Why Can Cows and Sheep Eat Grass

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Why Can Cows and Sheep Eat Grass?

• Dr. Ben Bruce
• University of Nevada Reno
• Cooperative Extension Department of Animal
  Biotechnology
• http//www.cabnr.unr.edu/nevada_beef/

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Cows and Sheep Are Ruminants

• They produce meat and milk from forages
• The rumen allows this to happen

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Advantage to Humans

• Provides food from a source that other wise is
  useless

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Ruminants

• The rumen is a large fermentation vat
• It is temperature and pH controlled
• Buffering occurs with saliva
• Grass enters the rumen after chewing
• The true stomach and intestines is behind the
  rumen

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The Rumen Is Inhabited by Microbes

• Mostly bacteria and protozoa
• They vary in size but all are microscopic
• Each does specific things and each digest
  different feeds at different speeds

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Microbes

• Large numbers of them, billions
• Many different kinds
• Each kind does a different job
• Some digest grass
• Some digest grains
• Some are predators
• The acid content of the rumen and the kind of
  feed determine which kind grows and how many

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Microbial Life Cycle

• Microbes exist on the feed the ruminant swallows
• Their waste products provide some nutrients to
  the ruminant
• Their life cycle is in hours

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The Microbes Die

• Microbes provide food for the ruminant in two
  ways
• Waste products absorbed from the rumen
• By their death
• The ruminants lower gut digests the dead bugs
  bodies

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Other Things Microbes Do

• They make nutrients that the ruminant can use
• They digest things that many other animals cannot
• They make complex nutrients from simple things

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Microbes Make Proteins and Vitamins

• Ruminants do not need pure protein like other
  animals
• With nitrogen and sulfur bugs make proteins
• Ruminants do not need many of the the vitamins
  other animals do
• Bugs make B vitamins
• Minerals like cobalt is needed

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Some Kinds of Bugs Like Grass

• There are many different kinds of microbes in the
  rumen
• Some of them specifically like grass
• When ruminants eat a lot of grass, there are more
  of the bugs that like grass

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Some Kinds of Bugs Like Grain

• Some kinds of bugs like grain, and they dont eat
  much grass
• When the ruminant is on a grain diet, mostly bugs
  that like grain live in the rumen

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Natural Diets and Ruminant Growth

• Ruminants evolved to eat grass
• Modern human diet tastes require some fat on the
  carcass
• It is difficult to get fat on ruminant carcasses
  with grass

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Nutrient Needs

• Nutrient needs go way up to put on fat
• Why?
• Fat has 2.5 times the amount of energy in it as
  does protein and carbohydrates
• This mean a high energy diet
• I.E. Grains

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Indicators of Finish

• Visual appraisal
• Brisket
• Tailhead
• Diet, performance
• Since it requires twice as much energy to put on
  fat, daily gains go down as they begin putting on
  fat

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This Means Grains

• Change from growing to finishing
• Means increasing the grain content of the diet
• This must be done carefully
• Concerns the rumen microbes

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Rapid Diet Changes

• When the ruminants diet is changed rapidly from
  mostly grass to mostly grain, the bugs that like
  grass get sick
• They then produce poisons that can kill the
  ruminant
• Diets must be changed slowly to allow the bugs
  that like grain to grow

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To Feed the Bugs Properly

• No rapid diet changes
• Enough nitrogen, as crude protein, for them to
  make protein
• Enough minerals to make vitamins
• Water for the ruminant to make saliva to buffer
  the rumen

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From a Healthy Rumen and Happy Bugs

• Absorption of microbe waste products from the
  rumen and digestion after the rumen of microbes
• Give the ruminant energy, protein, and vitamins
• Ruminants use this for meat and milk production
• In this way ruminants and bugs make food from
  grass

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Importance of Ruminants

• People can use grass for food
• Of useable land surface
• In the US, 21 farmable and 60 useful for
  grazing
• World wide, 11 and 70

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Summary

• Ruminants eat grass because of bugs
• Keep the bugs happy
• Keep the ruminant happy
• Many hats
• feeding
• management