Can grazing selectivity increase fatty acid and nutritive content of annual forages grown for dairy?

View the project final report

• 2016 annual report

Commodities

• Animal Products: dairy

Practices

• Animal Production: feed/forage, grazing management, grazing - rotational
• Education and Training: extension, on-farm/ranch research
• Farm Business Management: value added
• Production Systems: organic agriculture

Northeast organic dairy producers are increasingly considering annual forages to maximize their grazing potential by supplementing perennial pasture in times of low productivity. Sufficient grazing availability is important to organic farmers in general, and in particular to producers of increasingly popular “grassmilk” products produced without any grain feeding. Many consumers choosing organic dairy and grassmilk products do so because of the perceived health benefits derived from higher contents of desired bioactive fatty acids (FA), such as omega-3 fatty acids, conjugated linoleic acids (CLA), etc.

One challenge with summer annual forages is that they quickly drop in nutritional value and FA content with increasing plant maturity. However, as a stand of an annual forage species matures, grazing selectivity of primarily leaf blades may help to mitigate the drop in both nutritive quality and fatty acid content of dairy cows’ intake.

The objective of this study is to document the change in nutritive quality and FA content of annual forages as they mature over time, on a whole plant basis as well as on the basis of the plant fractions that are actually consumed by grazing dairy cows. Knowledge gained from this study will influence decisions of producers and extension professionals in regards to choosing grazing pressures that optimize feed quality and FA content and profile of annual forages, in regards to the economics of supplemental grazing of annual forages, as well as influencing future research.

We propose that shifting pseudostem and leaf blade proportions associated with decreasing leafiness lead to nutritive and FA declines as annual forage crops mature. Traditional agronomic study may only evaluate these annual forages on a whole-plant basis, which, while appropriate for stored forages, may underrepresent the nutritive and FA quality available to selectively grazing cows. This study aims to evaluate the reductions in nutritional quality and FA content of annual forages of increasing maturity, in regards to both pseudostem and leaf blade fractions, their summation on a whole-plant basis, as well as the summation of each fraction actually consumed during grazing.

This work will have implications for farmers employing this grazing methodology, as well as agricultural service providers and researchers considering the nutritive quality, and particularly the FA content, of any annual forage grazing system. This information will be useful for determining proper grazing pressure to optimize quality and FA content of grazed annual forages, and analyzing the economics related to incorporating annual forages to a grazing farm.

This research will be conducted at the Choiniere Family Farm in Highgate Center, Vermont. Guy Choiniere milks about 90 cows on his 100 acre farm, and was certified organic in 2002. In the past year, Mr. Choiniere switched to producing “grassmilk” for Organic Valley. Mr. Choiniere has all the equipment required to cultivate and strip graze annual forage crops, and already incorporates them into his grazing system.

In September of 2015, Guy Choiniere seeded four acres of a 12 acre field (silt loam) to winter rye for supplemental grazing in early spring 2016. Two varieties of summer annuals, ‘Hayking’ sundangrass and ‘Wonderleaf’ pearl millet, will be seeded over at least four acres of that same 12 acre field in late spring 2016 for supplemental grazing in mid-summer 2016. Manuring and seeding rate will be in accordance with the farmer’s current practice, and recorded. Grazing of the plots will also be in accordance with the farmer’s current practice: Briefly, dairy cattle will be appropriately fenced to strip graze the annual forages – rye in early spring, and warm season annuals in mid-summer – for approximately one to two hours prior to their P.M. milking. The annual forages are strip grazed from one end of the field to the other – therefore daily strip grazing progresses from an early vegetative stage at day 1 to a later elongation or early reproductive stage by the time the cows reach the other end of the field (approximately day 14 of the grazing cycle).

Sampling for each annual forage type will occur at four time points: I) the onset of grazing (day 1), II) early-mid (approx. day 5), III) mid-late (approx. day 10), and IV) final grazing of that grazing cycle (approx. day 14). The two summer annual species will be grazed concurrently, and the regrowth from the same plots will be grazed and sampled a second time after the completion of the first grazing cycle.

Each sampling site will include paired A and B samples taken prior to grazing (A) and following the grazing event (B). Paired samples will be selected within a two meter radius of each other, and chosen to be as representative of that two meter radius as possible. There will be five replications of each pair at each sampling date. See sampling map.

Pre- and post-grazing samples will be harvested using a 0.209 m² quadrant and cut at a 15 cm height using electric hand clippers. Each sample will be divided into leaf blade and pseudostem fractions, separated just above the ligule, dried at 45°C in a forced hot air walk-in drying room, and weighed to establish dry matter of both fractions. Leaf blade and pseudostem fractions of pre-grazing samples will then be ground with a Wiley mill (Arthur H. Thomas, Philadelphia, PA) to pass through a 2mm screen, and then a cyclone forage mill (UDY Corporation, Fort Collins, CO) to pass through a 1mm screen, and analyzed for forage quality using Near Infrared Reflectance Spectroscopy (NIRS) according to the procedure developed by the NIRS Consortium (NIRSC, Hillsboro, WI) program of the National Forage Testing Association (NFTA, Avoca, NE).

Grazing pressure will be analyzed and presented as number and average kg of animal per kg of total pre-grazing forage dry matter available.

Fixed costs and variable costs incurred in the production of supplemental annual forages will be recorded throughout the time period of the study, for the purposes of reporting in extension fact sheets.

Fatty acid methyl esters (FAME) will be extracted from the forage samples using a modified one step transesterification method of Sukhija and Palmquist (1988). Briefly: 1 mL of internal standard (1 mg C13:0/mL acetone), 2 mL of toluene, and 2 mL of 5% methanolic sulfuric acid added to 500 mg of ground forage samples. The mixture is incubated at 50°C overnight. 5 mL of 6% KHCO₃ solution and 2 mL of hexane are added. The samples are mixed and centrifuged for 2 minutes, and the hexane layer is collected. The extraction procedure is repeated two more times with 1 mL additions of hexane. Samples are then dried with Na₂SO₄ and filtered through silica gel and charcoal. A 1% FAME solution is used for gas liquid chromatography (GLC) analysis performed on a GC-2010 gas chromatograph (Shimadzu, Kyoto, Japan) equipped with a split injector, a flame ionization detector, and a 100 m SP-2560 fused-silica capillary column (100 m × 0.25 mm i.d. × 0.2 μm film thickness; Supelco) The injector and detector are both maintained at 250°C. Identification of FAME will be accomplished by comparison of relative retention times with commercial FAME standards. Total fatty acid content is determined using the C13:0 internal standard. The FA results will be expressed as proportions (weight/weight) of FA detected. The lowest level of detection is <0.001g/100g FA and will be reported as not detectable.

Dry weights of leaf blade and pseudostem fractions of pre-grazing (A) samples will be used to calculate DM yield, nutritional quality, and fatty acid contents of both fractions and total plant samples. Dry weights of leaf blade and pseudostem fractions of post-grazing (B) samples will be used to determine what proportions of those total (A) samples were actually ingested by the grazing cattle, and through subtraction of weighted means, the nutritive quality and fatty acid content of the grazed supplemental forage consumed.

Statistical analysis: Differences of yield, nutritional quality, and FA content between whole plant and “ingested” samples will be analyzed for the summer annual species using a split-plot design with grass species as the whole-plot treatment and day of grazing per grazing cycle as the sub-plot treatment, with consideration for repeated measures of the regrowth grazing cycle (adapted from Vogel et al., 1991). The differences of yield, nutritional quality, and FA content between whole plant and “ingested” samples will be analyzed for the cool season annual species with one way analysis of variance evaluating the effect of “day of grazing”. The repeated measure of a regrowth grazing cycle will not be present for the cool season annual.

Proposed Time Table

September 2015: seeding of cool season annual forage (prior to grant)

April – May 2016: strip grazing and sampling of cool season annual forage

May – June 2016: seeding of warm season annual forages

July 2016: strip grazing and sampling of first grazing cycle of warm season annual forages

August 2016: strip grazing and sampling of second grazing cycle of warm season annual forages. Pasture walk showing system and preliminary results

September 2016 –January 2017: processing and analysis of forage samples for nutritive quality and FA content and profile. Data analysis

January – March 2017: presentation of findings to farming/extension community at the Vermont Grazing and Livestock Conference and the Vermont Organic Dairy Association Conference, presentation of findings to a regional conference such as the Pennsylvania Association for Sustainable Agriculture annual conference, or similar.   Articles written for Northeast Organic Dairy Producers Association newsletter and the Vermont Crops and Soils webpage. Manuscript prepared to submit for publication in appropriate journal.

Dissemination of Results

Working with the University of Vermont’s Pasture Outreach Program (coordinator: Jenn Colby), we will coordinate a pasture walk/field meeting in the summer of 2016 at the farm site to highlight the research. This will also provide an opportunity for Guy Choiniere to discuss his approach and reasoning for using annual forages within his pasture program.

We also plan to present the results of this study at two well attended conferences in Vermont in 2017: 1) the Vermont Grazing and Livestock Conference which draws Vermont dairy and livestock farmers, extension personnel, and industry representatives, and 2) the 2017 Vermont Organic Dairy Conference which attracts approximately 100 organic dairy farms each year. We will also present the results at the 2017 New England Agriculture Service Providers Training in Portsmouth, NH which usually draws approximately 70 professionals from across the region.

In addition, results will also be presented at a regional conference, such as the Pennsylvania Association for Sustainable Agriculture annual conference, or similar.

An article summarizing the final results will be written for the Northeast Organic Dairy Producers Association Newsletter (http://www.nodpa.com/) and also posted on the Vermont Crops and Soils webpage (http://pss.uvm.edu/vtcrops/) and the NE-SARE website.

A manuscript will be submitted for publication to an appropriate peer-reviewed scientific journal.