Technically, abortion is the term used for the expulsion of the offspring before it can live out of the womb. Its expulsion before the normal time, but after it is capable of an independent existence, is premature parturition. In the cow this may be after seven and one-half months of pregnancy. Earl Spencer failed to raise any calf born before the two hundred and forty-second day. Dairymen use the term abortion for the expulsion of the product of conception at any time before the completion of the full period of a normal pregnancy, and in this sense it will be used in this article.
Abortion in cows is either contagious or noncontagious. It does not follow that the contagium is the sole cause in every case in which it is present. We know that the organized germs (microbes) of contagion vary much in potency at different times, and that the animal system also varies in susceptibility to their attack. The germ may therefore be present in a herd without any manifest injury, its disease-producing power having for the time abated considerably, or the whole herd being in a condition of comparative insusceptibility. At other times the same germ may have become so virulent that almost all pregnant cows succumb to its force, or the herd may have been subjected to other causes of abortion which, though of themselves powerless to actually cause abortion, may yet so predispose the animals that even the weaker germ will operate with destructive effect. In dealing with this disease, therefore, it is the part of wisdom not to rest satisfied with the discovery and removal of one specific cause, but rather to try to find every existent cause and to obtain a remedy by correcting all the harmful conditions.
NONCONTAGIOUS ABORTION.
As abortion most frequently occurs at those three-week intervals at which the cow would have been in heat if nonpregnant, we may assume a predisposition at such times owing to a periodicity in the nervous system and functions. Poor condition, weakness, and a too watery state of the blood is often a predisposing cause. This in its turn may result from poor or insufficient feed, from the excessive drain upon the udder while bearing the calf, from the use of feed deficient in certain essential elements, like the nitrogenous constituents or albuminoids, from chronic, wasting diseases, from roundworms or tapeworms in the bowels, from flat-worms (flukes, trematodes) in the liver, from worms in the lungs, from dark, damp, unhealthful buildings, etc. In some such cases the nourishment is so deficient that the fetus dies in the womb and is expelled in consequence. Excessive loss of blood, attended as it usually is with shock, becomes a direct cause of abortion.
Acute inflammations of important organs are notorious causes of abortion, and in most contagious fevers (lung plague, rinderpest, foot-and-mouth disease) it is a common result. Affections of the chest which prevent due aeration of the blood induce contractions of the womb, as shown experimentally by Brown-Sequard. Pregnant women suffocated in smoke aborted in many cases. (Retoul.)
Ergoted grasses have long been known as a cause of widespread abortion in cows. The ergot is familiar as the dark purple or black, hard, spurlike growths which protrude from the seeds of the grasses at the period of their ripening. ([Pl. V].) It is especially common, in damp localities and cloudy seasons on meadows shaded by trees and protected against the free sweep of the winds. The same is to a large extent true of smut; hence, wet years have been often remarkable for the great prevalence of abortions. Abortions have greatly increased in New Zealand among cows since the introduction of rye grass, which is specially subject to ergot. As abortion is more prevalent in old dairying districts, the ergot may not be the sole cause in this instance.
The riding of one another by cows is attended by such severe muscular exertion, jars, jolts, mental excitement, and gravitation of the womb and abdominal organs backward that it may easily cause abortion in a predisposed animal.
Keeping in stalls that slope too much behind (more than 2 inches) acts in the same way, the compression from lying and the gravitation backward proving more than a predisposed cow can safely bear.
Deep gutters behind the stalls, into which one or both hind limbs slip unexpectedly, strain the loins and jar the body and womb most injuriously. Slippery stalls in which the flooring boards are laid longitudinally in place of transversely, and on which there is no device to give a firm foothold, are almost equally dangerous. Driving on icy ground, or through a narrow doorway where the abdomen is liable to be jammed, are other common causes. Aborting cows often fail to expel the afterbirth, and if this remains hanging in a putrid condition it is most injurious to pregnant cows in the near vicinity. So with retained afterbirth in other cows after calving. That some cows kept in filthy stables or with slaughterhouses near by may become inured to the odors and escape the evil results is no disproof of the injurious effects so often seen in such cases.
The excitement, jarring, and jolting of a railroad journey often cause abortion, especially as the cow nears the period of calving, and the terror or injury of railway or other accidents proves incomparably worse.