Page 46 - New Mexico Horse Breeders 2019 Stallion Register

Prepping an Open Mare for Breeding
by Megan Petty, DVM
Typically, we think of breeding season start- ing around the 14th of February or once
a mare has delivered a healthy foal. What about when the mare is open, either because she is a maiden, or because she did not conceive the previous year(s)? Technically, breeding season can’t start until the sheds open (usually around that Valentine’s Day mark), but the preparation for an open mare starts months earlier. Mares are seasonally polyestrous, meaning they have multiple heat cycles during a particular time
of the year, and do not cycle outside of that season. A mare left to her own devices usually will not come into heat until mid-March or later, and will cycle every 21 days through the summer months. However, for our performance horses, there is an advantage (both real and perceived) for foals who are born earlier in the year. A 2 year old performance horse born in January versus one born in May competing
in May of the 2 year old year can look drasti- cally different. That disparity tends to be less noticeable as the years go by, but we all know that the size advantage can be the difference
in great sums of money for some performance horses. So how do we get a January foal when a mare will not come into heat on her own until mid-spring? Enter veterinary medicine. The approach for preparing the open mare for breed- ing season is essentially the same whether she is maiden or barren, with a few added steps for the barren mare. Typically we start this process in late October to early November.
HISTORY AND PHYSICAL EXAM
The first step requires a detailed history of the mare including her age, number of previ- ous foals, any known foaling complications,
and any other known underlying diseases or illnesses. A thorough physical exam should be performed focusing on the whole horse, and then narrowing the focus down to a reproduc- tive exam. The body condition score of the mare, her overall weight, and physical status should be carefully considered. If a mare is over or under weight she will have difficulty conceiv- ing and ultimately carrying a foal to term.
The ideal body condition on the BCS scoring system is 5/9 where the ribs can be easily felt, but not easily seen. Any lameness issues that would preclude the mare from ambulating with the extra weight of an in-utero foal should be evaluated as well. Mares should be evaluated for any endocrine or metabolic diseases as this can dramatically affect fertility too.
REPRODUCTIVE EXAM
The external reproductive exam includes both perineal and udder conformation. “Tipped” perineal conformation is a common abnormality that can be identified. This may occur with age, or if a mare is or has been
too thin. With this conformation, the anus becomes sunken in and will rest further in than the vulva. Mares with this conforma- tion are at risk of ascending uterine infections as well as urine pooling. Ascending uterine infections can cause placentitis once the
mare is in foal, or create such a contaminated uterine environment that the mare will be unable to conceive. Typically, this condition can be corrected with a Caslick’s procedure as suturing the vulvar lips together helps prevent contamination. Some mares have such poor conformation they also require a surgical peri- neal body transection to correct this problem.
Mares with elongated vulvas may require a Caslick’s procedure as well.
Evaluation of the udder is important for the end of pregnancy when the foal hits the ground. A mare with dramatically enlarged nipples when open, typically retains this udder confor- mation post-partum and the foal potentially will have a more difficult time suckling. Taking note of any and all external reproductive abnor- malities better guides the internal reproductive exam and prepares the examiner for what may be found going forward.
Internal reproductive exam should include
a vaginal speculum exam, rectal palpation of cervix, uterus, and ovaries, and an ultrasound exam of the same structures. A vaginal specu- lum exam allows the veterinarian to directly visualize the cervix as well as the vaginal vault and the vestibulovaginal seal. These three structures are the main barriers that prevent uterine infection, and if any of these are dam- aged or abnormal, appropriate intervention steps will need to be undertaken during and after the breeding process. Unfortunately, little can be done to improve a damaged cervix and this speculum exam allows cervical damage or changes to be identified early in the process before numerous covers and hundreds of dollars have been spent.
DIAGNOSTIC TESTS
The most common place for the prepara- tion process to diverge between maiden mares and mares who have previously foaled is in the following diagnostic steps. Maiden mares typi- cally do not require a uterine culture, however if a mare has foaled previously, particularly if there has been a year or more of being barren,
“The approach for preparing the open mare for breeding season is essentially the same whether she is maiden or barren, with a few added steps for the barren mare.”
44 New Mexico Horse Breeder