Adrenal gland was differentiated into cortex and medulla in the day old Gohilwadi goat which was surrounded by a thick fibrous capsule (Fig 1). The adrenal capsule composed of thick layer of collagen, reticular and few elastic fibers. The elastic fibers were mainly confined to blood vessels situated in capsular area. The connective tissue trabeculae made up of collagenous and reticular fibers arose from the inner aspect of capsule and infiltrate the cortical parenchyma of the gland (Fig 2, 3). Similar findings were observed by
Paul et al., (2016) and
Kale et al., (2003) in goat and
Kumar and Sharma (2019) in pig. The capsule contained many undifferentiated cells which were arranged in the form of follicles. The average thickness of capsule was 29.63±1.64 micrometer in group-I, 39.56±3.06 micrometer in group-II and 45.27±2.04 micrometer in group-III (Table 1). The increase in thickness of capsule was significant (P<0.05) from group-I to group-II, while it was non-significant between group-II and III. Increase in capsule thickness with progression of age was mainly due to increase in the connective tissue fibers. Whereas,
Al-Zubaidi and Nasif (2020) observed the average thickness of capsule was 4.75±0.32, 6.12±0.42, 7.50±0.64, 10.50±0.66, 8.50±0.70 micrometer, respectively in day 1, 1 month, 2 month, 6 months and 2 years of age in Awassi sheep. In buffalo,
Kumar et al., (2009) recorded the average thickness of capsule 230.66±33.45 micrometer in day 1 to 3 month of age, 240.13±9.04 micrometer in >3 month to 6 month of age and 243.54±6.22 micrometer in >6 month to 1 year of age.
The formation of different zones of adrenal cortex of goat was observed from day old goat. The adrenal cortex of day old goat was divisible into definite and fetal cortex. In early stage of development of group-I the definite cortex only comprised zona glomerulosa. Further differentiation was taken place and in the later stage of development of group- I the zona fasciculata was also formed between zona glomerulosa and fetal cortex. In group-II the fetal cortex was completely disappeared and all the three zones of adrenal cortex was observed. The development of different zones of adrenal cortex was well explained by
Mitani et al., (1999), they observed that in the rats, formation of adrenal zones started near the time of birth and the zonation was maintained by stem cells, localized between zona glomerulosa and zona faciculata.
Nwaogu et al., (2009) reported that in Kano brown goats, the area of definite cortex increased while fetal cortex decreased with the advancement of age.
The adrenal cortex of day old goat comprised definite and fetal cortex. The definite zone was comprised of zona glomerulosa, observed in the sub-capsular area and consisted of darkly stained basophilic cells with irregular nuclei and large number of sinusoidal capillaries (Fig 1). Similar findings were reported by
Nwaogu et al., (2009) in fetal goat,
Kumar and Sharma (2013) in day old foal and
Kumar et al., (2009) in buffalo. In the present study the cellular mass in this zone was arranged in clusters of columnar cells and had spherical or oval nuclei surrounded by a homogenous cytoplasm in all three groups (Fig 2, 3). Thickness of zona glomerulosa was 39.72±2.50 micrometer in group-I, 87.15±5.81 micrometer in group-II and 109.11±4.28 micrometer in group-III. Increases in thickness of zona glomerulosa from group-I to group-II are statistically significant (P<0.05). In contrast to present study,
Al-Zubaidi and Nasif (2020) observed that in Awassi sheep the average thickness of zona glomerulosa was 10.55±0.62, 11.60±0.3, 12.73±0.69, 16.82±0.85 and 14.55±0.25 micrometer respectively in day 1, 1 month, 2 month, 6 months and 2 years of age. In buffalo, the average thickness of zona glomerulosa was 177.42±21.14 micrometer in day 1 to 3 month of age, 202.75±11.78 micrometer in >3 month to 6 month of age and 252.73±11.51 micrometer in >6 month to 1 year of age
(Kumar et al., 2009).
Fetal cortex was made up of small to elongated fetal cortical cells which were having eosinophilic cytoplasm and were arranged into irregular cords. These cells were intermingled with medullary cells at cortico-medullary junction. With progression of age the fetal cortical cells were pushed towards the center of the gland, became closely packed and were moderately vacuolated (Fig 1). Similar observations were reported in day old buffalo calf by
Kumar et al., (2010a). Fetal cortex was not observed in group-II and group-III, however the remnant of fetal cortex was observed in the group-II. The average thickness of fetal cortex in group-I was 276.93±15.79 micrometer. However, the average thickness of fetal cortex was recorded as 353.45±46.88 micrometer in buffalo during day 1 to 3 months of age
(Kumar et al., 2009).
The zona fasciculata was interposed between the zona glomerulosa and fetal cortex in the later stage of development in group-I. In group-II and group-III this zone was located between zona glomerulosa and zona reticularis. Cells of this zone were arranged in single or double cords and were larger in size. Zona fasciculata was more organized with the progression of age and contained cells with foamy cytoplasm. Zona fasciculata was the widest zone amongst all the cortical zones. Thickness of this zone was 106.26±5.48 micrometer, 597.43±28.04 micrometer and 687.16±24.38 micrometer in group-I, group-II and group-III respectively. The average thickness of zona fasciculata increased from group-I to group- III. Similar pattern of increase in thickness of this zone was observed by
Kale et al., (2003) in goat,
Al-Zubaidi and Nasif (2020) in Awassi sheep and
Kumar et al., (2009) in buffalo. In the present study statistical analysis showed that this increase in thickness of zona fasciculata was significant (P<0.05) from group-I to group-II; while non-significant from group-II to group-III.
The zona reticularis was observed from group-II, below the zona fasciculata.
Hakeem et al., (1993) reported this zone first time in adrenal gland at the age of six month in goat. Cells of this zone were smaller than the cells of zona fasciculata. These cells were having little cytoplasm with pyknotic and heterochromatic nuclei. Zona reticularis was the innermost zone of the cortical parenchyma of the adrenal gland. Thickness of this zone was 252.74±14.37 micrometer in group-II and 358.93±26.40 micrometer in group-III. This increase in thickness of zona reticularis was significant (P<0.05). However,
Kumar et al., (2009) reported presence of zona reticularis in group-I (day 1 to 3 month of age). They also recorded the average thickness of zona reticularis as 141.23±23.40 micrometer in day 1 to 3 month of age, 329.95±17.30 micrometer in >3 month to 6 month of age and 393.14±34.17 micrometer in >6 month to 1 year of age.
There was no distinct line of demarcation between cortex and medulla. The bulk of the adrenal cortex was formed by zona fasciculata and zona reticularis however, the cortical parenchyma constituted a lesser proportion of the gland than the medulla. Similar findings were observed by
Kumar and Sharma (2013) in day old foal. Adrenal medulla formed greater part of the adrenal gland and occupied central portion of the gland. Medullary cells situated at the periphery of medulla were larger, arranged in follicular form and forming the outer zone. Similar pattern for outer medullary cell were observed in the adrenal gland of adult Bakerwali goat by
Kour et al., (2017) and in Buffalo by
Sethi and Roy (2007). While cells found in the center of the gland were smaller, compactly arranged and forming inner zone (Fig 4). Outer cells were having homogenous cytoplasm with spherical to round nucleus located more towards apical portion (Fig 5) whereas the inner cells had a less homogenous cytoplasm with a centrally placed nuclei. With progression of age the outer and inner zone of medulla were more clearly differentiated. Similar to present findings,
Kumar (2007) reported outer and inner zones in medulla during postnatal development of buffalo adrenal and stated that the cells of the outer zone of medulla were adrenaline secreting and the inner zone cells were nor-adrenaline secreting.
Average thickness of adrenal medulla was 626.71±63.04 micrometer in group-I, 1053.11±85.97 micrometer in group- II and 1242.92±36.46 micrometer in group-III. Thickness increased significantly (P<0.05) from group-II to group-III. The proportion of inner medullar zone was more than the outer medullary zone in all the age groups (Table 1). The cortico-medullary ratio decreased from 1:1.44 in group-I to 1:1.10 in group- III which may be due to rapid cortical growth.
Kumar et al., (2010b) recorded the average thickness of medulla as 1765.97±79.86 micrometer in day 1 to 3 month of age, 1833.40±342.18 micrometer in >3 month to 6 month of age and 1998.73±103.45 micrometer in >6 month to 1 year of age and they also observed decreased cortico-medullary ratio from group-I to group-III.