Equine Reproductive Procedures. Группа авторов. Читать онлайн. Newlib. NEWLIB.NET

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MM, Lopate C, Knottenbelt D, Pascoe R. 2003. The Mare. Equine Stud Farm Medicine and Surgery. London: Elsevier, pp. 113–213.

      2 McCue PM. 2008. The problem mare: management philosophy, diagnostic procedures, and therapeutic options. J Eq Vet Sci 28: 619–26.

       Patrick M. McCue

       Equine Reproduction Laboratory, Colorado State University, USA

      The 21‐day equine estrous cycle can be divided into two phases: estrus and diestrus, based on sexual receptivity to a stallion. Estrus is the period during which a mare is sexually receptive to the advances of a stallion. Behavioral estrus is stimulated by increasing levels of estradiol produced by the developing dominant follicle in the absence of progesterone. The average length of estrus has been reported to be 6.5 days, with a range of 4.5–8.9 days. Ovulation typically occurs 24–48 hours before the end of estrus. An increase in progesterone from the developing corpus luteum is responsible for the cessation of behavioral estrus. Behavioral diestrus largely overlaps the physiological luteal phase associated with high levels of progesterone produced by the corpus luteum.

      Equipment and Supplies

      Stallion, mare, lead shank, helmet, facilities (teasing rail, fence, chute, stall).

       A mare should be teased with a stallion that exhibits good libido in order to successfully evaluate estrous cycle stage.

       Adequate time should be taken to allow shy or nervous mares to express behavioral estrus.

       Knowledge of the mare’s previous behavioral patterns may be helpful.

       In addition, observation of the mare’s behavior with other horses in a pasture or paddock may indicate when a mare is in estrus.

      Individual Teasing

      An individual mare should be exposed to a stallion for an interval of time that is long enough for her to show estrus or diestrus types of behavior. It is preferable to have both the mare and stallion restrained for individual teasing; however, if only one handler is present, it is better to have the stallion restrained with the mare loose so that abnormal behaviors in the stallion may be corrected. Mares that remain indifferent may need to be teased longer, teased with a different stallion, or may just show more subtle signs. Mares may be reluctant initially and yet later show frank estrus behavior (i.e., “break down”). Sometimes full behavioral estrus is only expressed within a few hours of ovulation. It is also not unusual for a mare to fail to show signs of estrus while being directly teased to a stallion, and then break down as the stallion leaves. Mares may also display estrus at the mere sound or sight of a stallion. Mares with a foal by their side may be reluctant to display estrus behavior readily as they are concerned for their foal’s safety.

      Group Teasing

      A stallion may be used to tease more than one mare concurrently if he is brought to the edge of a pen or turned out adjacent to a group of mares. Mares are allowed to approach the stallion at will in such a teasing program. However, some mares will not approach the stallion and will not express estrus when teased as part of a group. It may be necessary to tease such mares individually.

      Behavioral Responses

       Tail raised and arched or deviated to one side

       Rhythmic eversion of the labia and exposure of clitoris (“winking”)

       Passive urination

       Ears relaxed and either held forward or in a neutral position

       Rear limbs slightly abducted (i.e., wide‐based stance)

       Stifles and hocks flexed

       Lowering of the pelvis (i.e., “squatting”)

       Leaning into fence or gate

       Vocalization (squealing)

       Calm behavior; does not try to bite or strike stallion

       Tail held down or aggressively switched from side to side

       Ears pinned back

       Aggressive toward advances of the stallion

       Biting at the stallion

       Attempt to move away from the stallion

       Squealing or vocalization

       Calm behavior; does not try to bite or strike stallion

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      It should be noted that expression of estrus does not always indicate that a mare is in the follicular phase of the estrous cycle. Seasonally anovulatory mares, ovariectomized mares, and pregnant mares have all been reported to occasionally show signs of estrus when teased with a stallion. This may be due to submissive behavior or a lack of progesterone.

      Records