Slide 1 Hi, everybody. My name is Oscar Rojas, and I am a second-year Ph. D. student in the Dr. Stein Monogastric Nutrition Laboratory. And today, I'm going to talk about the effects of reducing the particle size of corn on energy, phosphorus, and amino acid digestibility by growing pigs. Slide 2 This is the outline of my presentation for today. I will start with a brief introduction about feed technologies and the importance of grinding, and then I will move on to the digestibility experiments: energy, phosphorus, and amino acids. And then I will finish my presentation with some of the conclusions and the implications of this research. Slide 3 So why do we grind feed ingredients? Grinding of feed ingredients is used to reduce the particle size and to increase the energy and nutrient digestibility and thereby reduce the impact of feed costs on the total costs of production. It is recommended that corn grain be milled to an average particle size of approximately 650 microns. And this is usually accomplished with the use of either roller mills, hammer mills, or now with a combination of both systems – roller mills and hammer mills. And this new system is called two-stage grinding or multistage grinding systems, and they are used to minimize the variation in particle size and to maximize grinding efficiency. It has been reported that the digestibility of energy, dry matter, and nitrogen in corn increases as particle size of corn is reduced. And it has been reported that there is an increase in the digestibility of amino acids when we reduce the particle size of soybean meal. Slide 4 However, we need to know that there are some problems related to the reduced particle size. One of them is that there could be a problem with the flowability in our feeders and bins. Also, as we decrease the particle size, there are some evidence that there is an increase in the development of ulcers in the stomach. And also, there are some valid points mentioned that there is an increase of energy cost at the feed mill as we try to reduce the particle size. However, at this point, there are no data that demonstrate the effects of particle size on the digestibility of phosphorus or the digestibility of amino acids in corn fed to growing pigs. Slide 5 So in this slide, we can observe how is the processing of corn to obtain different particle sizes. In some previous experiments in which particle sizes of corn has been evaluated, the greatest particle size was achieved using a roller mill, whereas the smallest particle sizes were obtained using a hammer mill. Any by using this approach, it is not possible to distinguish between the effects of mill type – in this case, roller mill and hammer mill – and the effects of changing the particle size. Slide 6 So in these experiments, to avoid that situation, what we decided to do was first, use the corn grain, and roll it using an automatic roller mill. And then rolled grain was divided into four batches that were ground using a hammer mill with different screen sizes to obtain the average final particle sizes of 339 microns, 485 microns, 677 microns, and 865 microns. Slide 7 In this slide we can observe the chemical composition of the test ingredients. So we have in the Y-axis the values in percentage, and we have in the X-axis the four different particle sizes. The red bars represent crude protein, blue bars represent phosphorus concentration, and the green bars represent fat concentration. So we observed that as we increased the particle size, there is not a lot of difference between the concentration of crude protein in all the corn particle sizes, and we also observed the phosphorus concentration – we have that it ranged between 0.29 at 339 microns up to 0.34 at 677 microns. Slide 8 So the objective for these experiments was to determine the concentration of digestible energy and metabolizable energy, the standardized total tract digestibility of phosphorus, and the standardized ileal digestibility of amino acids in corn grain that was ground to different particle sizes and fed to growing pigs. Slide 9 So now, let's move on to the first experiment: amino acid digestibility. Slide 10 For this experiment, we used 10 barrows with initial body weight of 29.2 kg. We had 5 diets, and the experimental design was a Latin square repeated 5x5 with 5 periods and 5 diets. And ileal digesta samples were collected for 8 hours on day 6 and day 7 of each period. Slide 11 So in this slide, we can observe the ingredient composition of experimental diets. We have corn, ground limestone, dicalcium phosphate, and we also add chromic oxide and vitamin-mineral premix. We have 4 diets, as I mentioned before, and each of those diets contain each of the particle sizes. We also formulated a nitrogen-free diet to be able to calculate the basal endogenous loss of protein and amino acids. Slide 12 Here, we can observe the statistical analysis of this experiment. The data were analyzed by Anova using the Proc Mixed procedure of SAS. The fixed effect was the diet, and the random effects were the pig and the replication. Slide 13 Now, let's move on into the results for this experiment. Slide 14 Here, we are looking at the SID of lysine. We have in the Y-axis SID in percentage, and we have in X-axis each of the particle sizes. And we observe here that the SID of lysine was not reduced linearly as particle size of corn increased from 339 microns to 865 microns. Slide 15 When we look at the SID of methionine, we observe the same pattern as the previous amino acid. There is no linear reduction as the particle size increased from 339 to 865 microns. Slide 16 And that is the same case for the SID of threonine. There is not a linear decrease of digestibility as we increase the particle size of corn. Slide 17 However, in the case of AID of starch, there is a decrease in the digestibility as we increase the particle size of corn from 339 to 865 microns. And this is likely a result of the reduced access to the starch granules for alpha-amylase, which reduced the starch digestibility. Also, the reduced surface area of grain that was ground to a greater particle size maybe have contributed to the reduced access for enzymes. This indicates that reduction of cereal grain particle size may increase the effectiveness of starch-degrading enzymes. However, the fact that the AID and SID of crude protein and amino acids were not influenced by particle size indicates that protein-digesting enzymes were not hindered by the reduced surface area and greater particle size in corn ground to 865 microns. Thus, it appears that finer grinding and greater surface area is more important for the starch-digesting enzymes to gain access to the starch granules than it is for the proteases to get access to the dietary proteins. Slide 18 Now, let's move on to the second experiment: energy and phosphorus digestibility. Slide 19 For this experiment, we used 40 barrows with initial body weight of 22.8 kg. We had 4 treatments, 10 pigs per treatment, and feces and urine samples were collected for 5 days after 5 days of adaptation period to the diet. Slide 20 Here, we can see the ingredient composition of the experimental diets. We have corn, ground limestone, salt, vitamin and mineral premix. As you can see, we didn't add any source of phosphorus, so all the phosphorus is coming from corn. Slide 21 The data were analyzed by Anova using the Proc Mixed procedure of SAS. The fixed effect was the diet, and the random effects were the pig and the replication. Slide 22 Now, let's move on into the results. Slide 23 Here, we are looking at the digestibility of gross energy. We have in the Y-axis the ATTD in percentage, and we have in the X-axis each of the particle sizes. We observed that digestibility of gross energy was reduced linearly as particle size increased from 339 microns to 865 microns. Slide 24 When we looked at the digestible energy on a dry matter basis, we observed that the concentration of digestible energy also decreased linearly as we increased the particle size from 339 microns to 865 microns. Slide 25 And in the case of metabolizable energy, also on dry matter basis, we observed that there is a linear decrease as we increase the particle size. And the reason for the increased ME in corn ground to a smaller particle size is that the apparent ileal digestibility of starch is increased as corn particle is reduced. Slide 26 In the case of digestibility of phosphorus, it did not change as particle size of corn changed. So it appears that reduction in particle size or increases in surface area are not effective in improving the phosphorus digestibility in pigs. And the reason may be that to increase phosphorus digestibility in corn, the enzyme phytase is needed, and a pig has insignificant amount of endogenous phytase enzymes produced in the small intestine. Slide 27 So the conclusions for these two experiments are that reducing the particle size of corn from 865 microns to 399 microns linearly increased the ATTD of gross energy and the concentration of digestible energy and metabolizable energy in corn. However, there was no effect of corn particle size on STTD of phosphorus or the SID of indispensable amino acids. Slide 28 Thank you for your attention, and if you want to know more about swine nutrition, you can visit our website at nutrition.ansci.illinois.edu. Thank you.