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United States Department of Agriculture

Agricultural Research Service


Location: Plant Science Research

Title: Does Alfalfa-Hay NDFD Matter in a Dairy TMR?

item Raeth-Knight, Mary -
item Linn, Jim -
item Peterson, Paul -
item Jung, Hans Joachim

Submitted to: Forage Focus
Publication Type: Trade Journal
Publication Acceptance Date: March 8, 2010
Publication Date: March 15, 2010
Citation: Raeth-Knight, M., Linn, J., Peterson, P.R., Jung, H.G. 2010. Does Alfalfa-Hay NDFD Matter in a Dairy TMR? Forage Focus. March issue. p. 19.

Technical Abstract: Three feeding trials were conducted to study the effect of alfalfa-hay in vitro neutral detergent fiber digestibility (IVNDFD, 48-hour laboratory incubation in rumen fluid) on Holstein dairy cow performance. Treatments (Lh, Ll, Hh, and Hl) included four alfalfa hays selected for relatively low-(L) or high-(H) NDF concentration, and relatively low (l) or high (h) IVNDFD within NDF-concentration pairs. During Study 1, alfalfa hays were fed at 15% of total mixed ration (TMR) dry matter (DM) for 133 days. Study 2 was a short-term study (21 days) in which the hays were fed at 96% of diet DM. Analysis of alfalfa hay grab samples during Study 1 confirmed that the high-NDF hays (Hh and Hl) had similar NDF concentrations, but a 7 percentage-unit difference in IVNDFD. Within the low-NDF hays, however, the Ll hay had 4 percentage-units greater NDF than the Lh hay, and their IVNDFD values weren't different. As a result, the study objectives were modified to evaluate responses to: a) alfalfa-hay IVNDFD in high-NDF hay diets, and b) alfalfa-hay NDF concentration in low-NDF hay diets. When alfalfa hays were fed at 15% of TMR DM, neither NDF nor IVNDFD of the alfalfa hay affected cow DM intake, fat-corrected milk yield, milk fat, or protein yield. Within low-NDF hay diets, actual diet DM digestibility was 7 percentage-units greater for the Ll hay compared to the Lh hay. Within the high-NDF hay diets, a 7 percentage-unit difference in IVNDFD didn't affect actual diet DM or NDF digestibility. Neither alfalfa-hay NDF concentration nor IVNDFD affected rumen pH or VFA concentrations. When the four alfalfa hays were fed at 96% of diet DM for 3 weeks (Study 2), there were no differences in cow DM intake, milk production, milk fat, or protein yield. Within low-NDF hay diets, actual diet DM and NDF digestibility were 15 and 18 percentage-units greater, respectively, for the Lh compared to Ll diet. In contrast, within the high-NDF diets, actual DM digestibility was 11 percentage-units greater for the Hl compared to Hh hay, and there was no difference in actual diet NDFD. These results suggest that when alfalfa hay is fed at a low inclusion rate in a TMR, small differences in IVNDFD or NDF concentration are unlikely to affect dairy cow lactation performance. Given the challenges with forage sampling and IVNDFD repeatability, effectively implementing hay fiber digestibility variation in dairy cow diet formulation can be difficult.

Last Modified: 4/19/2014