Ultrasonographic observation in combination with progesterone monitoring for detection of ovulation in Labrador Retrievers

Although it is well known that the ovulation occurs during a period of time after LH surge in dogs, there are few reports of observing the entire process of development, ovulation, and luteinization of each follicle. This study aimed to detect the ovulation kinetics by ultrasonography in combination with progesterone monitoring, and therefore identify the time-range of the ovulation process in a dog. Daily transabdominal ultrasonography and progesterone monitoring was conducted for 24 natural estrus cycles of Labrador Retrievers. Ovarian follicles were observed as anechoic structure with contours before ovulation.
Ovulation (follicular collapse) was defined as when follicles became cloudy and contours obscure by transabdominal ultrasonography. Ultrasound imaging was capable of identifying the day of ovulation for 94.7% (178/188) of the follicles through the appearance of collapsed follicle or corpus luteum. Ovulation was observed between LH 0 (the day of LH surge) and LH 5, with 48.0%, 33.5%, and 15.0% for LH 2, LH 3, and LH 1, respectively.
  • The total number of ovulations on LH 2 and LH 3 accounted for 81.5% (141/173) of the total ovulation in 24 cycles examined. Ovulation occurred in 12 cycles for 2 d, and for 3 d in 12 cycles. Seventeen cycles (70.8%) with multiple days of ovulation showed the largest number of ovulations on LH 2.
  • The average follicle diameter 3 d before the LH surge was less than 5 mm, then exceeded 5 mm 2 d before the LH surge. The average follicle diameter at the time of ovulation (follicular collapse) was 6.1±1.0 mm (n=118). On the day before ovulation, the average diameters of the follicles ovulated on LH 1, LH 2, and LH 3 were 5.0±0.7 mm, 5.8±1.2 mm, and 6.2±1.3 mm, respectively.
  • There was a significant difference in the follicle diameter between on LH1 and LH2 (p<0.001), LH2 and LH3 (p<0.05), and LH1 and LH3 (p<0.001). Suggesting that it is difficult to estimate the ovulation day based on follicle size.
  • This study showed that combination of ultrasonography with progesterone monitoring could follow follicular development, ovulation, and luteinization of the ovary in Labrador Retrievers. The direct visualization of the ovulation was achieved in a non-invasive, labour-friendly way.
  • Furthermore, the time-range of the ovulation process was clarified in a dog. These results may contribute to an accurate understanding of the optimum timing of mating and improved breeding efficiency, including artificial insemination and embryo transfer for Labrador Retrievers.

Nuclear progesterone receptor regulates ptger4b and PLA2G4A expression in zebrafish (Danio rerio) ovulation

Previous studies have implicated the nuclear progesterone receptor (Pgr or nPR) as being critical to ovulation in fishes. This study investigated the expression of Pgr in zebrafish ovarian follicles throughout development as well as putative downstream targets of Pgr by searching the promoter regions of selected genes for specific DNA sequences to which Pgr binds and acts as a transcription factor. Expression of Pgr mRNA increases dramatically as follicles grow and mature. In silico analysis of selected genes linked to ovulation showed that the prostaglandin receptors ptger4a and ptger4b contained the progesterone responsive element (PRE) GRCCGGA in their promoter regions.
Studies using full-grown follicles incubated in vitro revealed that ptger4b was upregulated in response to 17,20β-P. Our studies also showed that the expression of phospholipase A2 (PLA2G4A) mRNA and protein, a key enzyme in prostaglandin synthesis, was upregulated in response to 17,20β-P treatment. pla2g4a was not found to contain a PRE, indicating that it is regulated indirectly by 17,20β-P or that it may contain an as-of-yet unidentified PRE in its promoter region. Collectively, these studies provide further evidence of the importance of Pgr during the periovulatory periods through its involvement in prostaglandin production and function by controlling expression of PLA2G4A and the receptor EP4b and that these genes appear to be regulated through the actions of 17,20β-P.

Effect of PGF  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 (PGF), 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; PGF 24 h after G1), PG2 (PGF 24 and 48 h after G1) and PG3 (PGF 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.

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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, PGF 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.