Theriogenology2017; 98; 108-115; doi: 10.1016/j.theriogenology.2017.05.001

Deep anestrous mares under natural photoperiod treated with recombinant equine FSH (reFSH) and LH (reLH) have fertile ovulations and become pregnant.

Meyers-Brown, GA
·
Loud, MC
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Hyland, JC
·
Roser, JF

Abstract: The most common equine breeding practice to decrease the time to the first ovulation of the year is to use artificial lights starting December 1 in the Northern Hemisphere. It can take 60-90 d for this lighting regimen to induce a fertile ovulation. The success rate for pharmaceutical compounds to carry out the same process has been variable. One compound that did induce an early ovulation was recombinant equine follicle stimulating hormone (reFSH), but neither pregnancy nor cyclicity was established in that study. Starting on December 1, 20 deep-anestrous mares of light horse breeds (4-15 y old) with follicles ≤ 20 mm in diameter and progesterone < 1 ng/mL were maintained under natural photoperiod while 10 control mares were maintained under artificial photoperiod. Starting on February 6, treatment mares were randomly assigned to one of two groups: reFSH (n = 10) or reFSH/reLH (n = 10). Jugular blood samples were collected daily from all mares, and luteinizing hormone (LH), FSH, progesterone (P), estradiol-17β (E) and immunoreactive (ir)-inhibin were analyzed by radioimmunoassay (RIA). When the largest follicle reached ≥32 mm in diameter, reFSH treatment was discontinued in both groups while reLH treatment continued in the reFSH/reLH group until a cohort of follicles reached ≥35 mm in diameter. Human chorionic gonadotropin (hCG) was administered intravenously (iv) to induce ovulation, and mares were bred to a fertile stallion every other day until ovulation. Mares receiving either reFSH or reFSH/reLH developed follicles ≥35 mm within 5-6 d of treatment compared with 15.8 ± 3.4 d in the control group. Both reFSH and reFSH/reLH induced ovulation in 100% of the mares within 10 d after treatment resulting in an 80% conception rate and a 70% pregnancy rate for both groups. Conception and pregnancy were designated as either presence of a 14 d old embryo (n = 16) or a fetal heartbeat at 24 d (n = 14), respectively. Only three mares in the control group ovulated within the same treatment period. Later ovulations in the control group resulted in 100% conception and pregnancy rates. At 25 d post-conception, treated mares that were pregnant (n = 7 per group) were administered prostaglandin (PGF2) to terminate the pregnancy and later returned to estrus. Treatment with reFSH or reFSH/reLH given to deep-anestrous mares under natural photoperiod induced fertile ovulations that resulted in pregnancy and cyclicity when pregnancies were terminated.

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Publication Date: 2017-05-08 PubMed ID: 28601147DOI: 10.1016/j.theriogenology.2017.05.001Google Scholar: Lookup

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Randomized Controlled Trial

Summary

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This study investigates the use of recombinant equine FSH (follicle stimulating hormone) and LH (luteinizing hormone) on deep anestrous mares under natural light conditions to reduce the time to first ovulation and enhance fertility. The results indicate that this form of hormonal treatment can swiftly induce fertile ovulations, resulting in a conception rate of 80% and pregnancy rate of 70%, thereby offering a potential alternative to traditional methods that employ artificial light and wait for 60-90 days.

Research Design and Methods

The study was conducted on 20 deep-anestrous mares aged between 4 and 15 years, with follicles ≤ 20 mm in diameter and progesterone < 1 ng/mL. The mares were maintained under natural light conditions, while 10 control mares were kept under artificial light regimes.
From February 6, these mares were randomly divided into two groups and treated with either recombinant equine FSH (reFSH) only or a combination of reFSH and LH (reLH).
Jugular blood samples were taken daily from all mares. Hormones like luteinizing hormone (LH), FSH, progesterone (P), estradiol-17β (E), and immunoreactive inhibin were analyzed.
Upon the largest follicle reaching ≥32 mm in diameter, the administration of reFSH was stopped while reLH treatment continued for the combined group. Human chorionic gonadotropin (hCG) was injected to induce ovulation, and the mares were bred with a fertile stallion every other day until ovulation.

Results and Findings

Both the reFSH only and the combination group ovulated within 10 days of the end of the treatments, with 80% conception and 70% pregnancy rates, significantly faster and higher success rates than the control group.
The control group, under artificial light conditions, required an average of 15.8 ± 3.4 days to develop follicles larger than 35mm, and only three of them ovulated within the treatment period.
However, all control group mares conceived and became pregnant after extended ovulation times.
Pregnant treated mares were given prostaglandin (PGF2) at 25 days post-conception to terminate the early pregnancies, which caused them to return to estrus.

Conclusion

The use of recombinant FSH and/or LH hormones on deep anestrous mares under natural light conditions can induce fertile ovulations faster than traditional artificial light-induced methods.
These hormonal treatments resulted in high rates of conception and pregnancy.
They could provide a reliable and efficient pharmaceutical alternative to traditional equine breeding practices that rely on specific lighting conditions, offering animal husbandry a new route to achieve time-effective equine reproduction.

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APA

Meyers-Brown GA, Loud MC, Hyland JC, Roser JF. (2017). Deep anestrous mares under natural photoperiod treated with recombinant equine FSH (reFSH) and LH (reLH) have fertile ovulations and become pregnant. Theriogenology, 98, 108-115. https://doi.org/10.1016/j.theriogenology.2017.05.001