Dard records that a low, overflowed meadow in the Soane bottom near Chalons, caused blindness in nearly all horses put upon it. Bouin quotes a case of a sewage irrigated meadow in Vendée which almost infallibly produced recurrent ophthalmia in the horses fed on its products. On the other hand, oats and hay from a dry, rich soil and well harvested, are the most trustworthy food when the disease is to be dreaded.
Damp night air on wet, impermeable soils is to be especially feared as not only relaxing the system and lowering its power of resistance, but also producing a chill and thereby increasing the susceptibility.
Damp, cold basement stables are concurrent causes acting like the wet soils, the damp air, and the attendant relaxing conditions. Thierry long ago noticed that improved stable hygiene around Strassburg led to a notable decrease of recurrent ophthalmia. In 1807 horses were blind to the extent of 16.5 per cent., in 1821 to 8.5 per cent., and in 1870 Zundel found but 1.79 per cent., and few of the latter from recurrent ophthalmia.
Again the ventilation, lighting and drying of close, low, dark damp stables where the disease had previously prevailed has often practically banished the affection. Hofgeismar states that during the prevalence of the disease in a detachment of the German army in Alsace, out of 84 attacks in 700 horses 52 appeared in February and March, the period of severe weather and close stabling.
Fodders of a heating, or starchy nature, like Indian corn, buckwheat, or wheat strongly predispose to the disease, probably by inducing costiveness, slight impactions and indigestions, and in bad, frequently recurring cases the writer rarely fails to find that the animal is being fed on corn. Beans, peas, vetches and other leguminous fodders are less injurious and when grown on high, dry soils and fed judiciously they are as a rule harmless. When grown rank, badly harvested, and used to excess they become distinctly hurtful. Any fodder which has been allowed to become musty is to be avoided, since any condition which lowers the general tone of health strongly predisposes to an attack. The same remark applies to irregularities and faults in feeding. The best food and the most abundant supply will fail under such circumstances to maintain the condition, and the horse that is losing condition is becoming increasingly susceptible to this malady.
The period of dentition and training is the most common occasion for the attack, partly because this is the time when the colt is taken from the pure air and exercise of the field, into the hot, close, impure atmosphere of the stable, partly because he is made to exchange the cooling succulent grass for the stimulating ration of hay and grain, partly because he is subjected to severe constraint and much excitement in the hands of the trainer, and partly because of the irritation of the gums, the jaws and the whole head in connection with the shedding and eruption of the teeth. When injudicious biting is resorted to, to give a special curve to the neck, the consequent obstruction of the jugulars and capillary congestion in the head is another potent cause. Heavy draught and overdriving have a similar effect. In 53 cases Schmidt found that 3 occurred under one year old, 5 in the 2d year, 10 in the 3d year, 16 in the 4th, 15 in the 5th, and 4 from the 5th to the 9th years.
Influence of Season. Mayer gives a statement of the percentages seen in the various months of the year as follows: January 4.9%, February 4.7%, March 10.1%, April 15.1%, May 13.4%, June 9.9%, July 11.9%, August 6.4%, September 4.9%, October 6.2%, November 6.7%, December 5.2%. The high rate in March, April and May may have a significance in connection with the debility connected with shedding the coat, and the resumption of more active work, when somewhat out of condition, it must also be noted that this is in Germany the season of the most active trade in horses and consequent change of ownership, stabling, feeding, work and management.
Heredity must be accepted as one of the most potent accessory causes. The lymphatic constitution is of course transmitted and with it the special susceptibility. This is notorious in the case of both parents, and is of course more potent if both sire and dam were predisposed, and have themselves suffered. In the latter case the heredity of the lymphatic temperament, and of the impaired organ of vision combine to render transmission more certain. A mare may have borne a number of sound foals before suffering from the malady and then have offspring that do contract the disease. So with the stallion. Möller quotes the case of the eastern horse Turk-Mayn-Atty which served for a length of time in Prussian Studs and left a great stock of blind progeny. Lafosse records the existence of a family of horses in Southern France all of which went blind. The same cause has greatly extended the disease among fast American horses in which the great strain of the track served to intensify the tendency. The writer has seen a colt which was born blind, by a blind dam and got by a sire with diseased eyes, but still held at $300 for service. Mangin, Marimpocy and Hamon record congenital cases from parents with affected eyes.
This hereditary susceptibility is so strong and pernicious that intelligent horsemen everywhere refuse to breed from either horse or mare that has once suffered from recurrent ophthalmia, and at the Government studs in France not only is every unsound stallion rejected but the service of the healthy stallion is refused to any mare which has suffered from disease of the eyes. A consideration for the future of our horses would demand that no stallion shall stand for the public service of mares unless he has been examined and licensed as a sound animal.
Yet, as already stated, heredity is not the one controlling factor, since the offspring of the victims of this disease will often escape when brought up in a high, dry locality.