NARROW PELVIS FROM FRACTURE OR DISEASE.
In a small cow the pelvis may be too narrow to pass a calf sired by a bull of a large breed, but this is exceptional, as the fetus usually accommodates itself to the size of the dam and makes its extra growth after birth. When the pelvic bones have been fractured repair takes place with the formation of a large permanent callus, which, projecting internally, may be a serious obstacle to calving. Worse still, if the edge of the broken bone projects internally as a sharp spike or ridge, the vaginal walls are cut upon it during the passage of the calf, with serious or fatal result. In other cases, where the cow has suffered from fragility of bone (fragilitas ossium) the thickening of the bone causes narrowing of the long passage of the pelvis and the crumbling fractures poorly repaired, with an excess of brittle new material, may form an insuperable obstacle to parturition. Cows affected in any of these ways should never again be bred, but if they do get pregnant and reach full time a careful examination will be necessary to determine whether natural parturition can take place or if the calf must be extracted in pieces. (See "Embryotomy," p. 202.)
OBSTRUCTION BY MASSES OF FAT.
This is not unknown in old cows of the beef breeds, the enormous masses of fat upon and within the pelvis being associated with weakness or fatty degeneration of the muscles. If the presentation is natural, little more is wanted than a judicious traction upon the fetus to compress and overcome the soft resisting masses.
OBSTRUCTION BY A FULL BLADDER OR RECTUM OR BY STONE.
In all cases of delayed or tardy parturition the evacuation of rectum and bladder is important, and it is no less so in all difficult parturitions. Stone in the bladder is fortunately rare in the cow, but when present it should be removed to obviate crushing and perhaps perforation of the organ during calving.
CALVING RETARDED BY NERVOUSNESS.
In a public fair ground I have seen labor pains begin early in the day and keep up in a weak and insufficient manner for many hours, until the stall was thoroughly closed in and the cow secluded from the constant stream of visitors and the incessant noise, when at once the pains became strong and effective and the calf was soon born.