PARTURITION AND THE PUERPERAL PERIOD: THE NEONATE
Parturition is mainly initiated by the fetus, although the mother is not without all influence; mares, for example, tend to give birth when conditions in the stable are quiet and settled.
The endocrine control of birth is complicated and beyond the scope of this book, but certain preparatory changes in the tissues may be mentioned. These take some time to develop, affect many structures, and largely comprise an increase in their water content and loosening of the larger collagen accumulations. The most familiar effect is the insinking of the tailhead of cows to the side as parturition impends. Similar but concealed changes soften the caudal reproductive tract, including, most significantly, the cervix. In some species there is considerable weakening of the pelvic symphysis, but articular changes in domestic animals are limited to some loosening of the sacroiliac joints. After parturition the reproductive organs tend to return toward their former condition, although the restoration after the first pregnancy is never complete. The uterine muscle contracts directly after delivery, and this organ loses much of the weight it gained during pregnancy within a few days.Before this chapter is concluded, a few sentences may be devoted to the status of the newborn, which exhibits interspecific differences that are both striking and important. Neonates of so-called precocial species possess a remarkable ability to fend for themselves more or less at once (Figure 5-72), while those of altricial species are initially much more reliant on maternal care and the warmth and protection of a nest (Figure 5-73). The young of the ungulate orders, both peris- sodactyls and artiodactyls, are generally precocial; those of carnivores and primates, including human infants, are predominately less developed. Young rodents are divided between the two categories; those like rats (myomorphs) are born naked, unable to maintain body temperature independently, barely capable of struggling to reach the dam’s teats, and have their eyelids joined and external ear canals closed
Figure 5-72 Developmental status shortly after birth. A, Neonatal foal with mother (the mare has yet to discharge the fetal membranes [after birth]).
B, Newborn guinea pigs, which are born in a more developed state.
Figure 5-73 Developmental status shortly after birth in altricial species. A, Newborn kittens. B, Three-day-old mouse pups.
Figure 5-74 Progress of skeletal ossification in puppy. A, B and C, 1, 14, and 28 days after birth, respectively.
by epithelial fusion; in contrast, guinea pigs and their close relatives (caviomorphs) are born fully haired, mobile, equipped with vision and hearing, and have the ability to seek and ingest solid food within hours of being born (although they may take milk during the first 2 or 3 weeks). The differences among domestic species are significant if less extreme. Foals, like most newborn ungulates, are able to stand and attend their mothers almost at once; their skeletons are well developed, and most secondary ossification centers are not only present but also well advanced in modeling toward their adult form. Relatively efficient locomotor coordination allows them to follow the herd or flock within a short time. Kittens and puppies, on the other hand, have skeletons that are less mature, and many ossification centers have yet to make their appearance (Figure 5-74); the forelimb musculature is sufficiently developed and controlled to enable them to scramble toward the teats, but that of the hindlimbs is less competent and contributes little to this progress. The development of the sense organs is somewhat retarded, and the eyelids do not part until the tenth day or shortly thereafter. These differences in neonatal status are gradually “ironed out” and most mammals—ourselves excluded—show comparable maturity by the end of the usual lactation period.