Performance of Lactating Holstein Cows as Influenced by Forage Species, Maturity, and Level of Inclusion

Abstract

Three trials were conducted with the objective of evaluating the influence of fiber and indigestible NDF as affected by forage species, maturity, and level of inclusion on intake and milk production parameters. In the first trial, 60 multipa-rous Holstein cows [109 ± 49 d in milk (DIM)]were fed alfalfa- or orchardgrass-based total mixed ration(s)(TMR)for 70 d. Diets did not differ in NDF, ADF, CP, or non-fibrous carbohydrate(NFC) content. Cows fed these diets did not differ in DMI or milk production, even though the alfalfa had greater lignin and indigestible NDF than the orchardgrass-based TMR. Similar ADF and indigestible fiber in alfalfa and late-cut orchardgrass forages might have contributed to the similar performance of cows fed these diets. In the second trial, 50 multiparous cows (57 ± 28 DIM) were fed early- or late-cut orchardgrass-based TMR for 50 d. Diets did not differ in NDF, ADF, CP, NFC, or indigestible NDF, but early-cut orchardgrass had less (P<0.05) ADF, NDF, lignin, and indigestible NDF and greater (P<0.05) NFC and soluble CP than late-cut orchardgrass. Cows fed the early-cut orchardgrass-based TMR had greater (P<0.05) DMI, milk production, and milk protein than those fed late-cut orchardgrass-based TMR. Fiber digestibility of early-cut orchardgrass was much greater than late-cut orchardgrass, contributing to the improved DMI of cows on the early-cut orchardgrass TMR. In Trial 3, 20 Holstein cows (183 ± 22 DIM) were assigned to a repeated 4 × 4 Latin square design with 5 cows per treatment and 21-d periods to evaluate the influence of level of orchardgrass inclusion (50 to 80%) on DMI and milk production parameters. Dry matter intake and milk production decreased linearly as forage included in the diet increased (P<0.05). Amount of NDF consumed per day did not vary among diets in this study, suggesting that when a single forage source is used, diet NDF content is highly correlated with DMI. Variations in fiber digestibility and indigestibility of fiber may account for differences in intake and milk production of cows fed diets similar in chemical composition but varying in ingredient composition.