Equine Nutrition

1

Equine Nutrition
2
Then and Now
3
Digestive Physiology
4
Digestive Physiology

• MOUTH
• Lips, tongue, and teethprehension, ingestion,
  and mastication
• Distinction from cattle the horse has upper AND
  lower teeth
• Graze closely to the ground
• More intense mastication resulting in 3 times
  faster ingestion of long stemmed hay compared to
  cattle/sheep
• However, horses chew slower and thus spend more
  time/day grazing

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Digestive Physiology

• MOUTH
• Teeth are vital to the wellbeing of horses
• Horses depend on their teeth to a much greater
  extent than ruminants
• Abnormal/diseased teeth can be a causative factor
  in digestive upsets/colic
• Can limit horses ability to utilize forages and
  compromise general health

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Digestive Physiology

• MOUTH
• Saliva
• No enzymatic activity
• Efficient lubricant to prevent choke
• Esophageal impaction
• Contains bicarbonate to neutralize pH in proximal
  region of stomach to allow for CHO fermentation
  to lactate
• Prevention of gastric ulcers

7
Digestive Physiology

• ESOPHAGUS
• 50-60 inches long
• Entrance to stomach is the cardiac sphincter
• Powerful, muscular valve
• Prevents regurgitation or vomiting

8
Digestive Physiology

• STOMACH
• Small organ comprising only 8 of GIT
• Food remains here for short period of time
• 15 minutes-2 hours
• Extent of digestion here is slight
• Thus, the small volume and rapid passage rate is
  the reason horses eat almost continuously
• Hay Burners

9
Digestive Physiology

• STOMACH
• Gastric anatomy very different
• Half mucosal surface is lined with squamous
  instead of glandular epithelium
• Nonglandular Esophageal and Saccus caecus
• Fermentation in saccus caecus region
• Glandular Fundic (HCL and pepsinogen) and
  Pyloric regions
• Sharp pH decline arresting fermentation and
  initiating proteolytic activity of pepsin

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Equine Stomach
Cardiac Sphincter
Saccus Caecus Region
Pyloric Sphincter
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Digestive Physiology

• SMALL INTESTINE
• Relatively short (21-25 m)
• Rapid transit time (30-90 min)
• No gall bladder!
• Bile secreted in response to HCl presence in
  duodenum
• Major site of nutrient absorption
• Major site of fat absorption (10-15 dietary fat)
• Unlike other speciesfat composition of diet
  impacts body fat composition

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Digestive Physiology

• SMALL INTESTINE
• Major site of nutrient absorption
• Efficiency of CHO absorption critical for
  prevention of digestive upsets caused by
  excessive CHO reaching the hindgut
• Major site of protein digestion/absorption from
  grain-based diets (50-70)
• Only 1/3 of protein from hay is digested/absorbed
  in SI

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Digestive Physiology

• LARGE INTESTINE
• Includes cecum, large colon, small colon, and
  rectum
• Contains an active population of bacteria similar
  to rumen
• Any feeding regimen that alters the homeostasis
  of the hind gut will result in digestive problems

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Digestive Physiology

• LARGE INTESTINE
• Fermentation
• FIBER ? VFA (energy source)
• STARCH ? VFA Lactic acid
• Excessive amounts of LA production digestive
  upsets
• Maximize starch digestion in fore gut
• MICROBES ? PROTEIN B-VITAMINS
• Horse can not use microbial protein
• THUS-poor quality protein is poor quality protein

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Digestive Physiology

• LARGE INTESTINE
• This is where a majority of the digestive
  problems occur
• Compaction
• Colic (Twisted Gut)
• Abdominal pain ceases LI contractions which
  result in accumulation of gases of fermentation
• More later on health problems related to
  nutrition and feeding!

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Nutrients

• As a general rule Most nutrients are digested
  and absorbed as in other monogastrics

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Water

• Largest single determinant of water intake is dry
  matter intake
• 2 L of water/kg DMI (5 L/100 kg BW)
• Exercise and hot environments will increase
  horses requirement for water
• 5-6 L/kg DMI (12-15 L/100 kg BW)
• Water repletion should be accompanied by balance
  electrolytes (Na, K)

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Water

• Excessive cold water intake can precipitate colic
  or founder
• Decreased water intake in the winter can
  predispose horse to impaction colic
• Provide warm water (7-18C 45-65F) to increase
  consumption

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Water

• Foals
• Daily milk yield of mares contains around 12 kg
  of water
• However, water intake is still vital to foals due
  to their inability to concentrate (or pull water
  out of) their urine
• As a of BW foals will have a higher water
  requirement than older, mature horses

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Nutrients

• Commercial horse diets generally contain
• 4 fat
• 7-12 protein
• 2/3 of diet CHO

21
CHO/Energy

• Digested to glucose in SI
• Preferred energy source for most tissues
• Fermented to VFA (acetate, propionate, and
  butyrate) in LI

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CHO

• Glucose main energy substrate when grain diets
  fed
• VFA main energy substrate when forage diets are
  fed

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Blood Glucose Response to Diet
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Practical Feeding Recommendation

• Horses consuming diets rich in concentrates
  (grain based diets) should be fed regularly and
  frequently to smooth out cyclic changes in blood
  glucose and to prevent colic.

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Protein/AA

• Necessary for tissue synthesis
• Inverse relationship between age and protein
  requirements
• Young horse is synthesizing more tissue and thus
  has a higher requirement
• Most expensive ingredient in horse diets
• Should not be used as a replacement energy source

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Protein for Maintenance

• Tissue proteins are broken down and resynthesized
  during normal maintenance
• 2.7 g digestible protein/kg BW0.75
• 900 lb horse 240 g digestible protein or 370 g
  dietary CP

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Protein for Growth

• Young horse with mature BW of 1000 lb normally
  gains 2 lbs/d from 3 to 6 mths of age
• However, must have adequate energy for protein
  utilization, so requirements are expressed as a
  proportion of DE
• TB and QH need 1.88 g lysine/ Mcal DE

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Protein for Growth

• Much of the growth of young horses occurs on
  pasture
• Leafy grass forages range from 5-13 g lysine/kg
  air-DM
• Meet requirements with a cereal protein source

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Macrominerals

• Ca and P
• Excessive amounts of Ca do not initiate the types
  of dietary problems encountered in other species
• 31 to 61 have been fed with no problem

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Macrominerals

• Ca and P for lactating mares
• Milk production for 5-6 months can produce a
  deficit of 1.8 kg Ca and 0.7 kg P derived from
  skeletal reserves and feed

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Macrominerals

• Na and Cl
• Most feedstuffs are deficient
• Added to ration or provided as free choice block
• Requirement ? when animal sweats
• Moderate work 100 g/d loss

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Microminerals

• Those affect bone formation
• Cu/Zn
• Horses less subject to Cu toxicity
• Mo and S do not affect Cu status as in cattle
• Deficiency fragile bones and cartilage
• Excess Zn ( 100 mg/kg) may exacerbate Cu
  deficiency

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Microminerals

• Those affect bone formation
• Mn/Si
• Required for cartilage/collagen and bone matrix
  formation Si is found in osteoblasts
• Si supplementation has been reported to extend
  work time before leg injury and reducing work
  withdrawal frequency in horses in training

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Microminerals

• Fe
• Most natural feeds rich sources of Fe
• Except milk
• Deficiencies unlikely unless heavy parasite load
• Most abused supplement in horse diets
• Mistaken belief that Fe supplementation ? PCV and
  Hb and will increase energy
• Toxicity and antagonism are more of a problem

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Microminerals

• Se
• Requirement 0.15 mg Se/kg feed
• Se content of forages/cereals determined by Se
  status of soil grown in
• Highly toxic
• 2-5 mg/kg feed
• Causes hair sloughing, bone lesions, hoof wall
  sloughing

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Se Toxicity
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Fat Soluble Vitamins

• Vitamin A
• Grazing horses meet requirement via fresh forages
• Conversion of carotenoid pigments in forages to
  actie Vitamin A
• Hay virtually devoid of Vitamin A value
• Horses off pasture can become deficient in 2
  months
• Deficiency excessive tear production
• Rare in stabled horses because all concentrates
  supplemented with synthetic Vitamin A
• Exception Feeding old feed

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Fat Soluble Vitamins

• Vitamin D
• Required for proper Ca and P metabolism
• Sufficient supplementation in concentrate feeds
  to meet daily requirement (1000 IU/kg)

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Fat Soluble Vitamins

• Vitamin E
• Works in conjunction with Se
• Necessary to prevent tying up of muscles and
  proper performance capability
• Important in maintaining normal immune function
• Fresh forages and germ of cereal grains rich
  sources
• Frequently supplemented due to instability under
  most storage conditions

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Fat Soluble Vitamins

• Vitamin K
• Required for proper clotting mechanisms
• Synthesized along with B vitamins by GIT
  microflora to meet horses requirements
• May be inadequate during first 2 weeks postnatal
  or during extended treatment with sulphonamides
• Leafy forages good source of Vit K
• Bleeders ? Vitamin K deficiency
• Expression of blood vessel fragility

41
Water Soluble Vitamins

• The horses requirement can generally be met by
  microbial synthesis of these vitamins
• However, there are situations where
  supplementation may be required
• Foals
• Horses receive extended AB treatment
• Sick horses
• Horses in hard work
• Horses receiving primarily grain diets with
  little forage

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Water Soluble Vitamins

• Biotin
• Only water soluble vitamin the have brought about
  clinically observable responses with adequate
  diets in healthy horses
• Unavailable in most cereals fed to horses
• Improves strength and growth rate of horse hooves

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Effect of Biotin Supplementation
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Feeding the Broodmare
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Feeding the Mare

• First priorityknow her body condition
• Need to ensure mare does not fall into negative
  energy balance
• How?
• Regular weighing
• Visual appraisal of BCS
• Mare should have fat covering ribs so they are
  not easily seen, but readily felt with minimal
  pressure
• Mare should be carrying her weight behind the
  shoulder and above the flank giving her a rounded
  appearance
• Should be enough fat cover over croup to prevent
  vertebrae visualization

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Maiden Mares

• Realize they are still growing
• Similar to first calf heifers or gilts
• Feed 14 CP grain mix containing 0.7 Ca and 0.6
  P and good quality hay/pasture
• Amount of feed/d 1 of BW
• It is important she enter the breeding season
  GAINING weight

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Barren Mares

• Need to know why mare is barren
• Foaling problems dystocia, foaling too late in
  season, uterine infection, old age
• Nutritional problems negative energy balance,
  too thin (lactational anestrus), loss of foal due
  to poor feeding
• Emphasize forage consumption
• May benefit from flushing (? plane of nutrition
  prior to breeding)
• No evidence that overweight mares are prone to
  infertilitymay cause foaling difficulties

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Pregnant Mares

• First 2 trimesters feed similar to barren mare
• Last 90 d of pregnancy ? in protein, energy,
  Ca, and P requirements
• 12 increase in energy requirements
• Possible to meet requirements with good quality
  forage
• Many breeders supplement with grain mix at 0.5
  of BW

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Lactating Mares

• Nutrient requirements greatest during lactation
  than any other time
• Exception hard training
• Avg. mare will produce 3 of BW in milk first 3
  months and 2 for last 3 months of lactation
• Undernutrition is SEVERE during lactation
• Greater impact on condition of the mare than on
  quality or quantity of milk produced

50
Lactating Mares

• Can affect milk production and composition with
  diet
• e.g. high fiber, low energy diets will increase
  protein and fat in milk and decrease yield
• Thus, poor pasture/hay situation would benefit
  from grain supplement (protein and starch)
• Mares that become too thin will not cycle/rebreed
  
• At weaning, it is common to remove grain
  supplements to slow milk production by the mare

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Feeding the young horse
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Young Horses

• Feeding the young horse is the most challenging
  area
• Firstthe young horse should be considered a
  potential athlete
• Secondthe young horse is growing rapidly and
  feeding errors can become greatly magnified
• Thirdall classes of nutrients must be considered
  when formulating the young horse diet

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Young Horses

• Dangerous to assume maximal and optimal growth
  are the same thing
• Rapid growth can result in a number of
  developmental disorders
• QUESTION how fast can you stimulate growth and
  not compromise proper skeletal development?
• Meet requirements for energy, protein, and
  macrominerals

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Young Horses

• Recognize that in foals up to 2 moths of age
• Nutrient requirements met solely by the mares
  milk
• Creep Feeding not recommended as free choice
  (rapid growth)
• Not exceed 1.5 of BW
• Rule of thumb 0.5 kg creep feed/month of age
• Post weaning growth lag will be minimized if
  foals are consuming creep feed prior to weaning

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Young Horses

• Energy Requirements
• Inadequate energy unthrifty appearance, slow
  growth rate, inefficient utilization of other
  nutrients
• DE requirement per kg gain increases as foal ages
  due to ? in maintenance reqt. And ?in efficiency
  of gain
• b/c ration consists of less milk and more forage

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Young Horses

• Energy Requirements
• Conservative approach to energy needs is
  necessary until relationship b/w energy intake
  and developmental disorders is determined
• Methods for reducing E intake to encourage
  moderate growth
• Increase forage consumption
• Feed small meals multiple times/day
• Feed fat instead of starch (15 fat max)

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Young Horses

• Protein Requirements
• Take into account CP and lysine concentrations
• Protein quantity and quality are important
• First 12 monthsmuscle and bone development
• Overfeeding protein is expensive and does not
  improve growth rate

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Young Horses

• Mineral Requirements
• IMPORTANT Ca and P
• 21 ratio is ideal, but 11 is more easily
  achieved
• Recognizemany of the energy sources utilized
  contain phytate bound P that is unavailable to
  the horse
• Supplement diets with inorganic P source

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Young Horses

• Weanlings
• Provide 1-1.5 of BW as concentrate
• Provide liberal quantities of high quality forage
• Free access
• Free access to voluntary exercise
• Increases bone density

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Young Horses

• Yearlings
• Assuming proper nutrition in previous
  stagesgrowth rate should be slowing
• Provide adequate protein and minerals and avoid
  excessive energy intakes
• ? muscle and bone deposition and ? fat deposition
• Feed 0.75-1.5 of BW as grain mix and liberal
  quantities of forage
• 14 CP ration

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Performance Horses
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Performance Horses

• Little is known about exact requirements
• Light work aerobic metabolism
• Uses fat stores first then CHO stores (glycogen)
• Strenuous work anaerobic metabolism
• Uses CHO stores and ATP

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Performance Horses

• Energy Requirements
• Greatest increase is here!
• Reqt. at high levels of work is 2X maintenance
• More strenuous the workmore of the diet should
  be provided as soluble CHO (starch)
• Cereal grains
• Can not meet reqt. on forage alone
• Small stomach and large reqt.
• Feed 1-1.75 of BW as grain mix and minimum of 1
  of BW as forage

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Performance Horses

• Protein Requirements
• No evidence that this requirement increases
• Increasing amount of feed to meet E reqt. Will
  increase protein intake
• This will replace protein loss to sweat and
  muscle catabolism

65
Performance Horses

• Vitamin Requirements
• Increasing vitamin intake not warranted and may
  result in toxicity
• May want to supplement B vitamins
• Involvement in energy metabolism
• Mineral Requirements
• Ca, P11 minimum
• Na, Clhuge losses via sweat
• 90 g Na
• Include 0.5-0.75 of diet as salt

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Performance Horses

• Forage!
• Still important
• Prevent stable vices (cribbing and wood chewing)
• Promotes efficient function of GIT
• 50 of needs can be met with good quality forage
• Prevent hay belly by feeding good quality,
  digestible forages cut in early stage of maturity

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Mature, Idle Horses
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Mature Horses

• Does very well on pasture or good quality hay
• 3.5 of BW/day
• If forage is limited, can supplement with grain
  mix to maintain body condition
• Generally, only supplementation required is free
  choice water and trace mineralized salt

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Stallions
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Stallions

• Specific information is lacking
• No reason to believe nutrient needs differ from
  mature horse
• Reqt. increase 25 during breeding season
• Greatest concern would be energy
• Protein, mineral and vitamin reqt. unlikely to
  vary
• Do not want stallions to be overweight
• Founder, colic, heart disease

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Stallions

• Feed 1 BW as grain and 1.3-1.6 BW as forage
• Exercise is important to maintain longevity

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Bottom Line

• Each horse is an individual and will vary in
  requirements
• Some horses get fat on air
• Some horses take much more feed than what is
  thought to be required to maintain body
  condition
• That is the art of feeding horses!!

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Common Nutritional Disorders
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Colic

• 2 categories
• Improper forage concentrate ratios
• Use of contaminated feedstuffs (minor cause)
• ? grain diets increase rate of passage providing
  rapidly fermentable CHO to LI
• ? in lactate and gas production, ? pH, changes LI
  microflora populationrelease of bacterial toxins

75
Colic

• Also, may see in spring on pasture
• Why? Immature grasses have high soluble CHO and
  H2O content, ? rate of passage and aberrant
  fermentation
• Solution DONT skimp on the hay!

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Developmental orthopedic disease

• A collection of disorders affecting the young,
  growing horse
• Epiphysitis (inflammation of cartilage in growth
  plates)
• Osteochondrosis (aberrant maturation of joint
  cartilage)
• Wobbler syndrome (OC in vertebrae causing spinal
  cord damage)
• Acquired flexural deformity

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Developmental orthopedic disease

• Causative Factors
• Strong genetic component
• Faster growing, earlier maturing, larger horses
• Injury/trauma
• Nutritional deficiencies, toxicities, imbalances
• Treatment recommendations
• Reduce energy intake
• NOT protein, minerals, or vitamins
• Offer quality hay liberally

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Fescue Toxicity

• Only affects pregnant mares grazing
  endophyte-infected tall fescue pastures
• Signs of toxicosis
• Abortion in latter months of pregnancy
• Prolonged gestation
• Dystocia
• Retained placenta
• Suffocation of foal due to abnormally thick,
  tough placenta
• Lack of udder development poor milk production
• Infertility due to damage to reproductive tract

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Blister Beetle Poisoning

• Confined to horses consuming hay produced in
  southwestern US
• Toxin produced by beetles is stable over long
  periods of time
• Beetles are baled with hay (mower conditioner vs.
  sickle mowers)
• Affected horses show severe colic, diahrea, and
  dehydration
• Death occurs within 48-72 h after ingestion

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Nutritional Poisoning

• Moldy corn (Blind Staggers)
• Mold produces toxin (fumonisin B) that is
  absorbed in GIT and has lethal effect on brain
  cells
• Cystitis (Prussic Acid Poisioning)
• Consumption of sudangrass
• Inflammation of urinary tract
• Other symptoms muscle tremors, nervousness,
  respiratory distress, death

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Wood Chewing

• NOT cribbing!
• Result of boredom or nutritional inadequacy
• Not enough forage!!!
• Direct relationship between wood chewing and
  amount of fiber in the diet
• Pastured horses will chew wood (mainly in
  spring-immature forages)
• Colic and wood chewing is reduced when hay is
  offered to grazing horses when extreme pasture
  growth is occurring

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Heaves

• Chronic obstructive pulmonary disease
• Similar to asthma in humans
• Horses may have nasal discharge, cough, and heave
  line from muscle hypertrophy caused by effort of
  expelling air
• Treatment
• Forage source ? hay
• Pasture NOT barn
• Ammonia, mold, dust irritants

83
Tying Up Syndrome

• Also referred to as Monday Morning Disease (stiff
  gait, painful muscles, sweating, etc.)
• Traditionallythought that grain feeding and no
  exercise after a consistent level of intense
  exercise was causative factor
• Treatment
• Management of grain intake
• Maintaining proper electrolyte balance

84
Founder (Laminitis)

• Excessive starch intake!!
• All about microbial ecology
• Starch fermentation lactate production
• Low pH kills all acid-intolerant bacteria
• e.g. Enterobacteriaceae, E. coli
• Dying bacteria release endotoxin (LPS)

85
Founder (Laminitis)

• Endotoxin and lactic acid in blood causes
  increased blood flow to foot and little to no
  blood flow to laminae
• Causes degeneration of the bond between hoof and
  bone to
• Rotation of pedal bone under horses BW
• Treatmentcall you vet
• Remove from feed, feed evacuation from GIT, AB
  treatment (kills lactic acid-producing bacteria)

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We are DONE!