Effect of ensiled or finely ground α-amylase–enabled corn grain on lactation performance, chewing, ruminal fermentation, digestibility, and nitrogen partition of dairy cows

α-Amylase-enabled corn (AAC) and ensiling of corn kernels can improve starch digestion, feed efficiency, and N partition into milk of dairy cows. This experiment evaluated the effect of AAC on cows fed finely ground (GRC) or rehydrated and ensiled (REC) corn kernels on the lactational performance, DMI, ruminal fermentation, digestibility, chewing behavior, and N partition of dairy cows. Twenty-four individually fed Holstein cows (37.1 ± 4.8 kg/d milk yield, 143 ± 100 DIM, 633 ± 64 kg body weight), arranged in 4 × 4 Latin squares (with 21-d periods), were assigned to 4 treatment sequences. Treatments were arranged in a 2 × 2 factorial with 2 corn processing methods (GRC vs. REC) and 2 corn types (AAC, 48.8% vitreousness vs. isogenic control [CTL], 51.1% vitreousness). Kernels were weekly ground, hydrated (61.7% ± 0.55% DM for AAC and 61.7% ± 0.45% of DM for CTL) and ensiled to maintain a constant storage duration (28 ± 3 d). Diets had 13.0% corn grain from each treatment, 22.4% total starch, and 9.6% starch from each treatment, on DM basis. No effect of treatment was detected for milk yield (36.1 kg/d) and DMI (22.4 kg/d). Milk fat tended to be lower for cows fed REC compared with GRC (3.68% vs. 3.74%). The ECM/DMI did not differ between treatments, but REC tended to increase milk yield/DMI compared with GRC (1.63 vs. 1.61). Cows fed REC had shorter meals than cows fed GRC (35.9 vs. 37.5 min/meal). Meal frequency was lowest with GRC-CTL than the other treatments (9.3 vs. 10.4 meals/d). Meal size was reduced in cows fed REC-CTL (2.2 kg DM/meal) compared with GRC-CTL (2.5 kg DM/meal), whereas no difference was detected between REC-AAC (2.3 kg DM/meal) and GRC-AAC (2.4 kg DM/meal). Cows fed AAC tended to have higher total-tract starch digestibility (93.7% vs. 92.9% of starch intake) and lower fecal starch concentration (4.3% vs. 4.8% of DM) compared with CTL. No effect of treatment was detected on NDF digestibility (48.6% of NDF intake), ruminal microbial yield and molar proportions of VFA. Ruminal pH was lower in cows fed REC compared with GRC (6.72 vs. 6.83) and tended to be lower on AAC compared with CTL (6.74 vs. 6.82). Fecal pH did not differ between treatments. Cows fed REC tended to have a greater proportion of N intake in milk compared with GRC (34.2% vs. 33.7%), but fecal N and urine N excretions (g/d and % of N intake), and urea N in milk and in plasma did not differ. Results showed few significant interactions between corn type and processing, suggesting that the mode of action of AAC was in the digestive tract, independently of ensiling. Overall, providing AAC to lactating dairy cows may enhance starch digestibility without affecting DMI or milk yield, regardless of the corn kernel processing method used.