1. INTRODUCTION - THE NEED FOR SUPPLEMENTATION
Ruminant diets in most developing countries are based on fibrous feeds: mainly mature pastures (particularly at the end of the dry season) and crop residues (e.g. wheat and rice straw, maize and sorghum stovers). These feeds are imbalanced as they are deficient in protein, minerals and vitamins and since they are highly lignified their digestibility is low. Both these characteristics keep intake and productivity low.
The principles for improving the use of these poor quality roughages by ruminants have been discussed by Preston and Leng (1984). They basically include:
satisfying the requirements of the rumen microorganisms to ensure efficient fermentation of fibre and increased production of microbial protein relative to volatile fatty acids.
balancing the products of fermentative digestion with dietary nutrients (mainly through the use of bypass protein) to meet the needs of growth, milk, meat and wool production.
In practice this can be achieved by supplying, in order of priority:
A supplement of fermentable nitrogen and minerals.
A small amount (10 to 20 percent) of good quality forage, preferably a legume or grass cut at an early stage.
A small amount of a supplement containing materials that by-pass the rumen: these include protein meal (e.g. toasted soya cake, solvent extracted groundnut cake) or starch based supplements (e.g. maize and sorghum).
This strategy is applicable in developing countries, e.g. in the Sahelian region of Africa, where ruminants are fed on pastures throughout the year with limited access to supplementary crop residues, or in Asia where they are fed mainly on rice straw and their diets are low in true protein for prolonged periods.
Mixtures of liquid molasses and urea, which provide fermentable nitrogen and are a good source of minerals, have been used for many years by ranchers in Australia and Southern Africa. Mineral licks (sometimes including urea) have also been extensively used in various parts of the world. However, small farmers have rarely benefitted from these supplements usually because of difficulties of handling these in small quantities. Molasses in the liquid form is difficult to transport (requiring expensive tanker trucks), to store (requiring tanks), to handle (it is highly viscous) and to distribute to animals (troughs or other receptacles being needed). Mineral licks which are usually imported are highly expensive and their cost/benefit ratio is often questionable.
By-pass nutrients, with the exception of legume leaves, come generally from rather expensive feeds which are either in demand for human nutrition (cereals) or exported for foreign exchange (oil cakes). However, because recent research has generally shown that their inclusion at a low rate in the diets is efficient, they should be economical to use in many situations.
2. BLOCK FORMULATION
The objective of the blocks is to provide the small farmer with a supplement for his ruminants which will improve the efficiency of use of the basal diet at an acceptable cost. The concept of using a molasses-urea block to provide nutrients is not new: about 25 years ago they were being used in Australia (Beames, 1963). However, the improvement in knowledge now indicates their strategic place in feeding strategies aimed at improving cattle production by the small farmer (Leng and Preston 1983).
The “solidification” of molasses is a way of solving the difficulties encountered in distributing and feeding molasses and also allows for the incorporation of various other ingredients.
Attempts have been made in many countries to manufacture solid blocks with a high molasses content, but their development has not been very successful. However, recent work in India under the leadership of Prof. R.A. Leng of the University of New England has revived interest in such blocks. Trials are under way, with the technical assistance of FAO, in several countries: Burkina Faso, Bhutan, Egypt, India, Iran, Mali, Mauritius, Pakistan, the Philippines, Senegal and Sudan. More than 30 other countries have shown their interest in this technology.
The blocks can be made from a variety of components depending on their availability locally, nutritive value, price, existing facilities for their use and their influence on the quality of blocks. They can also include specific components.
Molasses provides fermentable substrate and various minerals and trace elements (but low amounts of phosphorus). Because of its pleasant taste and smell, it makes the block very attractive and palatable to animals. The degree Brix of the molasses should be as high as possible, and preferably higher than 85, to ensure solidification.
Urea, which provides fermentable nitrogen, is the major component of the block. Campling et al. (1962) have shown that its continuous supply to cattle may increase the intake of straw by about 40 percent and its digestibility by 8 units (or 20 percent. The intake of urea must be limited to avoid toxicity problems but sufficient to maintain ammonia levels in the rumen consistently above 200 mg N/1 for growth of microorganisms and high rates of degradation of fibre. Blocks are an excellent way of controlling intake and allow continual access.
Wheat or rice bran has a multiple purpose in the blocks. It provides some key nutrients including fat, protein and phosphorus, it acts as an absorbent for the moisture contained in molasses and gives structure to the block. It may be replaced by other fibrous materials such as dry and fine bagasse or groundnut hulls which are finely ground but some loss of nutritive value occurs.
Minerals may be added where appropriate. Common salt is generally added because this is often deficient in the diet and it is inexpensive. Calcium is supplied by molasses and by the gelling agent, calcium oxide or cement. Although phosphorus is deficient, there is no evidence that its addition is beneficial where animals are at below maintenance when grazing on dry mature pastures or fed low-quality forage (Cohen 1980; Van Niekerk and Jacobs 1984). Mineral requirements are reduced at maintenance or survival levels. Deficiencies will generally become a problem only when production is increased, particularly when a bypass protein supplement is given and in these cases phosphorus should be included in that supplement.
A gelling agent or binder is necessary in order to solidify the blocks. Although the mechanism of gelling is unknown, various products have been tried successfully: magnesium oxide, bentonite, calcium oxide, calcium hydroxide and cement.
The use of cement has raised some questions, from various nutritionists and extension workers, about possible negative effects on animals. In fact, research on the use of cement or its by-product, cement kiln dust, as a mineral supplement in Canada (Bush et al. 1985; Nicholson, personal communication), Italy (Galvano et al. 1982), USSR (Karadzhyan and Evoyan 1984) and USA have not shown such adverse effects at levels of 1 to 3 percent of the total diet dry matter. Nevertheless, USDA has restricted the use of cement kiln dust since it could cause a deposit of heavy metals in animal tissue (Oltjen, personal communication).
Various chemicals or drugs for the control of parasites or for manipulation of rumen fermentation (e.g. anti-protozoal agents, ionophores) can be added to the molasses blocks which can be an excellent carrier for these products.
Recent work (Van Houtert and Leng, 1986) has shown that the addition of small amounts of rumen-insoluble calcium salts of long chain fatty acids could further increase the efficiency of the use of fibrous residues.
Finally, the formulae may vary according to the process adopted in manufacturing the block (Table 1).
3. THE MANUFACTURE OF MOLASSES-UREA BLOCKS
Different processes have been tried and can be grouped in three categories:
3.1 The “hot” process
This is the process which was first recommended in Australia. The molasses (60 percent) and urea (10 percent) were cooked with magnesium oxide (5 percent), calcium carbonate (4 percent) and bentonite (1 percent) at a temperature of 100–120°C for about 10 minutes. The content was brought to a temperature of about 70°C and then cottonseed meal (20 percent) was added while stirring. The mixture was left to cool slowly which enhanced solidification (George Kunju, 1981, unpublished data). It settled after some hours. The cooking was done in a double-jacketed rotating boiler with circulating water and steam.
3.2 The “warm” process
The molasses (55 percent) was heated to bring the temperature to about 40° – 50°C and the urea without water (7.5 percent) is dissolved in the molasses, (Choo, 1985). The gelling agent was calcium oxide (10 percent). The rest was made up of common salt (5 percent) and bran (22.5 percent).
The inconvenience of these processes, particularly the “hot” one, is the necessity for providing energy for heating. However, if it is possible to use the hot molasses as it leaves the sugar factory or if an excess of steam is available, the cost of energy may be acceptable. The advantages are the reduction of time for setting and the final product is not hygroscopic.
3.3 The “cold” process
It has been noted that, in tropical conditions, it was not necessary to heat the molasses in order to obtain a good block when 10 percent of calcium oxide was used as a gelling agent (Barker, 1984, personal communication). This observation is of primary importance when blocks are manufactured in a unit separate from the sugar factory as was the case in Senegal.
The “cold” process has been recently described in detail (Sansoucy, 1986). A horizontal paddle mixer, with double axes, is used to mix, in the following order of introduction, molasses (50 percent), urea (10 percent), salt (5 percent), calcium oxide (10 percent) and bran (25 percent). The mixture is then poured into moulds (plastic mason's pails or a frame made of four boards 2.5 m × 0.2 m). After about 15 hours, blocks may be removed from the mould and they may be transported by truck after 2 days.
Calcium oxide may be replaced by cement, but when cement is used it is important to mix it previously with about 40 percent of its weight in water, and common salt to be included in the block. This ensures its binding action, as the water in molasses does not seem to be available for the cement. The quality of the cement is of primary importance. Mixing the salt with cement accelerates hardening.
The disadvantage of the “cold” process is that it needs some time to set and the final product is somewhat hygroscopic. The advantages are the saving in energy, and the simplicity and ease of manufacture.
Independent of the process, the hardness of the block is affected by the nature and proportion of the various ingredients. High levels of molasses and urea tend to decrease solidification. The concentration of gelling agents and bran is highly important in the hardness of the final product. For example if the urea percentage is as high as 20 percent, molasses should be reduced to 40–45 percent and the gelling agent needs to be increased. Quick lime produces harder blocks than cement.
4. FEEDING MOLASSES-UREA BLOCKS TO RUMINANTS
4.1 Factors affecting the intake of blocks
The hardness of the block will affect its rate of intake. If it is soft, it may be rapidly consumed with the risk of toxicity. On the other hand if it is too hard its intake may be highly limited.
High levels of urea may reduce intake of the block as well as of straw, urea being unpalatable (Table 2).
The level of inanition or imbalance in minerals which lead to pica may result in excessive consumption in a short time also leading to urea poisoning. This has been noticed in at least one case in Senegal. Precautions should be taken to avoid this problem of over-consumption in drought prone countries particularly towards the end of the dry season when feed is scarce. The block should be introduced progressively, and it should be clear that the block, as it is presently formulated, cannot constitute the only feed and a minimum of roughage is necessary.
Where there is a bulk of dry feed the risk of toxicity from overconsumption is not apparent (Leng and Preston, 1983). In India, several thousand buffaloes in village herds have been fed blocks containing 15 percent urea without problems (George Kunju, 1986a and 1986b) and there is some indication that buffaloes learn to regulate their intake.
Finally, the intake of block obviously varies with the type of animals (Table 3).
4.2 Effects of blocks on intake of basal diet
Feeding blocks usually results in a stimulation of intake of the basal diet. With a basal diet of straw without any supplementary concentrate, the increase of straw consumption due to molasses urea blocks is between 25 and 30 percent. When some high protein concentrate is also given with the basal diet, the increase of straw consumption is less and varies between 5 and 10 percent (Table 4).
4.3 Effects of intake of blocks on digestibility of straw and some parameters of digestion
The digestibility of straw dry matter in dacron bags measured after 24 hours in the rumen of lambs (Sudana and Leng, 1986) increased from 42.7 to 44.2 percent when 100 g of molasses urea block was consumed, and to 48.8 percent by an additional supply of 150 g cottonseed meal.
Ammonia concentration in the rumen of lambs receiving molasses urea blocks increases to levels which are much higher than those generally recommended for optimal microbial development (60 to 100 mg NH3/1 of rumen fluid). This concentration increases with the urea content of the block (Table 5) and when a by-pass protein is added (Table 6). Krebs and Leng (1984) showed that the digestibility of straw in sheep increased even up to 250 mg NH3 - N/1.
The total volatile fatty acids in rumen fluid is increased when lambs consume the blocks with or without additional by-pass protein (Table 6). There is a small but significant shift towards a higher propionate and butyrate production, and a lower acetate production.
4.4 Effects of blocks on ruminant growth
Dry mature pasture or straw given alone are unbalanced in nutrients to provide for an active and efficient rumen and to ensure an efficient utilization of the nutrients absorbed. Feed intake and the nutrients absorbed from such diets are insufficient to ensure even maintenance requirements and animals lose weight if they do not receive any nitrogen and mineral supplement. Molasses-urea blocks added to such an unbalanced diet allow for maintenance requirements because they ensure an efficient fermentative digestion (Table 7). When some by-pass protein is added (e.g. cottonseed meal, noug cake) there is a synergistic effect which further improves considerably the average daily gain of ruminants and they become much more efficient in using the available nutrients. In addition total nutrients are often increased because feed intake is increased.
Compared to urea supplied by spraying on straw, urea from blocks give superior results (Table 8). It is assumed that part of the response may be due to the small amount of supplementary energy supplied by the molasses but also by a stimulatory effect of other ingredients in the blocks on the rumen ecosystem (Preston and Leng, 1986).
4.5 Effects of blocks on milk production
The use of multinutrient blocks has allowed for a substantial reduction in concentrate in the diet of buffalo cows fed on rice straw. The fat corrected milk yield was not diminished by replacing part of the concentrate with block. But the amount of straw in the diet and thus the profit per animal per day were greatly increased (Table 9).
Considerable commercial experience has now been acquired in the use of blocks for supplementing dairy buffaloes fed rice straw under village conditions in India (George Kunju, 1986b). Reducing the amount of concentrate given to buffalo cows from 5 to 3.5 or 4 to 2.5 kg/day, and distributing blocks, did not reduce milk production but increased fat percentage by about 10 percent and reduced the cost of feeding. In other observations the addition of blocks to the diet increased milk production by about 10 to 25 percent and fat content of milk by 13 to 40 percent. In one village where the initial production level was lower the increase was even greater.
Subsequent trials were conducted in Ethiopia with crossbred cows given meadow hay of low quality with two levels of noug cake (Table 10). They showed that milk yield was increased by 28 percent when feeding 2 rather than 1 kg of noug cake in the absence of blocks. However, there was no difference between the two levels of noug cake when the cows had access to blocks (containing 10 percent urea). It was then possible to save 1 kg nough cake by providing blocks without lowering milk production.
5. CONCLUSIONS
Molasses-urea blocks appear to be a simple way of improving the efficiency of utilization of fibrous feeds by ruminants. These feeds constitute the bulk of the diets of ruminants of small farmers in most developing countries.
The ingredients required are usually available locally at a reasonable price. Their nature and proportion may vary according to the process used for the solidification and the purpose for which these blocks are to be used.
Manufacture is easy and simple and different processes exist which may be used according to local conditions.
Molasses-urea blocks have proven to be an excellent tool for the improvement of ruminant feeding. They create an efficient rumen ecosystem which favours the growth of young animals and milk production but they may also affect conception rates and the size of a newborn animal.
The development of molasses-urea blocks should be encouraged in all developing countries which have a sugar industry and where small farmers feed their livestock on crop residues, communal pastures or agroindustrial byproducts, as a means to make better use of available feed resources at the small farmer level.
One of their greatest advantages resides in the versatility bestowed by the solid state and their ease of packaging which allows them to be easily transported and used by small farmers.
The main role of molasses-urea blocks is as a cheap, relatively safe and practical way of supplying in order of priority urea and sulphur for rumen microbes, trace minerals and macro elements for the rumen microbes and the animal in small amounts of highly critical nutrients such as amino acids B-vitamins and perhaps other growth factors.
In the future the widespread use of such blocks will give the scientist access to small-holder cattle for administration of drugs, microbial manipulators or even growth promotants.
REFERENCES
Beames, R.M. 1963 Provision of urea to cattle in a salt/urea/molasses block. Queensland Journal of Agricultural Sciences 20: 213–230.
Bush, R.S., Nicholson, J.W.G. and Calder, F.W. 1985 Growth and modification of digestion in lambs fed diets containing cement kiln dust. Canadian Journal of Animal Sciences 65 (2): 419–427.
Campling, R.C., Freer, M. and Balch, C.C. 1962 Factors affecting the voluntary intake of food by dairy cows. 3. The effect of urea on voluntary intake of straw. British Journal of Nutrition 16: 115–124.
Choo, 1985 B.S. 1985 Establishment of laboratories and other related activities. Terminal report. UNDP/FAO Project PAK/80/019, Islamabad, Pakistan.
Cohen, 1980 R.D.H. 1980 Phosphorus in rangelands ruminant nutrition: a review. Livestock Production Science, 7: 25–37.
Diallo, I. and Ngoma, 1985 A. 1985 Mesures de consommation de blocs de mélasse et d'urée comme complément chez des génisses Gobra recevant une ration d'entretien. Dahra, Sénégal, ISRA/CRZ. Document No. 012, May 1985.
El Fouly, H.A. and Leng, 1986 R.A. 1986 Manipulation of rumen fermentation to enhance microbial protein synthesis from NPN supplements In: Extended synopsis of International Symposium on the Use of Nuclear Techniques in Studies of Animal Production and Health in Different Environments. IAEA, Vienna, Austria, 17–21 March, pp 170–171.
Galvano, G., Lanza, A., Chiofalo, L. and Mal'an, M. 1982 Cement kiln dust as a mineral source in feeding ruminants; 1. The use of CKD in hay and straw based diets for lambs. World Review of Animal Production, 18 (4): 63–71.
George Kunju, P.J. 1986a Cattle feed utilization in milk cooperatives in India. In: Proceedings of the FAO Expert Consultation on the substitution of imported concentrate feeds in animal production systems in developing countries, held in Bangkok, Thailand, 9–13 September 1985. (Sansoucy, R., Preston, T.R. and Leng, R.A., editors). FAO, Rome, pp 189–197.
George Kunju, P.J. 1986b Urea molasses block lick, a feed supplement for ruminants. Paper presented at the International Workshop on rice straw and related feeds in ruminant rations, Kandy, Sri Lanka, 24 to 28 March, pp 27.
Karadzhyan, A.M. and Evoyan, A.A. 1980/81 Use of cement and cement kiln dust in fattening of young bulls. (Abstracts) In: Nutrition Abstracts and Review/Series B. 54(6):280.
Krebs, G. and Leng, R.A. 1984 The effect of supplementation with molasses/urea blocks on ruminal digestion. In: Animal production in Australia Volume 15: 704.
Leng, R.A. 1983 The potential of solidified molasses-based blocks for the correction of multi-nutritional deficiencies in buffaloes and other ruminants fed low quality agroindustrial by-products. In: The use of nuclear techniques to improve domestic buffalo production in Asia. IAEA, Vienna pp 135–150.
Leng, R.A. and Preston, T.R. 1983 Nutritional strategies for the utilization of agro-industrial by-products by ruminants and extension of the principles and technologies to the small farmers in Asia. In: Proceedings of the Fifth World Conference on Animal Production, Volume 1: 310–318.
Preston, T.R. and Leng, R.A. 1984 Supplementation of diets based on fibrous residues and by-products. In Straw and other fibrous by-products as feed (Sundstol, F. and Owens, E., editors). Elsevier, Amsterdam, pp 373–413.
Preston, T.R. and Leng, R.A. 1986 Matching livestock production systems to available resources. International Livestock Centre for Africa (ILCA) Publishing Unit, pp 331.
Sansoucy, R. 1986 Manufacture of molasses-urea blocks in the Sahelian region. World Animal Review 57:40–48.
Sudana, I.B. and Leng, R.A. 1986 Effects of supplementing a wheat straw diet with urea or urea-molasses blocks and/or cottonseed meal on intake and liveweight change of lambs. Animal Feed Science Technology. 16:25–35.
Van Houtert, M. and Leng, R.A. 1986 Strategic supplementation to increase the efficiency of utilization of rice straw by ruminants. University of New England, Armidale, Australia. Mimeograph p. 4.
Van Niekerk, B.D.H. and Jacobs, G.A. 1984 Protein, energy and phosphorus supplementation of cattle fed low-quality forage. South African Journal of Animal Sciences 15: 133–136.
| Ingredients | Process | |||
|---|---|---|---|---|
| Hot | Warm | Cold | ||
| Molasses | 60 | 55 | 50 | 50 |
| Urea | 10 | 7.5 | 10 | 10 |
| Common salt | - | 5 | 5 | 5 |
| MgO | 5 | - | - | - |
| CO3Ca | 4 | - | - | - |
| Bentonite | 1 | - | - | - |
| CaO | - | 10 | 5 | - |
| Cement | - | - | 5 | 10 |
| Cottonseed meal or bran | 20 | 22.5 | 25 | 25 |
| Urea content of block, % | 10 | 15 | 20 |
|---|---|---|---|
| Block intake | 136 | 112 | 18* |
| g/lamb/day | |||
| Straw intake | 441 | 550 | 326 |
| g/lamb/day |
* 4 out of 5 lambs did not lick and of their block
Source: After El Fouly and Lenc 1986
| Type of animals | Animal weight | Block intake per 100 kg LW | Authors |
|---|---|---|---|
| Lambs | 22 | 400 | Sudana and Leng 1986 |
| Calves | 66 | 250 | Van Wageningen and Premasiri 1986, personal communication |
| Young buffaloes | 100 | 380 | Leng 1983 |
| Jersey bulls | 300 | 185 | Gedrge Kunju 1986b |
| Jersey bulls | 350 | 150 | " " " |
| Zebu heifers | 280 | 110 | Diallo and Ngoma 1985 |
| Diet (*) | Oaten chaff alone | OC + B 10% Urea | OC + B 15% Urea | OC + B 20% Urea | |
|---|---|---|---|---|---|
| Rumen ammonia: (mg N/L) | mean | 23 | 131 | 210 | 317 |
| range | 8–66 | 93–209 | 131–305 | 285–342 |
(*) OC = Oaten chaff;B = Block; U = Urea.
Source : Krebs and Leng 1984
| Diet | Ammonia conc. (mg NH3 N/L) | Total VFA (mmoL/L) | Individual VFA (molar %) | ||
|---|---|---|---|---|---|
| Acetate | Propionate | Butyrate | |||
| A | 26a | 63a | 78a | 17a | 4.3a |
| B | 262b | 84b | 70b | 22b | 7.5b |
| C | 352c | 82b | 69b | 21b | 8.2b |
Source: Sudana and Leng 1986
a,b,c: Values within the same column with the same superscript are
not significantly different.
| Type of animals | Animal weight, kg | Increase of straw intake, % | Authors |
|---|---|---|---|
| STRAW WITHOUT CONCENTRATE | |||
| Lambs | 22 | 26 | Sudana and Leng 1986 |
| Jersey bulls | 300 | 29.5 | George Kunju 1986b |
| Dairy buffaloes | - | 24 | " " " |
| Young buffaloes | 100 | 23 | Leng 1983 |
| STRAW WITH HIGH PROTEIN MEAL SUPPLEMENTS | |||
| Lambs | 22 (1) | 8 | Sudana and Leng 1986 |
| Jersey bulls | 350 (2) | 6 | George Kunju 1986b |
| Crossbred cows | - (3) | 10 ) | Preston, Leng and Nuwanyapka, |
| " " | - (4) | 5 ) | unpublished data, quoted by |
| ) | Preston and Leng 1986 | ||
(1) with 150 g cottonseed meal
(2) with 1 kg concentrate
(3) with 1 kg noug cake (Guizotia abyssinica)
(4) with 2 kg noug cake
| Type of | Weight | Basal diet | Growth, | g/d | Authors |
|---|---|---|---|---|---|
| animals | kg | no B | +B | ||
| Lambs | 22 | S | -53 | 10 | Sudana and Leng 1986 |
| Lambs | 22 | S + CSM | 38 | 90 | Sudana and Leng 1986 |
| Jersey | 350 | S + 1 kg C | 220 | 700 | George Kunju 1986b |
| bulls | |||||
| Oken | - | S + 2 kg Ga | 220 | 570 | ILCA, quoted by |
| (5–6 years) | Preston and Leng 1986 |
C = Concentrates;
CSM = Cottonseed meal;
Ga = Guizotia abyssinica/(noug cake)
S = Straw
| Type of animals | Weight kg | Basal diet | Growth, Urea | g/d Block | Authors |
|---|---|---|---|---|---|
| Lambs | 22 | wheat straw | -59 | 10 | Sudana and Leng 1986 |
| Oxen | - | wheat straw | -190 | -70 | ILCA, quoted by |
| Preston and Leng 1986 |
| Diet | Dry matter intake, kg/d | S. dry matter intake, kg/d | Fat correct. milk, kg/d | Profit rupees/d |
|---|---|---|---|---|
| S + 7.75 kg C | 11.7 | 4.8 | 7.4 | 5.5 |
| S + 7.75 kg C | 11.4 | 4.9 | 8.1 | 7.3 |
| + Block | ||||
| S + 6 kg C | 11.0 | 5.8 | 7.0 | 6.9 |
| + Block | ||||
| S + 4.6 kg C | 10.5 | 6.0 | 7.2 | 7.8 |
| + Block | ||||
| + .450 kg CSM |
S = Straw;
C = Concentrate;
CSM = Cottonseed meal
Source: George Kunju, P.J., Tripathy, A. and Leng, R.A. Unpublished data, quoted by Leng 1983.
| 1 kg noug /day | 2 kg noug /day | |||
|---|---|---|---|---|
| no block | with block | no block | with block | |
| Milk yield, kg/d | 4.2 | 5.4 | 5.2 | 5.4 |
| Liveweight, kg | 395 | 396 | 336 | 371 |
| Liveweight change, kg/d | -0.64 | -0.39 | -0.27 | -0.27 |
Source: Preston, T.R., Leng, R.A. and Nuwanyapka, A. quoted by Preston and Leng 1986.
Pastos de mala calidad y residuos fibrosos constituyen la dieta básica de los rumiantes en la mayor parte de los países en desarrollo. Es una dieta desequilibrada, sobre todo en nitrógeno y minerales, y ha de ser suplementada para mejorar su eficiencia. Los nuevos tipos de bloques de melaza-urea, parecen ser un medio excelente para aumentar la productividad animal en esas condiciones.
Pueden utilizarse diversos ingredientes para la preparación de los bloques. Generalmente contienen alrededor del 50 por ciento de melaza y del 10 al 20 por ciento de urea. Se necesita un agente cuajante para la solidificación del producto final. Otros ingredientes pueden variar con arreglo a su disponibilidad y precios y al destino que se pretenda dar al bloque.
Existen tecnologías sencillas para su fabricación. La elaboración en caliente es aplicable cuando los bloques se preparan en la fábrica de azúcar o cuando se dispone de una fuente de energía barata. La elaboración en frío es más conveniente en otras situaciones.
Su consumo puede variar con arreglo a su dureza y al contenido de urea, pero el riesgo de intoxicación por urea es muy bajo.
Los principales efectos que se derivan de administrar estos bloques a los rumiantes pueden resumirse como sigue:
aumenta el consumo de la dieta básica (paja u otros piensos fibrosos);
aumentan las concentraciones de amoníaco y de ácidos grasos volátiles en el fluido del rumen;
mejora la digestibilidad de la paja;
aumenta la ganancia media de peso por día. Se mejoran aús los resultados incluyendo proteínas sobrepasantes. La utilización de estos bloques es mejor que la pulverización de urea sobre la paja;
aumenta la producción de leche y su contenido de grasa, economiza el concentrado requerido para suplementar la dieta.
