Accessory Corpora Lutea Research Articles

Histology, histochemistry and morphometry of the ovary of the adult plains viscacha (Lagostomus maximus) in different reproductive stages

Abstract Lagostomus maximus is a South American Hystricognathi rodent whose reproductive behaviour shows characteristics unusual for mammals, such as polyovulation (200–800 oocytes) and a high rate of embryo mortality. Thirty‐six mature females captured in the province of Buenos Aires showed different physiological reproductive stages. Most of them presented a postpartum oestrus in August–September. This characteristic is different from that reported in other geographical areas. The stages considered were: anoestrus, follicular phase, early pregnancy and late pregnancy. The ovaries were light‐pink and smooth and presented a tortuous cord‐like aspect. Many primordial follicles were found in all the females studied. Follicles in different states of maturation and primary and accessory corpora lutea were observed in the cortex. These structures were smaller than those present in other related species. Follicles did not project into the surface of the organ. Calcified follicles of diverse size were found in all the ovaries. Atretic follicles were found in all the stages analysed. Interstitial tissue surrounding the follicles and the corpora lutea was also observed. The number and proportion of different cortical structures varied in the physiological stages analysed. The ovaries of the viscacha have differential characteristics in comparison to other Hystricognathi, some of them related to polyovulation.

Comparison of gonadorelin products in lactating dairy cows: Efficacy based on induction of ovulation of an accessory follicle and circulating luteinizing hormone profiles

This study evaluated whether the four gonadorelin products that are commercially available in the United States produce comparable ovulation responses in lactating cows. Dairy cows at 7 d after last gonadotropin-releasing hormone (GnRH) treatment of Ovsynch (Day 7), with a corpus luteum (CL) ≥15 mm and at least one follicle ≥10 mm, were evaluated for response to GnRH treatment. Selected cows were randomized to receive (100 μg; im): (1) Cystorelin (n = 146); (2) Factrel (n = 132); (3) Fertagyl (n = 140); or (4) Ovacyst (n = 140). On Day 14, cows were examined for ovulation by detection of an accessory CL. Circulating luteinizing hormone (LH) concentrations were also evaluated in some cows after treatment with 100 μg (n = 10 per group) or 50 μg (n = 5 per group) GnRH. Statistical analyses were performed with the procedures MIXED and GLIMMIX of the SAS program. Percentage of cows ovulating differed (P < 0.01) among groups, with that for Factrel being lower (55.3%) than that for Cystorelin (76.7%), Fertagyl (73.6%), or Ovacyst (85.0%). There was no effect of batch, parity, or follicle size on ovulation response, but increasing body condition score decreased ovulation response. There was a much greater LH release in cows treated with 100 μg than in those treated with 50 μg, but there were no detectable differences among products in time to LH peak, peak LH concentration, or area under the LH curve and no treatment effects nor treatment by time interactions on circulating LH profile. Thus, ovulation response to Factrel on Day 7 of the cycle was lower than that for other commercial GnRH products, although a definitive mechanism for this difference between products was not demonstrated.

Uso da gonadotrofina coriônica eqüina em receptoras de embriões para avaliar o incremento da progesterona endógena no dia da inovulação e sua correlação com a taxa de prenhez

The experiment was carried out to evaluate the influence of pregnant Mare Serum Gonadotrophin (eCG) administration in embryo receptors on the formation of accessory corpus luteum and correlation with the pregnancy rate. Sixty-four beef cattle heifers -18 to 30 months old were used, ½ Simental, with 400 kg of average live weight. The heifers were evaluated through rectal palpation between days 7 to 12 after heat detection, considered as heat base. In this interval from 7 to 12 days after the heat, defined as zero day (D0), the animals identified with physiological corpus luteum were divided in four treatments. The animals in treatment 1 (control, n=21) received physiologic solution intramuscle (IM); in treatment 2 (n=16) received 200 IU of eCG (FOLLIGON - Intervet), IM; in treatment 3 (n=14) received 400 IU of eCG IM; and in treatment 4 (n=13) received 600 IU of eCG IM. Two days after (D2) eCG application all the animals received 2.0 mL of prostaglandin F2 alpha (PROSOLVIN - Intervet). Following, the animals' heat manifestation was observed, and, seven days after heat detection, the animals were evaluated for ultrasonography to select females able to receive frozen embryos. Twenty-three days after inovulation, the pregnancy diagnostic was detected through ultrasonography. There was no statistic difference (p > 0.05) for pregnancy rate. These results show that eCG used in receptors of frozen embryos neither improved the receptors' performance rate, nor the pregnancy rate.

Ovarian function in Nelore (Bos taurus indicus) cows after post-ovulation hormonal treatments

Maternal recognition of pregnancy in the cow requires successful signaling by the conceptus to block luteolysis. Conceptus growth and function depend on an optimal uterine environment, regulated by luteal progesterone. The objective of this study was to test strategies to optimize luteal function, as well as prevent a dominant follicle from initiating luteolysis. Nelore (Bos taurus indicus) beef cows (n=40) were submitted to a GnRH/PGF(2alpha)/GnRH protocol. Cows that ovulated from a dominant ovarian follicle (ovulation=Day 0) were allocated to receive: no additional treatment (G(C); n=7); 3000IU of hCG on Day 5 (G(hCG); n=5); 5mg of estradiol-17beta on Day 12 (G(E2); n=6); or 3000IU of hCG on Day 5 and 5mg of estradiol-17beta on Day 12 (G(hCG/E2); n=5). Ultrasonographic imaging of the ovaries, assessment of plasma progesterone concentration, and detection of estrus were done daily from Day 5 to the day of subsequent ovulation. Treatment with hCG induced an accessory CL, increased CL volume, and plasma progesterone concentration throughout the luteal phase (P<0.01). Estradiol-17beta induced atresia and recruitment of a new wave of follicular growth; it eliminated a potentially estrogen-active, growing ovarian follicle within the critical period for maternal recognition of pregnancy, but it also hastened luteolysis (Days 16 or 17 vs. Days 18 or 19 in non-treated cows). In conclusion, the approaches tested enhanced luteal function (hCG) and altered ovarian follicular dynamics (estradiol-17beta), but were unable to extend the life-span of the CL in Nelore cows.

Evaluation of the effect of a 3rd GnRH injection administered six days after the 2nd GnRH injection of Ovsynch on the reproductive performance of Japanese black cows

This study was designed to evaluate the reproductive performance of Japanese black cows following the 3rd injection of gonadotropin releasing hormone (GnRH) analogue administered concurrently with Ovsynch-based treatment on day 6 (day 1 = the day of ovulation). In Experiment 1, 12 cows were allocated into three groups: a control group that was subjected to Ovsynch treatment and then injected with a placebo on day 6; group 1 (Ovsynch + GnRH), which was subjected to Ovsynch treatment and was injected with GnRH analogue on day 6, and group 2 (Ovsynch + controlled internal drug-release (CIDR) + GnRH), which received Ovsynch-CIDR treatment and was injected with GnRH analogue on day 6. Blood collection and ultrasonographic observation of the ovaries were conducted daily. Both treatments induced the formation of an accessory corpus luteum and significantly increased the cross-sectional area of the luteal tissue when compared to the control. However, plasma progesterone (P4) was significantly higher in the treatment groups than in the control group on days 11, 12, 17 and 18 in the group 1 and from day 10 to 21 in the group 2. In Experiment 2, 41 cows were assigned to the same three groups described above and then artificially inseminated on day 1. The pregnancy rates on day 45 did not differ among groups. In conclusion, administration of GnRH analogue on day 6 following Ovsynch-based treatment did not improve the reproductive performance of Japanese black cows, even though the P4 concentration was higher in groups that received the GnRH.

Comparison of the Effects of Gonadotropin-Releasing Hormone, Human Chorionic Gonadotropin and Progesterone on Conception Rates in Repeat Breeder Dairy Cows

A slower than normal rise in progesterone concentrations and a lower total progesterone concentrations have been measured in low-fertility cows and repeat breeder (RB) heifers in the first six days after estrus. Several methods have been used to attempt to increase conception rates (CR) through a greater plasma progesterone (P4) concentrations during the luteal phase, including those that increase endogenous function of the existing corpus luteum (CL), induce accessory CL, or act as a direct progesterone supplement. The aim of the present study was to determine whether supplementing with exogenous P4 or the administration of gonadotrophin-releasing hormone (GnRH) or human chorionic gonadotrophin (hCG) during early luteal phase could increase CR in RB cows.

Progesterone and pregnancy status of buffaloes treated with a GNRH agonist

The primary aim of the present study was to establish whether the treatment with a GnRH agonist on Day 5 after AI may result in the formation of an accessory corpus luteum, greater progesterone secretion, and the increased likelihood of pregnancy success in buffaloes. The study was conducted during a period of increasing daylight length when progesterone secretion is suppressed and embryonic mortality is relatively high in buffaloes. In Experiment 1, treatment with a GnRH agonist (buserelin, 12 μg) on Day 5 after AI induced acute increases in circulating concentrations of LH, FSH and oestradiol-17β. Pregnant buffaloes (n=14) at Day 40 following AI showed an increase (P<0.01) in milk whey progesterone concentration between Day 5 (310±55 pg/ml) and Day 15 (424±50 pg/ml). The non-pregnant buffaloes (n=7) showed a decrease (P<0.01) in progesterone level from Day 5 (410±87 pg/ml) to Day 15 (188±30 pg/ml) following AI. In Experiment 2, the treatment with buserelin (12 μg) on Day 5 after AI induced ovulation in 62% of the buffaloes (31/50) and these buffaloes showed a progressive increase in milk whey progesterone concentration on Day 10, 15 and 20 of pregnancy. Buffaloes that did not ovulate, recorded a relatively constant milk whey progesterone level from Day 10 to Day 20 following AI. Milk whey progesterone concentrations increased after the administration of the GnRH agonist in 97% of the pregnant buffaloes and 68% of the non-pregnant buffaloes. The diameter of the largest follicle in buffaloes that ovulated (ovulated n=31) (8.9±0.04 mm; range 4.2 – 13.0 mm) did not differ significantly from the diameter of the largest follicle in buffaloes that did not ovulate (not ovulate n=19) (8.7±0.04 mm; range: 4.0 – 12.0 mm). The latter observation suggested that notional ovulatory size follicles in buffaloes are heterogeneous with respect to stage of follicle maturation and capacity to respond to plasma LH. The present study showed that treatment with a GnRH agonist on Day 5 following AI provides a strategy to increase progesterone secretion and the likelihood of pregnancy in buffaloes mated during periods of increasing daylight length.

Use of GnRH to induce an accessory corpus luteum in buffaloes fixed time artificially inseminated

The objective of this study was to induce an accessory corpus luteum (CL) in buffaloes fixed time artificially inseminated. Two hundred and forty buffaloes received the treatment sequence GnRH/PGF2α/GnRH after which were inseminated artificially. Six days after the insemination, the animals were divided in two groups (G1 = Control and G2 = GnRH) and received 0 µg or 25 µg of GnRH to induce an accessory CL. After twenty four days (D40), pregnancy diagnosis was performed by ultrasonography and 79 buffalo (G1, n = 39; G2, n = 40) were randomly selected to verify the ovary status by ultrasound. Fifty three pregnant buffaloes (G1, n = 32; G2, n = 21) were followed to verify the birth rate. Data were analyzed by Chi-square test. The conception rate, the accessory CL rate and the birth rate were higher in G2 than in G1 (P<0.05). The use of GnRH to induce an accessory CL in buffaloes increased the conception and birth rates. Thus, the increase of the cost of Ovsynch protocol with the thirty dose of GnRH is rewarded by the increment on conception and birth rates and reduction of days open.

Conception rates and serum progesterone concentration in dairy cattle administered gonadotropin releasing hormone 5 days after artificial insemination

The objectives of this study were to determine the effect of administration of exogenous GnRH 5 days after artificial insemination (AI) on ovarian structures, serum progesterone concentration, and conception rates in lactating dairy cows. In experiment 1, 23 Holstein cows were synchronized using the Ovsynch protocol. Five days after AI (day 0) cows were assigned randomly to receive either saline (saline; n = 11) or 100 μg GnRH (GnRH; n = 12). To examine ovarian structures, ultrasonography was performed on day 1 and every other day beginning on day 5 until day 13. On days 5 and 13 blood samples were obtained to measure serum progesterone concentrations. All cows in the GnRH-treated group developed an accessory corpus luteum (CL), whereas cows in the saline group did not. Mean serum progesterone concentrations did not differ between GnRH and saline groups on day 5 (1.64 ± 0.46 ng/ml versus 2.04 ± 0.48 ng/ml). On day 13 serum progesterone concentrations were greater ( P < 0.05) in the GnRH group compared with saline (5.22 ± 0.46 ng/ml versus 3.36 ± 0.48 ng/ml). In experiment 2, 542 lactating cows, at two different commercial dairies, were used to test the effect of administering GnRH 5 days after AI on conception rates. Cows were synchronized and detected for estrus according to tail chalk removal. Cows detected in estrus received AI within 1 h after detection of estrus. Five days after AI, cows were assigned randomly to receive either GnRH ( n = 266) or saline ( n = 276). Pregnancy status was determined by palpation per rectum of uterine contents approximately 40 days after AI. There was no effect of farm on conception rate. There was no effect of treatment as conception rates did not differ between GnRH and saline groups (26.7% GnRH versus 24.3% saline). Regardless of treatment, days in milk, parity, milk yield, and number of services had no effect on the odds ratio of pregnancy. In summary, the results of this study indicated that GnRH administered 5 days after AI increased serum progesterone by developing an accessory CL but did not improve conception rates in dairy cattle.

The use of a deslorelin implant (GnRH agonist) during the late embryonic period to reduce pregnancy loss

Embryonic and fetal mortality reduce reproductive performance of lactating dairy cows. The objectives of this study were to reduce pregnancy loss by administering a deslorelin implant (GnRH agonist) during the late embryonic period, to reduce follicular growth, induce accessory corpora lutea, and increase plasma progesterone concentrations. Lactating dairy cows received an implant containing 2.1 mg of deslorelin (Deslorelin group; n = 89) or no treatment (Control group; n = 92) on Day 27 of pregnancy. Pregnancy, ovarian structures and plasma progesterone concentrations were determined on Days 27 and 45, and pregnancy was re-confirmed on Day 90. On Day 45, mean ± S.E.M. numbers of class 2 (6–9 mm; 0.72 ± 0.19) and class 3 (≥10 mm; 0.86 ± 0.12) follicles for cows in the Deslorelin group were lower ( P < 0.01) than the numbers of class 2 (1.90 ± 0.18) and class 3 (1.92 ± 0.12) follicles for cows in the Control group. On Day 45, the number of accessory corpora lutea for cows in the Deslorelin group (1.80 ± 0.07) were greater ( P < 0.01) than for cows in the Control group (1.31 ± 0.07). On Day 45, plasma progesterone concentration was increased ( P < 0.01) for cows in the Deslorelin group (8.03 ± 0.33 ng/mL) compared to cows in the Control group (6.40 ± 0.31 ng/mL). Pregnancy losses did not differ between Days 27 and 45 and Days 45 and 90 for cows in the Control (15.2 and 11.0%, respectively) and Deslorelin groups (20.2 and 10.5%, respectively). However, in the Deslorelin group, pregnancy loss between Days 45 and 90 was lower ( P < 0.05) for cows that formed an accessory CL (0%) compared to cows that did not form an accessory CL (16.1%).

166 EFFECT OF TREATMENT WITH hCG OR GnRH AT THE TIME OF EMBRYO TRANSFER ON PREGNANCY RATES IN COWS SYNCHRONIZED WITH PROGESTERONE VAGINAL DEVICES, ESTRADIOL BENZOATE, AND eCG

Although several studies have investigated the relationship between circulating progesterone and pregnancy rates in cattle, the beneficial effect of treatments that increase progesterone concentrations, by insertion of a progesterone (P4) releasing device or induction of an accessory CL with hCG, GnRH, or LH treatment, has resulted in inconsistent effects on pregnancy rates in embryo recipients. An experiment was designed to evaluate the effect of hCG or GnRH treatment, given at the time of embryo transfer without estrus detection, on pregnancy rates in recipients treated with intrauterine P4-releasing devices, estradiol benzoate (EB), and eCG. The experiment was performed in two replicates; non-lactating Bos taurus × Bos indicus crossbred beef cows with a body condition score between 2.5 to 3.5 (1-to-5 scale) were used (replicate 1, n = 180; replicate 2, n = 140). All cows received 1 g of P4 via a P4-releasing device (DIB, Syntex, Argentina) and 2 mg EB i.m. (Syntex) on Day 0, and 400 IU of eCG i.m. (Novormon 5000, Syntex) plus 150 μg d(+)cloprostenol i.m. (Ciclase, Syntex) on Day 5. DIBs were removed on Day 8 and all cows received 1 mg EB i.m. on Day 9. Recipients were not observed for signs of estrus, and those &gt;1 CL, or a single CL with an area &gt;256 mm2, received 195 Grade 1 and 46 Grade 2 frozen/thawed “direct transfer” embryos on Day 17. At the time of embryo transfer, recipients were randomly allocated to 1 of 3 treatment groups to receive 1500 IU hCG (Ovusyn, Syntex), 50 μg Lecirelina (GnRH, Gonasyn, Syntex), or no treatment (control) at that time. Ovarian ultrasonography was performed on Day 0 to determine ovarian status (only cows with a CL or a follicle &gt;10 mm and uterine tone were used), on Day 17 to measure CL area, and 40 days after embryo transfer to determine pregnancy status. Data were analyzed by logistic regression and the effects of replication, technician, treatment, and embryo quality were considered in the model. From the 320 recipients treated with a DIB plus EB and eCG, 241 (75.3%) were selected to receive an embryo. Nine (3.7%) and 1 (0.4%) of the selected recipients had 2 and 3 CL, respectively. Pregnancy rates did not differ between replicates (replicate 1: 80/140, 57.1%; and replicate 2: 57/101, 56.4%; P = 0.84), technicians (technician 1: 65/118, 55.1%; and technician 2: 72/123, 58.5%; P = 0.64), or treatments (hCG: 43/80, 53.8%; GnRH: 45/83, 54.2%; and control: 49/78, 62.8% P = 0.99). However, pregnancy rates were higher (P = 0.001) in recipients receiving Grade 1 embryos (121/195, 62.1%) than in those receiving Grade 2 embryos (16/46, 34.8%). GnRH or hCG treatment at the time of embryo transfer did not increase pregnancy rates in recipients synchronized with P4 releasing devices, EB, and eCG. Research was supported by Syntex S.A., Estancia El Mangrullo S.A., and Agencia Cordoba Ciencia S.E.

Luteotrophic influence of early bovine embryos and the relationship between plasma progesterone concentrations and embryo survival

This study was carried out to evaluate the luteotrophic influence of early (before Day 7 as well as after Day 7; Day 0 = estrus) bovine embryos and the relationship between plasma progesterone (P4) concentrations and embryo survival. Virgin Holstein dairy heifers ( n = 325) from a single herd were randomly allocated to be nonbred, bred by artificial insemination (AI) or by embryo transfer (ET). Bred heifers were either treated with 1500 IU human chorionic gonadotrophin (hCG) on Day 7 of the estrous cycle or received no hCG treatment. Plasma P4 concentrations on Days 0, 5, 7, 10, 13, 15, 17, 19 and 21 were similar in pregnant AI- and ET-bred heifers and, this was observed in both hCG-treated and untreated females. Nonbred, AI- and ET-bred nonpregnant heifers (both hCG-treated and untreated) presented similar plasma P4 concentrations. Plasma P4 concentrations of pregnant heifers significantly deviated from those of nonpregnant and nonbred heifers on Day 17. In hCG-treated heifers, plasma P4 concentrations and Day 28 pregnancy rate were significantly higher in females with an induced accessory corpus luteum (CL) than in those females without an induced accessory CL. Treatment with hCG, although inducing the formation of accessory CL and significantly increasing plasma P4 concentrations had no significant effect on Day 28 pregnancy rate. In conclusion, this study does not support the existence of any peripherally detectable luteotrophic influence from early embryos (Days 5–7). Plasma P4 was only significantly related to embryo survival on Day 17, the time of expected onset of luteolysis.

18OVARIAN SUPPRESSION WITH THE PROGESTIN LEVONORGESTREL IMPROVES OVULATION INDUCTION FOR ARTIFICIAL INSEMINATION IN THE DOMESTIC CAT

Ovarian response to gonadotropin stimulation for artificial insemination (AI) is variable in the domestic cat. After ovulation induction with gonadotropins, a secondary wave of corpora lutea (CL) is often produced that alters endocrine profiles. This study assessed the impact of ovarian suppression with the progestin, levonorgestrel, before ovarian stimulation with equine chorionic gonadotropin (eCG) and human chorionic gonadotropin (hCG) on ovarian response in the cat. Queens were assigned randomly to: 1) levonorgestrel (LNG), 6 Norplant® rods implanted for 37d+eCG/hCG (n=6cats); and 2) Control, eCG/hCG alone (n=6). Ovarian response was graded (scale 1–4; 1=excellent, 4=ovulation failure) 36–40h post hCG (Day 5) using laparoscopy. Ovariohysterectomy (OVH) was performed on Day 23 and CL number and CL progesterone (P) content determined. Fecal samples were collected daily and metabolites of estradiol (E) and P quantified from &amp;gt;60d before inhibition through OVH. Estrus and luteal activity were defined as fecal E and P concentrations greater than two or three times baseline, respectively. Time data were analyzed using repeated measures analysis and remaining data were analyzed using ANOVA. LNG abolished ovarian activity in all cats. No E peaks were observed during LNG inhibition compared with pre-inhibition (mean±SEM; 1.8±0.3 peaks/37 days). In contrast, number of E peaks pre- v. during inhibition was similar (P&amp;gt;0.05) in control (pre, 2.2±0.3; during, 2.0±0.0) cats. All LNG cats had baseline E and P concentrations at eCG administration. Conversely, three of six control cats had elevated E and two cats had elevated P concentrations when eCG was given. Ovarian grade was higher (P&amp;lt;0.05) in LNG (1.3±0.2) v. control (2.9±0.4) cats. All LNG cats had ≤Grade 2 responses, whereas two control cats failed to ovulate (Grade 4) or had mature CL (Grade 3) at laparoscopy. For both LNG and control cats, mean peak E (overall mean, 117.4±14.4ngg−1 feces) was higher (P&amp;lt;0.05) and duration of estrus (6.8±0.9d) was longer (P&amp;lt;0.05) after eCG/hCG v. pre-inhibition values (81.4±5.3ngg−1 feces and 3.9±0.3d, respectively). However, P concentrations/luteal phase were higher (P&amp;lt;0.05)after eCG/hCG v. pre-treatment CL in control but not LNG cats. In cats with an ovarian grade of ≤2, control cats had more (P&amp;lt;0.05) CL at Day 23 (14.0±2.9CL/cat) compared to Day 5 (4.5±0.5).LNG cats showed no (P&amp;gt;0.05) accessory CL development on Day 23 (9.2±1.9CL/cat)compared to Day 5 (6.5±1.8). CL P content was not different (P&amp;gt;0.05) across treatments (overall mean, 90.8±18.7ngCL). Results show that inhibition of ovarian activity with levonorgestrel before eCG/hCG improves ovarian response and alleviates accessory CL development in the domestic cat.

Strategies to optimize reproductive efficiency by regulation of ovarian function

Pregnancy rate to the Ovsynch protocol can be improved if cows are presynchronized (i.e., two PGF 2α injections given 14 days apart and the second injection of PGF 2α given 12 days prior to the first GnRH of the Ovsynch program) so that a greater proportion of cows during the Ovsynch protocol ovulate to the first GnRH injection and have a CL at PGF 2α injection. Pregnancy rates were normal in anestrous cows (39.6%) if they ovulated to both injections of GnRH. Estradiol cypionate (ECP) can be used to replace GnRH to induce ovulation as a modification of the Presync-Ovsynch program (i.e., Presync-Heatsynch). Pregnancy rates after TI were 37.1±5.8% for Presync-Ovsynch compared to 35.1+5.0% for Presync-Heatsynch. Use of ECP to induce ovulation was an alternative to GnRH in which greater uterine tone, ease of insemination and occurrence of estrus, improved acceptance by inseminators. A GnRH agonist (Deslorelin; 750 μg) implant inserted at 48 h after injection of PGF 2α, as a component of the Ovsynch protocol, induced ovulation, development of a normal CL and delayed follicular growth until 24 d after implant insertion. Utilization of Deslorelin implants (450 μg and 750 μg) to induce ovulation compared to GnRH (100 μg) within the Ovsynch protocol resulted in 27 d pregnancy rates (GnRH 100 μg, 39%; Deslorelin implants 450 μg, 40% and 750 μg, 27.5%) with 12.7%, 5.0% and 9.5% embryonic losses by 41 d of pregnancy, respectively. Induction of an accessory CL with injection of hCG on day 5 after insemination improved conception rates by 7.1%. Bovine somatotrophin injected at first insemination following a Presync-Ovsynch program in cycling-lactating dairy cows increased 74 days pregnancy rates (57.1%>42.6%).

Functional anatomy of the ovaries of wild brush‐tailed porcupines (Atherurus africanus, Gray 1842) from Gabon

AbstractThe brush‐tailed porcupine Atherurus africanus is an important source of meat for local people in tropical forested areas of Central Africa. Information on the biology of this species in free‐ranging conditions is scarce. Data on its reproduction and productivity are essential to establish accurate management practices in the exploitation of this rodent. In order to provide data on the reproductive physiology and to assess the prolificacy of the brush‐tailed porcupine in the wild, the structural and functional anatomy of the ovaries of free‐ranging females were studied. Twenty‐two female carcasses were obtained from various markets in Libreville, Gabon, between August 1995 and February 1997. Reproductive tracts were macroscopically examined for the presence of embryos or foetuses. The ovaries were embedded in paraffin wax or plastic and examined by light microscopy. The morphology and constituent cell types of the ovaries were similar to those described for other hystricognath rodents. All pregnant females had only one embryo or foetus and the number of corpora lutea (CL) per female was 19.9 ± 5.4 (mean diameter ±sd, 1709 ± 421 μm), including one CL of pregnancy (diameter, 4821 ± 1364 μm). Also, 8.9 ± 6.8 accessory CL per female in the pre‐implantation and embryonic stages of pregnancy (diameter, 1629 ± 463 μm) were observed. The average active luteal volume was high (115.6 ± 73.5 mm3). The mean number of antral follicles in the adult females was 24.6 ± 9.9. The study confirms that the brush‐tailed porcupine is a mono‐embryonic species, as observed in captive breeding experiences, but polyovular, suggesting important ovum mortality. This unusual reproductive feature in a mammalian species gives this rodent a low reproductive productivity. Therefore, A. africanus could be more susceptible to the effects of hunting than generally thought.

Concentração plasmática de progesterona em novilhas receptoras submetidas à administração de rbST, GnRH ou hCG no quinto dia do ciclo estral

Avaliaram-se a habilidade de diferentes hormônios administrados no quinto dia do ciclo estral em induzir a ovulação do folículo dominante da primeira onda folicular (FDPO) e formar um corpo lúteo acessório (CLa) e seus efeitos sobre a concentração plasmática de progesterona (P4) em novilhas receptoras. Cinqüenta e duas novilhas mestiças Holandês-Zebu foram aleatoriamente distribuídas em quatro tratamentos: T1-controle, T2-administração subcutânea de 500mg de rbST, T3-administração intramuscular (IM) de 100mig de GnRH e T4-administração IM de 2000UI e endovenosa de 1000UI de hCG. Realizou-se palpação transretal nos dias 5, 13 e 60 para detecção de corpo lúteo original (CLo), de CLa e de gestação, respectivamente. A formação de CLa foi de: T1-0/12 (0,0%), T2-0/13 (0,0%), T3-5/12 (41,7%) e T4-10/15 (66,7%)(P&lt;0,05) sendo T1 e T2 diferentes de T3 e T4. A concentração plasmática de P4 foi determinada por radioimunoensaio a partir de amostras de sangue coletadas na veia jugular nos dias 5, 13, 17 e 21 do ciclo estral. Trinta e dois embriões foram transferidos para as receptoras no sétimo dia do ciclo estral (T1-8, T2-8, T3-7 e T4-9). Apenas novilhas não transferidas tiveram sangue coletado nos dias 17 e 21. Observaram-se diferenças na concentração plasmática de P4 (ng/ml) entre os tratamentos (P&lt;0,05) somente no 13ºdia do ciclo, com valores de T1=5,01± 1,04, T2=4,80± 1,26, T3=6,42± 1,47 (diferente de T1, T2 e T4) e T4=11,16± 2.79 (diferente de T1, T2 e T3), mas não houve efeito da presença do embrião (P&gt;0,05). As taxas de gestação, T1=37,5% (3/8), T2=62,5% (5/8), T3=28,6% (2/7) e T4=33,3% (3/9), não diferiram entre tratamentos (P&gt;0,05). Estes resultados mostraram que o FDPO no quinto dia do ciclo estral foi capaz de responder ao GnRH e à hCG, ovular e formar um CLa, o que elevou a concentração plasmática de P4 de novilhas no 13º dia do ciclo estral, período crítico para o estabelecimento da gestação em bovinos.

Luteal Deficiency and Embryo Mortality in the Mare

Four separate components combine to produce the progesterone and biologically active 5 alpha-reduced pregnanes needed to maintain pregnancy in the mare. The primary corpus luteum (CL) is prolonged beyond its cyclical lifespan by the down-regulation of endometrial oxytocin receptors to prevent activation of the luteolytic pathway and its waning progesterone production is supplemented from day 40 of gestation by the formation of a series of accessory CL which develop in the maternal ovaries as a result of the gonadotrophic actions of pituitary FSH and the equine chorionic gonadotrophin (eCG). From around day 100 the allantochorion secretes progesterone and progestagens directly to the endometrium and underlying myometrium and, in the last month of gestation, the enlarging foetal adrenal gland secretes appreciable quantities of pregnenelone which is also utilized by the placenta to synthesize progestagens. Between 10 and 15% of mares undergo foetal death and abortion at some time in gestation and the majority of these losses occur during the first 40 days of gestation when the primary CL is the sole source of progesterone. Yet, all the available evidence suggests that untoward luteolysis is not common in this period and the losses that do occur have other underlying causes. Beyond day 40 the secondary CL receive powerful luteotrophic support from eCG and from day 80-100 until term the supply organ (placenta) and target tissues (endometrium and myometrium) are in direct contact with each other over their entire surface. In the face of this interlocking and failsafe system for progestagen production throughout pregnancy, and despite a paucity of evidence that a deficiency of progesterone production is a cause of pregnancy loss in the mare, it is surprising, and worrying, that annually many thousands of pregnant mares throughout the world are given exogenous progestagen therapy during part or all of their gestation as a form of preventative insurance against the possibility of pregnancy failure. Basic investigative research is required urgently to validate or debunk the practice.

Effects of hormonal treatments on reproductive performance and embryo production

Developments in the use of drugs to improve reproduction and embryo production have focused on estrus and ovulation synchronization protocols and embryonic survival. Protocols for synchronization of ovulation eliminate the need for detection of estrus and allow timed insemination of all cows enrolled. Various estrogenic, progestational, GnRH and PGF 2α-like drugs are used to synchronize follicle development, CL regression and induction of ovulation. Strategies are discussed to optimize such programs to maximize herd pregnancy rates. Use of bovine Somatotrophin (bST) in combination with the Ovsynch protocol resulted in increased pregnancy rates, indicating possible effects on oocyte and embryonic development. Treatment of embryo donor cows with bST reduced the proportion of unfertilized oocytes and increased the number of transferable embryos. Furthermore, bST increased pregnancy rate when given to the recipient. Sub-luteal plasma progesterone concentrations after insemination have been associated with lower pregnancy rates. Injection of hCG on day 5 post-insemination resulted in induction of an accessory CL, increased plasma progesterone concentrations and increased conception rates. Strategies involving the use of sustained GnRH agonists to enhance CL development and alter follicular development are considered for future programs to enhance pregnancy rates.

Administration of gonadotropin-releasing hormone during metoestrus in cattle: influence on luteal function and cycle length

Gonadotropin-releasing hormone (GnRH) has been used to warrant the success of artificial insemination by accurately timing occurrence of ovulation. In practical conditions, GnRH may be administered too late, after ovulation, with an eventual reduction in pregnancy rate. The aim of this study was to investigate whether GnRH administration after ovulation would have a negative effect on luteal function. Three cows and six heifers of the Finnish Ayrshire breed were used. Oestruses were synchronised. After detection of ovulation, one of the following treatments was implemented: gonadorelin (250 μg, i.m.) at either 0–24 h (T1) or 24–48 h (T2) post-ovulation or control (no gonadorelin, C). Every animal was assigned once to each of these three manipulations. Ultrasonography was performed on days 1, 4 or 5, 7 or 8, 11 or 12, 14 or 15 post-ovulation and daily from the beginning of the next oestrous signs until ovulation (day 0=day of ovulation). Blood samples for progesterone (P 4) determinations were collected daily from day 1 after the occurrence of ovulation until recording of the next oestrus. Administration of GnRH during metoestrus did not induce ovulation of either large or small follicles and, thus, no accessory corpora lutea (CL) were formed. In T1, on day 14 or 15, the diameter of CL was 1.3±0.3 mm smaller than in C ( P<0.01), but no differences were found either on days 11 or 12 or on the same days of the T2 and C treatments. No significant differences in levels or profiles of P 4 curves were found between GnRH treatments and control. Neither had the treatments any effects on the length of the oestrous cycle. In conclusion, GnRH treatment during metoestrus does not seem to alter subsequent luteal function and, thus, this does not explain previous reports of reduced fertility post-treatment.

Anatomicohistological characteristics of the ovary of the coypu (Myocastor coypus).

Using histological, histochemical and macroscopic and microscopic measurement techniques, the macroscopic and microscopic structures of coypu ovaries were studied in sexually mature virgin females. The mature ovaries of the coypu were ovoid or elongated bodies, not encapsulated, covered by a single layer of epithelium. They had a parenchyma formed by follicles at different stages of evolution and true and accessory corpora lutea. The interstitial tissue was a prominent and permanent structure in the ovaries. Some ovaries contained a few rete ovarii in the hilus.