The team of international researches based at China Agricultural University and Auburn University in the US, examined the influence of storage time on the nutritional value of feed corn. The researchers published their work in the journal of Animal Nutrition.
“The present study determined the effects of storing corn up to 5 years in national barns on the performance, meat quality, and utilization of energy and nutrients in broiler chickens,” they said.
The research team found that several nutritional elements including starch, crude protein (CP), amino acids, fatty acids decreased over time and that chickens fed the stored grain saw performance losses.
“Although the digestibility of starch, CP, and AME [apparent metabolizable energy] of corn was not affected by storage for 5 years, corn stored for over 4 years resulted in decreased performance and meat quality in broilers,” the researchers concluded. “Therefore, when used as a feed ingredient, corn should be stored for no more than 4 years if possible."
Why stored corn analysis?
On a global scale, about 2.58bn tons of feed and cereal grains, including corn, wheat and rice, are produced annually, said the researchers. Many of these grains are stored, which may leave them open to damage.
In rice, alpha-amylase and beta-amylase decrease during storage while proteases, lipases and lipoxygenase are increased, they said. The changes mean that the solubility and digestibility of rice protein are reduced during storage.
Similarly, lipid oxidation and free fatty acid content are included in whole meal flour when stored, they said. Fat acidity also rises while iodine-binding values are decreased.
“Free fatty acids can be easily oxidized to produce H2O2 [hydrogen peroxide], and thus affect catalase (CAT) and peroxidase (POD) activities in corn (Bailly et al., 2002),” the researchers said. “The activities of CAT and POD are also affected by cell-membrane lipid peroxidation and are used as indicators to assess the quality of stored corn.”
In many countries, corn may be stored for two years or longer before being used in feed, they said. And while previous research found that protein efficiency in corn dropped after 5 years of storage, the growth rates of rats fed that corn were consistent.
It is considered that the chemical composition of corn kept in a storehouse is “relatively stable” for at least 110 months, and that the amount of metabolizable energy corrected for nitrogen (AMEn) was not altered, they said. But, long storage is thought to alter the nutritional value of corn.
“Previous studies have focused on the nutrient utilization of corn stored in good condition or the effect of stored corn on the growth of rats,” the researchers said. “Little attention has been paid to the effects of corn stored in a natural environment (room temperature in barns) on the animal performance and the utilization of nutrients in broilers.”
Methods and materials
The corn samples used for the feeding trials were stored in brick structures designed to hold 5,000 tons of corn, said the researchers. Corn was dried to 15% before storage, and was kept for 2, 3, 4 or 5 years and treated annually with phosphine for insect control.
Corn was analyzed for dry matter, crude protein, amino acids, fatty acids and activities of CAT and POD, they said.
In the study, two different feeding trials were used to examine the corn, said the researchers. In the first study, 192 broiler chickens were given one of four diets for a period of six weeks.
The diets were formulated to meet or exceed nutritional recommendations using corn stored for 2, 3,4 or 5 years, they said.
Chickens were weighed at hatching and in weeks 3 and 6, feed intake (FI) was noted from hatch to week 3 and week 4 to 6 and the feed conversion ratio (FCR) was calculated, the researchers said.
On day 42, a selection of birds was collected, weighed and samples of breast muscle were collected for pH and drip loss analysis, they said.
In the second feeding trial, female birds were given one of four diets again using corn stored for 2, 3, 4 or 5 years, they said. On day 19, birds were weighed and moved to metabolic cages at which point they received 23 hours of light and the temperature was reduced from 33 degrees centigrade to 21 degrees by day 21.
Excreta was collected and feed intake was noted, they said. Manure was checked for CP, starch, amino acids, fatty acids and gross energy.
For the corn samples, moisture content was similar and there were no differences in test weight save for corn stored 5 years, which was lighter, said the researchers. The amounts of CP, amino acids and fatty acids declined the longer the feed ingredient was held as did CAT and POD activities, while fat acidity grew over time.
“Collectively, the results suggest that the use of corn stored for 4 years in animal feed decreased the performance and meat quality of broilers,” they said. “Fat acidity, CAT, and POD activities can be used as indexes for evaluating the storage quality of corn.”
No differences in feed intake were seen, they said. But, storage time tended to linearly decrease bodyweight gain from hatch to week 3 and decreased it in a quadratic manner from week 4 to 6.
The rise in storage time tended to increase FCR from hatch through week 6, said the researchers. “Corn stored for 5 years significantly increased EPI [European production index] of broilers from 0 to 6 week as compared to corn stored for 3, or 4 years,” they added.
Corn kept for 5 years increased drip loss and lowered the pH of bird breast muscle, they said. But, metabolizable energy (ME) results were similar for all diets.
“There were no significant differences in the digestibility of most amino acids, except isoleucine, histidine, and arginine,” they said. “The digestibility of histidine and arginine quadratically changed with storage time, and the digestibility of isoleucine tended to be affected by storage time.”
Source: Animal Nutrition
Title: Effect of storage time on the characteristics of corn and efficiency of its utilization in broiler chickens
Authors: D. Yin, J. Yuan, Y. Guo, L. Chiba