Grazing preference of different livestock ecological implications

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Grazing preference of different livestock
ecological implications

• Anna G. Thorhallsdottir
• Agricultural University
• Hvanneyri, Iceland

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Introduction

• Grazing preference is a complex function of...
• morpho-physiological factors
• inhereded
• behavioural factors
• learned
• ...and interaction of those

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The plant world the food

• In general...
• Grasses monocots
• high in fiber slow digestion
• low in nutrients
• low in defences
• Flowering plants and shrubs dicots
• low in fiber fast digestion
• high in nutrients
• high in defences
• chemical and morphological

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The plant world the food

• Grasses are poor but safe food
• have to specialize to be able to eat
• long digestion in rumen or ceacum/colon
• big size of fermenting chambers in relation to
  bodyweight
• Flowering plants and shrubs are good food but
  with complications
• defences that have to be beaten
• have to specialize to beat defences
• proteins produced by salivary glands bind toxins

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Morpho-physiological factors

• Body size in relation to fermention chamber
• small animals need more energy/body weight than
  big animals (body surface, loss of heat)
• grasses take long to digest need big
  fermentation chambers
• In general
• Animals with bigger stomachs eat more grasses
• Bigger animals eat more grasses
• Exception Moose is big but with a little stomach

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Morpho-physiological factors

• Small animals with small fermentation chambers
  need to eat high quality food
• concentrate eaters specializing in flowering
  shrubs and plants
• need to beat defences by these plants
• produce salivary liquid with proteins that bound
  to toxic compounds produced by the plants
• concentrate selectors have much bigger parotid
  glands than grass eaters

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Morpho-physiological factors

• Some other factors
• lips and tongue
• thick and unflexable in grass eaters but thin and
  flexable in concentrate eaters
• teeth
• in both jaws (horses)
• to prehend corse material grass stems
• in lower jaw (ruminants)
• use the tongue to prehend food
• size and interior surface of stomach compartments

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Behavioural factors

• Foraging consequences nutritional wisdom
• there is a neural mediated interaction between
  the taste buds in the mouth and the viscera,
  which enables the animal to sense consequences of
  the food ingestion
• Unpleasant feeling or aversion occurs with
  excesses of nutrients, with nutrient deficits or
  by food toxins
• what causes unpleasant feelings or aversions
  depends on each animals morpho-physiology and
  nutritional requirements

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Behavioural factors

• Social learning
• one animal learns from another what food to
  select and what to avoid
• foraging information can be passed safely from an
  experienced to an inexperienced forager
• especially important when dealing with toxic
  plants
• an important determinant in the development of
  diet selection of animals
• social learning is very strong early in live from
  mother to offspring
• conspecifics can be very influencial later in
  live

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All together.....

• ....Thus, between animal species there is a
  genetic basis for different grazing preference,
  but between individuals within animal species
  there is a behaviour basis for different grazing
  preference.....

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The plant world - competition

• By selecting some plant species rather than
  others, grazing animals change competitive
  ability of plant species in the sward
• Individual plants that have been grazed once are
  higher in nutritional value than ungrazed
  individuals
• grazed plants are more likely to be grazed again
• repeated grazing can cause the plant to dissapear
  from the sward

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The plant world - competition

• When dominant plant species are selected
• more plant diversity in the sward
• When recessive plant species are selected
• less plant diversity in the sward

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The plant world - timing

• Timing of grazing of vital importance
• plants stand weaker over for leaf removal early
  in the growing season
• little leaf area
• root mass not well developed
• time of setting seeds
• grazing after seed setting secures continuation
  in the sward

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Sheep

• Selective grass eater/concentrate selector
• fair sized rumen in relation to body size
• sensitive lips and tongue
• variation between breeds
• icelandic sheep
• more concentrate selector
• selects forbs and shrubs
• selects newgrowth and regrowth

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Horses

• Very much of a grass eater
• Wild horses (zebra) specialize in grass stems
• good adaption with incisors in both jaws
• will leave shrubs alone as long as other food is
  available
• will take some forbs, but prefers grasses

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Cattle

• Grass eater
• less selective than sheep
• unflexable lips and tounge
• big fermentation chamber for long digestion of
  grasses

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Summary

• Grazing animals are highly selective in their
  food intake
• There are morpho-physiological differences
  between livestock species in their ability to eat
  and digest plant food
• Behavioural adaptions for food selected are very
  important
• Grazing changes competitive ability of plants in
  the sward
• Grazing livestock can be used to modify sward
  composition