In order to facilitate the correct sampling of water, we will be able to supply you with pre-treated and acidified sample bottles. We will also acidify the samples before they are submitted to the lab.

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The Challenge of Evaluating Feed Additives

During the recently held NuTec poultry day, Dr Nick Dale from the University of Georgia presented a paper entitled "The Challenge of Evaluating Feed Additives". This is one the most insightful talks I have attended in a long time and I have included the more philosophical sections of it here. The remainder of the paper deals with specific groups of products and should you require it a complete document is available.

Those involved in commercial formulation quickly become aware of the large number of additives available on the market. Much like the evolution of the species, many such additives at one time or another have made an appearance, and either gained a significant market share, maintained themselves in a modest but consistent role, or languished and finally disappeared. New additives are reintroduced each year, frequently with considerable public relations effort. Over time, the nutritionist tends to become a bit cynical about new products, having seen so many rise and fall. However, we also know that it would be foolish to blind ourselves to the possibility that a new and innovative additive might well be of significant importance in our feeding programs. As a result, many nutritionists have developed a mental balancing act, anxious to incorporate real innovations but suspecting (probably correctly) that the majority will be of little value.

Thus, we are faced with the question of how to consider the possible use of a new feed additive. Is there a rational approach that can be used? I feel we can certainly make a sensible start in this direction, but should acknowledge from the outset a certain reality of the situation. When considering new feed additives, we will not always be on firm ground. It may not be possible to design tests to precisely document the effects of an additive without altering the conditions under which it might be most efficacious. This we will simply have to accept.

If we hope to establish a means of evaluating new additives, it seems appropriate to first establish a frame of reference. To do so, let us consider three additives in common use today. We might ask what degree of certainty exists regarding the value of these additives, and how much if any confirmatory testing we demand prior to their use.

Vitamin D is routinely added to virtually all poultry and swine feeds. We accept the innumerable reports in the scientific literature confirming its value and may have experienced or heard of the field consequences of omitting this substance from the diet. Vitamin D is universally used, with the only question being level of supplementation. The second additive to be considered is synthetic lysine. Contrary to the case of vitamin D, lysine does not need to be added to all feeds. When it is determined that lysine is needed (by considering nutritional requirements and the composition of available feedstuffs), the nutritionist makes use of this substance with no doubt it will have the intended effect on growth and feed conversion. The third class of additives we might consider are growth promoting antibiotics. It is well known that these substances do not always "work". Generally speaking, their effect is inversely related to the quality of rearing conditions. In an extremely clean environment, it may be difficult to demonstrate any positive effect of these products. Thus, even though differences in response might be expected between flocks, it is generally recognised that in many situations a positive affect can be expected, and a decision is made regarding use.

The key point in this brief consideration of additives rests with the antibiotics. We recognise that the response to the additive will vary and, by extension, that pen studies carried out in experimental facilities may not necessarily give an indication of the full potential benefit of the additive. With this in mind, now we need to examine the additives that have been developed or introduced during the past several decades to see what perspectives might be gleaned.

From time to time, a real or perceived need of the poultry industry comes to the attention of feed additive suppliers. This presents a unique marketing opportunity, as an interest may exist in a product even before that product has been developed. The author refers to this scenario as a "vacuum". For our purposes, a vacuum is an unstable situation with a tendency to be filled by whatever might rush in. Whether products rushed to market to fill the vacuum always work may be questionable. All too often, the nutritionist may let his guard down in this situation hoping that the product in question will really be of benefit in alleviating a given problem. The classic example of vacuum type products are the toxin binders (mentioned elsewhere in the talk) which are purported to sequester multiple mycotoxins. Certainly, there would be a demand for such a product, if only it existed. The nutritionist and others in the company must be especially careful in such situations, because the hope that a product actually works may result in an unconscious loss of objectivity in its evaluation.

At the present time, at least three "vacuums" can be clearly identified in the feed industry. The search for the elusive multiple toxin binder has already been mentioned. The use of growth promoting antibiotics has been curtailed or brought into question in many countries. Also, the use of genetically modified (GM) ingredients is often controversial. We can be absolutely certain that a variety of products will be offered to address these areas. We can also be certain that decision makers in firms, who may not have a technical background, will be especially susceptible to being drawn into the vacuums. Nutritionists and others must be aware of products rushed to market to take advantage of perceived needs, particularly when these come from suppliers with product lines prone to include substances of questionable value.

From the above discussion, we can draw several tentative conclusions. First, we certainly have a right to expect a complete product description from the supplier. Mystical powders may play an important role in the metaphysical world but certainly not in the business of feed manufacture. If something is highly confidential, then the supplier might be urged to obtain patent protection prior to engaging in serious market development.

Second, the results of serious, well-designed, and repeated experimentation must be made available to the prospective customer. Unfortunately, not all experimental facilities (either private or public) have the same level of credibility. Some locations seem to have a remarkable record of positive results. Positive findings from several independent laboratories add considerable weight to supplier claims. Third, it is reasonable to expect the supplier to at least attempt to provide a credible hypothesis for the value and mode of action of a new product. If the hypothesis supporting the use of a given additive, such as the product mentioned above to improve egg shell quality, does not seem well founded, caution must be exercised in using the product. Finally, some consideration of cost/benefit must be made. At times, the expertise of accounting personnel will be needed for such calculation. A modest benefit in growth or feed conversion may not be enough to justify use of the product. In addition to product cost, there are hidden costs such as purchasing, warehousing, accidental spillage, and possible confusion by mill personnel.

Feed can become like an attic, full of forgotten odds and ends. Once we leave the relative comfort of essential nutrients behind, vigilance is essential. Many additives will have greater or lesser impact in different seasons of the year and at different ages in the life of the bird. Uncertainty is the rule, and a questioning mind is our most essential asset.

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The use of oil in poultry diets

The issue of (oil) fat usage in poultry diets is an ongoing one. During the process of oil extraction and refining, mostly from plant material, several waste products are obtained. These products are further processed, mostly by blending oils of different sources, for animal feeding purposes.

Two major issues arise out of this practice from a feed industry point of view. Firstly there is the issue of what energy level should be ascribed to them. Secondly, oils may be contaminated in some way. In this short article I will look briefly at both aspects.

In dealing with the energy level of fat and oil the first aspect which needs to be considered is it’s chemical structure. It is widely accepted that the degree of saturation and the free fatty acid content are major determinants of the dietary energy value of fats although other factors, including the degree of contamination with "non-nutritive" compounds are also relevant.

Unsaturated fats have higher dietary energy values than saturated fats. However a degree of synergism exists in that relatively unsaturated fat will promote the utilisation of relatively saturated fat. The combined dietary energy value of a mixture of the two is greater than that which would be predicted from values for the two fats separately. This effect is greater in younger birds than in older birds.

The Free Fatty Acid (FFA) content of fat is a major variable, particularly if there is a widespread use of a variety of high FFA ingredients in products such as acid oil. Physiologically, the greater the proportion of FFA in a fat, the lower the efficiency with which it is absorbed, a trend that is more pronounced the more saturated a fat is.

It needs to be borne in mind that any energy value ascribed to a diet or an ingredient is a function of the animal that is being fed and not a function of the ingredient itself. This is clearly illustrated in the case of fat utilisation by poultry where it was found that birds younger than 21 days of age utilise fat less efficiently than do older birds. This is principally because the enzymatic system of young birds is not fully developed.

Contamination of feed fats can be a problem, and one only has to look at the problems that the inclusion of high levels of dioxin containing industrial oil caused the industry in Belgium. Water is a common contaminant in oils and care must be taken to ensure that each delivery is free of water.

Some suppliers use restaurant grease (old cooking oil) in their products. While the use of restaurant grease is not in itself a problem the very manner of its collection gives cause for concern. Collecting small amounts of product from a large number of small suppliers makes quality control very difficult. Please ensure that your suppliers of feed fat do not use restaurant grease in their blends and if they do please satisfy yourself that the appropriate measures have been taken to prevent oil of industrial origin from finding their way into your feed.

Dr Julian Wiseman of Nottingham University has developed a prediction equation for the prediction of the AME value of fats and oils based on the unsaturated: saturated fat ration and the content of FFA. The equation, together with a worked example is shown below.

Where: FFA are the free fatty acids in g/kg

U/S is the unsaturated: saturated ratio

The constants to be used are as follows:

All fatty acids with carbon chains of C: 12 and shorter should be included as "unsaturated" fats.

In an example, a coconut oil containing 15.0% FFA and with the fatty acid profile shown below would yield different energies for starter and/or grower diets.

This gives us a U/S ratio of 2.4

The energy level for a starter diet is calculated thus:

= 7686 kcal/kg

= 32.165 MJ/kg

In a similar manner it is possible to calculate that the energy level in a Grower diet would be 34.9 MJ/kg.

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South African limestone: the cheap ingredient

Most South African (calcitic) limestone used as a calcium supplementation in the feed industry tends to be of average to poor quality and variable in Ca content. There are one or two exceptions to this however and the feed miller or farmer must look very carefully at what is available before deciding on a purchase.

Other sources of calcium include oyster shell, snail shell and dried eggshell although these are often not readily available. Scheideler (1997), compared oyster shell, eggshell and limestone and found no significant effect on feed intake, feed consumption or egg weight. Limestone and oyster shell improved egg specific gravity over eggshell, but particle size appeared more important than calcium source.

This picture has been removed because it is to big, please contact us for the picture.

Demir, E. et al compared pure CaCO3, limestone and eggshell and found significantly higher daily feed intakes on the limestone group. He found no significant differences between egg yield and egg weight. Eggshell thickness was greater with dried eggshell and pure CaCO3 than with limestone. Percentage egg deformity was lowest with dried eggshell and highest with the pure CaCO3. Particle size and calcium source solubility was not looked at in this trial.

Since it is estimated that between 14.3% to 21.3% of the total number of eggs laid, are cracked, calcium remains a very important issue. There are 4 areas of concern with respect to limestone and these are calcium content, heavy metal (impurity) content, solubility and particle size. If we look at each of these in more detail and restrict ourselves to poultry feeds, some interesting figures emerge:

This is the most important consideration and obviously has a direct influence on feed formulation. It has its greatest effect in layer diets and then in high-density diets. Pure calcium carbonate at 100% dry matter would be 40.04% Ca while commercial limestone is available at (registered) levels of 38%, 36%, 34% and 32%. In typical maize/soya based poultry diets, table 2 shows the effect of different Ca levels in a layer feed (layer 105) and n a broiler grower ration with limestone taken at a value of R220-00 per tonne:

The cost difference is shown from feed using 38% Ca lime while the average shows the average difference between each cost.

The above table may not look that impressive unless the farmer or miller is producing several thousand tones of feed per month! However, even a small feed mill will show some surprising figures if they do an evaluation of their current supply.

If we take a feed mill producing 500 tonnes of layer feed per month and look at a choice between limestone of 32% Ca and 36% Ca, least cost formulation gives inclusion per tonne of feed at 9.70% and 8.63% respectively. This means that the 500 tonnes would need 48.5 tonnes of 32% limestone or 43.15 tonnes of 36% limestone. Those selling limestone would argue that the price of 32% material at R195.73/t is equivalent to 36% at R220.00/t based on usage per month or R195.56 based on cost per unit calcium. Although this argument sounds logical, Nutritionists will tell you that the real difference in value is the cost in the feed formulation that shows a maximum price of R150.80 for 32% limestone vs. R220.00 for 36%! The real loss on 500 tonnes layer feed is then R44.93 X 48.5 = R2179.05 or R4.36 per tonne of feed produced. In addition, the more dense a diet becomes, the less the relative value of the lower calcium limestone becomes. A broiler grower diet which is more dense than the layer diet above gives a relative value of only R71.10 for 32% material. Discounts offered by suppliers for limestone testing below specification usually don’t cover these real differences.

Often we are reminded that feed quality is more a function of what has been left out rather than what has been included and the same applies to limestone. What fills the space in limestone that is not calcium carbonate? Smith, H.J.C. and Loock, A.H.; 1996 Proceedings of AFMA Symposium describe the impurities as clay minerals, heavy metals and other micro elements. The highest of these are shown as follows:

The amount of silicon present is inversely proportional to the amount of calcium in the limestone. The detrimental effects of certain heavy metals such as aluminium are well documented but will not be discussed here. The argument is overwhelmingly in favour of using only the best quality limestone available.

Particle Size and Solubility:

This is the area of biggest debate, with ongoing trials yet a huge amount of work has already been done. Particle size and solubility of calcium sources are negatively correlated so they really cannot be looked at in isolation. Terms such as "amorphic", "crystalline" or "marbelite" are loosely applied to limestone to indicate softness of the product. It is often assumed that softer (or amorphic) limestone are more bio-available but this is not strictly true. Several in vitro tests for "solubility" of calcium sources have been proposed. The popular resin test or "Hars" suspension test was derived from soil science work while Ajakaiye, A et al; 1997 used 0.1 M HCl solution over 10, 30 and 60 minutes. Ajakaiye compared seven sources of CaCO3, namely pure calcium carbonate, bivalve shell, periwinkle shell, oyster shell, eggshell, snail shell and marble dust. Two particle sizes were compared: sub 500 m m and more than 500 m m. Both calcium source and particle size (P<0.05) influenced Ca solubility in 0.1 M HCl:

Table 4: In Vitro Solubility:

It is important to note that the highly soluble marble dust was a hard crystalline limestone. Zhang BingFan and Coon C.N., 1997 demonstrated both in vitro and in vivo solubility of two limestone sources of varying particle size in 88 week old leghorn hens:

Table 6: In Vitro Solubility of two Limestone Sources:

They conclude that there is a negative correlation between in vitro and in vivo solubility and conclude that less soluble limestone is desirable in laying hens since it remains in the digestive tract for a longer period of time. Toppo et al. (1998), confirm the above by comparing the solubility of marble stone and oyster shell in varying strengths of acid (0.05M, 0.10M, 0.15M & 0.20M) and conclude that marble stone and oyster shell in fine particle size solubilised better than their coarse counterparts (P < 0.01).

Roland (1986) reviewed 44 papers comparing the availability of calcium from fine granular limestone to that of oyster shell. Over one third of the studies showed oyster shell to be a more available source of calcium, one trial showed limestone to be more available while the remaining nearly two thirds reported no differences. Several reports indicate that limestone and oyster shell of similar particle size show no difference in calcium availability.

Many factors such as magnesium, vitamin D3, calcium to phosphorus ratio, protein content of the feed, phytic acid in feed and age of the animal may also affect absorption of calcium, and this needs to be kept in mind.

	Buy limestone with as high a Ca level as possible.
	Hansard et al (1954) showed that young animals retain more calcium than older animals. Comparisons must be made on animals of similar age.
	Limestone that is totally insoluble in weak acid would also be unavailable to livestock.
	Finely milled marlbelite (or crystalline) limestone is as available a coarser amorphic limestone in all types of livestock not just poultry!
	For broilers, a finely milled limestone is desirable (< 500 m m). The choice of soft (amorphic) limestone should be more influenced by the wear and tear on mill equipment rather than solubility issues. After 21 to 24 days, broilers are able to utilise coarse, crystalline limestone of low solubility very well.
	Layer birds deposit eggshell at night while peak feed is during early morning. It is therefore important to feed a portion of the limestone as grit. The softer the limestone, the more the portion of grit that should be fed. Two thirds of the limestone is below 800 m m with around one third as grit or oyster shell.
	Feeding grit to layer birds allows them to select extra Ca for shell deposition when required.