Follicular Dynamics in Mares

Öz

The limited breeding season of horses makes it extremely important for breeding mares to conceive at the beginning of the breeding season. Imaging of the ovaries by ultrasonography in mares has shed light on the understanding of follicular dynamics. Follicle waves occur periodically in the ovaries of mares, but today this mechanism is still not fully elucidated. Follicular dynamic is the process of continuous growth and regression of antral follicles. In the estrus cycle, one wave of follicles occurs in ponies and two in thoroughbred and sport horses. Follicle waves in mares are divided into major and minor wave, in which the dominant and subordinate follicles develop. Only in major waves can the largest follicle reach the preovulator diameter. In addition, the major wave is divided into four distinct phases as common growth, selection, dominance, ovulation or atresia. The common growth phase is the process by which the follicles, which are usually 6 mm in diameter, continue to grow and develop. This stage lasts until the selection phase, when only one follicle continues to grow and the others have atresia. FSH stimulates the growth of follicles in the ovaries and exerts its effect thanks to insulin-like growth factor-1 (IGF-1). Luteinizing hormone (LH), which rises approximately 24-48 hours before the end of estrus, induces ovulation in the preovulator follicle with a peak average diameter of 45-50 mm. Monitoring follicle development in the ovaries with ultrasonography; diagnosis and treatment of reproductive problems, new perspective on reproductive biotechnological methods and control of reproduction has created great opportunities. In this review, first of all, the reproductive physiology of mares is mentioned and then information about follicular dynamics is given.

Anahtar Kelimeler

• Follicular wave
• follicular development
• FSH
• IGF-I
• mare

Kısraklarda foliküler dinamik

Öz

Atların sınırlı üreme sezonu, damızlık kısrakların üreme sezonunun başında gebe kalmalarını son derece önemli kılar. Kısraklarda ultrasonografiyle overlerin görüntülenmesi, foliküler dinamiğinin anlaşılmasına ışık tutmuştur. Kısrakların overlerinde folikül dalgaları periyodik olarak meydana gelirler, ancak günümüzde bu mekanizma hala tam olarak aydınlatılamamıştır. Foliküler dinamik, antral foliküllerin sürekli olarak büyümesi ve regresyon sürecidir. Östrus siklusunda ponilerde bir, safkan ve spor atlarında ise iki folikül dalgası oluşur. Kısraklarda folikül dalgaları dominant ve subordinat foliküllerin geliştiği majör ve minör dalga olarak ikiye ayrılır. Yalnızca majör dalgalarda en büyük folikül, preovulatör çapa ulaşabilir. Ayrıca majör dalga, kendi içinde ortak büyüme, seleksiyon-deviyasyon, dominantlık, ovulasyon ya da atrezi olarak dört ayrı evreye ayrılır. Ortak büyüme evresi, genellikle 6 mm çapında olan foliküllerin büyümeye ve gelişmeye devam ettiği süreçtir. Bu evre, sadece bir folikülün büyümeye devam ettiği ve diğerlerinin atrezi olduğu seleksiyon evresine kadar sürer. FSH, overlerde foliküllerin büyümesini uyarır ve etkisini insülin benzeri büyüme faktörü-1 (IGF-1) sayesinde gerçekleştirir. Östrusun sonlanmasından yaklaşık 24-48 saat önce yükselen luteinleştirici hormon (LH), piki ortalama 45-50 mm çapındaki preovulatör folikülde ovulasyonu indükler. Ultrasonografiyle overlerde folikül gelişiminin izlenmesi; reprodüktif sorunların teşhis ve tedavisi, reprodüktif biyoteknolojik yöntemlere yeni bakış açısı ve üremenin kontrol edilmesine büyük fırsatlar yaratmıştır. Bu derlemede, öncelikle kısrakların üreme fizyolojisine değinilmiş ve daha sonra foliküler dinamik hakkında bilgi verilmiştir.

Anahtar Kelimeler

• Foliküler dalga
• foliküler gelişim
• FSH
• IGF-I
• kısrak

Kaynakça

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