Impact of Alfalfa hay neutral detergent fiber concentration and digestibility on holstein dairy cow performance, diet digestibility and chewing behavior

Our objectives were to determine the effect of alfalfa hay in vitro neutral detergent fiber digestibility (IVNDFD), compared within relatively low and high neutral detergent fiber (NDF) concentration hay pairs, on Holstein dairy cow performance, apparent digestibility, chewing activity and rumen parameters. Treatments (Lh, Ll, Hh and Hl) included four alfalfa hays selected for low (L) or high (H) NDF concentration and low (l) or high (h) 48-h IVNDFD within NDF concentration pairs. Three studies were conducted. During Study 1 and 2, alfalfa hays were included at 15% of the diet DM. Study 3 was a short-term study (21-d) in which alfalfa hay was fed at 96% of the diet DM. Analysis of alfalfa hay grab samples taken during study 1 confirmed that within the high NDF hays (Hh and Hl) there was no difference in NDF concentration and the Hh hay was 6.8 percentage units higher in IVNDFD compared to Hl. However, within the low NDF hays (Lh and Ll), NDF concentration was 3.8 percentage units higher for the Ll compared to Lh hay and there was no difference in IVNDFD. Therefore, our original study design was not maintained. As a result, we evaluated the impact of alfalfa hay IVNDFD on response variables for the high NDF hay diets and the impact of alfalfa hay NDF concentration on response variables for the low NDF hay diets. When alfalfa hay was fed at 15% of the diet DM, there was no impact of alfalfa hay NDF concentration or IVNDFD on DMI, fat corrected milk (FCM) yield, milk fat, or protein yield among treatments. Within the low NDF hay diets, apparent total tract DM digestibility (DMD) was 6.6 percentage units higher for the Ll compared to the Lh hay diet and there was a trend for higher apparent total tract NDF digestibility (NDFD) for the Ll compared to Lh hay diet. For the high NDF hay diets, a difference in alfalfa hay IVNDFD of 6.8 percentage units did not affect total tract DM or NDF digestibility. Neither alfalfa hay NDF concentration nor IVNDFD affected rumen pH or VFA concentrations. When alfalfa hay was included at 96% of the diet DM, there was no difference in DMI, 3.5% FCM, milk fat or protein yield among treatments. Within the low NDF hay diets, apparent total tract DM and NDF digestibility were 14.7 and 18.4 percentage units higher for the Lh compared to Ll hay diet. In contrast, within the high NDF hay diets, apparent total tract DMD was 11.1 percentage units higher for the Hl compared to Hh hay and there was no difference in apparent total tract NDFD. Our results suggest that small differences in alfalfa hay IVNDFD or NDF concentration, especially when alfalfa hay is fed at a low dietary inclusion level, should not be expected to have a significant impact on dairy cow lactation performance. Given the challenges associated with forage sampling and IVNDFD repeatability, effectively implementing IVNDFD data in diet formulation for dairy cows is difficult.