Page 481 - Equine Clinical Medicine, Surgery and Reproduction, 2nd Edition

456 CHAPTER 2

VetBooks.ir MANAGEMENT OF THE FOALING CASE

There is a wide natural variation in the duration of preg-
2 weeks. This time frame is mare and age variable.
nancy in the mare (range 320–400 days), but for most parturition, becoming more noticeable in the last
mares it is between 330 and 340 days. This variation Final development is usually within 24–48 hours
may in part be due to embryonic diapause, when the before foaling. The mammary gland secretions change
embryo stops growing for a variable period of time. The in the last month from yellow and serous-like to colos-
fetus needs to be fully mature before it is delivered at trum, which is thick and pale yellow. Premature lacta-
parturition and a number of physiological changes need tion and leakage of milk may be a sign of a high-risk
to occur in the mare concurrently. This readiness for pregnancy and should indicate further investigation.
birth is associated with a variety of changes in the fetus Loss of the colostrum prior to foaling will lead to low
including increased fetal cortisol release, more fetal immunoglobulin transfer to the foal, and an increase
activity and digestive and respiratory tract maturation. in risk of developing neonatal disease. A waxy material
may accumulate on the ends of the teats and is part of
CHANGES IN THE MARE the initial colostrum production. It often occurs about
IMMEDIATELY PRIOR TO FOALING 24–48 hours prior to foaling, but this timing and the
amount produced are variable. Electrolyte concentra-
Endocrinology tions and the comparative concentrations of the vari-
There are high levels of fetoplacental-derived oestro- ous electrolytes in the milk prior to foaling can be used
gen until immediately after parturition. Progesterone to determine the readiness for parturition: calcium
rises during the last 20 days to a peak approximately >10 mmol/l (40 mg/dl), sodium <30 mmol/l (30 mEq/l)
5 days prior to foaling, while pregnanes, although and potassium >35 mmol/l (35 mEq/l) are indicators of
still high, are gradually decreasing. Both show a sud- fetal maturity and imminent parturition. When these
den drop to baseline levels following parturition. The values are reached, parturition generally occurs within
change in ratio of progesterone and oestrogens stim- 24–48 hours. The milk can be analysed at commercial
ulates uterine muscular ability prior to parturition. laboratories or stable-side kits can give an immediate
Placental relaxin hormone increases in late pregnancy result and help identify mares close to foaling.
and during parturition, leading to pelvic ligament and
cervical relaxation. Prostaglandin levels produced by NORMAL PARTURITION
the fetoplacental unit slowly increase in the last trimes-
ter of pregnancy, and more rapidly in the last few weeks. Normal parturition is divided into three stages:
Two peaks are reached during parturition, leading to
cervical relaxation and the onset of coordinated uter- • First stage (Fig. 2.64). Signs include: lying down;
ine contractions. There is a large release of oxytocin as rolling; pawing and other signs of abdominal pain;
the fetus enters the birth canal and the second stage of decreased appetite; sweating; frequent urination
parturition starts. Following birth of the foal, the oxy- and defecation; and occasionally a ‘Flehmen’
tocin levels drop, but smaller pulses are produced in the reaction. These signs are associated with mild
third stage of parturition when the placenta is expelled. uterine contractions and relaxation of the cervix,
Prolactin produced by the anterior pituitary increases lasting from 30 minutes to 6 hours, with an average
in late pregnancy and leads to the onset of lactation. duration of about 1 hour. Some mares show these
signs for longer periods. Mares have control over
Physical signs this stage and are able to interrupt it if they feel
Relaxation of the tail head and pelvic ligaments usu- disturbed. Fetal movements and the mare rolling
ally becomes evident in the last 2 weeks of pregnancy and getting up and down help the full-term fetus
and progresses towards parturition. The anus, and move from a dorsopubic (i.e. upside down) to a
especially the vulva, progressively soften, relax and dorsosacral position with its poll/neck and forelimbs
lengthen in the same period. The mammary gland flexed. With progression of this stage the foal
starts to develop slowly about 6–4 weeks prior to rotates the front of its body 180° and then extends