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Protein- What- Why- How

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Protein is a vital requirement for horses, performance, spelling, breeding, growing, and as you can expect the demand is greatest for the growing horse and the late trimester mare and less for the spelling horse, with performance horses needs being in- between those.

 Protein is utilised in the tissues of the horse predominantly the muscle, blood, organs, and skeleton. It is also a necessity for hormones, enzymes, antibodies and other body functions.
Protein is made up of amino acids – 22 of them of which many can be made within the tissues of the horse but the rest need to be provided in the feed  and are usually all readily supplied by a basic diet except possibly Lysine, which can be lacking in many feeds.

Lysine is the first limiting amino acid in the horse and threonine the second.  A limiting amino acid is described as one, that if not present, will prevent protein from being made even if other amino acids are present in adequate quantities.

The amount of protein in a diet has to be considered as underfeeding (especially the growing horse ), has negative consequences for the development of the structure of the horse. However overfeeding has negative consequences too for all horses, some of these effects to be highly detrimental to the young developing horse. Generally in New Zealand protein is most commonly over fed, deficiencies are rare in  managed horse care.


Measuring the amount of protein is sometimes confusing with feed labels stating a Crude Protein (CP) figure as a percentage of the feed; this is based on the amount of nitrogen in the feed.  However the Digestible Protein (DP) is the actual relative amount that the horse takes into the system. That is quality protein. Also affecting the usability of the DP is the necessity of the limiting amino acids to be present in sufficient quantity.  The actual quality of the protein is determined by its amino acid composition.

There are many attempts to work out an equation to provide the ratio between DP and CP ,  These measurements require faecal testing and a scientific input ,  also the results vary according to the composition of the actual feed and forage ratio, studies show that  quality protein (DP) is greater in grain diets than forage.    Suffice to say here that the DP is always lower than the CP and when assessing total protein make sure all figures are either CP or DP, and allow for  a higher % of protein if the horse is predominately on a forage/pasture diet..
Protein is measured in tables etc by in grams, but the details on the feed labels are often in %. Remember this is the CP% of that particular feed and, since it is invariably mixed with other feeds in the diet:  it is not the overall % of protein in the horse’s diet.  If a feed states a protein level of 14% it does not mean that the horse is getting an overall 14% protein content.  It is actually about quantity and the mix of the feed intake.
The NRC is an internationally recognised institution that provides data on feed requirements for horses. One of their tables below shows the CP in grams , required by various types of horses :
Mature Weight  500kg
Class Weight, kg CP,  gm Lysine, gm
Maintenance 500 656 23
Breeding Stallion 500 820 29
Pregnant Mare      
9 months 500 801 28
10 months 500 815 29
11 months 500 866 30
Lactating Mare      
Foaling to 3 months 500 1427 50
3 months to weanling 500 1049 37
Working Horses      
Light work 500 820 29
moderate work 500 984 34
Intense Work 500 1312 46
To consider how much protein to feed, first of all look at overall feed total intake as shown below:                                  
Amount of total intake as a % of Body Weight
Mature Horse maintenance                             1.6 
Stallion                                                                 1.6
Pregnant Mares                                                  1.6
Lactating Mares                                                  2.3
Lactating 3 months to weaning                        2.0
Working Horse – light work                              1.8
moderate Work                                                   1.9
hard Work                                                            2.3
Weanling 6 months                                            2.5
Yearling                                                                2.3
18 months                                                            2.0
2 Year old                                                            1.9
( ref Equi-analytical laboratories ).
Therefore a lightly worked 500 Kg horse should consume at least 8 Kg of part forage (at least 65%) and part concentrate feed (35%).
A lactating brood mare should intake 11.5 Kg in the first few months and 50% forage and 50% concentrate.
So just for a simple example let’s take a light working horse
 1 Kg of Lucerne chaff  (or similar  fibre mix type forage ) , the average protein ( CP) is 18% so is 180 gms of CP
1 Kg of extruded barley   average CP is 12% so 120 gms
1 Kg Coprameal , the average (CP) protein is 17% so 170 gms of CP
5 Kg Meadow Hay / Grass at   CP 8%  is 400 gms of CP
Total is 870 gm CP – according to the table above that is spot on for a light workhorse , that is an overall CP of 10.8 %

 Looking at quality protein here,  the Coprameal is low in Lysine so the release of the quality protein is limited by that, so an addition of 30 gms  of Lysine will then make this feed with more DP quality protein. If Soybean was substituted this has a higher level of lysine and so provides more of the quality protein but at a greater cost. Generally it is more economic to use Coprameal and supplement as needed, the addition of Lysine positively influencing the quality protein in all the feed.  The minimum level of lysine should be about or above 4 percent of the total crude protein intake, especially for growing horse’s diets. Again it may be possible to assess the lysine in the feedstuff if they are pre- mixed feeds with full labeling. Consideration should always be give to the Lysine content when calculating the protein intake, too low and the protein differential between CP and DP is much greater, so less quality in the final percentage .

As stated above the protein requirement will increase under various demands, in order to provide for that increased need ,  all that is necessary is to feed more of the full diet, not increase the % protein in the diet. Balance as always is the key to good nutrition and therefore health, and the ratio of fat – carbohydrate - protein is an important balance criteria.

The negative effects of over feeding protein young horses have been studied and documented , findings indicate potential blood insulin levels become too high, negative bone disorders can occur and they have suggested that even in growing young horses, it is more advantageous to reduce  protein  when the diet is proportionately supplemented with Lysine and it will still support maximum growth response. Actual results (E.A. OTT et Al) shows that reduction of concentrate protein and subsequently the feed intake of the animal, decreases the blood insulin concentrations which may be advantageous in helping minimise bone development problems. “There is no question that gross overfeeding of high protein grain feeds will help precipitate DOD in susceptible horses “ (L. H Breur KER Library”)
More research data such as Growth of Thoroughbreds (W.B. Staniar et al) fed a low protein intake but fortified with lysine and threonine concludes that fortifying the diet with Lysine and Threonine, improves protein quality and enables full realisation of genetic potential for growth, while raising horses on forages with a lower protein concentration.

bodybuilderIn addition other research has shown that horses in work and strenuous exercise may benefit from lower protein concentrate and lysine threonine supplementation.  Heat production from higher levels of protein may interfere exercise by attenuating fatigue (Kronfeld) and an increased acidity will interfere with glycolysis and muscle fibre contraction (Mainwood and Reynaud), i.e. restriction of dietary protein may be beneficial during strenuous exercise by diminishing production of heat and acid. (P.M. Graham-Thiers et al).
Excess protein may be utilised as energy but this produces blowing & overheating. The Urea levels in the blood increase leading to greater urea excretion into the gut which increases the risk of gut disturbances and enterotoxaemia. Also it causes increases in blood ammonia creating nerve irritability edgy behaviour plus disturbances in carbohydrate metabolism . ( Pagan)

An indication of high protein in stabled horses is the ammonia smell in the bedding, this too can create respiratory issues fro the stabled horse.
There is evidence that over developing the muscles actually has a binding effect on them – a good analogy is that of the body builders who make themselves looked bulked for competition but in no way could work as an effective athlete.

Horses overfed protein, or unnecessarily given protein supplements in the hope of increasing growth rate or obtaining a muscled-up look,  are in fact in danger of all the above mentioned issues.

There is no substitute for a balanced diet and horses in poor condition are healthier if they improved by a regime containing a higher fat ratio  than too high a protein level. Once the energy portion of the fat has been utilised the rest will create condition. That is another article ...

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