Grazing ingestion

Beef cattle farming Farming Dairy cattle farming

An essential component for the success of a ration, ingestion at pasture reminds us that ruminants do not only seek to select the best. Focusing on ingestion at pasture allows to:

Motivate animals to consume forages they previously refused without reducing production: farming practices guide the rations selected by ruminants at pasture (and at the trough). Most of the animal's behavioral blinders emerge from farmers' habits.
Successfully feed the herd year-round with the forages available on the farm: it is possible to meet higher than expected needs by increasing ingestion of forages with lower nutritional value. Indeed, forage digestibility is necessary but not sufficient information to understand animal performance at pasture in diverse environments.

Succeeding in the ration, for a ruminant, means ingesting forages whose digestion will provide the expected nutrients. This success therefore relies on two components: ingestion (what the animal chooses to eat) and digestion (what it transforms into nutrients). These two components are closely linked by feedback loops, and largely influenced by farming practices.

The efficiency of digestion has long been considered the limiting factor of zootechnical performance. Yet, at pasture in diverse environments, it is the animal that decides the nature and quantity of its food.. The ingestion function thus becomes even more decisive than at the trough.

Ruminants make their food choices facing plants very different in quality and size. These choices affect food intake, potentially leading to the formation of a ration sufficient or insufficient to meet their energy needs.

Ingestion: the first step of feeding

The pitfall of focusing production on digestion

For a long time, the digestion function has been studied and used to improve animal farming performance. Efforts then focused on breed genetics (improving digestion and production capacities) and forage production techniques (forage improvement seeking low fiber and high nitrogen). However, ruminants have specialized during species evolution to succeed in their ration on forages more fibrous than other herbivores. They have anatomical capacities (mouth shape, additional stomachs, ingestion capacity) and metabolic capacities (microbial fermentation) to succeed on fibrous forages.

Importance of forage ingestion

For ruminants managed at pasture, ration success depends primarily on the motivation they show towards the resource. This behavioral function has been the subject of recent research. It helps illuminate farmers' observations and knowledge.

The animal at pasture voluntarily selects its forage. It then makes food choices, largely influenced by its habits, activity rhythms (daily, seasonal…), previous experiences and learning (size of its rumen, composition of its microbiota). It gradually establishes its preferences, reinforcing the selection of plants that provide a certain comfort:

during selection (bite size, texture, taste, smell, etc.) = own feeding experience

during digestion (feeling of fullness, increase in nutrient levels in the blood) = feeling of satiety

The feeling of satiety in an animal causes ingestion to stop. Satiety involves both a physical response (rumen stretching) and a metabolic one (sufficient blood nutrient levels). Ruminants seek to reach both forms of satiety. Alternating varied food intakes, as well as expressing food preferences, contribute to this. These lead them to select all or part of plants according to their need (nitrogen/fiber).

A ration formed by successive food choices

To compose its diet according to its preferences, available forages and management driven by the farmer: the animal can choose indifferently to increase quality (nutrient content expressed as a percentage) or quantity (expressed in kg of dry matter) of ingested forages.
To increase ingested quantity, the animal can indifferently extend its grazing time or increase its ingestion rate (expressed in grams of dry matter ingested per minute).
To increase ingestion rate, the animal can indifferently increase bite mass (bite size), or bite frequency (number per minute).

Farming practices influence the outcome of this mathematical equation. They must aim for a balance between the four components of this equation, by guiding animal behavior and building available resources during a meal, throughout a day, across seasons and throughout the animal's life.

Guiding ingestion through farming management

Helping the animal compose its ration

The quality of a ruminant's ration is determined by the digestibility of ingested nutrients. Nutrient density in the ration varies greatly depending on plant species and plant parts selected, and seasons. A high fiber content can be synonymous with quality, provided the fibers are digestible, and the diet contains sufficient nitrogen. Nitrogen is indeed necessary for the cell multiplication of rumen microorganisms, which themselves degrade fibers. It also depends on the animal's digestion capacity linked to the composition of its rumen flora. This evolves constantly in response to the diet.

Farming practices can influence digestion capacities and thus the quality of forages chosen by the animal:

Ensure animals have the right digestion capacity according to offered food resources: by exposing animals to a particular diet, the farmer gradually strengthens their digestion capacities. And allows animals to experience "positive experiences": nutrient release in the blood provides nutritional well-being sensations.
Ensure a diversity of available foods at pasture and their complementarity: offering dietary diversity in a pasture paddock, or moving animals across different areas within a day gives them the opportunity to make a ration with a balanced nutrient composition.
Ensure positive interaction between pasture intake and supplementation: for example, providing grass silage or regrowth rich in nitrogen and low in fiber will guide the animal to select fibrous plant parts to balance the rumen and avoid acidosis.
Ensure transition of the rumen microbiota: by favoring ingestion of fibrous forages, the farmer can progressively shift the rumen microbiota towards a cellulolytic flora. This improves the animal's ability to digest long fibers.

Promoting ingestion time at pasture

Ruminants must manage the balance between several distinct activities: feeding, ruminating, resting, interacting with conspecifics, moving, being milked, etc. The time they can devote to grazing is thus both adjustable and limited. If they extend grazing time, it will be at the expense of other activities.

Farming practices can modify the time the animal devotes to ingestion at pasture:

Ensure animals have enough time to eat. Intake time varies greatly depending on milking practices, herd movements during the day, etc. Moreover, weather (rain, storm, heat, light…) can cause animals to stop eating early, to split or delay meals, etc. On the same paddock, their feeding behavior varies by season and time of day.
Ensure animals are motivated by the offered forages. Animals' curiosity can be stimulated to boost ingestion (changing paddock, offering something new, etc.). Waiting phenomena must be avoided. Providing palatable feed at fixed times may cause early cessation of pasture ingestion. Likewise, if animals already have a half-full rumen, a "ballast" effect demotivates them at pasture. Also, changing feeding behavior from one vegetation to another takes time. This requires farmer perseverance not to remove animals from the paddock too quickly or to provide supplementation.

Helping the animal harvest forage efficiently

Ingestion rate results from the bite mass chosen by the animal and the bite frequency it can maintain. Bite mass an animal can take is extremely variable. For example, a ewe can take bites on trees foliage up to 1000 times heavier than on very short grass. Bite mass is a selection criterion to stabilize ingestion flow over time (eat what the animal prefers but also fill up quickly enough). During a meal, animals preferentially target medium bites and then widen the range of bite sizes to maintain ingestion flow (very small bites on already grazed plants, very large bites on large plants). Moreover, bite diversity stimulates ingestion and breaks the animal's routine.

Farming practices can encourage the animal to modify its preferred bite mass and frequency:

Ensure animals have learned to diversify their food intakes: feeding learning occurs early and through contact with plants or plant parts the farmer wants them to select. The animal learns to position its head, mouth and tongue according to the plants or plant parts selected.
Ensure animals have a diversity of bite sizes during the meal: this bite diversity relates both to botanical diversity and structural diversity, which is shaped by different uses of vegetation (effect of grazing on availability). The animal's inability to vary bite size (alternating large and small bites) after a few days in paddocks will limit ration success. Entry and exit criteria of paddocks will thus influence this success.

Autres fiches Pâtur’Ajuste

Sources:

SCOPELA, with the contribution of farmers. Technical sheet of the Pâtur’Ajuste network: Ingestion at pasture. April 2019. Available at: https://www.paturajuste.fr/parlons-technique/ressource/ressources-generiques/lingestion-au-paturage