Follicular Deviation and Acquisition of Ovulatory Capacity in Bovine Follicles1

Abstract

Selection of dominant follicles in cattle is associated with a deviation in growth rate between the dominant and largest subordinate follicle of a wave (diameter deviation). To determine whether acquisition of ovulatory capacity is temporally associated with diameter deviation, cows were challenged with purified LH at known times after a GnRH-induced LH surge (experiment 1) or at known follicular diameters (experiments 2 and 3). A 4-mg dose of LH induced ovulation in all cows when the largest follicle was > or =12 mm (16 of 16), in 17% (1 of 6) when it was 11 mm, and no ovulation when it was < or =10 mm (0 of 19). To determine the effect of LH dose on ovulatory capacity, follicular dynamics were monitored every 12 h, and cows received either 4 or 24 mg of LH when the largest follicle first achieved 10 mm in diameter (experiment 2). The proportion of cows ovulating was greater (P < 0.05) for the 24-mg (9 of 13; 69.2%) compared with the 4-mg (1 of 13; 7.7%) LH dose. To determine the effect of a higher LH dose on follicles near diameter deviation, follicular dynamics were monitored every 8 h, and cows received 40 mg of LH when the largest follicle first achieved 7.0, 8.5, or 10.0 mm (experiment 3). No cows with a follicle of 7 mm (0 of 9) or 8.5 mm (0 of 9) ovulated, compared with 80% (8 of 10) of cows with 10-mm follicles. Thus, follicles acquired ovulatory capacity at about 10 mm, corresponding to about 1 day after the start of follicular deviation, but they required a greater LH dose to induce ovulation compared with larger follicles. We speculate that acquisition of ovulatory capacity may involve an increased expression of LH receptors on granulosa cells of the dominant follicle and that this change may also be important for further growth of the dominant follicle.

Preovulatory follicle diameter, growth rate and time of ovulation during induced oestrus using a CIDR® in trypanotolerant female Bos taurus N’Dama cattle

“…These differences could be attributed to speculation and therefore the different physiological statuses of the B. taurus breeds. In this breed, ovulation can be observed when the diameter of the follicle is close to 10 mm (Ginther et al 1996;Sartori et al 2001). Dairy cattle respond in different ways to eCG administration.…”

“…Thus, after injection of 400 or 600 IU of eCG, the growth rate and diameter of the ovulatory follicle were, respectively, 3.9±0.6 mm/day and 14.5±1.1 mm, and 3.5±0.5 mm/day and 13.9±1.2 mm (Ferreira et al 2013). It does not appear that a reduction in the diameter of the ovulatory follicle is a determining factor for infertility (Sartori et al 2001;Perry et al 2005) as long as a minimal value close to 10 mm is observed (Martinez et al 1999;Sartori et al 2001). Thus, in Senepol cattle (B. taurus) and Nelore cattle (B. indicus), ovulation of the follicle with a diameter less than 8.5 mm is considered as physiological (Sartori and Barros 2011).…”

“…In cattle, the dominant follicle ovulates when its diameter reaches between 15 and 20 mm (Lussier et al 1987) or between 10 and 20 mm (Monniaux et al 2009). The dominant follicle is capable of ovulating when its diameter is close to 10 mm (Ginther et al 1996;Sartori et al 2001). In heifers and beef cattle, the success of artificial insemination depends on gestation rates, which are themselves significantly influenced by the size of the follicle which has ovulated (Perry et al 2005(Perry et al , 2007Meneghetti et al 2009).…”

Influence of Follicular Growth Stimulation on Fertility of Beef Cows Treated with eCG or FSH in FTAI Protocols

“…Na etapa fi nal do processo que precede a ovulação, o crescimento folicular está associado à maturação do oócito e, consequentemente, a sua capacidade fecundante [18]. As relações entre o tamanho do FO, formação do corpo lúteo, a produção de progesterona e o desenvolvimento embrionário inicial estão associadas ao estabelecimento da prenhez em novilhas e vacas de corte [2,11,19].…”

“…Esses fatores podem ser explicados devido à ovulação de um oócito imaturo, que compromete a fertilização e sobrevivência embrionária, estando também associados à baixa produção e liberação de estradiol pelo FO [9,18]. O uso de eCG [1,6,12] ou FSH [16,17] no fi nal do tratamento para a sincronização do estro e da ovulação para IATF tem como objetivos: promover maior crescimento folicular, maior produção de estradiol e a maturação do oócito.…”