Quantifying Seasonal Nutritional Quality Changes in Managed Pastures

Final Report for FNC98-228

Project Type: Farmer/Rancher
Funds awarded in 1998: $5,000.00
Projected End Date: 12/31/2003
Region: North Central
State: Wisconsin
Project Coordinator:
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Project Information


During the time of the study, the farm consisted of 110 Holstein milk cows rotationally grazed during the grazing season (May-early Oct.) on 100 acres of pasture and 100 young stock raised on dry lots. Approximately 90 acres of corn silage and 100 acres of alfalfa and other forages were raised for feed, as well. Essentially all feed was stored as silage/haylage. Our ration consisted of either pasture or haylage, along with high moisture corn, protein supplement ‘to production needs’, and 12 lbs/cow/day of corn silage.

I had bee grazing my dairy herd since 1994. Other sustainable practices utilized included the use of manure and paper mill sludge as primary fertilizer sources, as well as minimizing wasted capital by hiring custom harvesters for forage production.

The project goals are to gain understanding of forage quality changes that occur during the grazing season, learn which forage species mixes may allow overcoming of quality slumps and begin to develop in field quality estimators.

Greg Williamson, Tom Nejedlo and Johnny Stolk (both rotational grazers in the Northland Grazer’s Association), and Scott Reuss, UW Extension Crops/Soils Agent, Marinette County, Wisconsin.

The idea for this project came about as the result of the realization by myself and other members of the Northland Grazers Association that in field forage quality was the major limiting factor to maintaining high production from our rotationally grazed dairy herds. Although some work had been done on this topic, there had been no research performed in far Northeastern Wisconsin, known for its light soils and drought prone climate during summer. It was very challenging to try to balance rations based on a forage based that changed quality almost daily, with no real data as basis for making such decisions. As we had been working on a study that was examining the dry matter yield of grazed areas, we more fully realized that quality and quantity of forage were too often nor highly correlated.

Realizing these things, we started discussing the concept that turned into this research project. With the primary thought of learning as much as we could about in field grazed forage quality, but also looking at seasonal patterns, we devised a protocol that would allow each of the three participating farms to minimally affect their daily operations, yet give god, reliable data. Each Wednesday, as the fences were being moved for the evening paddock, three samples of forage were collected from the area in which the animals would be placed. Each producer estimated (based on neighboring day paddocks), what height the cows would harvest the forage at and used that as their clip height for these samples. To make the entire project more cost effective, the samples were immediately frozen until delivered to the University of Wisconsin Marshfield forage analysis laboratory for analysis. One of the three samples from each farm for each date was randomly selected to have a full mineral analysis performed as well. Mineral content in grazed forage can be a limiting factor in milk production, so this was a critical area in which to gain knowledge, as well. Lastly we felt that it was very important to be able to relate what we find as to forage quality to potential milk production changes, so milk production data was maintained and analyzed.

Forage quality findings: in general, the findings followed anticipated patterns for the forage quality parameters. However, there were a few surprises. For example, the NDF levels were higher than anticipated, especially at the Nejedlo and Stolk farms. Also, Crude Protein levels were higher than expected. Both the Nejedlo and Williamson operations were actually balancing ration needs on the assumption that the CP levels were lower than the actual results.

Values of all four parameters measured were highly variable, especially dry matter, with only one farm – Williamson’s having an identifiable trend of generally increasing dry matter % as the season progressed. Early season results were consistent across all three farms, with the first four weeks of grazing seeing a steady increase in ADF and NDF, and a corresponding decrease in protein levels.

One trend that is worth noting is that for the non seasonal Nejedlo and Williamson herds, there was a noticeable correlation between measured quality and milk production. In particular, if you compare the NEL values with daily milk production, there was a definite correlation in their patterns. Of course, the relationship is not perfect, but is strong enough to have shown through.

Mineral analysis results: the mineral analysis portion of the study also stayed fairly true to the anticipated results. The strongest relationship noted on all three farms was the inverse relationship between calcium and potassium levels in the forages: as potassium level increases, calcium levels in the forages decrease. This does have implications for herd management, as the dairy herd needs to have a minimum calcium intake and heifers and dry cows should not be feeding on high potassium forages, or problems will likely arise at calving time.

Magnesium levels also followed the expected pattern of significantly lower levels in early spring and increasing as the season progressed. There was extreme variability in the mineral readings, both within a farm and from farm to farm. The following table indicates the differences in the average mineral content readings for the four major minerals.

Phosphorus, Potassium, Calcium, Magnesium
Nejedlo, 0.35%, 2.48%, 0.66%, 0.23%
Williamson, 0.36%, 2.53%, 0.85%, 0.28%
Stolk, 0.40%, 3.02%, 0.73%, 0.31%

The results of this study led all of us involved in the project to better manage our pastures for optimum forage and milk production. We were able to utilize the results to better match our supplements to meet the nutritional needs our herd was not able to receive from forage and adjust for seasonal differences. Although we were not able to find worthwhile forage species linkages as a direct result of this study, some observations will allow us to probably select our forage species better in the future. The relatively high quality forage analysis results reinforced to our group that rotational grazing is a viable enterprise in far Northeastern Wisconsin. However, these results did not seem to sway the opinions of non grazers to more strongly consider grazing. This study was done at a time of fairly high milk prices, and it is very possible that more attention would have been brought to the data if farm profitability in the area were lower at that time period.

A variety of methods were used to inform other producer in Wisconsin and the Upper Peninsula of Michigan of this project and its results. Two pasture walks were held on participating farms of which this project was a primary topic of discussion. The Nejedlo walk in 1999 allowed 45 people from 18 farms to gain understanding of the study and the initial results. The Stolk walk in September, 2000 gave more information about the study results to 29 people from 10 farms. In addition, one local seminar, and two state wide presentations were conducted that allowed approximately 200 producers to have direct discussion about this project and its results. It is likely that this data will be utilized in additional UW-Extension fact sheets in the future as the UW-Extension Team Forage is working on such items.


Participation Summary
Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.