In the present study, the liver of both the breeds was covered by two distinct layers i.e outer peritoneal layer and inner connective tissue covering (Fig. 1) as earlier reported by Pareek (2000) in Magra sheep. The outer peritoneal layer covered each lobe of liver of both Bakerwali and nondescript goats except at places where it was reflected as ligaments and dorso-caudally a small area where the organ was directly related to the diaphragm. Similar observations were made earlier by Pareek (2000) in Magra sheep. The inner connective tissue covering was in the form of a capsule i.e. Glisson’s capsule as reported by Trautmann and Fiebiger (1957) in cattle, Bamaniya (2013) in Marwari goat and Rashad et al. (2017) in buffalo. The liver was encapsulated with capsule which comprised of mainly collagen (Fig. 2) and reticular fibres irrespective of the breed as also reported by Modekar et al. (2003) in goats, Bamaniya (2013) in Marwari goat and Thakur (2020) in buffalo. Few fibroblasts were also observed in between these fibres (Fig. 3). From the capsule connective tissue extended into the liver lobes, as interlobular connective tissue, to surround individual liver lobules and support the vascular and bile duct systems. The connective tissue fibers comprised of loosely arranged collagen fibres and reticular fibers forming network within parenchyma. The reticular fibers also formed a delicate framework around the hepatocytes and sinusoids as also observed earlier by Pareek (2000) in Magra sheep. The fine collagenous fibers surrounded each hepatocyte and thick collagenous fibres were also seen around bile ductules. The interlobular connective tissue was very less in non-descript goats. The interlobular connective tissue (collagen and elastic fibres) were seen surrounding the lymph vessels, branches of the hepatic artery, branches of the portal vein and a bile duct throughout section of liver as also reported by Thakur (2020) in buffalo.

The hepatic lobules formed the anatomical structural unit of the liver in both the breeds under study and were present throughout the parenchyma of liver as also reported by Thakur (2020) in buffalo. The lobules were polyhedral or prismatic in outline (Fig. 4) in both the breeds. Similar observations were made by Modekar et al. (2003) in goats and Madhan and Raju (2014) in sheep, goat and cattle. However, Khan et al. (1989) observed irregular shaped liver lobules with few hexagonal shaped lobules in goat. The hepatic lobules were easily recognized in Bakerwali goat whereas in non-descript goats the interlobular connective tissue was minimal making it difficult to recognized the hepatic lobules (Fig. 5). Prunescu et al. (2002) also showed no connective septa around the hepatic lobules in liver of European bison. In present study, each lobule had central vein in the centre and peripheral portal area (Fig. 5) irrespective of the breed. The number of central veins in a section indicated the number of lobules. An anastomosing network of bile canaliculi, formed by the apposed cell membranes of hepatocytes was present throughout the laminae as reported by Mariappa (1981) in calves. Various blood vessels filled with blood and ducts filled with fluid were also seen in hepatic lobules.

In both Bakerwali and non-descript goats, the portal lobule was functional unit of the liver. It was a triangular area consisting of the parenchyma of three adjacent hepatic lobules that was drained by the bile ductule in the portal canal (Fig. 6). Similar observations were made Modekar et al. (2003) in goats. The group of the portal vein, hepatic arteriole, bile ductule and lymph vessels appeared at the each angle of hexagonal hepatic lobule and in centre of portal lobule (Fig. 7). It was supported by loose areolar connective tissue. The collagenous fibers encircled the portal veins and the hepatic arterioles and the elastic fibers invested the arterioles and the bile ductile predominantly in both Bakerwali and non-descript goats.

The liver acinus was a diamond-shaped area in both the breeds and comprised of hepatic parenchyma of parts of two classic lobules. It presented three ill-defined zones irrespective of the breed (Fig. 8). Zone 1 which was nearest to the vascular axis of liver acinus, was metabolically most active from where the hepatocytes receive excellent nutrient and oxygen supply. Also these cells were first to be exposed to toxins entering into the liver. The second zone i.e. zone 2 was intermediate in activity and the last one i.e. zone 3 borders the central vein and was the least supplied with nutrients and oxygen. The hepatocytes of zone 3 were darker stained as compared to zone 2 and 1. The cytoplasm of hepatocytes was darkly eosinophilic in zone 3 and light in zone 2 and 1 as also reported by Eurell and Frappier (2006) in cattle.

In both the breeds under study, the liver parenchyma was primarily comprised of hepatocytes (Fig. 9) which appeared as polygonal epithelial cells with abundant eosinophilic, granular cytoplasm and large, centrally located round nuclei as reported by Modekar et al. (2003) in goats and Eurell and Frappier (2006) in cattle. Hepatocyte nuclei contained a prominent nucleolus and scattered clumps of heterochromatin. Occasionally, binucleated hepatocytes (containing two nuclei) were also found in adult Bakerwali goat (Fig. 9) similar to the findings of Pareek (2000) in Magra sheep. Hepatocytes were arranged in radiating cords (hepatic cords) approximately one to two cells in thickness as earlier reported by Pareek (2000) in sheep. This type of pattern of radiating cords was more prominent in Bakerwali goats. In non-descript goats these cords anastomosed with one another showing interconnected network of hepatic arch, enclosing spaces “the sinusoids”. Each hepatic cord was supported by fine meshwork of reticular fibres. Pareek (2000) reported one cell thick hepatocytes arrangement in sheep whereas Bevelander and Louis (1961) observed two cell thick hepatocytes arrangement in mammals. The hepatocytes were arranged in cords forming laminae, one cell thick with their free surfaces facing the sinusoids as reported by Bamaniya (2013) in goats.

Every hepatic lobule had central vein which was lined by reticulo-endothelial cells resting on a thin basement membrane and encircled with collagenous and reticular fibers irrespective of the breed. The central veins connected with sublobular veins at the periphery of the lobules and communicated directly with sinusoids as reported by Eurell and Frappier (2006) in cattle. The hepatic sinusoids were blood capillaries, located between hepatic cords that courses through the lobule carrying blood from terminal branches of the interlobular hepatic arterioles and interlobular portal venule to the central vein. The sinusoids often communicate with each other via spaces in between hepatocytes and cords through a perisinusoidal space. This arrangement might ensure that each hepatocyte have at least one surface adjacent to a sinusoid. Sinusoids were lined by two types of cells; endothelial cells and stellate marcophages (kupffer cells). The sinusoids in both the breeds of goats were non porous with continuous basal laminae. However, Eurell and Frappier (2006) in goat stated that endothelial lining was discontinuous and a sinusoidal basal lamina was absent. Bamaniya (2013) reported that kupffer’s cells (stellate macrophages) were scattered among the sinusoidal endothelial cells in Marwari goat. These specialized cells had a large blue stained nucleus and prominent pink cytoplasm. They appeared as inconspicuous flattened cells or as prominent triangular active phagocytic cells or as rounded cells within sinusoids as darkly stained cells. Nucleus was indented and the indentation was facing the bulk of the cytoplasm (Fig. 10). Similar observations were made by Banks (2007) in domestic mammals.

In Bakerwali and non-descript goats, the portal vein entered into the liver at a hilus, called the porta, on its visceral surface and finally ended into the sinusoids. It was composed of a prominent internal elastic lamina and endothelium, tunica media was thin and consisted of smooth muscle layer and bundles of collagenous fibers and a prominent tunica adventitia, comprised of layers of smooth muscle cells, collagenous and elastic fibers. The hepatic artery entered into the liver through the hilus and form interlobular hepatic arterioles found in the portal area. These arterioles had a smaller lumen with a thicker muscular wall lined by elastic fibers.

Lymph vessels were also observed in capsule as well as in portal areas along with portal vein and hepatic artery irrespective of the breed as also observed by Pareek (2000) in sheep. The hepatic lymph node was surrounded by a capsule which sends trabeculae into the parenchyma of the node (Fig. 11). The inner portion of capsule and trabeculae contained smooth muscles. The cortex contained sinuses, diffuse lymphatic tissue and lymphatic nodules. A network of fine branching reticular fibres provides a supporting framework for the diffuse and nodular lymphatic tissue. The continuity of the subcapsular sinus with the cortical sinus was also evident. The medulla of lymph node was composed of medullary cords and sinuses as also reported by Eurell and Frappier (2006) in cattle. The medullary sinuses also contained smooth muscle cells. Lymph node was surrounded by loose areolar connective tissue comprised of fine collagen and reticular fibers and abundant of adipose tissue.

In both the breeds, the small bile ductules were lined by high cuboidal epithelium to simple columnar epithelium. These bile ductules joined to form the large intra-hepatic ducts and finally leave the glands via the main hepatic duct, at the hilus. The bile ductules were located in the portal area with variable size and shape lined with low cuboidal epithelium and closer to lining became oval with nuclei located toward the base. Interlobular bile ducts lined with high cuboidal epithelium converge to form larger intrahepatic ducts, which finally leave the liver lobes through the hepatic ducts. The large bile ducts were lined with ciliated columnar epithelial cells with occasional goblet cells. Apical blebs were evident in all the ducts indicating the secretory activity in both Bakerwali and non-descript goats. The eosinophilic secretory material was seen within lumen of these ductules and ducts (Fig. 12).

The capsule showed weak reaction for neutral mucopolysaccharides (PAS), negative reaction for glycogen (Best carmine) and weak reaction for lipids (Sudan black) in both breeds of goats (Bakerwali and non-descript goats). Modekar et al. (2003) in goat liver observed mild positive PAS reaction in capsule and moderate reaction for glycogen. Rashad et al. (2017) in buffalo, PAS and Best’s carmine to Glisson’s capsule gave positive results for carbohydrates.

In both the breeds, the portal area showed moderate reactions for neutral muco-polysaccharides (PAS) and lipids (Sudan black) whereas weak reaction for glycogen (Best carmine). Thakur (2020) in male buffalo reported that hepatocytes below portal vein showed intense reaction for PAS. As also reported by Thakur (2020) in buffalo, hepatocytes showed intense reaction in all regions for PAS except at apex of caudate lobe in female where hepatocytes showed weak reaction and below the portal vein in male where hepatocytes showed intense reaction.

The cytoplasm of hepatocytes showed moderate reaction for neutral muco-polysaccharides (PAS), moderate reaction for glycogen (Best carmine) and strong reaction for lipids (Sudan black) in both breeds of goats (Bakerwali and non-descript goats). As also reported by Thakur (2020) in buffalo, hepatocytes showed intense reaction in all regions for PAS except at apex of caudate lobe in female where hepatocytes showed weak reaction and below the portal vein in male where hepatocytes showed intense reaction. Modekar et al. (2003) in goat liver observed mild positive PAS reaction in hepatocytes and moderate reaction for glycogen. The hepatocytes of buffalo liver showed high reactivity to the amount of glycogen by best’s carmine method and PAS which also stained the neutral mucopolysaccharide and this referred to the normal function of the liver in synthesis of glycogen from glucose and storing it in the hepatocytes upon somatic demand. Similar findings were reported by Banks (2007).

Around the central veins, the neutral muco-polysaccharides (PAS) showed strong reaction for glycogen (Best carmine) and for lipids (Sudan black) showed intense reaction in both breeds of goats (Bakerwali and non-descript goats) (Fig. 13, 14). As also reported by Thakur (2020) in buffalo, Hepatocytes showed intense reaction in all regions for PAS except at apex of caudate lobe in female where hepatocytes showed weak reaction and below the portal vein in male where hepatocytes showed intense reaction. PAS and Best’s carmine to central vein gave positive results for carbohydrates as also reported by Rashad et al. (2017) in fresh buffalo. Modekar et al. (2003) in goat liver observed mild positive PAS reaction around central vein and moderate reaction for glycogen.