Grazing Behaviours
Content
Grazing Behaviour
Foraging Theory What is the survival value of feed choices? Benefits (for animal) - nutritional value Costs - energy expended, time lost, exposure Cost:benefit balance - most valuable food yields most energy per unit of time or energy expended Foraging Theory and Cost:Benefit With abundant valuable feed, what strategy gains the most energy per unit of time? Taking only the most valuable Take less valuable feeds as most valuable becomes scarce Grazing Animal Behaviour Herbivores born with certain behavioural predispositions and abilities (genetic) Accumulate knowledge, refine skills Learn by experiences and from others Herd behaviour impacts individual behaviour
Bite: Which Plants? Leaves upright or horizontal, strong or weak Leaf:stem; leafy or stemmy; Nutrient value high or low Toxins or bitter contents
Good height for easy, rapid intake Prior experience with the particular species of plant Patch Abundance - how far to go between plants Familiar species attract animals Quality - colour, texture, moisture, odour, sugar, post-ingestion feeling Topography - ease of access to patch Social - who else is there? Home Range Abundance affects carrying capacity, body condition, growth rate, milk production Species influence palatability, productivity of the sward Topography affects ease of access, energy expended to get the grazeable plants Water - 900-foot rule (cattle), wider limits on dry range - they need to access water at least once daily Cover - modify effects of wind and sun to keep in the zone of thermal neutrality (minimize energy need for homeothermy) Horses prefer open range Social - are there opportunities for natural herd and band formation? Diet Selection Based on Digestive Consequences Leafy green plants, easy to harvest, readily digestible energy and nutrients Animals have adaptive behaviours that allow them to choose forages that are more nutritious and less toxic than the average Hypothesis: Consequences of foraging direct an animal's foraging decisions Learning results in conditioned flavour aversions and preferences Animals acquire preferences if positive consequences follow ingestion, such as energy or protein enrichment, recovery from nutritional deficiency, or recovery from illness. Aversions vs. Pleasures Herbivores form aversions to foods when consumption is followed by gastrointestinal distress, especially if post-ingestive feedback stimulates nausea. Hedonic (relative to pleasure) value of flavour is modified by the feeling of well-being or illness after eating Good vs. Bad Memories Plants taste good because consumption makes the herbivore feel better
Plants taste bad because consumption makes the herbivore feel lill or unsatisfied Searching and selective grazing are cognitive processes, reinforced by other animals or humans
Ontogeny: origin and development of an organism Expression of Diet Selection Morphological characteristics are (mostly) inherited and can affect ability to digest dry matter and energy E.g. Inheritance of enzyme systems Enzyme systems for detoxifying plant chemicals are inherited Genetic Selection Interacts with Environment Selection in a domestic environment may alter ability to harvest nutrients in specific environments E.g. Holstein cattle from New Zealand, have larger mouths and use longer grazing times per day (they graze more) than US Holsteins Forage Decisions Based on Physiological State Demands vary depending on what was eaten earlier, ambient conditions (temperature, wind, moisture) and animal physiological condition (stage of production - rapid growth, slow growth, pregnancy, lactation, level of work, body condition) Do Animals Have "Nutritional Wisdom"? Lambs fed diets deficient in sodium, energy, or protein show a strong preference for foods high in sodium, energy, or protein, respectively Evidence for an ability to select foods high in other minerals which are deficient is not as clear Knowledge and Experience in Making Forage Decisions Lambs exposed to barley for thirty minutes at six months of age, readily consumed it two years later With maturity and experience, animals get more efficient at harvesting certain plants Social Interactions
Lambs raised on onion-flavoured milk preferred onion-flavoured feed later Nursing calves/foals/humans mimic their mothers Sheep averse to a pelleted diet, eat more of it with non-averse peers around Primary influence is their own experience, secondary influence is the mother, and tertiary influence is others Plant Attributes Influence Diet Plant preferences are higher for plants with rapid digestive feedback (high digestibility) Excess or deficient levels of nutrients decrease palatability (unusual ratios of nutrients as well) When consumption is followed by illness and nausea, plant aversion follows Toxins cause digestive distress, low palatability, and reduced eating drive Plant-Microbe Effects Ergot alkaloids in tall fescue or ryegrass affect receptors for neurotransmitters GABA from alfalfa may bind to neural receptors and alter suckling and nursing Some plant compounds affect internal parasites, which lower the grazing drive Selection and Rejection of Forage Patches Conditioned habitat preferences depend on escape from: fear, predators, pain, stress, hunger, heat, cold, or nausea Positive influences on preferences: satiety, relief of thirst, thermal neutrality, no pain, com for, security, or rest Dung deposits avoided, possibly to avoid parasites (smell of indole and skatole) Manure Aversion Tall green leafier forage near old dung may be avoided unless stocking density is high
Dung and Urine Patches
High N from urine encourages grass up to 4 months In hot weather, urine-soaked areas are scorched and killed Ungrazed areas around dung can reach 45% of a pasture. High stocking rate can bring this down to 10%. High hoof density breaks up manure Foraging Strategies Maximize net E gain/unit foraging time Grazing upper horizons = heavier bites Forage quality declines Time spent grazing at a location depends partly on sward structure, grazing intensity, and herbage allowance Theory: maximize E gain/unit E expended Ingestive Behaviour On new pasture, the first 20-30 bites are cautious, then new forage stimulates grazing On sparse pasture, high herbage allowance allows same daily intake as a lower allowance on denser pasture Herbivores prefer forages that can be consumed quickly (high intake rates) Recognizing Preferred Plants Sward height, leaf shape, leaf orientation, density, greenness are visual cues Flavours and memories Low stocking density = conscious decision-making High stocking density, uniform monocultures = more intuitive grazing behaviours, less selective Influence of Sward Height on Diet Selection by Horses The number of bites on patches with the highest sward height was greater than that on short patches Horses behaved as selective grazers, feeding mainly on grass taller than 7 cm A horse rarely resided on a preferred patch for a long duration of time Sampled their environment continuously, but almost exclusively returned to long patches for feeding Social Interactions Affect Selection of Feeding Areas Herd behaviour may override certain individual grazing behaviours Herd boss may initiate commencement and cessation of grazing At low stocking rates with little human interference, herd tendencies may be strong Suppression of herd behaviours may be a consequence of intensive grazing systems
Inter-Species Effects In co-grazing cattle and horses, cattle graze in the roughs (ignored by horses_ because structure of the pasture suits grazing mechanics of cattle and because they are not deterred by horse dung Cow vs. Horse Horse digestive system does not have the restriction to digest flow Horses accelerate the rate of passage of low-quality feeds Management Applications Watch behaviour of individuals and herd before planning strategies Watch resulting behaviours after implementation Adjust management to promote energetic feeding behaviour and healthy, happy horses Where animals congregate frequently, high nutrient levels and frequent smothering and trampling wil kill plants. Weeds tend to come in before grasses Horses foul the same area repeatedly Provide a small grazing area at the start of the season. This reduces the area that horses leave for droppings and maximizes grazing area Trampling Trampling makes some plants unavailable for grazing for weeks Higher stocking rates can reduce dry matter yields on pastures Trampling can cause soil compaction and puddling, adversely affecting plants by decreasing oxygen availability at root level Trampled forage will break down and contribute to soil organic matter, similar to grass clippings on a lawn Much trampling damage is repaired by frost action and activity of worms and other organisms in the soil Horse run more than ruminants on pasture, causing more trampling damage and thus requiring about 2 to 3 times more space per livestock unit (1000lbs) Grazing Activities 7-12 hours/day If hot, more at night When good forage is abundant, bigger, fewer bites/day Shorter forage requires more bites per minute and more hours of grazing per day Given the opportunity, animals will eat only what they like, resulting in spot grazing Favoured areas become overgrazed Selectivity
Plants not grazed become mature and produce seeds. With time, less attractive plants become the dominant species in the pasture As the forage supply per animal decreases, degree of selectivity decreases Stocking rates should be high enough to eliminate most, but not all selective grazing Last Words on Grazing Behaviour Horses prefer grasses to legumes Horses tend to spot graze, grazing one area close and leaving other areas Horses need space to run, so paddocks should be long rectangles
Foraging Theory What is the survival value of feed choices? Benefits (for animal) - nutritional value Costs - energy expended, time lost, exposure Cost:benefit balance - most valuable food yields most energy per unit of time or energy expended Foraging Theory and Cost:Benefit With abundant valuable feed, what strategy gains the most energy per unit of time? Taking only the most valuable Take less valuable feeds as most valuable becomes scarce Grazing Animal Behaviour Herbivores born with certain behavioural predispositions and abilities (genetic) Accumulate knowledge, refine skills Learn by experiences and from others Herd behaviour impacts individual behaviour
Bite: Which Plants? Leaves upright or horizontal, strong or weak Leaf:stem; leafy or stemmy; Nutrient value high or low Toxins or bitter contents
Good height for easy, rapid intake Prior experience with the particular species of plant Patch Abundance - how far to go between plants Familiar species attract animals Quality - colour, texture, moisture, odour, sugar, post-ingestion feeling Topography - ease of access to patch Social - who else is there? Home Range Abundance affects carrying capacity, body condition, growth rate, milk production Species influence palatability, productivity of the sward Topography affects ease of access, energy expended to get the grazeable plants Water - 900-foot rule (cattle), wider limits on dry range - they need to access water at least once daily Cover - modify effects of wind and sun to keep in the zone of thermal neutrality (minimize energy need for homeothermy) Horses prefer open range Social - are there opportunities for natural herd and band formation? Diet Selection Based on Digestive Consequences Leafy green plants, easy to harvest, readily digestible energy and nutrients Animals have adaptive behaviours that allow them to choose forages that are more nutritious and less toxic than the average Hypothesis: Consequences of foraging direct an animal's foraging decisions Learning results in conditioned flavour aversions and preferences Animals acquire preferences if positive consequences follow ingestion, such as energy or protein enrichment, recovery from nutritional deficiency, or recovery from illness. Aversions vs. Pleasures Herbivores form aversions to foods when consumption is followed by gastrointestinal distress, especially if post-ingestive feedback stimulates nausea. Hedonic (relative to pleasure) value of flavour is modified by the feeling of well-being or illness after eating Good vs. Bad Memories Plants taste good because consumption makes the herbivore feel better
Plants taste bad because consumption makes the herbivore feel lill or unsatisfied Searching and selective grazing are cognitive processes, reinforced by other animals or humans
Ontogeny: origin and development of an organism Expression of Diet Selection Morphological characteristics are (mostly) inherited and can affect ability to digest dry matter and energy E.g. Inheritance of enzyme systems Enzyme systems for detoxifying plant chemicals are inherited Genetic Selection Interacts with Environment Selection in a domestic environment may alter ability to harvest nutrients in specific environments E.g. Holstein cattle from New Zealand, have larger mouths and use longer grazing times per day (they graze more) than US Holsteins Forage Decisions Based on Physiological State Demands vary depending on what was eaten earlier, ambient conditions (temperature, wind, moisture) and animal physiological condition (stage of production - rapid growth, slow growth, pregnancy, lactation, level of work, body condition) Do Animals Have "Nutritional Wisdom"? Lambs fed diets deficient in sodium, energy, or protein show a strong preference for foods high in sodium, energy, or protein, respectively Evidence for an ability to select foods high in other minerals which are deficient is not as clear Knowledge and Experience in Making Forage Decisions Lambs exposed to barley for thirty minutes at six months of age, readily consumed it two years later With maturity and experience, animals get more efficient at harvesting certain plants Social Interactions
Lambs raised on onion-flavoured milk preferred onion-flavoured feed later Nursing calves/foals/humans mimic their mothers Sheep averse to a pelleted diet, eat more of it with non-averse peers around Primary influence is their own experience, secondary influence is the mother, and tertiary influence is others Plant Attributes Influence Diet Plant preferences are higher for plants with rapid digestive feedback (high digestibility) Excess or deficient levels of nutrients decrease palatability (unusual ratios of nutrients as well) When consumption is followed by illness and nausea, plant aversion follows Toxins cause digestive distress, low palatability, and reduced eating drive Plant-Microbe Effects Ergot alkaloids in tall fescue or ryegrass affect receptors for neurotransmitters GABA from alfalfa may bind to neural receptors and alter suckling and nursing Some plant compounds affect internal parasites, which lower the grazing drive Selection and Rejection of Forage Patches Conditioned habitat preferences depend on escape from: fear, predators, pain, stress, hunger, heat, cold, or nausea Positive influences on preferences: satiety, relief of thirst, thermal neutrality, no pain, com for, security, or rest Dung deposits avoided, possibly to avoid parasites (smell of indole and skatole) Manure Aversion Tall green leafier forage near old dung may be avoided unless stocking density is high
Dung and Urine Patches
High N from urine encourages grass up to 4 months In hot weather, urine-soaked areas are scorched and killed Ungrazed areas around dung can reach 45% of a pasture. High stocking rate can bring this down to 10%. High hoof density breaks up manure Foraging Strategies Maximize net E gain/unit foraging time Grazing upper horizons = heavier bites Forage quality declines Time spent grazing at a location depends partly on sward structure, grazing intensity, and herbage allowance Theory: maximize E gain/unit E expended Ingestive Behaviour On new pasture, the first 20-30 bites are cautious, then new forage stimulates grazing On sparse pasture, high herbage allowance allows same daily intake as a lower allowance on denser pasture Herbivores prefer forages that can be consumed quickly (high intake rates) Recognizing Preferred Plants Sward height, leaf shape, leaf orientation, density, greenness are visual cues Flavours and memories Low stocking density = conscious decision-making High stocking density, uniform monocultures = more intuitive grazing behaviours, less selective Influence of Sward Height on Diet Selection by Horses The number of bites on patches with the highest sward height was greater than that on short patches Horses behaved as selective grazers, feeding mainly on grass taller than 7 cm A horse rarely resided on a preferred patch for a long duration of time Sampled their environment continuously, but almost exclusively returned to long patches for feeding Social Interactions Affect Selection of Feeding Areas Herd behaviour may override certain individual grazing behaviours Herd boss may initiate commencement and cessation of grazing At low stocking rates with little human interference, herd tendencies may be strong Suppression of herd behaviours may be a consequence of intensive grazing systems
Inter-Species Effects In co-grazing cattle and horses, cattle graze in the roughs (ignored by horses_ because structure of the pasture suits grazing mechanics of cattle and because they are not deterred by horse dung Cow vs. Horse Horse digestive system does not have the restriction to digest flow Horses accelerate the rate of passage of low-quality feeds Management Applications Watch behaviour of individuals and herd before planning strategies Watch resulting behaviours after implementation Adjust management to promote energetic feeding behaviour and healthy, happy horses Where animals congregate frequently, high nutrient levels and frequent smothering and trampling wil kill plants. Weeds tend to come in before grasses Horses foul the same area repeatedly Provide a small grazing area at the start of the season. This reduces the area that horses leave for droppings and maximizes grazing area Trampling Trampling makes some plants unavailable for grazing for weeks Higher stocking rates can reduce dry matter yields on pastures Trampling can cause soil compaction and puddling, adversely affecting plants by decreasing oxygen availability at root level Trampled forage will break down and contribute to soil organic matter, similar to grass clippings on a lawn Much trampling damage is repaired by frost action and activity of worms and other organisms in the soil Horse run more than ruminants on pasture, causing more trampling damage and thus requiring about 2 to 3 times more space per livestock unit (1000lbs) Grazing Activities 7-12 hours/day If hot, more at night When good forage is abundant, bigger, fewer bites/day Shorter forage requires more bites per minute and more hours of grazing per day Given the opportunity, animals will eat only what they like, resulting in spot grazing Favoured areas become overgrazed Selectivity
Plants not grazed become mature and produce seeds. With time, less attractive plants become the dominant species in the pasture As the forage supply per animal decreases, degree of selectivity decreases Stocking rates should be high enough to eliminate most, but not all selective grazing Last Words on Grazing Behaviour Horses prefer grasses to legumes Horses tend to spot graze, grazing one area close and leaving other areas Horses need space to run, so paddocks should be long rectangles
