Pregnancy or gestation is that period of time during which the fetus is undergoing de velopment in the uterus of the mother, a period extending from the time of fertilization of the ovum until the birth of the young. The modi fications which necessarily talce place during this period are of a very profound character, and exert an important influence upon the life and nutritive powers of the mother. The vol ume of the uterus becomes greatly increased in order to accomodate the fetus and its mem branes. Pregnancy is manifested in several ways by the female. However, no single sign observed should be considered diagnostic hut when several of the indications are manifested and noted in conjunction the diagnosis of preg nancy may be made with certainty. The signs of pregnancy are: the cessation of estrum; a more quiet and peaceful disposition; a tendency to talce on lat more rapidly; and the enlarge ment of the abdomen so that it bulges below and to each side. Further and more positive signs are: movements of the living fetus which may be observed in the flank and along the sides of the abdomen; touching or feeling the fetus through the walls of the flank; and aus cultation of the fetal heart-beat The earliest positive diagnosis of pregnancy may be made in the larger animals by palpation of the uterus through the rectum.
The duration of pregnancy or what is known as the period of gestation in domestic animals varies with the species. In the mare gestation is 330 to 340 days, in the cow 280 to 285 days, in the sheep and goat 21 to 22 weeks, in the pig 16 weeks, in the dog 9 weeks, in the cat about 60 days, and in the rabbit 30 days.
Parturition is the birth or expulsion of the living fetus at the natural time in a state of development which enables it to live. Although parturition is physiological it is accompanied by pain and severe exertion on the part of the inother and brings about sudden changes in the life of both mother and fetus which in a meas ure imperil the well-being of each. The causes of parturition are not definitely known. On nearing the completion of pregnancy there ap pear certain signs in animals which indicate the approach of birth. One of these is the in creased functional activity of the milk glands; another is the relaxation ef the sacro-sciatic ligaments which allows the muscles passing over them to drop inward; this causes deep hollows to appear on either side of the base of the tail; the vulvar lips becorne swollen and tend to stand apart more loosely than ordi narily. As the time for birth draws nearer the animal appears to be somewhat uneasy and anxious, and, if at liberty, she will withdraw from other animals of her kind or of other spe cies and seek a quiet and secluded place. in parturition there are certain attitudes of the fetus which make its passage possible while others render it virtually impossibk. The possi bility of a fetus being born alive and with out assistance depends fundamentally upon which parts of the fetal body present at the outlet, and secondarily upon the relations of the parts which present to the circumference of the pelvis. The natural and normal presen tation is that of the two fore-feet with the front side of the feet and lcnees upward or next to the tail of the dam and the nose lying between the knees. With a well-formed dam and fetus and a normal presentation parturition in animals is usually prompt and easy. When
ever birth becomes difficult or impossible with out artificial aid the condition is lcnown as dystocia. It has been noted that dystocia runs parallel in frequency to the confinement of the animal. Consequently those females which are most closely housed and least exercised are the ones which suffer most frequently and seriously from dystocia. The immediate causes of the dystocia are many and varied. It may be de pendent upon some defect, disease, or displace ment of the maternal organs such as: failure of the mouth of the uterus to dilate; twisting or torsion of the uterus; tumors in the vagina; dropsy in the uterus or abdomen; undue nar rowing of the passages; the disturbance of the animal by the presence of persons; or by un accustomed and unnatural noises. Or it may be due to some disease or abnormality in the sire, form, presentation or position of the fetus such as its back being turned downward or to one side in place of upward toward the spine of the dam; the bending backwards of one or more limbs or of the head into the body of the uterus; the presentation of the back, shoulder, or croup; the presentation of all four feet at once; dropsy or other disease of the fetus; or excessive or imperfect development of the fetus.
In overcoming dystocia in animals a number of operations may be demanded. Depending upon the animal in dystocia and the lcind of dystocia present the operation for relief is selected to suit the case. The chief obstetric operations are: (1) Mutation, or changing the position of the fetus; (2) forced extraction; (3) embryotomy; (4) Cmsarian section. Muta tion, forced extraction and embryotomy are most commonly performed in dystocia of the larger animals (mare, cow, sheep and goat). In the smaller animals (pig, dog and cat) Canarian section is performed. Pregnant ani mals are subject to an infectious disease which frequently destroys pregnancy. The disease is infectious abortion and consists in an infec tion of the fetus and its membranes which causes the death and expulsion of the fetus, or its expulsion in a living and enfeebled state at any titne in the pregnancy. period without di rectly inducing material evidence of disease in the mother.
There are also a few accidents and diseases grouped about the act of parturition which re quire great care and attention. They occur in all animals, althougii one or another accident or disease may be move frequent in one species than in another. Retention of the afterbirth is one of the most common and at the same time one of the tnost serious diseases of the puer peral state. It is observed most frequently in the cow. Rupture of the uterus may occur but is not frequent. Eversion or prolapse of the uterus is a common and formidable accident, es pecially liable to occur in cows. Metritis or in flammation of the uterus is common and occurs in all species. Parturient paresis or milk fever is a very common malady of the parturient state, but is observed only in cows. Present methods of treatment have made milk fever a disease not to be feared if attended early, where it was once a highly fatal malady. For bibliography consult works referred to under article VETERINARY SURGERY.