Parturation is the expulsion of the foetus and its membranes from the uterus through the birth canal by natural forces and in such a state of development that the foetus is capable of independent life or in brief it is process of giving birth to a young one.
This process of cattle is called ‘calving’. It is an absolutely normal physiological process.
Causes of Parturation:
The exact cause of Parturation is still a mystery but different prevalent views are there. These are summarized in brief as below:
A. Physical Factors:
Progressive: increase in irritability of uterus: Increase in size of foetus towards the period of gestation-enhances the irritability & sensitivity of uterus resulting of reflex expulsion of foetus.
Distension of Uterus: The action of extensive distension is followed by an equal & opposite reaction by uterus on foetus where it attempts to reduce to its original size thus expels the foetus.
Infracts in Placenta: All full term infracts are noticed in the placenta due to distension & consequent pressure on arteries. The blood supply is diminished & placenta becomes sensible. The nutrition of foetus interfered with it and becomes anarchic gaps which stimulates respiratory centre & concentration of uterine started.
Fatty degeneration in Placentas: During last stage of pregnancy, fatty degeneration of outer layer of placenta occurs resulting into separation of foetus. The foetus becomes foreign body & expelled out
B. Biochemical factors:
Carbon dioxide tensions: Accumulation of CO2 in blood occurs due to metabolic activities of foetus which sets uterine contractions.
Exciting substances: A full term foetus transmits certain substances to the maternal circulation due to insufficient nutrition. Believed to initiate Parturation.
Antigen: An excessive quantity of foetal antigen enters the maternal blood sream towards the end of pregnancy which interacts with existing liberated substances by blood antigens & initiates labour.
C. Hormonal Factors:
In total complex process, the known and unknown hormones from pituitary, ovary, adrenal, placenta, foetus & uterus act in coordinated manner but at end the estrogen level increases than progesterone making release of oxytocin which in turn initiates the contractions of uterus.
D. Neural Factors:
There is no evidence that functional relationship of the intrinsic innervations of uterus to its activity during labour. It is independents of center nervous system.
Stages of Parturation:
The act of Parturation is a continuous process but for the sake of understanding, the process is explained in four stages as:
The preliminary stage: Stage continuous for some hours to even days. External symptoms – swelling of udder, entire external genital organ becomes swollen & becomes reddish, clear, straw Coloured mucus secreted. The quarters droop/ slackening of muscles & ligaments of pelvic region. Behavior signs – animal looks for solitary place, cow feels uneasy, bellow and get excited.
Dilation of Cervix Stage: This lasts for 30 minutes to 3 hrs. The uneasiness increases and followed by labour pain, animal show signs of pain in its abdomen. It may lie and rise again several times. Labour pains become more acute with short intervals. The pulse quickened, breathing distressed and rapid. The water bag7 appear at vulva followed by fore feet of young one. At this time cervix is fully dilated.
Expulsion of foetus stage: It is period from complete dilation of the osuteri to the delivery of foetus. The back of cow arched, chest expanded, and muscles of abdomen became broad with each labour pain. At each contraction, water bag protrudes further from vulva till front hoof of young one is visible. Water bag bursts & fluid thrown off. When hoofs and nose are at genital, the head of calf is at pelvic which will have to pass through small pelvic opening; this moment is of supreme effort & greatest point of labour pain. At least, uterine contractions, combined with additional abdominal force on uterus, results in driving away the foetus through cervix, vagina & vulva.
Expulsion of the after birth: After expulsion of calf, the uterus tends to throw out the placental membrane which is now merely a foreign body. As a result of uterine contraction, the placenta separates from the cotyledons & passes into the vagina, where from it is expelled. Early expulsion of placenta is desirable to avoid putrefaction causing infection of uterus. Expulsion within 6-8 hrs is normal, beyond that manual removal is advised.