Location: Forage and Range Research
Project Number: 2080-21000-018-021-R
Project Type: Reimbursable Cooperative Agreement
Start Date: Oct 1, 2017
End Date: Jul 31, 2021
There are over 3.5 million milk cows in the western U.S. region, making dairy one of the dominant sectors of western agriculture. Organic pasture-based milk production is the fastest growing segment of U.S. organic agriculture, with 31% of organic milk cows found in the western states of CA, ID, OR, and WA. One recent dynamic change to the dairy industry has been the increase in pasture-based milk production. Grazing dairies report a $2 to $3 per cow per day savings in feed costs, and in 2005, organic dairies had a profit margin of $1.91 per cwt milk. However, organic dairies using the highest amount of pasture-based forage (75-100%) had the lowest net returns (-$10.36) due to 32% decrease in milk production. Thus the profitability of pasture-based dairy pivots on milk production, but low dry matter intake (DMI) of pasture by grazing dairy cows is a major factor limiting milk production. Dairy herd fertility is also one of the most important factors affecting profitability, but concerns about the effect of nutrient-rich pastures and excess rumen-degradable protein on oocyte and embryo viability remain unanswered. Finally, organic dairies are faced with the daunting task of producing sufficient nutritious pasture-based herbage, and trying to extend the grazing days with limited land resources and without use of synthetic commercial fertilizer. Thus improved grass-legume pastures that require fewer inputs, have high herbage and nutritive value, improve ruminate utilization of nitrogen (N), and have high DMI are critical to the economic viability of pasture-based organic dairies. Previous research by this team showed that a pasture mixture of tall fescue and the condensed-tannin (CT) containing legume, birdsfoot trefoil (BFT), improved nitrogen utilization, steer weights, grazing season length, and net return as compared to fertilized fescue monocultures. They also demonstrated that supplementing nutritive energy into fescue-legume mixtures improved ruminal nitrogen utilization resulting in less ammonia and methane production. They did not evaluate other grasses. Thus critical questions remain, particularly as it applies to pasture-based dairy, including: (1) which grass-legume mixtures can provide both high tannin and increased energy levels, (2) what will be the synergistic effect of tannins and energy on reproductive fertility and nutrient cycling and, (3) how will these grass-legume mixtures directly affect DMI? This research proposes to evaluate these questions.
A multi-disciplinary team of animal and plant scientists will conduct this research. Birdsfoot trefoil (BFT) will be grown in mixtures with four grasses (tall fescue, meadow bromegrass, and high-sugar orchardgrass and perennial ryegrass) that inherently vary in energy, root structure (nitrogen capture), and preference in replicated university and on-farm pastures. At the university research facility, Holstein dairy heifers (750 lbs) will rotationally graze treatments throughout the summer, and dry matter intake (DMI), weight gain, blood urea nitrogen (BUN), herbage mass and nutritive value will be determined every 28 days. Heifers will be synchronized and artifically inseminated and oocyte/embryo development and conception rates will be determined. Production and economic comparisions will be made between dairy heifers grazing the mixtures and fertilized monocultures of the grasses, and those fed high- and low-protein total mixed rations (TMR). Participating producers will evaluate herbage mass and DMI by lactating cows of the grass-BFT monocultures and mixtures using on-farm trials. The impact of tannins (birdsfoot trefoil), increased plant sugars and digestibility, and varying plant root structure on nitrogen cycling will be determined. A mass balance approach will compare nitrogen outputs (plant material, soil, leachate) against nitrogen imputs. Soil water (leachate) nitrogen will be monitored via zero-tension lysimeters. Grass monocultures will be compared to grass-birdsfoot trefoil mixtures. High and low-sugar grasses, and deep and shallow rooting grasses will be compared. An innovative education and outreach plan will be used to reach a diverse audience of producers, educators, and the public.