The effects of organic grass and grass-birdsfoot trefoil pastures on Jersey heifer development: Herbage characteristics affecting intake

摘要

Low dietary energy and decreased intake of herbagehave been attributed to the reduced performance ofgrazing dairy cattle. We hypothesized that grasses withinherently greater energy would interact in a complementaryway with condensed tannins (CT) in birdsfoottrefoil to increase herbage intake by grazing dairy heifers.Eight pasture treatments comprising high-sugarperennial ryegrass (Lolium perenne L.), orchardgrass(Dactylis glomerata L.), meadow bromegrass (Bromusriparius Rehmann), and tall fescue [Schendonorusarundinaceus (Schreb.) Dumort] were established inLewiston, Utah as monocultures and binary mixtureswith birdsfoot trefoil (Lotus corniculatus L.; BFT).Pasture treatments were rotationally stocked by Jerseyheifers for 105 d in 2017 and 2018, and herbage sampleswere collected pre- and postgrazing for each 7-d grazingperiod and analyzed for herbage mass, nutritive value,and apparent herbage intake. We observed differencesamong pasture treatments in herbage quantity and nutritivevalue, as well as differences in herbage intake bygrazing Jersey heifers. On average, grass-BFT mixtureshad greater herbage intake than grass monocultures,and every grass-BFT treatment individually had greaterherbage intake than their respective grass monocultures.Using multivariate analyses, we determined thatapproximately 50% of the variation in herbage intakewas due to nutritive and physical herbage characteristics,with the most explanatory being characteristicsrelated to fiber and energy, followed by those related tothe percent of BFT in the herbage. Grass monoculturesexhibited a range of inherent dietary energy, but therewas indication that an imbalance of energy to crudeprotein (e.g., protein deficient) reduced intake of grassmonocultures. Moreover, there was some evidence of acomplementary effect between increased dietary energyand CT; however, low CT levels made it impossible todetermine the effect of CT on herbage intake per se.This study confirmed that chemical and physical characteristicsinherent to different pasture species have alarge effect on herbage intake by grazing cattle. Pasturesplanted to binary mixtures of nutritious grassesand birdsfoot trefoil increase herbage intake of temperatepastures by grazing Jersey heifers.