Grass-birdsfoot trefoil mixtures to improve the economic and environmental sustainability of pasture-based organic dairies in the western U.S.

View the project final report

Commodities

• Agronomic: grass (misc. perennial), trefoil
• Animals: bovine
• Animal Products: dairy

Practices

• Animal Production: grazing - multispecies, grazing - rotational, rangeland/pasture management
• Crop Production: nutrient cycling, organic fertilizers
• Education and Training: extension, on-farm/ranch research, workshop
• Farm Business Management: budgets/cost and returns
• Production Systems: organic agriculture

With over 3.5 million milk cows in the western U.S., dairy is a dominant sector of western agriculture, and pasture-based organic dairies are becoming more prevalent in the region. Organic milk is marketed for the health and environmental benefits of pasture-raised milk; however, organic dairies using the most pasture forage (75-100%) have the lowest net returns due to a 32% decrease in milk production. Reduced dry matter intake (DMI) by grazing dairy cows is one of the major factors limiting milk production. Moreover, dairy cattle breeds are finicky-grazers, resulting in even lower DMI of traditional pasture species like tall fescue. Dairy herd fertility is critical to dairy sustainability, but nutrient-rich pastures may reduce pregnancy rates further complicating pasture-based dairy.

Previous Western SARE research (SW10-088) demonstrated that mixtures of tall fescue and the condensed-tannin containing legume, birdsfoot trefoil (BFT) improved beef steer performance. Critical questions, particularly for pasture-based dairy include, are there grass-BFT mixtures that increase both tannins and energy, and what will be their synergistic effect on dairy cattle performance? This research proposes to use university and on-farm trials to assess dairy heifer DMI, health, reproductive performance, economics, and impact on nitrogen cycling in response to grazing grass-BFT mixtures containing various protein, energy, preference, and tannin levels. An innovative outreach plan will reach a diverse audience of producers, educators, and the public, and include traditional field tours and web-based outlets such as eOrganic. These objectives are in direct response to stakeholder feedback, and it is anticipated that pasture mixtures will be identified that improve the sustainability of organic pasture-based dairy.

Objective 1. Determine the relationship between forage mass, total metabolizable energy, water-soluble carbohydrates, and condensed tannins on dairy heifer forage intake and weight gain in response to grazing grass monocultures and grass-legume mixtures.

Sub-objective 1.1. Determine the effect of forage metabolizable energy on dairy heifer performance and forage intake. Determine dairy heifer dry-matter intake (DMI) and performance (weight gain), forage mass, and forage nutritive value when rotationally grazing replicated grass-legume pastures characterized by various levels of forage mass, metabolizable energy (ME) [both as water-soluble carbohydrates (WSC) and fiber-based carbohydrates (cellulose and hemi-cellulose)], protein, fiber, digestibility, tannins, and livestock preference. Analyses will determine which forage characteristics primarily contribute to differences in dairy heifer DMI and performance. Our investigation will determine if different forms of metabolizable energy affect heifer weight gain and DMI. In particular, we will examine both the WSC and fiber components of ME to determine how ratios of WSC (immediately available energy) to cellulose and hemi-cellulose (slowly available energy) differ in their effect on DMI and weight gain. One would hypothesize that increased available energy would improve heifer performance, but it is also possible that greater ratios of WSC could lower rumen pH and decrease overall performance. Our mixtures with BFT will allow us to test if the tannins in BFT overcome negative effects of greater WSC.

Sub-objective 1.2. Determine the effects of different planting methods on BFT establishment, persistence, and dairy heifer utilization. Determine relative BFT establishment, persistence, and utilization when grass-BFT mixtures are drilled together in same row, drilled in alternating rows, or BFT drilled into existing stand of grass.

Sub-objective 1.3. On-farm validation of forage mass, nutritive value, and dairy cattle utilization.  Grass and BFT treatments will be planted on existing pasture-based dairies (producer participants), and producers will estimate forage mass and cattle utilization. Data will be analyzed, compared to USU pastures, and presented at field days. Producers will be trained how to use Rising Plate Meters (RPM) and clipped samples to estimate forage mass and cattle utilization, increasing their ability to quickly estimate available forage and potential stocking rate. We will also complete pre- and post-grazing forage nutritive analyses of the on-farm samples, helping them make better management decisions in choice of plant materials and grazing duration.

Objective 2. Determine the effect of grass-legume mixtures containing various levels of metabolizable energy, tannins, and other nutritive components on dairy heifer health, growth, and reproductive performance.

Sub-objective 2.1. Describe the effect of grazing treatments on body condition, rumen pH, and systemic markers of growth. Determine effect of total metabolizable energy, water soluble carbohydrates, and excess dietary protein from nutrient-rich pastures on body condition, rumen pH, Blood Urea Nitrogen and other systemic markers of growth. Results will be compared to predict which plant species best meet nutritional requirements for dairy heifer growth and reproductive fertility. We propose to determine the effect of different forms of metabolizable energy on rumen pH. This will be done in-vivo using pH monitoring boluses. We hypothesize that increased water-soluble carbohydrates in some forage mixtures will lower rumen pH, and perhaps decrease performance.

Sub-objective 2.2. Evaluate the effect of tannins and varying levels of metabolizable energy on parasite load. The parasite load (fecal egg count) within the gastrointestinal tracts of the growing heifers will be determined for individual animals within each treatment and compared to systemic growth markers. The effect of excess protein, metabolizable energy, and tannins on parasite load will be determined.

Sub-objective 2.3. Effect of excess dietary protein and varying levels of forage metabolizable energy on conception and early embryo development. Embryos will be flushed from heifers and evaluated for number and quality. Conception rates will be determined. Data will be analyzed to determine the effect of pasture total metabolizable energy, water soluble carbohydrates, and excess dietary protein on superovulation response, embryo recovery.

Objective 3. Determine pasture-based dairy impact on nitrogen and phosphorous cycling in response to grazing grass-legume mixtures containing various protein, total metabolizable energy, water-soluble carbohydrates, and tannin levels.

Sub-objective 3.1. Impact of BFT tannins on nitrogen and phosphorous cycling. A mass balance approach will compare nitrogen and phosphorous outputs (plant material, soil, leachate) against nitrogen inputs. Both nitrogen and phosphorous loss from farm fields is a common environmental concern in the U.S. We propose to add phosphorous cycling to the analyses and to look at nitrogen outputs at six, instead of three, soil depths.

Sub-objective 3.2. Impact of increased forage metabolizable energy and water-soluble carbohydrates on nitrogen and phosphorous cycling. Same approach as sub-objective 3.1 to compare high- and low-sugar grasses.

Sub-objective 3.3. Impact of pasture root structure on nitrogen and phosphorous capture. Evaluate the impact of different grass species and their root structure on nitrogen and phosphorus capture.

Objective 4. Assess the economic sustainability of the proposed pasture grazing-based heifer development programs.

Sub-objective 4.1. Determine the cost differences from each of the heifer development programs. Costs associated with developing each of the different pasture based program treatments will be determined and compared to the cost of dry-lot heifers on TMR.

Sub-objective 4.2. Quantify the impact of the animal performance on the economic value of the dairy heifers and determine the most profitable method of raising the dairy heifers. Actual costs differences and revenue differences from the alternative heifer development programs will be combined to determine the program that offers the greatest economic return.

Objective 5: Execute an innovative and impactful outreach program on the successful implementation of grass/legume grazing for organic dairy production systems.

Outreach plan: Enhance communication among producers, processors, marketers, researchers, and Extension personnel by building an interactive communications network facilitated by e-Organic and Utah State University and University of Idaho Extension.

Miller, R. L., J. Long, B. Waldron, S. C. Isom, K. Rood, J. E. Creech, M. Peel, J. Briscoe, M. Rose, J. Hadfield.  2020.  Impacts of grass-legume mixtures versus monocultures on nitrogen cycling in an organic dairy grazing system.  Pacific and Mountain West Nutrient Cycling, Soil Health and Food Safety Virtual Conference.  Oct. 27-28, 2020.  Pullman, WA:  Washington State University.  Available at:  https://www.youtube.com/watch?v=CT93ojQfQe8&feature=youtu.be

Miller, R. L., J. Long, B. Waldron, S. C. Isom, K. Rood, J. E. Creech, M. Peel, J. Briscoe, M. Rose, J. Hadfield.  2020.  Improving organic grazing systems.  Pacific and Mountain West Nutrient Cycling, Soil Health and Food Safety Virtual Conference.  Oct. 27-28, 2020.  Pullman, WA:  Washington State University.  Available at:  https://www.youtube.com/watch?v=vYp4ucfNzxs&feature=youtu.be