7.1 - Horses

horse

monogastric herbivore

post-gastric fermentation

• non-ruminant herbivores/hind-gut fermentors

• small stomach capacity (2-4 gallons)

  • empties when only 2/3 full → safety mechanism; prevents stomach rupture

    • horses can NOT vomit

• hind-gut capacity of 23-30 gallons

• feed movement

  • stomach → SI → hind-gut

    • SI is where most starch, sugar, fat, vitamins, minerals, & ~half of protein is digested and absorbed

    • hind-gut holds fiber material while bacteria & microorganisms work to digest it

      • fiber digesting bacteria produce VFAs (used by both bacteria & horse for energy)

    • horses on total forage receive ~70% of energy from VFAs

horses evolved as grazers

• estimated that a horse spends ~10 - 17 hours grazing each day

  • broken up into ~15 - 20 grazing periods

• 70% of daylight hours & 50% of night hours spent grazing

• horses that have restricted grazing time eat with greater intensity when they have access to pasture; can ingest a quantity of pasture far above what the avg. horse eats

wild vs stabled horse

• stabled horses are deprived of normal grazing activity

• horses grazing in natural state, eating & non-eating periods are interspersed

  • eating periods rarely separated by more than 2-3 hours

• stabled horses fed 2-3x/day → long periods between meals

• horses consuming typical hay & concentrated diet may spend less than 6 hours a day in eating activities

• horses in pasture environments spend 10-17 hours

• for stabled horses, hay availability should be maximized and should be offered 1 hour before any concentrates are fed

• oral vices/problems are associated with no hay/roughage being provided

pasture plants

• low in starch

• horse digestive system very efficient if fed mainly grasses & hay

• GIT doesn't work well if fed more than a few lbs of grain

  • too high in starch (50-75%), not enough enzymes to break it down

  • digestive system designed to digest grasses & hay (fiber)

• some grains better than other because of starch digestion

  • oats → very palatable, nutrient balanced (contain ~50% starch, 12% protein & fiber)

    • starch is easily digestible by enzyme in foregut

where is the starch in corn digested

in hindgut where its rapidly fermented

• can be digested in foregut if its ground, pelleted, or extruded)

• contains 72% starch — comes from whole or cracked corn

starch altering bacterial fermentation

• when horse consume lots of corn, there aren’t enough enzymes to break it down

  • starch is very compact and dense

• starch digested by bacteria that produces lactic acid in the hindgut

  • the addition of lactic acid to the hind gut lowers pH

dense corn — starch can overload gut bacteria → starch digesting bacteria produces lactic acid → lactic acid decreases pH → fiber digesters die → toxins are released → can lead to colic and founder

• feeding 5 lbs or less of grain reduces risk of colic and founder

• oats are better than corn → starch is digestible in the foregut

grazing behavior

more time devoted to grazing/eating than any other behavioral activity

• behavior has direct effect in consumption patterns & selection of feeds

• no factor is as important to animals wellbeing & productivity as the feed & forage it consumes

• ingestive behavior explains why forage is so important

what affects grazing time

• type & availability of forage

• consumption behavior

• level of nutrient demand

*during times of limited feed/drought, horses will eat when feed is present

patterns of grazing behavior

• when feed is plentiful: patterns develop

  • in response to environmental cycles (light, temperature)

  • influenced by learned behavior

    • heaviest grazing at dawn & late afternoon

    • sometimes at night (more in summertime)

    • hot weather affects grazing more than cold

    • heavy rain, strong wind, & snow cover have impact

• 10-17 hours/day spent grazing

• generally, horses will spend less time grazing good quality pasture

  • may graze poor quality pastures longer to meet nutritional requirements, horses on high quality pasture may consume forage for much longer than necessary

• horses do not stop eating when nutritional demands are met

  • leads to obesity, digestive, & lameness problems

grazing selectivity

• horses have mobile lips & large mouth

• graze close to ground & bite off selected part of plants → bite it off with upper & lower incisors

• spot grazers — eat portions of pasture down to bare ground

*selectivity decreases with decreased availability ; hunger decreases selectivity

preference

• leaves > stems

• grass > alfalfa

• green material > dry, coarse material

senses used when selecting forages

• sight

  • used to recognize conspicuous forage species

• touch

• taste

  • the sense that is most likely used to influence selection

• smell

  • plays a minor role

broodmares

• proper nutrition is critical for maintaining high reproductive efficiency

• body stores used to meet nutrient demands of fetal growth & milk production if adequate nutrients aren’t consumed

fatter mares

• have NOT been shown to have lower reproductive efficiency

• maintain a condition score of at least 5

  • with severe winters, may be desirable to have mares at a score of at least 6 (thermoregulation + gestation)

length of gestation

~340 days

last trimester of gestation

• majority of fetal growth occurs in the last third of gestation

  • may experience the greatest weight gain in the second third of gestation

    • not known if weight gains are associated with placental tissue & fluids, or whether they are actual increases in body weight

    • this pattern of weight gain is normal

can mares be pregnant & lactating at the same time?

yes — if its a broodmare that is regularly bred

• lactation & gestation often overlap

• mare can have a fertile heat 7 days after giving birth

  • if not bred at this time, bred at next estrus (21 days later)

• mare rebred for next foal within weeks of partition

weight fluctuations throughout gestation and lactation

• during 1st part of gestation, amount of fetal tissue that accumulates is very small → mare’s nutrient requirements are not substantially increased above maintenance

• mare’s nutrient requirements begin to increase in the 5th month of gestation → continues to increase into lactation

• if mare loses weight during lactation & enters 2nd trimester of gestation in suboptimal body condition:

  • nutrient intake should be increased

  • body condition score should be at least 5 by end of 2nd trimester

  *changes in body weight in gestating mares do NOT appear to coincide directly with the growth curve

weight gain during gestation

over the course of a 345 day gestation, a 500 kg mare is expected to gain 60 - 70 kgs

• foal: ~50 kg

• placenta: 10 - 20 kg

1 kg =2.22 lb

milk production

• after foaling, nutrient needs increase to meet demands of lactation

• milk production highest in first 2 months after foaling, then it declines

• amount & composition of milk is maintained even when mares are fed diets containing marginal amounts of critical nutrients

  • energy, protein, Ca, P

• mares that lose body condition during lactation may be difficult to rebreed

• feed intake usually increases after foaling

feed intake after foaling

• lactating mares can consume 2 ½ - 3 kg of total feed (forage & concentrate together) per 100 kg of body weight

• should be fed high quality forages & sufficient concentrates to maintain both their body weight & body condition score

growing horses nibble

• foals begin nibbling on solid food within a few days of birth

  • consume significant amounts of hay, pasture, or grain by 2 months

• body weight/growth rate of foals can be estimated if expected mature body weight is known

  • avg. daily gain in 1st month: 1.2 kg/day

  • decreases to 0.9 kg/day at 4 months

• if foals are NOT growing at an acceptable rate, it may be advisable to provide supplemental feed

growing horses

• foals should be fed a diet formulated to meet their needs, rather than a diet formulated for mares

• foals should not be given unlimited access to to concentrate feeds

  • daily concentrate intake for foals ranges from 0.2-0.5 kg per month of age

• each mare & foal pair should be fed individually at least 1x/day

  • foal should be given its own feed tub

acceptable concentrate feeds for nursing foals

• 16% CP

• 0.9% Ca

• 0.6% P

creep feed for growing horses

• can be used if several foals & mares are fed together

• creep feeders constructed from a variety of designs

• key feature: entryway that allows foal to enter, but excludes mares

creep feed

highly nutritious feed thats available to the nursing animal, but presented in a way so that the mare cannot steal it

• ex. creep pen, creep feeder with narrow bars, creep stall in barn

concentrate

complete diet in pelleted form

• pasture, hay, grain

weaning

• most foals weaned at 4-6 months of age

  • contribution of milk to total nutrient requirements of foal declines at ~3 months of age

  • by 4 months, supplemental feed if necessary even if foal is not weaned

• supplemental feed is critical for nutritional stress

• can minimize social stress by weaning foals into a cohort group

• weaning can cause a period of reduced weight gain

  • depression in rate of gain may be as brief as a week if foals are accustomed to eating significant amounts of pasture, hay, or concentrate PRIOR to weaning

• after weaning, foals should be fed diet that meets their nutritional needs

weaning & rebreeding

• by 6 months of age, milk provides less than 50% of foals total daily nutrient intake → appropriate weaning time

• if mare has been rebred, she will be entering the middle of gestation period — weaning of foal enables her to redirect nutrients used for lactation to the developing fetus & for replenishment of body stores

growing too fast?

• rate of gain during first 2 years of life will NOT affect mature size, but may affect age at which animal reaches maturity

• very rapid growth associated with an increase in bone & joint problems

• when more rapid growth is desired, the potential for problems can be minimized by feeding diets that have adequate levels of all required nutrients, not just energy

*optimum, not maximum growth

developmental orthopedic disease (DOD)

• include:

  • osteochondrosis

  • physitis

  • flexural & angular limb deformities

• some types of DOD may affect the soundness & future athletic capacity of horses

• nutritional factors that may contribute to DODs include:

  • low dietary Ca

  • high or low levels of P

  • unbalanced Ca & P ratio

  • low dietary Cu

  • high dietary Zn

  • excessive dietary energy

*balanced diets will minimize DODs: optimal growth

osteochondrosis

occurs when growing cartilage in the young animal fails to mineralize normally

• most commonly affects the articular region of the long bones

• may result in significant lameness

physitis

• most common in the growth plates of the long bones in the forelegs

• young horses may experience enlarged joints — very painful

flexural & angular limb deformities

include conformation deviations (standing very upright in pasterns, being knock kneed)

nutritional requirements

feeding management & dietary requirements vary with type & level of activity

• quarter horse — compete at max speed for only 400 yards

• arabian horse — competes over distances of 50-100s of miles

feeding programs for performance horses must consider factors such as: environment, stage of training, & age

exercising horses

• virtually impossible to estimate requirements for every level & type of activity for horse

• nutrient reccomendations for exercising horses is based on 4 categories of work efforts

  • light, moderate, heavy, or very heavy

light exercise

1-3 hours/week at slow speeds

moderate exercise

3-5 hours/week at slow speeds (recreational riding, lessons, shows )

heavy exercise

4-5 hours of work at higher speeds

• activities such as: jumping, polo, reining

very heavy exercise

horses that are used for racing or for elite levels of 3-day eventing or endurance competitions

notes on heavy exercise

when horse unable to maintain their body weight on a diet of 50% forage & 50% concentrate, several dietary modifications are possible

• use highest quality forage

  • early maturity hay — more nutrient dense, more palatable

• consider using fat

  • higher fat ration (4-8%)

  • top-dress veg. oil (gradual introduction)

• for endurance exercise horse on forage diet

  • need more water — hydration exercise affects electrolytes

  • significant sweat losses Na, K, Cl

  • electrolytes are NOT stored, they are needed daily

body condition scoring in exercise horses

• values show do not necessarily represent optimum BCS

• represent the common range of scores found for horse in the listed activities

colic

• severe abdominal pain

• horses may kick/bite at their abdomen, roll, & repeatedly attempt to urinate

• sweating & general signs of anxiety and discomfort

• can be mild & resolved quickly, may require surgery, or even result in death

• some cases may be cause by dietary factors

  • sudden changes in diet

  • lack of water availability

  • lack of manure

• horses with 24 hour access to pasture tend to have a decrease incidence

• horses that receive high levels of concentrate tend to have increased incidence

laminitis (founder)

may be caused by overconsumption of concentrate or lush growing pasture

• acute laminitis

  • exhibit pain & heat in the hooves

  • reluctant to move

  • often leads to permanent lameness

    • may cause death in some cases

• caused by wearing the support laminate within the hoof, leading to painful tearing of the supportive structure that suspends bones within the hoof

  • if not treated properly, the bone drops or rotates downward, causing horse to stand on tips of bone

• to reduce the potential for laminitis, horses should be prevented from eating too much pasture or concentrate

  • if a horse requires large amounts of concentrate to meet its energy need such as a race horse, it should be adjusted to diet slowly

• horses should NEVER be given more than 3 kgs of concentrate at any meal

toxic plants

trees, weeds, ornamental shrubs

• thistles, nettles, burrs

  • mechanically injurious (damage to nose & mouth)

• St. Johns wort & buckwheat

  • may produce photosensitization (in unpigmented areas) & dermatitis

• Mountain Laurel, azalea, oak, buttercups, jimsonweed, field bindweed

  • may cause colic or diarrhea

• plants that may be fatal:

  • serviceberry

  • elderberry

  • foxglove

  • oleander

  • yew

minimizing forage intake

• to allow for a more natural feeding environment, hay availability in stall should be maximized

  • offer at least 1 hour before concentrate

  • most desirable method of providing concentrate to several horses together on pasture is to bring horses into stalls for individual feeding once or twice a day

feeding concentrates

• when mature horses are maintained on good quality pasture, feeding concentrate may not be necessary

• if pasture quality is low or if horses have high nutrient requirements, supplemental hay or concentrate feed is necessary

• most desirable method: bringing horses into stalls to be fed individually

• pastured horses may be fed concentrate from individual fence feeders, ground feeders, or feed troughs

  • space far enough apart to limit fighting

• if using long trough

  • close observation necessary to ensure one horse doesn’t dominate

  • most effective for young horses

• can be fed directly on ground

  • higher feed wastage

  • increased potential for transmission of parasites

group feeding management

• when hay is fed in a group situation, waste will probably be increased

  • feeding allowances should be increased 10-20% beyond the amount that would be required if horses were fed individually

  • hay should be provided in feeders that allow enough room for all horses on pasture to eat at once

  • hay feeders designed for horses are the safest option

stocking rates

number of horses per unit of land area

• overgrazing severely limits forage intake of horse

• recommendations vary based on all variables

• most common: 1.5-2 acres per horse on improved pasture

  • fertilized, treated for weeds, cared for as source of animal feed

grass/pasture length

• grass should be 4-6 inches in length to provide optimum intake levels

  • grazed to min. of 2-3 inches, then managed so that grass doesn’t become too short or too mature

  • when height of grass decreases below 3 in, it severely reduces the nutrient intake of horses — OVERGRAZED

factors that affect stocking rates

• size of horses

• forage species

• soil type

• season

• moisture level

• fertilization

• time (access to pastures)

summary

• feed forage at rate of 1.5 - 2% of horses body weight

• if concentrates are fed: should be fed 2x/day (or more if possible), with no more than 00.5% of body weight/feed

• be aware of social hierarchy (especially when feeding horses in groups_

• anytime diets are changed, should be done gradually

• keep pastures 4-6 inches tall to avoid overgrazing

• know signs of common feed related disorders

• feed forages first