title: Mean retention time in digestive tract and digestion of fresh perennial ryegrass by lactating dairy cows: influence of grass maturity and comparison with a maize silage diet.
abstract: The effects of grass maturity on the mean retention time of liquid and particles, digestibility and duodenal nutrient flows were measured by feeding second cuts of perennial ryegrass to 3 fistulated lactating dairy cows over 2 successive periods (late June and mid-July, 28 and 49 d regrowth, respectively). Fresh forage was given ad libitum with 12% (dry matter (DM) basis) concentrate. The increase in maturity lowered grass nitrogen content, organic matter (OM) digestibility and non-ammoniacal nitrogen flow into the duodenum, but did not affect OM intake (13.2 kg/d). Neither the fractional outflow rate of liquid in the rumen (FOR; 17.3%/h) nor the concentrate total mean retention time (TMRT; 32.9 h) were affected. With maturity forage TMRT tended to increase (43.0-48.8 h), certainly because of the longer comminution time of coarse particles. These results were compared with data obtained 2 months earlier with the same cows fed on a maize silage diet (25% DM basis of the same concentrate) ad libitum (17.4 kg OM/d). Despite a lower total OM intake, FOR was much higher with the grass than with the maize silage diet (12.1%/h) and this may explain the lower retention time in the rumen of the small particles when grass diets were given (19.0 vs 24.3 h for maize silage diet).
authors.affiliation: INRA, Station de Recherches sur La Vache Laitière, Saint-Gilles, France.
authors.forename: M
authors.initials: M
authors.lastname: Mambrini
authors.forename: J L
authors.initials: JL
authors.lastname: Peyraud
mesh_terms: D000821:Animal Feed; D000818:Animals; D002417:Cattle / Q000502:physiology*; D004063:Digestion; D004064:Digestive System / Q000378:metabolism*; D005260:Female; D007774:Lactation / Q000502:physiology*; D008129:Lolium; D012820:Silage; D013997:Time Factors; D003313:Zea mays