Preovulatory Follicle Size Research Articles

PSXII-20 Ovarian dynamics and fertility in beef cows administered a 5-day or 6-day CO-Synch protocol for timed artificial insemination

Abstract The 5-day CO-Synch is an extensively used TAI protocol; however, it requires multiple administrations of prostaglandin F2α (PGF). The objective of the present study was to evaluate the effect of increasing progesterone (P4) device insertion from 5 to 6 days during a TAI protocol on ovarian dynamics and fertility in beef cows. Suckled beef cows (n = 867) at six locations were randomly assigned to either a 5-day or 6-day CO-Synch. Cows received an intravaginal P4 device (CIDR, Zoetis) and 100 µg of gonadorelin acetate (GnRH, Parnell) on d-9 (6-day) or d-8 (5-day). On d-3 CIDR’s were removed, an estrus detection patch applied (Estrotect, Rockway Inc.) and either one (6-day) or two (5-day) doses of PGF (500 µg of cloprostenol sodium, Estroplan, Parnell) was administered. On d0 (72 h after CIDR removal) all cows received 100 µg of GnRH, estrus expression was evaluated, and AI was performed. Pregnancy was determined by ultrasonography 34 days after TAI. Ovarian dynamics were evaluated in a subset of animals (n = 20) between d-3 and d7 to determine preovulatory follicle size, time of ovulation and corpus luteum (CL) size. Data were analyzed using generalized linear mixed models (SAS 9.4). Cows in the 6-day group tended (P = 0.09) to have a larger maximum follicle diameter (16.2±0.4mm) than cows in the 5-day group (15.0±0.6mm). In addition, CL volume on d7 was greater (P = 0.01) in the 6-day (4302±495mm3) than 5-day (2406±455mm3) group. There were, however, no differences (P = 0.15) in the interval between CIDR removal and ovulation. Cows assigned to the 6-day group had greater (P < 0.05) estrus expression [56.1% (215/385) vs 41.5% (161/388)] and pregnancy rate [54.6% (236/438) vs 47.4% (207/435)] than cows in the 5-day group. In conclusion, extension of the period of P4 device insertion in a prolonged proestrus protocol increases preovulatory follicle size, estrous expression, and fertility to TAI.

Pregnancy rate in ewes injected with zinc oxide during an estrus synchronization protocol

Objective: To measure the effect of zin injection, during an estrus synchronization protocol, on pregnancy rate in sheep from the “Valle de Mexicali”.Design/methodology/approach: The experimental units were 157 ewes, which wereallocated in five farms (UP): UP1 (n=19), UP2 (n=27) UP3 (n=20) UP4 (n=71) and UP5(n=21). In each farm, the ewes were randomly assigned to one of three treatments:control, z-100 and z-200. The ewes from control groups were subcutaneously injectedwith 4 mL of olive oil as placebo. The ewes from groups z-100 and z-200 weresubcutaneously injected with 100 and 200 mg of zinc oxide. The response variableswere the preovulatory diameter of the largest follicle and pregnancy rate.Results: The differences between experimental groups on diameter of the largestpreovulatory follicle and pregnancy rates were not significant different (p>0.05). Limitations of the study/implications: The ewe’s reproductive response to zincinjection might be affected by the animal mineral status, it is recommended to carry onsupplementation with base on mineral blood concentrations.Conclusion: The subcutaneous injection with 100 or 200 mg of zinc oxide did not affectthe size of the largest preovulatory follicle and pregnancy rate in ewes.

Effect of PGF2α treatments during early corpus luteum development on circulating progesterone concentrations and ovulation in breeding-age Holstein heifers

The objective of this study was to test the effect of low circulating concentrations of progesterone (P4) on pre-ovulatory follicle development in heifers as part of an overarching objective to develop a model to understand this phenomenon in dairy cattle without the confounding factors of lactation. Holstein heifers between 12 and 13 mo of age were pre-synchronized to ensure all heifers were on d 6 of the estrous cycle at the start of the Ovsynch program. Only heifers with CL regression and ovulation to the following pre-treatment strategy were used in the study: 0.5 mg cloprostenol (PGF2α), 2 d later, 0.1 mg GnRH, 6 d later, GnRH (G1; 1st GnRH of Ovsynch). Heifers (n = 159) responding to pre-treatment were randomly assigned to 4 groups and completed the Ovsynch program: high P4 control (HPC), low P4 control (LPC; PGF2α 24 h after G1), PG2 (PGF2α 24 and 48 h after G1) and PG3 (PGF2α 24, 48, and 96 h after G1). Only heifers that had ovulation to G1 remained in the study. Blood samples were collected in all heifers on d 7 (n = 157) and in a subset of heifers on d 1, 2, 3, 4 (n = 82) after G1 to measure serum P4. Pre-ovulatory follicle size at G1 (13.0 ± 0.1 mm; P = 0.53) and mean serum P4 24 h after G1 (d 1; 3.62 ± 0.11 ng/mL; P = 0.46) did not differ among treatments. HPC heifers had greater (P < 0.001) mean serum P4 compared to LPC, PG2 and PG3 on d 2, 3, 4, and 7. On d 2, 3 and 4, mean serum P4 of LPC, PG2 and PG3 heifers did not differ (P > 0.10). On d 7, LPC heifers had greater (P < 0.001) serum P4 compared to PG2 and PG3 heifers. Mean ± SEM serum P4 on d 7 after G1 was 8.43 ± 0.39, 2.55 ± 0.36, 1.58 ± 0.20, and 1.21 ± 0.15 ng/mL for HPC, LPC, PG2, and PG3, respectively. Percentage of heifers with P4 < 0.50 ng/mL on d 7 was greater (P < 0.05) for LPC, PG2 and PG3 (27, 32 and 26%, respectively) compared to HPC (0%). A greater (P < 0.05) proportion of heifers ovulated before G2 in the LPC, PG2 and PG3 than in the HPC. For heifers that ovulated after G2, low serum concentrations of P4 in LPC, PG2 and PG3 induced double ovulations in 6/97 heifers after the final GnRH of Ovsynch compared to 0/33 in HPC. In summary, PGF2α treatments during early CL development reduced circulating P4 concentrations 7 d after G1 compared with both HPC and LPC. However, it did not effectively control CL and follicle function to be utilized as a model to test high vs. low serum P4 on fertility parameters in Holstein heifers.

Effect of dietary supplementation of crushed soybean and flaxseed on ovarian response in postpartum crossbred dairy cows

The effect of dietary supplementation of crushed soybean and flaxseed on ovarian function in postpartum crossbred dairy cows was studied. Total 20 postpartum normally calved cows from 2nd to 4th lactation were randomly divided into two equal groups. In addition to routine feed, cows from group T1 were fed with dietary supplementation of crushed soybean @ 10% of DM requirement from the day of calving to day 50 postpartum and thereafter continuation with curshed Flaxseed @ 15% of DM requirement of animal from day 51 to day 85 postpartum respectively, whereas cows from Group T2 was considered as control and supplemented with routine feed. All the animals from both groups were synchronized on day 60 postpartum with Ovsynch protocol. The Follicular dynamic study with the help of USG was undertaken at every 24 hrs interval before the first injection of GnRH of Ovsynch protocol and during Ovsynch protocol (Day 0 to Day 9) of synchronization. It was observed that mean number of class II follicles and total number of follicles were significantly increased in T1 group as compared to T2 group, whereas the mean number of class I and class III follicles did not differ significantly in T1 and T2 groups on day 0. During the synchronization period the mean number of class I, class II, total numbers of follicles and preovulatory follicles size were significantly larger in T1 as compared to T2 groups. The present research findings concluded that the dietary supplementation of crushed soybean and flaxseed showed significant increase in class I, class II, total number of follicles and size of preovulatory follicle in crossbred cows as compare to control group.

Effect of Dietary Supplementation of Crushed Soybean and Flaxseed on Estrus Attributes in Postpartum Crossbred Cows

The objective of the present study was to examine the effect of dietary supplementation of crushed soybean and flaxseed on estrus attributes and preovulatory follicle size in postpartum cows. A total 20 postpartum crossbred multiparous cows from 2nd to 4th lactation with normal calving history were selected and randomly divided into two groups viz. Group 1 (T1) cows fed with roasted crushed soybean @10% of DM (300 g /100 Kg of body weight/day) till 50 and then after continued with crushed flaxseed @ 15% of DM (300 g /100 Kg of body weight/day) and group 2 (T2- without additional fat). Cows from both the groups were subjected to an ovsynch synchronization protocol on day 60 postpartum and observed for induced estrus response, time required for onset of induced estrus, intensity and duration of induced estrus. The diameter of preovulatory follicles was studied transrectaly with a linear-array 7.5 MHZ probe before the second buserelin acetate injection. The dietary supplementation of soybean and flaxseed influenced estrus response, intensity of estrus and time required for onset of induced estrus and duration of estrus however the difference was statistically non significant. At the same time the mean preovulatory follicle diameter was significantly higher in supplemented group.

Efficacy of clomiphene citrate in augmenting fertility of anoestrous goats

A study was designed to assess the efficiency of clomiphene citrate in augmenting fertility in anoestrous goats. Fifty-two pluriparous goats (2-6 yr old) with the history of anoestrus since last kidding were taken for the study. Animals were divided into two groups. Animals of Gr-I (n=26) were treated with TANUVAS mineral mixture type 2 (10 g/day) for 20 days orally. Animals of Gr-II (n=26) were treated with TANUVAS mineral mixture type 2 (10 g/day) for 20 days followed by clomiphene citrate 150 mg (Ovulanta-Kit, Vet Mankind, India) orally for five days. Follicular activity was observed by ultrasonography after supplementation of mineral mixture in both the groups until pre-ovulatory follicle size of > 5 mm, followed by administration of buserelin acetate (40μg, intramuscular). In Gr-I, 16 (61.5%) animals showed pre-ovulatory follicles in 52 days interval whereas in Gr-II, 24 (92.3%) animals showed in five days post treatment with clomiphene citrate. In both the groups, 50.0% of the animals were allowed for natural mating and the remaining were artificially inseminated (AI) with frozen semen. In Gr-I, 37.5% (3/8) and 62.5% (5/8) animals conceived by natural mating and AI, respectively; whereas, the corresponding values in Gr-II were 75.0% (9/12) and 100.00% (12/12). The results showed the potent efficiency of clomiphene citrate in the treatment of anoestrus in goats.

Effects of immunization against inhibin α-subunit on ovarian structures, pregnancy rate, embryonic and fetal losses, and prolificacy rate in goats where estrus was induced during the non-breeding season

The objectives of the study were to determine the dose-dependent effects of active immunization against inhibin α-subunit (AIINHA) on ovarian dynamics, concentrations of progesterone (P4), pregnancy rate (PR), embryonic and fetal losses (EFL), and prolificacy during the non-breeding season when there was imposing of a progestin-based treatment regimen to induce estrus in Beetal goats. Goats (n = 30) were randomly assigned into following groups: 1) saline (G-CON-0 mg; n = 10), 2) small dose (G-AIINHA-0.5 mg; n = 10), and 3) large dose (G-AIINHA-1 mg; n = 10). The primary administration of inhibin immunogen was administered at Day -48, followed by another administration at Day -20, and subsequently there was induction of estrus using a progestin based treatment regimen that included a single administration of progestin-containing sponge and PGF2α at Day -8. The sponge was removed, and GnRH was administered at Day -3 followed by breeding (Day 0) at standing estrus. Results indicated mean diameter of the follicles, size of pre-ovulatory follicles and corpora lutea, and post-breeding P4 concentrations were greater (P < 0.05) in the goat does of the G-AIINHA-0.5 than G-CON-0 group. The PR, and EFL, however, did not differ (P> 0.05) among groups, whereas prolificacy rate was greater (P = 0.04) in goat does of the G-AIINHA-0.5 than G-CON-0 groups. The data from this study indicate G-AIINHA-0.5 is the recommended dose of inhibin immunogen to enhance the reproductive performance during non-breeding season in Beetal goats when estrus is induced using a progestin-based treatment regimen.

Factors influencing pre-ovulatory follicle diameter and weaning-to-ovulation interval in spontaneously ovulating sows in tropical environment.

Follicle development and timing of ovulation are indicators of the reproductive performance of sows. The present study aimed to determine factors influencing pre-ovulatory follicle diameter and weaning-to-ovulation interval (WOI) in spontaneously ovulating sows in tropical climates with special emphasis on breed, parity and backfat thickness at weaning. In total, 80 sows were included in the study. Follicle development was determined by using transrectal real-time B-mode ultrasonography every 6hr after standing oestrus. Weaning-to-oestrous interval (WEI), oestrous-to-ovulation interval (EOI), WOI and the diameter of graafian follicles were investigated in relation to breed, parity number (1, 2-3 and 4-7) and backfat thickness (low, moderate and high) of sows. Overall, WEI, EOI, WOI and the pre-ovulatory follicle diameter were 92.5±21.6hr, 64.3±19.3hr, 156.3±29.1hr and 10.3±2.0mm, respectively. Pre-ovulatory follicle size was smaller in primiparous sows compared with sows of greater parity, 4-7 (9.7±0.51 and 11.7±0.52mm, respectively, p<.05). Weaning-to-ovulation interval was positively correlated with WEI (r=0.75, p<.001) and EOI (r=0.66, p<.001), but negatively correlated with size of the graafian follicle (r=-0.34, p<.01). Sows with a shorter WEI had a larger pre-ovulatory follicle diameter (at 64hr after oestrus) (r=-0.37, p<.01). Sows with low backfat thickness had a WOI 23.4hr longer than those with moderate backfat thickness (p<.05) and 17.6hr longer than sows with a high backfat thickness (p=.140). The follicle diameter in primiparous sows with high backfat thickness (11.7±1.1mm) was higher than in those with low (8.9±0.7mm, p<.05) or moderate (8.6±0.8, p<.05) backfat thickness. In conclusion, factors influencing follicle diameter and WOI in sows included parity number and backfat thickness at weaning. The impact of backfat thickness on follicle diameter, WEI and WOI was most pronounced in primiparous sows.

Associations among thermal biology, preovulatory follicle diameter, follicular and luteal vascularities, and sex steroid hormone concentrations during preovulatory and postovulatory periods in tropical beef cows

The objectives were to evaluate effects of tropical seasons on thermal biology, preovulatory follicle (POF) diameter, POF and luteal vascularities, and estradiol (E2) and progesterone (P4) concentrations; and to determine the associations among the values for these variables during preovulatory and postovulatory periods in Thai native cows in tropical climates: cold, hot, and rainy seasons. Development and vascularity of the POF and corpora lutea (CL) were evaluated using color Doppler ultrasonography. The temperature-humidity index (THI) was greater when the preovulatory period occurred during the rainy season when compared with the occurrence during the hot and cold seasons of the year. Furthermore, POF diameter was less when the THI was greater. The THI was greater when the postovulatory period occurred during the rainy season when compared to the occurrence of the postovulatory period during the hot and cold seasons of the year. Furthermore, the CL vascularity and P4 concentration were less when the THI was greater. The THI was inversely correlated with CL vascularity and P4 concentrations. When the THI was greatest during the hot and rainy seasons of the year, there were the greatest negative effects on POF size, POF and CL blood flow, and concentrations of E2 and P4 during the preovulatory and postovulatory periods. While native Bos indicus are capable of adapting to tropical conditions, there are still negative effects, such as impaired POF and CL functions, when the THI induces heat stress.

Effects of twin pregnancy prevention strategies such as GnRH dose and drainage of the smaller follicle on ovulation in dairy cows with two follicles of pre-ovulatory size in the same ovary.

We examined the effects of a single or 2.5-fold dose of dephereline [a gonadotropin-releasing hormone (GnRH) analogue] as well as the drainage of the smaller follicle at the time of insemination on ovulation in dairy cows with two follicles of pre-ovulatory size in the same ovary. The three study groups included 220 monovular cows (control), 110 non-drained cows with two follicles, and 110 cows with two follicles, of which one was drained. In each group, cows treated with a single dose or 2.5-fold dose of dephereline showed similar results following treatment. Ovulation failure of the non-drained follicle occurred in 29.1% of the drained cows, whereas ovulation occurred in 96% of the non-drained and control cows. Twin pregnancy was recorded in 19.4% of the pregnant non-drained cows with two follicles. In conclusion, the increased dephereline dose did not improve the ovulation rate in any group. Follicular drainage, however, prevented twin pregnancy in cows with two follicles, but also resulted in an increase in the non-drained follicle’s rate of ovulation failure.

Effect of dietary n-3 polyunsaturated rich fish oil supplementation on ovarian function and interferon stimulated genes in the repeat breeding cow

Dietary n-3 polyunsaturated fatty acids (n-3 PUFA) improve utero-ovarian functions and embryonic survival in postpartum dairy cows. Because early embryonic mortality is the major cause of repeat breeding (RB) in cows, there was investigation of the effect of dietary supplementation of n-3 PUFA [eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA)] rich fish oil (FO) from −2 to +2 weeks of artificial insemination on the size of preovulatory follicle (POF), serum progesterone (P4) and relative abundance of the mRNA of interferon stimulated genes (ISG) that encode for these proteins in the peripheral blood leukocytes (PBL) in the RB cow (n = 12). The diet of control group was supplemented with palm oil (PO). The results indicated serum concentrations of EPA and DHA were greater by 4.6- and 3.5-fold, respectively at the end of feeding study in the RB cows of the FO group. The diameter of POF was larger by 2.2 mm in FO group; however, serum P4 did not vary from day 14–20 post-artificial insemination. Greater abundance of ISG mRNA transcripts such as ISG15, RTP4, Mx2 and OAS1 in the PBL of pregnant cows of FO group indicates day 20 conceptuses produced more IFN-τ. It is concluded that supplementation of FO during the breeding period increased the size of POF and enhanced the abundance of ISG mRNA transcripts in RB cows that became pregnant.

Follicular dynamics and in vivo embryo production in Santa Inês ewes treated with smaller doses of pFSH

To evaluate follicular dynamics, there was assessment of superovulatory response and in vivo embryo production in ewes treated with relatively smaller doses of exogenous pFSH than typically used in combination with a dose of eCG at the beginning of the gonadotropin treatment period. Santa Inês ewes (n = 24) were randomly divided into three groups, based on mg dose of pFSH administered: G200 (n = 8), G133 (n = 8) and G100 (n = 8) in eight decreasing doses at 12 -h intervals. All ewes were treated with 300 IU of eCG concomitantly starting with first pFSH administration. Ovulatory follicular dynamics and follicular wall vascularization (FWV) were evaluated using a B-mode and color Doppler ultrasonic machine, respectively. Superovulatory response and embryo production were evaluated 6 days after estrous detection. In the G200 group, the preovulatory follicle size (PFS) were less (P < 0.05), ovulation time later (P < 0.05), and PFS rate greater (P < 0.05); while in the G100 group ovulation rate, and number and percentage of unfertilized eggs were greater (P < 0.05) than in the G133 group (P < 0.05). Number and percentage of viable embryos were greater in the G200 and G100 compared to G133 group (P < 0.05). The dose of 100 mg of FSH was as efficacious as the traditional dose of 200 mg, in combination with a dose of eCG, for superovulatory response and viable embryo production but there was a greater percentage of unfertilized eggs with this treatment.

A novel strategy for resynchronization of ovulation in Nelore cows using injectable progesterone (P4) and P4 releasing devices to perform two timed inseminations within 22 days.

We aimed to evaluate the reproductive performance of Nelore lactating cows submitted to a resynchronization 12days after timed artificial insemination (TAI) with or without a long-acting progesterone (P4-LA) treatment. Nelore cows were submitted to a P4/oestradiol-based TAI protocol (D0=insemination). On D12, cows in the control group (n=184) received a new P4 intravaginal device (0.96g), whereas cows in the P4-LA group (n=192) received the P4 device and 75mg P4-LA. Cows identified as non-pregnant (n=120) by regression of corpus luteum using colour Doppler ultrasonography on D20 had the P4 device removed and received 500ug of sodium cloprostenol, 1mg of oestradiol cypionate and 300IU of eCG and were re-inseminated on D22. There was no difference (p>0.10) in the pregnancy rate at D20, D30 and D60 after first TAI between the control (69%, 59.7% and 57%, respectively) and P4-LA (67%, 55.7%, and 55.2%, respectively) groups. Pregnancy losses were similar between both groups (p>0.1). For cows submitted to the second TAI, the pre-ovulatory follicle size did not differ (p>0.1), but the oestrous detection and pregnancy rates were greater (p<0.05) in the P4-LA group (92.2% [59/64] and 60.9% [39/64], respectively) than in controls (75% [42/56] and 44.6% [25/56]). The cumulative pregnancy rate after two TAIs did not differ (p>0.1) between control (73.3% [135/184]) and P4-LA (76% [146/192]) groups. The use of P4-LA at 12days after TAI potentially increases the pregnancy rates for a new early resynchronization strategy associated with the Doppler imaging for pregnancy diagnosis and results in an alternative to perform two TAIs in 22days in beef cows.

Corpus luteum development and angiogenesis

Summary. Development of the corpus luteum (CL) is vital for the early increase in postovulatory progesterone that drives embryo development and the successful establishment of pregnancy. Following ovulation, rapid and dramatic cellular reorganisation and intense angiogenesis are required to support the timely transition to progesterone secretion. In addition to inherent physiological challenges, this process is sensitive to any imbalance in metabolism or health, particularly in the modern high yielding dairy cow. This makes luteal inadequacy a common cause of poor early embryo development and low conception rates in dairy cows. This review will explore the potential mechanisms that underlie this disorder. It will describe the impact that the pre-ovulatory follicle infrastructure, gonadotrophin support and size of the LH surge have on subsequent luteal development and function. A crucial component for rapid luteal growth is the formation of new blood vessels or angiogenesis. Several recent studies have highlighted the critical importance of fibroblast growth factor 2 (FGF2) in regulating this process. In particular, FGF2 has a profound influence on endothelial cell sprouting and branching. There is increasing evidence that pericytes, immune cells and platelets are also integral regulators of luteal angiogenesis and development. The complex and dynamic nature of luteal development means that it is likely to be sensitive to potential inadequacies particularly, in the high producing dairy cow.

Environmental effects and repeatability of the follicular diameter in mares

ABSTRACT The objective of this study was to evaluate the effect of environment on follicular diameter and repeatability of the size of preovulatory follicles of mares. Temperature, rainfall, and photoperiod were measured, and their effects were evaluated on follicular dynamics. Data were studied by analysis of variance of follicular size and environment traits. During the five years, 7% double ovulations and 159 anovulatory follicles were recorded. Mean preovulatory follicle diameters of left and right ovaries were 39.3±3.8 and 39.2±3.5 mm [...]

Pre-ovulatory follicle size at induced estrus and post-ovulatory luteal profiles, and pregnancy rate in Murrah buffalo (Bubalus bubalis) using estradiol-17β + CIDR protocol

Pre-ovulatory follicle size at induced estrus and post-ovulatory luteal profiles, and pregnancy rate in Murrah buffalo (Bubalus bubalis) using estradiol-17β + CIDR protocol

Optimizing timed AI protocols for Angus beef heifers: Comparison of induction of synchronized ovulation with estradiol cypionate or GnRH

This study compared estradiol cypionate (ECP) or GnRH as ovulation inducers at the end of a timed AI (TAI) protocol in Angus heifers. On day 0, heifers (n = 415), between 22 and 24 months of age, were treated with an intravaginal 1 g progesterone (P4) insert and 2 mg of estradiol benzoate. On day 8, heifers had P4 removed, received 500 μg cloprostenol, and were randomized into two groups: ECP [n = 214; 0.5 mg of ECP on day 8] or GnRH [n = 201; 25 μg of GnRH analog licerelin acetate on day 10]. All heifers received TAI on day 10; 48–50 h after P4 insert withdrawal. Estrus was determined by removal of tail paint. Ovaries of heifers were evaluated by ultrasound on day 0 to determine CL presence (with CL = 213, without CL = 202) and on day 10 to measure preovulatory follicle size. Heifers were divided into three categories based on preovulatory follicle diameter: <8.5 mm (smaller than deviation), 8.5–10.9 mm, or ≥11 mm. Pregnancy diagnosis was performed 32 days after TAI. Heifers treated with ECP had greater expression of estrus than GnRH-treated heifers (93.9% vs 67.7%; P < 0.0001), regardless of CL presence at beginning of protocol. Heifers with CL at beginning of protocol had larger preovulatory follicle diameter (10.4 mm vs 9.6 mm; P = 0.0058) and greater pregnancy per AI (P/AI; 61.0% vs 50.5%; P = 0.032) than heifers without CL at day 0. In heifers with CL at day 0, GnRH treatment increased P/AI compared to ECP treatment (68.0% vs 54.9%; P = 0.0498). Expression of estrus was greater in ECP-treated than GnRH-treated heifers that had small (<8.5 mm; 77.1% vs 5.6%; P < 0.001) or medium-sized (8.5–10.9 mm; 98.4% vs. 61.7%) follicles, but not in heifers with large follicles (≥11 mm; 97.9% vs 98.3%). The P/AI was very low in both treatments for heifers with follicles <8.5 mm (ECP-14.3% vs GnRH-16.7%). In heifers with medium-sized follicles (8.5–10.9 mm), ECP treatment tended to increase P/AI compared with GnRH-treated heifers (62.9 vs 46.7%; P = 0.074). In contrast, P/AI was greater for GnRH-treated than ECP-treated heifers with large preovulatory follicles (≥11 mm; 79.7% vs 60.4%; P = 0.032). Thus, the optimal inducer of ovulation in a TAI protocol for beef heifers appears to depend on the presence of a CL at beginning of protocol (GnRH > ECP if CL present) and size of the preovulatory follicle, with ECP increasing expression of estrus and tending to increase fertility in heifers with medium-sized follicles but GnRH increasing fertility in heifers having large preovulatory follicles.

Preovulatory follicle growth dynamics indicates daily spawning synchronicity in wild-caught Atlantic horse mackerel off Portugal

The Atlantic horse mackerel, Trachurus trachurus, is a commercially important species whose daily spawning dynamics are not yet fully understood. Existence of spawning synchronicity would facilitate application of the daily egg production method for estimating the spawning biomass of the southern stock of the species in the Northeast Atlantic. The intent of this work was to study preovulatory follicle (PREF) growth dynamics in wild Atlantic horse mackerel to determine the existence of daily spawning synchronicity in the population. The size and translucency of hydrated oocytes increased significantly between early morning and late afternoon; this pattern was the same for two study years. This morpho-developmental shift led to the appearance of previously indistinguishable oil drops in ovarian whole mounts which is an easily observed microscopic descriptor of PREF growth. The results clearly suggested that PREF growth was well synchronized between Atlantic horse mackerel that were capable of spawning and provided evidence for the existence of daily spawning synchronicity in the population. Apart from sampling time of day, the size of hydrated oocytes was shown to be affected by body size: a 10 cm difference in maternal length corresponded to a 0.030 mm difference in the diameter of hydrated oocytes. In contrast, the size of early germinal vesicle migration oocytes was correlated neither to sampling time nor to maternal size which suggests that the abrupt increase in PREF size only commences after the onset of the actively spawning sub-phase.

Effect of preovulatory follicle on fertility in Graded murrah buffaloes (Bubalus bubalis)

An investigation was taken up to study the relationship of preovulatory follicle size at the time of first postpartum AI and CL biometry with conception using transrectal ultrasonography in 70 parous Graded Murrah buffaloes maintained under rural conditions. POF sizes were measured ultrasonographically and grouped in to small preovulatory follicle (SPF), medium preovulatory follicle (MPF) and large preovulatory follicle (LPF). Serum progesterone concentration at the time of AI and pregnancy status was negatively correlated indicating that when progesterone level declined to less than 0.3 ng/ml (basal level) at the time of AI, the chances of the animal becoming pregnant was increased. The size of the POF was positively correlated to the size of the CL on day 10 in pregnant buffaloes. The overall POF diameter at the time of estrum was 12.31 ± 0.29 mm (Range 9 to 16 mm) in Graded Murrah buffaloes and 50 % of the buffaloes had POF size &gt; 12 - £14 mm. They conceived only if the POF diameter was more than 9 mm at the time of AI however there was no significant correlation between the POF size at the time of AI and conception. Thus, it was concluded that physiological maturity rather than the diameter of the follicle influenced the fertility in Graded Murrah buffaloes under field conditions.

Effects of preovulatory follicle size on estradiol concentrations, corpus luteum diameter, progesterone concentrations and subsequent pregnancy rate in buffalo cows (Bubalus bubalis)

The present study was undertaken to investigate the effects of preovulatory follicle (POF) size on estradiol concentrations, luteal profile (CL diameter and progesterone concentration) and subsequent pregnancy rate in Murrah buffalo cows. The buffalo cows (n = 49) were synchronized for estrus by two doses of PGF2α given 11 days apart. The buffalo cows were inseminated during standing estrus and again after 24 h. Ovaries were scanned at estrus and 24 h intervals until ovulation, thereafter on days 5, 12 and 16 post-ovulation to examine the POF and CL diameter. Size of POF at estrus was divided into three categories; I: 10 to ≤12; II: >12.0 to ≤14.0; III: >14.0–16.0 mm. Blood samples were collected for estradiol (on day of estrus) and progesterone concentration (on days 5, 12 and 16). The estradiol concentrations were greater (P < 0.05) in category II than category I with the greatest (P < 0.05) concentrations estimated in category III. A positive correlation (P < 0.05) between POF and progesterone concentration, CL diameter and progesterone concentration was observed on all sampling day. Pregnant buffalo cows exhibited greater (P < 0.05) plasma progesterone as compared with their non-pregnant counterpart. Greater pregnancy rates were observed with an increased size of POF (χ2 = 2.9, P > 0.05). It was concluded that the POFs having diameters between 12 and 16 mm are mature enough to be transformed into CL of such optimum diameter and can secrete optimum progesterone concentrations that can sustain the pregnancy in Murrah buffalo cows.