07 Jan Iron as a trace mineral in performance horses
Iron (Fe) is the trace mineral most often associated with exercise, even though its true relevance is questionable.
Well known function of the Iron is being a part of heme molecule.
This is but one of the important functions of Iron but is the basis of the interest in iron and the performance horse.
In early 1886 it was shown that hemoglobin of horse contained 0.33% iron, approximately 67% of Iron in body is contained in red blood cells in the form of hemoglobin, when these RBC ‘die’ iron contained in the heme is released and utilizes to synthesize new Heme molecule and RBC as well, there is rarely net loss of iron in the body but there are exceptions to this :
severely parasitized horses, horses which suffering EIPH (exercise-induced pulmonary hemorrhage) and horses with ulcer and erosion in gastric mucosa which leads to blood loss.
Also, peroxidases and catalases and cytochromes are Iron containing compounds in body which cytochromes, like hemoglobin are associated in Oxygen utilization via electron transport.
Hemoglobin requires Fe for its synthesis and is the component of the red blood cell which allows oxygen to be carried to the tissues.
The first symptom associated with iron deficiency is anemia. Anemia occurs when there is a decrease in the number of red blood cells, which can be measured by red blood cell count or hemoglobin concentration.
It can develop from loss, destruction, or lack of production of red blood cells. Anemia is classified as regenerative or nonregenerative.
The anemia associated with iron deficiency is hypochromic, microcytic anemia.
There are few instances, however, when practical diets would result in iron deficiency anemia.
In the previously mentioned study of Carlson, horses which received supplemental iron had iron levels which were in the normal range for adult horses.
Very few of the supplemented horses examined had any evidence of anemia and those with resting hematocrits below 34% (defined as anemia) showed no evidence of impaired iron status.
This scenario is frequently the case and it is rare that a horse with a lowered hematocrit responds to supplemental iron. Lawrence et al.
(1987) failed to show an increase in hemoglobin, hematocrit or serum iron when ponies were supplemented with high 322 Micromineral Requirements in Horses levels of iron.
More times than not, low hematocrits are an indicator of infection, low-grade systemic disease or even marginal B vitamin status.
Meyer (1987) suggested that the iron requirement of the 500 kg horse is 500, 600 and 1200 mg/day for light, moderate and heavy exercise, respectively.
High levels of iron supplementation may affect the availability of other minerals in the diet. Lawrence et al.
(1987) reported that high levels of dietary iron supplementation (500 and 1000 mg/kg) depressed both serum and liver zinc. Pagan (1998b), however, failed to show any correlation between iron content and mineral digestion in diets with a wide range of iron content (127-753 ppm).
Most of the iron in this study was not supplemented and was probably in the form of iron oxide.
Main Sources of Iron in the Horse’s Diet
The typical equine diet will provide at least 100 mg of iron per kg of dry matter daily.
That means that our 500 kg horse eating 2 percent of its body weight in dry food per day (10 kg) will consume at least 100 mg x 10 kg = 1,000 mg of iron per day.
In many cases, however, this amount may be much higher because of soil contamination in the forages our horses eat. It’s not unusual to see iron analysis on hay samples between 200 to 500 mg per kg of dry matter (of the forage).
Some of this iron will be part of the grass plant, but a substantial proportion of it will be from the soil contamination inherent in stored forages for horses.
Soil is loaded with iron, and despite our best efforts, horses inadvertently consume it.
Even horses on pasture will be consuming some soil, but the good news is that much of the iron in soils is not available for absorption in the small intestine of a horse.
If the iron consumed cannot be broken down to the absorbable form Fe2+ in the acidic environment of the stomach, it will pass through the digestive tract of the horse and into the manure.
Iron in Forages or Feeds Like Beet Pulp
The iron inherent in grass plants, such as pasture or hay, could be from either digestible or indigestible iron sources.
Plants use iron in photosynthesis and store iron as a substance called phytoferritin.
This stored iron is usually, but not always, available for uptake in the small intestine.
The digestibility of iron in plants is a function of the maturity and fiber content of the plant.
Fermentation of the forage fiber in the hindgut will release any iron associated with it, but iron cannot be readily absorbed by the horse once it passes from the small intestine.
Beet pulp is an excellent example of this. An analysis of beet pulp will show that it often contains high iron levels, but two factors significantly reduce its potential impact on the iron status of the horse.
Firstly, the iron in beet pulp is largely in a form unavailable to horses, and therefore will pass through the gut into the manure. Secondly, beet pulp is loaded with a hindgut fermented complex carbohydrate called pectin.
The iron in beet pulp tends to be associated with these complex carbohydrates and will only have the potential to become free iron once the beet pulp has undergone fermentation in the hindgut.
Because the horse’s gut absorbs iron primarily in the small intestine, the chance of free iron in the hindgut being absorbed is greatly reduced, if not entirely eliminated.
Iron in Water
Water can actually be a more potent source of free iron in your horse’s diet than any feed because frequently the iron in water is in the soluble ferrous (Fe2+) form, as opposed to the more stable ferric (Fe3+) form.
Water can be a more insidious source of available iron in the equine diet, and should be tested if you have concerns.