Effect of ensiled alpha-amylase enabled corn grain at two 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 (28.7% starch, 24.6% corn, 2.5% citrus pulp) vs Low (21.5% starch, 14.1% corn, 13.8% citrus pulp) and type (T): AAC (48.8% vitreousness) vs 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 vs 1.297 kg/d) and ECM (33.2 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 corn had greater proportion of daily intake in the morning (49.9 vs 44.4%) and longer duration of the first daily meal (69.7 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 corn reduced the ruminal acetate to propionate ratio (2.45 vs 2.95) and pH (6.59 vs 6.74) relative to Low corn. Cows fed High-AAC had lower MUN than Low-AAC (17.4 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.