Fitting Prediction Equations of the Metabolizable Energy of Corn Obtained from Different Harvests for Piglets

This study aimed to fit prediction equations of the metabolizable energy (ME) from the chemical composition of corn obtained from different harvests for piglets. Two experiments were carried out in a controlled temperature room to determine the ME values of 18 corn cultivars. In the experiments I and II, the corn from the second (planting from January-March) and the first (planting from August-December) harvests were evaluated, respectively. In each experiment, 40 crossbred barrows (9.48 ± 0.06 kg, experiment I; 8.75 ± 0.22 kg, experiment II) were individually housed in metabolic cages, allotted in a randomized block design with nine treatments (corns replaced 25% of the reference feed), four replicates and one animal per experimental unit. The amount of daily feed was calculated based on metabolic weight (BW^0,75). Feed was provided four times a day (07:00, 10:30, 13:30, 16:00) and the water was provided on the same feeder at 5 mL/g of feed. The experiment lasted 12 days, with a 7-day adjustment period followed by a period of 5 days of total collection of feces and urine. The fit prediction equations of ME of corn were carried out by means of the simple and multiple linear regression procedure through indirect disposal techniques (Backward). The regressors used to fit the model were gross energy (GE), crude protein (CP), ether extract (EE), ash, starch (ST), neutral detergent fiber (NDF), acid detergent fiber (ADF), calcium (Ca) and phosphorus (P), on a dry matter basis. In general, the ME values of corn for the first and second crops ranged from 3281 to 3509 and from 3143 to 3652 kcal/kg, as fed basis, respectively. The greater variation of the ME in the second crop justified the fit of equations for the different crops or that corn from both crops was used to fit these equations. The equations fitted to predict ME presented determination coefficients (R²) that demand the validation of these equations. The best fit to predict the ME of corn for piglets was represented by ME = -6306.15 + 400.652ADF + 117.286ST + 24924.7Ca + 2489.66P – 148.406CP (R² = 0.44) for the first corn crop; ME = -7560.08 + 2.66895GE – 120.688ADF (R² = 0.48) for the second corn crop, and ME = 2848.95 + 68.5714NDF + 161.938EE – 5563.51Ca – 1454.15P for the combined period of both crops.