During the breeding season, the effect of constant administration of an agonist analog of gonadotropin-releasing hormone (GnRH; goserelin acetate) on reproductive activity of mares was determined. Twenty-four mares undergoing estrous cycles were allocated at random to 6 groups (n = 4/group) and, on May 29 (day 0), received no treatment (group 1, controls), 120 micrograms (group 2), 360 micrograms (group 3), 600 micrograms (group 4), or 1,200 micrograms (group 5) of GnRH agonist/d for 28 days via a depot implanted subcutaneously. The final group of mares (group 6) was treated with 120 miocrograms of GnRH agonist/d for 84 days (3 occasions at 28-day intervals). During a pretreatment period (April 19 to May 29) and for 90 days after initiation of GnRH agonist treatment, follicular development and ovulation were monitored by transrectal ultrasonography of the reproductive tract at 2- to 3-day intervals. On each occasion a blood sample was collected for determination of luteinizing hormone (LH) and progesterone. Estrous behavior was monitored by teasing of mares with a stallion. Initiation of agonist treatment was random, relative to the stage of the estrous cycle, and all mares ovulated within 11 days before or after implantation. in 3 of 4 nontreated control mares, estrous cycles were observed throughout the study, with interovulatory intervals ranging from 18 to 26 days. In the remaining mare, concentration of progesterone was high after asynchronous double ovulation during the pretreatment period, suggestive of persistent corpus luteum. In group-2 mares, ovulation occurred in all mares 7 days before and 2 days after initiation of treatment; however, the next anticipated ovulation was delayed in 3 of 4 mares (interovulatory interval, 33 to 70 days). Estrous cycles were not disrupted in the remaining mare. At higher doses (groups 3-5), 1 mare each from groups 3 and 5 ovulated between days 0 and 2 of treatment initiation.

Plasma luteinizing hormone and progesterone concentrations, time to onset of estrus, and pregnancy rates were determined in nonlactating anestrous does given 1 of 4 treatments: subcutaneous ear implants containing 3 mg of norgestomet for 9 days (NOR; n = 6); subcutaneous administration, using osmotic minipumps, of 250 ng of gonadotropin-releasing hormone (GnRH)/h for 48 hours (GnRH; n = 6); 3 mg of NOR for 9 days, followed immediately by 250 ng of GnRH/h for 48 hours (NOR + GnRH; n = 6); or no treatment (control; n = 6). During the 72-hour period after removal of NOR or insertion of GnRH pumps, 6 of 6, 0 of 6, 6 of 6, and 3 of 6 does were observed in estrus at a mean (+/- SE) of 49 (+/- 3.0), 0(+/- 0), 32 (+/- 2.0), and 35 (+/- 13.8) hours in groups NOR, GnRH, NOR + GnRH, and control, respectively. Time from end of treatment to peak concentrations of luteinizing hormone were 56 +/-4.0, 28 +/- 4.7, 34 +/- 4.3, and 41 +/- 9.7 hours (mean +/- SE) for NOR, GnRH, Nor +/- GnRH, and control, respectively. Peak concentrations of luteinizing hormone were significantly greater and occurred significantly later in does given NOR. Progesterone concentrations in does that became pregnant increased to concentrations greater than or equal to 1.0 ng/ml 3 to 5 days after breeding and remained high. Functional corpora lutea (CL) was found in 6 does that did not become pregnant, 1 CL was associated with pseudopregnancy and 1 CL was associated with ovulation prior to placement of the GnRH pumps. Functional CL failed to form in 10 of the 12 does in groups GnRH and control. Does had either continual low concentrations of progesterone (3 does) or short-term increases in concentrations of progesterone (7 does). Conception rates for does in groups NOR, GnRH, NOR + GnRH, and control were 83%, 0%, 50% and 0%, respectively. Four does given GnRH and 3 control does were observed in estrus and were bred during the subsequent 2-week period. All of these does, except 1 control became pregnant subsequent to these breedings. The treatments NOR and NOR + GnRH were effective in inducing a synchronized estrus in dairy goats. However, the use of bucks to detect estrus may have introduced the buck effect and enhanced the performance of NOR alone, which has not been this effective in other studies with small ruminants.

This study was performed to investigate the patterns of progesterone secretion after induction of estrus in premature, metestrous and anestrous bitches. A total of 22 bitches were used. 18 bitches were treated with hormone to induced estrus and 4 bitches were untreated and served as controls. Estrus was induced with PGF 2 alpha, estrone, estradiol-17 beta, PMSG and HCG (Treatment A), and with PMSG and HCG (Treatment B). Blood samples were collected via the cephalic vein at 2 to 5 days interval. Blood samples were centrifuged (1,200g, 10min.) within 30 minutes after collection and plasma was stored at -20deg C until analyzed for the progesterone concentrations. Plamsa progesterone concentrations were measured by radioimmunoassay. The results of estrous induction were determined by estrous signs, overain response, egg recovery and progesterone patterns. All bitches in treatment A showed estrous signs, however the ovarian response and egg recovery were not detectable and the levels of progesterone were nearly same as before. In the treatment B, premature and metestrous bitches showed only estrous signs, however 5 of 7 anestrous bitches (71.4 %) showed estrous signs, ovarian response and changes of progesterone levels. In conclusion, clinical estrous behavior can be induced during any phase of the estrous cycle, but ovulation should be induced only if induction occur approximately 4 months or more after the previous estrus.

Repeat breeding is a serious reproductive disorder in dairy cattle. The causes of repeat breeding are multifactorial and there are two main mechanisms: failure of fertilisation or early embryo death, mainly due to poor quality of oocytes and an inadequate uterine environment. Many methods have been used to increase the pregnancy rate for repeat breeder cows, such as intrauterine infusion of antibacterial agents or antibiotics, hormonal treatments for oestrus synchronisation and induction of ovulation, and progesterone supplementation or induction of accessory corpus luteum; however, the results were inconsistent between studies. Embryo transfer (ET) has the capability to minimalise the effects of poor oocyte quality and unfavourable uterine environments on early embryo development during the first seven days after ovulation in repeat breeder cows, and several studies showed that ET significantly improved the pregnancy rate in this group of animals. Thus, ET can be considered an option to increase the conception rate in repeat breeder dairy cows.

Introduction: The ovarian follicular dynamics, vaginal electrical resistance (VER), progesterone (P4) and oestrogen (E2) profiles were investigated during the oestrous cycle in four indigenous ewes. Material and Methods: Daily VER values were recorded with a heat detector. The follicles were observed and measured by trans-rectal ultrasonography. Blood was collected daily for hormonal profiles. Results: A significant variation in VER values (P < 0.05) in oestrus by ewes and position in the sequence of cycles was observed. Trans-rectal ultrasonography of ovaries revealed the presence of 2–4 waves of follicular growth. Study of hormonal profiles by ELISA revealed a positive correlation between E2 concentration and development of follicles and a negative correlation between P4 concentration and their development. The concentrations of oestradiol increased in oestrus and then decreased to a basal level. Follicular growth was accompanied by a rise in the concentration of serum oestradiol. Inversely, when follicles received the stimulation for ovulation, concentration of progesterone started to fall, but after ovulation, it climbed back to its peak and remained at this state until next ovulatory follicle reached its maximum diameter. Conclusion: This study could help to set up a manipulative reproductive technique for improving genetic values in indigenous sheep.

OBJECTIVE To evaluate use of flunixin meglumine as a treatment to postpone ovulation in mares, mare fertility after flunixin meglumine treatment during estrous cycles, and effects of flunixin meglumine on function of the corpus luteum after ovulation. ANIMALS 13 healthy mares. PROCEDURES A single-blinded, placebo-controlled, crossover study was conducted. Flunixin meglumine (1.1 mg/kg, IV, q 24 h) or lactated Ringer solution (placebo treatment) was administered for 2 days to mares with a dominant follicle (≥ 35 mm in diameter) and behavioral signs of estrus. Mares then were bred by artificial insemination. Number of days to ovulation from initial detection of a follicle ≥ 30 mm in diameter, uterine edema score, and pregnancy were determined by ultrasonography; the examiner was unaware of the treatment of each mare. Serum progesterone concentrations were evaluated 5 and 12 days after ovulation by use of radioimmunoassay. RESULTS Data were available for 45 estrus cycles of the 13 mares. Number of days to ovulation from initial detection of a follicle ≥ 30 mm was not significantly affected by administration of flunixin meglumine versus the placebo. Per-cycle pregnancy rate was not significantly different between flunixin meglumine (20/24 [83%] breedings) and the placebo (13/19 [68%] breedings). Flunixin meglumine did not significantly affect behavioral signs of estrus, uterine edema, or serum progesterone concentrations. CONCLUSIONS AND CLINICAL RELEVANCE Findings did not support the use of flunixin meglumine to postpone ovulation in mares.

The objective of this study was to determine the effect of additional human chorionic gonadotrophin (hCG) on the ovarian response of gilts previously treated with 200 IU hCG combined with 400 IU equine chorionic gonadotrophin (eCG) (eCG/hCG). Seventy-one prepuberal gilts (105 ± 7.5 kg) were assigned to groups: i) eCG/hCG (hCG-0; n = 25); ii) eCG/hCG followed by 100 IU of hCG at 24 h (hCG-100; n = 24); iii) eCG/hCG followed by 200 IU hCG at 24 h (hCG-200; n = 10); and iv) controls (CON; n = 12). Ovulation response was assessed by ovarian dissection or real-time ultrasonography. Additional hCG did not significantly improve numbers of gilts ovulating. Numbers of corpora lutea increased with hCG, and was higher in hCG-200 (P < 0.01). Compared to hCG-0, the frequency of cysts in gilts was higher in hCG-100 (P < 0.05) and further increased in hCG-200 (P < 0.01). The number of cysts per gilt was dose-dependently increased by additional hCG. We conclude that supplemental hCG will increase the number of corpora lutea but will be associated with follicular cyst development in a dose dependent manner.

The safety of moxidectin 1% injectable anthelmintic (0.6 mg/kg of body weight, 3 times the recommended dose) was evaluated in 145 reproductively sound, beef cows undergoing estrous cycle. Five treatment groups received moxidectin 1% injectable at specific times relative to a synchronized estrus (day 0): preovulatory treatment (day -2, treatment group 1), treatment at ovulation (day 0, group 2), and treatment after ovulation (days 7, 14, and 28, group 3, 4, and 5, respectively). Two groups of control cows received an injection of vehicle only at times corresponding to treatment in the other groups (6 at days -2, 7, and 28; 7 at days 0, 7, and 14). A final control group (8) received neither product or vehicle. Adverse clinical reactions were not observed in moxidectin- or vehicle-treated cows. Cows were bred by artificial insemination between days -2 and 25 and, subsequently, by breeding-sound bulls through day 65 of the study. Treatment and control groups did not differ in pregnancy rate or time to conception. Moxidectin (at 3 times the therapeutic dose) did not have deleterious effects on cow reproductive performance as examined (eg, at folliculogenesis, ovulation, and the early embryonic phase of development).

The rabbit corpus luteum becomes an estradiol-dependent tissue by day 6 of gestation, and adequate estrogen is critical to avoid pregnancy failure. The aim of this study was to investigate the effect of parity (primiparous or multiparous), day of mating (11 or 21 d postpartum), and suckling status (suckling or nonsuckling) on various reproductive traits in hybrid rabbit does (n = 96). Ovarian structures on day 6 after coitus were evaluated by means of ultrasonography. Blood samples were collected that day, and the serum was analyzed for estradiol-17β by radioimmunoassay (RIA). Parity and suckling had significant effects on mating rate (P < 0.01 and P < 0.05, respectively). More does accepted the male on day 11 than on day 21 (P < 0.05). Ovulation frequency was significantly affected by parity (P < 0.05), day of mating (P < 0.01), and suckling (P < 0.01). Fewer ovarian large follicles and lower estradiol-17β levels were detected in suckling compared with nonsuckling rabbits (P < 0.01). Since estrogen concentrations are commonly used to assess follicular growth and steroidogenic capacity, the lower hormonal levels in the suckling rabbits may reveal poorer ovarian activity, which could result in reduced reproductive efficiency. Our observations confirm the existence of a partial antagonism between lactation and reproduction in rabbits. Further research is needed to elucidate these phenomena, including when artificial insemination is done. Ultrasonography could represent a noninvasive and reliable method for studying several reproductive functions and dysfunctions in rabbits.

Changes in luteinizing hormone (LH) secretion after 17beta-estradiol (E2) injection were evaluated during sexual maturation in 10 prepubertal Nelore heifers. Heifers were divided into 2 groups: intact (I) and ovariectomized (OVX). 17beta-estradiol (2 micrograms/kg) was administered to both groups at 10, 13, and 17 mo of age. Only at 10 mo of age was there a greater mean LH concentration in OVX heifers (1.33 +/- 0.29 ng/mL) compared with the I group (0.57 +/- 0.15 ng/mL). At 13 and 17 mo of age there was no significant difference between the 2 groups in any of the evaluated variables (number of peaks, total peak area, greatest peak area, and time to greatest peak occurrence). This suggests a decrease in negative E2 feedback associated with an increase in positive feedback to LH secretion during sexual maturation, and these were likely the key factors that determined the time of first ovulation in Nelore heifers.