What is protein? (R)
polymers of amino acids
- usually the most expensive nutrient = so storage component = must be provided constantly
- often a limiting factor in equine nutrition
What makes up the ideal protein?
A combination of individual amino acids
Essential (indispensable) amino acids (R)
phenylalanine histidine isoleucine leucine lysine methionine tryptophan valine arginine threonine
Why is there a requirement for AAs? (R)
- growing horses are building protein (muscle)
- increased protein turnover
- all tissues are being replaced continuously
- all tissues contain protein (muscle, bone, skin, hair, hooves, even fat)
- all enzymes contain protein
- blood constituents contain protein
- some hormones contain protein
Where does protein absorption mainly occur?
small intestinal cells
- as AA’s and dipeptides
- dipeptide transport is more efficient than AA
What happens to non-protein nitrogen and protein that escapes digestion in the foregut?
enters hindgut where they are available for synthesis of microbial protein
- AA, NPN are used in cecum/colon to build bacterial protein OR absorbed as is in the blood + CO2 –> urea –> kidneys –> excretion
What is dietary NPN
- most absorbed in the SI –> excreted in urine (never reaching colon/cecum)
- little NPN is used in horse (excess is toxic)
Do AA from microbial protein synthesis contribute to AA pool?
No
- bacterial synthesis of AA - high velocity Lys transporter in colon (so horse is really only able to absorb some Lys)
What is protein quality dependent on? (R)
- protein content
- protein digestibility
- amino acid composition
What is the most labile pool of AA?
blood proteins
What is the effect of blood protein mobilization during fasting?
Lose strength
- performance goes before visual loss in muscle
What is the effect of prolonged periods of food deprivation on protein?
contractile proteins will be sacrificed to maintain metabolism
- immunosuppression may also occur
What is seen with protein deficiency
reduced growth, weight loss, poor performance, poor growth
Symptoms:
- slow hair growth
- poor hoof quality
- decreased appetite (catabolizing protein –> breakdown products –> sick feeling)
What happens when protein is in excess?
- excess nitrogen
- converted to urea
- increased urine output - Energy production
- metabolism produces heat (protein take energy to burn as its providing energy)
- storage of excess
3, contribution to developmental orthopaedic disease (DOD)
What is the major error associated with the protein digestibility calculation?
- microbial/bacterial protein = reason this experiment isn’t done in ruminants
- can feed a diet with no protein and still get protein i the faces (endogenous)
AA digestion
All show up to ribosome
- the lowest AA controls the others = limiting AA theory (limiting in the diet NOT animal)
- if AA is at 50% –> protein synthesis is limited
the “barrel” analogy
Explain protein partitioning
- loss in feces
- loss in urine
- loss in skin/hair
- retained
The protein needs of the horse are satisfied by?
- providing minimum levels of essential AA in diet to meet requirement
- provide sufficient non-essential AA and/or sufficient minerals (N) to satisfy horses needs to maintain protein balance
In the case of protein requirements, how would maintenance be defined?
the ins = outs
Protein requirements depend on?
- body weight
- bigger = more - rate of growth
- most at weaning - pregnancy
- monstrous increase - lactation
- exercise
- resistance exercise or more muscled animals = more
Dietary considerations regarding protein
- grains and their by-products are often low in certain EAAs (poor quality) and may be provided in inadequate amounts
- a wide variety of ingredients are used –> vary greatly in overall quality –> not always going to be a compliment protein
What is the problem with measuring CP?
CP = measure of nitrogen, but AA are actually what’s important
What is the relationship between protein and energy?
Energy goes up so should protein - this ratio is important!
Effect of intense exercise on protein?
Fast contractile proteins –> way greater increase in protein –> lysine requirements
