Managed intensive rotational grazing
In agriculture, Managed intensive rotational grazing (MIRG), also known as cell grazing, mob grazing and holistic managed planned grazing, describes a variety of closely related systems of forage use in which ruminant and non-ruminant herds and/or flocks are regularly and systematically moved to fresh rested areas with the intent to maximize the quality and quantity of forage growth.
MIRG can be used with cattle, sheep, goats, pigs, chickens, turkeys, ducks and other animals. The herds graze one portion of pasture, or a paddock, while allowing the others to recover. The length of time a paddock is grazed will depend on the size of the herd and the size of the paddock. Resting grazed lands allows the vegetation to renew energy reserves, rebuild shoot systems, and deepen root systems, with the result being long-term maximum biomass production. MIRG is especially effective because grazers do better on the more tender younger plant stems. MIRG also leave parasites behind to die off minimizing or eliminating the need for de-wormers. Pasture systems alone can allow grazers to meet their energy requirements, and with the increased productivity of MIRG systems, the grazers obtain the majority of their nutritional needs without the supplemental feed sources that are required in continuous grazing systems.
One key element of this style of animal husbandry is that either each grazed area must contain the resources for the animals (water source, for instance) or the resources must be moved each time the animals are moved. Having fixed feeding or watering stations defeats the rotational aspect, leading to degradation of the ground around the water supply or feed supply if additional feed is provided to the animals.
Herd health and welfare
Animal health risks
Bloat is a common problem in grazing systems for ruminants, although not for pigs or poultry, that if left untreated can lead to animal death. This problem occurs when foam producing compounds in plants are digested by cows, causing foam to form in the rumen of the animal and ultimately prohibiting animals from expelling gas. The risk of bloat can be mitigated by seeding non-bloating legumes with the grasses. Animals are especially susceptible to bloat if they are moved to new pasture sources when they are particularly hungry. It is therefore important to ensure that the herd is eating enough at the end of a rotation when forage will be more scarce, limiting the potential for animals to gorge themselves when turned onto new paddocks.
Several problems are related to shade in pasture areas. Although shade provides relief from heat and reduces the risk of heat stress, animals tend to congregate in these areas which leads to nutrient loading, uneven grazing, and potential soil erosion. Taller shade trees move the shade area around as the day progresses minimizing this problem.
Animal health benefits and animal welfare
Herd health benefits arise from animals having access to both space and fresh air. Freedom of movement within a paddock results in increased physical fitness, which limits the potential for injuries and abrasion, and reduces the potential of exposure to high levels of harmful disease-causing microorganisms and insects.
In a concentrated animal feeding operation (CAFO), it is considered normal for a large number of animals to continuously occupy a very small area. The aisles that animals use to move around are consequently constantly coated with a moist layer of manure and urine from the many animals, leading to ailments such as foot rot due to the constant wet exposure. The manure and urine is usually just scraped off into gutters below slatted surfaces, and the surfaces and gutters are rarely washed completely clean, so molds, bacteria, and insects can grow and thrive in the potentially infectious waste. Feeding areas in a CAFO are also rarely stripped bare and washed with a disinfectant, as this would reduce the time available for animals to eat continuously, so molds and bacteria are also able to become established where the animals eat. The close confinement and lack of general environmental cleanliness leads to easier spread of infection and increased sickness, requiring the regular feeding of antibiotics to keep the confined animals healthy but which also leads to antibiotic resistance for bacteria constantly present in the CAFO.
By comparison, with managed grazing, the animals are able to spread out and exist in a natural environment more suited for their natural growth and development. As the animals move to a new paddock, wastes are left behind and allowed to decay without the animals nearby. The animals experience less disease without the need for regular antibiotic dosing, and fewer foot ailments.
In general, a well managed rotational grazing system has rather low pasture weed establishment because the majority of niches are already filled with established forage species, making it hard for competing weeds to emerge and become established. The use of multiple species in the co-grazing helps to minimize weeds. Established forage plants in rotational grazing pasture systems are healthy and unstressed due to the "rest" period, enhancing the competitive advantage of the forage. Additionally, in comparison to cash grain crop production, plants which would be considered weeds are not problematic in row crops. Many of these plants are actually nutritious to grazers and control of these plants is therefore not necessary in management intensive rotational systems. However, certain species such as thistles and various other weeds, are indigestible and possibly poisonous to grazers. These plant species will not be grazed by the herd and can be recognized for their prevalence in pasture systems.
A key step in managing weeds in any pasture system is identification. Once the undesired species in a pasture system are identified an integrated approach of management can be implemented to control weed populations. It is important to recognize that no single approach to weed management will result in weed free pastures; therefore, various cultural, mechanical, and chemical control methods can be combined in an integrated weed management plan. Cultural controls include avoiding spreading manure contaminated with weed seeds, cleaning equipment after working in weed infested areas, and managing weed problems in fencerows and other areas near pastures. Mechanical controls such as repeated mowing, clipping, and hand weeding can also be used to effectively manage weed infestations by weakening the plant. These methods should be implemented when weed flower buds are closed or just starting to open to prevent seed production. Although these methods for managing weeds greatly reduces reliance on herbicides, weeds problems may still persist in managed grazing systems and the use of herbicides may become necessary. Use of herbicides may restrict use of a pasture for some length of time, depending on the type and amount of the chemical used. Frequently weeds in pasture systems are patchy and therefore spot treatment of herbicides may be used as a least cost methods of chemical control.
Nutrient availability and soil fertility
If pasture systems are seeded with more than 40% legumes, commercial nitrogen fertilization is unnecessary for adequate plant growth. Legumes are able to fix atmospheric nitrogen, thus providing nitrogen for themselves and surrounding plants. Although grazers remove nutrient sources from the pasture system when they feed on forage sources, the majority of the nutrients consumed by the herd are returned to the pasture system through manure. At a relatively high stocking rate, or high ratio of animals per hectare, manure will be evenly distributed across the pasture system. The nutrient content in these manure sources should be adequate to meet plant requirements, making commercial fertilization unnecessary. Management intensive rotational grazing systems are often associated with increased soil fertility which arises because manure is a rich source of organic matter that increases the health of soil. In addition, these pasture system are less susceptible to erosion because the land base has continuous ground cover throughout the year.
High levels of fertilizers entering waterways are a pertinent environmental concern associated with agricultural systems. However, management intensive rotational grazing systems effectively reduce the amount of nutrients that move off-farm which have the potential to cause environmental degradation. These systems are fertilized with on-farm sources, and are less prone to leaching as compared to commercial fertilizers. Additionally, the system is less prone to excess nutrient fertilization, so the majority of nutrients put into the system by manure sources are utilized for plant growth. Permanent pasture systems also have deeper, well established forage root systems which are more efficient at taking up nutrients from within the soil profile.
Although milk yields are often lower in MIRG systems, net farm income per cow is often greater as compared to confinement operations. This is due to the additional costs associated with herd health and purchased feeds are greatly reduced in management intensive rotational grazing systems. Additionally, a transition to management intensive rotational grazing is associated with low start-up and maintenance costs. Another consideration is that while production per cow is less, the amount of cows per acre on the pasture can increase. The net effect is more productivity per acre at less cost.
The main costs associated with transitioning to management intensive rotational grazing are purchasing fencing, fencers, and water supply materials. If a pasture was continuously grazed in the past, likely capital has already been invested in fencing and a fencer system. Cost savings to graziers can also be recognized when one considers that many of the costs associated with livestock operations are transmitted to the grazers. For example, the grazers actively harvest their own sources of food for the portion of the year where grazing is possible. This translates into lower costs for feed production and harvesting, which are fuel intensive endeavors. MIRG systems rely on the grazers to produce fertilizer sources via their excretion. There is also no need for collection, storage, transportation, and application of manure, which are also all fuel intensive. Additionally, external fertilizer use contributes to other costs such as labor, purchasing costs.
It can also be demonstrated that management intensive rotational grazing system also result in time savings because the majority of work which might otherwise require human labor is transmitted to the herd.
Many pastures undergoing MIRG are less susceptible to soil erosion and are associated with higher soil fertility than continuously grazed pastures, depending on the skill of the manager and the management system he is using. As a result, the paddocks require fewer commercial inputs, which have been associated with negative environmental impacts. In addition, because these systems tend to be more resilient and stable they are more capable of responding to changing environmental conditions and perturbations while not compromising productivity.
Managed intensive rotational grazing paints a wide brush over many different managed grazing systems. Managers have found that rotational grazing systems can work for diverse management purposes, but scientific experiments have demonstrated that rotational grazing systems do not always necessarily work for specific ecological purposes. This controversy stems from two main categorical differences in rotational grazing, prescribed management and adaptive management. The performance of rangeland grazing strategies are similarly constrained by several ecological variables establishing that differences among them are dependent on the effectiveness of those management models. Depending on the management model, plant production has been shown to be equal or greater in continuous compared to rotational grazing in 87% of the experiments.
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