Morphological changes of reproductive organs during egg formation of autochthonous Oravka hens

The poultry oviduct provides the biological environment for the egg formation and fertilization of ovulated oocyte. The hens are born with a pair of ovary and oviduct, however, the development of the right ovary and oviduct cease and gradually regress. The left ovary and the oviduct remain functional and contribute in the egg formation. The oviduct is a long tubular structure consisting of five functionally and histomorphologically distinct segments namely: infundibulum, magnum, isthmus, utterus and vagina (Pollock and Orosz, 2002; Mishra et al., 2019).


Introduction
The poultry oviduct provides the biological environment for the egg formation and fertilization of ovulated oocyte. The hens are born with a pair of ovary and oviduct, however, the development of the right ovary and oviduct cease and gradually regress. The left ovary and the oviduct remain functional and contribute in the egg formation. The oviduct is a long tubular structure consisting of five functionally and histomorphologically distinct segments namely: infundibulum, magnum, isthmus, utterus and vagina (Pollock and Orosz, 2002;Mishra et al., 2019).
The poultry oviduct provides the biological environment for the egg formation and fertilization of ovulated oocyte. The hens are born with a pair of ovary and oviduct, however, the development of the right ovary and oviduct cease and gradually regress. The left ovary and the oviduct remain functional and contribute in the egg formation. The oviduct is a long tubular structure consisting of five functionally and histomorphologically distinct segments namely: the infundibulum (site of fertilization), the magnum (production of components of egg white), the isthmus (formation of the eggshell membranes), the uterus (formation of calcified eggshell), and the vagina (oviposition or egg laying). Following ovulation, the ovum passes through the entire length of the oviduct, where the constituents of the egg are secreted and deposited from respective parts of the oviduct (Iwasawa et al., 2010;Rahman, 2013;Vijayakumar et al., 2014).
The aim of the study was to analyze the morphological changes of the ovary and oviduct during egg formation of autochthonous Oravka hens.

Material and methods
Experiment was realised in deep litter system in pens with density 7 hens/m 2 . Feeding of hens was providing by feed mixture HYD-10 (crude protein 158.06 g/kg, metabolic energy 11.32 MJ/kg). Feeding and watering were ad libitum. Birds were exposed to natural light as a practiced in rural areas of South-West Slovakia.
The changes of ovary and oviduct in defferent time were investigated on 66 Oravka hens at the top of the laying. Hens were randomly selected and slaughtered by decapitation. Immediately after slaughtering, whole ovary with follicular hierarchy and oviduct were removed in different stage of egg fromation (Table 1). Ovary weight, the weight of the first, second, third, fourth and fifth largest follicles were measured by Mohammadi and Ansari-Pirsaraei (2016). The oviduct weight, total length of oviduct, length of individual parts of oviduct were considered by modified method of Halaj (1983). The data generated during the experiment were subjected to one-way analysis of variance per Duncan's Multiple Range Test (Duncan, 1955) and with the help of JASP 0.8.6 software (JASP, 2018).

Results and discussion
The ovary weight increased depending on the location of the follicle in the ovary. We found the lowest ovarian weight after laying an egg (46.29 g), which causes follicle to fall out after ovulation. During the period of egg white formation, the ovum weight gradually increased to 47.81 g, to the eggshell membranes formation to 49.08 g and most to the eggshell formation (51.55 g). The ovary reached its maximum weight 20 hours after the egg was laid, which means that the follicle growth had already stopped during this period and was matured the next time. These weight changes were significant (p <0.05) in last two stages of egg formation ( Table 2). The weight of the largest follicle varies from 13.22 to 17.46 g, the second from 9.51 to 14.89 g, the third from 6.65 to 10.41 g, the fourth from 3.09 to 7.74 g and the fifth from 0.92 to 4.71 g. Number of visible follicles on ovaries varies from 1000-3000 and in modern hybrids even more. Follicles of smaller diameter are pale, whereas follicles that already started to grow and develop are yellow (Hocking et al., 1987;Hocking and McCormak, 1995;Robinson et al., 1996;Peris et al., 2005).
Hobson and Lewis (2009) respectively Head (2010) recorded that variability in follicle weight is related to several factors, e.g. laying intensity, length egg series and laying rhythm.
The current findings of oviduct which appeared to be long, less convoluted, highly vascular tube and occupied the most left side are similar to those recorded by Khokhlov and Kuznetcov (2007), Mahmud (2017). Similarly, Veterany and Jedlička (2002) reported that the oviduct of the hen was well-developed at the left side, atrophied at the right side and consisted of all five regions as described in the present study.
The oviduct weight significantly increased with increasing time of egg formation. After ovulation, the oviduct weight averaged 71.89 g, egg white formation 75.30 g, eggshell membranes 75.84 g and eggshell 76.31 g (Table 3). Similarly, the functional parts of oviduct change their weight. The infundibulum did not change its weight significantly (from 4.74 to 7.82 g). The magnum reaches its highest weight just after ovulation (36.29 g), when proteins ready for secretion during egg white formation were formed. Gradually, the weight of this portion decreased to 35.75 g, eggshell membranes 32.86 g and eggshell 31.22 g. The isthmus increases weight especially in the period of the formation of eggshell membranes (6.21 g). The uterus records an increase in weight during the period of eggshell formation (25.87 g), but has the lowest weight after ovulation (22.51 g). The vagina during period of eggshell formation has the highest weight (6.82 g).
As shown  In the adult hen, the oviduct receives the ovum from the ovary and provides the biological environment for the formation and potential fertilisation of the egg. During egg formation, albumin, from the magnum is deposited