Kansas State University
Department of Animal Sciences and Industry
Manhattan, KS
U.S.A.
An expanding drought in the upper Midwest and spotty dry areas in some parts of the corn belt have led to a several less than perfect growing seasons with reduced yield and poor quality grains. In some areas, corn was so severely affected that much of the crop was deflected to silage production. Drought may have several effects on grain quality. If the dry weather has occurred throughout the season, the kernels will be small, somewhat low in test weight, and of highly variable composition. In some cases, light test weight corn can still meet specs for animal feed, having 90 to 100 percent of the feed value of normal corn. Yield loss will be the biggest concern of growers, however, the composition is of utmost concern of nutritionists. If the dry weather occurs later in the season, kernel fill will be less, protein likely low (in both corn and soybeans), and test weight reduced. There is an increased likelihood of mycotoxins in drought-stressed corn.
The actual toxin content depends primarily on temperatures, the higher temperatures favoring aflatoxin, lower temperatures favoring the Fusarium toxins. More research is needed on methods to process toxin containing grains to lessen the effect on animal performance.
The oil, protein, starch, and fiber content of corn and corn by-products will affect not only the nutritional value, but also the feed milling characteristics. Although expected composition differences due to weather, hybrid, and drought appear small (protein +/-1.7%, oil +/- 0.8%, starch +/- 2.0%), because corn is usually the largest component of poultry rations, one could expect the biggest impact on feed milling to be due to even small changes in nutrient composition. The grain moisture content must also be considered when grinding and pelleting rations for meat birds. All of these factors will affect pellet quality. If changes in some of these factors result in reduced pellet quality, it is likely to reduce bird performance, especially feed efficiency. It may be possible to determine the effect of the ratio of these nutrients and make adjustments so that pellet quality is not impacted. For example the effect of just .5% added moisture can increase mill throughput while improving pellet quality. With the introduction of new corn varieties with altered oil and starch properties, more information is needed about the impact of changes in the macronutrient content of corn so that milling may be optimized.
Not many producers consider moisture and it's affect on milling when formulating feed. 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 (Beyer, et al, 2002).
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). 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. In our own studies, we have found that moisture addition to feed mash generates 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 is most markedly affected in the three-to six-week period. Pelleted treatments produced significantly higher live weight gains and feed efficiencies compared to mash treatments. Surfactant/water additions to high moisture treatments created a dilution of nutrients. Feed efficiencies were adjusted to 12.5% calculated moisture content in order to place all treatments at a similar nutrient density. 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). Mortality was not affected by moisture additions; however, pelleted treatments produced significantly greater mortality percentages compared to mash treatments.
Other work has been conducted to clarify the relationships between moisture addition, pellet manufacturing and quality, nutrient density and broiler performance. Studies have shown that adjustments in the moisture content of mash feed could overcome the often detrimental effect of added oil on pellet durability (Moritz, et al, 2002).
Under processing conditions using heat and moisture, starches gelatinize and help bind feed particles together. Starch gelatinization is 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 semi crystalline regions. It is thought 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. 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. Allred et al., 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 (Naber, et al 1969; Sloan, et al, 1971). Moreover, Plavnik et al., 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.
We have conducted studies to determine the effect of starch gelatinization on broiler feeding (Moritz, et al, 2002a). Fractions of corn were 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. 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 feed milling processes does not improve nutrient utilization of broilers during the 0-to-3-week starter phase.
We found that broilers fed gelatinized starch during the 0-to-3-week starter phase did not show improved feed utilization. However, in these studies, gelatinizing the starch may have influenced particle size, even after regrinding the samples, which may subsequently affect broiler performance. Further research is necessary to determine what the nutritional value of starch gelatinization in poultry rations.
Particle size is another manufacturing parameter that has received little attention in previous research. This is particularly surprising since feed particle size imparts influence on the anatomy and physiology of the digestive system, it's function, it's relationship between certain organs, and even gut microflora and pH. Birds fed feeds, which have been finely ground then pelleted with, have atrophied gizzards. This loss of gizzard function may affect other parts of the digestive tract including the small intestine where much nutrient breakdown and absorption occurs in birds. Corn quality impacts milling characteristics and grinding parameters, which will affect pellet quality and bird performance. It may be necessary to manufacture feeds that allow us to take advantage of the benefits of pelleting while also maintaining gizzard function. Perhaps many researchers discounted the importance of particle size since the feeds were fed in pelleted form. It is true that a smaller particle size will improve pellet quality. However, when the pellet is exposed to moisture in the crop, the feed dissolves into the particles that are sized according to the grind of the grain and thus are in mash form when exposed to the gizzard. The poultry industry needs to conduct further research on particle size.
We are beginning to determine that the gross composition of grain may have an impact the requirement of certain nutrients. Although wet lab analysis can easily determine the protein and amino acid content of a particular load of grain, what may be more difficult to elucidate is how the relationship of starch, moisture and protein, impacts pellet quality which indirectly impacts the requirement of certain nutrients. If feeds with higher pellet quality increase the productive energy value of the rations, does this then impact the requirement of other nutrients? Research diets often used to determine digestible amino acid needs of poultry are usually semi-purified or corn-soybean meal-based mash diets. While the lack of feed manufacturing equipment or the cost and time associated with processing research diets may necessitate feeding diets in mash form, this is not a common practice in the broiler industry.
The effect of feed form on amino acid requirements has received little attention even though the physical form of feed could be a factor influencing the variability in digestible requirements. Jensen (2000) has suggested that pelleting diets may increase amino acid requirements when expressed per unit of feed. Pelleting increases the density of a diet which reduces the time spent consuming meals, resulting in an increase in productive energy of a ration without changing metabolizable energy (Reddy et al., 1962). Increasing the energy available for protein synthesis may require higher dietary levels of lysine and other essential amino acids to maximize growth performance and efficiency.
A preliminary trial was conducted to determine the effects of feed form on digestible lysine necessary for maximum BWG and FE of broilers from 16-30 days of age. A corn, soybean meal, and corn gluten meal-based diet (1435 kcal ME/lb and 21% CP) was formulated on a digestible amino acid basis to obtain a lysine deficient diet. Digestible essential amino acids were estimated from a composite of reported data. A 2x5 factorial treatment arrangement was achieved by feeding diets in two forms (mash and steam-conditioned pellets) with five levels of dietary digestible lysine (0.75, 0.85, 0.95, 1.05, and 1.15%). Six pens of 25 chicks were fed each dietary treatment.
Average feed intake and kcal ME consumed/bird were significantly higher for pellet fed birds. Performance of birds fed pelleted diets with digestible lysine levels above 0.95% was generally superior to that of birds fed the mash diets, regardless of lysine level. Maximum BWG and FE responses were observed at 0.95% dietary digestible lysine for the mash fed birds. Pellet fed birds achieved maximum BWG and FE responses at 1.05% and 1.15% digestible lysine, respectively. Our lab is further investigating the effects of feed form on lysine intake and utilization, but the preliminary data suggests that feed form is a factor affecting estimated lysine needs.
Take home message
Grain quality not only affects the nutritive value of feed, but it also has far reaching effects on milling characteristics and feed manufacturing parameters. Small changes in the starch, protein, and moisture content of the corn will have a major impact since corn makes up the largest fraction of poultry rations. Pellet quality and particle size are affected by changes in the composition of the grain and feed rations. These parameters may have an impact on the requirement of certain marginal nutrients if savings in the productive energy of feed can be realized from improvements in pellet quality.
Acknowledgments
This work was supported in part by a grant from the Midwest Poultry Association and the USDA Regional Grant Project. The authors would like to thank Myron Lawson and Robert Resser for their technical assistance.
References
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From Proceedings of the "Midwest Poultry Federation Convention", St. Paul, Minnesota, U.S.A.
