Fats and oils

Nutritional Characteristics:

Fats provide a concentrated source of energy, and so relatively small changes in inclusion levels can have significant effects on diet ME. Most fats are handled as liquids, and this means heating of most fats and fat blends that contain appreciable quantities of saturated fatty acids.

Depending upon the demands for pellet durability, 3 - 4% is the maximum level of fat that can be mixed with the other diet ingredients. To this, up to 2 - 3% can be added as a spray-on coat to the formed pellet. Alternate technology of spraying fat onto the hot pellet as it emerges from the pellet die means that much higher inclusions are possible since the hot pellet seems better able to adsorb the fat. Under these conditions, there is concern for manufacturers who demand extreme pellet durability, since fines will already be treated with extra fat, prior to their recycling through the pellet mill.

All fats and oils must be treated with an antioxidant which ideally should be added at the point of manufacture. Fats held in heated tanks at the mill must be protected from rancidity. The more unsaturated a fat, the greater the chance of rancidity. Fats also provide varying quantities of the essential nutrient linoleic acid. Unless a diet contains considerable quantities of corn, it may be deficient in linoleic acid, because all diets should contain a minimum of 1%. A major problem facing the industry at the moment is the increasing use of restaurant grease in feed-grade fats. These greases are obviously of variable composition in terms of fatty acid profile and content of free fatty acids. Also, dependent upon the degree of heating that they have been subjected to, these greases can contain significant quantities of undesirable break-down products.

In order to ensure adequate levels of linoleic acid, and to improve palatability and reduce dustiness of diets, all diets require a minimum of 1% added fat, regardless of other economic or nutritional considerations. There is considerable information published on factors that influence fat digestibility, but in most instances, this knowledge is not used during formulation. In large part variability is due to the fact that digestibility is not a static entity for any fat, but rather its utilization is variable with such factors as bird age, fat composition and inclusion level. Unfortunately, these variables are difficult to factor into formulation programs. Other concerns about fats are their potential for rancidity and effect on carcass composition. Following are descriptions of the major types of fat used in the feed industry. Table 2.8 summarizes the fatty acid profile and ME of the most common fat sources used in poultry nutrition. An attempt has been made to predict fat ME based on bird age.

19a. Tallow

Tallow has traditionally been the principle fat source used in poultry nutrition. However, over the last 10 years, there has been less use of pure tallow and greater use of blended fats and oils. Tallow is solid at room temperature and this presents some problems at the mill, especially when heated en oo

  • W S m s n
  • s- H s Z
Table 2.8 Nutrient composition of fats and oils

Metabolizable energy (kcal/kg)

Fat

MJ.U.5

Fatty acid profile (%)

Ingredient

l1

22

%

%

12:0

14:0

16:0

18:0

16:1

18:1

18:2

18:3

19a

Tallow

7400

8000

98

2

4.0

25.0

24.0

0.5

43.0

2.0

0.5

19b

Poultry fat

8200

9000

98

2

1.0

20.0

4.0

5.5

41.0

25.0

1.5

19c

Fish oil

8600

9000

99

1

8.0

21.0

4.0

15.0

17.2

4.4

3.03

19d

Vegetable oil

8800

9200

99

1

0.5

13.0

1.0

0.5

31.0

50.0

2.0

19e

Coconut oil

7000

8000

99

1

50.04

20.0

6.0

2.5

0.5

4.0

2.1

0.2

19 f

Palm oil

7200

8000

99

1

2.0

42.4

3.5

0.7

42.1

8.0

0.4

19g

Vegetable soapstock

7800

8100

98

2

0.3

18.0

3.0

0.3

29.0

46.0

0.8

19h

Animal-Vegetable blend

8200

8600

98

2

2.1

21.0

15.0

0.4

32.0

26.0

0.6

19i

Restaurant grease

8100

8900

98

2

1.0

18.0

13.0

2.5

42.0

16.0

1.0

'ME for young birds up to 3 weeks of age; 2ME for birds after 3 weeks of age; sContains 25% unsaturated fatty acids □ 20:4; 'Contains 15% saturated fatty acids nl0:0; 5Moisture, impurities, unsaponifiables.

'ME for young birds up to 3 weeks of age; 2ME for birds after 3 weeks of age; sContains 25% unsaturated fatty acids □ 20:4; 'Contains 15% saturated fatty acids nl0:0; 5Moisture, impurities, unsaponifiables.

fats are added to very cold ingredients originating from unheated outside silos. Being highly saturated, tallow is not well digested by young chickens, although there is some evidence of better utilization by young turkeys. The digestibility of tallow can be greatly improved by the addition of bile salts suggesting this to be a limiting feature of young chicks. However, the use of such salts is not economical and so inclusion of pure tallow must be severely restricted in diets for birds less than 15 - 17 d of age.

19b. Poultry Fat

This fat source is ideal for most types and ages of poultry in terms of its fatty acid profile. Due to its digestibility, consistent quality and residual flavor, it is in high demand by the pet food industry, and this unfortunately reduces its supply to the poultry industry. As occurs with poultry meal, there is a concern with integrated poultry operations that fat-soluble contaminants may be continually cycled (and concentrated) through the birds. This can obviously be resolved by breaking the cycle for a 1 or 2 bird cycle.

19 c. Fish Oil

There is current interest in the use of fish oils in diets for humans and animals, since its distinctive component of long chain fatty acids is thought beneficial for human health. Feeding moderate levels of fish oils to broiler chickens has been shown to increase the eicosapentaenoic acid content of meat. However, with dietary levels in excess of 1%, distinct fish type odour is often present in both meat and eggs, which is due mainly to the contribution of the omega-3 fatty acids.

19d. Vegetable Oil

A large range of vegetable oils is available as an energy source, although under most situations, competition with the human food industry makes them uneconomic for animal feeds. Most vegetable oils provide around 8700 kcal ME/kg and are ideal ingredients for very young birds. If these oils are attractively priced as feed ingredients, then the reason(s) for refusal by the human food industry should be ascertained e.g. contaminants.

19e. Coconut Oil

Coconut oil is a rather unusual ingredient in that it is a very saturated oil. Coconut oil is more saturated than is tallow. It contains 50% of saturated fatty acids with chain length less than 12:0. In many respects, it is at the opposite end of the spectrum to fish oil in terms of fatty acid profile. There has been relatively little work conducted on the nutritional value of coconut oil, although due to its saturated fatty acid content it will be less well digested, especially by young birds. However recent evidence suggests very high digestibility by young birds of medium chain triglycerides, such as C:8 and C:10 as found in coconut oil. These medium length fatty acids do not need bile for emulsification or prior incorporation within a micelle prior to absorption.

19f. Palm Oil

Palm oil production is now only second to soybean oil in world production. Palm oil is produced from the pulpy flesh of the fruit, while smaller quantities of palm kernel oil are extracted from the small nuts held within the body of the fruit. Palm oil is highly saturated, and so will have limited usefulness for very young birds. Also, soap-stocks produced from palm oil, because of their free fatty acid content, will be best suited for older birds. There is potential for using palm and coconut oils as blends with more unsaturated oils and soapstocks, so as to benefit from potential fatty acid synergism.

19g. Soapstock (Acidulated soapstock)

As a by-product of the vegetable oil refining industry, soapstocks provide a good source of energy and essential fatty acids. Soapstocks can be quite high in free fatty acids, and so stabilization with an antioxidant is essential. Soapstocks may also be acidulated, and this may pose problems with corrosion of metallic equipment. Some impurities may be added to soapstocks as a means of pollution-free disposal by refineries, and therefore quality control becomes more critical with these products. Moisture level may also be high in some samples, and this simple test is worthwhile for economic evaluation.

19h. Animal-Vegetable Blend Fat

Some manufacturers mix animal and vegetable based fats, to give so-called blended products. The vegetable source is usually soapstock material. The blend has the advantage of allowing for some synergism between saturated fatty acids of animal origin and unsaturates from the soapstock. Animal-vegetable blends are therefore ideally suited for most classes of poultry without the adverse problem of unduly increasing the unsaturates in meat which can lead to increased rate of oxidative rancidity (reduced shelf life).

19i. Restaurant Grease

An increasing proportion of feed fats is now derived from cooking fats and oils, and the generic product is termed restaurant grease. Its use has increased mainly due to problems of alternate disposal. Traditionally restaurant greases were predominately tallow or lard based products and this posed some problems in collection and transportation of the solid material. In recent years, due to consumer concerns about saturated fats, most major fast food and restaurant chains have changed to hydro-genated vegetable cooking fats and oils. The fats are hydrogenated to give them protection against high-temperature cooking. Today, restaurant greases contain higher levels of oleic acid, and much of this will be trans-oleate. Assuming there has not been excessive heating, and that the grease has been cleaned and contains a minimum of impurities, then the energy value will be comparable to that of poultry fat. Future use of non-fat 'cooking fats' will lead to considerable variation in the nutrient profile of these products.

19j. Conjugated Linoleic Acid (CLA)

CLA is an isomer of conventional linoleic acid, but unlike linoleic, there are numerous health benefits claimed for CLA. It is claimed to help control glucose metabolism in diabetic mammals, and more importantly to prevent and/or control the growth of certain cancerous tumors. CLA is normally found in dairy products, representing around 0.3% of total fat. Turkey meat is also high in CLA. Feeding CLA to layers results in bioaccumulation in the egg, much as for any fatty acid, and so there is potential for producing CLA enriched designer eggs. It seems as though the AMEn of CLA is comparable to that of linoleic acid, suggesting that the two fatty acids are comparably metabolized.

It is possible that CLA is not elongated as in linoleic acid during metabolism and so this has posed questions about adequacy of prostaglandin synthesis, and hence immune function. There are some reports of altered lipid metabolism in embryos and young chicks from eggs hatched from hens fed 1 g CLA daily. There is some discussion about whether or not synthetic sources of CLA actually mimic the beneficial anti-cancerous properties of 'natural' CLA found in dairy products.

Important Considerations:

Fats and oils are probably the most problematic of all the ingredients used in poultry feeds. They require special handling and storage facilities and are prone to oxidation over time. Their fatty acid profile, the level of free fatty acids and degree of hydrogenation can all influence digestibility. Unlike most other ingredients, fat digestion can be age dependent, since young birds have reduced ability to digest saturated and hydrogenated fats.

a. Moisture, Impurities, Unsaponifiables

Feed grade fats will always contain some non-fat material that is generally classified as M.I.U. (moisture, impurities and unsaponifiables). Because these impurities provide no energy or little energy, they act as diluents. A recent survey indicated M.I.U's to range from 1 - 9%. Each 1% MIU means a loss in effective value of the fat by about $3 - $4/tonne, and more importantly, energy contribution will be less than expected. The major contaminants are moisture and minerals. It seems as though moisture can be quickly detected by Near Infra Red Analysis. Moisture and minerals also lead to increased peroxidation.

b. Rancidity and Oxidation

The feeding value of fats can obviously be affected by oxidative rancidity that occurs prior to, or after feed preparation. Rancidity can influence the organoleptic qualities of fat, as well as color and 'texture' and can cause destruction of other fat soluble nutrients, such as vitamins, both in the diet and the bird's body stores. Oxidation is essentially a degradation process that occurs at the double-bond in the glyceride structure. Because presence of double-bonds infers unsaturation, then naturally the more unsaturated a fat, the greater the chance of rancidity. The initial step is the formation of a fatty free radical when hydrogen leaves the a -methyl carbon in the unsaturated group of the fat. The resultant free radical then becomes very susceptible to attack by atmospheric oxygen (or mineral oxides) to form unstable peroxide free radicals. These peroxide free radicals are themselves potent catalysts, and so the process becomes autocatalytic and rancidity can develop quickly. Breakdown products include ketones, aldehydes and short chain fatty acids which give the fat its characteristic 'rancid' odour. Animal fats develop a slight rancid odour when peroxide levels reach 20 meq/kg while for vegetable oils problems start at around 80 meq/kg.

Oxidative rancidity leads to a loss in energy value, together with the potential degradation of the bird's lipid stores and reserves of fat-soluble vitamins. Fortunately we have some control over these processes through the judicious use of antioxidants. Most antioxidants essentially function as free radical acceptors - these radical-antioxidant complexes are, however, stable and do not cause autocatalytic reactions. Their effectiveness, therefore, relies on adequate dispersion in the fat immediately after processing. As an additional safety factor, most diets will also contain an antioxidant added via the premix. The Active Oxygen Method (AOM) is most commonly used to indicate potential for rancidity. After 20 h treatment with oxygen, quality fats should develop no more than 20 meq peroxides/kg.

Time is a very important factor in the AOM test, because peroxides can break down and disappear with extended treatment. For this reason, some labs will provide peroxide values at 0, 10 and 20 hr. A newer analytical technique is the Oil Stability Index (OSI). This is similar to AOM, but instead of measuring initial peroxide products, measures the accumulation of secondary breakdown compounds. The assay is highly automated and records the time necessary to produce a given quantity of breakdown products such as short chain volatile fatty acids.

c. Fatty Acid Profile

Fat composition will influence overall fat utilization because different components are digested with varying efficiency. It is generally recognized that following digestion, micelle formation is an important prerequisite to absorption. Micelles are complexes of bile salts, fatty acids, some monoglycerides and perhaps glycerol. The conjugation of bile salts with fatty acids is an essential prerequisite for transportation to and absorption through the microvilli of the small intestine. Polar unsaturated fatty acids and monoglycerides readily form this important association. However, micelles themselves have the ability to solubilize non-polar compounds such as saturated fatty acids. Fat absorption is, therefore, dependent upon there being an adequate supply of bile salts and an appropriate balance of unsaturates:saturates.

Taking into account the balance of saturated to unsaturated fatty acids can be used to advantage in designing fat blends. This type of synergistic effect is best demonstrated using pure fatty acids (Table 2.9). In this study, the metabolizable

Table 2.9 Metabolizable energy of layer diets containing various fatty acids

Determined

Expected

ME (kcal/kg)

Oleic

2920

Palmitic

2500

50:50 mixture

2850 (+5%)

2710

  • Atteh and Leeson, 1985)
  • Atteh and Leeson, 1985)

energy of the 50:50 mixture of the unsaturated oleic acid with the saturated palmitic acid, is 5% higher than the expected value based on the mean value of 2710 kcal/kg. We therefore have a boost of 5% in available energy that likely comes from greater utilization of the palmitic acid because of the presence of the unsaturated oleic acid.

This type of synergism can, however, have a confounding effect on some research results. If we want to measure the digestibility of corn, it is possible to feed just corn for a short period of time and conduct a balance study. For obvious reasons, it is impossible to feed only fats, and we have to conduct studies involving graded fat additions to a basal diet, with extrapolation of results to what would happen at the 100% feeding level. In these studies, we assume the difference in digestibility between any two diets is due solely to the fat added to the diet. If, because of synergism, the added fat improved digestibility of basal diet components, then this 'boost' in digestibility is attributed to the fat and an erroneously high value is projected. However, it can be argued that this 'boost' to fat's value occurs normally when fats are added to diets, and that these higher values more closely reflect the practical value of fat in a poultry diet. We have proposed this synergism to account for some of the so-called 'extra-caloric' effect of fat often seen in reported values, where metabolizable energy can sometimes be higher than corresponding gross energy values (which theoretically cannot occur). Table 2.10 shows results from this type of study where corn oil was assayed using different types of basal diet.

Table 2.10 Variation in ME value of corn oil attributed to fatty acid saturation of the basal diet

Basal diet

Corn oil ME

(kcal/kg)

Predominantly unsaturated

8390a

Predominantly saturated

9380b

Corn-soy diet

8510a

When the basal diet contains saturated fatty acids, there is an apparent increase in the ME of corn oil. This effect is possibly due to the unsaturates in corn oil aiding in utilization of the basal diet saturates. However, because of methods of diet substitution and final ingredient ME calculation, any such synergism is attributed to the test ingredient (corn oil).

ME values of fats will therefore vary with inclusion level, although this effect will be influenced by degree of fat saturation. A ratio of 3:1, unsaturates:saturates is a good compromise for optimum fat digestibility for all ages of bird. However, this ratio may not be the most economical type of fat to use, because of the increased cost of unsaturates relative to saturates.

d. Level of Free Fatty Acids and Fatty Acid Hydrogenation

Concern is often raised about the level of free fatty acids in a fat, because it is assumed these are more prone to peroxidation. Acidulated soapstocks of various vegetable oils contain the highest levels of free fatty acids, which can reach 80 - 90% of the lipid material. For young birds there is an indication that absorption of fatty acids is highest in birds fed triglycerides rather than free fatty acids and this may relate to less efficient micelle formation or simply to less bile production. Wiseman and Salvadore (1991) demonstrated this effect in studying the ME value of tallow, palm oil and soy oil that contained various levels of free fatty acids (soapstock of the respective fat). Table 2.11 shows a summary of these results, indicating energy values for the respective fats containing the highest and lowest levels of free fatty acids used.

Table 2.11 Effect of level of free fatty acid and bird age on fat ME value (kcal/kg)

Table 2.11 Effect of level of free fatty acid and bird age on fat ME value (kcal/kg)

10 d

54 d

Tallow

13% FFA

7460

7940

95% FFA

4920

6830

Palm

6% FFA

6690

7800

92% FFA

3570

6640

Soy

14% FFA

9290

9300

68% FFA

8000

8480

Adapted from Wiseman and Salvador (1991)

Adapted from Wiseman and Salvador (1991)

These data suggest that free fatty acids are more problematic when the fat is predominantly saturated and this is fed to young birds. Contrary to these results, others have shown comparable results with broilers grown to market weight and fed tallows of varying free fatty acid content.

Hydrogenation of fats becomes an issue with the general use of these fats in restaurants, and the fact that restaurant grease is now a common, and sometimes the major component of feed-grade fat blends. Hydrogenation results in a high level of trans oleic acid (40 - 50%) and such vegetable oils have physical characteristics similar to those of lard. There seems to be no problem in utilization of these hydrogenated fats by poultry with ME values of restaurant greases being comparable to those of vegetable oils. The long-term effect of birds eating trans fatty acids is unknown at this time.

e. Bird Age and Bird Type

Young birds are less able to digest saturated fats, and this concept has been known for some time. With tallow, for example, palmitic acid digestibility increases from 50 to 85% through 14 to 56 d of age, which together with corresponding changes for other fatty acids means that tallow ME will increase by about 10% over this time period. The reason why young birds are less able to digest saturated fats is not well understood, although it may relate to less bile salt production, less efficient recirculation of bile salt or less production of fatty acid binding protein.

f. Soap Formation

When fats have been digested, free fatty acids have the opportunity of reacting with other nutrients. One such possible association is with minerals to form soaps that may or may not be soluble. If insoluble soaps are formed, there is the possibility that both the fatty acid and the mineral will be unavailable to the bird. There is substantial soap formation in the digesta of broiler chicks and this is most pronounced with saturated fatty acids, and with increased levels of diet minerals. Such increased soap production is associated with reduced bone ash and bone calcium content of broilers. Soap production seems to be less of a problem with older birds. This is of importance to laying hens that are fed high levels of calcium. In addition to calcium, other minerals such as magnesium can form soaps with saturated fatty acids. In older birds and some other animals, there is an indication that while soaps form in the upper digestive tract, they are subsequently solubilized in the lower tract due to changes in pH. Under these conditions both the fatty acid and mineral are available to the bird. Control over digesta pH may, therefore, be an important parameter for control over soap formation.

g. Variable ME Values

It seems obvious that the use of a single value for fat ME during formulation is a compromise, considering the foregoing discussion on factors such as inclusion level, bird age, soap formation etc. Table 2.8 gives different ME values for birds younger or older than 21 d, and this in itself is a compromise. Following is an attempt to rationalize the major factors affecting ME of a given fat, although it is realized that such variables are not easily incorporated within a formulation matrix (Table 2.12).

Table 2.12 Factors affecting fat ME values

Relative f fat ME

Table 2.12 Factors affecting fat ME values

Relative f fat ME

28 d+

100%

Bird age:

7 - 28 d

95%

1 - 7 d

88%

(esp. for saturates)

0 -10%

102%

Free fatty

10 - 20%

100%

acids:

20 - 30%

96%

30%+

92%

(esp. for saturates)

1%

100%

2%

100%

Inclusion level:

3%

98%

4%

96%

5%+

94%

<1%

100%

Calcium level:

>1%

96%

(esp. for birds <56 d

of age)

h. Trans Fatty Acids

Trans fatty acids are isomers of naturally occurring cis fatty acids. Trans fatty acids are often produced by the process of hydrogenation, as commonly occurs in production of margarine and other cooking fats. Hydrogenated (stabilized) soybean oil, which is a common component of cooking oils, contains around 20% trans fatty acids. With increasing use of restaurant grease in animal fats and fat blends, it seems inevitable that fats used in the feed industry will contain higher proportions of trans fatty acids than occurred some 20 years ago. It is thought that 'overused' frying oil, that contains trans fatty acids as well as oxidized and polymerized materials, is harmful to human health. These trans fatty acids can be found in human adipose tissue, and have been associated with immune dysfunction and unusual lipid metabolism in heart tissue. There is very little information available on the effect of trans fatty acids on health of broilers or layers.

OTHER INGREDIENTS 20. Oats

Oats are grown in cooler moist climates although they are of minor importance on a global scale, representing only about 1.5% of total cereal production. Most oats are used for animal feed, and about 85% of this quantity is used locally and there is little trade involved. The hull represents about 20% of the grain by weight, and so this dictates the high fiber - low energy characteristics of oats. The amino acid profile is however quite good, although there is some variation in protein and amino acid levels due to varietal and seasonal effects. The best predictor of the energy value of oats, is simply the crude fiber content which is negatively correlated with ME. Oat lipids are predominantly oleic and linoleic acid, although a relatively high proportion of palmitic acid leads to a 'harder' fat being deposited it the bird's carcass.

As for other small grains, oats contain an appreciable quantity of ft-glucans, and these cause problems with digesta and excreta viscosity. Most oats contain about 3-7% ft-glucans and so with moderate inclusion levels of oats in a poultry diet it may be advantageous to use supplemental ft-glucanase enzyme. There has been some interest in development of so-called naked oats, which are similar in composition to oat groats. Naked oats contain up to 17% CP with 0.68%

lysine and 1% methionine plus cystine. The ME value is around 3200 kcal/kg, making these oats comparable to wheat in most characteristics. As with regular oats, G-glucans can still be problematic and their adverse effect can be overcome with use of exogenous enzymes, and to a lesser extent antibiotics such as neomycin. Much of the phosphorus in naked oats is as phytic acid, and so availability is very low. There have been some reports of reduced skeletal integrity in birds fed naked oats unless this reduced phosphorus availability is taken into account. There are reports of broilers performing well with diets containing up to 40% naked oats, and with layers, up to 50% has been used successfully.

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