Effect of ensiled alpha-amylase–enabled corn grain at 2 concentrations in the diet on lactation performance, chewing activity, ruminal fermentation, nutrient digestibility, and nitrogen partition of dairy cows

This experiment evaluated the effect of α-amylase-enabled corn (AAC) on cows fed ensiled mature kernels at 2 concentrations in the diet. Twenty individually housed Holstein cows, arranged in 4 × 4 Latin squares (with 21-d periods), were exposed to each of 4 treatments in a 2 × 2 factorial combination of corn concentration (C): high corn concentration (High; 28.7% starch, 24.6% corn, 2.5% citrus pulp) versus low corn concentration (Low; 21.5% starch, 14.1% corn, 13.8% citrus pulp) and type (T): AAC (48.8% vitreousness) versus isogenic control (CTL; 51.1% vitreousness). Kernels were ground weekly, hydrated (62.2 ± 1.3% DM on AAC and 63.1 ± 1.4% DM on CTL), and ensiled for 28 ± 3 d. The statistical model had the effects of square, cow (square), period, C, T, and the C × T interaction. No effect of treatment was detected for milk yield (34.1 kg/d) and DMI (22.8 kg/d). High corn reduced the daily yield of fat (1.209 kg/d vs. 1.297 kg/d) and ECM (33.2 kg/d vs. 34.4 kg/d) and increased milk protein concentration (3.12% vs. 3.09%). When fed with Low, AAC increased ECM/DMI relative to CTL (1.54 vs. 1.49). Meal frequency was reduced on High-AAC (9.8 meals/d) relative to Low-AAC (10.3 meals/d). Cows fed High had greater proportion of daily intake in the morning (49.9% vs. 44.4%) and longer duration of the first daily meal (69.7 min vs. 62.0 min) than cows fed Low. There was a tendency for AAC to increase the total-tract NDF digestibility (49.9% vs. 48.0%), but starch digestibility did not differ (98.4%). Ruminal microbial yield did not differ (335 mmol/d of allantoin in urine). High reduced the ruminal acetate to propionate ratio (2.45 vs. 2.95) and pH (6.59 vs. 6.74) relative to Low. Cows fed High-AAC had lower MUN than Low-AAC (17.4 mg/dL vs. 18.8 mg/dL), and plasma urea-N was lower on High-AAC than on High-CTL and Low-AAC (17.2, 19.0, and 18.7 mg/dL, respectively). High starch reduced urine-N excretion (g/d) and partition (% of daily N intake) relative to Low starch and also tended to reduce fecal-N excretion and partition. Overall, Low starch increased milk solids yield, N loss in urine and feces, and the ruminal acetate to propionate ratio. Cows fed AAC and Low had the highest feed efficiency, and cows fed AAC and High had the lowest proportion of N intake in total excreta.