Introduction

The skin is an effective barrier which prevents desiccation of electrolytes and macromolecules from the body (Dyce et al., 2002). The skin glands derive from interactions of the epidermis and dermis within the skin (Widelitz et al., 1997). Two different types of glands are located in the dermis of the skin serving a variety of functions. The sebaceous gland which were budding from around the hair follicles at 90-95 days (Shahrooz and Ahmadi,  2004), is an outgrowth of the external root sheath of the hair follicle and the gland empties its oily product directly into the follicle itself. The glands may be simple, branched, or compound alveolar types based on their histology (Dellmann, 1993). The sweat glands were budding at 115-120 days (Shahrooz and Ahmadi,  2004) and are tubular glands that classified into two types: the merocrine types are simple tubular glands that open directly onto the skin surface and found mainly in special skin area such as the planum nasolabiale of the ox. The apocrine types are simple coiled tubular or saccular glands that the most extensively developed in the domestic mammals and located throughout most of the skin. The structure of these glands varies considerably among species. (Dellmann, 1993).

Iran possesses 20 breeds of sheep and almost all sheep breeds are indigenous (Kiyanzad et al., 2003). One of main area with respect to sheep production is Charmahal va Bakhtiari province in West of Iran. The most sheep breed ecotype is Bakhtiari sheep. No histological information is yet available on skin glands of Bakhtiari sheep. Therefore, the present study was undertaken.

Materials and Methods

For this study, twenty-four Bakhtiari sheep were used and divided into four age groups: neonatal (1-10 days), young (5-8 months), young adult (1-2 years) and old adult (3years and more). In each age group, six animals (3 each sex) were utilized. Skins samples were collected from eight regions namely neck, shoulder, hip, rump, leg, forearm, belly and flank and were fixed in 10 percent neutral buffered formalin solution.

Tissues were stained with Hematoxylin eosin, Van Giesson, Ayoub-Shklar, Masson trichrome, Foot’s method for reticulum (Luna, 1968) and Verhoeff (Mallory, 1968). By using light microscope, histological studies of sebaceous glands and sweat glands were carried out in all the four age groups and in all the regions of skin in both sexes.

Results and Discussion

The sebaceous glands in all the skin regions were simple branched alveolar types in the Bakhtiari sheep. Dellmann (1993) has stated that the types of sebaceous glands were simple, branched, or compound alveolar in domestic animals. In the present study, the sebaceous glands were always associated with hair follicles and located just above the sweat glands, between hair follicles and arrector pili muscle. Unlike Dellmann (1993) has reported that the sebaceous glands were located only in the deep layer of dermis, they present only in upper part of papillary layer of dermis in all the skin regions of Bakhtiari sheep (Fig. 1).

The duct of sebaceous glands in most regions was mainly consisted of a simple to stratified cuboidal lining, which opens directly into the hair follicles. However, in some regions, it was changed to simple squamous. The lining of sebaceous gland duct in domestic animals were reported as stratified squamous epithelium (Dellmann, 1993).

In none of the age groups and sexes of Bakhtiari sheep, the sebaceous glands were not observed around of the deepest primary hair follicles which infiltrated in reticular layer of dermis. Also, the arrector pili muscle which

associated with sebaceous glands were not seen any (Fig. 2). By age increasing, the size and number of secretory units of the sebaceous glands were increased (Fig. 1,3).

In the present study, an abundance of blood capillaries and collagen fibers were found around the sebaceous glands and these glands possessed a thin layer of reticular and elastic fibers which were became the thinnest around the sweat glands (Fig. 4). These findings have not yet reported.

The sweat glands in all the skin regions were mostly below the sebaceous glands, just between the hair follicles and the boundary of papillary and reticular layer of dermis in all the four age groups and in all the regions of skin (Fig. 5). The sweat units were composed of simple coiled saccular types whose secretory portion consisted of a single layer of squamous to cuboidal epithelial cells. The types of sweat glands in other species were reported as simple saccular, tubular (Dellmann, 1993) or tubuloalveolar glands (Pourlis, 2010).

In all the age groups studied, the secretory cells of sweat glands were lined with a simple. The lining varied from flattened cuboidal to low columnar cells, depending on the stage of their secretory activity which correlates to the findings of Pourlis (2010) in Karagouniko sheep and domestic animals (Dellmann , 1993).

The free apical cytoplasm of the secretory cells had protruded into the lumen, called secretory caps (Fig. 4), that indicated their secretory activity which were similar to those of domestic animals (Dellmann, 1993) and Karagouniko sheep (Pourlis, 2010).

The secretory cells surrounded by one row of myoepithelial cells. These findings were similar to that of Dellmann (1993). The duct of sweat glands was mainly consisted of a row of squamous to cuboidal cell which penetrated the epidermis of the hair follicle just before it opens onto the skin surface. But in other sheep breed (Pourlis, 2010) and domestic animals (Dellmann, 1993), the sweat gland duct was made up of two layers of flattened cuboidal cells.  The sweat glands similar to sebaceous glands, present only in upper part of papillary layer of dermis in all the skin regions of Bakhtiari sheep (Fig. 2,3), whereas in some textbooks of veterinary histology has reported that they located only in the deep layer of dermis (Aughey and Frye, 2001; Dellmann, 1993).

The sweat glands were observed around of all the hair follicle types in all the age groups studied (Fig. 2), while Dellmann (1993) has stated that the secondary hair follicles may have the sebaceous glands but lack the sweat glands.

As the age increased, the size and number of secretory units of the sweat glands were also increased (Fig. 1,3). In the present study, the sweat glands surrounded by a thin layer of elastic (Fig. 1), reticular (Fig. 5) and collagen fibers (Fig. 2,4).

In this research, no significant difference in skin glands between male and female was observed, but the following significant histological differences among the regions and different age groups were found: The sebaceous glands were not observed around of the deepest primary hair follicles which infiltrated in reticular layer of dermis. The sweat glands in 1-10 days age groups were smaller, more and incipient. All the skin glands were larger and well organized in young adult sheep and more. The sweat glands were observed around of all the hair follicle types in all the age groups studied. Secretory caps in the sweat glands were existed only in the skin of young adult sheep and more.

Conclusion

Histological characteristics of the sweat glands and sebaceous glands of skin not only differ among different breeds but also differ among different ages and regions in each breed.

Acknowledgements

The author is grateful to the School of Veterinary Medicine of Islamic Azad University, Shahrekord Branch, for providing financial assistance.

References

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