Feed Formulation for Livestock

Principles of Ration Formulation for Ruminants

Feeding standards as practised in developed countries could be misleading when nonconventional feed resources are used in formulating rations for ruminant livestock in developing countries. They tend to reject the poor-quality feeds that are available in vast quantities. The nonavailability of good quality forage throughout the year and the need to optimise the efficiency of utilisation of locally available feed resources have led to the application of basic nutritional principles when considering ration formulation. The alternative approach to the use of feeding standards would be to ensure that the production system matches the available resources. The development of feed supplementation strategies based on locally available feed resources requires the understanding of the relative roles and nutrient needs of the two-compartment system represented by the micro-organisms in the rumen and the host animal.

 

A. Feed Resources Available for Ruminant Livestock

The availability of feed resources is determined by the land utilisation pattern. This reflects the demand of the human population and the nature of the ecosystem which in turn is a function of land and soil characteristics including terrain, availability of water, rainfall, soil fertility, and so on. Due to the ever-increasing human population and the consequent increase in demand for food, livestock feed tends to be derived from residues and by-products of the food industry.

The major problems with the feeding of livestock occur in those areas subjected to long dry seasons when there is insufficient plant biomass carried over from the wet season to support the domestic livestock population. The situation becomes more acute as the dry season becomes established, when the protein content of the natural grazing falls, often from 12 – 14% to about 6 – 8%. The fall in crude protein content is also accompanied by an increase in fibre content. Thus, the animal is faced with insufficient amounts of low-quality and relatively indigestible feed. The situation is intensified by drought.

Feed resources available for livestock production in the tropics can be categorised into four groups:

1. High fibre-low protein feeds.

These include fibrous residues arising from crops grown for human consumption, such as straws and stovers from rice, millet, sorghum and maize, and sugarcane bagasse. The production of crop residues and by-products can be estimated fairly accurately from estimates of the primary product (e.g., grain), using multipliers which assume grain: residue ratios. The uncertainty of such ratios can be judged by the different multipliers used by different people. Notwithstanding such discrepancies in grain residue ratios for estimating residue yields, it is quite evident that vast quantities of residues are produced as a result of crop cultivation. A conservative estimate would be over 5 billion tonnes of dry matter (DM) per year.

Crop residues are characterised by their high fibre content (>700 g of cell wall material/kg DM), low metabolizable energy (< 7.5 MJ/kg dry matter), low levels of crude protein (20 – 60 g of crude protein/kg DM) and mineral nutrients and low to moderate digestibility (< 30 – 45% organic matter digestibility). Their daily intakes are often limited to less than 20 g dry matter/kg live weight. Most residues are also deficient in fermentable carbohydrates, reflected by the relatively low organic matter digestibility.

2. High fibre-high protein feeds.

By-products derived from crop production (tops and haulms from ground nut, sweet potato vine, cassava leaves, bean straw) and industrial processing (bran from cereal milling —rice, wheat and maize bran, brewer’s grain), fall into this category of feeds. They are generally less fibrous (below 700 but above 400 g of cell wall material/kg of DM) than those in the first category but have relatively high amounts of crude protein (> 60 g/kg DM). Leaves from tree legumes and browse plants such as Glyricidia, Leucaena and Erythrina, which have around 250 – 350 g/kg of crude protein in DM, can also be considered in this category.

3. Low fibre-low protein feeds.

These include feed resources derived from crops grown for renewable energy such as sugarcane by-products and root crops. They are generally rich in energy and low in protein content. Examples of this category would be molasses, oil palm juice and waste material arising from the fruit processing industry (citrus pulp, pineapple waste) and root crops (cassava waste).

4. Low fibre-high protein feeds.

These are the feeds traditionally called concentrates and include oilseed meals and cakes (coconut cake, soybean meal, cotton seed cake, groundnut meal or cake) and animal byproducts (fishmeal, blood meal, feather meal). They are valuable sources of good-quality protein for both ruminant and non-ruminant animals. Oil seed meals and cakes may contain variable amounts of crude protein: coconut meal contains around 200 g crude protein/kg of dry matter while decorticated oil seed meals such as groundnut meal, and cottonseed meal (or cake) may contain as much as 400 – 500 g of crude protein/kg of dry matter. The amount of oil contained in the by-product may affect the keeping quality of the feed. It varies according to the method of extraction of the oil; solvent-extracted meals or cakes will contain less oil than expeller-extracted meals or cakes.

Animal by-products are very good sources of high-quality protein and can improve the nutritive value of low-quality forage-based diets for ruminants. Fishmeal is often used for balancing the amino acid content in monogastric feeds. Even for ruminants, fishmeal can provide a high proportion of rumen non-degradable protein acting as a reservoir of amino acids for high levels of production. Natural pastures fall into the first and/or the second category depending on the time of harvesting, the nature of the pasture species, climatic conditions, and so on. The proximate composition of some common feeds found in developing countries and classified according to the above criteria.

 

B. Ration Formulation for Ruminants and Alternative Approach

If one considers that the use of traditional feeding standards as practised in developed countries is inappropriate for developing countries with limited resources, then there must be an alternative approach when formulating rations for ruminants. This alternative approach would require that the livestock production system is matched with the resources available and optimises the utilisation of locally available feed resources. Such an alternative approach for formulating rations for ruminants should consider that:

• The efficiency of the rumen ecosystem cannot be characterised by any form of feed analysis currently in use. This raises the question: can the feed support optimum rumen function? What is the nature, amount, and proportion of end products of fermentative digestion?
• Feed intake on some diets bears no relationship to the digestibility of the feed.
• Feed intake is often influenced by supplementation.
• The availability of amino acids cannot be inferred from the crude protein content of the diet. This reflects the potential escape of nutrients from the rumen and their digestibility in the small intestine.
• The energy value of a diet and the efficiency of its utilisation are largely determined by the relative balances of glucogenic energy, long-chain fatty acids and essential amino acids absorbed by the animal.

Therefore, when considering ways to optimise the utilisation of feed resources for ruminants it is necessary to apply three basic concepts:

1. Ensure optimum conditions for microbial growth in the rumen to make the digestive system of the animal as efficient as possible.
2. Supply deficient nutrients to balance the products of digestion to requirements, optimising production.
3. Any further production increases should be by the use of supplements of protein, starch, and lipids.

 

The Feed Composition Value of Sheep and Cattle Feed

The ultimate goal of feed analysis is to predict the productive response of animals when fed diets of a given nutrient composition.

So, what is the value of showing composition data for feeds? An actual analysis of a feed to be used in a diet is much more accurate than using tabulated composition data, and actual analysis should be obtained and used whenever possible. But it’s often difficult to determine the actual composition in a timely way; therefore, tabulated data are the best source of information.

In using tabulated values, one can expect organic constituents (e.g., crude protein, ether extract and fibre) to vary as much as ± 15%, mineral constituents to vary as much as ± 30% and energy values to vary up to ± 10%. Thus, the values shown can only serve as guides. That’s why they are called “typical values.” They’re not averages of published information, since the judgment was used in arriving at some of the values in the hope that they will be realistic for use in formulating cattle and sheep diets.

New crop varieties may result in nutrient composition changes. Genetically modified crops may result in feeds with improved nutrient content and availability, and/or decreased anti-nutrient factors.

 

A. Chemical Constituents Vs Biological Attributes

Feeds can be chemically analysed for many things that may or may not be related to the response of an animal when fed the feed. Thus, in the accompanying table, certain chemical constituents are shown. The response of cattle and sheep when fed a feed, however, can be termed the “biological response” to the feed. It’s a function of the feed’s chemical composition and the ability of the animal to derive useful nutrient value from it. The latter relates to the digestibility or availability of a nutrient in the feed for absorption into the body and its ultimate efficiency of use depending upon the animal’s nutrient status and the productive or physiological function being performed by the animal. Thus, ground fence posts and shelled corn may have the same gross energy value but markedly different useful energy values (total digestible nutrients — TDN — or net energy) when consumed by the animal.

Therefore, a feed’s “biological attributes” have much greater meaning in predicting the productive response of animals. Unfortunately, biological attributes are more difficult to precisely determine because of the interaction between the feed’s chemical composition and the animal’s digestive and metabolic capabilities. Biological attributes of feeds are more laborious and costly to determine and are more variable than chemical constituents. They’re generally more predictive, however, since they relate to the animal’s response to the feed or diet.

 

B. Using Table Information

• Feed names: The most obvious or commonly used feed names are used in the table. Feeds designated as “fresh” are feeds that are grazed or fed as fresh-cut materials.
• Dry matter: Typical dry matter (DM) values are shown, but the moisture content of feeds can vary greatly. Thus, DM content can be the biggest reason for variation in feed composition on an “as-fed basis.” For this reason, the chemical constituents and biological attributes of feeds shown in the table are on a DM basis.

Since DM can vary greatly, and one of the factors regulating total feed intake is the DM content of feeds, diet formulation on a DM basis is preferable to “as-fed” values. However, to convert a value to an as-fed basis, simply multiply the decimal equivalent of the DM content times the compositional value shown in the table.

• Energy: The table lists four measures of the energy value of feeds. TDN is shown because there are more determined TDN values, and it’s been the standard system for expressing the energy value of feeds for cattle and sheep. There are several technical problems with TDN, however.

For one, the digestibility of crude fibre (CF) may be higher than for nitrogen-free extract (NFE) in certain feeds due to the partition of lignin in the CF analysis. TDN also overestimates the energy value of roughages compared to concentrates in producing animals. Some argue that since energy isn’t measured in pounds or per cent, TDN isn’t a valid energy measure. This, however, is more of a scientific argument than a criticism of TDN’s predictive value.

Digestible energy (DE) values aren’t included in the table. There’s a fairly constant relationship between TDN and DE in cattle and sheep; DE (Mcal/cwt.) can be calculated by multiplying the %TDN content by 2. The ability of TDN and DE to predict animal performance is therefore the same.

Interest in using net energy (NE) in feed evaluation was renewed with the development of the California net energy system. This is due to the improved predictability of the productive response of animals depending on whether feed energy is being used for maintenance (NEm), growth (NEg) or lactation (NEl). The major problem in using these NE values is predicting feed intake and thus the proportion of feed that will be used for maintenance and production. Some only use NEg but this suffers the equal but opposite criticism mentioned for TDN; NEg will overestimate the feeding value of concentrates relative to roughages.

The average of the two NE values can be used, but this would be true only for cattle and sheep eating twice their maintenance energy requirement. The most accurate way to use these NE values to formulate diets is to use the NEm value plus a multiplier times the NEg value, all divided by one plus the multiplier. The multiplier is the level of feed intake relative to maintenance.

For example, if 350 kg cattle are expected to eat 9 kg of DM, 4 kg of which will be required for maintenance, the diet’s NE value would be:

 

 

When predicting animal performance, there is little doubt that NE is theoretically preferable to TDN when choosing an energy system. But this superiority is lost if only NEg is used to formulate diets. If NE is used, some combination of NEm and NEg is best.

NEl values are also shown but few have been determined. NEl values are similar to NEm values except for very high- and low-energy feeds.

• Protein: Crude protein (CP) values are shown, which are Kjeldahl nitrogen times 100/16 or 6.25 since proteins contain 16% nitrogen on average. CP provides no information on the actual protein and non-protein nitrogen (NPN) content of a feed.

Digestible protein (DP) has been included in many feed composition tables. But because of the contribution of microbial and body protein to the protein in faeces, DP is more misleading than CP. One can estimate DP from the CP content of the diet fed to cattle or sheep by the following equation: %DP = 0.9(%CP) – 3 where %DP and %CP are the diet values on a DM basis.

Undegradable intake protein (UIP; rumen “by-pass” or escape protein) values represent the percentage of CP passing through the rumen without degradation by rumen microorganisms. Degradable intake protein (DIP) is the per cent of CP degraded in the rumen and is equal to 100 minus UIP. Like other biological attributes, these values are not constant. UIP values on many feeds have not been determined and reasonable estimates are difficult to make.

How should these values be used to improve the predictability of animal performance when fed various feeds? Generally, DIP can supply CP with up to 7% of the diet. If the required CP in the diet exceeds 7% of the DM, all CP above this amount should be UIP. In other words, if the final diet is to contain 13% CP, six of the 13 percentage units, or 46% of the CP, should be UIP.

Once the relationships between UIP and DIP have been better quantified, CP requirements may be lowered, especially at higher CP levels. For diets high in rumen fermentable carbohydrates, DIP requirements may determine the total CP required in the diet.

• Crude, acid detergent and neutral detergent fibre: After more than 125 years, crude fibre (CF) is declining in use as a measure of poorly digested carbohydrates in feeds. Its major problem is that variable amounts of lignin, which isn’t digestible, are removed in the CF procedure. In the old scheme, the remaining carbohydrates (NFE) were thought to be more digestible than CF despite many feeds having higher CF digestibility than NFE. One reason CF remained in the analytical scheme was its apparent requirement for the TDN calculation.

Improved analytical procedures for fibre have been developed, namely acid detergent fibre (ADF) and neutral detergent fibre (NDF). ADF is related to feed digestibility and NDF is somewhat related to voluntary intake and the availability of net energy. Both measures relate more directly to predicted animal performance and thus are more valuable than CF. Lignification of NDF, however, alters the availability of the surface area to fibre-digesting rumen microorganisms; lignin, therefore, may be added to future tables.

Recently, effective NDF (eNDF) has been used to better describe the dietary fibre function in high-concentrate, feedlot-type diets. While eNDF is defined as the per cent of NDF retained on a screen similar in size to particles that will pass from the rumen, this value is further modified based on feed density and degree of hydration.

Rumen pH is correlated with dietary eNDF when diets contain less than 26% eNDF. Thus, when formulating high-concentrate diets, including eNDF may help to prevent acidosis in the rumen. In feedlot diets, the recommended eNDF levels range from 5 – 20% depending on bunk management, the inclusion of ionophores, digestion of NDF and/or microbial protein synthesis in the rumen.

Estimated eNDF values are shown for many feeds. These should be decreased depending on the degree of feed processing (e.g., chopping, grinding, pelleting, flaking) and hydration (fresh forage, silages, high moisture grains) if these feed forms aren’t specified in the table.

• Ether extract: Ether extract (EE) shows the feed’s crude fat content.
• Minerals: Values are shown for only certain minerals. Calcium (Ca) and phosphorus (P) are important minerals to consider in most feeding situations. Potassium (K) is more important as the concentration level increases and when NPN is substituted for intact protein in the diet.

Sulfur (S) also becomes more important as the NPN level increases in the diet. High dietary S levels compounded by high S levels in drinking water, however, can be detrimental. Zinc (Zn) is shown because it’s less variable and is more generally near a deficient level in cattle and sheep diets. Chlorine (Cl) is of increasing interest for its role in dietary acid-base relationships.

The level of many other trace minerals in feeds is largely determined by the level in the soil on which the feeds are grown or other environmental factors that preclude showing a single value. Iodine and selenium are required nutrients that may be deficient in many diets, yet their level in a feed is more related to the conditions under which the feed is grown than to a characteristic of the feed itself. Trace mineralised salt and trace mineral premixes are generally used to supplement trace minerals; their use is encouraged where deficiencies exist.

• Vitamins: Vitamins aren’t included in the table. The only vitamin of general practical importance in cattle and sheep feeding is the vitamin A value (vitamin A and carotene) in feeds. This depends largely on maturity and conditions at harvest and the length and conditions during storage. Thus, it is probably unwise to rely entirely on harvested feeds as a source of vitamin A value.

Where roughages are fed that contain good green colour or are being fed as immature, fresh forages (e.g., pasture), there will probably be sufficient vitamin A value to meet animal requirements. Other vitamins, if required, should be supplied as supplements.

 

Feed Composition Tables

All values except dry matter (DM) are shown on a DM basis.

 
See PDF 

Ration Balancing for Sheep

 
A homemade ration.
 

Rations can be balanced by hand (using simple math), online, and using ration balancing software. No matter which method is used to balance the ration, the same information is required: a description of the animals, nutrient requirements of the animals, available feedstuffs, and composition of feeds.

If rations are balanced online or ration-balancing software is used, nutrient requirements and feed inventories will be built into the programs. Programs usually allow the user to alter the nutrient requirements and feed compositions and add custom feeds.

 

A. Balancing Rations by Hand

Rations can be balanced by hand using paper, a pencil, and simple math.

Step 1: Describe the animals to be fed.

You’re going to balance a ration for mature ewes that average about 75 kg. They are nursing three-week-old twin lambs.

Step 2: Look up the ewes’ nutrient requirements – this refers to implementing a nutritional program.

Ewes – first 6 – 8 weeks lactation suckling twins.

kg	DMI (kg)	TDN (kg)	CP (kg)	Ca (g)	P (g)
70	2.8	1.8	0.42	11	8.1

Step 3: Determine what feedstuffs are available.

You have barley, a mixed clover-grass hay, and a commercial protein supplement.

Step 4: List the components of the available feeds.

List of available feeds.

Feedstuff	% DM	% TDN	% CP	% Ca	% P
Whole barley	89	84	12	0.06	0.38
Clover-grass hay	88	58	15	0.84	0.31
Commercial protein supplement	89	72	38	1.6	0.95

The values for barley were taken from the feed composition tables. The hay was analysed at a forage testing laboratory, so actual values are given. For the commercial protein supplement, we used the values from the feed label.

Step 5: Balance the ration.

The easiest way to balance a ration is to start with the forage (usually hay). Determine how much hay you are feeding or how much hay they are consuming (if the hay is fed free choice). Be sure to factor in waste, as there can be considerable waste when feeding hay, particularly lower-quality hay.

 

You can use Pearson’s Square or the substitution method to determine the ratio of barley to commercial protein supplements.

 

B. Pearson’s Square

Pearson’s Square is an old mathematic tool that can be used to balance rations by blending two ingredients. The value in the middle of the square must be between the two ingredients that are to be mixed. Subtraction is done diagonally. Negative signs are ignored.

This example shows Pearson’s Square being used to determine the ratio of grain to supplement to create the 16% protein ration needed in our example.

 
Pearson’s Square used to establish grain-to-supplement ratio for 16% protein feed.
 

Pearson’s Square shows that you need to mix 85% barley with 15% of the protein supplement to make a 16% protein grain ration for your lactating ewes.

Similar calculations should be done to determine if the ration is meeting the calcium and phosphorus needs of the ewes. Earlier calculations show that the hay portion of the ration already meets the calcium requirements of the ewe.

The final ration as calculated.

Feed	As-Fed	DMI	TDN	CP	Ca	P
Hay	4.5	4	2.3	0.6	15	5.6
Barley	1.91	1.7	1.43	0.2	0.5	2.9
Supplement	0.34	0.3	0.22	0.11	2.1	1.3
Totals	6.75	6	4	0.91	17.6	9.8

 

C. Adjusting Balanced Rations

There are times when adjustments may need to be made to otherwise balanced feeding programs. You may wish to increase the feed intake of animals that are in poor body condition and likewise reduce the intake of obese sheep. This kind of feed adjustment should not be made during critical periods during the production cycle.

For example, reducing the intake of a fat ewe during late gestation can cause her to develop pregnancy toxaemia. Conversely, increasing the feed intake of a thin ewe during late gestation may increase the size of her unborn foetus(es), making the pending delivery more difficult.

Activity can alter nutrient requirements. Livestock that have to travel farther for their food and water have higher nutritional requirements, as they expend more energy. For this reason, sheep on pasture have higher nutritional requirements than housed sheep.

Weather and climate can have a significant effect on nutrient requirements. When it is cold, sheep require more energy to maintain their body temperature. The critical temperature is the lowest temperature or wind chill at which no additional energy is required to maintain core body temperature.

There is a 1% increase in energy requirement for each 1 °C that the temperature is below the sheep’s critical temperature. A sheep’s critical temperature depends upon the length of its fleece (and other factors). It is about 2 °C for a sheep with a 6.35 cm fleece and about 10 °C for a freshly shorn sheep.

 

The Processing and Manufacturing of Animal Feeds

The principal objective in feed mixing is to assure that an animal receives all of its formulated nutrient allowances every day. Uniformity of particle size and number of particles per unit weight are important considerations for assessing mixing accuracies of the various micro ingredients. Many of the micro-ingredients (particularly feed additives) are expensive and elevated levels may be toxic. Thus, small uniform particle size is a very important criterion in the selection of micro-ingredients.

Low density and a wide variety of particle sizes and shapes characterise forages. The creation of uniform feed mixes is made more difficult by the physical variety and density of the individual feed ingredients. Getting a uniform feed mix presents a unique challenge due to vitamin and feed additives. Their densities resemble those of ground grain and oilseed meal more closely. As a result, uniform mixing shouldn’t be a problem. They do, however, only make up a very small portion of the mixture.

 
Processing and manufacturing of animal feed.
 

A. Proper Mixing – An Essential Step of Feed Mixing

Feed manufacturing consists of a series of steps or processes, in which individual ingredients are combined into a homogenous mix, further processed as per the customer’s desired requirements (coarse dairy rations, pellets, flakes, and so on), and packaged for onward delivery.

One of the most essential and critical operations in the process of feed manufacturing is mixing. Where the individual ingredients are combined into their proper ratios and uniformity distributed throughout the entire mass, yet it is frequently given little consideration.

Creating a completely homogeneous blend is the objective of mixing; if the ingredients are not properly mixed, then the nutritional quality cannot be assured. The mixer performance can be affected by other factors such as particle size and shape of the ingredients, ingredient density, static charge, sequence at which ingredients are added, worn, altered, or broken equipment, improper mixer adjustment, poor mixer design, and cleanliness.

The nutrient variation in feeds is most likely to occur due to the following reasons:

• Variation in the composition or quality of ingredients from batch to batch or from time to time.
• Poor mixing or segregation after mixing.
• Errors during weighing or proportioning.

 

B. Poor Mixing

To confirm that the mixing is done properly, the major dry ingredients are added first, from largest to smallest. The last dry ingredients to be added are the minors – composed of the premixes, which are usually vitamins, minerals, and other additives. After all dry ingredients are added and allowed to mix, the operator proceeds to add the liquid ingredients. Understandably, mixing is then one of the most critical steps in the feed manufacturing process and, if not done correctly, it can have adverse effects on the nutritional and physical quality of the finished product or pellet.

A complete homogeneous mix will produce uniform pellets. Poor mixing can harm the pellet quality. If pelleting aids, such as a binder, are not added in the correct sequence, their distribution in the meal will be inadequate to produce pellets with the desired hardness or durability. In this item, excess fines will be produced, and the additive will be lost. The direct impact of fines will be on costs, as they increase the shrink and re-process costs in the process. The fines that are recovered in the process increase cost because they need to be re-processed. Most of the time, the fines are recycled back to the pellet surge bin; however, if excessive fines are put into the pellet mill, the pellet quality will continue to degenerate as the fines tend to lose their binding capacity.

 

C. Incomplete Mixing

Incomplete mixing occurs when one or more ingredients are not present in a feed sample taken at mixer discharge in the same percentage as the percentage of the ingredients used to charge the mixer.

Possible problems that occur with vertical and horizontal mixers.

Mixer Type	Possible Problems
Vertical Mixer	The design does not allow complete mixing. Design results in slow mixing. Insufficient mixing time. Worn screw. Electrostatic hang-up.
Horizontal Mixer	The design does not allow complete mixing. Design results in slow mixing. Overfilling results in a non-mixing layer at the top. Insufficient mixing time. Agitator clearance allows a layer of immobile ingredients next to the mixer shell. The agitator design does not move ingredients throughout the mixing area. Worn agitators. Electrostatic hang-up.

 

Source of Incomplete Mixing Problems:

Incomplete mixing can often be corrected by adjustments of mixers or by replacing components that are worn or otherwise inadequate for the purpose. An example is the adjustment of mixer ribbons to reduce the space between the ribbons and the mixer shell. Another example is the replacement of worn or damaged ribbons, paddles, or screw conveyors. Procedural changes may improve feed mixing. Factors affecting the ease of mixing a component in the whole composition include the sequence of compounds and additives inside the mixer.

Additions of the small volume materials to part of the protein source early in the mix cycle allow more time for complete mixing to occur. Improvement of feed mixing uniformity is associated with increased mixing time. Small-volume items such as drug or mineral premixes should be added directly to the mixer rather than through an auger system. If added through an auger, it should be followed with sufficient corn or protein to flush it into the mixing chamber.

Loading Over or Under the Capacity of the Mixer:

Once the batch size is derived, it should be maintained as a constant. Mixing performance affected by the increase and decrease of batch size from the derived value will overload or underload the mixer.

 

D. Ensuring Proper Mixing

Nutritional imbalances can happen if minor ingredients (vitamins, minerals, antibiotics, pelleting aids, and other additives) are not homogeneously distributed in the mixed meal. The imbalances can be in both directions – one of nutrient deficiency if some ingredients are not mixed, and one of excess or even toxicity (minerals, vitamins, antibiotics) if ingredients are in excess. Testing at least every 6 months to ensure suitable mixing quality, is necessary. The mixer test measures the coefficient of variation (CV) which is the standard deviation (σ) divided by the mean (µ) multiplied by 100. The mixer is adjusted at different time intervals, and the one with the least amount of mixing time that is below 10% CV should be selected. The mixing time can vary with formulation type. Therefore, a mixer test must be achieved for each formula type. Mixer efficiency can be affected by the amount of accumulation on the paddles and ribbons. The ingredient’s physical properties (density, particle size, hygroscopicity and electrostatic charges) can build up in the discharge gates that inhibit them from tightly closing, and cause wear of the paddles and ribbons. It is consequently important to ensure that the mixer is kept clean and appropriately functioning to ensure a homogeneous blend and optimum pellet quality.

 

E. Different Mixers and Mixing Systems

Good mixing begins with an understanding of the equipment used. Feed-mixing equipment can be divided into two broad types:

1. Continuous mixing – The continuous mixing system used on swine farms is metering mills. These mills meter ingredients into a mixing auger in set proportions.
2. Batch mixing – Batch mixing systems mix a set amount depending on their capacity. Most continuous systems are stationary, while batch systems can be stationary or portable.

Mixing procedures are different for batch and continuous systems.

Continuous Mixing Systems:

The automatic operation of a continuous mixing system is a significant advantage. When you start the mill, it will continue to mix until it runs out of ingredients, fills a finished feed bin, or is turned off. The proportioner, which controls the volume of each ingredient added, is the system’s main unit. This proportioner must be calibrated regularly to ensure the proper mix. Changes in ingredient density (that is, changes in test weight) will alter the weight proportions and thus the nutrient content of the mix. For example, if a mill is calibrated for maize weighing 56 kg per bag and the next load of maize weighs only 54 kg per bag, the diet that should contain 1 700 kg of maize only contains 1 640 kg.

Simple methods are used to calibrate these mills. One such method involves weighing the amounts of each of the ingredients being metered in at the same time. Under each ingredient auger, place a weighted container. Pour the ingredients into the container, then start the mill. When you have a sufficient supply of the smallest ingredient (2 – 5 kg), turn off the mill. Subtract the weight of the containers from the weight of each ingredient. Add the weights of each ingredient together and divide the total by 2 000. This provides a factor for converting the amounts collected to a tonne basis. Multiply this correction factor by the weight of each collected ingredient. The resulting number represents the amount of that ingredient added to a ton of feed.

 
Schematic of a continuous mixing system.
 
Principle of operation of a continuous mixing unit.
 

Batch Mixing Systems:

Batch systems take more time but generally are more accurate because each ingredient is weighed. Vertical mixers are more popular than horizontal mixers because they take less space. Horizontal mixers typically provide a better mix and have a shorter mixing time. Some stationary systems combine both a horizontal mixer for combining ingredients used in small amounts and a vertical mixer for mixing the complete feed.

The mixing accuracy of a horizontal mixer is because of its mixing action. Horizontal mixers have one of two mixing mechanisms-a ribbon or a paddle. Both will provide a good mix, but the ribbon provides a more uniform final mix.

 
Vertical feed mixer.

Horizontal ribbon mixer. 

Horizontal paddle mixer. 

Horizontal auger mixer. 

Principle of operation of a batch mixing unit. 

 

Ribbon and auger mixers operate most efficiently if they are filled to 70 – 90% of capacity. With paddle mixers, satisfactory mixing may be obtained at much lower levels of loading (25% of capacity). However, the application of fat and/or molasses to mixers that are not adequately loaded may cause the coating of the sides of the mixer and mixer bars, resulting in decreased mixer efficiency and contamination. The mixer should not be overloaded. Overloading the mixer will cause some of the feed to float above the mix and not blend properly. With paddle and ribbon mixers, the mixer bars should rise at least 12 cm above the level of the mix. Improper mixing can also occur if the tolerances between the mixer bars and the sides of the mixer are not set properly. Mixers are factory-set with an agitator clearance of .3 – 9 cm. If that clearance increases to 1.3 cm, mixer efficiency will be impaired. Mixers should be visually inspected periodically.

 

F. Guidelines for Mixing Feed

• Premix.

Before adding them to a supplement, premix micro-ingredients like vitamins, trace minerals, and feed additives with a suitable diluent.

Diluents work to dilute the micro ingredient, which speeds up the process of mixing. The macro-minerals that are typically included in a feed mix, such as salt, limestone, dicalcium phosphate, and magnesium oxide, are examples of suitable diluents. To allow for a more consistent dispersion of individual micro ingredient particles, diluents should be dry. To prevent entrainment and clumping, moisture must be avoided (hygroscopic substances like urea are not suitable diluents).

The premix (micro ingredients plus diluent) should represent 3%, by weight, of the supplement. Premixing may be done by hand in a large container. However, it can be performed more easily and efficiently utilising a small portable cylinder mixer (cement mixer). Protective clothing, gloves and a dust mask should be worn when handling micro ingredients.

• Supplement.

Get a supplement ready. The remaining minor dry ingredients in the diet, such as minerals, urea, and additional protein sources, will also be included in this supplement along with the premix and a suitable carrier. Carriers are feed ingredients that interact with the premix’s micro-ingredients to change their physical properties. The very small particles of the micro-ingredients can move through the mixture more quickly and uniformly by adhering to the carrier. This rapid movement of micro-ingredients through the mix is important to assure adequate distribution before the addition of molasses.

Carriers should resemble meals made from ground grains or oilseeds in terms of physical composition. Each of these two could serve as a carrier. But there aren’t many adsorptive qualities in ground grain and oilseed meals. This restriction can be lifted by first blending the premix with the ground grain or oilseed meal and 2% fat. The thin film of fat covering the carrier will aid in the adsorption of the micro-ingredients in the premix. Poultry litter, rice hulls, wheat bran, vermiculite, alfalfa meal, ground maize cobs and beetroot pulp are all good micro-ingredient carriers. How much “space” is left in the diet formulation will determine how many carriers should be added to the supplement. The supplement must account for at least 3% of the finished feed’s overall weight.

The carrier should be added first, followed by the other major ingredients, which should be added to reach the central shaft line, the premix, and other minor ingredients, and finally the remaining major ingredients. The specifications of the specific mixer being used will determine the volume and duration of the mixing process. Even though some mixers can mix feed effectively at low volumes, most cannot. Review the available information on your mixer, and then confirm that the feed volume being mixed and the mixing intervals are appropriate for the mixer. Avoid overfilling or underfilling the mixer.

Preparation of Finished Feed:

• Add the grain portion of the diet to the mixer.
• Add the dry supplement to the centre of the mixer (keep in mind that the supplement should make up at least 3% of the finished feed; if you can, add it on the end opposite from where the feed is discharged).
• Allow feed to mix for a minimum of 1 minute.
• Add a forage component to the diet.
• Add a fat component to the diet.
• Add molasses or liquid components to the diet.
• Allow mixing for the time specified for the mixer (usually not less than 8 minutes).

Maintaining Good Manufacturing Practices (GMPs):

The management of a feed mill must uphold current GMPs – the basic operational and environmental conditions required to produce safe foods. They ensure that ingredients, products, and packaging materials are handled safely and that food products are processed in a suitable environment.

The use and endorsement of appropriate and proper procedures and practices in the production of feeds do not cost the feed industry, they pay dividends. The feed mill manager is a key individual involved in the daily activities associated with the management of people, facilities, and resources, that ensure the procedures appropriate for the production of feed in his or her feed mill are enforced. The feed mill manager, as his or her supervisors and the people working under their direction, have an obligation to the animal food industry to maintain high-quality standards in the production of feeds for animals – to produce meat, milk, eggs, and so on, for the consumer.

GMPs deal specifically with the manufacturing of any feed containing one or more feed additives. If any feed obtains a feed additive, it is a medicated feed. The feed mill management should have written instructions that cover GMPs and quality assurance programs. GMPs cover all areas involved in the production of feeds including personnel, facilities, feedstuffs, quality assurance checks, inventory control checks, processing methods, mixing procedures, finished feeds, and feed delivery. Although commercial feed mills that produce and sell a complete line of feeds to the general public have a somewhat greater task in assuring quality and prevention of cross-contamination of feed additives, the obligation and importance of all feed mills are still great.

Adding Molasses:

Molasses is a common ingredient in dietary supplements. However, it is highly viscous, which causes several issues in feed mixing. Indeed, if improperly added to the diet, it can cause significant increases in the variation of the equal distribution of the micro-ingredients throughout the feed mix.

Molasses should be added to the mixer as the final step in the process. If the molasses is added to the mixture before the supplement has had a chance to mix with the other major ingredients in the diet, the entrainment of sequestering of the micro-ingredients may occur. This will increase what is called the “Poisson Error” or the variance associated with the decreased spatial distribution of micro ingredient particles.

Additionally, molasses that is added to a mixer before it is full will come into contact with the mixer and stick to its sides and moving parts, reducing mixer efficiency, and calling for more frequent cleaning. While the formation of feed balls or clumps is the obvious difficulty with adding molasses to the mixture, the more significant issue in terms of animal performance is the potential improvement in a poor distribution of the micro-ingredients if the molasses is not added in the correct order.

Blackstrap molasses (standardised at 80E Brix) is especially lethal. When mixing black strap molasses with other dietary ingredients, it is more effective if it is first diluted with water (i.e., dilute to 70E Brix). Heating significantly reduces the viscosity of molasses. For example, increasing the temperature of molasses from 23E C to 27E C (a 4% increase) reduces its viscosity by 50%. Molasses should not be heated above 43 °C, except for very brief periods, as this may result in caramelisation.

Why use molasses and what are the benefits of molasses?

Molasses is highly palatable and an excellent source of energy. In addition to its use as an energy feed, is also used in the following ways.

• As an appetiser.
• To reduce the dustiness of a ration.
• As a binder for pelleting.
• To stimulate rumen microbial activity and
• To supply unidentified factors.
• To reduce the dustiness of a ration.

The quality of molasses is measured by its sugar content, which is expressed by the term Brix. Brix is determined by measuring the specific gravity of molasses. After the specific gravity has been obtained, the value is applied to a conversion table from which the level of sucrose can be determined. As sugar content increases, degrees brix likewise decreases.

Feed Quality and Feed Preservation Techniques:

Feed quality is dependent on both the original plant material and also how the material has been processed to arrive at the final feed.

Problems that might arise in rations include:

• Mould growths can grow on feed crops before or after harvest and on feeds during storage. These may result in the production of mycotoxins (the most important being aflatoxin). Sometimes moulds form in feeds such as maize, peanuts, cottonseed, and ryegrass. Some animals such as cattle can tolerate a little mould in their rations, but moulds are particularly toxic to horses and pregnant animals.
• The presence of anti-nutritional factors. These may include:
  • Factors affecting protein utilisation and digestion e.g., tannins.
  • Factors affecting metal ion Utilisation.
  • Anti-vitamins.
  • Others such as saponins (lucerne), cyanogens, alkaloids, photosensitising agents, and isoflavone.
  • Contamination with poisons or poisonous plants such as oleander can cause problems in mixed or complete feeds.
• When plant material is harvested mechanically small animals such as frogs, mice and even snakes may get killed in the process. They end up in the bulk feed bins and are processed along with the feed.
• If the quality of the original plant material is poor then the preserved feed, or the mixed feed ration manufactured there will also be of poor quality. In this sense, poor quality feed may include a raw material like lucerne that is harvested at a mature stage, when it is very dry and has already lost most of its leaves.

 
Silos to receive and store grain products.
 

South Africa is known for having seasons with abundant feed production and seasons with a scarcity of high-quality feed. It stands to reason that feed should be collected and stored during times of plenty so that there is plenty of feed available during times of scarcity.

In general, livestock farming in South Africa, particularly ruminant production, takes place under harsh conditions. Feed preservation is most commonly practised in these farming systems. The most common form of feed preservation in South Africa is the production of hay or silage. Pig and poultry production systems, on the other hand, are intensive. The feeds provided to monogastric animals in these systems are produced either by the farmer or by commercial feed manufacturers. This has enabled the formulation of feeds for mono-gastric animals to the point where specific amino acids are perfectly balanced to meet the needs of mono-gastric animals at a given level of production.

The success of haymaking depends on the rapid and almost complete removal of moisture from plant material. It is thus highly dependent on hot, dry weather. Several factors influence the final quality of hay. These include:

• The type of material from which the hay is produced. Hay made from legumes is higher in protein than hay made from grass or grain materials.
• The growth stage at which the material is harvested. As a plant matures its dry matter content increases, its fibre content increases and its digestibility decreases.
• The method used to make the hay. Methods include sun-drying, drying in a shed with warm air, drying in a shed with cool air or artificial drying.
• The form in which the hay is fed to the animal. More wastage and poorer intake occur with hay in the long form, versus hay which has been chopped, ground and pelleted. Hay fed in the long form is also often prone to selection by the animal (in other words the animal selects the tastier bits and leaves the less palatable bits). Chopped and pelleted hay also takes up much less storage space.
• When feeding hay, the farmer should always be on the lookout for moulds (perhaps if the bale was accidentally wet during storage). Moulds are particularly dangerous to pregnant animals and horses.

The success of silage-making depends on the ability to preserve plant material in a wet form. It does not depend on the weather for its success. Several factors influence the final quality of silage. These include:

• The type of material from which the silage is produced.
• The dry matter content of the material that is ensiled.
• The rate at which the required pH is reached.
• Whether anaerobic conditions in the silage are maintained.
• Whether the silage is protected from rain and sun.
• The size of the particles that are ensiled influences the degree to which the material can be compacted and thus has a direct influence on the anaerobic circumstances in the silo.

 

G. Animal Feed Contaminants and Health Hazards Associated with Animal Feed

There is a global concern about the presence and prevalence of feedstuff contaminants in animal feed. These contaminants have different effects and pose specific risks to animal health, and human health and they can also be a food safety risk.

Mycotoxins:

Mycotoxins are toxic compounds that are naturally produced by certain types of moulds (fungi)

There has been an increased number of cases of mycotoxin detection in raw materials used in animal feed and/or human food, especially in grain cereals and oil seeds. The growth, multiplication and subsequent production of mycotoxins are favoured by particular environmental factors. Controlling environmental factors is extremely difficult if not impractical. Therefore, contamination of grain cereals and oil seeds is unavoidable, which makes it a challenge to food safety. Although new mycotoxins are being discovered at comparatively high concentrations, few have been identified as posing a dangerous threat to animal and human health.

The mycotoxins that are considered to be important are Aflatoxins (AF), Deoxinivalenol (DON), Zearalenone (ZEA), Ochratoxin (AC) and Fumonisin (F), because they are the most common contaminants in foods and feeds. Furthermore, the negative effects that they exert on animals are highly detrimental even at low concentrations.

In the last decade, many studies have been conducted on mycotoxins. The most frequently occurring mycotoxins include:

• Aflatoxin B1.
• Ochratoxin A.
• Zearalenone.
• Fumonisin B1.
• Deoxynivalenol.
• T-2.
• HT-2.

These above-listed mycotoxins are currently considered for their effects on animal health. However, when focusing on how mycotoxins play a role in food safety, attention should be limited to mycotoxins that are known to be transferred from feed to food of animal origin, as this food represents a significant route of exposure for humans.

Detecting mycotoxins is expensive and difficult. An estimate of the precise and accurate levels of mycotoxins in a large bulk feed is difficult, owing to the large variability associated with test procedures. A representative sample from a whole lot must be obtained by proper sampling procedures.

The scientific community is aware of the following transfers from feed to food:

• Aflatoxin B1 to liver.
• Aflatoxin B1 to milk as aflatoxin M1.
• Aflatoxin B1 to eggs as aflatoxicol.
• Ochratoxin A to meat.
• Deoxynivalenol to meat as DOM1.
• Zearalenone to meat as zearalenol.

Although the scientific community is aware of the above-listed transfers from feed to food evaluating the transfer rate and route of exposure in humans is restricted to aflatoxin B1 for animals producing milk. Farmers should bear in mind that animals fed on aflatoxin-contaminated feed do not show symptoms of aflatoxin toxicity. Feeds most susceptible to aflatoxin are:

• Cereals (especially maize).
• Cottonseed.
• Peanut.
• Copra.
• Palm kernel.
• Rice bran.

However, caution is required with any feed products grown in tropical and subtropical regions, particularly where they are not dried or processed promptly after harvesting. Aflatoxin contamination is not homogeneous; it is therefore very important to apply an appropriate sampling method. Feeds having significant aflatoxin contamination should not be fed to dairy cows or other animals producing milk for human consumption or to other food-producing animals.

There is some evidence to suggest that mycotoxins can concentrate in dried distillers’ grains with solubles (DDGS) during the processing of grains for ethanol production. They also concentrate on cereal bran.

Heavy Metals:

Cadmium is a ubiquitous contaminant that is present in many feed and feed ingredients, in particular minerals, and forages grown near smelting and mining areas. Arsenic and mercury are heavy metals which are widespread in the environment, and which can be found in many feeds, in particular in feeds of marine origin. Lead is also a ubiquitous contaminant. The following Table summarises the most relevant minerals, their sources and bioaccumulation in animal tissues.

The most relevant minerals, their sources and bioaccumulation in animal tissues.

Mineral	Sources	Bioaccumulation in Animal Tissues
Arsenic	Sea plants. Fish products. Supplemental minerals.	Fish.
Cadmium	Mineral supplements (such as phosphate, and zinc sources). Forage or grains (depending on geographical area). Manure, sewage, sludge or phosphate fertilisers can enrich the soil.	Kidney and liver. Shellfish, oysters, salmon, and fungi have the highest concentrations. There are low concentrations in fruits, dairy products, legumes, meat, eggs and poultry.
Mercury or Methyl	Anthropogenic contamination. Fish meal.	Liver. Kidney. Fish. Marine mammals.

 

Veterinary Drugs:

Residues of veterinary drugs can be present in the feed when ingredients of animal origin (terrestrial and aquatic) are used, but this is not a very significant route of exposure. Veterinary drug residues may be found in food products as a result of the carryover of veterinary drugs in feed during feed production. Therefore, it is important to follow the code recommendations (flushing, sequencing, cleaning) when the feed for food-producing animals is produced after the production of a medicated feed.

It is also important to consider the illegal use of drugs in animal feed which may result in unsafe residues in meat, milk, or eggs (e.g., chloramphenicol or nitrofurans in shrimps and chloramphenicol in milk powder). There is some evidence to suggest that antibiotics used in the fermentation process to control microbiological contamination during the processing of grains for ethanol production may concentrate in dried distillers grains (DDGs).

Organochlorine Pesticides:

The continued presence of organochlorine pesticides in the environment, as well as their ongoing use in some countries, can cause exposure through food as a result of accumulation in the fat tissues of animals that have been fed on contaminated feed. Such animals will usually not exhibit specific clinical symptoms of the contamination. Animal products such as meat could accumulate these substances, which are extremely persistent, and which decompose very slowly. Contaminated animal products can cause food safety issues for humans.

Microbiological Hazards:

The primary sources of microbiological hazards in the feed are contaminated pastureland, forages and animal and vegetable protein meals fed directly to animals.

• Brucella.

In some countries, where Brucella infection occurs, infected ruminants can deliver offspring or abort in fields that are grazed or from which pasture is harvested and used for animal feed. It is well known that the placentas of infected animals contain high levels of Brucella microorganisms. If contaminated forage is fed to milking animals, the micro-organisms may be excreted in their milk. If this milk is not pasteurised before consumption by humans, it is a risk to food safety.

• Salmonella.

Salmonella is still of worldwide human health concern. Infection in animals has a direct impact on transmission to humans via food of animal origin. Contaminated feed might represent an important route of exposure to Salmonella.

Endoparasites:

Some endoparasites of animals, such as Echinococcus, Toxoplasma gondii, Cysticercus and Trichinella, present a risk to human health, and ingestive stages can contaminate animal feeds. These pathogens can colonise or infect farm animals and may pose a threat to human health if infected or contaminated products are ingested.