Induction of estrus and ovulation in the cat and dog

The Clinical Follow-Up of Estradiol Benzoate Priming During Induction of Estrus With Cabergoline in Dogs

Induction of estrus is used to improve reproductive efficiency of female dogs. In this study, 11 adult healthy female dogs were selected at anestrus stage. The dogs were assigned to treatment (6 dogs) and control groups (5 dogs). Single dose of estradiol benzoate was injected in treatment group at day 0 (0.01mg/kg, IM). Dogs in both groups received cabergoline (5μg/kg orally) from day 7 to the onset of proestrus. Vaginal cytology and blood samples were taken twice a week during study. Average time to the onset of proestrus was 10.33 ± 4.2 and 15 ± 7.5 days in the treatment and control groups, respectively (P = .08). The differences in time to the onset of estrus phase in the treatment group (14.67 ± 5.9 days) and control group (18.67 ± 10.8 days) were significant (P < .05). The average length of proestrus phase in treatment and control groups was 5.33 ± 2.2 and 8 ± 4.6 days, respectively and their differences were significant (P < .05). Average length of estrus phase in treated dogs with estradiol benzoate was 8.57 ± 3.5 days but it was 8 ± 4.6 days in control group (P > .05). Administration of cabergoline caused significant decrease of prolactin concentration in both groups (P < .01). The difference in serum prolactin concentration between treatment and control was not significant. The effect of cabergoline on serum prolactin concentration was not affected by administration of estradiol benzoate in treatment group (P > .05). As a result, administration of estradiol benzoate 1 week before cabergoline improved induction and synchronization of estrus in dogs.

Estrus induction and synchronization in canids and felids

Indications for estrus induction in the dog and cat include potential missed breeding opportunities or conception failure, the treatment of primary or secondary anestrus, out-of-season breeding (feline) and synchronization of ovulation for embryo transfer programs. Reported methods for estrus induction in bitches and queens include the use of synthetic estrogens (diethylstilbesterol), dopamine agonists (bromocriptine and cabergoline), GnRH agonists (lutrelin, buserelin, fertirelin, deslorelin, and leuprolide), exogenous gonadotropins (LH, FSH, hCG, PMSG, and human menopausal gonadotropin) and opiate antagonists (naloxone). These methods vary widely in efficacy of inducing estrus as well as in the fertility of the induced estrus. The applicability of some of these methods for clinical practice is questionable. This review will summarize published reports on estrus induction in canids and felids, both wild and domestic, and provide an update on research using a long-acting injectable deslorelin preparation in bitches.

Induction and synchronization of estrus in dogs

Indications for estrus induction in the bitch include missed breeding opportunities or conception failure, the treatment of primary or secondary anestrus and synchronization of ovulation for embryo transfer programs. Reported methods for canine estrus induction include the use of synthetic estrogens (diethylstilbesterol), dopamine agonists (bromocryptine and cabergoline), GnRH agonists (lutrelin, buserelin, fertirelin, deslorelin, and leuprolide) and exogenous gonadotropins (luteinizing hormone, follicle stimulating hormone, human chorionic gonadotropin, pregnant mare serum gonadotropin, and human menopausal gonadotropin). These methods vary widely in efficacy of inducing estrus, as well as in the fertility of the induced estrus. The applicability of some of these methods for clinical practice is questionable. This review will summarize published reports on estrus induction and synchronization in bitches and summarize preliminary results using a long-acting injectable preparation of deslorelin.

Effect of immunization with bovine luteinizing hormone receptor on ovarian function in cats

OBJECTIVE

To determine the effect of immunization with bovine luteinizing hormone receptor (LH-R) on ovarian function of cats.

ANIMALS

9 adult female domestic cats.

PROCEDURE

7 cats were immunized with 0.5 mg of LH-R encapsulated in a silastic subdermal implant (3 x 10 mm); 2 served as control cats. Receptors had 80% specific binding to 125I-human chorionic gonadotropin with a binding capacity of 2,682 pM/mg. Cats received booster injections of LH-R. Cats were induced to ovulate with luteinizing hormone (LH) releasing hormone on day 345. Samples of venous blood and vaginal cells were collected through day 395. Observation of estrus behavior continued until day 516. Serum concentrations of estradiol, progesterone, thyroid gland hormones, LH, and LH-R antibody were determined.

RESULTS

LH-R antibody was detected in the sera of immunized cats within 21 days after implantation. Detection of LH-R antibody was associated with suppression of serum progesterone to < or = 0.5 ng/mL during the study period, compared with concentrations of 5 to 10 ng/mL in control cats. Immunized cats did not display signs of estrus. Release of LH after administration of LH-releasing hormone indicated an intact hypothalamic-pituitary axis but poor corpus luteum function. Serum estradiol concentrations remained between 30 to 40 pg/mL in immunized and control cats. With the decrease antibody titers, hormone concentrations returned to a pattern consistent with that during fertility.

CONCLUSIONS AND CLINICAL RELEVANCE

Active immunization with LH-R suppressed corpus luteum function in cats. The effect was reversible. An LH-R-based antifertility vaccine may have clinical application in other vertebrates.

Modulation of ovarian function in female dogs immunized with bovine luteinizing hormone receptor

Adult female dogs were immunized with 0.5 mg bovine luteinizing hormone receptor (LH-R) encapsulated in a silastic subdermal implant and subsequently with four intramuscular booster injections of 0.1 mg LH-R each. Circulating LH-R antibody was detected in the sera 3 weeks post-implant. The appearance of LH-R antibody was associated with a decline in the serum progesterone concentrations to a range of 0-0.5 ng/ml until day 365 in the immunized dogs in comparison with a range of 5-10 ng in the control animals, suggesting a lack of ovulation and corpus luteum function in immunized dogs. The immunized dogs did not show signs of 'standing heat' and failed to ovulate when induced by LH-RH challenge. Serum oestradiol levels, however, remained in the range of 30-40 pg/ml in both the immunized and the control dogs. With the decline in the antibody titres, the hormonal profile and vaginal cytology returned to a fertile state and the dogs exhibited signs of 'standing heat', as well as vaginal bleeding. Dogs immunized with LH-R did not show any serious metabolic, local or systemic adverse effects. The hypothalamic--pituitary gonadal axis remained intact as indicated by little difference in pituitary LH levels between control and immunized animals, and by the release of LH by LH-RH challenge. These studies demonstrate that active immunization of female dogs with LH-R could immunomodulate ovarian function to cause a reversible state of infertility. It may be postulated that, due to extensive interspecies homology, a recombinant LH receptor-based immunocontraceptive vaccine may also be effective in other vertebrates.

Longitudinal fecal steroid excretion in maned wolves (Chrysocyon brachyurus)

This study used a fecal steroid monitoring technique to evaluate reproductive cycles in male (4) and female (15) maned wolves, endangered South American canids. A radiolabeled testosterone infusion on a male revealed a fast and predominantly fecal route of excretion for this steroid. Testosterone was also excreted as eight unidentified metabolites, which was not the primary form of this steroid quantified in our assays. Fecal steroid concentrations (estradiol, E2; progestins, P; testosterone, T) in males and acyclic, nonpregnant (pseudo-pregnant), and pregnant females were monitored over four breeding seasons (October-January). Significant differences were detected between longitudinal P profiles of cyclic and acyclic females during estrus, luteal phase, and after birth/end of pseudo-pregnancy. Concentrations of P were also significantly higher in pregnant, compared to nonpregnant females, from proestrus to the end of the pregnant luteal phase. Although levels of T were higher in males than in females throughout the breeding season, no cyclicity in male fecal T concentrations was detected. Values of fecal P, T, and the ratio P/T were useful for differentiating gender and detecting pregnancy in females. Similarities to available data on other canids and the management and conservation implications of these findings were discussed.

Feline breeding management

A comprehensive understanding of behavioral-gonadal-endocrine interrelationships is a prerequisite for the effective management of any feline breeding program. Some of the topics discussed in this article are seasonality of breeding behavior, problems associated with copulation, suggested mating schemes, and pharmacologic control of reproductive cyclicity.