4.1 Performance objectives
4.3 Feed intake
4.3.1 Using digestibility data
4.3.2 Using markers
4.4 Nutrient value of feed
4.7 Feeding techniques
4.9 References and reading materials
Module 4 is intended to enable you to:
Preceding modules described the production systems in sub-Saharan Africa (SSA) and stressed the following facts:
The above factors indicate that nutrition must be part of any strategy to increase productivity. In this module we will highlight (i) nutrient requirements and (ii) availability and use of feed resources. More details about ruminant nutrition (methods of feed evaluation and nutrition strategies) can be accessed in manuals produced by ILRI (ILCA 1990; Osuji et al. 1993b).
Insufficient forage during the dry season is a major constraint to ruminant productivity. Forage availability determines the overall carrying capacity of the land. In SSA human population is increasing, forcing farmers to use grazing areas for arable farming. Even though this may have a negative effect on pastoralists, it also results in a symbiotic relationship. Pastoralists can graze their animals on crop residues in the dry season and the settled farmers crops benefit from the animal manure that is left in the fields.
To assist you in learning the following sections, Box 4.1 contains the definitions of some basic concepts of nutrition and feed. Solutions to nutritional constraints depend on the nature of the system. In pastoral systems the scope is limited as the situation is complicated by land tenure and stocking rates. In mixed croplivestock systems there is potential for improvement. The following are a few strategies to improve ruminant livestock nutrition through technological solutions:
Box 4.1. Definition of concepts related to nutrition and feeds
Crude protein. The amount of protein in the feed available to the ruminant. It is calculated using nitrogen content of the feed corrected by a factor of 6.25 based on the assumption that feed protein contains, on average, 16% nitrogen. Assumes that all faecal nitrogen is in the form of proteins.
Crude fibre. A fraction of feed that contains the cell wall and consists of carbohydrates (hemicellulose and cellulose) and lignin.
Digestibility. The digestibility of a feed determines the amount that is actually absorbed by an animal and therefore the availability of nutrients for growth, reproduction etc.
Energy. Derived from organic constituents of food and used as fuel for body functions and production.
Maintenance. This is the condition where an animals energy requirements are in balance (equilibrium) and it is not reproducing or producing output.
Metabolism. The sum of all the physical and chemical processes taking place in living organisms. For example the excretion of waste (manure and urine) products from the body is part of the metabolic process.
Scientists conduct research to develop feeding systems that provide sets of tables that give nutrient requirements of the animal and the nutritive value of feed both expressed according to the feed evaluation system. The feeding systems are prepared to help farmers calculate rations for their animals. Scientists conduct research to find solutions to nutritional problems. This involves studying the relationship between nutrition and performance, management and grazing conditions. To achieve this goal, data are collected to:
This module presents some concepts and methods used to collect these data (Table 4.1). For further details, you are referred to the reading materials.
Table 4.1. Types of animal data used to diagnose animal nutrition problems.
Type of data
Liveweight gain, condition scores, traction power, milk and wool production
Amount of feed consumed
Composition of feed consumed
Rumen fistula samples, faecal samples and grazing behaviour
Detailed methods for data collection are described in ILCA (1990).
Feed intake is the amount of feed an animal consumes. It can be estimated by using either digestibility data or markers.
When digestibility data are available, intake can be estimated by multiplying the dry matter (DM) weight of faeces by a digestibility factor. The factor is known as the feed:faeces ratio and is expressed as:
where digestibility is in per cent.
For example if the dry-matter weight of faeces of an animal is 870 g/day and the percentage digestibility of the feed consumed is 60%, then the amount of dry feed consumed would be:
Digestibility and intake data can be derived from the indigestible components of a diet, known as markers. Markers are classified as internal, if they are ordinarily present in the diet (e.g. lignin), or as external if they are added to the diet (e.g. chromic oxide, iron oxide and barium sulphate). They are used when the measurement of feed intake and faecal output is difficult.
The formula used to estimate faecal output is:
For example an animal is dosed with 50 g of chromic oxide per day to determine its daily faecal output. The concentration of marker in the dry faeces sample is 5.75% and the dry-matter weight of the faecal output is:
If the proportion of marker in the diet is 3.4%, then we calculate dry-matter intake as follows:
It is important to know the supply of different nutrients to ruminant livestock in systems in relation to their need for these nutrients. This module will cover energy, protein, water, minerals and vitamins. Methods to estimate amounts of these nutrients can be found in ILCA (1990).
The energy yield of a source of feed (such as natural pasture) can be estimated from its dry-matter weight per unit area. Feeds with a high biomass per unit area are often low in energy since they also contain a high proportion of indigestible fibrous matter.
Protein is the basic structural material from which all body tissues (e.g. muscles, nerves and blood cells) are formed. It is therefore essential for production and maintenance and cannot be replaced by other nutrients in the feed. The requirements of the animals are for essential amino acids, which are the building blocks of the protein. This is expressed as protein requirements, where crude protein (CP) is obtained by using this equation:
where the value 6.25 is based on the assumption that feed protein contains, on average, 16% nitrogen.
Crude protein is highly related to grain yield at the time of harvest (Church and Pond 1982). On a per hectare basis, grain yield is related to CP in the leaf. Such relationships can be used to indicate the availability of CP in the different sources and/or at different stages of plant growth.
When estimating the CP content of browse plants and crop residues, it should be kept in mind that the presence of certain chemical compounds (e.g. tannins) in these feeds can affect the availability of nitrogen to the ruminant.
It is important to know that ruminants are able to synthesise protein from non-protein nitrogen sources (e.g. urea) by microbial action in the rumen.
Calcium, phosphorous, magnesium, sodium, potassium, sulphur, chlorine, iron, copper, cobalt, iodine, manganese, selenium, zinc, chromium, fluoride, molybdenum, nickel, silicon and vanadium are essential for tissue growth and regulation of body functions in ruminants. If one of these minerals is missing in the diet, symptoms of deficiency occur; if any mineral is in excess the animal experiences toxicity. Mineral deficiencies in the soil and flora can lead to these deficiencies in the ruminants. Excess of selenium in the soil may result in levels in plants which are toxic to the animals. Usually under extensive livestock systems in the tropics, mineral imbalances are rarely seen. Analysis for minerals should only be attempted if mineral deficiencies are clearly evident. Even then, if other nutrients such as energy or CP are more limiting (as is likely to be the case in African rangelands), the mineral constraint should be dealt with only after the primary deficiencies have been rectified. A more detailed account of symptoms of mineral deficiency and the role of minerals in ruminant nutrition can be found in basic nutrition texts (e.g. Church and Pond 1982).
Ruminant livestock require vitamins in very small amounts, to regulate body functions. Although vitamin deficiencies do occur in ruminant animals in the tropics, in general they are of minor importance. Under more intensive systems (e.g. peri-urban dairy), vitamin supplements should be provided. Many of the vitamins are synthesised in the rumen especially many of the members of the vitamin B complex and vitamin C. If animals are exposed to the sun, they are able to manufacture vitamin D. Vitamin A is essential during pregnancy; cattle can obtain provitamin A from green forage and convert it into vitamin A. Young herbage and cereal grains contain enough vitamin E to meet livestock needs.
Ruminants require water because:
For animals kept under the pastoralist system, the frequency of watering is very important. During the dry season water is available only from wells or some lakes/streams. This leads to overgrazing around the watering points forcing pastoralists to move their animals far away from water sources to obtain pasture. The situation presents a dilemma to nomads because water intake increases as watering frequency is decreased and food conversion efficiency becomes lower as watering intervals increase.
Heat stress increases the water requirement of cattle. It is recommended that cattle be given water ad libitum. The water requirements increase when cows are pregnant or lactating. Lactating cows require 50% more water during early lactation and 25% more during late lactation. The extra water required is equivalent to the amount of milk produced.
The chemical composition of a feed determines its nutritive value. The difference in energy value of feeds is due to their differing digestibility. The digestibility of a feed determines the amount that is actually absorbed by an animal and therefore the availability of nutrients for growth, reproduction etc. A few methods to evaluate feed for digestibility are listed. [For more details about the methods consult Osuji et al. (1993b)].
A feeding trial is used to obtain data to calculate digestibility values. Faeces from several animals is collected for at least 1 week following an adaptation period of 2 weeks. The following equation is used:
where DMfood is the dry matter consumed and DMfaeces is the dry matter excreted in the faeces.
You place samples of feed in small nylon bags, which are then placed in the rumen through a fistula. The degradation of the feed is recorded after two days.
An indigestible marker such as chromic oxide is mixed with the feed. The concentration of chromic oxide in the feed and faeces is used to calculate digestibility as follows:
Apparent digestibility (%) = 100 [100 – (100 × % marker in feed/% marker in faeces)]
There are several in vitro methods for measuring digestibility.
Natural pastures are the most important feed resource for cattle in SSA. Pastures differ in their species composition and canopy coverage. The canopy coverage depends on the amount of moisture in the soil and sunlight. UNESCO (1979) adopted the following classification for natural pastures:
The potential carrying capacity of the pasture is determined by the quantity of vegetation. The productivity of cattle on pasture is affected by the quality of the vegetation. The quantity and quality of pasture is affected by:
At the start of its growth, natural pasture has high water and protein contents which are not advantageous for animals because of limited energy intake; cellulose increases thereafter. Natural pasture with 3040% cellulose content is adequate for the maintenance requirements of ruminant livestock. Higher cellulose content is undesirable because rumen micro-organisms are unable to degrade it, thus pasture with high cellulose content is low in nutritive value. Grasses reach their highest quality during stem elongation and the quality decreases after heading.
The yield and quality of natural pastures can be improved by:
Improving pasture in the dry zones of the tropics is limited by cost such that only simple measures can be implemented. There is more scope for improvement in the subhumid and humid zones of SSA provided there is a way to control tsetse fly and associated cattle diseases.
Introducing new species to pastures must be done carefully. An aggressive species will dominate the less aggressive ones. Introduced species should be able to:
The list of species and the methods used to establish and maintain pasture are beyond the scope of this manual. Specialised texts can be consulted for more details (see Crowder and Chheda 1982). The successful use of improved pastures depends on grazing control. The use of barbed wire or electric fences is beyond the means of resource poor farmers. The use of fodder trees or non-palatable shrubs as fences has been demonstrated as a possible means of controlling grazing (Charray et al. 1992). However, the use of this technology is limited by lack of enough labour and inadequate knowledge of the management of trees/shrubs.
Even though natural pastures are used extensively in SSA, they can only support the desired productivity of cattle to a certain level and for a short period. Cultivated pasture or fodder crops are grown with the aim of:
When choosing a fodder crop we should ask the following questions:
Fodder crops are not yet widely used in SSA because of the high cost of inputs such as land, labour and fertiliser. These crops are attractive when grown as:
Fodder crops must give higher yields or have better quality than pastures (Mohamed-Saleem 1985). Legume fodder is known to have these attributes.
Fodder banks were found to improve the nutritional status of livestock during the dry season. These are special plots of legumes grown by pastoralists adjacent to their homes to serve as supplements to dry-season grazing. For Nigerian pastoralists, ILRI developed fodder bank technology packages which use low inputs. The farmers received the technology well and researchers and extension teams worked with them to overcome difficulties related to establishment, utilisation and regeneration.
Dry natural pastures can only provide low-quality roughage and therefore cattle will benefit from any form of supplementation of the roughage. Supplements usually consist of at least one of the following:
These supplements can be fed to animals separately, incorporated into a complete diet or as feed blocks. When supplementing roughage you must remember that:
Supplements to roughage are beneficial to cattle because:
During the dry season, the quality of pasture is low and forages are scarce. One way to solve this problem is to conserve forages. Conservation aims at retaining the feed value of the forage. Fodder can be conserved as hay or silage.
Hay is dried fodder. To produce hay of high quality, it is essential to harvest the fodder at the right time. When fodder is harvested too early, its moisture content is too high resulting in hay with reduced dry-matter content. If fodder harvest is delayed, the plants develop high lignin content. Hay made from fodder with high amounts of lignin is of poor quality because its digestibility is low. In the humid zone, heavy rainfall forces farmers to delay fodder harvest until the dry season resulting in fodder with high lignin content. In addition, at the end of the rainy season, most crops are ready for harvest so hay-making competes with crop harvests for labour.
Hay can be sun dried to 1015% moisture content. Low air humidity is needed to achieve this level of moisture in the hay. This is easy to achieve in the arid and semi-arid zones but difficult in the humid zone where the rainfall and relative humidity are higher.
There are many methods for making hay. The simplest and cheapest method is drying the forage on the ground. The grass is cut (using a machete) early in the morning and is spread on the ground in the field. The heaps of forage are turned over many times to avoid picking up moisture from the soil. Sophisticated methods for drying forages and haymaking are available but they are costly and beyond the reach of smallholder farmers. Hay should be protected from rain and the sun as exposure to these factors reduces its feed value. Cattle may refuse hay of low quality unless they are starving. Hay can never be equal in feed value to the fresh forage from which it is made.
How do farmers use hay?
Fermenting the sugars in green herbage under anaerobic conditions produces silage. The desired product is reached when enough acids are produced (low pH which prevents bacterial decomposition) and fermentation stops. Silage can be stored for at least a year.
Silage can be made in silos of various shapes. The easiest method is to use pit and trench silos, which can be built using simple materials. The silo and its wall must be completely air tight to prevent the fodder putrefying. The bottom of the silo must be covered with stones to allow the liquids resulting from fermentation to drain off. To ensure successful silage making:
There are many crop residues which can be used for feeding cattle. Farmers with no animals may use crop residues to improve fertility of the soil or sell the residues.
Straw is mostly a by-product of cereal crops that is used as roughage for ruminants. Straw of the following crops is used in SSA: maize, millet, sorghum, wheat, barley, rice and teff. Crop residues from other crops are also used on a small scale: sugar-cane, cocoa, banana, cotton, cassava and legume crops.
Straw has low nutritive value. The energy content of straw ranges from 5.5 to 9.6 MJ metabolisable energy (ME)/kg DM. Energy values vary with the cereal variety and the management of the residue after grain harvest. Straw is high in lignin, which lowers its digestibility. Straws of most crops are low in CP and minerals (especially phosphorous). The nutritive value of straw and its coarse physical form limit the activity of micro-organisms in the rumen and contribute to the low rate of passage through the digestive system. All these factors result in low voluntary intake. You can improve the feed value of straw by:
Bran is produced from cereals and it consists of the outer parts of the hulled grains, some broken grain and germ. Bran is palatable and is a valuable feed for cattle. Its CP content is 12%. The main problem with bran from rice and maize is its relatively high oil content (around 10%). Fatty acids turn rancid with storage and this lowers the nutritive value and palatability of the bran.
Cottonseed cake, when available, is an excellent feed for cattle. It has a high content of protein (2540%), fat (1023%) and cellulose (2530%). Once the animal gets used to cottonseed cake, intake increases. Kumwenda and Msiska (1990) fed dairy cows in government research stations in Malawi maize bran in combination with cottonseed cake at the ratio of four parts of maize bran to one part of cottonseed cake. They found that the diet increased milk production and the inclusion of cottonseed cake in maize bran-based dairy rations would raise dairy farmers profit. Other researchers obtained good results by mixing cottonseed cake with salt and molasses. It had been tried with West African Dwarf ewes and a mixture of 50:50 molasses and cottonseed cake gave good results (Charray et al. 1992). The high protein content allows the amount of cottonseed cake to be reduced without detrimental effects. Unfortunately cottonseeds contain the toxic substance gossypol, which reduces the growth of young animals, but has little effect on adults. However, there are cotton varieties that are glandless and their seeds are free of gossypol.
Oilseed cakes (oilmeals) are by-products of processing a variety of oil crops: groundnut, sunflower and soybean. These cakes are like cottonseed cakes: rich in protein and fatty acids. They can be used alone or mixed with molasses for effective results. Research at ILRI (Osuji et al. 1993a) showed that sunflower cake was utilised effectively by Menz sheep in the Ethiopian highlands in terms of rumen microbial nitrogen synthesis, nitrogen retention and growth. The addition of small amounts of energy such as crushed maize grain increased microbial nitrogen synthesis, nitrogen retention and live weight gain. The cost and availability of the cakes will determine the likelihood of their adoption by farmers.
When beer is made, the residues are the spent grains and yeast. Cattle readily accept these as feed. Sources for these by-products are beer factories, which are increasing in SSA (including home made installations). The by-products from home installations are richer in energy and protein than the residues from the factories.
The by-products from sugar-cane factories are dried sludge, molasses and bagasse. Cattle can be fed all three by-products. Farmers mostly use molasses, a thick dark brown liquid which contains 5065% sugar with little protein or water. It is thus a high energy feed. When added to cottonseed cakes, it increases the intake of coarse and less readily accepted cakes. It can be added to the herbage during silage production. Molasses therefore is an excellent feed provided it is supplemented with protein and minerals.
Example: Supplementation with molasses
At ILRIs research station in Debre Zeit, Ethiopia, four rumen fistulated crossbred (Bos taurus × Bos indicus) steers (mean live weight 468 kg) were fed twice daily a basal diet (Diet MO) comprising native grass hay ad libitum (free eating) and 4 kg dry matter (DM) of wheat bran. Three other diets were tested: 1. Native grass hay plus 750 g wheat bran per kg DM; and 250 g molasses per kg DM; 2. Native grass hay plus 500 g wheat bran per kg DM and 500 g molasses per kg DM; and 3. Native grass hay plus 250 g wheat bran per kg DM and 750 g molasses per kg DM. The native grass hay was predominantly Pennisetum species. Wheat bran and molasses were mixed and fed together from a bucket. Increasing the level of molasses did not affect the intake of hay. There was no effect on digestibility of wheat bran. The researchers concluded that replacing wheat bran with different levels of molasses did not affect the function of microbes in the rumen. Rumen microbes utilised energy equally from molasses fermentation compared with wheat bran.
Source: Osuji and Khalili (1994).
The integration of cattle with tree crops is common practice in many places in SSA. Farmers in the Kenya highlands feed leaves of Leucaena to cattle. The dry-matter yield of Leucaena is between 2 and 20 tonnes per hectare per year. The tree leaves contain mimosine which is toxic to cattle. Many other tree species are used for fodder, e.g. Sesbania sesban, Calliandra spp and Gliricidia sepium. Fodder from trees is especially useful during the dry season when it is used to supplement roughage or hay. Fodder trees were found to affect lactation of cows when fed as supplements to Napier grass. Leucaena supplementation increased total dry matter intake and milk yield (Muinga et al. 1992). Research at ILRI concluded that Erythrina abyssinica has high forage potential and can effectively serve as a cheap source of protein supplement for low quality diets during the dry season for resource-poor farmers with stall-fed sheep and goats (Larbi et al. 1993). Supplementation of pasture in Zimbabwe with 110 g Acacia angustissima per goat per day was found to result in an increase of 12 g per goat per day.
Example: Feeding multi-purpose trees as supplements
Many multi-purpose trees have been tested as supplements to feed of livestock ruminants. In this example we will focus on results of an experiment that used Leucaena leucocephala. The literature has ample examples of other fodder trees. The feeding value of L. leucocephala leaves was evaluated with crossbred cows in Kenya. The crossbred cows were fed Napier grass ad libitum and supplemented with 4 or 8 kg fresh Leucaena leaves per day from day 15 to 112 of lactation. The results showed that there was an increase in the intake of Napier grass and total dry-matter intake due to Leucaena leaves supplementation. Supplementation resulted in significant increases in milk yields. Milk yield increased over the Napier grass ad libitum treatment by 0.8 kg and 1.7 kg per day from the 4 and 8 kg Leucaena supplementation treatments, respectively.
Source: Muinga et al. (1992).
This module will only provide a list of feeding techniques. For more information consult Charray et al. (1992).
The following are common feeding techniques:
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