Impaction of the rumen or manifolds, and obstinate constipation with the resulting straining or compression must be named as an accessory cause.
Severe constitutional diseases, especially the infectious fevers, aphthous fever, lung plague, rinderpest, etc., are occasional causes of abortion.
It may be brought about by direct irritation of the womb, as in ovariotomy or dilatation of the cervix, or again by death of the fœtus through twisting of the umbilical cord.
Where cattle are subjected to dry winter feeding, in the absence of ensilage or roots, on the magnesian limestones, small calculi in the kidney are almost the rule in winter and the irritation caused by these conduces to abortion.
Nor must mental influence be altogether ignored. Cows and even mares are exceedingly sensitive to the smells of decomposing animal matter, as seen every day in the vicinity of abattoirs, or in case the carcass of one of their fellows has been opened, and not infrequently in connection with carrion, and the occurrence of abortions after such excitement has been frequently noticed. Cases are on record of specially susceptible cows having had active labor pains, from being with another cow at the time of parturition. Shepherds have noticed that violent thunder storms have been followed by numerous abortions in the flocks.
The Contagious Form. Any of the usual causes of sporadic or accidental abortion may coöperate with the true infectious element and give unusual energy to it, yet it is of the utmost importance to recognize the contagion as the essential cause in all cases in which it is present. This can usually be done by a careful inquiry into the history of the outbreak.
When a herd has been continuously healthy up to the date of the introduction of a cow brought from a herd where abortion has been prevailing, and when following her arrival, one after another of the original members of the herd abort, without any apparent cause in the way of change of feed, water, barn, stalls, or general management, the evidence of the introduction of contagion by the cow in question is very circumstantial and forcible. If pregnant cows standing next to the new cow, or near to her, abort, the argument for contagion is still further corroborated. If the trouble continues in the herd year after year, attacking fresh animals some months after their purchase, the case becomes still stronger.
Or if a cow from a healthy herd is sent to a bull, that has been allowed to serve an aborting cow, and if the resulting pregnancy in the first cow is terminated by abortion, and if this is followed by successive abortions in the previously healthy herd, we may reasonably conclude that we are dealing with the infectious form. If no other appreciable cause for the trouble can be found we may reasonably conclude that this was the channel for infection.
Or a bull is brought from a herd where abortions have taken place, and some time after his arrival, the cows of the previously sound herd begin to abort, the first cases being in those that the new bull has served. The occurrence is manifestly the result of contagion.
Or a newly purchased cow aborts, and is disposed of in consequence, and another cow, placed in the same stall, in due time aborts also, and others follow in succession, especially those that stood next or near to the stall in question. Everything points to an introduced infection.