Ultra-high Stocking Density Grazing

Case Study: Dairies Using Ultra-high Stocking Density Grazing in New York and Pennsylvania
Dr. Kathy Soder, USDA-ARS Pasture Systems and Watershed Management Research Unit, University Park, PA

Full factsheet (PDF)

Ultra-high stocking density (UHSD) grazing, sometimes referred to as “mob grazing”, is characterized by:

  • high stocking density (units bodyweight/units area 500,000 + lb/ac)
  • small paddock size
  • mature forage
  • short grazing durations
  • long forage recovery times (90 to 180 days)

Some perceived benefits include:

  • increased profitability (via increased carrying capacity)
  • improved animal performance
  • improved forage species diversity
  • increased soil quality (improved organic matter, improved microbial action, and greater water holding capacity)

Ultra-high stocking density grazing was developed using beef cattle, often in arid rangeland environments. Little science-based evidence exists about the application of this grazing management practice on dairy farms in the northeastern U.S.

The Case Study

Four farms (3 in PA and 1 in NY) participated in this study. All dairy farmers were self-described UHSD graziers, with 15+ years of grazing experience. Farmers were initially surveyed to capture experience and management practices.

In June 2012, one representative pasture on each farm was identified to be study pasture. Farm visits to collect data occurred each time the study pastures were grazed from June to November of 2012 and from April to June of 2013. During each farm visit, researchers collected information about the number of cows grazing, pre- and post-grazed forage height, pre-grazed canopy stratification, and forage samples for forage quality analysis. In May of 2013 soil samples were collected from each study pasture.

Findings

  • Stocking densities were lower (44,091 to 337,161 lb/ac; Table 1) than UHSD grazing with beef cattle (500,000+ lbs/ac).
  • Pastures were rested longer (30 to 49 days) than usually seen with rotational grazing (21 day cycle).
  • Pastures were grazed taller (8 to 17 inches) than usually seen with rotational grazing (6 to 8 inches).
  • Forage utilization = 45% of total available dry matter.
  • Most forage consumption was from the upper canopy.
  • Forage quality was high throughout the season
  • Soil organic matter values (3.2 to 4.1 %) were as expected, but did not exceed values typical for this region.

Conclusions

The dairies in this study have taken a modified approach to current UHSD definitions by grazing slightly more mature (taller) forages and implementing slightly longer periods of forage rest, compared to rotational grazing.

UHSD grazing with beef cattle allows for more mature forage within a production system that is more forgiving on a daily basis (ADG) compared to a dairy system. Grazing forages that are too mature could result in an overestimation of nutrient availability and intake for lactating dairy cows, resulting in reduced animal production immediately reflected in the bulk tank.

Grazing dairy farmers who are interested in adopting UHSD grazing should proceed by taking small steps and allowing the system (animals, forages, soils) to respond before making further grazing management modifications.


This was a collaborative project between USDA-ARS and Penn State Extension. Funding was provided by Northeast SARE grant #PG12-021.

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Orchardgrass persistence survey

Dear Orchardgrass Task Force, Extension agents, Professors, Industry members, and others,

I am a PhD student in Crop and Soil Environmental Sciences at Virginia Tech. I am working with Dr. Ben Tracy on understanding the causes of reduced persistence in orchardgrass hay stands around the region.

One component of my work is to survey orchardgrass stands in the hay-growing regions of Virginia, West Virginia, Maryland and Pennsylvania (See attached map). I would like to ask your help in finding orchardgrass stands to include in the survey.

It is my hope to be able to sample 30 to 50 fields across this region during and around my spring break, March 7-16. I will collect plant and soil samples, assess stand cover, and scout for insects and diseases. I will revisit these stands in August 2014, March 2015, and August 2015 to assess persistence. With a little bit of information from producers about their management practices, this survey should help to identify agronomic and ecological factors related to reduced orchardgrass persistence.

Right now, I’d like to generate a list of potential stands to include in the survey and collect some information from their producers. There are a variety of logistical challenges in terms a large area to cover in a short window of time, so I may not be able to visited every field submitted.

To be a good candidate for the survey, an orchardgrass field should:
- Be approximately within the region marked on the attached map.
- Contain 50% or more orchardgrass.
- Be approximately 2 – 5 years old.
- If possible, be located on a farm where some OG stands are in good condition and others poor – farms where are I can sample paired fields like this are especially valuable.

If you know producers with stands that meet these criteria, please:
- Work with the producer to fill out the attached one-page Stand Description sheet and return it to me. Please use one sheet per orchardgrass stand; multiple sheets per producers are encouraged.
- Provide me the exact location of this field. Three ways of doing this are to: send me latitude and longitude of the field, email me a Google Earth placemark, or send a NRCS soil map with the field outline.

Attached is a sample field submission.

With a list of potential fields, I will determine the route I’ll take between them and contact producers with when I’d like to visit their stands. This will be in early March, and I will not need any assistance from the producers during the actual sampling.

Please send me stand information by February 28.

I very much appreciate your help with this. Please do not hesitate to contact me with any questions or issues. Feel free to share this email with whoever may be interested.

I’m quite interested to see what the survey turns up and hopefully be able to provide some recommendations to improve orchardgrass persistence.

Gordon

_____________
Gordon B. Jones

Doctoral Degree Student
Crop & Soil Environmental Sciences
Virginia Tech
gjones89@vt.edu

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2014 Grazing Monitoring Charts

Central New York RC&D has prepared the 2014 version of its grazing monitoring charts. These and other resources are available at their website.

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Evening grazing

Grazing few hours during the afternoon and evening
Dr. Kathy Soder, USDA ARS Pasture Systems and Watershed Management Research Unit

full report (PDF)

Facts

  • Cattle concentrate grazing during the afternoon and evening.
  • Pasture presents the highest sugar, digestibility and less fiber concentrations in the afternoon and evening.
  • Afternoon pasture allocations increases duration and intensity of afternoonevening meals and pasture intake at that time of day, improving animal performance.
  • Pasture intake rate is increase with “hunger”, therefore pasture intake during the afternoon-evening may not yet be maximized.

Test

These facts led an Argentinean research team A planned morning fasting generates (National University of La Plata) to assess the impact of morning fasting periods combined with afternoon pasture allocations on grazing behavior, pasture intake and performance of beef heifers.

cattle grazing

When heifers were fasted:

  • Grazing time during afternoon-evening hours increased.
  • Idling increased and was concentrated during the morning.
  • Performance and pasture intake were not affected.

Potential Implications

A planned morning fasting generates longer, more intense afternoon-evening meals, increasing the intake of higher nutritive pasture, resulting in equal cattle performance with shorter grazing periods.

This management reduce residence time on pasture; therefore reducing injuries to plants and soil compaction. Consequently, this management would enable northeastern US graziers to improve future pasture production.

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Pasture Seed Banks

Pasture Seed Banks
Dr. Matt Sanderson, USDA ARS Pasture Systems and Watershed Management Research Unit

full report (PDF)

What is a Seed Bank?

It is a reserve of dormant seeds in the soil that enables some types of plants to re-establish themselves after a drastic disturbance of the established vegetation. In some ways it forms a “memory” for the pasture, a record of its vegetation history.

What Types of Plants Occur in Seed Banks of Northeastern Pastures?

In our surveys of northeastern pastures, we found the equivalent of more than 8 million seeds per acre in the surface soil (the top four inches) from the seed bank study. These seeds came from 58 species of plants. Seed bank composition of northeastern pastures

The annual forbs (all broadleaf plants with the exception of legumes and trees) dominated the seed bank with more than 4 million seeds per acre in the top four inches of soil. This class of plants included mainly weeds such as yellow rocket, lambsquarter, mustard, and shepherd’s purse. Dandelion and broadleaf plantain contributed most of the 1.2 million seeds per acre of perennial forbs in the seed bank.

Green and yellow foxtail along with annual bluegrass and barnyard grass dominated the 1 million seeds per acre we found of the annual grasses. Kentucky bluegrass was the most abundant perennial grass seed found in pasture soils, equivalent to about l lb of seed per acre.

White clover contributed to about 1 to 2 lbs of seed per acre in the legume component of the seed bank. Thus, in the northeastern U.S., bluegrass and white clover will supply most of the forages in the seed bank that may contribute to maintaining a pasture stand.

Even though most of the seeds in the soil seed bank were annual forbs, the plants growing above ground were nearly all bluegrass and white clover. There was only a 44% correspondence between the plant species found in seeds below ground and the plants found growing aboveground. Thus, you cannot exactly know what is in the soil seed bank by looking at what is growing in the pasture.

The plant species found in pasture seed banks fall into four main categories

The first type of seed bank is a short-term (usually lasting less than one year) seed bank formed from plants that shed seed in the summer, germinate in the fall, and grow mainly in the early spring of the following year. These plants fill in gaps, holes, or bad spots in pastures that predictably occur in fall, winter, and early spring.

The second type of seed bank is also short-term but the plants that contribute to this seed bank shed their seed in the fall, germinate the following spring, and make most of their growth in late spring and summer. These are the summer-annual plants such as common ragweed, the foxtails, and crabgrass. These plants fill in pasture gaps that predictably occur in late spring and autumn.

The third and fourth types of seed banks are both longterm seed banks that differ in how much of each seed germinates right away and how much remains dormant. For example, the bluegrasses and bentgrasses produce a lot of seeds, most of which germinate quickly and the small remainder stay dormant and persist in the soil On the other hand, hard-seeded legumes such as white clover do not germinate right away. Instead their hard seed coat and seed dormancy ensure that the bulk of seeds persist for a long time in the soil.

How can a Farmer Draw Upon the Seed Bank for Pasture Management?

There are three main items to focus on. First, a supply of seeds must be present from desirable plant species. Remember, in our survey, the most abundant supply of forage seeds came from Kentucky bluegrass and white clover (about 1 to 2 lb per acre of each). Thus, forage in pastures developing mainly from the soil seed bank will be mostly bluegrass and white clover. Second, seeds from undesirable species (weeds) must be absent or few. Unfortunately, these types of plants dominated that pasture seed bank in our surveys. This means that producers must emphasize the third item, maintain suitable conditions for the germination, establishment, and maintenance of the desired forage species. In other words, producers need to do the right things to foster the desirable species including maintaining optimal soil pH (6.0 to 7.0) and fertility levels (especially phosphorus for legumes) along with appropriate grazing and clipping management to control weed growth and encourage forage growth.

The large number of weedy seeds in the pasture seed bank means that any gaps or bare spots in the sod will likely be filled by a weed from the seed bank. If not controlled, these weeds can contribute more seeds to the seed bank in a vicious cycle of weed invasion. Thus, maintaining a dense, vigorous pasture is critical.

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Total mixed ration for pasture-based dairy

Using a total mixed ration on a pasture-based dairy
Dr. Kathy Soder, USDA ARS Pasture Systems and Watershed Management Research Unit

full report (PDF)

Background

Feeding dairy cows on pasture challenges nutritionists and producers due to changing pasture quality and availability which make dry matter intake (DMI) difficult to monitor and control. Milk yield per cow and milk fat percentages in pasture-based systems are frequently lower than in confinement. Some producers are using a ‘hybrid’ approach- many dairy producers have the knowledge and equipment for total mixed ration (TMR) feeding systems and have incorporated a “partial” TMR (pTMR- partial since the pasture is not physically part of the mixed ration) into their summer grazing management.

cow eating TMR

Why Feed a pTMR with Pasture?

Increasing numbers of dairy producers in the northeastern and midwestern US are using or have expressed interest in using a pTMR with their grazing dairy cows to maintain or improve milk production and composition, particularly as herd size increases with the land base remaining constant. Few recommendations exist regarding the use of a pTMR. Therefore, we rely on basic ration balancing methods and practical experience for developing feeding recommendations.

A pTMR incorporated into a pasture-based diet provides
the advantages of:

  • A more uniform ration throughout the grazing season
  • Improved monitoring of DMI
  • Less chance of rumen digestive problems due to slug feeding of grain
  • Potentially higher milk yield and components
  • Environmental benefits due to better utilization of nutrients.
  • Higher energy intake and body condition.

Formulating a pTMR

Balancing a ration for cows on pasture is the same as formulating a ration for confined cows. Pasture is simply an ingredient that is not mixed in the mixer wagonrather, it is mixed in the rumen with the other pTMR ingredients. Since pasture quality can vary widely, Forage Testing of pasture as well as the pTMR is crucial in balancing the diet.

While this may seem an obvious statement, in a case study conducted at our location that monitored pTMR use on 13 farms in PA and NY, we found that some producers and nutritionists are not fully aware of the nutritional quality of pasture. In our study, the most common change in the pTMR was to replace pasture for grass silage on a 1:1 DM basis since grass silage most closely matches pasture in terms of nutrient content of any pTMR ingredient.

cow grazing

The second most common change was to reduce the protein level in the pTMR, usually through reducing or eliminating protein supplementation to compensate for the typically high rumen degradable protein levels in well-managed pastures. Other changes may include the addition of other fiber (forage or non-forage) sources to compensate for low pasture fiber, particularly during the spring season. Other farms, however, were found to be overfeeding protein, particularly rumen degradable protein. Not only does this waste money, it causes greater nitrogen losses in urine.

Is Feeding Pasture Plus TMR Economical?

Research at our location, using a whole-farm simulation model, showed that utilizing a pasture plus pTMR was comparable economically to feeding a TMR in confinement, and both TMR systems increased net return per cow by an average of $260 annually when compared to pasture plus concentrate. In addition, the pasture plus pTMR provided environmental advantages in terms of lower phosphorus and potassium accumulation when compared to the confinement system.

How Much pTMR Should I Feed?

The amount of pTMR fed will depend on the cows’ requirements, pasture quality and quantity, and land availability. While there are no set guidelines for minimum amount of forage to include in a pTMR, a minimum of 6-7 lb. of forage dry matter per cow is recommended to serve as:

  • A source of effective fiber (to promote cud chewing)
  • A rumen buffer
  • A carrier for other components in the pTMR

As pasture quantity decreases, the amount of forage in the pTMR can be increased to meet this deficiency.

When to Feed a pTMR?

Timing of pTMR feeding in relation to milking and grazing may affect intake of both TMR and pasture. Feeding a pTMR before cows graze will encourage greater pTMR consumption but it may lower pasture intake. A pTMR may also provide better synchronization of nutrients in the rumen; energy and effective fiber in the pTMR and protein in the pasture. Alternatively, offering pTMR after an initial period of grazing may decrease pTMR intake and maximize pasture utilization.

Guidelines for Feeding a pTMR

While pTMR can be used to complement pasture and provide a balanced ration, pasture variables such as pasture DMI, quality and quantity, and selective grazing behavior still challenge nutritionists and producers. These management practices below can help to effectively incorporate a pTMR in a pasture-based system.

  1. Provide adequate feed bunk space Cows have a limited time to consume pTMR before returning to pasture. It is important to provide sufficient bunk space (25 to 30 inches/cow) so all cows have sufficient opportunity to consume the pTMR. This ensures that aggressive cows do not dominate the feed bunk by keeping more submissive cows from consuming their share of the pTMR.
  2. Including Corn Silage Corn silage in a pTMR can be an excellent supplemental forage as it adds rumen fermentable carbohydrates as a source of energy for the rumen microbes (to recapture the abundant pasture protein) and also ‘dilutes’ the high protein in pasture. Corn silage also adds effective fiber that can complement high-quality pastures. Corn silage is a highly palatable feed, an excellent carrier for supplemental grains, and may allow for a reduction of concentrate fed.
  3. Flexibility Many farms in the case study were flexible in pTMR formulation, reacting quickly to perceived changes in pasture quality or quantity. Flexibility is key in utilizing a pTMR on pasture-based operations- flexibility in ingredients used in a pTMR to keep costs low, to meet nutrient demands, to maintain satisfactory milk production and milk components, and flexibility on the part of producers and nutritionists in reacting to changes in environment, pasture quality and quantity, feed prices, and animals.
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Soil carbon sequestration in pastures

Soil Carbon Sequestration in Pastures
Dr. Curtis Dell, USDA ARS Pasture Systems and Watershed Management Research Unit

full report (PDF)

Background

Sequestration of carbon (C) in soils is being promoted as a way to remove carbon dioxide (CO2) from atmosphere and lower the potential for global climate change. Cultivation typically resulted in the loss of 20 to 50% of the native soil C, because disturbance of the soil speeds the decomposition of plant residues and soil organic matter. Eliminating tillage and establishing perennial plant cover can return C to the soil by slowing the break down of plant residues and allowing a greater portion of the plant C to be retained as soil organic matter.

Conversion to pasture

The conversion of croplands to pasture usually adds 0.2 to 0.5 tons of soil C per acre each year. Converted soils generally accumulate C for 15 to 25 years then reach a saturation point where C inputs and losses are about equal. Maximum C content varies by soil series, but the root zones of pasture soils in the northeastern US seldom exceed 5% C (~9% organic matter).

Pastures as a carbon sink

Even when mature pastures are no longer sequestering new carbon, they are an important pool of stored carbon. Pastures in the northeastern US typically contain 25 to 50 ton of C in the upper 1 foot of soil. With about 8.5 million acres in the northeastern US, pasture soils in the region store as much as 425 million tons of C (~1500 million metrics tons of CO2).

soil profile

Sequestration in established pasture

The potential to sequester additional C in mature pastures (>25 years old) is limited, because C levels are typically near the soil’s saturation point in well managed pastures. In pastures that have not been managed intensively, soil C sequestration can possibly be increased through management practices that increase plant biomass production (such as liming, optimal fertilization, pasture renovation, and improved grazing management). The addition of deeper rooted plant species also has the potential to increase sequestration by putting plant carbon inputs deeper in the soil profile.

Measuring soil carbon

Soil carbon can be measured very accurately, but verifying changes in soil carbon over time requires extensive soil sampling. C content of soil can vary greatly within a few feet in the hilly terrain of the northeast. Spatial variation in soil C in a mixed-use watershed in central PA is shown below. At that location, it was shown that sampling at 30 ft or smaller intervals (with several sub-samples at each point) was needed to obtain soil samples that captured the range of high and low C values and accurately represented the average C concentration of a field. The labor requirement for sampling and analysis cost should be consider in the design of C credit programs if measured verification is required.

Carbon Trading Markets

Many carbon credit and marketing programs have been proposed, but the Chicago Climate Exchange (CCX) (http://www.chicagoclimatex.com) is the only organization currently selling soil carbon credits in the US. CCX, through registered aggregators, offers carbon credits for planting new pastures. The program assumes a sequestration rate of 1 metric ton CO2/acre/year (0.3 ton C/acre/year) for pasture establishment and does not require the landowner to measure soil C. Payment rates have ranged from less than $1 to about $5 per metric ton of CO2 (~$2 in Feb. 2009). To be eligible, pastures must have been established in 1999 or later. There are currently no programs that apply to older pastures.

Implications for producers

Establishing and maintaining pastures plays a valuable role in efforts to reduce atmospheric CO2 levels as well as contributing to the overall improvement of the environment. At current payment rates for C offsets, opportunities for income from soil C sequestration in pastures are limited. However if caps are imposed on CO2 emissions, much higher offset payments are expected to make soil C sequestration much more profitable.

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Pasture diversity and management

Pasture diversity and management
Dr. Sarah Goslee, USDA ARS Pasture Systems and Watershed Management Research Unit

full report (PDF)

Background

There are 120 million acres of pasture in the United States, along with 406 million acres of rangeland and 62 million acres of hay. These grazing and forage crops contribute to more than $80 billion in yearly farm sales. On the farm, pastures can lower feed and energy costs and improve livestock health. Regionally, permanent grasslands reduce soil erosion and nutrient losses, and provide open space for wildlife and bird habitat.

Despite the importance of pastures, not much is known about their ecology. We have been studying the diversity and composition of pastures, and how that contributes to:

  • Productivity of both plants and grazing animals.
  • Stability of pasture production under stress (for example drought).
  • Ability of pastures to recover after stress.

This fact sheet will focus on what we have learned about pasture diversity and pasture monitoring.

Regional Survey

From 1998 to 2005, we surveyed 44 farms from Maryland to Maine. All farms had grazing animals, usually dairy cows. In 2-8 pastures on each farm, we collected information on plant species number and total cover, bare ground, and number and cover of each species present. We made complete species lists for a 0.25 acre area (1000 m2), and estimated species cover in ten smaller quadrats (11 ft2, or 1 m2) within the larger plot.

We also collected soil test results, slope, elevation and aspect (for example, north- or south -facing) for each pasture, and annual precipitation and temperature for each farm.

butterfly in pasture

Pasture Diversity and Composition

Northeastern pastures are very diverse. We found 310 species of plants. The average number of plant species in a pasture was 32, but we found anywhere from 9 to 73. Nearly half of the species identified were native. Most species were rare, but some were common and abundant. Many of these were forage species, such as orchardgrass, Kentucky bluegrass, tall fescue, timothy and red and white clovers. Other common species included quackgrass, English and common plantains, curly dock and dandelion.

The average pasture:

  • has 32 species.
  • has 6% bare ground.
  • has 67% grass cover.
  • has 21% legume cover.
  • has 23% broadleaf cover.

Pasture Condition Score

The NRCS has developed a pasture monitoring method called the Pasture Condition Score. It uses ten criteria, each ranked on a scale of 1 (major effort required) to 5 (no change needed):

  • Percent desirable plants: Plants that livestock will graze readily
  • Plant cover: Important to forage production, soil and water protection
  • Plant residue: Amount of standing dead, litter, and thatch
  • Plant diversity: Number of different forage plants well represented
  • Plant vigor: Indicates health of desirable species
  • Legume content: Source of N, improves forage quality
  • Uniformity of use: Indicates “spot” grazed, over grazed, avoided areas
  • Livestock concentration areas: Indicates where livestock congregate and potentially damage pastures
  • Erosion: Presence, severity of wind, water erosion
  • Soil compaction: Indicator of impaired water infiltration capacity

The ten criteria are added, for a score ranging from 10 to 50. More information can be found in the “Guide to Pasture Condition Scoring.”

Pasture Monitoring

As part of the regional survey, we recorded 182 pasture conditions scores. Only 1% of the pastures were very high-scoring, but most of the pastures needed only minor or moderate changes. None of the pastures we sampled scored in the lowest category.

Pastures scored lowest in two areas, plant diversity and legume content. Manipulating plant diversity would improve the pasture condition score for many of these farms. The lowest-scoring pastures were rated poorly for plant cover, uniformity of use and soil compaction, and generally lower for all criteria. Changes in grazing management, to reduce under- and over-use, could improve the ratings of these pastures.

Future Work

We are working to understand how the complex mixtures of planted and unplanted species found in Northeastern pastures contribute to pasture production and forage quality. Manipulating species diversity and content would improve the pasture condition score rankings of many pastures in the Northeast. We are investigating the benefits and drawbacks of forage mixtures containing grasses, legumes and broadleaf plants. The next step will be to identify effective methods for establishing and maintaining the most useful of these mixtures on a range of site types.

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Diet and behavior

Diet Selection and Grazing Behavior
Dr. Kathy Soder, USDA ARS Pasture Systems and Watershed Management Research Unit

full report (PDF)

A grazing ruminant is presented with a smorgasbord of choices when turned out onto a pasture. However, little is understood on how selection decisions are made by the animal, including:

  • How do these animals know what plants to eat and what to avoid?
  • Can grazing ruminants ‘balance’ a diet by consuming various plants that complement each other nutritionally?
  • Do their diet preferences change throughout the day, throughout the grazing season?
  • Why do preferences change?
  • How can we manage for these changes?

sheep

Grazing behavior research is attempting to address these issues to improve animal and pasture productivity. Studies conducted in the United Kingdom with perennial ryegrass and white clover pastures showed that, when given a choice, cattle and sheep preferred clover over ryegrass and consumed clover more rapidly than ryegrass. However, these animals do not consume a 100% clover diet. Why is that? If they prefer clover over ryegrass, wouldn’t we expect them to consume clover and ignore grass?

The UK work showed that, in reality, cattle and sheep preferred a diet (based on the choices presented to them) that is 50-70% clover, and 3050% ryegrass. Furthermore, clover was preferred in the morning while grass was preferred in the afternoon.

What is causing the switch from one forage to another? Why not continue eating the forage preferred first thing in the morning (in this case, clover)? Although we don’t yet have definitive answers, clues in the scientific literature and additional research may help solve this puzzle.

Grazing ruminants have 3-5 major ‘meals’ throughout the day (with mini grazing bouts in between the major meals), with the largest meal in the evening and the second largest meal in the early morning. Cattle, sheep and goats are prey animals that evolved to consume large quantities of high-fiber feeds in a relatively short time (often in open meadows where they were more prone to predation), then find a safe place to lie down and further chew (ruminate) their food. Ruminant animals typically lie down after dusk and remain relatively still during the night unless disturbed.

grazing cow

After chewing cud much of the night, their rumens have emptied substantially. In the UK work, the morning meal tended to consist of primarily clover (the preferred forage)…But why do they stop eating clover, and switch to grass (or vice versa)? Why does the evening meal contain primarily grass, when we know clover is the preferred forage?

Several theories exist concerning why preferences change. First, grazing animals may have learned through trial and error that clover causes bloat or other discomfort. Researchers at Utah State University conducted research on these post-ingestive feedback mechanisms and showed that when animals are made ill after consuming a food (particularly novel foods), they develop a strong aversion to that food.

Additionally, they will teach their offspring to avoid that food (even though under normal circumstances it may be a perfectly fine food for a ruminant). And those offspring remember those early lessons from ‘mom’ long into their lives. These researchers have also shown that ruminants are able to learn to ‘selfmedicate’. Ruminants may consume a high clover diet, only to have bloat result. They relate the discomfort of bloat to the clover, and so, to avoid bloat, perhaps ruminants learned (through trial and error) to switch from clover to grass after they reach a particular satiation point, since grass is higher in fiber, has a slower passage rate, and may mediate the bloat affects.

The USU group has also shown how animals can ‘mix’ diets to mediate the effects of secondary compounds. For example, the ruminants consumed a certain level of a plant containing high tannin content, then switching to a plant containing high terpene level. By themselves, dietary consumption was low for each plant species, but when combined in the diet, dietary intake of each (and total dietary intake) increased.

Grazing ruminants may have inherently learned that grass ‘fills them up’ more for that long night-time fast, since grass typically contains more fiber than clover, causes more cud-chewing activity (which has been linked to deep-sleep patterns in ruminants), and has a slower passage rate out of the rumen.

The sugar content of grasses is higher in the afternoon than in the morning, which may influence preference for grasses throughout the day.

goat

There is much to be learned about grazing behavior of ruminants. Pastures in the United States tend to be much more diverse than the ryegrass/clover pastures used in the UK studies. We do not yet know whether the same preferences occur with our diverse forages as what was seen in the previous studies with relatively few choices.

The USDA-ARS Pasture Systems and Watershed Management Research Unit is currently conducting research to answer these questions. Gaining a better understanding of diet preferences of grazing ruminants will help in developing improved grazing strategy recommendations, improved pasture mixture, and ultimately, improved animal and pasture productivity.

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Greenhouse gas emissions from dairy production

The Dairy Greenhouse Gas Model: A tool for estimating the greenhouse gas emissions and carbon footprint of dairy production systems
C. Alan Rotz and Felipe Montes, USDA ARS Pasture Systems and Watershed Management Research Unit, University Park, PA

full report (PDF)

The Problem

Animal agriculture is a recognized source of greenhouse gas (GHG) emissions, but good information does not exist on the net emissions from our farms.

What are Greenhouse Gases?

GHGs include carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O). Dairy cows emit CH4 through enteric fermentation in the rumen and CO2 through respiration. Microbial processes in manure release CO2, CH4, and N2O during storage and handling, and microbial processes in the soil release CO2 and N2O as crops are produced.

What Affects Greenhouse Gas Emissions?

Many management factors on farms affect these gas emissions such as breed, milk yield, fiber level in animal diets, type of manure storage, cropping strategy, and pasture productivity.

Estimating Emissions

A software tool called the Dairy Greenhouse Gas Model or DairyGHG estimates GHG emissions and the carbon footprint for various farm management strategies.

What is a Carbon Footprint?

This is a term that has evolved to represent the net total GHG emission associated with a product or service. For our model, this is the net exchange of the three important GHGs per unit of milk produced. Carbon footprints for dairy farms typically range from 0.4 to 0.9 lb CO2e per lb of milk depending upon the management of the farm.

Model Availability
DairyGHG can be downloaded from the internet and installed on computers that use a Microsoft Windows operating system.

A Comparison of Production Systems

DairyGHG was used to compare the emissions of the following dairy production strategies:

  1. Full confinement system. 100 large framed Holstein cows; 80 heifers; high grain:forage diets; milk production of 22,000 lb/cow; housed in free-stall barns.

  2. Winter confinement and summer pasture system. 100 average-sized Holsteins; 80 heifers; high forage:grain diets; milk production of 18,700 lb/cow; housed and fed in free-stall barns when not on pasture; rotational grazing of older heifers and all cows during the growing season.

  3. Year-round outdoor system. 120 Holstein-Jersey crossbred cows; 96 heifers; high forage:grain diets; milk production of 13,200 lb/cow; spring calving cycle; all farmland is rotationally-grazed perennial pasture with excess forage harvested, stored, and fed as bale silage.

Conclusions

  1. Use of a well managed rotational grazing system may reduce the net GHG emission per animal, but the emission per unit of milk produced (carbon footprint) will likely increase.

  2. A transition from cropland to perennial grassland will stimulate carbon sequestration, which will greatly reduce GHG emissions and the carbon footprint for 20 years and maybe more.

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