Newly harvested corn used in feed often leads to diarrhea in livestock and poultry and a lower feed conversion rate. What causes these effects? Is newly harvested corn less nutritious than corn stored for a year? In my view, discussions of the nutritional value of newly harvested versus aged corn should be based on scientific trial data, especially animal trial data. Analysis of some current animal trial results indicates that the negative effects seen when newly harvested corn is used in feed are mainly caused by its higher moisture content and coarser grind. The digestibility of nutrients in newly harvested corn is generally higher than that of corn stored for a year.
Let us look at several assumptions about newly harvested corn that circulate in the industry:
❖ High resistant starch content, resulting in low digestibility in animals;
❖ High pentosan content, increasing the viscosity of digesta in the animal gut and reducing nutrient digestibility;
❖ High trypsin inhibitor content, affecting protein digestibility;
❖ High moisture content in newly harvested corn, reducing its nutritional value;
❖ The particle size of newly harvested corn is relatively coarse, reducing the digestibility of nutrients.
We analyzed these hypotheses one by one to determine which is the main factor affecting the negative effects of newly harvested corn on animals.
First, regarding the hypothesis that newly harvested corn has a high resistant starch content. Since resistant starch has multiple types, resistant starch measured using in vitro methods is not necessarily indigestible by animals. Yin Dafei (2014) measured the resistant starch content of different types of corn during storage. The resistant starch content of newly harvested corn was as high as approximately 4.5%, and decreased to between 1%-1.5% after two weeks of storage. However, in a broiler feeding trial, they found (Table 1) that the ileal digestibility of corn starch in broilers did not differ for corn stored for 0-8 weeks, and was higher in all cases than in the control group (corn stored for one year). Our laboratory also studied the ileal digestibility of corn starch in pigs at different storage times and found that digestibility in pigs was 100% for unstored corn starch and 97% after 1 years of storage (Table 2). This indicates that the resistant starch content of newly harvested corn is not the main factor causing a decline in animal production performance; on the contrary, newly harvested corn has higher starch digestibility.
Second, regarding the hypothesis that newly harvested corn has a high pentosan content, which increases intestinal digesta viscosity in animals and reduces nutrient digestibility. The soluble pentosan content in corn is 0.10% (0.02%-0.19%), and the insoluble pentosan content is 3.53% (4.19-2.99%) (unpublished data). Soluble pentosans are generally considered to be the main factor causing intestinal digesta viscosity in animals. However, the soluble pentosan content of corn is very low, and further research is needed to determine the extent to which it affects intestinal digesta viscosity in animals.
Some studies have reported that newly harvested corn contains approximately 20% more water-soluble pentosans than corn stored for one year. The jejunal digesta of broilers fed newly harvested corn also had significantly higher viscosity than that of broilers fed corn stored for one year. However, the broilers’ metabolizability of organic matter and crude protein was higher or comparable when they were fed newly harvested corn than when they were fed corn stored for one year (卞晓毅, 2014). Therefore, the water-soluble pentosan content of newly harvested corn may not be a major factor causing a decline in animal production performance.
Third, the hypothesis that the content of antitrypsin factors is high. Wang Liqun’s study (2017) showed that, after three different types of corn had been stored for 4 weeks, the content of plant protease inhibitors in all of them decreased significantly, from 2.14-2.81 mg/g to 1.61-1.79mg/g. However, other studies have shown that the tolerance levels of laying hens and broilers to protease inhibitors are 3-4mg/g; when the content of protease inhibitors in soybean meal is 1.4-6.2 per mg/g, the digestibility of nutrients in piglets and growing pigs is not affected (李德发, 2003). Wang Liqun’s study (2017) also showed that crude protein digestibility was not affected in newly harvested corn compared with corn stored for one year. This indicates that antitrypsin factors are also not a major factor causing a decline in animal production performance.
Fourth, regarding the assumption that newly harvested corn has a higher moisture content. In general, newly harvested and dried corn has a moisture content 2-4 percentage points higher than corn that has been stored for one year. In particular, some smaller-scale livestock farmers may be unable to control corn moisture content, in which case using newly harvested corn may result in an even higher moisture content.
Higher moisture content may reduce the nutritional value of corn, particularly its available energy value. Based on corn’s digestible energy for pigs of 3450kcal/kg and metabolizable energy for poultry of 3220kcal/kg, a moisture increase of 2 percentage points would mean 78kcal/kg of digestible energy for pigs and 73kcal/kg of metabolizable energy for poultry. With corn used at 60% in feed, the digestible energy in complete pig feed may decrease by 50kcal/kg, and the metabolizable energy in complete poultry feed may decrease by 44kacal/kg. A reduction in the available energy value of feed may cause an imbalance in the energy-to-nitrogen ratio, leading to reduced animal growth performance, diarrhea, and other effects.
Finally, regarding the hypothesis that newly harvested corn has a coarser particle size after grinding. The grinding characteristics of newly harvested corn differ considerably from those of corn stored for one year. Research by Liu Yonghui (2011) shows that storage can significantly reduce corn hardness. Compared with newly harvested corn, corn stored for more than 12 months has a smaller particle diameter and a higher proportion of fine particles after grinding. For pigs, a reduction in corn particle size after grinding generally means increased nutrient digestibility (Huang Wei, 2016). For poultry, a coarser corn particle size may also result in poorer production performance and product quality (Zhang Jiaqi, 2018).
Trial evaluating the nutritional value of newly harvested corn
The most reliable methods for evaluating the nutritional value of newly harvested corn are animal digestion and metabolism trials, and animal growth trials. Bian Xiaoyi (2014) conducted metabolism trials with broiler chickens using different types of corn (dent, intermediate, and flint) stored for 0-2 months and old corn stored for 1 years. The results showed that, over 0-2 months, the apparent metabolizability of organic matter, crude fat, and crude protein in the three types of newly harvested corn was no lower than, or was higher than, that of old corn stored for 1 years. Wang Liqun (2017) formulated broiler diets using new corn and old corn stored for 1 years. The results showed that the broilers fed new corn had better growth performance and feed conversion efficiency than those fed old corn. Liu Yonghui (2011) conducted metabolism trials with broiler chickens using new corn from different regions of China and old corn stored for 1 years. The results showed that the metabolizability of dry matter, organic matter, crude protein, and gross energy in new corn was significantly higher than in old corn stored for 1 years. The metabolizability of most amino acids in new corn was significantly higher than in old corn. The average metabolizability of lysine in new corn was 89%, while that in old corn was 85%. Zhang Lei (2016) studied changes in the available nutrients for pigs in 4 corn varieties during storage. The results showed that after 10 months of storage, the digestible energy of corn for pigs decreased by 0.3 MJ/kg; the digestibility of corn gross energy, crude protein, crude fat, neutral detergent fiber, and acid detergent fiber all decreased significantly. These animal trials indicate that the digestibility of nutrients in newly harvested corn is higher than that in old corn stored for 1 years, and that using newly harvested corn to formulate feed improves animal growth performance.
Precautions for using newly harvested corn:
(1) Monitor the moisture content of newly harvested corn.
(2) Monitor the particle size of newly harvested corn after grinding.
(3)When using enzyme preparations, I personally recommend protease and xylanase as the first choice for newly harvested corn.
Let us look at several assumptions about newly harvested corn that circulate in the industry:
❖ High resistant starch content, resulting in low digestibility in animals;
❖ High pentosan content, increasing the viscosity of digesta in the animal gut and reducing nutrient digestibility;
❖ High trypsin inhibitor content, affecting protein digestibility;
❖ High moisture content in newly harvested corn, reducing its nutritional value;
❖ The particle size of newly harvested corn is relatively coarse, reducing the digestibility of nutrients.
We analyzed these hypotheses one by one to determine which is the main factor affecting the negative effects of newly harvested corn on animals.
First, regarding the hypothesis that newly harvested corn has a high resistant starch content. Since resistant starch has multiple types, resistant starch measured using in vitro methods is not necessarily indigestible by animals. Yin Dafei (2014) measured the resistant starch content of different types of corn during storage. The resistant starch content of newly harvested corn was as high as approximately 4.5%, and decreased to between 1%-1.5% after two weeks of storage. However, in a broiler feeding trial, they found (Table 1) that the ileal digestibility of corn starch in broilers did not differ for corn stored for 0-8 weeks, and was higher in all cases than in the control group (corn stored for one year). Our laboratory also studied the ileal digestibility of corn starch in pigs at different storage times and found that digestibility in pigs was 100% for unstored corn starch and 97% after 1 years of storage (Table 2). This indicates that the resistant starch content of newly harvested corn is not the main factor causing a decline in animal production performance; on the contrary, newly harvested corn has higher starch digestibility.
Second, regarding the hypothesis that newly harvested corn has a high pentosan content, which increases intestinal digesta viscosity in animals and reduces nutrient digestibility. The soluble pentosan content in corn is 0.10% (0.02%-0.19%), and the insoluble pentosan content is 3.53% (4.19-2.99%) (unpublished data). Soluble pentosans are generally considered to be the main factor causing intestinal digesta viscosity in animals. However, the soluble pentosan content of corn is very low, and further research is needed to determine the extent to which it affects intestinal digesta viscosity in animals.
Some studies have reported that newly harvested corn contains approximately 20% more water-soluble pentosans than corn stored for one year. The jejunal digesta of broilers fed newly harvested corn also had significantly higher viscosity than that of broilers fed corn stored for one year. However, the broilers’ metabolizability of organic matter and crude protein was higher or comparable when they were fed newly harvested corn than when they were fed corn stored for one year (卞晓毅, 2014). Therefore, the water-soluble pentosan content of newly harvested corn may not be a major factor causing a decline in animal production performance.
Third, the hypothesis that the content of antitrypsin factors is high. Wang Liqun’s study (2017) showed that, after three different types of corn had been stored for 4 weeks, the content of plant protease inhibitors in all of them decreased significantly, from 2.14-2.81 mg/g to 1.61-1.79mg/g. However, other studies have shown that the tolerance levels of laying hens and broilers to protease inhibitors are 3-4mg/g; when the content of protease inhibitors in soybean meal is 1.4-6.2 per mg/g, the digestibility of nutrients in piglets and growing pigs is not affected (李德发, 2003). Wang Liqun’s study (2017) also showed that crude protein digestibility was not affected in newly harvested corn compared with corn stored for one year. This indicates that antitrypsin factors are also not a major factor causing a decline in animal production performance.
Fourth, regarding the assumption that newly harvested corn has a higher moisture content. In general, newly harvested and dried corn has a moisture content 2-4 percentage points higher than corn that has been stored for one year. In particular, some smaller-scale livestock farmers may be unable to control corn moisture content, in which case using newly harvested corn may result in an even higher moisture content.
Higher moisture content may reduce the nutritional value of corn, particularly its available energy value. Based on corn’s digestible energy for pigs of 3450kcal/kg and metabolizable energy for poultry of 3220kcal/kg, a moisture increase of 2 percentage points would mean 78kcal/kg of digestible energy for pigs and 73kcal/kg of metabolizable energy for poultry. With corn used at 60% in feed, the digestible energy in complete pig feed may decrease by 50kcal/kg, and the metabolizable energy in complete poultry feed may decrease by 44kacal/kg. A reduction in the available energy value of feed may cause an imbalance in the energy-to-nitrogen ratio, leading to reduced animal growth performance, diarrhea, and other effects.
Finally, regarding the hypothesis that newly harvested corn has a coarser particle size after grinding. The grinding characteristics of newly harvested corn differ considerably from those of corn stored for one year. Research by Liu Yonghui (2011) shows that storage can significantly reduce corn hardness. Compared with newly harvested corn, corn stored for more than 12 months has a smaller particle diameter and a higher proportion of fine particles after grinding. For pigs, a reduction in corn particle size after grinding generally means increased nutrient digestibility (Huang Wei, 2016). For poultry, a coarser corn particle size may also result in poorer production performance and product quality (Zhang Jiaqi, 2018).
Trial evaluating the nutritional value of newly harvested corn
The most reliable methods for evaluating the nutritional value of newly harvested corn are animal digestion and metabolism trials, and animal growth trials. Bian Xiaoyi (2014) conducted metabolism trials with broiler chickens using different types of corn (dent, intermediate, and flint) stored for 0-2 months and old corn stored for 1 years. The results showed that, over 0-2 months, the apparent metabolizability of organic matter, crude fat, and crude protein in the three types of newly harvested corn was no lower than, or was higher than, that of old corn stored for 1 years. Wang Liqun (2017) formulated broiler diets using new corn and old corn stored for 1 years. The results showed that the broilers fed new corn had better growth performance and feed conversion efficiency than those fed old corn. Liu Yonghui (2011) conducted metabolism trials with broiler chickens using new corn from different regions of China and old corn stored for 1 years. The results showed that the metabolizability of dry matter, organic matter, crude protein, and gross energy in new corn was significantly higher than in old corn stored for 1 years. The metabolizability of most amino acids in new corn was significantly higher than in old corn. The average metabolizability of lysine in new corn was 89%, while that in old corn was 85%. Zhang Lei (2016) studied changes in the available nutrients for pigs in 4 corn varieties during storage. The results showed that after 10 months of storage, the digestible energy of corn for pigs decreased by 0.3 MJ/kg; the digestibility of corn gross energy, crude protein, crude fat, neutral detergent fiber, and acid detergent fiber all decreased significantly. These animal trials indicate that the digestibility of nutrients in newly harvested corn is higher than that in old corn stored for 1 years, and that using newly harvested corn to formulate feed improves animal growth performance.
Precautions for using newly harvested corn:
(1) Monitor the moisture content of newly harvested corn.
(2) Monitor the particle size of newly harvested corn after grinding.
(3)When using enzyme preparations, I personally recommend protease and xylanase as the first choice for newly harvested corn.