Characters of reproductive system, ovarian follicle and the resulting oocytes
Weights of reproductive systems and ovaries were increased in ewes compared to lambs. Weights (g) of ovaries were higher in the luteal phase (P<0.05) than the follicular phase of ewes. The numbers of small follicles were higher (P<0.05) in lambs compared to ewes. Furthermore, the numbers of medium follicles were higher (P<0.05) in pubertal sheep during follicular phase compared to other groups. Besides, the numbers of large follicles were higher (P<0.05) in ewes compared to lambs. The quality of oocytes was high of the luteal phase compared with the follicular phase (Table 1). The percentage (%) of recovered oocytes of aspirated follicles was higher in ewes compared to female lambs. Oocytes of grade I and II were comparable among groups whereas oocytes of grade III were higher in pubertal sheep (Fig 1).
Follicular fluid biochemistry
The concentrations of total protein (g/dl), urea (mg/dl), glucose (mg/dl), total cholesterol (mg/dl) and triglycerides (mg/dl) are presented in Table (2). The total protein values were high (P<0.05) in FF of ewes compared to that of female lambs versus urea values. The values of glucose were high (P>0.05) in FF of ewes compared to FF of female lambs. Additionally, the values of total cholesterol and triglycerides were low in FF of ewes compared to FF of female lambs. Finally, the values of determined metabolites were comparable in FF of follicular or luteal phase FF of ewes.
The results of the present study demonstrate the weight of reproductive system and ovary, ovarian follicle numbers in relation to sizes, oocyte recovery, oocyte quality, in addition to follicular fluid biochemistry (Fig 1 and Table 1-2). The weights (g) of reproductive system and ovary were increased in ewes compared to female lambs due to simultaneous increase of body weight and presence of corpora lutea
(Mohammed et al., 2012; Mohammed and Kassab 2015). Corpora lutea weight on days 14 was 4.7 g, which represents about 30.1% of the ovarian weight
(Fields and Fields, 1996;
Osman and Shehata, 2005).
The number of small follicles was not differed among groups whereas the number of medium and large follicles were increased in ewes groups, which might be due to the changes of FSH and LH hormonal values (
Gordon, 2003;
Morton et al., 2023). The highest number of medium follicles was found in follicular phase of ewes group compared to luteal phase or female lamb groups. This might be attributed to follicular wave emergence, which is primarily controlled by follicle-stimulating hormone during estrous cycle
(Bartlewski et al., 2011). In addition, the number of antral follicles is highly variable among animals
(Murasawa et al., 2005). The number of antral follicles in heifers and beef cows is influenced by birth weight and age but not by stage of the estrous cycle
(Cushman et al., 2009). Although the percentage of oocyte recovery increased in ewes compared to female lambs, the oocytes quality was not differed among groups (Table 1). The higher follicle sizes in ewes than female lambs, the higher pressure inside the follicle resulting in improvement of oocyte recovery and quality
(Sarwar et al., 2020).
Follicular fluid plays pivotal roles in follicle growth and development, maturation of oocytes and development of preimplantation embryos
(Lopes et al., 2019; Azari-Dolatabad et al., 2021;
Gabryś et al., 2022). The values of FF metabolites of female lambs and ewes (total protein, urea, glucose, total cholesterol and triglycerides) are presented in Table (2). Follicular fluid is liquid surrounding the developing oocyte within the ovary. It is originated from blood plasma components and the secretory activity of the oocyte and the surrounding cells
(Mohammed et al., 2005; Hashemitabar et al., 2014; Aljubran et al., 2023). Certain biochemical constituents of follicular fluid changes with the follicle growth and maturation to influence various processes
(Deka et al., 2014).
The total protein values were high (P<0.05) in FF of ewes compared to FF of lambs due to the high follicle size or follicular wave (Table 1)
(Aller et al., 2013). The values of urea in FF were significantly low of ewes compared to female lambs. This finding is in agreement of other studies
(Mohammed et al., 2019a,b). This might be attributed to differences in follicle sizes among groups (Table 1). Studies of
Leroy et al., (2004) and
Mohammed et al., (2011) indicated that urea concentration decreased from small to large follicles in dairy cows and sheep, respectively.
The values of glucose were slightly high (P>0.05) in FF of ewes compared to FF of female lambs, which might attributed to larger follicle diameter in ewes compared to female lambs (
Tabatabaei and Mamoei, 2010;
Tabatabaei et al., 2010). Glucose plays a pivotal role in ovarian tissue metabolism because it is the major energy source for the ovarian tissues. There is a possibility that glucose metabolism is less intensive in the large follicles compared to the small follicles in addition to increase permeability of the follicle-blood barrier during follicular growth
(Leroy et al., 2004).
Finally, the values of total cholesterol (P>0.05) and triglycerides (P<0.05) were low in FF of ewes compared to FF of female lambs, which consistent with earlier studies (
Thangavel and Nayeem, 2004;
Tabatabaei and Mamoei 2010;
Tabatabaei et al., 2010). The decreased cholesterol value in large follicle might be attributed to the conversion of cholesterol to estrogen and progesterone hormones. Additionally, the significant increase of triglycerides in smaller follicle because they might be the alternate sources of energy for follicle cells in addition to triglycerides did not pass through the follicular membrane
(Harlow et al., 1987; Grummer et al., 1988).
The continuous needs of oocyte and FF are required for
in vitro embryo production concerning development of oocyte maturation, fertilization and culture
(Mohammed et al., 2005; 2019a,b;
Al-Zeidi et al., 2022a,b;
Al-Jubran et al., 2023;
Mohammed et al., 2024a,b). It has been found that follicular fluid obtained from large follicles or after LH surge and supplemented to maturation medium (20-50%) were found to increase oocyte maturation and embryo development
(Mohammed et al., 2005; Spacek and Carnevale, 2018). Furthermore, supernatant from cultured cumulus-granulosa cells and follicular fluid were found to improve
in vitro maturation in patients with polycystic ovarian syndrome (POS)
(Madkour et al., 2018).