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. 2022 May 26:9:903195.
doi: 10.3389/fvets.2022.903195. eCollection 2022.

Exogenous Melatonin Directly and Indirectly Influences Sheep Oocytes

Yang Chen  1 , Xuesong Shan  1 , Huaizhi Jiang  1 , Zhenhua Guo  2
Affiliations

Exogenous Melatonin Directly and Indirectly Influences Sheep Oocytes

Yang Chen et al. Front Vet Sci. .

Abstract

Understanding whether and how melatonin (MT) may impact sheep oocyte development competence is central to our ability to predict how sheep oocytes will respond to artificially regulated estrus. Implanting MT can make sheep enter estrus during the non-breeding season. One study found that the blastocyst rate increased under MT treatment, while another found that the blastocyst rate decreased. Therefore, we conducted a meta-analysis of MT directly and indirectly influencing sheep oocytes. A total of 433 articles were collected from which 20 articles and 34 treatments were finally selected. A method for estimating the default value was established for the litter size analysis. We found that exogenous MT add into in vitro maturation medium was positively related to the blastocyst rate in the lab. However, subcutaneous implanting MT did not affect the in vivo ovulation rate, fertilization rate, blastocyst rate, or pregnancy rate at farm. MT did not affect the in vitro cleavage rate. However, MT improved the in vivo cleavage rate. We hypothesized that implanted MT could increase the concentration of MT in oviduct fluid in vivo, and also that in vitro MT could increase the early cleavage rate of sheep zygotes without affecting the total cleavage rate. In the analysis of oocyte apoptosis caused by injury, the results suggested that pyroptosis would be more suitable for further research. MT produces responses in all body organs, and thus implanting of MT during non-breeding seasons should consider the effect on animal welfare.

Keywords: animal welfare; development; ewe; follicle; meta-analysis.

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Conflict of interest statement

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Figures

Figure 1
Figure 1
Summary of the study selection process. Pub, PubMed; Ovi, Ovid; Pro, ProQuest; Sci, ScienceDirect.
Figure 2
Figure 2
Forest plot of melatonin (MT) treatment effects on sheep oocytes. The subgroup analysis was based on different follicle diameters, different culture treatments, and different months. (A) SMD for the effects of in vitro culture of exogenous MT on follicle diameter and blastocyst cell number. Blastocyst cell number analysis culture droplet subgroup I2 = 36%. (B) RR for the effects of in vitro culture exogenous MT on follicle normal rate, IVM rate, cleavage rate, and blastocyst rate. Cleavage rate analysis of the culture droplet subgroup and the culture well subgroup yielded I2 = 0%. (C) SMD for implanted exogenous MT effects on ovulation rate and fertilization rate. (D) RR implanted exogenous MT effects on cleavage rate, blastocyst rate, and pregnancy rate. (E) Implanted exogenous MT effects on litter size.
Figure 3
Figure 3
Bias analysis and TSA of MT of sheep oocytes. Funnel plots of IVM rate (A) and implant ovulation rate (B). TSA of IVM rate (C) and implant ovulation rate (D).
Figure 4
Figure 4
Proposed mode of action of MT in relation to sheep oocyte developmental competence. (A) MT treatment of sheep oocytes cultured in vitro has antioxidant effects and can increase oocyte development potential. MT can improve early cleavage. Implantation of MT in ewes and rams can promote estrus. There is no evidence to indicate whether implanting MT in ewes inhibits the hypothalamus-gonadal axis. Implanted MT can be enriched in follicles through the blood ovum barrier. Our statistical results show that implanting MT can increase the number of fetuses. (B) MT is involved in many oocyte-related signaling pathways.
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