Prediction of the nutritive value of South African maize hybrids for broiler chickens

Abstract

Maize is a major component of broiler feed and consequently contributes largely to dietary energy values. Previous research showed nitrogen-corrected apparent metabolisable energy (AMEN) of maize varied due to differences in proximate composition, as well as intrinsic kernel factors such as kernel hardness, density, size, and vitreousness. Most studies performed in the past used the total excreta collection method for the determination of AMEN. However, the utilisation of indigestible markers in the feed reduces the errors of the total collection method that occur due to incorrect measurement of feed intake and excreta output. Different markers/indicators have been included in feed such as chromic oxide, titanium dioxide or acid insoluble ash. The present study compared in vivo techniques to determine AMEN of European and South African maize samples and prediction of AMEN by using the Danisco Animal Nutrition near-infrared transmittance (NIT). The effects of maize AMEN on the energy uplift of a xylanase, amylase, and protease (XAP) enzyme combination were also investigated. For the first study, white (n = 471) and yellow (n = 639) maize samples from the 2015/2016 (n = 338) and 2016/2017 (n = 772) harvest seasons were collected from different regions in South Africa and analysed for moisture, crude protein, crude fat, milling index, grit yield all, AMEN, and hectolitre mass (L/kg) using near-infrared transmittance (NIT). The Pearson product moment correlation coefficient of all variables was determined using the multivariate analysis test. The relationship between AMEN and all parameters was analysed using the multiple regression model fit test. Factors were included in the final model using stepwise regression to reduce the Bayesian information criterion (BIC). This resulted in the following final model: AMEN = 3589.8 + 37.59 * crude fat + 9.76 * crude protein - 30.32 * moisture + 0.3 * milling index. The R2 of this model was 0.89 with a root mean square error (RMSE) of 8.95 kcal/kg. For the second study, the treatments comprised of five maize samples using two methods to determine AMEN. For the total collection (TC) method, birds were fasted for 6-hours followed by a 6-hour feeding and an additional 12-hour fasting period. Excreta was collected during feeding and additional fasting periods. For the basal substitution (BS) method, birds were placed onto treatment diets 14 hours before the 3-day collection period. Excreta was collected every 24 hours. Results showed no significant effect of Method between TC and BS, or interaction of Method x NIT AMEN value of maize. This implies that BS can be used as an effective method to determine the AMEN value of maize. Significant differences were observed between NIT AMEN, and measured AMEN, regardless of the method. For the third study, the basal substitution method was used with/without the inclusion of enzyme. On average the XAP enzyme increased the AMEN value of maize by ~60 kcal/kg DM, with absolute effects of XAP on maize varying numerically between maize variants (P>0.1).