The effects of varying the interval from follicular wave emergence to progestin withdrawal on follicular dynamics and the synchrony of estrus in beef cattle

Abstract

The objective of this experiment was to examine the effects of varying the interval from follicular wave emergence to progestin removal on follicular dynamics and the synchrony of estrus. The experimental design was a 2x2x2 factorial with GnRH or estradiol-17 beta (E 2 ) + progesterone (P 4 ), controlled internal drug-releasing device (CIDR) treatment duration, and PG or saline treatment as main effects. Cycling, Angus cows (n=49), on d 6 to 8 of the estrous cycle, were randomly assigned to receive a CIDR treatment for 7 or 9 d. Approximately half of the cows from each CIDR group received either GnRH (100 mcg) or E 2 +P 4 (1 mg E 2 + 100 mg P 4 ) at CIDR insertion. Cows in GnRH or E 2 +P 4 groups were further divided into those that received PG (37.5 mg) or saline at CIDR insertion. All cows received PG (25 mg) 1 d prior to CIDR removal. The interval from follicular wave emergence to CIDR removal was longer for cows treated with GnRH (6.6 d) or a CIDR for 9 d (6.5 d) compared to those treated with E 2 +P 4 (4.7 d) or a 7-d CIDR (4.8 d) (P < 0.05). Cows treated with PG or GnRH at CIDR insertion or a 9-d CIDR had a larger dominant follicle (DF) at CIDR removal than those treated with saline, E 2 +P 4 , or a 7-d CIDR. (P < 0.07). Altering the interval from wave emergence to progestin removal created differences in size of the DF at CIDR removal but did not affect the synchrony of estrus.

Effect of the ovulatory follicle diameter and progesterone concentration on the pregnancy rate of fixed-time inseminated lactating beef cows

“…However, it is important to take into account that although all cows enrolled in this study were homogeneous regarding body condition score, lactating period and progesterone concentration during synchronization, a high amplitude in the size of ovulatory follicles among cows was detected (ranging from 10 to 24 mm). There is no certainty about the nature of this high variation among individuals; however some factors that affect the diameter of follicle in FTAI programs have been already described and might be involved on the high variability detected, such as the interval between follicular emergency and the progestin removal (Utt et al, 2003), and the ovulation that may occurs during progestin based protocols . Ovulatory follicles larger than 19 mm resulted in larger corpus luteus than for cows detected with ovulatory follicles <15 mm in diameter (P<0.001; Figure 1C).…”

“…While progesterone is directly related with the size of the dominant follicle and with the steroidogenic ability of the future corpus luteum, apparently, according to this study, in low-progesterone-treated cows, pregnancy rate is more related with an adequate diameter of ovulatory follicle (13-15 mm). Follicles <11.5 mm that were induced to ovulate had smaller corpus luteum and secreted less progesterone than cows which ovulated larger follicles (Vasconcelos et al, 2001). The induction of ovulation of small follicles may result in low pregnancy rate (Lamb et al, 2001;Perry et al, 2005) and increase in embryonic mortality rate (Perry et al, 2005) in postpartum cows subjected to FTAI.…”

“…In addition, it was possible to detect that the relationship between fertility and diameter of ovulatory follicle presented a quadratic response, whereas the small ( £12 mm) and large follicles ( ³16 mm) had lower pregnancy rates (Figure 2). The quadratic relationship that exists between the diameter of ovulatory follicle and pregnancy rate in Bos taurus females had been previously described (Perry et al, 2005;Perry et al, 2007;Vasconcelos et al, 2001). However, apparently, in Bos indicus females, this relationship was not detected, because the larger the ovulatory follicle detected at FTAI, the higher the probability of pregnancy (Meneghetti et al, 2009;Sá Filho et al, 2010).…”

“…The larger the follicle, the higher the number of granulosa cells and consequently, the higher the esteroidogenic potential of the future corpus luteum. Curiously, the ovulation induction of large follicles is also related to low fertility (Austin et al, 1999;Fricke et al, 1997;Shaham-Albalancy et al, 2000;Utt et al, 2003); notwithstanding, after luteinization, corpora lutea originated from these follicles secrete higher concentrations of progesterone (Pfeifer et al, 2009).…”

“…Based on these considerations, it becomes evident that the success of gestation establishment is directly associated to the competence and diameter of the ovulatory follicle. Cows which were induced to ovulate small follicles (<11.5 mm) developed small corpus luteum, which secreted less progesterone (Vasconcelos et al, 2001), and consequently, had lower pregnancy rate (Lamb et al, 2001) and an increase in embryonic death (Perry et al, 2005).…”