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  Discussion on Research Study: Slower Ovulation in Older Mares
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DrO

Posted on Monday, Feb 23, 2009 - 9:23 am:

Older mares (> 18 years) on average take a day extra to ovulate when compared to mares less than 14 years of age. Good to know when trying to time insemination. The later ovulation can be seen as the follicles develop slower when measured sequentially on ultrasound even though FSH concentrations were similar between the older and younger mares. However LH developed slower in the older mares and may be the cause of the slower development and later ovulation.
DrO

Reprod Fertil Dev. 2008;20(8):955-63.
Effects of age on follicle and hormone dynamics during the oestrous cycle in mares.

Ginther OJ, Gastal MO, Gastal EL, Jacob JC, Siddiqui MA, Beg MA.

Eutheria Foundation, Cross Plains, WI 53528, USA. ginther@svm.vetmed.wisc.edu

The effects of age (young: 5-6 years; intermediate: 10-14 years; old: > or =18 years) on follicle and hormone dynamics during an interovulatory interval (IOI; n = 46) and on preovulatory oocytes and concentrations of follicular fluid factors (n = 44) were studied in mares. Old mares were not approaching senescence, as indicated by regular lengths of the IOI (19-27 days) during the period May-October. The IOI was 1 day longer (P < 0.05) in the old group than in the two younger groups and was associated with a slower (P < 0.05) growth rate of the ovulatory follicle. The old group had diminished follicle activity, as indicated by significantly smaller and fewer follicles. Concentrations of FSH did not differ among age groups, except that the maximum concentration was greater (P < 0.05) in the old group. Concentrations of LH were greater (age x day interaction; P < 0.03) in the young group throughout the ovulatory LH surge and may have played a role in a shorter (P < 0.05) interval from maximum diameter of the preovulatory follicle to ovulation. Maximum circulating concentrations of oestradiol during the preovulatory surge were greatest (P < 0.05) in the young group. No effects of age were detected on oocyte morphology. Concentrations of ovarian steroids in preovulatory follicular fluid were not affected by the age of the mares, but concentrations of free insulin-like growth factor-1 were greater (P < 0.05) in the old group. The results indicate the importance of considering the potential confounding effects of age in experimental protocols and for considering age in the development of theriogenology programmes.
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