallholder livestock owners in the semi-arid areas of Zimbabwe wish to thank the following for their contribution to the research:
The views expressed are those of the authors.
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