Learning About Horses - Young Horse Nutrition

In my quest of knowledge I found out about a webinar "Young Horse Nutrition" from Kentucky Equine Research featuring Dr Clarissa Brown-Douglas PhD. It was being held in Australia (7pm Melbourne time - so 3am my time) so the time difference was a bit of a problem as I was teaching during it so I could only be in the live part for 30 min. But I rewatched it and this is the information I got from it.

Equine growth rates and monitoring growth
Nutrition for foals
Feeding weanling and yearling
Developmental orthopaedic disease - prevention and management
Bone development

1. Equine growth rates and monitoring growth

high growth rates undesirable
balanced growth is vital

similar growth between birth and 18 months
mature size around 4-5 years
future of horse determines how rapidly they are grown
slow and steady growth important for skeleton soundness
monitoring weight gain against a growth curve allows
KER GrowTrac

Birth weight

birth weight @10% of mature weight
Heavy horse @7% mature weight
Shetland ponies @13% of mature weight
Bone mineral content at birth @17% of mature BMC
Larger mares deliver larger foals
Mares 7-11 and those that have foaled before have larger foals
Colts heavier than fillies
Foals born early in season smaller than later born

Foal to Weanling (0-6 months)

rapid growth
5 weeks of age - double birth weight
Average Daily Gain (ADG) 0.8-1.5kg, declining with age
6 months - 43% of mature weight 83% of mature height

ponies mature earlier than larger horses

Birth month effect on growth

winter born foal smaller than spring/summer
winter born foals grow faster at 3 months than spring born

Weanling to Yearling

seasonal factors, nutrition, genetics
weaning can influence growth (ADG - average daily gain)
ADG declines throughout winter months and increases in spring

spring pasture flush
onset of puberty

12 months 61% of mature weight 92% of mature height

2. Nutrition for foals

future equine athletes
period of rapid skeletal growth

minerals being deposited in bone
poor nutrient intake = poor skeleton

nutrition mistakes result in reduced performance potential
feed for different growth stages

foal
weanling
yearling
sales prep

Nursing supplies 100% of foal's requirements for 6-8 weeks postpartum (normal mare)
digestibility of mare's milk 98%
TB foals drink average 14.7kg milk per day
Frequency of nursing

1st day nursing @ 10 times/hour
1st week nursing @ 7 times/hour
4th week nursing @ 3 times/hour
17th week nursing @ 1.5 times/hour

Orphan Foals

if orphaned at birth, colostrum should be fed before starting on milk replacer
but only permeable to passing large immunoglobulins for 1st 24 hours after birth
nurse mare is ideal solution
if orphaned a few days after birth start on equine milk replacer
bottle feed, teach to drink from bucket
older foals may develop adequately on diet of high quality forage and creep feed
orphans on milk replaces can be weaned at 10-12 weeks of age but must be accustomed to hard feed already

Eating Solid Food

Some foals start to nibble hay or grain within days of birth

1 wk old spends 8% of day eating solid food
4 wk old spends 25% of day eating solid food
21 wk old spends 47% of day eating solid food
5 month old spends 73% of day eating solid food

foals can learn from dams to eat solid food
Foals kept in stalls with dam more likely to learn faster to consume grains or hay than horses on pastureCreep Feeding

provide nutrient dense source of feed to nursing foal

have higher daily gains
had lower weaning stress

Advantageous for some circumstances

unsure of milk production
mother excluding foal from feed
higher desired growth rate
pre-weaning desired adaptation to a post-weaning nutritional program

3. Feeding weanling

MOST CRITICAL stage of growth for preventing DOD (Developmental orthopaedic disease) is weaning to 12 months
Skeleton is most vulnerable to disease
Monitoring growth rate is vital
different diet scenarios for different breeds

Weanling Feeding Scenarios

Slow and Steady

Warmbloods, Arabs, Ponies, Heavy, non-sale Thoroughbreds
good pasture - Balancer pellet
poor pasture - quality hay + Breeding feed

Sales or Show Prep

TB, Standard Breed, Futurity Quarter Horse, etc
Quality forage
breeding feed, or balancer plus added grain, beet pulp, oil, Stabilised Rice Bran

4. Developmental orthopaedic disease - prevention and management

term used to describe a group of diseases that affect the skeleton of growing horses
often causes young horses to be removed from sales or sell below their value
include

physitis

inflammation of the growth plate also known as epiphysitis or physeal dysplasia
occurs when endochondral ossification is interrupted in the metaphyseal growth cartilage
signs are usually seen in the distal radius and tibia and distal MCIII and MTIII (cannon bones)
affected physes have the typical flared appearance
often warm to touch with or without associated lameness
horses generally present between 4 to 8 months of age
most outgrow condition as bone remodels

osteochondritis dissecans (OCD)

disturbance in articular cartilage resulting in necrosis of thickened cartilage causing joint pressure, strain, and fissures in the damaged cartilage
Dx lameness, swelling, and radiograph
most common reason to fail pre-sale radiographs
surgery considered is lesion displaced
surgical removal if economic benefit of a "clean" joint outweighs the cost of the procedure and convalescence

wobbler syndrome
Angular limb deformities

Factors that contribute to DOD

nutrition
genetics
environment
management
injury
stress - mechanical

OCD and body size

evaluate the relationship between size and skeletal problems
318 foals from 12 individual foal crops
6 Thoroughbred breeding farms in Kentucky 2013-2017
Survey radiographs (winter/spring of yearling year) showed 16% had OCD (most in hock) and 24% sesamoiditis
heavier and taller foals had greatest incidence of OCD
during their first month, foals that were heavier than the population median (50th percentile) had 3 times greater chance of developing OCD

Irregular Growth Rates

fluctuating growth rates with periods of slow or decreased growth followed by growth spurts may affect DOD
non-uniform growth rates can occur due to dietary and environmental stress and puberty
a pattern of slow, early growth is more appropriate for foals that will not be sold as yearlings
delaying rapid growth until after the 'window of vulnerability' for bone and joint disease (<12 months of age) significantly reduces the risk of growth related orthopaedic disease

Nutrition play an important role in pathogenesis of developmental orthopedic disease in horses

Deficiencies
Excesses
Imbalances

Mineral Deficiency or Excess

Deficiency or excess of the major bone and cartilage forming minerals: Calcium, Phosphorus, Copper, Zinc
Horse can tolerate fairly high levels of minerals
Excess in calcium, phosphorus, iodine, fluoride, and heavy metals lead and cadmium may lead to DOD
Calcium (+300% daily requirement) may lead to 2 degree mineral deficiency - interfering with absorption of other minerals P, Zn, I

Inappropriate grain choice or inadequate fortification in grain

most common scenarios:

feeding a feed for mature horse to growing horse
feeding straight cereal grain with no additional vitamin/mineral mix
feeding a premixed feed below the recommended intake
feeding a premixed feed diluted with straight cereal grains

these errors can be easily corrected by feeding a concentrate feed balancer

Mineral Imbalance

Ratio of minerals to one another is as important as the actual amount of individual minerals in the ration
Ratio of calcium to phosphorus should never dip below 1:1 and ideally should be around 1.5:1
Ratio of zinc to copper should be maintained at around 3:1 to 4:1

Best method of diagnosing mineral deficiencies, excesses and imbalance is through RATION EVALUATION

Feeding practices that contribute to DOD

Overfeeding

leads to rapid growth rate and increased body fat, which is believed to be a factor in the manifestation of DOD
Larger foals are more likely to develop OCD lesions and inflammation of growth plates
Hock and stifle OCDs tend to occur in heavier foals indicating that biomechanical forces probably involved

Avoid Overfeeding

NO simple rules about how much grain is too much
forage availability and quality will dictate grain reg
ration evaluation helpful
to reduce total intake - grass hay over lucerne
balancer pellet over complete feed
regularly weigh and body condition score young stock, ideally would like to see the last two ribs on weanlings and yearlings
NOT NOT FEED THEM too much
high protein intake is NOT a factor in DOD

Excessive Calories linked to DOD

Excessive energy intake = rapid weight gain = increased incidence of DOD
source of calories may also be important
Hyperglycemia or hyperinsulinemia implicated in pathogenesis of DOD
Hyperinsulinemia may affect chondrocyte maturation, leading to altered matrix metabolism and faulty mineralization or altered cartilage growth by influencing other hormones such as thyroxine

Glycemic Response and OCD

overall 11.5% multiple joints, mostly stifle, hock, fetlock
about half of lesions identified through routine radiography in Jan-Feb
Plasma glucose and insulin was higher in weanlings with OCD than unaffected weanlings
a high glucose and insulin response to a meal was associated with an increased incidence of OCD
OCD foals were larger
foals with extreme glycemic responses had atypical incidence of OCD

high response = high OCD
low response = low OCD

Glycemic index of the feed a possible factor
based on results of study - it would be prudent to feed weanlings concentrates which produce LOW glycemic responses

How to reduce the risk of DOD through nutrition

Broodmare nutrition
monitor growth rates
balanced nutrition during growth
feed low glycemic feed

5. Feeding the yearling

once horse has reached 12 months less likely to develop DOD
lesions that are clinically relevant as yearlings are typically formed at younger ages
correct nutrient balance is important
growth monitoring important
if clinical DOD evident, manage nutrition and growth rate

Yearling feeding considerations

colts may need more calories than fillies
good spring grass - careful not to over feed

balancer pellet

sales or show prep - increase caloric intake but monitor BCS

quality forage, lucerne hay
breeding feed plus oil, beet pulp, stabilized rice bran

6. Bone development

Maximising bone development

maximum BMC not achieved until at least 6 years
birth 17% of adult BMC
6 months 68.5% of adult BMC
12 months 76% of adult BMC
height or long bone growth is the developmental priority for young horses
Energy, protein, minerals, and vitamins are first directed to maintenance requirements, and any additional nutrients are used for skeletal growth

Exercise and bone development

free choice exercise and forced exercise increase bone mass
weanlings that underwent forced exercise up to yearling age had increased cannon bone mass when compared to non-exercised horses
TB weanlings - controlled sprint exercise plus free pasture exercise associated with increases chondrocyte viability and bone size and strength
in many cases this positive effect persisted throughout subsequent 2 and 3 year old racing