Lactational Abnormalities in Mares

Introduction

Lactational abnormalities are not found usually in mares. However, when there is a risk to the foal (of a particular mare), concern of mare owner’s increases.  However, equine lactational have got less documentation in veterinary literature as compared to other species as there is adequate availability of  mare’s milk substitute. Lactational  abnormalities can be classified as functional  or infectious. The former includes agalactia, galactorrhoea,  precocious lactation, premature lactation. However, the latter mainly includes mastitis as infectious abnormality.

Functional lactational abnormalities include:

1. Agalactia
   Agalactia can be understood as the failure of milk secretion due to any cause other than the normal lactational ending. Firstly, it has to be differentiated with complete failure of milk let down. Agalactic mares have slacked udder, and not engorged with milk. However, some maiden mares with tender oedematous mammary glands or nervous mares are encountered for their reluctance to relaxation and nursing. Thus, there occurs milk retention in glandular alveoli. To compensate the problem,  administration of phenothiazine  tranquilizers and warm towel massages on the udder  can be practiced. The former, with its calming effect will also, stimulate the release of prolactin in order to augment lactation.  Once, mares are relaxed, 10-20 units of oxytocin administration can be of good help to stimulate milk let down.

In some maiden and multiparous mares, that have small udders , and honey-like mammary secretions, agalactia has been found as delayed onset of lactation. However,  agalactia in mares without development of udder is considered as a case of fescue toxicity. This occurs due to the feeding of mares with infected fescue by endophyte fungus-  Acremonium coenophialum. The fungus produces  an ergot alkaloid toxin , which suppresses  prolactin release. Similar symptoms are observed , due to ingestion of (ergot) Claviceps purpura. This fescue toxicity  is mostly  encountered in last trimester of mares. Moreover, in addition to  agalactia, the  toxicity may lead to reduced fertility, prolonged gestation, thickened placenta, neonatal asphyxia etc. If there is prolonged gestation, then mare may have developed udder upto the due date, but  as udder involutes, agalactia  occurs by the time of delivery.

Such mares, can be treated for overcoming the suppression of prolactin  and probably TRH. In fescue-related agalactia, dopamine receptor antagonist–perphenazine can be used at the dose rate of 0.3mg/kg PO twice a day. However,  this may have some side effects as well like,  colic, hyperesthesia, ataxia, posterior paresis etc. So, dose has to be adjusted and monitored accordingly. Others include administration of  domperidone  @  1.1 mg/kg  PO once a day.

Prevention is always better than cure. So, pregnant  mares must be fed with non-fescue pastures. There should be toxin dilution by including legume diet in the pastures up to 20%. Infected fescue must be killed with herbicides. Mares must not be fed with fescue diets in last trimester of their gestation. Insufficient energy intake, negative energy balance must be considered. As, when adequate ration is there, chances of  occurrence  of stress, pain or even some disease decreases.

2. Hypogalactia
   It can be understood as a condition of lower milk production . This, may be a result of malnutrition, and inadequate ration to mares. Lactating mare requires about 1.7 times, and 1.5 times of the energy  during  early and late lactation, (respectively) as required in non-lactating mares. Hence, its necessary to have a sound feeding program in order to maintain normal lactation. Ration adequacy can be judged by the body condition score (BCS) of the animal .Certain other etiologies may include stress, decreased water intake,  mineral deficiencies like selenium deficiency etc.

3. Galactorrhoea
   Galactorrhea can be understood  as  premature lactation or the occurrence of milky discharge from teats before the actual time of lactation (i.e. post-delivery). Lactation in yearling, weanling fillies and non-pregnant or even maiden mares  may also found due to unknown reasons. As the cause is unknown, so the treatment is done empirically in such cases. It may also include prevention of nursing by other animals, feed and water restrictions  etc. Theoretically, galactorrhoea  is associated with prolactin levels elevation. Thus, prolactin suppression can be of good help for the same.

Premature lactation occurring between mid to late gestation may arise different problems with pregnancy. Placental separation, death of one twin, placentitis, abortions etc. can be found associated with the condition. Progesterone supplementation is helpful. It is considered that , there is no specific treatment for galactorrhea. Semi-synthetic ergot alkaloid like bromocriptine must not be administered (for suppressing prolactin levels), as this may suppress the progesterone levels in the affected mares, and thereby leading to dystocia, placental thickening, and reduced neonatal survival etc. in later stages of gestation.

However, premature lactation, during pregnancy has no direct effect on post-partum lactation, but the colostrum level of the latter may get affected.

4. Lactational Tetany
   Lactational tetany can be considered as a metabolic disease arising due to hypocalcemia appropriately rather as a functional disease. Its an uncommon condition occurring due to feeding of mares on lush-green pastures but producing large quantities of milk. The incidence of disease are more in first two weeks of lactation, foal heat or it may also occur after weaning.  It may or may not occur with hypomagnesemia. However, few cases may be associated with hypermagnesemia. Heavy load of work and  prolonged transport are precipitative causes for the same. Clinical signs may include gait stiffness, excitability, muscle fasciculation, muscle paresis, tachycardia, sweating, flared nostrils etc. Others include absence of deification and urination; reduced intestinal motility; hindered swallowing; convulsions; coma ; and  death in severe cases. The disease has to be differentially diagnosed with  diseases like early stages of tetanus; or hypocalcemia occurring due to other reasons like pancreatic diseases,  renal diseases, equine rhabdomyolysis, beetle toxicity etc.

The treatment of choice  is intravenous infusion of 20% calcium gluconate solution. Dose of 250-500ml diluted with saline or dextrose  is usually efficient to treat 500kg mare. This can be followed by second dose  at interval of 15-30 minutes  with the previous one(in case when signs don’t get suppressed effectively). Hypomagnesemic mares can be benefitted from calcium preparations containing magnesium (which are designed for  use in cattle).

Infectious cause of lactational abnormality primarily includes mastitis.

1. Mastitis
   Mastitis can be understood as the  inflammatory condition of the udder tissue .Its rarely encountered in mare and if occurs, then as isolated case instead as  herd problem.  Although  the disease can occur at any stage , but mostly found during weaning,  and in mares who haven’t been pregnant for a long time. Clinical signs may include red, inflammed, hot, swollen, painful udder, loss in apatite,  ventral edema,  hind limb stiffness,  lameness etc. The milk if secreted is thick in consistency and may contain inflammatory cells depending upon severity of infection. Most common etiologies for mastitis include Streptococcus spp. ( S. zooepidemicus, S. agalactia, S. viridians), Klebsiella spp., Actinobacillus spp., Pastuerella spp., Enterobacter spp.,etc. Mycotic mastitis can also occur in mares as disseminated infection, in Coccidioides immitis infection. Gangrenous mastitis and verminous mastitis may  also occur in mares (as a result of  Cephalobus infestation).

Treatment may include systemic anti-biosis, intra-mammary infusions,  hot packs, frequent  milking, NSAIDs and  additional supportive therapies if required. The choice of antibiotic depend upon the culture and sensitivity of bacteria/ micro-organisms. Penicillin,  gentamicin and trimethoprim-sulfonamides are good choices till the culture and sensitivity test haven’t been performed. Administration of intramammary- infusions of bovines is difficult in mares. Treatment may be unsuccessful, if not treated carefully and may lead to glandular system atrophy, and persistent infection.

References

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