Cattle and buffaloes in developed and developing countries provide meat, milk, traction power and manure to the beneficial integration of agricultural and livestock farming. To achieve the good performance of those animals, correct feeding methods need to be done by understanding first the factors governing rumen function and secondly the role of bypass nutrients (Preston and Leng 2009).
Ruminants are able to use nutrients arising from poor quality forage or cellulosic biomass especially forages of low digestibility, such as crop residues, agro-industrial by products, weeds, grasses from rangeland, foliage of trees and shrubs. These are the basal feed resources of ruminants in developing countries (Preston and Leng 2009). Thus rice straw is the roughage that is usually fed to cattle as the main diet during the dry season in many Asian countries, particularly in Cambodia. It has low content of essential nutrients and low digestibility, which results in low performance and poor health.
The ruminant derives essential nutrients for metabolism from the combination of the products of rumen microbial fermentation and unfermented feed that bypasses the rumen. Poor-quality diets (hay and crop residues) are followed by poor animal productivity, resulting from the lack of one or more essential nutrients required for rumen microbial activity, typically nitrogen and minerals and nutrients required for efficient metabolism of the absorbed nutrients which also must meet the requirement for production (tissues, milk and hair). Supplements are required to correct these deficiencies.
Supplementation with urea and minerals has been shown to markedly improve rumen function and hence the utilization of rice straw (Perdok and Leng 1989). However, urea has increased in price as it is made from natural gas, which is a declining resource (Leng 2008). It is therefore important to evaluate locally available feeds which could replace the urea.
Protein-rich foliages that are rapidly degraded in the rumen could be a source of ammonia for rumen micro-organisms. If the foliages are also rich in minerals this could be an added advantage in correcting any minerals deficiencies. Water hyacinth is an aquatic plant that grows profusely on water in all tropical countries. It is an easily accessible feed resource for livestock while at the same time by harvesting it there would be environmental benefits. The leaves are relatively rich in crude protein and also contain a high level of minerals.
There are many studies on the nutritive value of water hyacinth but the results are confusing. On the basis of proximal analysis the leaves of water hyacinth appear to have a relatively high nutritive value. The DM digestibility is reported to be close to 60% (Abdelhamid and Gabr 1991) while the crude protein approaches 20% in DM (Paper I). Despite what appears to be a relatively high nutritive value, the results of feeding it to cattle have been poor, with reports of low feed intake which was insufficient to support maintenance when the leaves were the sole diet of cattle (Hentges 1970). Khan (1977) also found that when fed a diet solely based on only fresh water hyacinth, the cattle lost body weight. However, when rice straw was given together with the water hyacinth (1:1 ratio) the cattle increased their DM intake by 67% and gained 68g/day of live weight. It would appear from these results that the beneficial effect of the rice straw was to dilute a compound in the water hyacinth that was depressing intake since, both in digestibility and protein content, rice straw is much inferior to water hyacinth.
The presence of anti-nutritional compounds in water hyacinth could thus be the explanation of the poor performance when this plant was the sole feed. Yet here also the reports in the literature are variable. Gohl (1994) reported that fresh water hyacinth contained prickly crystals (supposedly oxalate salts), which reduced its palatability. However, according to Lareo and Bressani (1991) the levels of oxalate and other anti-physiological factors present in the plant were either very low or non-existent. They reported that the level of tannins was less than 1 per cent of the DM in the whole plant and only 2 per cent in the leaves. The plant had no trypsin inhibitors and the tests for saponins and alkaloids were negative. The level of oxalates was only 0.8 per cent in DM. Low levels of tannins in water hyacinth were also reported by El-Serafy et al. (1981), Mishra et al (1987) and Dutta et al (1984).
The findings from the experiment reported in Paper I, would appear to confirm the presence of some anti-nutritional factor in the water hyacinth leaves, since the cattle lost weight when fed only rice straw and water hyacinth leaves, but gained in weight when the rice straw was supplemented with a urea-mineral mixture.
Lead is highly toxic to humans, plants and animals. Lead poisoning (plumbism) causes plant and animal death as well as mental deficiency, anemia, brain damage, kidney dysfunction, and behavioral problems in humans (Mo et al 1988). Varying degrees of lead (Pb) poisoning were recorded in cows and buffaloes near a primary lead-zinc smelter in India; affected animals had history of clinical signs characterized by blindness, head pressing, violent movement and salivation (Dwivedi et al 2001).
In a study of lead poisoning in animals grazing near a lead smelter, Hammond and Aronson (1964) reported that a dose of 6 mg lead/kg live weight for 60 days was toxic to young growing cattle. This equates to a daily concentration in feed DM of about 200 mg/kg. In the UK the maximum acceptable limit of lead in feeds is set at 10 mg/kg DM (Statutory Instrument 1995), while in the USA it is 30 mg/kg DM (NRC 1980).
Abdelhamid and Gabr (1991) reported that the lead (Pb) content in water hyacinth leaves and stems was in the range from 90 to 100ppm and 120 to 146 ppm (DM basis), respectively. These values are intermediate between generally accepted limits of 10 to 30 mg/kg DM) and levels causing toxicity (about 200 mg/kg). Thus it appears likely that the concentrations of lead in water hyacinth leaves (about 100 mg/kg DM) could be close to the toxic levels of this element.
Toxicity in goats consuming water hyacinth as the sole feed was reported by Dutta et al (1984) and Mishra et al (1987). The symptoms were stiff legs and cardionephrotic failure. Most of the animals died. Sheep fed on water-hyacinth alone lost live weight and suffered from hepatic failure followed by death in a study reported by Singh et al (1988). In the study reported by Abdelhamid and Gabr (1991), one of the sheep fed only water hyacinth died after a week of tetany and “stiffy” legs without response to Ca-injection.
Cassava (Manihot esculenta) is an annual root crop which grows well on low quality soil, in regions with low rainfall and high temperature. Therefore, it is a cash crop cultivated by small-holder farmers within the existing farming systems in most SE Asian countries. The main purpose to grow cassava is for root production. However, after harvesting the roots there is the aerial part of the plant which can be used for animal feed. Cassava leaves have relatively high levels of crude protein some of which can apparently by-pass the rumen because of the formation of a tannin-protein complex (Wanapat 1995). Beside tannins that are found in cassava foliage, there are other substances which can be toxic, namely the cyanogenic glucosides which can give rise to hydrocyanic acid (HCN). However, both sun-drying and ensiling are effective ways of reducing HCN to safe levels (Bui Huy Nhu Phuc et al 2001).
The roots as energy sources and leaves as protein sources have been used successfully in ruminant rations (Wanapat 2008). Thus supplementation of urea-treated rice straw with cassava hay at 1-2 kg/head/day to dairy cattle markedly decreased the requirements of concentrate and improved the yield and composition of milk. Studies with fresh cassava leaves in diets for fattening cattle based on minerals showed that it supported the same high growth rate as a supplement of soybean meal (Ffoulkes and Preston 1978). When used as a supplement to untreated rice straw the growth rates in local “Yellow” cattle (in Cambodia) were increased threefold by supplementing them with fresh cassava foliage (Seng Mom et al 2001). Similar findings for positive effects of cassava foliage on growth rates of cattle fed untreated rice straw were reported by Keo Sath et al (2008) and Ho Thanh Tham et al (2008), the former using sun-dried foliage and the latter the sun-dried leaves in the form of meal.
In the experiment reported in Paper I, supplementation with sun-dried cassava foliage had a dramatic positive effect on animal performance. Cattle, which lost body weight when the only supplement to rice straw was water hyacinth leaves or leaves + stems, gained weight when sun-dried cassava foliage was also fed. Furthermore, better results were obtained when the water hyacinth leaves (or leaves + stems) were the source of rumen nutrients compared with the urea-mineral mixture. In the absence of the cassava foliage the contrary was the case: cattle gained weight with the urea-mineral supplement but lost weight with water hyacinth.
The effect of feeding cassava foliage to cattle on a rice straw diet is to enhance the protein status of the animal since it is believed that much of the protein in the cassava leaves escape from the rumen fermentation for enzymic digestion in the small intestine (Wanapat 2008).
· It appears that the constraint to the use of water hyacinth as live stock feed may be related to sub-clinical concentrations of heavy metals, especially lead. It should not therefore be fed as the sole feed but complemented with other feeds with known low concentrations of “heavy metals” so as to dilute the overall concentrations of these toxic elements in the diet.
· The other approach is to improve the protein status of animals fed water hyacinth in view of the known beneficial effects of an increased supply of amino acids when the immune system is challenged as part of the host’s defense processes against, for example, the ingestion of toxic compounds (Leng 2005).
· The feeding of cassava foliage could therefore be especially important as a means of neutralizing the presumed presence of anti-nutritional compounds (lead??) in water hyacinth.
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