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Corn grown under drought-stressed conditions does not have lower energy content than corn grown in a previous “normal” year
Record-breaking heat and lack of rainfall during the 2012 growing season resulted in drought-stressed growing conditions. An experiment was conducted to investigate the impact of these conditions on nutrient composition and apparent total tract digestibility (ATTD) of energy in corn, and determine if relationships exist among corn quality measurements, nutrient content and digestibility of energy. Twenty-eight samples of corn from the 2012 crop were collected across the Midwest using yield as an initial screen for drought impact; 2 samples from 2011 served as a control. Yields ranged from <3.1 to >15.7 t/ha (<50 to >250 bu/acre). Each sample was graded by an official U.S. grain inspection agency and also analyzed for ether extract and crude protein content (dry matter basis). Diets were formulated using each of the 30 corn samples plus vitamins, minerals, and 0.4% titanium dioxide as an indigestible marker. Diets were fed at a level of approximately 2.6 times the estimated energy required for maintenance (NRC 2012) based upon the average initial BW of the pigs at the beginning of 4 collection periods. Each of the 4 collection periods consisted of 6 days adjustment to the test diet followed by 3 days of fecal sample collection followed by 5 days of feeding a fully balanced grower diet; the latter was fed to ensure that the low amino acid test diets did not impair digestive function in subsequent collection periods. Sixty individually-housed barrows (PIC 359 X C29; initial BW=34.2±0.2 kg) were randomly allotted in an incomplete crossover design with 30 diets and 4 periods. Diet and fecal samples were analyzed for dry matter (DM), titanium dioxide and gross energy (GE). ATTD coefficients were then determined. Mean ATTD coefficients of GE between the 2011 and 2012 corn samples were not different (84.3 % vs. 83.1 %, respectively; P>0.10). Comparing 2011 with 2012, there were no differences in ether extract (4.07 % vs 3.96 %; P>0.10) or crude protein content (8.56 % vs 9.19 %; P>0.10) of corn samples. There were no differences in physical characteristics, except for 1,000 kernel weight, which varied among samples by 220% (176 to 386 grams). No relationships were found between any single corn quality measurement, physical or chemical, and digestibility of energy (P>0.10). In conclusion, ATTD of the energy of corn grown under drought-stressed conditions was not different from corn grown in the previous year under “normal” conditions.
Keywords: pig, drought, corn, digestibility