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

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 complementary way with condensed tannins (CT) in birdsfoot trefoil to increase herbage intake by grazing dairy heifers. Eight pasture treatments comprising high-sugar perennial ryegrass (Lolium perenne L.), orchardgrass (Dactylis glomerata L.), meadow bromegrass (Bromus riparius Rehmann), and tall fescue [Schendonorus arundinaceus (Schreb.) Dumort] were established in Lewiston, Utah as monocultures and binary mixtures with birdsfoot trefoil (Lotus corniculatus L.; BFT). Pasture treatments were rotationally stocked by Jersey heifers for 105 d in 2017 and 2018, and herbage samples were collected pre-and postgrazing for each 7-d grazing period and analyzed for herbage mass, nutritive value, and apparent herbage intake. We observed differences among pasture treatments in herbage quantity and nutritive value, as well as differences in herbage intake by grazing Jersey heifers. On average, grass-BFT mixtures had greater herbage intake than grass monocultures, and every grass-BFT treatment individually 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 nutritive and physical 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 imbalance of energy to crude protein (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 herbage intake per se. This study confirmed that chemical and physical characteristics inherent to different pasture species have a large effect on herbage intake by grazing cattle. Pastures planted to binary mixtures of nutritious grasses and birdsfoot trefoil increase herbage intake of temperate pastures by grazing Jersey heifers.

The effects of organic grass and grass-birdsfoot trefoil pastures on Jersey heifer development: Heifer growth, performance, and economic impact

“…In this particular area (Cache County, Utah), the precipitation from winter snowfall is stored in reservoirs and used in the summer for irrigated crop production (Utah Climate Center, 2018). Yearly precipitation and temperature data for 2016, 2017, and 2018 are presented in Rose et al (2021).…”

“…This study was conducted using organic dairy grazing protocols, so no treatment received commercial fertilizer. However, as previously described by Rose et al (2021), approved organic sources of nitrogen were applied to the treatments. Chilean nitrate (sodium ni-trate, 15-0-2, N-P-K; SQM) was applied at 28 kg of N ha −1 in April to all treatments (both monoculture and mixtures) in both 2017 and 2018.…”

“…In addition, grass monocultures also received a second application of 28 kg of N ha −1 of Chilean nitrate in July, and further received 35 kg of N ha −1 in the form of hydrolyzed poultry feathers in June 2017 and March 2018 (80% CP/6.25 = 12.8% N) as a slow-release source of N. Paddocks were irrigated one week before grazing and within a week after grazing, so that pastures received 8.89 cm of water every 14 to 20 d. Precipitation data for the site pasture samples were taken pre-and postgrazing to determine yield, as well as nutritional quality of the individual pasture. An in-depth analysis of pasture samples and DMI has been previously reported (Rose et al, 2021). Table 1 shows the average nutritional quality for each of the 9 treatments found from the analyses of pasture samples, as well as the TMR.…”

“…Because the BFT mixed treatments were seeded twice to ensure proper seed depth of each species in the mix, costs associated with planting BFT mixed treatments were assumed twice ($47.24/ha) those of the monocultures. The seed costs ($/ha) ranged from $66.68/ha (TF) to $160.52/ha (OG+BFT), based on previously described seeding rates (Rose et al, 2021). Planting and seed costs were combined to estimate the establishment costs ($/ha) for each of the treatments.…”

“…Total establishment costs were calculated as the product of the establishment costs per hectare and the estimated required hectares for each pasture treatment. Mean herbage mass values from Rose et al (2021) were used together with predicted DMI using previously described equations to calculate the required number of hectares for each treatment to produce the necessary feed assuming an 85% harvest efficiency (Saha et al, 2010). The required number of hectares ranged on average from 6.5 ha (MB+BFT) to 16.6 ha (PR).…”