Defining the energy content (DE, ME, and NE) of drought-stressed corn and identifying risk factors that lower energy

Record-breaking heat and lack of rainfall during the 2012 growing season resulted in drastically reduced corn yield and the prospects of a very poor quality corn crop. Unfortunately, there was no information in the literature describing the nutritional value of drought-stressed corn fed to growing pigs. It was impossible to provide the feed and pork industries with recommendations on the feeding of drought-stressed corn. Therefore, the objective of this study was to develop information on drought-stressed corn and make it available to the feed and pork industries. Because corn is a major source of energy in pig diets, energy was the focus of this study. We used 28 corn samples from the 2012 crop which were collected across the Midwest using yield as an initial screen for drought impact. Yields ranged from <50 to >200 bu/acre. It was assumed that corn collected from low yield fields would be the most drought-stressed and thus provide us with the best range of samples to support our evaluation. Additionally, 2 corn samples from the 2011 crop were used in this study to serve as controls. Each corn sample was screened for mycotoxins, tested for 1,000 kernel weight and NIR values, and graded by an official U.S. grain inspection agency before use in this study. Corn samples were analyzed in the lab for neutral detergent fiber (NDF), crude protein (CP), and fat (EE) content. A total of 60 individually-housed barrows with an average initial weight of approximately 35 kg were randomly assigned to one of the 30 diets. This was repeated 4 times to provide 8 observations per treatment. Diet and fecal samples were analyzed in order to determine digestible energy (DE) content of the corn samples. Metabolizable energy (ME) and net energy (NE) were then calculated using equations provided by the NRC. Relationships were evaluated between DE and a variety of measured traits including: NIR values, yield, test weight, 1,000 kernel weight, total damaged kernels, broken kernels and foreign material, NDF, EE, and CP.

The mean DE content of the 2011 and 2012 corn samples were 3.72 and 3.68 Mcal/kg of dry matter (DM), respectively, and varied among samples by approximately 8%. The mean ME content of the 2011 and 2012 corn samples were 3.50 and 3.47 Mcal/kg DM, respectively, and varied among samples by approximately 5%. The mean NE content of the 2011 and 2012 corn samples were 2.61 and 2.57 Mcal/kg DM, respectively, and varied among samples by approximately 8%. Test weight, broken kernels and foreign material, density (measured using NIR), starch (measured using NIR), and fat (measured using both NIR and wet chemistry) were similar for both 2011 and 2012 crop samples. CP did tend to be slightly higher in the corn grown in 2012 (9.18%) compared with the 2011 control samples (8.56%). Neutral detergent fiber was significantly higher in the corn grown in 2012 (8.19%) when compared with 2011 (6.92%). Total damaged kernels were also significantly higher in the 2012 (1.65% vs 0.90). Mean 1,000 kernel weights of the 2011 and 2012 corn samples were 338 and 284 grams, respectively, and varied among samples by approximately 120%. Yield, the criterion used for the initial screening of drought-impact on the corn, ranged from 39 to 236 bu/acre among samples. Overall, there were no major differences in energy values (DE, ME, NE) between the 2011 control samples and the 2012 samples when fed to growing pigs. The variation in energy of corn grown under drought-stressed conditions was no different than what we expect to see in variation during a “normal” year. Additionally, no relationships were found between DE and any corn quality measurement, physical or chemical, which may be due to only observing relatively small variation in energy digestibility among the corn samples. Therefore, we can conclude that corn grown under drought-stressed conditions, irrespective of yield, can be utilized in swine diets and fed the same as corn grown under “normal” conditions without concern of large energy differences. This agrees with the industry remarks that performance problems were not observed when feeding corn grown in 2012.