It has already been stated that each horse will require something over 15,000 feet of pure air per hour, but this by no means implies the necessity for large cubic space in the stable, as any quantity of air may be passed into and out of a space which is only sufficient to allow the animal to stand in it. Major Fred. Smith remarks that a very common error is made in considering that cubic space will supplant ventilation, and consequently too much stress has been laid on the importance of a large cubic capacity. In illustration of the error included in this assumption he takes examples of two stables . one of 600 cubic feet, and the other of 1500, a variation which is by no means uncommon. Obviously a horse stabled in each of the two spaces would require the same amount of air; and, in order that this might be supplied to each of the animals, it would be necessary that the whole of the air in the former should be changed a little over fifty.four times per hour, while in the 1500.cubic. feet space the air need not be changed more often than a little over twenty. one times per hour. The advantage, therefore, of a large cubic space is that it does not necessitate so frequent a change of air. So far as the contamination of the atmosphere included in either space is concerned, the value of a large cubic capacity is comparatively trifling, being only the difference of time which will be necessary for the contamination of the air it contains in each case, and it is hardly necessary to observe that when the air is equally contaminated the effect would be precisely the same on the animal organism, whether the stable contains 600 or 6000 cubic feet.
Breathing space for one horse in cubic feet.
Ratio of CO2 per 1000 at the end of first hour.
if there has been no change of air.
Amount of air necessary during the first hour.
Amount necessary every hour after the first.
The cubic space for army stables has been fixed at 1605 cubic feet per head, and for infirmary stables at 1900 cubic feet per head; these dimensions render it necessary, in order to provide the horse with the 15,000 cubic feet of air per hour, to change the air in the first stable (1605 cubic feet per head) about nine and a half times per hour. These dimensions suggest the necessity for very complete and perfectly controllable means of ventilation.
It is not probable that a space of more than 1000 cubic feet will be allotted to each horse in ordinary stables when only a few horses are kept, and this, with proper ventilation, will prove to be quite sufficient. Where new stables are being built under the control of the owner, the common plan of placing living rooms or lofts over the stables may advantageously be abandoned. Great height is not at all desirable, and where the roof is carried up, and ventilators are put in the ridge, a height of 10 to 12 feet to the eaves may be taken as a standard height.
The most violent advocate of fresh air and free ventilation will not deny the stableman's assertion that in a warm stable the animals' coats are rendered fine and glossy, and the horses do better on a smaller amount of food than they would in a large, cold stable, in which, whatever is done to protect them, they always put on a half-starved appearance, as the groom will designate it. The problem of how to provide a sufficient quantity of pure air in a reasonable cubic space, without keeping the animals too hot or too cold, is one that cannot be solved without incurring the expense of a somewhat elaborate system of warming and ventilation.
Where the cost of warming the air required for ventilation is prohibitive, the best method is to provide windows on opposite sides of the stables and perhaps also in one end, the windows themselves being of the "hopper" type, so that the air enters the building with an upward current, Triangular side-pieces or cheeks should be fixed to the frames so that, when the windows are open, the air cannot enter except at the top. The windows at the rear should be well above the horses' heads. As windows are provided on opposite sides of the stable, it will always be possible to open some of them, without creating excessive draughts, whatever the direction of the wind may be. If the ceiling is flat, these windows will in many cases serve adequately for inlets and outlets, but where practicable it is better to provide one or more outlets at a higher level. The continuous ventilator along the ridge, with louvre boards on both sides, is certain to prove draughty, and cannot fail to admit air when the wind is blowing strongly against it. There are many different cowls or exhaust ventilators which are more suitable for the purpose.
Much of the coldness complained of in stables is clue to defective construction; for example, the roof tiles may not be laid in mortar or "torched" with mortar underneath, and the ceiling may be neither plastered nor boarded. The result is that the warmth given off by the horses is rapidly dissipated, and in winter the stable is much too cold while in summer it may be too hot. Tiles laid in the way described above do indeed allow a constant passage of air, and are therefore useful for ventilation, but the ventilation is not (as it ought to be) under control. The windows which have been recommended can be opened and closed at will, and the exhaust ventilators are fitted with valves, operated with cords and pulleys, and by these means the inlet and outlet of air can be controlled.
According to the table, 15,000 cubic feet of air are required by each horse per hour. If the velocity of the air entering the stable is 2 feet per second, the size of the inlet opening must be 15000/2x60'x60"= 2 1/12 sq. feet.
This area would be provided by a window 3 feet wide, opening to the extent of about 8 inches. If the windows on the opposite sides of the building - that is to say, two for each horse - are of this size, the required amount of air will be admitted when only one is open. To prevent excessive velocity in the inflowing air, the top of the opening of the hopper is sometimes covered with finely-perforated zinc, but this necessitates a larger opening, as the effective area is reduced about one-half by the metal gauze.
A higher velocity may be allowed for the air escaping through the exhaust ventilator, (say) 5 feet per second, and on this basis the area, required for each horse will be 5/6 sq. foot. A ventilator with the internal circular shaft 20 inches in diameter would, therefore, serve for three horses.
In practice the areas of inlets and outlets are often less than those given above, as a certain amount of ventilation takes place through the walls and roofs and through open doors, and somewhat higher velocities are considered to be admissible.
When all is done, however, there are many days in our variable climate, when it is impossible with safety to provide by the system of "natural" ventilation the full amount of fresh air which is theoretically required. The cold draughts which would follow the attempt would be dangerous to many animals, and the choice must be made between the two evils of cold draughts and insufficient ventilation. In nine cases out of ten the latter will be considered to be the less of the two.