(T2) Lecture 7b - Nutrient requirements of horses Flashcards
What is the definition of a mature horse dependent on?
Breed and use
- can reach maturity as early as 2yr, or as late as 6-8yr
- horses reaching 20yr considered “aged”
How do you define maintenance energy requirements?
Talking about an ADULT animal, NOT growing or reproducing, and expressing NORMAL activity level within their TNZ.
- 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)
What is the definition of a mature horse?
Maturity ~ Skeletal maturity
- growth-plate conversion to bone
- conversion goes from bottom up
OR
Reach 86% of mature body weight at 36 months
- considered mature but that means you are no longer allocating energy for growth
What are 4 factors influencing energy requirements of horses?
- Breed
- Age
- growth
- geriatric - Reproduction
- gestation and lactation - Activity level
- maintenance
- exercise
*Some other factors: body composition, environment, disease
What is energy derived from?
Macronutrients
1. Starch
2. Fiber
3. Protein
4. Fat
What macronutrient do horses generally consume the most of?
FIBER!
- herbivorous species using fiber as an energy source; massive fermentation takes place in intestine
How is MER established/expressed in horses?
- Can be expressed as metabolic BW (BW^0.75 or BW^0.67)
- In equids, MER varied linearly with BW so there is not an urgent need to use metabolic body weight.
What forms the heat increment?
- heat of product formation
- heat of digestion and absorption
- heat of waste formation and excretion
- heat of fermentation
What would influence heat of fermentation (HfE)? Aka what macronutrient is associated with an increase in heat increment (heat loss goes up)?
Fiber and protein
- lower HI when starch and fat go up in diet
- if we want to increase the horse’s ability to maintain body temp in a colder temp we would increase protein and fiber (increase HI).
What factors influence the energy requirements of horses?
Heat production increased with hay vs. mixed diets (grain)
- fermentation
- gut size: more fiber = more fermentation = thicker gut wall = more metabolic tissue
What are five climatic variables that effect energy?
- ambient temperature
- wind velocity
- global solar radiation
- precipitation
- relative humidity
*horse must maintain constant core body temperature
What responses do extreme temperature changes cause?
Physiologic, metabolic, and behavioural responses
What are the physiologic, metabolic, and behavioural responses to cold weather?
- increased eating
- increased hair coat
- decreased rectal temperature
- decreased respiratory rate
What are the physiologic, metabolic, and behavioural responses to hot weather?
- increased sweating rate
- increased respiratory rate
- decreased feed intake
- increased water intake
How does cold increase eating?
Animal needs more energy to stay warm.
Thermoneutral zone
Metabolic heat production does not need to increase to maintain thermo-stability.
LCT = -15
UCT = +35
*varies with age, BCS, breed, season, adaptation
How much should DE intake increase for each degree below LCT?
DE intake should increase 2.5%
- no established requirements for conditions above UCT
How can feed management help animals cope with hot or cold temperatures?
Below LCT: Add fiber and protein, take out starch and fat
Above UCT: Take out fiber and protein, add starch and fat
What is total body water in adult horses?
62-68%
- decreases linearly as horse ages
Can horses tolerate water restriction for extended periods?
Yes
- most tolerated with lack of feed
- total lack of water more fatal than lack of feed
When is water balance achieved?
If: water loss = water intake
What are 4 reasons for water losses?
- Fecal losses
- more loss with hay diets - Urinary losses
- total loss varies due to diet, fluid availability and metabolic responses to temperature, exercise, and health - Respiratory losses
- Cutaneous losses
How can diet influence water loss?
High protein diet means more AA need to be deaminated; N bind together in urea and need to be excreted = more water needed to get rid of the extra N from the body.
What are 3 sources of water intake?
- Direct drinking
- Food
- fresh pasture > hay and grain
- dependent on amount eaten and dietary composition - Metabolic water
- produced during oxidation of energy-containing nutrients in the body
What are 3 water requirement guidelines for horses?
- Body weight is the main determinant of total water intake
- Healthy horses readily self-regulate water intake
- extreme cold can decrease intake - Always access to fresh, clean drinking water
How would water intake change if you switched the horse from hay to pasture?
Pasture (fresh) grass = would consume less fresh water
Hay = would consume more fresh water
What are the protein requirements of a horse?
- Require individual AA rather than proteins
- Horse is sensitive to quality (digestibility) of protein in diet
- direct correlation btw blood and dietary AAs
- thought to be little to no nutritional value of added urea or non-protein nitrogen sources
What is the first limiting AA for a horse?
Lysine
Why can you feed ruminants non-protein nitrogen (to meet AA requirements) but potentially not horses?
- Rumens are designed for converting fiberous material into microbial protein and serve as AA source digested in the SI.
- Monogastrics do not have this system. But what about horses? Some uncertainty how this happens. Hypothesis: protein in the diet can only absorb essential AA in the SI, in the LI the essential AA cannot be absorbed.
What contributes to evidence that AA in the hindgut may contribute to homeostasis? (aka does the horse actually absorb some essential AA in the LI).
- Microbes can use non-protein nitrogen to produce AA
- AA transporters in jejunum = expression in the cecum and colon
- Maximal lysine transport velocity across the large colon = to jejunum
- Free AA detected in colon of humans
What is protein digestibility correlated to?
Dietary CP content
- increase CP = increase protein digestibility
- prececal digestibility (SI) = ~51%; total tract digestibility = ~79%
Why is prececal protein digestibility so low in a horse?
Plant based diet and protein = not just free protein, substantial amount bound in the fiber that will only get released in the LI
How are protein requirements determined for a horse?
Determined through linear and non-linear regression
- increase in N = increase in protein synthesis up to a certain point
What are 3 propesed levels of DE energy for a horse at maintenance?
Minimum, Average, Elevated
- minimum = -15%
- elevated = +15%
How are lysine requirements estimated?
Based on dietary Lys content
What is a relatively crude way of getting a handle of AA requirements for a horse?
Ideal Protein
- based on formulating diet with proper AA rations and amounts
- defined as including the minimum quantity of each AA with maximum utilization of the protein as a whole
- compare all essential AAs to lysine (lys = 100)
- use ratios to estimate requirements for essential AA
What happens if a horse experiences a protein deficiency?
Deficiency decreases growth, despite adequate energy.
- weight loss in adult horses
- fetal loss in pregnant mares
- decrease milk production in lactating mares
- loss of muscle in exercising horses
What happens if a horse consumes excess protein?
Excess increases urea
- increases water loss
- decrease growth in young horses
- increase Ca and P loss in weanling horses
What would excess protein intake do to water requirements?
more protein = more urea loss, no ability to concentrate urea in the urine = have to increase H2O to get rid of nitrogen
What is the principal source of energy for horses?
Carbohydrates
- fiber, starch, sugars
What are some examples of CHO containing feeds?
hay, grass, grain
How are fiber, starch, sugars (aka CHOs) similar? How are they variable?
Contain similar amounts of gross energy. Variable amounts of DE, ME, and NE.
What fractioning systems are currently used for carbohydrates? What would be a limitation of these ‘systems’?
Non Detergent Fiber (NDF) and Non Fiber CHO (NFC)
- systems only determine total amount of fraction in the diet and don’t say anything about how fast or slow they are digested or absorbed
What are the 3 new proposed systems with 3 fractions?
- Hydrolyzable CHO (CHO-H): digested in SI
- Rapidly Fermented CHO (CHO-Fr): readily available for fermentation
- Slowly Fermented CHO (CHO-FS): slow fermentation by microbes
What can meet up to 50-70% of MER?
Cecal VFA production
- up to 70% of MER can come from digesting fiber
Digestion and metabolism of structural CHO may meet MER
- additional energy needed for exercise, growth, lactation, etc.
What are fats and fatty acids used for in the diet of a horse?
Generally used to increase energy density
- improve energetic efficiency
- enhance body condition
- diminish excitability
- help increase fat oxidation during exercise
What are the 2 essential fatty acids for a horse
- linoleic acid
- alpha-linolenic acid
How can fat digestibility be increased?
With added fats or oils
*does not affect digestibility of other nutrients
What are fats used to facilitate absorption of?
Vitamins A, D, E, and K , and source of EFA
What ratio should calcium and phosphorus be given in?
Calcium and phosphorus
~1.4:1
Calcium
- 99% found in bones and teeth for strength and rigidity
- important for muscle contraction, cell membranes, and enzymes
- homeostasis in blood is critical
Phosphorus
- 14-17% found in bone
- important for energy reactions and synthesis of nucleic acids
What dietary factors affect Ca/P absorption? How?
- Phytates
- Oxalates
- binds divalent cations
- rich in tropical grasses
Reduce availability
Examples
- napier
- guinea grass
- buffel
- pangola
- millet
- lucern
How can minerals be provided to a horse?
In a premix or block
- plant based materials are rich in phytate and oxalates that bind minerals and make them inaccessible to the horse
What 4 minerals do horses require?
Calcium, phosphorous, potassium, sodium
Potassium
- major intracellular cation
- acid base balance
- osmotic pressure
- typically met through forages
Sodium
- important for CNS, action potentials, transport systems, electrolytes
- Na and chloride requirements met with supplementation of salt; can provide a salt block
What 3 vitamins have hard requirements for horses?
- Vitamin A
- important role in night vision - Vitamin D
- key role in Ca absorption
- typically met through sunshine - Vitamin E
- for immune fxn
What is a possible mineral toxicity in prairies?
Selenium
When are horses susceptible to Selenosis?
If grazed on high selenium soil
What are 3 characteristics of selenium toxicity?
- corrugated hoof lesions
- hoof necrosis
- tail alopecia
