Choosing Mowing Practices

Beef_cattle_farming Farming Dairy_cattle_farming

Choosing mowing practices well allows to:

Make mowing dates vary without impacting the quantity/quality ratio of forage, and spread out the harvesting work.
Question what makes the quality of harvested forage.
Recognize that mowing practices influence vegetation and do not penalize grazing, at the risk of having to distribute the harvested forage too quickly.

The purpose of this sheet is to understand the links between mowing practices, the feeding behavior of the herd and the functioning of vegetation.

In livestock farming, mowing has different functions. It allows to:

Harvest forage to feed the herd when access to pasture is impossible.
Resolve seasonal mismatches between the nutritional needs of animal groups and the nature of resources available standing.

It constitutes a safety net in case of a bad year.

While stockpiling is legitimate, it must be considered that mowing practices have consequences on yield, forage value, the annual distribution of feed supply, and the role of grazing in the herd's diet. Keeping in mind the diversity of possible harvesting methods and their implications allows choosing mowing practices consistent with one's own objectives.

This sheet provides knowledge elements to help choose mowing practices adapted to one's system and dare to vary them calmly. It proposes:

To identify the different growth and maturation profiles of vegetation present on the farm.
To determine the quantity and quality of forage needed according to the desired production level and feeding management implemented.
To consider the implications of mowing on the availability of standing resource throughout the year.
To anticipate the consequences of mowing practices on the long-term evolution of flora.

Broaden your view of harvesting and vary your mowing practices

Vary mowing dates according to pasture types

The principle of a trade-off between forage quantity and quality is well known in livestock farming. If mowing early, green forage is harvested. Its nitrogen value is high but dry matter quantity is low. And vice versa.

This principle results from the progressive sequence during spring of leafy growth, then flowering, and finally fruiting. The latter is associated with vegetation ripening. Indeed, once seed production is ensured, plants enter summer dormancy which causes sap descent and leaf senescence. Forage quantity gradually increases, initially with a decrease in nitrogen content, an increase in digestible fiber content, then an increase in indigestible fibers.

In early and productive pasture, a trade-off between quantity and quality must be made, as plants mature quickly, then their tissues degrade.

However, while this principle holds true in pastures with simplified flora and rapid growth, it becomes less accurate in pastures with slower or more diverse flora that offer mowing flexibility. Indeed, their nutritional value is maintained for a longer time. This property makes it possible to harvest later a similar forage quality for an equal or even higher quantity. Thus, depending on the growth and maturation profile of the different pastures on the farm, one can delay mowing dates without changing the desired trade-off between quantity and quality of harvested forage:

Depending on the diversity and type of plant species in the plot, the seasonality of growth and senescence varies. Here are some reasons:

Growth start of species can occur from the very first temperature rises, or only after several weeks of mild temperatures.
Grass heading is quickly associated with cessation of leafy growth. It is therefore the time when biomass quantity to harvest is maximal. Heading varies by species: it can be early or very early (in the first part of spring) or late or very late for other species (during summer).
Grass heading is also associated with a decrease in grass digestibility. However, depending on plant species, it is not always correlated with a loss of palatability. It is therefore not necessarily the time when forage value decreases.

Evaluate hay quality

The value of hay for a group of animals is often summarized by its biochemical composition. This reasoning is incomplete because it does not take into account the animal's point of view, i.e. its real motivation to consume the forage provided. Indeed, the biochemical composition of hay is obviously decisive for digestion and animal metabolism. But, the animal's capacity to ingest, digest and produce from forage is built and modulated by several farmer practices presented below.

Animal production level

The production level of animals (growth rate or milk quantity) is largely decided and organized by farmers through choice of breeding periods, marketing periods or according to the genetic background of animals. It modifies the nutritional needs the farmer seeks to cover by feeding and conditions the type of forage distributed. To valorize all forages produced on the farm without supplementation, the farmer can differentiate harvested hays to adapt them to variations in nutritional needs. The farmer can also decide to limit production level at the animal scale and/or according to periods of the year. For example, distribution of high nutritional value forages, which are costly to produce and limited in quantity on the farm, is prioritized for animals for which the farmer seeks a high production level.

Forage intake level

Forage intake level is only partly determined by its nutritional value. It is also determined by its palatability, which depends on the animals' motivation to ingest the offered forage(s). Some practices motivate or demotivate the animal to eat. For example, distributing less palatable hay at the start of the ration takes advantage of the animals' appetite, provided another more appreciated forage is not introduced too quickly. Similarly, when distribution is combined with grazing during the day, the type and quantity of forage distributed are chosen to create synergy with the grazed resource and not competition.

Knowledge of forage characteristics

Prior knowledge of forages by animals is an important factor of palatability. Taste, texture, smell, digestive consequences, physiological effects, are characteristics animals can memorize long-term and mobilize when forming their ration. Thus, coarse hay can be palatable. Food learning is easier when animals are young. For example, young animals can learn to voluntarily consume large quantities of fibrous forage poorly valued by a group of mothers, thanks to adapted management allowing learning.

Fiber, an essential element for ruminants

Ruminants have a particular digestive system that allows them to use forages as the main source of nutrients. A ration that does not contain enough fiber can lead to rumen dysfunctions, which may result in pathologies (acidosis is probably the best known) and performance decrease. A fiber-balanced ration promotes rumination, a time-consuming but essential activity for rumen pH regulation, preparation of food for microbial degradation, and nutrient absorption. For example, early mowing produces nitrogen-rich forages that deteriorate ruminant nutritional balance if given alone. Farmers often add a fiber source such as straw to the ration.

Animal intake capacity

Intake capacity conditions animals' ability to valorize coarse and bulky forages. Animals with high intake capacity can ingest large quantities of forage and achieve zootechnical performances equivalent to those obtained with more nitrogenous forage but consumed in limited quantity. An animal's intake capacity is partly innate as it depends on species and breed. But it is also partly acquired. Indeed, it can be increased in young animals by appropriate management. After that, it is too late. The rumen of ruminants develops according to its stimulation in early life (before first calving).

For example, distributing coarse and palatable forages ad libitum to young animals stimulates the rumen and defines its volume for life.

Optimize regrowth through mowing

Mowing, like grazing, modifies the growth and reproduction cycle of plants during the year. It thus impacts the intensity and seasonality of regrowth of pastures. One can choose mowing practices to obtain regrowth
well positioned in the year (date, quantity, quality adapted to a given animal group). Mowing practices can differ, among others, according to:

Mowing date

Mowing during spring will cause leafy regrowth if weather conditions are favorable.
Mowing in late spring or early summer will be followed by vegetative rest of plants, so no regrowth before autumn.

Cutting height

High cutting leaves more leaves standing which continue to produce photosynthesis. This limits mobilization of plant root reserves during regrowth. It allows to reuse the plot more quickly (by mowing or grazing).

Preparation by early spring grazing

Déprimage (grazing of first leaves) forces plants to restart growth in early spring. Flowering is delayed but does not prevent the nutritional value drop linked to grass heading.

On half of the plot (right), déprimage delayed growth and heading. The pasture holds better until conditions are favorable for hay mowing, and the forage will be more palatable for the animals.

Topping (grazing of first leaves and young ears) forces plants to restart growth, but without new flowering for most of them. This generally causes lower yield in the second cycle, but nutritional value does not drop. A low-fiber forage is harvested.

Select flora through mowing practices

Mowing is a complete exploitation of grass with biomass export. Its combination with other uses of the plot during the year (mowing or grazing) leads to flora evolution. To understand the link between mowing practices and flora evolution, three processes must be kept in mind:

Energy reserve storage

It occurs when leaves are photosynthetic (green color). It is necessary for the plant to have enough energy to restart growth after each exploitation that deprives it of leaves. It can be penalized if the rest period between two successive uses is reduced.

Plant seeding

It is necessary for reproduction of many species (except those reproducing vegetatively by stolons, rhizomes, etc.). It must be respected to sufficiently feed the seed bank in the soil, which can be ensured by irregular seeding (one year out of 3 or 4 for example), or by seeding in borders, hedges or neighboring plots.

Soil fertility level

It corresponds to the soil's capacity to release nutrients useful to plants. Fertility level results from soil activity:

Bedrock degradation.
Soil aeration.
Activity of fauna and microorganisms.
Mineralization of organic matter.

Autres fiches Pâtur’Ajuste

Sources

SCOPELA, with farmers' contribution. Technical sheet from the Pâtur’Ajuste network: Choosing mowing practices. October 2018. Available at: https://www.paturajuste.fr/parlons-technique/ressource/ressources-generiques/choisir-ses-pratiques-de-fauche