Premature lactation
Keywords: lactation, abortion, premature, equine
In humans and primates, a common sign of impending abortion is vaginal hemorrhage. In carnivores, it is a greenish (canids) or brownish (felids) vaginal discharge. In ruminants, there may be a mucous discharge or vulvar swelling. By contrast, in a mare that is about to abort, there is little or no vulva swelling and no vaginal discharge. Owners become alarmed when blood is seen to drip from the vulva lips of a heavily pregnant mare but this is not a harbinger of abortion. Instead, the blood is probably originating from varicose veins in the vestibule.
The first sign of impending abortion is mares is premature lactation.
When an owner first notices a sudden increase in the size of a mare's mammary gland, it may only be possible to express small volumes of milk from the teats as shown in this image. In other cases, milk may stream from the teats, drying on the inner surface of the hind limbs.
Image size: 1200 x 1008 px
The nature of the mammary secretion probably differs according to the stage of gestation at which abortion occurs but the presence of casein in the fluid appears to be constant, giving it the appearance of milk. If abortion occurs in the first half of gestation, premature lactation is unlikely.
The author considers premature lactation to be the production of a milk-like secretion before the number of days at after which most newborn foals can survive i.e. about 290 days of gestation. This being said, one also has to consider the fact that mares have gestation lengths that are highly variable; varying as much as two months, even within a single breed. Normal gestation may be as short as 290 days or as long as as 419 days within this species. However, significant positive correlations have been demonstrated between the durations of sequential pregnancies within individual mares. Therefore, for example, the onset of lactation may be be significantly early than usual if it occurs at 310 days in a mare that usually foals after 350 days. It may be a harbinger of abortion or premature birth in that mare but not in other mares.
In most cases there is no uncertainty as to whether lactation is premature or not. Indeed, lactation before 290 days should always be viewed with alarm. Even if there is no abortion in some of these cases, there is loss of colostrum and failure of passive transfer is likely.
It is impossible to predict when a mare will abort after premature lactation has been first been noticed. Sometimes abortion will follow in a matter of days, in other cases, the mare may lactate for several weeks before aborting.
In all cases of premature lactation, one should examine placental thickness by transrectal ultrasonography (CTUP) to determine if placentitis is present. To prepare owners for almost inevitable abortion in a mare, one should also attempt to detect twins by transabdominal ultrasonography.
References:
Coutinho da Silva M.A. et al 2013 Serum amyloid A concentration in healthy periparturient mares and mares with ascending placentitis. Equine Vet J. 45:619-24.
Davies Morel, M.C.G et al 2002 Factors affecting gestation length in the Thoroughbred mare. Anim. Reprod. Sci. 74: 175–185
Takahiro Aoki, T. et al. 2013 Factors Affecting Gestation Length in Heavy Draft Mares. J. Equine Vet. Sci. 33:437-440
Valera, M. et al. 2006. Genetic study of gestation length in Andalusian and Arabian mares. Anim. Reprod. Sci. 95:75–96
Walkowicz, E. et al. 2014. The effect of selected factors on the length of gestation period in Silesian mares. Anim. Sci. Papers and Reports 32: 55-64
