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

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

Summary

The objective of this project is to document the change in nutritive quality and fatty acid 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 fatty acid content and profile of annual forages, in regards to the economics of supplemental grazing of annual forages, as well as influencing future research.

All samples have been collected and analyzed for nutritive quality and fatty acid content and profile. Data analysis is ongoing, with a scheduled presentation of results at the Vermont Grazing and Livestock Conference in January, 2017 and at the Northeast Pasture Consortium annual meeting in Hagerstown, MD in March 2017.

Objectives/Performance Targets

A: Sample overwintered cool season annual forage (winter rye) as it matured for:

1. Nutritive quality of leaf and “pseudostem” (leaf sheath, stem, and culm) components, as well as their summation on a whole plant basis
2. Fatty acid content and profile of leaf and “pseudostem” components, as well as their summation on a whole plant basis.

The cereal rye overwintered well, and samples were collected at the first, middle and last grazings, between May 12 and May 24, ranging from stage 8 (flag leaf emerging) to stage 10.5 (emergent head) on Feeke’s scale.

B: Sample two warm season annual forages (pearl millet and sudangrass) as it matured for:

1. Nutritive quality of leaf and pseudostem components, as well as their summation on a whole plant basis
2. Fatty acid content and profile of leaf and “pseudostem” components, as well as their summation on a whole plant basis.

Only pearl millet was grown mono-culturally, and an annual forage mix used by our farmer partner with sudangrass in it was found to be too heterogeneous to sample. Subsequently only the pearl millet was sampled.  Because of the reduced number of species, and a concern that regrowth sampling would not be feasible, sampling events were increased for the pearl millet planting. Six samplings were performed between July 18 and August 5, ranging from early vegetative stage to head emergence.

C: Estimate proportions of leaf and pseudostem components actually ingested at grazing through a subtraction weighted means of pre-grazing (A) and post-grazing (B) samples

The summer of 2016 was very dry in Highgate and at the first overwintered rye grazing, it became clear that forage needs necessitated heavy grazing of the supplemental annual forages. As such, a third set of samples was collected to compare dry weight proportions of leaf and pseudostem available to the cows. The samples were from then on: A) pre-grazing samples, B) mid-grazing samples (1 hour after the start of grazing), C) post-grazing samples (typically 2 hours after the start of grazing).  The use of subtraction of weighted means of leaf and pseudostem components (e.g., B – A=ingested) worked well to estimate the dry matter yield and quality of grazed winter rye, showing a non-significant, though consistent, elevated quality of ingested forage relative to whole-plant forage analysis, and at the last sampling a trend towards mitigation of the quality reduction associated with later maturity. However, the dry matter intake estimation method was found to be insufficient with grazing behavior exhibited in the pearl millet.  Entire plants were uprooted and subsequently a reasonable estimate of intake was impossible.

D: Outreach and Presentations

Project findings were presented at the farm to a Sterling College class of six students on August 5 and at a field meeting to 13 farmers and agriculture service providers held at the farm on August 23.  The project was also highlighted at a mid-summer farm tour of NE-SARE personnel and advisors.

Yield, nutritive quality, and fatty acid data for both species was presented at the annual meeting of the American Society of Agronomy/Crop Science Society of America in November 2016 in Phoenix, AZ:
Goossen, C.P., S.C. Bosworth, J. Kraft. Can grazing selectivity reduce fatty acid intake declines in maturing annual forages? Poster presented at the American Society of Agronomy, Crop Science Society of American, and Soil Science Society of America annual meeting. November 9, 2016. Phoenix, AZ, USA.

Accomplishments/Milestones

The project timetable was as follows:

September 2015: seeding of cool season annual forage

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.

All of the above has proceeded as proposed, with the exception of sampling the second species and second grazing cycle of warm season annual forages. As described above, the farmer utilized a complex multi-species annual forage mixture for their sudangrass planting which made accurate sample collection unfeasible. It also became apparent that the dry summer and heavy grazing (and subsequent uprooting) by the cows threatened a sampling of the second grazing cycle. In response, we increased sampling of the pearl millet to achieve a more nuanced look at quality changes with increasing maturity over the first grazing cycle.

January – April 2017: Farmer partner Matthieu Choiniere and PhD candidate Caleb Goossen are scheduled to present results from this project to the Vermont Grazing and Livestock Conference in Fairlee, Vermont on January 21, 2017, and Caleb Goossen will also be presenting results from this project at the Northeast Pasture Consortium Conference in Hagerstown, MD on March 3, 2017.   An article will be written for Northeast Organic Dairy Producers Association newsletter and the Vermont Crops and Soils webpage.  Manuscript prepared to submit for publication in appropriate journal.

Impacts and Contributions/Outcomes

This project is demonstrating the need to stagger warm season annual plantings in order to have grazing options that maximize yield and quality, as well as providing a greater insight into the changing fatty acid content and profile of annual forages. The results of this project show that, much like many other quality measures, the decline in fatty acid quality of maturing annual forages is resultant from stem elongation, and the resultant dilution of high quality leaf material with fibrous, lower quality pseudostem material.

Our findings from this project were presented at on-farm meetings in the summer of 2016 and will be highlighted at the two farmer conferences in 2017.  A poster of the project was presented at the annual meeting of the American Society of Agronomy in November 2016 and will be presented at the Northeast Pasture Consortium annual meeting in March 2017.

Collaborators: