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Digestive Anatomy
Type of Digestion
Foregut Capacity % of the GIT
Enzymatic Stomach 8-15 L 8
Enzymatic Small Intestine (70 feet)
68 L 30
Hindgut
Microbial Cecum (4 feet) 28 – 36 L 15
Microbial Large colon (10 – 12 feet)
86 L 38
Microbial Small colon (10 – 12 feet)
16 L 9
Adapted: Atlas of Topographical Anatomy of the Domestic Animals, Popesko, P., W.B. Saunders
Purpose of Feeding
• Physiological Stage• Growth, pregnancy, lactation• Geriatrics
• Environment• Health & Well Being (body condition)• Clinical Conditions• Exercise
Feeding Behavior and General Considerations
• Feeding behavior affects feed intake• Forages of considerable variety are primary diets consumed by wild horses
• 65% Grasses and Sedges• 25% Shrubs• 5% forbs (such as wildflowers)
• Preference between wild and domestic horses for grasses is similar but difficult to measure and data are inconsistent.
• Highly selective grazers and will graze down to ground level.
• Prefer young, rather than mature plants
• Grasses are preferred to legumes and herbs.
Appropriate & Palatable Forage Species
• Cool Season Grasses– Perennial ryegrass, meadow fescue, timothy, orchardgrass, creeping red
fescue, Kentucky bluegrass, brome grass, tall fescue• Warm Season Grasses
– Bermuda grass, crabgrass, prairie grass, India grass, canary grass, wheat grass, switch grass
• Legumes– Alfalfa, white clover, vetch
• Herbs– Dandelion, ribgrass, chicory
• Cereals– Oats, barley Soft brome
Forage quality
Forage DE (Mcal/Kg) TDN, % CP, % DP, %
Alfalfa – early bloom 2.42 55 17.2 13.4
Alfalfa – full bloom 2.16 49 15.0 10.1
Bluegrass 2.15 50 15.0 12.6
Orchardgrass 2.2 50.0 16.0 13.5
Anti – Nutrients in Forage
• Many warm season grasses contain higher concentrations of oxalates and phytates – can lead to Calcium/Phosphorus concerns.
• Cyanogenic glycosides are high in Sorghum, Sudan grass, hybrid Johnson grass, and Sorghum – Sudan hybrids; therefore, not recommended for horses.
Anti-Nutrients in Forage
• Clostridium, Listeria can be issues with ensiled forages
• Endophyte contamination• Mycotoxins• Yellow and White Sweet Clover – Penicillium
spp. – product dicoumarol poisoning• Toxic plants
Insect Contamination - Blister beetles
• 2 species of concern– Epicauta vittat– Epicauta pennsylvanica
• Toxin = cantharidin• Fatal
Grazing Time• Constant Grazers
– http://www.youtube.com/watch?v=s5FJgsHx6gY– Accounts for up to 1.5 – 3 miles per day– Move more than cattle (damage to pasture)
• Horses will graze for 10 – 17 hours per day– Compared to cattle? – http://www.youtube.com/watch?v=L5xRBoyNIzc
• Affected by light and season– 20 – 50% nocturnal (higher in summer)
• Affected by group– Herd animals > single
• Affected by gender, age, breed– Mares > stallions– Mature > weanlings– Yearlings > 2 year olds– Arabians > ThoroughbredsCrowell-Davis, et al., 1985; Kaseda, 1993; Mesochina et al., 2000, Rogalski, 1977
How much will a horse eat?
Maximal DMI = 3 – 3.2% Body weight
Classification DMI (Kg per 100 Kg BW)
Mature horses 1.8 – 3.2
Growing horses 2.0 – 3.0
Mature ponies 1.5 – 5.2
Donkeys 2.3 – 2.6
Diet type
Hay 2.0 – 2.4
Corn silage 0.97
Mixed forage + concentrate > 2.0
General Feeding Considerations
• Meet nutrient needs while maintaining normal feeding behaviors.
• Forage based rations– Benefits? – Grain by-products, pasture, harvested forages– Forages should be a minimum of 1% of the body
weight. – Example: 1,000 Lb horse• 1% = 10 Lb
Feeding Considerations
• Does diet affect behavior? • http://www.youtube.com/watch?v=NyYLfUlwfMs– Goal is to prevent boredom that could lead to stable
“vices” and “sterotypies”• Orosensory sensations of feeds are extremely
important for horses and contribute to palatability. – Smell, texture, and taste– Prefer variety
Feeding considerations – oral behaviors
• Lack of fiber, too much grain in the diet– Reduce gastric pH (3.3 compared to 5.5)– Lower saliva production– Associated with increase oral behaviors such as “cribbing”
• Hay should be at least 14 Lb per day if pasture can’t be offered.
• Feed at least 2 types of forage, provide pasture if possible.• Feeding frequency of grain (more often is not better)• Limit concentrate feeding
– http://www.youtube.com/watch?v=b4lmVaIqZIo&feature=related
Considerations for Senior Horses• Age related changes in nutrient digestion, absorption
and metabolism may occur – Reduction in digestion and absorption in the large intestine
(5% lower digestion of CF)– 5-10% reduction in protein digestibility
• Supplemental lysine (20 g/d) and threonine (15 g/d) – may help reduce the lean tissue loss
• Dental issues• Energy requirements – decrease 15 – 20% – In the absence of disease– With disease can increase as much as 40%
Considerations for heat and cold stress
• Water – during hot periods, voluntary water intake increases 30 – 75%
• Salt should be available during hot weather• Additional vitamins and minerals do not seem
to be useful• During cold weather – DE should be increased 2
– 3%• Hay should be offered ad lib to allow horses to
feed to energy requirement
Considerations for exercise• How exercise is defined
• Light • 1-3 hours weekly• Mean heart rate is 80 beats/min• Recreational trail riding
• Moderate• 3-5 hours weekly• Mean heart rate is 90 beats/min• Show horses, light ranch work
• Heavy• 4-5 hours weekly• Mean heart rate is 110 beats/min• Eventing, race training
• Very Heavy• 6-12 hours weekly (or 1 hour speed work)• Mean heart rate is 110-150 beats/min• Elite eventing, racing
Exercise Considerations - Energy
• Digestible Energy– Light work = (0.0333 x BW) x 1.20– Moderate work = (0.0333 x BW) x 1.40– Heavy work = (0.0333 x BW) x 1.60– Very heavy = (0.0363 x BW) x 1.90
Ex. 500 Kg race horse= (0.0363 x 500) x 1.9 = 34.5 Mcal per day (> 70% more energy than light working)
Exercise Considerations - Protein• Protein requirement for maintenance
– BW x 1.26g CP/Kg BW– 500 Kg horse x 1.26 = 630 grams Crude Protein– Range of 1.08 – 1.44 as the multiplier
• Exercise losses in protein are due to: – Muscle gain– Nitrogen lost as sweat– Add protein to basal requirement
• Light = BW x 0.089 g CP (630 + 44.5 g = 675 g CP)• Moderate = BW x 0.177 g• Heavy = BW x 0.266 g• Very heavy = BW x 0.354 g (630 + 177 = 807 g CP)
– 20% more protein needed than lightly worked horses
Clinical Nutrition
• Hyperkalemic periodic paralysis (HYPP) • Polysaccharide storage myopathy (PSSM)• Developmental orthopedic disease (DOD)• Laminitis• Nutritional Secondary Hyperparathyroidism• Gastric ulcer syndrome• Colic• Enterolithiasis• Recurrent airway obstruction• Obesity
Body Condition Scoring• Necessary means of managing weight when
weighing isn’t possible. • Farm/Stable Dependent.• What is function? • It is dependent on
structure