12. therio- bovine parturition

what determines when a calf will be born?

calving is initiated by the calf

how does the fetus/calf initiate parturition?

fetal stress--> ACTH (stress induced by mild hypoxia, uterine contractions)

-result of complex interplay between dam and fetus

-fetal pituitary-adrenal axis is required for initiation of parturition

what is the duration of the first stage of labor?

2-8 hours

what occurs during the first stage of labor?

-cervix relaxes and opens up

-intrauterine pressure increases and calf rotates into position

-contracting uterus pushes calf towards cervix

-water bag expelled at end of stage 1

what is the duration of the second stage of labor?

<2 hours (0.5hrs-4hrs)

what occurs during the second stage of labor?

starts once the calf touches the cervix:

-uterine contractions push calf's feet and head against placenta until it ruptures

-first water bag ruptures, then second bag ruptures within 1 hour or less

-once front feet are visible, the calf is normally delivered within 30 mins for cows, 60 mins for heifers

what is the name of the first and second water bags?

first water bag: chorioallantois (in contact with uterus)

second bag: amnion (surrounds calf)

what is the duration of the third stage of labor?

2-12 hours

what occurs during the third stage of labor?

afterbirth is normally passed within 12hr after calving

how does progression of labor differ between heifers and cows?

heifers: progress every 60 minutes

cows: progress every 30 minutes

what are signs of impending parturition in cows?

-sunken tailhead (due to relaxin)

-release of mucus plug

-full udder/teats (no wrinkles seen on teats)

what is the ferguson reflex?

pressure-sensitive nerves in the cervix result in uterine contractions when contacted by the calf

what are indications for induction of parturition in dairy cattle?

-accidental breeding of very young females

-unwanted pregnancy in feedlot heifers

-normal or abnormal pregnancy

what is used to induce parturition from days 7-150?

prostaglandin

cant give prostaglandin before day 7 bc the CL may not be responsive (not fully mature)

what is used to induce parturition from days 150-250?

combination of PGF and corticosteroid are required:

-PGF2a to lyse CL

-corticosteroid to remove extra-ovarian progesterone sources

when should abortion occur after administration of PGF2a and corticosteroids in days 150-250 of gestation?

5 days (95% effective)

repeat treatment if no abortion within 10 days

what is used to induce parturition from days 250-term (283 days)?

can use prostaglandin or corticosteroid alone or in combination

premature parturition in 2-3 days

what is a possible complication of inducing parturition from days 250-term?

these animals generally have retained fetal membranes