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Feed Processing And Nutrient Enhancement

While it is true that the main factors influencing the nutritive value of a diet are the ingredients employed and their chemical composition, there are many other factors that can have a marked influence on the feeding value of a diet. Unfortunately since many of these are routine steps in feed manufacturing, often a minimum amount of effort is put into making sure that they are optimized so as to maximize diet efficiency.

Grinding
One of the first steps in feed processing is the grinding of cereals. The main effect of grinding is to improve feed utilization. This is accomplished by increasing the surface area of the grain portion of the diet by a marked reduction in particle size. Eley and Bell (1948) fed fine, medium or coarse mash feeds and observed an increase in feed consumption and less feed wastage with the coarser feed. Reece et al. (1985) reported that feed containing roller milled corn, having larger particle size, resulted in heavier weight broilers than a similar diet containing hammer milled corn, when diets were fed in the form of mash. However, steam pelleting the diets resulted in equal bird performance. A point of interest was the author's statement that the energy involved in grinding corn could be reduced b 14.5 % by the use of the roller mill.

Energy Costs Of Grinding
Deaton et al. (1989) pointed out that the energy required for grinding grain is the second largest energy cost after the pellet mill. Since in many cases layer feeds are not pelleted, grinding is the largest energy cost in producing these rations. The above authors prepared yellow corn by passing it through a hammer or roller mill. Laying diets were formulated, using up to 67% of the corn samples. No difference was noted in hen performance (Table 1) when fed these diets even though particle size averaged 1422 m from the roller mill and 844 m from the hammer mill. If such results are consistent under commercial conditions, significant savings in energy cost may be made by evaluating grinding conditions.

Table 1.

Particle Size
Reece et al. (1986 a,b) looked at particle size of hammer milled corn and concluded that for pelleted diets variability in fineness of grind had very little influence on the nutritive value of the diet, nor on pellet quality (Table 2). However, a marked reduction in the use of energy for grinding resulted from the use of a 6.35 versus a 4.7 mm screen opening, since the grinding rate was 27% higher for the larger screen.

Table 2.

Whole Grain Feeding
McIntosh et al. (1962) fed Leghorn pullet diets containing whole, ground or pelleted wheat and compared performance at different ages (Table 3). While the whole wheat diet was significantly inferior to the ground and pelleted wheat diets to 5 weeks of age, these differences decreased with age and by the 11-15 week period the whole wheat diet equalled the performance of the ground wheat diet. Such findings are of interest in view of the implementing of whole grain feeding to improve the economics of feeding (Forbes and Shariatmadari, 1994), as well as reports that whole grain feeding may improve the health of the bird by developing a healthier digestive system (Cumming, 1988). Formulation

Table 3.

Table 4.

Whole Soybeans
White et al. (1967) compared the heat treatment of whole soybeans, either by infra-red heating (temperature in a generator of  beans treated for 4 to 6 minutes had an exit temperature of 235!F), extrusion (beans preconditioned at 212!F to 18-21% moisture, temperature in extruder reaching 240 to 290V), autoclaving (autoclaved for 30 minutes with 30% of water added at 6 pounds pressure). All these heat treatments significantly improved the feeding value of the raw soybeans (Table 4), as well as reducing pancreas weight to levels similar to that of the control, dehulled, extracted soybean meal.

Arnold et al. (1971), heat treated soybeans in a still-air oven. Three samples of beans, harvested with 10.0, 12.5 and 16% moisture were subjected to various temperatures for 5 or 10 minutes. As can be noted in Table 5, a critical quantity of heat is required to deactivate the "toxic factors" and this will vary with the time the beans are exposed to heat and the amount of moisture in the beans. In a further study Simovic et al. (1972) utilized higher temperatures than used in the above study and utilized an infra red apparatus with a endless wire mesh belt under the heater strips, the speed of which could be controlled. It was found that the time and temperature could be varied over a wide range with performance of birds being similar if the critical quantity of heat applied to the beans was similar. The optimum times for various temperatures are shown in Table 6.

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 the positive physical effect of pelleting there are also chemical effects which enhance the feeding value of a diet. This is demonstrated in Table 7 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 7). 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.

Diet Enhancement Through Supplements
Supplementary Fat While it is obvious that subjecting a diet to various physical treatments, as outlined above, will enhance it's nutritive value, there is increase attention being paid to dietary supplements that can improve the availability or utilization of dietary nutrients. One of the most common ingredients added to poultry diets is supplementary fat. There have been many reports published showing the benefits of fat supplementation over and above it's contribution as an energy source. Much o this work has been reviewed in the papers of Mateos and Sell (1981 a,b,c). Of interest is the demonstration by Mateos and Sell (1981 c) that the extra caloric effect of fat, reported by a number of workers, is due in large part to fat slowing down the rate of food passage in the gut, thus allowing enhanced digestive activity resulting in increased nutritive value of the diet. This is demonstrated in Table 8, where it can also be noted that type of carbohydrate (starch versus sucrose) can also influence rate of passage.

Other Dietary Supplements
While the use of antibiotics and growth promoters have been in use for many years, in relatively recent years there has been a renewed interest in the use of enzymes, as well as probiotics, to enhance the nutritive value of a diet, through their action on the utilization of nutrients, as well as improved health of a flock. Recently oligosaccharides have been investigated as dietary additions that act through competitive inhibition, to tie up enteric pathogens and also to stimulate or interact on the immune system.

Nutrient Balance
Essential Amino Acids
Another area to look at and one that is receiving increased attention is formulating to more precisely meet nutrient requirements and thus improve nutrient efficiency by enhancing nutrient balance. There is a lot of evidence to suggest that enhanced utilization of essential amino acids occur when there is less non-essential nitrogen in the diet. Any essential amino acid in excess of requirements is, in effect, non essential nitrogen as far as the bird is concerned. This is covered in some detail by the report of Bedford and Summers (1985). Thus in order to enhance essential amino acid utilization and, in turn, reduce diet costs, more attention should be paid to EAA balance and their ratio to non- essential amino acids. It has been shown by Boomgaardt and Baker (1973) and Morris et al. (1987) that the essential amino acid requirement remains constant as a percent of dietary protein. Obviously this means that they would increase as a percent of the diet as dietary protein levels increased. This demonstrates that there is a reduction in the efficiency of EAA utilization as dietary protein level increases. From the data of Boomgaardt and Baker (1973), it was shown that the lysine requirement to maximize weight gain was approximately 4.7% as a percent of the dietary protein with levels of protein of 14, 18 and 23%, however, as a percent of the diet the requirements were .66, .88 and 1.05% respectively.

Minimum Levels And Balance Of Essential Amino Acids
Parr and Summers (1991) fed chicks a "perfectly" EAA balanced diet (NRC 1984) by formulating 23% protein, corn, soybean meal diet then reducing the protein level, in a step-wise manner, while at the same time keeping the ratio of corn to soya constant, until the last essential amino acid histidine, just met NRC requirement levels. As dietary protein level was reduced, EAA supplements were made to keep them at minimum requirement levels. For example, methionine was the first EAA to be limiting, then lysine, arginine, etc. Hence, increased quantities of these amino acids were added to the diets as dietary protein level was reduced. The intact protein level, where histidine just met minimum requirements, was around 14% with a crude protein level of around 16%. Weight gain and feed intake of the birds at the minimum histidine level are shown in Table 9.

The minimum EAA diet resulted in greater weight gain than the control and this diet did not respond to additional histidine or NEAA supplementation. Thus it was assumed that the balance of EAA in diet 2 was a reasonable estimate of a "perfectly" balanced EAA die

Lipstein et al. (1975) concluded that increased deposition of carcass fat in the growing chicken was the result of the bird increasing it's feed intake to try and obtain the minimum amounts of omittin EAA required for growth. If this is the case, the inference is that birds consume feed in an attempt to meet their amino acid requirements. Parr and Summers (1991) formulated three diets containing either 2560, 2850 or 3050 kcal of ME/kg using the balanced minimum EAA diet shown in Table 9 (diet 2). Thus the diets varied only in their energy concentration which differed by the amount of glucose monohydrate and cellulose added. In Table 10 it can be noted that weight gain increased as dietary energy increased. However, feed intake was identical. Thus, it would appear that the birds ate to satisfy their protein requirement. In doing so birds fed the high energy diet consumed more energy, were fatter, as shown by carcass fat content, and were thus heavier. While carcass protein, as a percent of dry weight, was reduced with the higher energy diet, based on total carcass protein deposition, the diets resulted in similar body protein deposition. Thus it would appear that with an ideal balanced EAA diet, growing birds will eat to satisfy their protein not their energy requirement.

If the above is the case, then in commercial formulation an effort has to be made to get closer to that ideal essential amino acid balance in order to improve the efficiency of EAA utilization and hence increase diet profitability.

Whole Grain Feeding
There has been renewed interest in investigating the use of feeding whole grains, especially in Europe where wheat is the commonly used cereal. Leeson and Caoston (1993) fed whole wheat and cracked corn, free choice, to broilers (Table 11). The main effects noted were a poorer feed:gain ratio and less abdominal fat with the free choice cereals, as well as a significant reduction in feed costs. During the 35 to 49 day period the birds were eating approximately 40% of the free choice cereals. Similar results were found by Svihus et al (1997) when whole or ground barley were fed to broilers (Table 12). As has been reported previously, they noted a marked increase in gizzard size by the feeding of whole as compared to ground barley.

Pellet Quality
With the use of more by products in North America, pellet durability index (PDI), which is a measure of the percent of intact pellets, was deteriorating to almost unacceptable levels. Hence, studies were initiated to investigate this problem. Fairchild and Greer (1999) had reported that by increasing the water content of the feed in a mixer PDI was enhanced with a significant decrease in energy usage by the pellet machine. Moritz et al. (2001) showed that the addition of up to 5% water to a feed mix, resulted in improved feed efficiency when fed to broilers to 6 weeks of age (Table 13). It has been suggested that surfactants facilitate absorption of water into grain and thus should improve feed utilization. However, Moritz et al. (2002), failed to show any positive effect in feed utilization, both with a regular and a higher fat supplemental diet, with the addition of a surfactant to the diet (Table 14).

Feed Processing Procedures
Another feed processing procedure that has been introduced to the feed industry is what is called "friction compaction". A chamber with a screw auger to pull feed through an insulated jacket at 80 - 85!C, forces the heated mash through a V shaped compression chamber with rollers that help to compact the feed and raise the temperature to around 95!C. Feed leaving the adjustable friction ring has a crumbled texture and is fed directly into the pellets.

Leeson et al. (1998) compared conventional pelleted and compacted feed when fed to broilers. They looked at a corn, soya as well as a corn, soya diet containing by-products. While 21-day weight was superior for the compacted feeds, by 49 days of age there were no differences in performance (Table 15). A relatively new type of feed processing was introduced in Europe in the nineties. Customers had been complaining about the low PDI and due to the fact that most poultry operations were not integrated, like in North America, the feed processors were challenged to look into the matter. This was also the time when more by-products were finding their way into poultry rations and also governments were pushing for some control of pathogens in feed. Hence, the goal was to come up with a process where by-products could be utilized, also investigate thermal processing as a means of reducing pathogens, while at the same time, maintaining or increasing plant output. Expander technology was investigated. An expander is similar to an extruder with a heavy duty screw in a barrel which is equipped with an adjustable annular gap. The annular discharge gap controls the degree of pressure on the mash feed. Material exiting the annular gap is referred to as "expandate¡ã

Expandate on exiting expands, resulting in moisture to flash evaporate, thus lowering the moisture in the finished feed. An expander is basically used to pretreat feed prior to pelleting and after going through a conditioning chamber. Usually the mash temperature is higher, thus there is more starch gelatinization. However, total energy expenditure is greater. Feed particles are usually more porus, thus better absorption of liquids is gained. The process is reported to improve feed digestibility, as indicated in Table 16.

Future Diet Formulations
In Table 17 several laying diets have been formulated and compared with the NRC (1994) requirements. Diet 1 is a regular 17% protein, corn, soya diet. It would be slightly deficient in total sulphur amino acids. Diet 2 has all the protein coming from soya and when formulated to just meet the minimum valine level, meets all other EAA minimum levels except for total sulphur amino acids. Diet 3 would be a regular 13% corn, soya laying diet. Not only does it require methionine and lysine supplementation, but it is also deficient in valine. Diet 4 is a 13% protein diet with all the protein coming from full-fat soybeans. It is slightly deficient in methionine and perhaps valine. (For EAA levels, see Table 18.) Most diets are formulated using a grain base and then adding a protein supplement to provide the proper level and balance of protein (amino acids). Soybean meal is the most common protein supplement used in poultry diets and while corn is the cereal commonly used in North America, this is not the case in many other parts of the world. Thus consideration should be given to using soybean products to supply the protein (amino acid) portion of the diet, then dilute it down with local cereals, by-products, high carbohydrate ingredients (cassava, sugar) etc., keeping in mind minimum amino acid requirements and balance, energy concentrations and above all, economics of production. It is of interest that diet 2, with all the protein coming from soya, has a similar level of soya as diet 1 (Table 17). Thus in many instances this would be a more economical diet to produce and still meet the minimum EAA levels for the laying hen (Table 18). Diet 4 is of interest as it shows that with full-fat soybeans the nutrient requirement of the laying hen can be put in a much smaller "package" (Table 17) than diets 1 and 2, while sti meeting the hen's requirements. Diet 5 has the same EAA levels as diet 3, but with the use of fat, i available, can provide the proper level of nutrients in a smaller "package With the significant increase in poultry production around the world, there is going to be an increased use of local ingredients to supply a significant portion of dietary nutrients. For the immediate future this will probably consist mainly of products that contribute to the energy portion of the diet (e.g. Cereals, by-products, fat, etc.) Thus, more emphasis will be placed on maximizing the efficiency of the protein portion of the diet in order to reduce production costs. This may well mean changes in diet formulation and the manner in which the diets are fed.

Tags · Feed Processing · Nutrient Enhancement

17.02.2008. 12:55

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