Effects of chronic treatment with a gonadotrophin-releasing hormone agonist on peripheral concentrations of FSH and LH, and ovarian function in heifers

Abstract

The effect of chronic treatment with a gonadotrophin-releasing hormone agonist (GnRHa) on ovarian function in cattle was investigated by injecting heifers i.m. twice a day with saline, 5 micrograms GnRHa (Buserelin) or 10 micrograms GnRHa (n = 7) for 21 days. Blood samples were taken twice a day during the treatment period, and then three times a day for 7 days and once daily for a further 4 days. Frequent samples were also collected on day 1, day 10 and day 21 of treatment. The ovaries of all heifers were examined daily using real-time ultrasonography throughout the experimental period. No significant differences in the response were observed between two doses of GnRHa. The first GnRHa injection produced a large LH and FSH surge and this acute response was still present by day 21 of treatment, but both the magnitude and duration of response were significantly attenuated (P < 0.01). After an initial increase, LH returned to the basal concentration, which was maintained until the termination of treatment, when concentrations increased significantly, with a preovulatory surge occurring approximately 6 days later. Peripheral FSH concentrations during the oestrous cycle in control animals displayed a pattern of three waves, each of which closely preceded a wave of follicular development. Concentrations of FSH in GnRHa-treated heifers showed a normal pattern for the first wave after the start of treatment. During the next wave, concentrations increased and remained at the peak values until about 4 days after the end of treatment. An additional ovulation was induced in 11 of 14 GnRHa-treated heifers within 2-3 days of the start of treatment, and a significant (P < 0.05) increase in serum progesterone concentrations was detected 2 days later. All GnRHa-treated heifers then showed a normal follicular wave, with the development and regression of a dominant follicle. The dominant follicles from the next wave grew to only 7-9 mm in diameter and remained at this size until the end of treatment, when they resumed growth, ovulated approximately 7 days later and formed corpora lutea. We conclude that chronic treatment of heifers with GnRHa for 3 weeks suppresses pulsatile secretion of LH and blocks the development of dominant follicles beyond 9 mm in diameter, preventing the preovulatory LH surge and ovulation. However, GnRHa did not suppress the secretion of FSH within the 3 week treatment period. The maintenance of the dominant follicles for an extended period should provide an ideal model to study the control of follicular atresia in cattle in vivo.

Follicular dynamics and production of oocytes in young Nellore heifers with energetic supplementation

“…The concentrations of FSH, similar to those observed in other studies (Adams et al, 1994;Gong et al, 1995), varied according to the day of the cycle, although no difference between days resulted from the nutritional treatment in the total concentration of this hormone (P>0.05). Similarly, LH showed no difference between the treatments (P>0.05) ( Table 2).…”

“…These data indicate that the increased intake of energy affects the recruitment of smaller follicles but does not alter the dominant follicle in Bos indicus animals, as previously observed by Gutierrez et al (1997) and Armstrong et al (2002) in Bos taurus. Some studies have demonstrated the increased number of smaller follicles in Bos taurus in response to increasing the amount of energy consumed or the application of GH (Gong et al, 1991), but few data are shown in Bos indicus. In a previous study, Maurasse et al (1985) demonstrated that changes in the nutritional plan produced changes in the appearance of follicles of various sizes and a sharp increase of the follicles in cattle, as partially observed in this experiment.…”

Long-term effects of deslorelin implants on reproduction in the female tammar wallaby (Macropus eugenii)

“…This may be accompanied by a reduction or maintenance of basal LH concentrations. Basal LH concentrations are reduced in women (Shaw et al 1985) and macaques , while in marmosets (Lunn et al 1992) and heifers (Gong et al 1995, Bergfeld et al 1996 basal LH concentrations remain unchanged. Despite the variable effects on basal LH, the preovulatory LH surge appears to be universally inhibited, as is ovulation.…”

Plasma Steroid Profiles Following Follicle-Stimulating Hormone or Equine Chorionic Gonadotropin Injection in Cows Chronically Treated with Gonadotropin-Releasing Hormone Agonist.

“…The repeated treatment with GnRH-A has been reported to suppress pulsatile secretion of LH and block the development of dominant follicles [7]. These resulted in the prevention of preovulatory LH surge and ovulation in heifers [7].…”

“…These resulted in the prevention of preovulatory LH surge and ovulation in heifers [7]. In the absence of pulsatile LH secretion, FSH stimulates the growth of large and estrogenic follicles which, when stimulated, ovulate to produce viable corpora lutea in the ewe [16].…”