Document Type

Thesis - Open Access

Award Date


Degree Name

Master of Science (MS)

Department / School

Dairy Science

First Advisor

Jill Anderson


The objective of this study was to examine the effects of feeding exogenous amylolytic and proteolytic enzymes on lactation performance of dairy cows fed freshly ensiled corn silage-based diets. We hypothesized that the addition of these enzymes would improve nutrient utilization and consequently lactation performance. Thirty-six Holstein cows [15 multiparous and 15 primiparous; DIM = 132 ± 48 and 6 cannulated (3 multiparous and 3 primiparous; DIM = 164 ± 50] were blocked by milk yield, DIM, parity, and body weights and used in a 9 wk randomized complete block design study.. Treatments were a 40% (DM basis) corn silage TMR with 1) no enzymes (CON), 2) amylolytic enzymes (AMY; 10g/hd/d), and 3) amylolytic and proteolytic enzymes (AMYP; 10g/hd/d +15 g/hd/d). Corn silage was ensiled for 48 d before the start of the trial. Cows were fed individually with a Calan Broadbent system to determine daily intakes and milked 2×/d with weights recorded. Feed, milk, rumen fluid, fecal, and blood samples collected every 3 wk. An in situ digestibility experiment was conducted during wk 10 with TMR, corn, and triweekly composites of corn silage. Data were analyzed using MIXED procedure of SAS 9.4 with repeated measures and means compared using Tukey’s test. Significance was declared at P ≤ 0.05. There was a treatment effect for milk fat yield, and percent protein and lactose. A treatment by week interaction was observed for ECM.A treatment effect was observed for rumen isovalerate percentage and a treatment by week interaction was observed for rumen butyrate percentage. There was a treatment by week interaction for Prevotella populations. Apparent total tract DM degradation increased in AMY compared to CON and AMYP diets. Ruminal DM rate of degradation for TMR samples decreased in AMY compared to CON and AMYP diets. Ruminal degradation of corn grain tended to increase in DM and Starch digestibility for AMYP compared to CON and AMY diets. Under the conditions of this study, the addition of exogenous enzymes altered the rumen microbiome and fermentation pathways, but maintained lactation performance compared to CON.

Library of Congress Subject Headings

Dairy cattle -- Feeding and feeds.
Corn -- Silage.
Proteolytic enzymes.


Includes bibliographical references



Number of Pages



South Dakota State University

Included in

Dairy Science Commons



Rights Statement

In Copyright