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Importance Of Nutrient Levels And Variability In Feedstuffs

Formulating to meet a specific set of nutrient requirements, in an attempt to ensure maximum performance of a particular class of poultry, is the aim of the poultry nutritionist. However, there are many factors to consider when formulating diets, and in feeding poultry, which would counter the belief of many producers, that purchasing a diet, calculated to meet the nutrient requirements of the birds in question, is a guarantee for a high performance flock.

Economic Considerations
The economics of production must always be a prime consideration and this is not always easy to evaluate as the most economical diets can be the most costly when considered on a per unit basis. People have tried to overcome this by looking at feed to gain or feed to product ratio. However, this approach does not consider feed costs, with the result that there is a move to look at cost to produce a unit of poultry meat or eggs, as the proper approach to evaluating diet performance. While such an approach goes some distance in the proper economic evaluation of a diet, with today¡ãOs markets ther is increasing pressure to look at yield of specific carcass parts when calculating the net worth of a diet.

Diet Evaluation
The greatest single cost of any poultry diet is providing nutrients to meet the energy needs of the bird. Since the requirement for energy far exceeds the requirement for any other dietary nutrient, the energy level of the diet is the main factor influencing feed intake. For this reason, most other dietary nutrients are required in relation to the energy level of the diet. This being the case, it is important that a fairly precise estimate of the energy content of a diet be made, if intake of other nutrients are going to meet calculated nutrient requirements of the animal.

While energy values of feed ingredients and diets can be measured by classical methods, with relatively good precision, such assays are time consuming and costly. Even the more rapid bio-assays for metabolizable energy developed by Farrell and Sibbald can take close to a week and are still costly. Since cereal grains make up the majority of the dietary ingredients in most poultry diets, and account for a large portion of the energy, it is important to have reasonable, reliable estimates of their energy values. A similar situation exists for vegetable protein supplements, as they often make up the majority of the supplemental protein and thus they also make a significant contribution to the energy content of a diet.

There has been increased interest in using near infrared reflectance (NIRA) for evaluating the energy content of feedstuffs. NIRA is fast, requires no chemical reagents and is inexpensive after the initial capital costs for equipment. No sample preparation is necessary, other than grinding, and after calibrations are developed, little skill is required in producing reliable energy values. An example of the type of precision to expect is shown in Table 1, for ingredients, diets and several fat products. Since fish and meat meals make up a relatively small fraction of the dietary energy, chemical methods are often used to give some measure of their energy value. For fish meals, protein levels correlate relatively well with ME values. However, this does not work well with meat meals due to their higher mineral content. Thus, ash values are a better estimator of the ME of meat meals.

Quality Control
Ingredients must be continually monitored to ensure consistency of nutrient profile and presence of contaminants. The frequency of assays will depend on class of ingredient, history of supplier and perhaps season of the year.

For example, if fish meal is used extensively, and represents a significant proportion of dietary amino acids, then some check on protein quality should be made periodically and frequent screening for gizzard erosion factors carried out.

Some of the testing that is carried out is as follows.
a.bulk density - mainly for cereals
b.rapid NIRA (for ME, amino acids, minerals)
c.urease testing of soybean meal
d.protein solubility
e.gizzard erosion factor
f.tannins (sorghum)
g.gossypol (cottonseed meal)
h.fats - ME assay, moisture, iodine number
i.mineral solubility (limestone)

As reported by Araba and Dale (1990) in Table 2, soybean meal should be assayed for both trypsin inhibitor and protein solubility. Protein solubility values in excess of 85% or less than 70% indicate under or over processing of soybean meal respectively.

In a recent report of Lilburn (1996), a good review is given with regard to the variability in quality encountered with various fat, corn and protein supplements and the effect such differences can have on nutrient availability.

Ingredient Variability
Variability in feed ingredients can be quite marked when considering milling by-products. A good example of this is the report of Dale (1996) where he studied the ME of wheat by-products. Of 15 samples from various countries tested, the range in composition varied markedly (Table 3).

True metabolizable energy along with proximate analysis were conducted on the samples in an attempt to develop prediction equations for estimating energy values. Only crude fiber gave a significant correlation with TMEn.

eg.
1.TMEn (kcal/kg) = 3157-166(%CF)
R2=.67 (87% DM)

2.TMEn (kcal/kg) = 3497-39 (%NDF)
R2=.77 (87% DM)

From a search of the literature, 42 AMEn values from studies where CF was reported, were used to develop a prediction equation, as follows:

3.AMEn=3086-165(%CF)
R2=.77(87%DM)

Combining both data sets (57 observations):

*4.MEn=3182-161(%CF)
R2=.73(87%DM)
* Assuming TME and AME values equal

Equation 1, (TMEn values) obtained with adult cockerels, yielded higher values than did equation 3, which was derived from AMEn assays with young chicks.

It is not clear whether the variation is due to differences in methodology, age of the test animals or both. However, the negative factor associated with CF, (-165 for chicks versus 116 for adults) suggest that adult chickens might digest wheat by-products more efficiently. Thus equation 1 should be used for pullets and hens and equation 3 for young chicks and broilers.

The above demonstrates the marked variability that can be encountered by using average or book values for various ingredients which may vary widely depending on source and nomenclature. Developing prediction equations as shown above, and updating them with current analytical values, should provide a better estimate of the energy of ingredients then the use of published book values.

Improving Nutrient Value

Grinding
Cereal grains are ground before being mixed in a diet to improve nutrient utilization as well as to ensure thorough mixing. There has been recent interest in investigating the energy input into grinding. It would appear that a marked saving in energy inputs can be achieved with a coarser grind, without any decrease in nutritive value of the cereal. This essentially confirms the earlier work of Farrell et al. (1983).

In Table 4 is shown the ME determinations of corn and wheat with different degrees of grinding and fed as mash or steamed crumble to chicks or cockerels. There were no significant differences in the energy value of the corn, depending on fineness of grind, or mash versus pellets. However, pelleting improved the energy content of wheat for both chicks and cockerels while the corn energy value was reduced for the adult birds.

Processing
There has been an increased interest in feed and ingredient processing during recent years in enhancing of processing can be divided into two categories;
a.Thermal
b.Non-thermal

Thermal can be divided into,
Dry heat: - roasting, popping, micronizing
Wet heat:- pelleting, expanding, micronizing, extruding, compacting, steam flaking

Examples of non-thermal processing would include roller or hammermill grinding, blending or mixing of ingredients and feeding of whole cereals.

Steam Pelleting
The advantages of steam pelleting diets for poultry have been demonstrated on numerous occasions. With steam pelleting, heat, moisture and pressure are involved, all factors which are known to enhance chemical reactions. Thus besides a positive physical effect of pelleting there are also chemical effects which enhance the feeding value of a diet. This is demonstrated in Table 5 where a sample of corn and wheat bran were steam pelleted and then reground to mash. The above ingredients, along with similar samples of regular bran and corn, were mixed 50:50 with a corn, soybean meal basal diet. These diets were then fed as mash, as dry-pellets (pelleted in a small dry pelleting machine), or as regular commercial steam pellets. Since the diets were fed to young

White Leghorn cockerels the pellets were reduced to crumbles for feeding. Dry pelleting the wheat bran ( a physical change) resulted in a marked improvement in weight gain, but no change in ME of the bran, while steam pelleting (a physical and chemical change), gave a further increase in weight gain and a marked improvement in the ME value of bran (Table 5). The processed wheat bran further increased the ME value of the bran, especially for the double steam-pelleted treatment. Dry and steam-pelleting the corn diet also gave a response in weight gain, however, with the processed corn diets the mash and dry pelleted diets did not alter weight gain while birds fed the double steam pelleted diet showed a marked reduction in weight gain. Such an effect is obviously due to too much heat being applied to this diet with the possible tying up of lysine. The ME of the test corn was little affected by pelleting treatment.

Steam pelleting has also been shown to increase the available phosphorus in a diet. This is especially true for diets high in organic phosphorus. As can be seen in Table 6, steam pelleting a diet containing wheat bran was as effective as adding additional inorganic phosphorus to the diet.

Work has been undertaken recently in evaluating the effects of further feed processing procedures. A good review of this work can be found in the report of Behnke (1996). Examples of some of the results reported are shown in Table 7.

In general, it can be concluded that thermal processing;
a.decreases feed wastage
b.improves performance due to less ingredient separation and picking over of diet
c.less energy expended in eating
d.improves palatability
e.increases feed intake

Diet Variability
Many of the further thermal processes which are designed to improve pellet quality, result in less variability in nutritive value as well as physical form of the diet, thus enhancing diet performance, as well as increasing pellet output.

Enzyme supplementation has also been reported to significantly reduce the variability between wheat and barley samples as well as improving their nutritive value.

Conclusions
There is no question but that marked variability can occur in nutrient levels in various feedstuffs thus resulting in similar variability in diet quality. Realizing that such is the case, the nutritionist must take care not to blindly use ¡ã¡Þbook values¡ã¡À for ingredients varying widely in source of origin and processi and handling procedures.

It is essential that the quality of ingredients from various suppliers be monitored as consistency of product is important in ensuring consistency in diet quality.

While it is essential that chemical analyses and biological assays be conducted on ingredients, from time to time, one of the best measures of diet quality the nutritionist has available to him is to monitor the performance of the flocks fed. Increased feed consumption, with similar product output, suggests that energy content of the diet is low. While a reduction in weight gain, along with a decrease in feed:gain ratio, suggests that protein level or quality could be a problem.

More attention to ingredient supply and flock performance and less concern about ingredient costs usually results in reduced cost per unit of product produced.

There are a number of ways to enhance diet quality in spite of ingredient variability. This is an area that the nutritionist must spend more time pursuing as ingredient costs continue to escalate.

References
Araba, M. and N.M. Dale, 1990. Evaluation of protein solubility as an indicator of under processing of soybean meal. Poultry Sci. 69:1749-1752.
Behnke, K.C., 1996 Hydrothermal feed processing; Processing effects on animal performance. 57th Minnesota Nutrition Conference, pp305-320.
Dale, N., 1996 The metabolizable energy of wheat by-products. J. Appl. Poultry Res. 5:105-108.
Farrell, D.J., E. Thomson, A. Choice, J. R. Ashes, N.J. Peck and J.P. Hogan, 1983. Effects of milling and pelleting of maize, barley and wheat on their metabolizable energy value for cockerels and chicks. Animal Feed Science and Technology 9:99-105.
Summers, J.D., S.J. Slinger and G. Cisneros, 1967. Some factors affecting the biological availability of phosphorus in wheat by-products. Cereal Chemistry 44:318-323.
Summers, J.D., H.U. Bentley and S.J. Slinger, 1968. Influence of method of pelleting on utilization of energy from corn, wheat shorts and bran. Cereal Chemistry 45:612-615.
Lilburn, M.S., 1996. Ingredient quality and the impact on digestion and absorption in poultry. J. Appl. Poultry Res. 5:78-81.
Valdes, E.V. and S. Leeson, 1992. Use of NIRA to measure ME in poultry feed ingredients. Poultry Sci. 71:1559-1563.
Valdes, E.V. and S. Leeson, 1994. Measurement of ME, G.E. and moisture in feed grade fats by NIRA. Poultry Sci. 73:163-171.

Tags · Feedstuffs · Nutrition · Feed Formulation

17.02.2008. 09:54