13: Nutrient requirements of horses Flashcards
What is a mature horse
Depends on breed/use
- can reach maturity as early as 2 years, late as 6-8 years
- horses reaching 20 years considered “aged”
What might be a better definition of mature horse
Development of skeleton (skeletal maturity)
Growth plate conversion to bone
Why might the definition of considering a horse ‘mature’ when they reach 86% of mature body weight at 36 months be problematic?
Growth is still required, so just feeding MER will not allow for growth
Factors that influence energy requirement of horses
- Breed*
- Age: growth, geriatric
- Reproduction: gestation and lactation
- Activity level: maintenance, exercise
- Environment
- Sex
- Muscle mass
Energy is derived from which nutrients? In what proportion would the horse generally consume these nurients?
Macronutrients
- starch
- fiber
- protein
- fat
Fiber > starch > protein > fat
Slide 9
Look
What is the maintenance energy requirement? Does not include… In horses?
Amount of dietary energy needed to prevent change in total energy contained in the body of a horse
Does not include energy needed to support additional activity (gestation, lactation, growth, performance)
MER expressed as BW in horses (not metabolic BW); MER varied linearly
Seven factors of daily heat production
- heat of basal metabolism
- het of voluntary activity
- heat of thermal regulation
- heat of product formation
- heat of digestion and absorption
- heat of waste formation and excretion
- heat of fermentation
Which parts of daily heat production form the “heat increment”
- heat of product formation
- heat of digestion and absorption
- heat of waste formation and excretion
- heat of fermentation
How does diet affect heat increment
Go up or down depending on diet (more fiber or protein = goes up, more starch or fat = goes down)
Depending on efficiency of conversion into E of the macronutrients (massive E losses in protein as excess needs to be converted to urea)
Slides 11, 12
Heat increment
Daily MER requirement of horses
30.3 kcal DE x kg BW
What type of energy is used to calculate horse MER? Why??
Digestible energy
It would be more difficult to calculate ME values in horses (would need to collect feces and urine daily)
MER in horses is calculated for… What problems could this cause?
Calculated for confined animals, used as minimum or base
Provides a low requirement, not accounting for moderate/regular activity of MER
Calculate average and elevated requirements using 33.3 kcal DE/kg for average (10% increase) and 36.3 kcal DE/kg for elevated (20% increase)
Slide 14
Minimum, average and elevated requirements
Five climatic variables that effect energy
- ambient temperature
- wind velocity
- global solar radiation
- precipitation
- relative humidity
Physiologic, metabolic and behavioural responses to cold vs hot tempertures
Cold: increased eating, increased hair coat, decreased rectal temperature, decreased respiratory rate
Heat: increased sweating rate, increased respiratory rate, decreased feed intake (reduce heat increment), increased water intake
What is the thermoneutral zone? What affects it/what are the values in horses
Metabolic heat production does not need to increase to maintain thermo-stability
Varies wit age, BCS, breed, season, adaption
- lower critical temp = 15C
- upper critical temp = 35C
How can feed management help animals cope with hot or cold temperatures?
Heat increment
- if it is hot, prepare a diet that has more fat and starch (lower heat production)
- if it is cold add more protein and fiber. Also increase DE intake by 2.5% for each degree below LCT
What is the main determinant of water intake in horses? Average maintenance water intake?
Body weight
5 L/100kg BW/d (but varies a lot)
Four forms of water loss? What is water balance
- Fecal losses (more loss with hay diets)
- Urinary losses (varies due to diet, fluid availability, protein, moisture content of food)
- Respiratory losses
- Cutaneous losses
when water loss = water intake, water balance = 0
Sources of water in horse diet
- Direct drinking
- Food (fresh pasture contains 80% moisture, hay and grain 10-15%): depends on amount eaten and dietary composition
- Metabolic water: produced during oxidation of energy-containing nutrients in the body
Protein/amino acid requirements
Require individual amino acids rather than protein
Lysine first limiting aa
Horse is sensitive to what related to protein?
Quality of protein in diet
Adding urea or non-protein nitrogen sources to horse diets. Why is this different than cows?
Little no nutritional value
In ruminants, rumen microbes can convert some non-protein nitrogen back into microbial protein that can be degraded in the SI into individual aa’s
Might be some microbial protein production in horses, but it would be in the LI
Slide 22
Look
How to increase protein digestibility in horses? Why is ileal digestibility so low?
Increase CP in diet (add high quality protein sources)
Protein in forage has poor digestibility
Slide 24
Slide 26
Look
Effects of protein deficiency in horses
- Decreased growth
- Weight loss in adult horses
- Fetal loss in pregnant mares
- Decreased milk production in lactating mares
- Loss of muscle in exercising horses
Effects of protein excess in horses
- Increases urea
- Increases water loss
- Decreases growth in young horses
- Increases Ca and P loss in weanlings
Principle source of E in horses?
Carbohydrates
Look at slide 28, 29
What are fats and fatty acids used for in horse diets?
- to increase energy density
- improve energetic efficiency
- enhance body condition
- diminish excitability
- help increase fat oxidation during exercise
Essential fatty acids in horses? Requirements?
Linoleic acid and a-linolenic acid
No set requirements
Fat digestibility of different sources of fat? How to increase fat digestibility
42-49% for forages
55-76% for grains
88-94% for added fats and oils
Increase fat digestibility with added fat or oil
Fat is used to facilitate absorption of… and as a source of…
Vitamins A, D, E and K (fat soluble vitamins)
And as a source of essential fatty acids
Why is calcium required?
- Strength and rigidity of bones and teeth
- Important for muscle contraction, cell membranes and enzymes
- Homeostasis in blood is critical
Why is phosphorus required? Ideal Ca:P ratio for horses?
- important for energy reactions, and synthesis of nucleic acids
~1.4:1
Dietary factors affecting Ca/P absorption? Examples of dietary components?
Phytates, oxalates; reduce availability of Ca/P
E.g. napier, guinea grass, pangola
Mineral requirements in horses? What are their functions?
Potassium: intracellular cation, acid base balance, osmotic pressure
Sodium: CNS, action potentials, transport systems, electrolyte
Vitamins required in horses and why
Vitamin A: role in night vision
Vitamin D: role in Ca absorption, met through sunshine
Vitamin E: for immune function
