AMBULATORY PRACTICE


variation in the degree of proceptivity (solicitous- ness), receptivity (tolerance of mounting), and at- tractivity (stallion sexual response) of mares without ovarian steroid influence, both among mares and from day to day within-mare. Only one of the 20 mares was observed to exhibit estrus on all 15 observation days of the study. In a follow-up study of steroid hormone treatment of ovariecto- mized mares, it was demonstrated that estrogen treatment increased the intensity and decreased variation in estrus as well as correspondingly in- creased the intensity and decreased the variation in stallion response.2 Estrogen-treated mares showed strong estrus for 80% of the tests and weak estrus for an additional 3%. Untreated mares showed strong estrus in only 23% of tests and weak estrus for an additional 33%. This report presents our experience with selection


of candidates for stimulus/mount mares as well as preparation and estrogen treatment of ovariecto- mized mares for comfortable, effective, and safe use in an equine reproduction and behavior teaching clinical and research facility with a variety of unknown and known stallions of various breeds. These circumstances necessitate year-round avail- ability of reliable stimulus mares that are also com- pliant with mounting for semen collection, novice stallion schooling, and a variety of other reproduc- tion teaching exercises involving rotating staff and students of various levels of handling ability and horse breeding experience.


2. Candidate Selection


Initial Considerations When considering particular mares as candidates for preparation to be a stimulus/mount mare, we first try to identify candidates with (1) a behavioral history of excellent temperament and interaction with humans and other horses, both for general ground handling as well as when interacting with a stallion for estrus detection or breeding, and (2) generally good health, soundness, and ease of main- taining good body and particularly foot condition. We also consider the age of the mare because there is considerable effort and expense to preparation, and we prefer to expect as many years of service as possible. Although there are no data to confirm the concepts, we consider the tendency for (1) demon- strative estrus for several days each cycle and (2) less frequent and demonstrative aggressive re- sponses to stallions during diestrus to be predictive of better performance and comfort as a stimulus/ mount mare. If this history is known, we certainly take it into consideration. Also, because of our ex- perience with apparent color, breed, and size pref- erences and aversions among stallions, we aim to maintain a variety of these characteristics among our available stimulus/mount mares.


24 2013  Vol. 59  AAEP PROCEEDINGS Systematic Behavior Evaluation


If a mare meets those initial behavior and sound- ness selection criteria, we then systematically eval- uate her behavioral comfort and compliance with a battery of anticipated breeding shed protocols for semen collection, breeding, and schooling of stallions specific to the environment in which she will be used. Winter anestrus presents an ideal opportu- nity for this evaluation because it most closely approximates the ovariectomized condition. How- ever, for mares that are not anestrus, we of course evaluate the specific breeding shed tasks when she is in estrus. Comfort and compliance with tasks specific to the stimulus/mount mare occupation in our teaching and clinical environment include tolerance and comfort with application of a twitch, breeding cape, hobbles, breeding boots, and tail wrap; expression of proceptive and receptive responses as well as attrac- tivity to stallions both with and without a twitch; easy “steerability” with and without a twitch; ease and comfort with loading, standing for long periods, and unloading in stocks or adjacent the dummy mount; absence of tendency for non-receptive or dis- comfort responses (striking, squealing, biting, kick- ing, striking, “bunny hopping,” rearing, slapping or swishing tail, moving away, pinning ears, tensing up, cowering) even with prolonged teasing; tolerance of mounting by a test stallion wearing an “apron” (for teaching purposes). We aim to evaluate the stallion and mare response with stallions of various ages, experience, breeds, and breeding tempera- ments. Because we are a teaching facility with day-to-day variation in the handling team, we also try to assess the candidate’s cooperation and comfort with handlers of various skill levels and handling styles. A particular concern is to identify behavior that would pose safety threats for less experienced student handlers in a teaching environment. Fig. 1 illustrates an example check sheet that we use to record test session findings. Fig. 2 includes a series of images from a candidate evaluation session.


3. Preparation


The goal of a dedicated stimulus mare is to remove the limitations of cyclicity and seasonality encoun- tered when selecting mares to aid in semen collec- tion. This can be achieved through ovariectomy and subsequent estrogen replacement or estrogen replacement alone for mares with non-functional ovaries.


Ovariectomy


Various approaches for ovariectomy in the mare include colpotomy, flank laparotomy, paramedian celiotomy (oblique or caudal), ventral midline celiot- omy, and various laparoscopic techniques, either conventional or hand-assisted as summarized by Loesch and Rodgerson.3 A complete discussion of surgical technique is beyond the scope of this report;


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