Introduction : Cereal gains are important source of energy in livestock diet due to high amount of starch they store in their endosperm, but there is a paradox in grains nutrition in ruminants. Without processing, most of grains, specially corn and sorghum, starch will not be effectively digested, but most of processing methods can increase starch degradability in rumen and therefore increase acidosis risk. The dynamic of starch fermentation in rumen is an important indicator of nutritional value of cereal grain in ruminants nutrition. Due to reduced loss of methane and heat, available energy supply for the animal is greater when starch digested in the small intestine compared to starch fermented in either the rumen or large intestine. Several chemical and physical methods are commonly used for feed processing; however, chemical processing methods have been criticized recently because of toxic chemical remnants. Physical methods such as grinding, rolling, steam flacking and newly microwave irradiation are commonly used for grain processing. Among these, steam flacking and microwave irradiation have been considered as the most favorite methods for horse and ruminants. Steam flacking can increase starch availability and therefore the rate of degradation in rumen, but microwave irradiation has the reverse effect, so that overall degradability and digestibility of starch will be decreased. Yeasts have been used in human food processing for a long time, but recently it has been received considerable attention as a potential method of animal feed processing method. Every processing method will affect the extent and location of starch digestion in a different way, but for ruminant nutrition, the aim of all methods should be to optimize the place and amount of starch digestion in the different parts of digestive tract, so that both the rumen fermentation and intestinal digestion have optimum rate and host animal can achieve the most effective rumen microbial growth and also high glucose absorption in small intestine. None of processing methods can show such a combined effect itself. Therefore, this study was conducted to investigate the effects of different combinations of physical and biological methods of processing on chemical composition and rumen degradability parameters of corn grain.
Materials and Methods: This experiment was carried out in a completely randomized design with six treatments, each with three replicates. Experimental treatments includes: 1) un-processing corn grain (control), 2) Steam-flaked corn grain, 3) yeast treated and then steam-flaked corn grain, 4) microwaved (850 W for 3 minutes) corn grain, 5) yeast treated and then microwaved corn grain 6) yeast treated, steam-flaked and then microwaved corn grain. In order to treat with yeast, corn grains were mixed with solution of 4 percent yeast (Saccharomyces cerevisiae) in a 2:1 ratio and then incubated in 35°C for 24 h. Dry matter, organic matter, crude protein and crude fat were determined using AOAC standard methods, and NDF and ADF was determined. Dry matter degradability of samples was determined using nylon bag technique. Samples were placed in the polyester bags and incubated for 0, 3, 6, 12, 24, 36, 48, 72, and 96 h in the rumen of three mature Dalagh rams. Degradability parameters were estimated using non-linear model and all data were finally analysed using SAS (9.1) statistical software.
Results and Discussion: Results of this experiment showed that type of processing method had significantly effects on chemical composition. Processing methods including microwave irradiation increased dry matter, organic matter, crud protein, neutral detergent fiber, acid detergent fiber, total digestible nutrients, and decreased the amounts of ether extract, non-fiber carbohydrates and neutral detergent soluble fraction of corn grain. treatment have no significant effect on dry matter degradability of corn grain, however, methods including yeast treatment especially the combination of yeast, flaking and microwave methods caused a non-significant reduction in the effective degradability and rapidly degradable fraction and also an increase in slowly degradable fraction of corn grain. Both of non-combined methods (steam flacking or microwave irradiation) caused a reduction in slowly degradable fraction of corn grain. The highest amounts of rapidly degradable fraction were also observed in these two treatments.
Conclusion: The results of this study demonstrated a significant effect of different processing methods on chemical composition of corn grain and had considerable effects on rumen dry matter degradability. Based on these results, it can be concluded that wet or dry heat processing methods are not appropriate processing methods of corn grain for ruminants nutrition, whereas combination of yeast treatment with steam flacking and microwave irradiation can be considered as the most appropriate methods.
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