Impact of stage of maturity and method of preservation of alfalfa on digestion in lactating dairy cows.

Four multiparous Holstein cows in midlactation were fed 60:40 forage:grain (dry basis) diets containing first-cutting alfalfa harvested at the early bud or early flower stage of maturity. Each of the two maturities was preserved as silage and hay. A 4 x 4 Latin square design experiment (28-d periods) was conducted to measure the impact of alfalfa maturity and method of preservation on milk production and composition, intake, digestion, digesta passage, and particle size of digesta. Milk production and composition were not affected by treatment. Increases in fiber intake resulted from increased maturity and preservation as hay, but this did not appear to limit DMI or milk production. Both increased maturity and preservation as hay resulted in the following effects in cows: more time spent ruminating, greater total chewing time, greater wet and dry rumen fill, and a greater volume of rumen contents. Rumen retention time of La applied to forage was 6 h less, and 0-h disappearance of DM from dacron bags was greater for silage than hay. In situ DM disappearance rates averaged 15%/h for silage and 9.5%/h for hay. Lag time was related inversely to 0-h disappearance. Masticates and mixed rumen samples from cows fed hay showed a greater percentage of DM as particles greater than or equal to 9.5 mm in length. Gross feed efficiency was greater for cows fed alfalfa silage than for those fed alfalfa hay, probably because of more rapid digestion and passage. The potential for rumen fill to limit intake in high producing cows appears to be greater for alfalfa preserved as hay than that preserved as silage.