Abstract
Effects of non-steroidal aromatase inhibitor letrozole on ovarian function in ewe were investigated through testing the hypothesis that letrozole will arrest the growth of dominant follicles, resulting in the emergence of a new follicular wave at a predictable post-treatment interval. Treatment ewes (n = 10) were treated using an intravaginal sponge (regardless of the stage of estrus) containing 7.5 mg letrozole for five days followed by prostaglandin injection. The control group (n = 10) was treated with gonadotropin prostaglandin gonadotropin (GPG) protocol for ovarian synchronization. Ovarian structures were daily monitored with trans rectal ultrasonography concomitant with blood sampling. Commercial enzyme-linked immunosorbent assay Kits assigned steroid concentration of estradiol, testosterone and progesterone. Some biochemical parameters including blood glucose, total proteins, lipid profiles were measured as a preliminary screening for the effect of applied letrozole treatment on ewes general health condition. Treatment with letrozole decreased serum concentrations of estradiol during sponge insert in the vagina while its concentration increased following removal correlated with the number of ovulatory follicles. On the other hand, the concentration of Progesterone increased correlated with increased number and diameter of corpora lutea resulting from increased diameter and number of ovulatory follicles. The onset of estrus was about 54.00 ± 0.40 hrs. After sponge removal and continued for 25.17 ± 0.24 hrs. Ovulation was synchronous and occurred at 78.70 ± 0.21 hrs after sponge removal. There was no effect of letrozole treatment on measured metabolic parameters. We concluded that letrozole proved to have potential as a non-steroidal treatment for controlling ovarian function and onset of estrus in the ewe.
Highlights
Number of large sized follicles did not differ between letrozole group (0.80 ± 0.21 ) and gonadotropin prostaglandin gonadotropin (GPG) Group (Fig. 2B)
Just from two decades, non-steroidal aromatase inhibitors were used for induction of ovulation ( Mitwally and Casper, 2001, 2002;Navarro et al, 2008; Mitwally et al 2008).The results obtained from clinical observations of species other than ruminants has inspired many scientists to apply this substance on animals testing its effect on ovarian function and synchronicity of estrus (Rogan et al, 2011;Yapura et al, 2016.,2018)
Diameter of ovulatory follicles were increased for letrozole treated group over GPG. group and this were the same result observed in cattle by yapura (Yapura et al, 2018); estradiol withdrawal was associated with prolonged dominance of ovarian follicles which produced by elevated LH secretion from anterior pituitary gland resulting in increased period of FSH suppression which hinders the emergence of a new follicular wave
Summary
Increasing concern regarding the toxicity ofSheep production is considered a suitable candidate for increasing lamb and meat production covering daily increasing human demands with a profitable role in solving local shortage in animal proteins (LENG, 1990), with the lower cost of production when compared with that of cattle (Martin, 2016).especially when intensive managemental practices such as application of estrus synchronization were adopted (Kulaksiz and Ucar, 2013, Gootwine, 2017).hormonal preparations used to promote growth rates in cattle and the hazard of the potential carcinogenicity of steroid hormone residues in meat or milk concluded to prohibiting the use of estrogens and other steroid hormones as growth promoters in animals designated for human consumption in all states of the European Union as of 1 January 1989(Andersson, and Skakkebaek, 1999; Daxenberger et al, 2001 and Official Journal of the European Union, 2003). P450arom is a unique member of family 19 (Simpson et al, 2002) which is located in the endoplasmic reticulum of mammalian cells in which the CYP19 gene is expressed, such as adipose tissue, brain, adrenal glands, gonads, liver and placenta (Vanselow et al.,2001), P450arom contains a heme group in its structure and is functionally associated with another member of P450 cytochrome family, NADPH reductase, which acts as a donor of reductive equivalents (Simpson et al, 2002) It is responsible for catalyzing the final, rate-limiting step in the production of estrogens (estrone and estradiol) from C19 substrate (androstenedione and testosterone). Examples of these Type II estrogen synthetase-specific inhibitors are letrozole, anastrozole, and fradozole (Goss and Strasser, 2001)
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