Feed Manufacturing Effects On Poultry Feed Quality And Nutrition

Poultry Processing Articles >> Feed, Nutrition and Water

The most important cost factor when producing poultry is feed costs. Feed represents up to 65% of the cost of growing broilers. How that feed is prepared, mixed, and manufactured impacts the nutritional quality and costs of production. When many nutritionists today are asked “what is the importance of feed manufacturing to the nutrition of poultry?” most will recall the importance of pellet quality, and others will recall how certain nutrients could be damaged during processing. However, few of us tend to think of the feedmill as a kind of ‘chemistry lab’ in which heat, time, and reactants are combined to form a final product. Many years ago when we thought about the feedmill, it was just a place to mix cereal grains into a mash feed, but today, with new enzyme technology, developing antibody additives, genetically modified grains, and new processing techniques, the feedmill will become more integral to the feed formulation process. Yesterday, we worried about getting adequate nutrients to the bird, tomorrow we will worry about the entire process. Those who are able to utilize the correct time, temperature, and chemical reactants that result in the most economical feed at economical processing charges will produce lower cost products.

When thinking about today’s feed manufacturing process, it may require thinking out of the box just a bit. For example, is water in a formula all that important other than knowing that too much is a bad thing, that it has no caloric content and that you have to pay for transportation costs to the farm? What about the conventional dogma that says that to improve pellet quality you simply need to increase the gelatinization of the cereal starches, which we have all been led to believe will improve poultry nutrition? Is this true?

Almost all animal feed nutritionists are taught the importance of water as a nutrient at least in the sense that it present in high amounts in animal tissues. Since water makes up 60-70% of all animal tissues and products, it is required by the animal in large quantities. Not many nutritionists consider water when formulating feed. This could be because of concerns with feed quality when stored since elevated levels could result in mold growth.

However, adding water to feed will decrease the cost of making pellets and could improve feed conversion and growth rates. When given a choice, birds will choose feed with added water because it is more palatable to them. They tend to consume more wet feed than dry, even after the level of moisture is adjusted. It has been shown in bird growth competitions, that birds fed feed with water grow at a faster growth rate.

Feed manufactures work hard to produce pelleted diets of high quality while minimizing production expenses (Mommer and Ballantyne, 1991). Pellet quality (intact pellets) greatly improves broiler growth and feed conversion (Briggs et al., 1999). Fairchild and Greer (1999) have demonstrated that increasing feed mash moisture at the mixer can increase pellet durability and decrease pellet mill energy consumption, consequently improving pellet quality and reducing milling expense. Decreasing pellet mill energy consumption alone provides an incentive for feed manufacturers to consider moisture addition during the manufacturing process. However, potential improvement in pellet durability adds even more enticement for the use of moisture in broiler feeds since past research has illustrated positive relationships between pellet quality and broiler feed efficiency (Moran, 1989; Nir et al., 1994). The evidence these past studies provide warrant further research involving the application of pelleting broiler feeds with added water as well as determining the effect of this process on broiler performance.

We have found that moisture addition to feed mash generated extensive differences in pellet durability and starch gelatinization between low moisture and high moisture treatments. High moisture pellets for both starter and grower diet formulations produced higher durabilities and gelatinization percentages compared to their respective low moisture equivalents. Broiler performance was most markedly affected in the three-to six-week period. Pelleted treatments produce significantly higher live weight gains and feed efficiencies compared to mash treatments. Surfactant/water additions to high moisture treatments created a dilution of nutrients. Adjusted feed efficiency values illustrated that high moisture pelleted treatments produced significantly higher feed efficiencies compared to any other treatment. A possible explanation for these findings is that broilers fed high moisture pellets were able to better utilize feed energy for growth (productive energy) as opposed to using feed energy for food prehension (maintenance). Broilers fed intact pellets of high durability would expend less energy in the act of feeding compared to broilers fed pellets of low durability and high percentages of fines. This speculation has been supported in past research (Moran, 1989; Nir et al., 1994). Mortality was not affected by moisture additions; however, pelleted treatments produced significantly greater mortality percentages compared to mash treatments.

We have begun to conduct other studies with the primary objective of clarifying the relationships between moisture addition, pellet manufacturing and quality, nutrient density and broiler performance. Differences in formulation density significantly affect pellet quality. The production rate of the formation of pellets where treatments have adjusted formulation densities produced higher rates of production as compared to non-adjusted formulations. This finding may be the result of the high soybean oil content of the adjusted formulations, which would aid in lubricating the pellet die. Adjusted formulation treatments produced pellets of significantly lower durabilities and higher percentages of fines as compared to NRC formulated treatments. Nonetheless, when the experimental treatments’ pellet qualities were compared to that of the control treatments, moisture addition significantly improved durability and decreased the percentage of fines. This finding is especially important since the adjusted formulation treatments contained high percentages of soybean oil. Past research has shown that increasing fat above 2% in a corn-soybean broiler diet prior to pelleting will decrease pellet quality with respect to durability and the percentage of fines (Richardson and Day, 1976). In some of our studies, fat added at 6.5% prior to pelleting in conjunction with added moisture can produce pellets of 75% durability and less than 27% fines. These results conclude that the addition of moisture, even if ordinary tap water, can potentially increase pellet mill production rates and significantly increase pellet quality. Broiler performance was similarly unaffected by moisture type additions, however formulation density can significantly impact performance, if left unadjusted, of course. Broilers fed adjusted formulation treatments exhibited significantly higher live weight gains and significantly lower feed intakes that collectively produced significantly higher feed efficiencies.

These data support the adjusted feed efficiency calculations derived in the first study. Mortality percentages were not affected due to experimental treatments. The adjusted formulation diets were the only treatments to improve live weight gain compared to their control treatment. The two control treatments were superior in regards to feed efficiency compared to their corresponding experimental treatments. This finding was probably a result of both controls being more nutrient dense than their respective experimental treatments, which caused feed intake to be significantly decreased. Contrary to the speculations of the first study, the adjusted formulation control, which possessed the lowest durability of all treatments produced the highest feed efficiency value. It should be noted, however that the live weight gains produced by the adjusted formulation control were the lowest of all treatments, despite this formulation having the most concentrated nutrient profile (growing broilers in this manner would not be cost effective). A possible explanation for this finding could be that the current study was conducted through the months of March and April during ideal broiler-rearing outside temperatures, whereas broilers in the previous study were reared during the much colder months of November and December. Ideal outside environmental temperatures could have dictated a lessened need for broiler maintenance energy. Nir et. al. (1994) define productive energy as net feed energy less bird maintenance energy. Although improved pellet quality would be expected to increase productive energy, this energy gain could be in excess relative to low maintenance energy requirements as well as the fixed protein content of the diet. Past research has also illustrated that broilers raised from 3 weeks to marketing during favorable outside environmental temperatures demonstrated decreased feed efficiency despite improved pellet quality (Acar et al., 1991). Mortality percentages did not differ among control treatments and experimental treatments. These data conclude that adjusted broiler grower diet formulations that include added moisture of either experimental type prior to conditioning and pelleting may improve (3-6) week performance, without negatively acting on broiler survivability.

Problems concerning feed mold should be insignificant since feed moisture content in both studies did not exceed 16%. Poultry can be negatively affected by feed mycotoxins produced by the fungi Fusarium, Aspergillus and Penicillium. However, these fungi require a minimum moisture content of 19 to 25 percent (Trigo-Stockli and Herrman, MF-2061), though few nutritionists would be comfortable with this level.

Feed manufacturing produces physical and chemical changes in ingredients, and these may include the gelatinization of starch. The effect of gelatinized starch on animal performance has been inconsistent in past research. Broiler diets typically contain high percentages of grain and, therefore, high proportions of starch. Under processing conditions using heat and moisture, starches gelatinize and help bind feed particles together (Mommer and Ballantyne, 1991). Hoover (1995) defines starch gelatinization as an order-disorder phase transition that includes the diffusion of water into a granule, hydration and swelling, uptake of heat, loss of crystallinity and amylose leaching. Leached amylose immediately forms double helices that may aggregate (hydrogen bond) to each other and create semicrystalline regions (Thomas et al., 1998). Lund (1984) speculates that as the gelatinized starch cools, the dispersed matrix forms a gel or paste-like mass that may function as an adhesive or binding agent. Past research has associated dietary gelatinized starch both positively and negatively with pellet quality and broiler performance (Moritz et al., 2001; Moritz et al., 2002a; Moritz et al., 2002b). However, it has been speculated that gelatinized starch per se may affect broiler performance aside from its contribution to pellet binding.

Gelatinizing cereal starch has generally been thought to improve enzymatic access to glucosidic linkages and consequent digestibility (Moran, 1989; Colonna et al., 1992). Allred et al. (1957) reported a significant improvement in weight gain and feed conversion in chicks fed pelleted/re-ground corn that was incorporated into a complete diet over chicks fed similar diets with unprocessed corn. However, later research examining processed/re-ground corn-based diets concluded there was no nutritional benefit to broilers despite increased diet starch gelatinization (Sloan et al., 1971; Naber and Touchburn, 1969). Moreover, (Plavnik et al., 1997) found that feeding broilers pelleted/re-ground corn-based diets resulted in decreased bird performance compared to broilers fed similar unprocessed diets.

One strategy for producing high quality pellets has been to gelatinize as much ingredient starch as possible. High quality pellets are desirable as they are correlated with improved broiler performance. However, improving pellet quality through increasing starch gelatinization may negatively affect nutrient utilization, thus antagonizing performance enhancements of pelleting.

In the current study, corn was processed using typical feed industry practices and incrementally incorporated into complete diets at the expense of unprocessed corn (UC). The objective was to create diets with different levels of gelatinized starch produced from different commercial processes. Corn was the only ingredient manufactured to avoid confounding processing effects of high fat or high protein ingredients. Corn was either pelleted (PC) or extruded (EC) and subsequently re-ground prior to diet incorporation. Pelleted corn provided dietary starch gelatinization percentages indicative of conventional pelleted feeds, while EC provided extreme levels of gelatinization. Diets were fed to broilers during the 0-to-3-week starter phase to determine effects of processing-derived starch gelatinization on performance.

Unprocessed and processed corn types had numerically similar bulk density post-grinding. Creating this similarity was important since dietary starch density may influence broiler feed intake (Naber and Touchburn, 1969). Moisture content of diets relative to nutrient density may also influence feed intake (Moritz et al., 2001; Moritz et al., 2002a). However, moisture percentages among corn types were similar, and corn was not the only ingredient contributing to dietary moisture. Despite grinding unprocessed and processed corn through the same hammer mill screen, particle size among corn types differed. However, standard deviations among corn type particle size were similar. Starch gelatinization percentages were calculated relative to unprocessed corn (1). Pelleting and extruding corn increased starch gelatinization 29 and 92%, respectively. The diet containing 3/3 pelleted corn had a similar percentage of calculated gelatinized starch as the diet containing 1/3 extruded corn. Peak gelatinization temperatures were similar among corn types.

Interactions between processed corn type and level of inclusion were not apparent. Feeding broilers diets that utilized pelleted corn resulted in lower feed intake and higher feed efficiency compared to broilers fed diets containing extruded corn. Broiler live weight gain and mortality were not affected by processed corn type. The performance differences may be explained by variations among corn type particle size. Corn particle size of mash diets has been shown to influence feed preference, weight gain, growth efficiency and metabolism of broilers (Portella et al., 1988; Healy, 1992; Nir et al., 1994; Nir et al., 1994). The particle size of pelleted corn in our study averaged 231 μ m less than extruded corn. Healy (1992) found that decreasing the particle size of dietary cereals (corn, hard sorghum or soft sorghum) from 900 to 300 μ m in 200 μ m increments resulted in a linear increase in 0-to-3-week broiler FE (P = 0.001). For corn-based diets, improved FE was associated with decreased broiler feed intake and increased metabolizable energy corrected for nitrogen, but (Healy, 1992) did not statistically analyze broiler performance produced by individual cereals. Wondra et al., (1995) found that reducing the particle size of dietary corn from 1,000 to 400 μm in 200 μm increments in mash and pelleted diets linearly increased finishing pig FE (P < 0.001). The increase in pig FE coincided with a linear decrease in average daily feed intake (P < 0.002) and increase in digestibility of gross energy (P < 0.001). The authors suggest that reduced particle size increases surface area and makes nutrients more accessible to digestive enzymes.

Nir et. al., (1994b) observed significant 1-to-3-week FE and LWG improvements for broilers fed diets containing 900 μ m corn compared to broilers fed diets containing either 1,000 or 2,000 μ m corn. The authors speculate that these differences may have occurred due to changes in the gastrointestinal tract. In a subsequent study, Nir et al., (1994c) found that broilers fed coarse grain (2,000 μ m corn, wheat or sorghum) had higher gizzard weight at 21 d of age compared to broilers fed similar grain of 600 or 1,000 μm (P = 0.01). Similarly, (Healy, 1992) observed significant increases in 23 d broiler gizzard and proventriculus weight when broilers were fed 900 μm cereals as compared to 300 μ m cereals. Nir et al., (1994c) propose that physiological changes in the gastrointestinal tract may effect broiler appetite and feed passage rate. Healy (1992) speculates that gastrointestinal tract organ weight may affect maintenance energy requirements of broilers.

Inclusion level of gelatinized starch in general did not affect broiler performance parameters. However, increasing dietary inclusions of pelleted corn resulted in a linear decrease in broiler feed intake and weight gain. The aforementioned studies concerning particle size reported similar dietary effects on feed intake (Healy, 1992; Nir et al., 1994b; Nir et al., 1994c; Wondra et al., 1995). Since LWG paralleled feed intake and FE was not affected (P = 0.3009), it does not appear that increasing gelatinized starch through pelleting or decreasing particle size improved nutrient digestibility. Increasing dietary inclusions of extruded corn, which increased gelatinized starch and particle size, did not significantly affect broiler performance, although broilers fed diets that contained increasing amounts of extruded corn showed a numerical trend of decreased FE.

Live weight gain of broilers fed the control diet were lower than LWG produced by diets containing either pelleted or extruded corn. However, LWG did not significantly differ between broilers fed the control diet and the diet containing 3/3 pelleted corn. Additionally, feed intake and FE were similar among diets containing pelleted corn and the control diet. These findings are inconsistent with past research on dietary particle size (Healy, 1992; Nir et al., 1994b; Nir et al., 1994c; Wondra et al., 1995). Perhaps particle size differences were too small between diets containing pelleted and unprocessed corn to significantly affect broiler performance. Most previous studies used 200 μ m increments, whereas the difference in our study was less than 110 μ m. In contrast, feed intake increased (P = 0.0158) and FE decreased (P = 0.0179) when broilers were fed diets containing extruded corn as compared to the control diet.
Diets that incorporated pelleted corn, containing low levels of gelatinized starch, seemed to effect broiler feed intake as opposed to nutrient utilization. Sibbald (1977) found that steam pelleting various diets, which included a corn-soybean chick starter diet, did not change dietary true metabolizable energy. Bayley et al., (1968) fed broilers various corn-soybean mash diets from 0-23 d. The authors found no significant difference in energy metabolism or performance between broilers fed diets containing pelleted/re-ground corn and unprocessed corn. Diets that incorporated extruded corn, containing comparably high levels of gelatinized starch, seemed to affect broiler feed intake through decreasing nutrient availability, since broilers eat to meet there requirements. Sloan et al. (1971) fed diets containing unprocessed and expansion-extrusion processed corn to broilers from 0 to 4 weeks. The diets were described as similar in texture and bulk. The authors reported no significant difference in weight gain or feed utilization among broilers fed diets containing unprocessed corn and diets containing varying levels of processed corn. However, (Hongtrakul et al., 1998) found that feeding diets containing extruded cereals (corn, cornstarch, broken rice, wheat flour, and grain sorghum) to pigs from 0-7 d post-weaning decreased gain to feed ratios compared to pigs fed diets containing unprocessed cereals (P < 0.05).

The authors also varied extrusion processing conditions of corn to create diets containing increasing levels of gelatinized starch. Feeding pigs these diets from 0-18 d post weaning had a quadratic effect on dry matter, crude protein and energy apparent digestibility (P < 0.01). Digestibility values initially increased then decreased with increasing levels of gelatinized starch. The authors attributed these effects to variations in extrusion processing conditions, which may have generated retrograded starch, Maillard products and loss of available amino acids and/or vitamins.

Gelatinization percentage for diets containing 3/3 pelleted corn and 1/3 extruded corn were calculated to be similar. However, feed intake was significantly increased for broilers fed diets containing 1/3 extruded corn compared to broilers fed diets containing 3/3 pelleted corn. Despite differences in particle size, broilers fed each diet had LWG that imitated feed intake and had statistically similar FE. This finding does not follow typical particle size relationships found in the literature (Healy, 1992; Nir et al., 1994b; Nir et al., 1994c; Wondra et al., 1995), and perhaps is more indicative of extrusion processing impairing nutrient availability and requiring broilers to consume more feed to meet nutritional requirements.

In general, variation in diet particle size confounded effects of gelatinized starch on broiler performance. However, particle size was likely influenced by starch gelatinization. When performance effects could not be explained by particle size, the amount and derivation of gelatinized starch in diets may have influenced feed intake and/or nutrient utilization. Broiler feed intake may have been modified due to the effect of gelatinized starch on appetite, feed passage rate, gut morphology and related factors. Extrusion processing may have reduced nutrient availability of corn. Nevertheless, the data suggest that gelatinizing starch through commercial feedmilling processes does not improve nutrient utilization of broilers during the 0-to-3-week starter phase.

Particle size may well be the next real area of research in poultry nutrition. All forms of poultry have been fed ground diets for many years since it has been thought that the gizzard was able to adequately reduce all feed particles to the preferred size. As a result, the gizzard atrophies since it has less function. However, the gizzard may well have other not completely understood functions. Some workers have shown that the gizzard retains larger Soybean meal particles longer and does not release them to the small intestine until the mean diameter is actually smaller than had they ground the particles to a small size before feeding (Kilburn and Edwards, 2004). The birds were able to obtain more phosphorus from the ration when fed diets with large SBM particles. Thus, poultry may be able to function more fully if the gizzard remains in good condition. If the gizzard is able to retain more function when given less ground particles, the same might be considered for the remainder of the digestive tract. Does course ground grain improve the tone and integrity of the digestive system of poultry? This is an important question to consider since better muscle tone could lead to less breakage of the intestinal tract and thus fewer concerns with microbial contamination in the processing plant. More work is desperately needed in the area of particle sizes for poultry.

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