cows in field

Raw Milk as a Pasture Biostimulant


By Bridgett Jamison Hilshey, Graduate Student, Unversity of Vermont, and Sid Bosworth,
Extension Associate Professor, University of Vermont

Added June 3, 2013.


The cost to renovate poor quality, low productive pastures can be very high for organic farmers. To manage this problem, some graziers are experimenting with highly active biological compounds known as positive plant growth regulators, metabolic enhancers, and biostimulants. These compounds, which are neither fertilizers nor pesticides, promote efficient plant nutrient uptake and enhance plant growth and development through a wide variety of mechanisms. They are typically applied in very small amounts to the soil or sprayed directly onto the plant. Humic acids and seaweed extracts are well known examples.

Raw cow milk has been suggested as an effective pasture biostimulant. Raw milk has been used as a crop amendment for centuries. It contains proteins and other compounds which are established fungicides and viricides. The amino acids present in milk proteins enhance plant tolerance to heat stress and nutrient uptake capabilities. Furthermore, many of the bacteria ubiquitous in raw milk are established beneficial, plant growth promoting, soil microbes.
Farmers and extension researchers in Nebraska, who applied raw milk to pasture at the rate of 20 gallons to the acre, in a study in 2004, reported increased forage dry matter yield, forage quality, soil porosity, and grass brix content. However, the study was never repeated nor thoroughly replicated, yet the results have garnered widespread community interest and are greatly extolled in blogs, newsletters, and other internet resources.

The aim of our study was to test this observation of the affect of milk on pasture growth in Vermont by assessing the effect of diluted raw milk on pasture soil health, and forage production, quality, and composition. We hope this information will help farmers make well informed decisions before investing their time and/or money into implementing this novel practice.



Field experiments were carried out in 2012 at two Vermont dairy farms- Applecheeck Farm, a diversified organic farm located in Hyde Park, Vermont and the Choiniere Family Farm, a family run organic dairy located in Highgate, Vermont.

Raw Milk _figure2

Our trial was very simple. We compared an application of raw milk to no milk application, our control treatment. The treatments were replicated at each farm using a paired-comparison design with each pair of treatments (milk supplement verses a no milk control) replicated six times. Raw milk was sprayed on the pasture once, in June 2012, at the rate of 20 gallons/acre diluted 1:1 with tapwater within five days. Treatment application occurred within five days of the pasture being grazed, when the forage was still short, to help facilitate some of the solution reaching the soil. Plots were sampled twice during 2012, approximately 30 and 60 days post milk application immediately prior to grazing.

During each sampling event, 360 forage and soil samples were collected from randomly selected points at each farm. Pasture pre-grazing and post-grazing mass was measured using cut samples and a rising plate meter. Soil samples were analyzed to measure organic matter, nutrient content and moisture content. Forage samples were tested for ADF, NDF, and crude protein in a typical wet chemistry analysis. In addition, forage botanical composition, brix content, and percent standing dead material was also measured in each study.

Raw Milk _table1

Generally, we found little to no effect of the raw milk on pasture growth or productivity at either farm. There were no consistent differences in soil or forage quality measurements as well. Participating farms were not able to distinguish the areas that had been treated with milk from the controls. A selection of the forage results is displayed in the table below.


Two separate greenhouse experiments were also conducted. The first aimed to measure the effect of milk on forage growth parameters. Perennial ryegrass was grown from seed in 12 pots. After 21 days, milk, diluted 50 fold with water, was applied to the surface of half of the pots at rate comparable to 20 gal/acre. The forage above and below ground mass, tiller elongation rate, tillering rate, and other characteristics of the forage above ground and below ground biomass was monitored for 43 days over two cuttings.

Grasses treated with raw milk tillered significantly more rapidly than grasses which did not receive the treatment; this resulted in significantly greater above ground biomass in pots treated with milk. Other forage growth parameters including root density, shoot elongation, and forage Brix Content, were not affected by the application of raw milk.

In a second greenhouse experiment, the impact of raw milk on soil nitrogen dynamics and organic matter decomposition was investigated by destructively sampling soil microcosms. Fresh, sieved, pasture soils were packed into small pots. Mesh bags containing dry, ground grass were buried 1 cm beneath the soil surface. Diluted raw milk was applied to the surface of half of the pots at the rate of 20 gal/acre. After periods of 1, 7, 14, 21, and 28 days, pots were destructively sampled to determine litter decomposition rates and soil mineral nitrate and ammonium concentrations.

Ammonium-N concentrations spiked 1 day after milk application in pots treated with milk. However, ammonium concentration on other days as well as nitrate concentrations and litter decomposition rates was not affected by the milk treatment.


Raw milk stimulated grass tillering and slightly increased forage above ground biomass under greenhouse conditions. The positive benefits attributed to the milk were short-lived and did not appear after the initial cutting. These results are promising and offer some insight into the most likely mechanism of action. However, because yield increased only slightly and because the benefits were no sustained over the duration of the experiments, they by no justify the widespread use milk as a biostimulant. Furthermore, we found no effect of milk on pasture growth or yield within the first 60 days of application in the field.

Raw Milk _table2

There are several possible explanations. First, the dry conditions present during the summer of 2012 may have inhibited any stimulatory effect milk might otherwise have had. During the summer of 2012, the experimental sites received less than 1.5 inches of rain – roughly half of the average for that period of time. As a result, very little milk sprayed onto plant leaves may have been washed into the soil via a natural precipitation event. In addition, under the droughty summer conditions soil microbial activity and nutrient cycling would process slowly. The dry conditions may have inhibited the movement of the beneficial bacteria into the soil thereby negating the potential for milk to positively influence soil and forage parameters.
It may also be that there are too many environmental variables in the field for the slight benefits we found in the controlled environment of the greenhouse to be expressed and be biologically or economically significant.

This results of the greenhouse experiment allude to the possibly that minute applications of raw milk may positively influence forage growth. However, the merits of milk in the field setting have yet to be demonstrated. The results of these experiments indicate that the application of raw milk onto pasture is not an economical means of enhancing forage production or forage and soil quality. However, additional field studies under varied environmental conditions should be conducted to confirm these results. In addition, greater care should be taken to ensure that the milk comes in contact with the soil.

Despite the inclusive results, spraying milk on pasture is still a great way to dispose of waste milk. We recommend that those wishing to experiment with raw milk on their own farm should spray to solution immediately before a rainstorm and after the forage was grazed to maximize the amount of milk reaching the soil. Although you probably shouldn’t expect a substantial change in forage production and quality, it may positively affect your pastures in ways not measured during this experiment.

Bridgett Jamison-Hilshey is a graduate student at the University of the Vermont Plant and Soil Science Department. The research described above was funded by a Northeast SARE (Sustainable Agriculture Research and Education) Partnership Grant. Contact Bridget by email: