Dromaius novaehollandiae - Tubitak Journals

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Apr 7, 2016 - e.g., racing pigeon (Columba livia domestica), rock dove. (Columba livia), or collared dove (Sterptopelia decaota), the cranial lobe of the kidney ...
Turkish Journal of Zoology

Turk J Zool (2016) 40: 314-319 © TÜBİTAK doi:10.3906/zoo-1506-21

http://journals.tubitak.gov.tr/zoology/

Research Article

Anatomical and morphological study of the kidneys of the breeding emu (Dromaius novaehollandiae) 1,

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Katarzyna MICHAŁEK *, Danuta SZCZERBIŃSKA , Marta GRABOWSKA , Danuta MAJEWSKA , Maria LASZCZYŃSKA 1 Department of Physiology, Cytobiology, and Proteomics, Faculty of Biotechnology and Animal Husbandry, West Pomeranian University of Technology in Szczecin, Szczecin, Poland 2 Department of Poultry and Ornamental Bird Breeding, West Pomeranian University of Technology in Szczecin, Szczecin, Poland 3 Department of Histology and Developmental Biology, Pomeranian Medical University, Szczecin, Poland Received: 15.06.2015

Accepted/Published Online: 05.01.2016

Final Version: 07.04.2016

Abstract: We analyzed 16 kidneys obtained from 15-year-old emus, Dromaius novaehollandiae. Emus were kept at an experimental farm in Poland. The results showed that each kidney was composed of 3 parts: cranial, medial, and caudal divisions. Histological results demonstrated that the kidneys consisted of 2 zones: the cortex and the medulla. The cortex made up the majority of the kidney, while the medulla formed only a small portion of the organ. Proximal and distal tubules and 2 types of glomeruli (looped and loopless) were localized in the cortex. Each of these glomeruli was characterized by tightly arranged mesangial cells. Proximal and distal tubules had a distinctive simple low cuboidal epithelium. The luminal surface of the proximal tubules had a brush border membrane, formed by numerous microvilli. The renal medulla of emu kidneys formed irregularly positioned characteristic cones of different sizes. The medulla was composed of thin and thick segments of Henle’s loops lined with a simple cuboidal epithelium and collecting ducts with a simple columnar epithelium. In the absence of detailed information in the literature about the anatomy and morphology of emu kidneys, our study provides new information and undoubtedly complements the knowledge in this field with respect to this species of bird. Key words: Emu, Dromaius novaehollandiae, kidney, anatomy, histology

1. Introduction The emu (Dromaius novaehollandiae) is a large, flightless, ratite bird, which in the wild occurs in most parts of Australia, mainly in sclerophytic forests and woodland savannas (del Hoyo et al., 1992). The emu is considered the world’s second largest bird. Adults of this species can measure up to 190 cm and weigh about 55 kg. Emus are day birds, living alone or in pairs, sometimes forming small groups (Szczerbińska et al., 2007). An unusual characteristic of this species is that the males incubate eggs and look after the nestlings alone (Buttemer and Dawson, 1989). Emus are omnivorous birds, but predominantly eat herbage with shoots, seeds, fruits, insects, and flowers (Dawson et al., 1984). Emus can also eat the leaves and berries of salt bushes; however, intake of high NaCl loads may threaten their water balance (Skadhauge et al., 1991). Due to the climatic conditions in Australia, typical for semidesert areas, one of the adaptation features characteristic of the emu is low demand for total energy, protein, and water and a low rate of water turnover. In summer, adult emus usually drink twice a day, while during drought, when they have access to succulent plants, they can * Correspondence: [email protected]

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go a few days without drinking (Dawson and Herd, 1983). Despite the fact that emus are well adapted to Australian semidesert conditions, these birds have a limited renal concentrating capacity, with a maximal urine to plasma ratio of only 1.4–1.5 (Dawson et al., 1991). However, unlike other species of this subdivision (Palaeognathae), in the emu, the cloaca-rectum significantly contributes to the modification of ureteral urine composition (Dawson et al., 1985). In comparison to other birds, the cloacal-rectal epithelium of the emu has considerably higher rates of water and electrolyte absorption. Thus, the limited capacity of the kidneys to produce concentrated urine seems to be compensated for through intensive processes taking place precisely in this section of the excretory system. According to some authors, these findings suggest that in the emu the cloaca-rectum is the primary organ of osmoregulation, and that the kidney’s role is secondary (Dawson et al., 1991). In recent years, there has been an increase in the popularity of emu breeding, mainly due to the versatile possibilities of their use. Meat, eggs, leather, and highgrade oil can be obtained from these birds (Beckerbauer,

MICHAŁEK et al. / Turk J Zool 2001; Majewska et al., 2008; Abimosleh et al., 2012; Szczerbińska et al., 2014). Moreover, emus show high adaptive abilities to different climatic conditions. Emu farms are present on virtually every continent, even in the coldest parts of Canada, where the temperature drops to –40 °C (Szczerbińska et al., 2007). Although interest in this animal species is growing, there are still limited data in the literature on the detailed anatomy of individual emu organs. Considering the fact that emu kidney functions are somewhat different from those of other species of birds, and in view of the lack of information on the morphological structure of these organs, we conducted a study to analyze in detail the anatomy and histology of adult emu kidneys (Dromaius novaehollandiae). 2. Materials and methods We analyzed 16 kidneys obtained from 15-year-old emus, Dromaius novaehollandiae (6 males and 10 females). Emus were kept at the experimental farm of the Department of Poultry and Ornamental Bird Breeding, West Pomeranian University of Technology, in Szczecin (Figure 1). Emus were derived from hatching and rearing. Birds were reared in a heated rearing house with optimal temperatures for the respective periods of the bird’s life. During the day, from the fifth week of rearing, emus stayed behind a fenced run, overgrown with grass, while during the night they stayed inside. During the rearing period, certain types of complete feed were used, the composition of which was consistent with the nutrient needs of growing birds (Smulikowska and Rutkowski, 2005). Adult emus were kept in an unheated building, lined with hay chaff. Throughout the year, regardless of weather conditions, the

birds had unrestricted access to the grassy run. They were fed ad libitum with complete feed in the form of granules, the nutritional value of which was consistent with the nutritional needs of birds (Smulikowska and Rutkowski, 2005). In addition to feed, the birds ate vegetation growing on the run (leaves of shrubs and trees, grass, herbs, young shoots and roots of plants), as well as small invertebrates living in the soil. Emus were slaughtered by decapitation in July, during a laying break. Immediately after slaughter, the kidneys were removed and washed twice with ice-cold 0.9% NaCl solution and subsequently twice with ice-cold KrebsHEPES (20 mM, pH 7.4). The birds and kidneys were weighed (left and right kidneys were measured separately). The kidney to body weight ratios, means, and standard deviations were calculated. The resulting data were analyzed using Student’s t-test (software: Statistica 10.0). Tissue pieces were cut into blocks, fixed in 4% buffered formalin, embedded in paraffin blocks, and sectioned at 3 µm on a rotary microtome. To conduct morphological and histochemical studies, sections were stained with hematoxylin and eosin (H&E) and periodic acid–Schiff (PAS). Sections were examined using an Olympus BX41 light microscope coupled to an Olympus digital camera (Olympus Optical Co., Tokyo, Japan). 3. Results Anatomical and morphological results showed that female kidneys were statistically significantly (P < 0.05) larger compared to male kidneys (Table). The average weight of males was statistically significantly (P < 0.05) lower than that of females. Therefore, the recorded lower kidney

Figure 1. Healthy adult emus (Dromaius novaehollandiae) at the experimental farm of the Department of Poultry and Ornamental Bird Breeding, West Pomeranian University of Technology in Szczecin.

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MICHAŁEK et al. / Turk J Zool Table. Body weight, right and left kidney weights, and kidney/body weight ratios in adult emu (Dromaius novaehollandiae). Sex of the emu

Body weight (kg)

Left kidney weight (gm)

Right kidney weight (gm)

Kidney/body weight (%)

Female (n = 10)

40.94 ± 5.35a

84.25 ± 18.91a

80.51 ± 15.07a

1.84 ± 0.26

Male (n = 6)

33.92 ± 4.74

54.24 ± 4.42

59.13 ± 8.91

1.72 ± 0.16

b

b

b

Values represent means ± SD. Letters are used to shown statistical significance level at P < 0.05.

weight seems to be proportional to the body weight. This may indicate relatively similar kidney/body weight ratios in both females and males. The emu kidneys had an elongated shape and were located in the depression along the central surface of the synsacrum and covered by the peritoneum (Figure 2). The kidneys of the studied emus were very similar in external morphology. Each kidney consisted of 3 lobes, the cranial, medial, and caudal divisions (Figure 3). Histological analysis showed that the kidneys of all the birds were composed of 2 zones, the cortex and medulla (Figures 4a–4f). The cortex made up the majority of the kidney, while the medulla formed only a small portion of the organ. The medulla was arranged in discrete medullary structures named cones, which are randomly distributed in the kidney (Figures 4a, 4d, and 4e). Cross-sections of the cortex demonstrated 2 types of glomeruli, mammalian and reptilian. Compared to the reptilian glomeruli, the Figure 3. Kidneys of emu (Dromaius novaehollandiae). A - Right kidney. B - Left kidney: 1 - cranial division; 2 - middle division; 3 - caudal division.

mammalian glomeruli were larger and had Henle’s loops (Figures 4a and 4e). The Henle’s loops extended from the cortex into the cones (Figures 4c, 4d, and 4e). Each glomerulus consisted of Bowman’s capsule, a urinary space, and a large central mass of mesangial cells (Figures 4b and 4f). The proximal and distal tubules were lined with a simple cuboidal epithelium. The luminal surface of the proximal tubule epithelial cells formed the brush border membrane (Figures 4a, 4b, 4d, 4e, and 4f).

Figure 2. Ventral view of the kidneys of a male emu (Dromaius novaehollandiae). a - Right kidney. b - Left kidney: 1 - cranial division; 2 - middle division; 3 - caudal division. c - Testis. d Liver.

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4. Discussion It is generally known that the kidneys of birds differ both functionally and morphologically from the kidneys of mammals. As mentioned earlier, a characteristic trait of these animals is a common orifice for ureters and fallopian tubes or the vas deferens in the distal part of the gut. Urine produced in the kidneys is refluxed into the cloaca-rectum, where it is finally modified before elimination. Due to the fact that the end product of nitrogen metabolism is uric acid, bird kidneys produce less concentrated urine than

MICHAŁEK et al. / Turk J Zool

Figure 4. Kidney histology sections in emu (Dromaius novaehollandiae). a, b, c, and d – H&E staining. a - Transverse section showing C - renal cortex; MC - medullary cone; MG - mammalian glomerulus; RG - reptilian glomerulus. b - Renal cortex; P - proximal tubule; D - distal tubule. c - Medullary cone; CD - collecting duct; arrow - thick limb of Henle’s loop. d Transverse section though the area around the intralobular vein - V; C - renal cortex; P - proximal tubule; MC - medulla cone; CD - collecting duct. e and f - PAS staining. e - Transverse section showing C - renal cortex; MC - medullary cone; MG - mammalian glomerulus; RG - reptilian glomerulus; CD - collecting duct; arrow - brush border of the proximal tubule. f - Renal cortex; D - distal tubule; U - urinary space; arrow - brush border of the proximal tubule.

mammals. Hence, the relatively higher water content in the produced urine protects the renal tubules against deposition and clogging by the accumulating sparingly soluble uric acid (Dawson et al., 1991). The kidneys of birds constitute from 1% to 2.6% of body weight, while those of mammals constitute an average of 0.5% (Frazier et al., 1995). In the studied emus, the percentage of kidney weight of the whole body weight was 1.78%. Typically, the average female emu is larger and heavier than the male; hence, in the present study, the females had higher kidney weights. Compared to other birds, the average percentage of the kidney to body weight is most likely associated in the emu with a lower mass-specific metabolic rate, as evidenced by lower glomerular filtration rate in this species of bird (Yokota et al., 1985). As in other birds, the emu’s kidneys are elongated and clearly divided into 3 parts, cranial, medial, and caudal. In the emus examined, as in other species of this class, e.g., racing pigeon (Columba livia domestica), rock dove (Columba livia), or collared dove (Sterptopelia decaota), the cranial lobe of the kidney bulges more than the others (Nabipou et al., 2009; Al-Ajeely and Mohammed, 2012). Histological results showed that the kidneys of the emu had a typical structure and arrangement of renal cortex and renal medulla. The renal cortex made up the greater area of the kidney, while the medulla constituted only a small portion. A similar medulla to renal cortex ratio was

also observed in the coot (Fulica atra) and the rock dove (Columba livia) (Nabipour et al., 2009; Batach, 2012). In nectarivorous birds, the renal cortex may form up to 90% of the total volume, while the medulla forms only 2% (Warui, 1989; Casotti et al., 1998). A very large cortex and relatively small medulla has also been observed in the mallard duck (Anas platyrhynchos) (Warui, 1989). The renal cortices of the tested emus contained proximal tubules, distal tubules, and 2 types of glomeruli. Proximal and distal tubules, as in other avian species, have a characteristic low cuboidal epithelium. The luminal surface of the proximal tubule in the emu kidneys is strengthened by a thick layer of microvilli forming a brush border. This result is consistent with the results of other authors who have studied the renal structure of birds from Australia and North America (Richardson et al., 1991; Nabipour et al., 2009; Batach, 2012). As described earlier, the cross-sections of the kidneys showed 2 types of nephrons, mammalian and reptilian. All renal corpuscles consisted of an outer Bowman’s capsule separated from a centrally located glomerulus by Bowman’s space. Mammalian nephron glomeruli have a much larger diameter and Henle’s loops. In the studied emus, this type of nephron was usually situated deeper in the medullary cones. Reptilian nephrons have smaller renal glomeruli and do not have Henle’s loops. This type of glomerulus was frequently observed in the present study. Similar results

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MICHAŁEK et al. / Turk J Zool were obtained by other authors, who claimed that most avian nephrons were loopless. Only about 10%–30% of the nephrons were of the mammalian type (Wideman, 1988; Casotti and Braun, 2000; Lumeij, 2000; Carpenter, 2003). Both types of glomeruli in the emu contained tightly arranged mesangial cells. Similar results were obtained, e.g., by Snelgrove-Hobson et al. (1988), who also observed a large mass of mesangial cells in the renal glomeruli in the kidney of the Peking duck. The renal medulla of the emu kidneys was arranged in cones of different size, randomly distributed within the kidney. Collecting ducts were located within the medullar cones, lined with columnar epithelium, between which thick and thin limbs of Henle’s loops were located. Limbs consisted of a simple cuboidal epithelium. This characteristic was similar to other species (Nishimura, 2008; Nabipour et al., 2009; Al-Ajeely and Mohammed, 2012). Overall, it appears that the avian medullary cones are structurally similar to the outer medulla of mammalian kidneys (Casotti et al., 2000; Nabipour et al., 2009). In summary, it can be said that the kidneys of the emu (Dromaius novaehollandiae) represent an average of 1.78% of body weight. The kidneys are elongated and clearly divided into 3 parts, the cranial, medial, and

caudal divisions. Histological results demonstrated that the kidneys consisted of 2 zones, the cortex and medulla. The cortex made up the majority of the kidney, while the medulla formed only a small portion of the organ. Proximal and distal tubules and 2 types of glomeruli (looped and loopless) were localized in the cortex. Each of these glomeruli was characterized by tightly arranged mesangial cells. The renal medulla of the emu kidneys formed irregularly positioned characteristic cones of different sizes. The medulla was composed of thin and thick segments of Henle’s loops and collecting ducts. The relatively low renal mass of the emu and the relatively large area of the renal cortex seem to confirm the suggestion of Dawson et al. (1991) that the cloacarectum plays a major role in osmoregulation in this species of birds. Limited capacity for concentrated urine production, resulting from specific morphology, may indicate the secondary role of the emu kidneys in the final regulation of water and NaCl excretion. In view of the growing interest in this unique species of birds, and in the absence of detailed information in the literature about the anatomy and morphology of emu kidneys, the current results undoubtedly complement the knowledge in this field concerning this species of birds.

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