PSII-24 Relationship Among Color, Physicochemical Traits, and Ruminal in Situ Dry Matter Digestion of Corn Grains from Argentina, Brazil, and the United States

Abstract

Abstract Corn-derived starch and rumen-degradable protein (RDP) available for rumen microbial fermentation vary significantly with corn hybrid and environmental conditions. Identifying corn physicochemical traits potentially correlated with ruminal DM digestibility would facilitate the prediction of its nutritional value compared with more time-consuming determinations. We assessed 1) the effect of corn origin on color, physicochemical traits, and 22-h in situ DM digestibility (22h-DMD), and 2) the relationship of color and physicochemical traits with 22h-DMD on Argentinian (AR, n = 29), Brazilian (BR, n = 4), and North American (US, n = 15) corn samples. The hardness-associated properties measured were: color (Hue angle; H) and physicochemical traits [crude protein (CP), thousand kernel weight (TKW), test weight (TW, Schopper chondrometer with ¼ L capacity), floaters (FLO, percent of kernels floating in a sodium nitrate solution), kernel density (KD, pycnometer method), vitreousness (VIT), and coarse-to-fine milling ratio (C:F)]. In situ 22h-DMD was determined using two ruminally cannulated steers receiving a 53:47 forage-to-concentrate ratio diet. Mastication was simulated by grinding a 100-g sample for 10 s using a 0.625-cm screen. For each steer, three sets of 4-g (DM basis) of each corn sample were placed into R1020 Ankom bags and introduced in the ventral sac of the rumen at two independent events separated by 48 h. Four bags per sample were placed in a water bath (39 °C, 15 min) to determine the soluble fraction (0h-DMD). Corn origin effect on color and physicochemical traits and on 0h-DMD and 22h-DMD were tested using GLM and MIXED procedures, respectively. Means were compared by Tukey-Kramer test. Relationships among variables were studied using a correlation matrix (PROC CORR) and stepwise multiple linear regression (PROC REG). All traits differed (P < 0.01; Table 1) among corn origin, being AR corns intermediate in hardness-associated properties between BR and US samples, though more similar to BR ones. Correlation coefficients (P < 0.01) of 22h-DMD with H, FLO, TW, KD, C:F, and CP, were 0.43, 0.80, −0.77, −0.71, −0.82, and −0.72, respectively; TKW was unrelated (P = 0.26) to 22h-DMD. The predictive 22h-DMD equation (P < 0.01) based on physicochemical traits was 22h-DMD (%) = 160.31 – 1.16 × TW (kg/hL) – 7.49 × C:F (g/g; RMSE = 3.54, R2 = 0.74). Softer kernels with higher H and FLO and lower TW, KD, C:F, and CP, demonstrated greater 22h-DMD than harder samples. Indeed, TW and C:F resulted in reliable predictors of 22h-DMD to describe the nutritional value of corn samples. Succinctly, AR and BR corn hardness-associated properties contrasted with US ones. We hypothesized that greater CP and reduced 0h-DMD and 22h-DMD of harder genotypes may reduce or eliminate the need for RDP supplementation when those grains are included in beef cattle finishing rations; however, more research is warranted on this topic.