FBA issue 32: May / June 2010
Feed Processing & Nutrient Enhancement
by John D. Summers, PhD, University of Guelph, Guelph, Ontario, Canada
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.
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 by 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 1422mm from the roller mill and 844mm from the hammer mill. If such results are consistent under commercial conditions, significant savings in energy cost may be made by evaluating grinding conditions.
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.
Nir et al. (1990) also compared the grinding of sorghum by a hammer and roller mill. Their data would suggest that at similar particle size there is no difference in feeding value of hammer or roller milled sorghum.
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