Keywords
cattle - heat stress - kidney - morphometry - stereology
Introduction
The bovine kidney is lobulated due to its multilobar structure,[1] and the left kidney is mobile in order to avoid the pressure from the rumen when
it is full.[1] The functional urine filtration unit of the kidney is the nephron,[1] and all nephrons are placed in the Bowman capsule, in the cortical region.[1] The primary function of the kidney is to keep the body fluid ingredients within
the physiological limits. The morphometric features of the kidney may be useful for
the diagnosis of diseases.[2]
[3] Changes in some of the morphometric parameters may indicate the health status of
the organs.[2]
[3] For example, the total volume of the kidney is directly related to its functional
reserve, and its weight is related to chemical changes.[4]
In the present study, morphometric measurements were performed on the left and right
kidneys of both male and female Holstein cattle. The kidney samples were collected
in the summer and winter seasons to assess the effects of heat stress on them. A scale,
water overflow, and a Mitutoyo CDN-P20PMX caliper (Mitutoyo Corporation, Kanagawa,
Japan) were used to obtain the morphological dimensions of the total kidney, and the
stereological sampling methods with microscopy were performed to investigate the glomerulus
density per unit area and the diameter of the glomerulus.
Materials and Methods
In the summer and winter seasons, the left and right kidneys of 40 Holstein cattle
(10 male and 10 female for the summer season. and 10 male and 10 female for the winter
season) were collected from the slaughterhouse. Immediately after the slaughtering,
all kidneys were weighted using a Kern scale (Kern, Balingen, Germany). The widths
of the cranial pole, of the middle region, and of the caudal pole, as well as the
total length, were measured with a Mitutoyo CDN-P20PMX caliper. The total kidney volume
was estimated using a graded cylinder according to the principle of Archimedes.
After all the morphometric measurements, the kidneys were sliced into equal intervals
according to the stereological systematic uniform sampling procedure.[5]
[6]
[7] The chosen slabs were fixed in neutral buffered 10% formalin, sliced in a thickness
of 5 µm, and stained with hematoxylin. The number of glomerulus per unit area and
the diameter of the glomerulus were calculated with an Olympus BH-2 (Lang MS316) motorized
staged light microscope (Olympus Corporation, Tokyo, Japan) attached to a computer
running the MShot Image Analysis System 1.3.10 software (Micro-shot Technology Limited,
Guangzhou, China). For the number estimation, the motorized stage moved 2 mm along
equal step lengths and the glomeruli were counted, falling into the 917,534 µm2 long frame in 10 consecutive areas ([Fig. 1]).
Fig. 1 A glomerular view from the (A) small and (B) big kidneys.
The independent sampling t-test was used for the statistical evaluations.
Results
In the summer season group, the length of the left kidneys was statistically shorter
and the width of the caudal pole was wider than the right kidney in the male Holstein
cattle (p < 0.05).The cranial pole width of the female Holstein cattle left kidneys was smaller
and its caudal pole was statistically longer than those of the right kidneys (p < 0.05) ([Fig. 2]). In the winter groups, no statistical differences were detected in the left and
right kidneys of male and female cattle.
Fig. 2 Kidneys of the female (A) and male (B) Holstein cattle. The left kidneys are on the
upside and the right kidneys are on the downside.
When the average of both kidneys was calculated in the summer season, the volume and
the length of the male Holstein cattle kidneys and only the length of the female Holstein
cattle kidneys were statistically longer than the measurement obtained during the
winter season (p < 0.05).
No differences were detected in the male Holstein cattle kidneys when the averages
of the left kidneys in the summer season were compared with the averages of the left
kidneys in the winter season. However, in the female Holstein cattle kidneys, the
kidney length was longer, and the width of the cranial pole was narrower in the summer
season (p < 0.05). Besides, the length of the right kidney of the male Holstein cattle was
statistically longer in the summer season (p < 0.05), and no differences were detected in the female Holstein cattle kidneys.
Finally, the weight, length, volume, width and glomerular diameter of female Holstein
cattle kidneys in both groups were statistically larger compared with the kidneys
of the male Holstein cattle kidneys (p < 0.05).
Discussion
The milk yield is affected by the heat in the summer season. The heat has negative
effects on the milk production.[8] The heat stress also affects the glomerular and tubular functions and urine concentrations
in the kidneys.[9]
[10] Cincovic et al[9] found that the warming air decreases the milk production, and it affects negatively
the milk quality and increases the amount of urea and bilirubin in the milk. All these
studies tried to estimate the heat effects on different body conditions, and no morphological
studies were found in the literature, except in the report by Pitesky et al[11], who stated that the environmental heat stress decreases the number of functional
glomerulus in dogs. However, in the present study, depending on the season, no change
was detected in the number and in the diameter of the glomerulus.
In the present study, it was observed that the front width of the left kidney decreases
and that the back width increases in the summer season. Therefore, the front region
of the left kidney gets thinner and the back region of the left kidney gets thicker.
The alteration in the structure of the left kidney may be caused by the stomach rumen
of the Holstein cattle. One must remember that the left kidney is mobile because of
the protection against the pressure caused by the fullness of the rumen.
According to the comparison of the mean kidney parameters in the summer and winter
seasons, the length and the volume of the male Holstein cattle kidneys were much longer
and larger, respectively; and the length of the female Holstein cattle kidneys was
much longer in the summer season than in the winter season. The right kidney of the
male Holstein cattle was smaller in the winter season than in the summer season. Besides,
in the female Holstein cattle, in the summer season, the kidneys length was getting
bigger, while in the winter season the front widths were getting bigger. No statistically
significant changes were observed in the glomerulus density per unit area and in the
diameter of the glomerulus when the seasons were compared.
Conclusion
In the present study, the morphological effects of the seasonal heat changes were
observed on the Holstein cattle kidneys.
