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

Authors: ROSE, MARCUS - Bureau Of Land Management; Waldron, Blair; ISOM, S. - Utah State University; Peel, Michael; THORNTON, KARA - Utah State University; MILLER, RHONDA - Utah State University; ROOD, KERRY - Utah State University; HADFIELD, JACOB - Utah State University; LONG, JENNY - Utah State University; HENDERSON, BRACKEN - University Of Idaho; CREECH, J. - Utah State University

Submitted to: Journal of Dairy Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/22/2021
Publication Date: 4/30/2021
Citation: Rose, M.F., Waldron, B.L., Isom, S.C., Peel, M., Thornton, K., Miller, R., Rood, K., Hadfield, J.A., Long, J., Henderson, B., Creech, J.E. 2021. The effects of organic grass and grass-birdsfoot trefoil pastures on Jersey heifer development: Herbage characteristics affecting intake. Journal of Dairy Science. 104. https://doi.org/10.3168/jds.2020-19563.
DOI: https://doi.org/10.3168/jds.2020-19563

Interpretive Summary: The number of grazing dairies is increasing, but decreased grazing intake reduces the performance of dairy cattle. Therefore, it is important to identify herbage characteristics inherent to various pasture species and varieties that affect intake. We confirmed that grass-birdsfoot trefoil mixtures have greater intake by grazing dairy heifers than grass monocultures. Furthermore, 50% of the intake differences were due to physical and nutritive characteristics of the herbage; with fiber, energy, and percent birdsfoot trefoil most predictive. These findings indicate that mixtures of high-energy grasses and as little as 14% birdsfoot trefoil increase intake of temperate pastures by grazing dairy cattle.

Technical Abstract: Low dietary energy and decreased intake of herbage have been attributed to the reduced performance of grazing dairy cattle. We hypothesized that grasses with inherently greater energy would interact in a complimentary way with condensed tannins (CT) in birdsfoot trefoil to increase herbage intake by grazing dairy heifers. Eight pasture treatments comprised of high-sugar perennial ryegrass (Lolium perenne L.; PR), orchardgrass (Dactylis glomerata L.; OG), meadow bromegrass (Bromus riparius Rehmann; MB), and tall fescue (Schendonorus arundinaceus [Schreb.] Dumort; TF) were established in Lewiston, Utah, USA as monocultures and binary mixtures with birdsfoot trefoil (Lotus corniculatus L; BFT). Pasture treatments were rotationally stocked by Jersey dairy heifers for 105 days in 2017 and 2018, and herbage samples were collected pre- and post-graze each 7-day grazing period and analyzed for herbage mass, nutritive value, and apparent intake. We observed differences among pasture treatments in herbage quantity and quality, as well as differences in herbage intake by grazing dairy heifers. On average, grass-BFT mixtures had greater herbage intake than grass monocultures, and individually every grass-BFT treatment had greater herbage intake than their respective grass monocultures. Using multivariate analyses, we determined that approximately 50% of the variation in herbage intake was due to physical and nutritive herbage characteristics, with the most explanatory being characteristics related to fiber and energy, followed by those related to the percent of BFT in the herbage. Grass monocultures exhibited a range of inherent dietary energy, but there was indication that an energy to crude protein imbalance (e.g., protein deficient) reduced intake of grass monocultures. Moreover, there was some evidence of a complementary effect between increased dietary energy and CT, however, low CT levels made it impossible to determine the effect of CT on intake per se. This study confirmed that physical and chemical characteristics inherent to different pasture species have a large effect on herbage intake by grazing dairy cattle. Pastures planted to binary mixtures of high-energy grasses and CT containing birdsfoot trefoil, and managed for greater herbage allowance, increase herbage intake of temperate pastures by grazing dairy cattle.