Protein

Protein Overview:

• Required by animals for normal growth and development

• Some are found in the diet, others are synthesized by the animal

• Vital component of blood, enzymes and hormones

• Required for milk production

• Found in cell walls of plants, cell membranes in animals, hormones, bones, skin, hair and muscles

• Composed of amino acids (acid compounds linked together)

  • Contain nitrogen, carbon, hydrogen and oxygen

  • Each type of protein maintains the same specific proportions of amino acids

Measuring Protein:

• Total protein in feed is called "crude protein" — an indirect or "crude" estimation of the feed's protein content

• Crude protein is not fully digestible; the digestible amount is called "digestible protein," roughly 40-80% of the crude protein amount

• Proteins are measured and expressed in grams

Food Triangle: Forage (Crude Protein %) — from Iowa State:

• Mature/maintenance horses: 8%

• Weanlings: 15%

• Adult working: 12%

• Takeaway: Unless they are growing, lactating, or in hard work, good quality hay should meet the need

Protein: Amino Acids:

• Reminder: Amino acids are the building blocks to proteins

• Complex molecules containing carbon, hydrogen, oxygen, and nitrogen compounds

• A short chain of amino acids is called a peptide; when peptides join together, we call them proteins

• More than 20 amino acids have been discovered

• Growth, development, and almost every bodily function depends on protein, but the quality of protein is dependent on the correct supply of amino acids

• For tissue formation to occur, all necessary amino acids must be in the digestive tract simultaneously

Protein: Amino Acid Categories:
Amino acids can be divided into 3 categories:

1. Essential — the body cannot produce sufficient amounts itself; must be provided by the diet; condition and circumstance determine the specific type needed

   • Limiting (a type of Essential): when the absence of it causes growth depression; must be supplied by a quality protein source (e.g., Lysine)

2. Non-Essential — synthesized or produced by other amino acids and nutrients in the digestive tract (not required in diet)

Amino Acid Chains:

• If the first three limited amino acids are present in the horse's diet in correct quantities, you can be sure the rest are there for proper protein synthesis

• If there is not enough lysine (the first limiting amino acid), there is a break in the "chain" that limits the horse's protein synthesis from proceeding

• The break cannot occur in any of the first three limiting amino acids or the chain stops there — lysine, methionine, and threonine must all be present in adequate amounts

High quality protein feed:

Lots of digestible, essential amino acids → the horse can build lots of muscle proteins → there are not many amino acids left over that the horse has to excrete

Low quality protein feed:

Not many digestible, essential amino acids → the horse can't build many muscle proteins → there are lots of amino acids left over that the horse has to excrete

Essential Amino Acids:
There are 10 essential amino acids, each needing to be provided to horses daily:

• Arginine

• Histidine

• Isoleucine

• Leucine

• Lysine — very involved in growth/development (first limiting amino acid)

• Methionine — very important for hoof and hair quality

• Phenylalanine

• Threonine — very important in tissue repair

• Tryptophan

• Valine

Protein Relevance:

• When conditioning horses, muscles are torn down with exercise and need additional amino acids

• For just a 45-minute workout, replacing 4-10 ounces of amino acids can greatly benefit a horse

• Research has also shown a relationship between minerals and amino acids, suspecting a lack of amino acids can negatively affect how minerals are utilized in the diet

• Given the huge impact minerals tend to have on skeletal and soft tissue development, this could cause major problems in these areas

• Amino acid content in body structures (The Horse Portal)

• Hair and Hoof: 95%

• Muscle: 73%

• Tendon: 93%

• Bone: 30%

• Skin: 90%

Protein Rations:

• When formulating a ration, we have to consider protein quality and quantity

• QUALITY refers to the amino acid makeup

• Rations with fewer ingredients may not contain a good variety of amino acids (e.g., Hay and Oats)

• Feeding a variety of proteins is the easiest way to ensure your horse has enough of the "amino acid alphabet"

• Including several different grains and/or protein sources is advantageous

Protein Sources:

• Feed processing and handling methods can influence quality and digestibility

• High temperatures or inadequate drying time can reduce amounts of amino acids

• High quality protein includes legumes, young grass pastures, soybean meal, canola meal and linseed meal

  • Soybean meal is rated the best quality due to a higher amino acid profile

• Moderate to low quality proteins are cereal grains — these often appear high in crude protein, but low in quality

Deficiency:

• Protein deficiency is quite rare; EAA (essential amino acid) deficiency is more common

• In young horses: impairs growth (slower development or stunted)

• In older horses: decreases appetite, creating lower BCS, rough hair coat, delayed hoof growth

• In lactating mares: lower milk production, weight loss, and subsequent poor foal growth rate

Excess:

• Can simply be stored as fat, used for energy, or eliminated in the urine

• However, utilizing protein as a source of energy is not efficient

• Too much protein will increase water demand, due to waste products during protein metabolism requiring large quantities of water — this could strain the kidneys

• Excess is common if a horse is being fed pure legumes

• May result in protein bumps