28 August 2012

5 minute read

Grazing Behaviour Affects Forage Management

Why cattle moved from pastures to confinement or vice versa lose their appetites, get sick, or perform poorly for a time, even when offered more nutritious foods? Why livestock on pastures with only a few plants to eat perform less well than when they have more plants to choose from? Why changes in grazing management can reduce livestock performance for long periods of time?

All herbivores need to adapt to changes within themselves and the food they are eating. An animal’s nutritional needs vary with age, physical activities, stage of life, and other factors. In a grazing situation, livestock are challenged to meet the changing nutrient demands of their own body while dealing with variations in nutritional qualities, toxicities, and physical attributes of plants. In order to most effectively operate a successful managed grazing system, livestock producers need to consider and understand the natural interaction between plants and animals.

Social influences interact with individual experiences to generate behavior. Much behavior is learned at a young age from animals’ mothers and from other animals in a herd. By observing and following what mothers and peers do, diet and habitat selection patterns develop in young animals. However, continuation of behavior learned at a young age depends on consequences to the individual. Even if a young animal was conditioned to prefer a certain food at a young age, if the animal experiences negative feedback – such as nausea, bad taste, or other negative eating experience - after eating the food, preference will be lessened.

Palatability of foods is a term we use often in grazing management, and preference for foods by livestock is influence by palatability. But what is palatability? This term can have several different meanings, but research in animal behavior shows palatability to be the interrelationship between a food’s flavor (odor, taste and texture), and its postingestive effects (results of feedback from nutrients and toxins).

Animals use the flavor-feedback relationship to acquire preferences and aversions to certain foods. They also use this process to differentiate between different foods in a meal. For example, if an animal eats several familiar foods and several new or novel foods in a meal and experiences a negative eating experience then they will develop an aversion to the new foods. Postingestive feedback and the resulting influences in palatability happen automatically without any recognized or conscious memory of the feedback.

Palatability also depends on an animal’s nutritional state. Animals are able to maintain the proper ratio of energy and protein in their diet when given the choice. They are also able to consume foods that are higher in toxins when foods are available that are high in macronutrients. This behavior is made possible by feedback from the body.

Plants influence grazing behavior of herbivores by several mechanisms. All plants vary in nutrient composition (energy, protein, vitamins and minerals), defense mechanisms (toxin levels, physical features), and spatial and temporal variation (quantity and availability). Plants evolve to protect themselves from harm and they do this several ways. Plants contain toxins such as tannins, terpenes or alkaloids. They may have physical features such as stickers, thorns, waxy leaf coatings. Some plants have leaves that collapse against the stem in response to touch. Features such as these developed to limit consumption of the plant by grazing or browsing animals, and therefore allow the plant to reproduce and/or survive. These features influence the palatability of the plant to herbivores, and affect grazing behavior.

Skin and gut defense systems also illustrate the use of feedback to select foods. Experiments have shown that both auditory and visual stimuli (skin defense system) and taste and odor of foods (gut defense system) can be used to influence preference for foods or habitats. Animals that experienced negative feedback after an eating event acquired aversions to the food based on whether the negative experience was related to the taste (gut) or a physical effect such as pain (skin). This information suggests that livestock can be conditioned to avoid certain foods which could be a valuable technique for grazing managers.

Variety is the spice of life for livestock: they thrive on variety in the diet. When we limit the ability of livestock to select different foods, we only meet the needs of some of the individuals in a herd. We do this by feeding total mixed rations or by planting only one or two species of forage in a pasture or hayfield. Each individual is different in a multiple ways that affect their foraging behavior – dental structure, organ mass, age, sex, and breed, among others. Some animals prefer high energy foods, some prefer medium or even low energy. Animals vary in their susceptibility to toxins. Ultimately, diets and habitats that allow animals to select a variety of foods enable each individual to best meet its needs.

All of this information has implications for grazing management. The way a grazing system is managed can affect how animals forage. Low stock density tends to encourage more selective grazing, while high stock density encourages more diet mixing. Traditional “proper grazing management” – rotational grazing at lower stock densities – may have trained generations of livestock to “eat the best and leave the rest” which over time can result in a decline of biodiversity. Patterns of foraging behavior are transmitted from one generation to the next. Understanding foraging behavior and taking advantage of it can be a tool to improve the biodiversity of rangelands, to restore pastures dominated by weeds or to reduce overuse of sensitive areas by livestock. Ultimately, knowledge of grazing behavior can be used to improve economic viability as well as ecological integrity of pasture or range based livestock operations.