​​Comparative Micro and Macro Anatomical Observation on Preen Gland of Kamrupa (Gallus domesticus), White Leg Horn (Gallus domesticus) and Daothigir Fowl (Gallus domesticus) of Assam

The Indian poultry sector is one of the most vibrant, fastest growing, agro-based, techno-commercial industry which is characterized by its industrialization, faster growth in consumption and trade than any other major agricultural sectors in the world (Bhadauria et al., 2014). Kamrupa is a multi-coloured bird for rural poultry production developed under All India Coordinated Research Project on Poultry Breeding at Assam Agriculture University, Khanapara, Guwahati, Assam. It is three ways cross developed using Assam local ecotype (25%), coloured broiler (25%) and Dalhem Red (50%) population. This variety has coloured plumage, mediocre body weight and longer shanks with optimum egg production. Under backyard system, the body weight at 8 and 20 weeks is 500-650 grams and 1300-1500 grams, respectively.  The male birds weigh 1800-2200 grams at 40 weeks of age the annual egg production is 118-130 eggs with an egg weight of 52 grams. In Kamrupa, the organs are not studied yet except female reproductive system. Further poultry meat as dish is very popular in North East region being 90% of the population of the meat eaters. White Leghorns are good layers  laying on an average of 280 per year and sometimes reaching 300-320, with a weight of at least 55 g. White Leghorns have been much used to create highly productive egg-laying hybrids for commercial and industrial operations. Daothigir fowl is found in Bodoland region of Assam. They are mainly found in Kokrajhar, some part of Barpeta, Nalbari, Bongaigaon and Dhubri on the north bank of Brahamaputra River. These birds are reared by Bodo community of Assam. They rear mainly for meat and eggs. The estimated population of these breeds are 14000. The preen gland or uropygial gland or rump gland or oil gland is a sebaceous gland. It secretes preen oil which maintain the flexibility of feathers and keeps feather barbules from breaking. It also secrets fatty acids, antimicrobial agent and vitamin D precursors. The preen gland also preserved feather structures by keeping keratin flexible and also maintains feather water proofing. (Shafiian and Mobini, 2014). Though extensive information is available on the preen gland of birds in general (Lucas and Stettenhein,1972), the paucity of literature in the comparative micro and macro anatomical aspects in the Kamrupa, White leg horn and Daothigir fowl of Assam promoted to undertaken the present work.

The present study was conducted on the preen gland of fifteen healthy, adult birds of Kamrupa, White leg horn and Daothigir fowl of Assam in Department of Anatomy and Histology, College of Veterinary Science, Assam Agricultural University, Khanapara, Guwahati, Assam, India for period of one year from 2020-2021. Those fowl were procured from different apart of Assam. The experimental birds were brought to the Department of Anatomy and Histology, College of Veterinary Science, Assam Agricultural University, Khanapara, Guwahati and were sacrificed according to the method of Gracey (1968). After sacrifice, the birds were placed on a clean dissecting table and skin and fascia were reflected carefully without disturbing the organs. Then preen gland were removed very carefully from the base of the tail of fowl. After collection, the tissue samples were fixed in 10% neutral buffered formalin solution and were processed as per the standard technique of procedure (Luna, 1968). The paraffin blocks were sectioned in Shandon Finesse microtome at 5 µm thickness and the sections were stained with Mayer’s Haematoxylin and Eosin staining technique for cellular details as per the standard method of Luna (1968).

Macro anatomical observation of preen gland of Kamrupa, white leg horn and daothigir fowl of Assam
 
In present investigation, it was found that the preen gland or oil gland or rump gland or Uropygial gland of Kamrupa, White leg horn and Daothigir fowl of Assam located just below the skin, on the dorsal aspect of the base of the tail. The glands were bilobed structure and it opened on to the surface of the skin by a nipple-like eminence (Fig 1, Fig 2 and Fig 3). The two lobes and the nipple like structure together form a somewhat heart shaped structure. The apexes of the glands were pointed whereas the bases of the glands were broad.



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In present investigation, it was found that the preen gland or oil gland or rump gland of Kamrupa, White leg horn and Daothigir fowl of Assam located just below the skin, on the dorsal aspect of the base of the tail. The glands were bilobed structure and it opened on to the surface of the skin by a nipple-like eminence. Similar findings were reported by Sadoon (2011) in Starling birds, Salibian and Montalti (2009) in various avian species and King and Mclelland (1975) in domestic fowl. The two lobes and the nipple like structure together form a somewhat heart shaped structure. These findings were in accordance with the findings of Hodges (1974) in fowl. The apical portion of the glands were pointed whereas the base was broad.
 
Micro anatomical observation on the preen gland of Kamrupa, white leg horn and daothigir fowl of Assam
 
The capsule of the preen gland of Kamrupa, White leg horn and Daothigir was bounded by connective tissue capsule.  The thickness of capsule of preen gland of Daothigir, White leg horn and Kamrupa were 40.32±1.61µm, 38.41±2.31 µm and 36.51±µm, respectively. The thickness of capsule of preen gland was more in Daothigir (Fig 4) compared to the Kamrupa and White leg horn. The thickness of capsule of preen gland of Kamrupa was thin compared to the White leg horn. The capsule was rich in blood vessels (Fig 4). The interlobular connective tissue observed among the secretary tubules of the gland. The interlobular connective tissues arise from the capsule of the gland. The inter tubular connective tissues also is rich in blood vessels. Numerous fibroblasts were observed in the interlobular connective tissues (Fig 5). The number of fibroblasts were abundant in the preen gland of Daothigir compared to the Kamrupa and White leg horn. The number of secretary tubules of preen gland in Kamrupa were less compared to the tubules of preen gland of White leg horn. The secretary tubules of the preen gland of Kamrupa, White leg horn and Daothigir were open in lumen of the gland (Fig 6). The preen gland parenchyma composed of secretary tubules; duct, which were differentiated by inter tubular connective tissue. The structure of the tubules was similar throughout the whole gland. The tubular epithelial cells were divided into basal or germinative, intermediate, secretary and degenerative layers (Fig 7). The basal or germinative layer consisted of one row of flat shaped cells lied on the basement membrane of the secretary tubules in the preen gland of Kamrupa, White leg horn and Daothigir. The intermediate layer was composed of 2 rows of polygonal cells which laid above the basal layer. The secretary layer was composed of 4 rows of polygonal cells contained lipid droplets as well as secretary granules in the preen gland of Kamrupa, White leg horn and Daothigir. The degenerative layer was adjacent to the lumen of each tubule, composed of few cells with pyknotic nuclei. Each secretary tubules classified into two zones, i.e., peripheral zone and central zone (Fig 8).

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The preen gland of Kamrupa, White leg horn and Daothigir was bounded by connective tissue capsule. These findings concurred with the findings of Kanasiya et al., (2017) in Kadaknath and White Leghorn breeds of poultry and Ushakumary et al., (2011) in Guinea fowl. The thickness of capsule of preen gland of Daothigir, White leg horn and Kamrupa were 40.32±1.61µm, 38.41±2.31 µm and 36.51±µm, respectively. However, these could not be compared due to non-availability of literature. The thickness of capsule of preen gland was more in Daothigir compared to the Kamrupa and White leg horn. The thickness of capsule of preen gland of Kamrupa was thin compared to the White leg horn. The capsule was rich in blood vessels. The interlobular connective tissues were observed among the secretary tubules of the gland. The interlobular connective tissues that arise from the capsule of the gland was also rich in blood vessels. Numerous fibroblasts were observed in the interlobular connective tissue stroma The number of fibroblasts were abundant in the preen gland of Daothigir compared to the Kamrupa and White leg horn. The number of tubules of preen gland in Kamrupa were less compared to the alveoli of preen gland of White leg horn. The tubules of the preen gland of Kamrupa, White leg horn and Daothigir were open in lumen of the gland. Similar observations were reported by Harem et al., (2010) in osprey. The preen gland parenchyma composed of secretary tubules; duct as well as trabeculae, which were differentiated by inter tubular connective tissue. These findings were in total agreement with the findings of Sawad (2006) in Moorhen and Al-mehdawi (2003) in broiler birds. The structures of the tubules were similar throughout the whole gland of Kamrupa, White leghorn and Daothigir. Similar findings were reported by Hodges (1974) in domestic fowl. The tubular epithelial cells were divided into basal or germinative, intermediate and secretary layers which corroborated with the observations recorded by Mohamed (2019) in Mule duck. The basal or germinative layer consisted of one row of flat shaped cells lied on the basement membrane. In Kamrupa, White leg horn and Daothigir, the intermediate layer was composed of 2 rows of polygonal cells lied on the basal layer. The secretary layer composed of 4 rows of polygonal cells contained lipid droplets as well as secretary granules in Kamrupa, White leg horn and Daothigir. Each secretary tubules classified into two zones, i.e. Peripheral zone and central zone. The observation in this study was similar to that of Mohamed (2019) in Mule duck.

Thorough knowledge of the histology of preen gland of Kamrupa, White leghorn and Daothigir of Assam is very essential in elucidating its role in physiology, histopathology, microbiologist and poultry scientist. In current investigation, it was observed that, macroscopically, the preen gland or oil gland or rump gland or uropygial gland of Kamrupa, White leg horn and Daothigir fowl of Assam situated just below the skin, on the dorsal aspect of the base of the tail. The glands were bilobed structure and it opened on to the surface of the skin by a nipple-like eminence. Microscopically, the preen gland of Kamrupa, White leg horn and Daothigir fowl of Assam was bounded by connective tissue capsule rich in blood vessels. The interlobular connective tissues were observed among the secretary tubules of the gland. The interlobular connective tissues were arises from the capsule of the gland. The inter tubular connective tissues also rich in blood vessels. Numerous fibroblasts were observed in the interlobular connective tissues. The number of fibroblasts were abundant in the preen gland of Daothigir compared to the Kamrupa and White leg horn. The preen gland parenchyma composed of secretary tubules; duct as well as trabeculae, which were differentiated by inter tubular connective tissue. The structures of the tubules were similar throughout the whole gland. The tubular epithelial cells were divided into basal or germinative, intermediate, secretary and degenerative layers. Each secretary tubules classified into two zones, i.e., peripheral zone and central zone. This study will be helpful to poultry scientist, microbiologist and pathologist in disease control regime. If we establish a normal anatomy of preen gland then it will helpful to the pathologist and microbiologist to detect any abnormality in the preen gland for control disease because it has antibacterial and antifungal property as well as precursor of Vitamin D for proception of skin. If the disease is control, then the production of meat and egg will increase.

The authors are grateful to the Dean, College of Veterinary Science, Assam Agricultural University, Khanapara, Assam, India for providing the required facilities to conduct this experiment.