INTRODUCTION
Evaluation of breeding soundness and potential fertility of poultry cock have been made from the knowledge of basic morphometric characteristics of the reproductive organs (Togun et al., 2006). The size of the testis has been reported as a good indicator of present and future sperm production as well as breeding quality of the male (Ezekwe, 1998; Perry and Petterson, 2001; Togun and Egbunike, 2006).
Measurable reproductive criteria of tropical breeds of bulls have been reported to include growth, scrotal circumference, testicular development, sperm morphology and fertility (Osinowo et al., 1981; Daudu and Shoyinka, 1983). According to Kenagy and Trombulak (1986), smaller animals are expected to allocate greater proportion of body weight and energy expenditure to testicular tissue than larger animals. Togun et al. (2006) reported live weight to be significantly correlated with testes weight. Togun (2006) reported scrotal circumference as the most superior of all testicular parameters in estimating testis size. Brito et al. (2004) also reported that body weight is a good predictor of sexual maturity. Kwari and Ogwuegbu (1998) reported that scrotal, gonadal and epididymal traits were more closely related to bodyweight than the age of the bull. Quantitative aspects of spermatogenesis are particularly important to the livestock industry since there is a relationship between spermatozoa production and the number of offspring that can be produced by a sire. It becomes more important now that artificial insemination has become very prominent in animal species. The relative importance of the various cell components in the seminiferous tubules of most farm animals have been enumerated in literature (Hafez, 1987). According to Senger (1998) the time required for the duration of the cycle of the seminiferous epithelium is constant and unique for each species.
The White Fulani (WF) is a fairly large breed (Olaloku, 1972) that is very popular in Nigeria, but most of the animals are reared under the extensive system of management, which dose not allow detailed records on birth, age and growth characteristics. However, the relationship between growth, testicular development and spermatogenesis is of importance in Artificial insemination centers and progeny test stations. Such knowledge would enhance the possibility of early commencement of semen collection from bulls at a young age. The importance of WF breed to the impending national breeding programme makes it mandatory to establish the live weight related changes in the dimensions and weight as well as the histometric characteristics of its genitalia. These needs serve as the basis for this study and would allow an effective prediction of the sperm production capabilities of the breed in its natural environment, based on the live weight at any point in time. It will also satisfy the need for a greater exploitation of the spermatogenic potential at the young age, thus allowing a longer period of use of individual bull in each herd.
MATERIALS AND METHODS
Site and period: The study was carried out in Ibadan, South West of Nigeria. Ibadan is situated at an elevation of 200 m above sea level. It is in the rain forest zone, with main seasons (wet and dry) of about equal period. Vegetative growth is retarded in the dry season when temperature is highest. The study spanned a period of 2 years, between 2003 and 2005, which allowed data collection twice during the two different seasons in the two years. The data represent the means of data, spanning the experimental period.
Animals: Fifty-two White Fulani bulls of body weight range 171-320 kg involved in this study were owned by nomadic Fulani herdsmen. The animals were railed down from the Northern part of the country and placed principally on extensive system of management, where they were grazed from place to place with no attempt to feed any form of supplement. Attempts were made to supply water only as much as could be available.
Experimental design: The bulls were randomly selected from different
White Fulani herds and placed in a Giant Star grass paddock for a period of
one week prior to slaughter. The animals were weighed at slaughter and from
their weights; they were grouped into four body weight groups viz.
| • |
Group I |
: |
171-200 (11 bulls) |
| • |
Group II |
: |
201-230 (16 bulls) |
| • |
Group III |
: |
231-260 (19 bulls) |
| • |
Group IV |
: |
261-320 (6 bulls) |
Morphometric studies
Measurements before slaughter: Scrotal circumference was measured with
a tape, which was passed round the broadest point of the scrotum.
Scrotal width was measured with a veneer caliper as the distance between the two sides of the broadest part of the scrotum.
Scrotal length was taken as the length of the testis while still in the scrotum. The upper part of the testis was located with the forefinger and a steel tape was used to measure from this end to the lower part of the testis in the scrotum.
Scrotal skin fold thickness was measured with a veneer caliper taking care not to make the caliper too tight as this would underestimate the thickness of the skin.
Measurements immediately after slaughter: The testes were removed immediately after slaughter and taken to the laboratory for further processing. They were weighed individually after the epididymis has been trimmed off each of them. The length and width of each testis were taken by the use of a veneer caliper. The volume of each testis was recorded, using Archimedes principle of water displacement. The tunica albiginea were then peeled off the testes and weighed individually to know the weight of testicular parenchyma.
Histometric studies
Histology: The testes were cut mid-sagitally and tissue samples were
taken from each half of each testis. The epididymides were cut into the differentiating
parts of caput, corpus and cauda. A part of each, along with the testicular
samples were fixed in more than 20 times the volume of each in Bouin’s
fixative for 24 h, dehydrated in series of ethyl alcohol, cleared in chloroform
and embedded in paraffin. The completed histological procedures were according
to the instructions detailed in previous studies (Togun, 1981). Histological
sections, 7 μ thick were cut and left to float and flatten out on water
(40°C) and then picked up carefully with clean slides, which have been smeared
with Mayer’s egg albumin. Successful sections, about 140th away were mounted
(i.e., every 21st section) so as to ensure that the positions of the tissue
examined were not of the same portion of the testis and epididymis. The slides
were stored in air incubator for 30 min and later stained with Haematoxylin-Eosin
(H and E). Each slide was clean-blotted and mounted in Canada balsam under a
cover slip. Four slides, made up of two slides per testis, were prepared for
each bull.
Histometric measurements
Testis
Seminiferous tubule diameter: Tubular diameters of seminiferous tubules
were determined by measuring twenty approximately round tubules per slide with
a microscope, having its eyepiece already calibrated with a stage micrometer.
Two measurements at right angles to each other were taken on each tubule and
the average recorded (i.e., two slides per testis). Twenty tubules were measured
in each of the four slides to give a total of eighty tubules per animal.
Volumetric proportions of cellular elements in the seminiferous epithelium were determined by the method of Chalkley (1943) as modified by Egbunike and Steinbach (1972). It essentially involved the counting of the number of hits by cellular elements in 20 fields in each of the four slides per animal with an integrating eye piece (Zeiss Oberkochen) having 25 points asymmetrically arranged in a cycle and calculating accordingly.
Stages in the cycle of seminiferous epithelium were determined by classifying twenty seminiferous tubules in each of the four slides per bull. The frequency of occurrence of each stage was calculated on percent basis.
Epididymis: Tubular diameters of the epididymal tubules were separately determined for the caput, corpus and cauda epididymides. Twenty tubules were measured (each with two measurements at right angles to each other) per slide to give a total of forty tubules per section of the epididymis.
Epithelial heights of epididymal tubules were measured from the basement membrane to the coat of the tubule for the caput, corpus and cauda epididymides.
Statistical analysis: Data were expressed as Mean±SEM. They were subjected to General Linear Model (GLM) of the Analysis of Variance (ANOVA). Means, where significant, were separated by Duncan multiple range test (SAS, 2002).
RESULTS
Scrotal and testicular morphometry: The mean scrotal circumference,
width and length were significantly (p<0.05) higher in group IV bulls than
all the other groups, which did not significantly (p>0.05) differ from one
another, except that group III value for scrotal circumference was significantly
(p<0.05) higher than group I value (Fig. 1). The mean paired
testicular parenchyma weight and paired testicular volume were significantly
(p<0.05) higher in group IV than all other groups, which did not differ significantly
(p<0.05) from one another except that group III values were significantly
(p<0.05) higher than group I value (Fig. 2). The mean group
testes length and width are shown in Fig. 3 group IV values
were significantly (p<0.05) higher than the values observed in all the other
groups, which did not significantly (p>0.05) differ from one another.
|
| Fig. 1: |
Scrotal morphometry |
|
| Fig. 2: |
Testicular morphometry |
|
| Fig. 3: |
Mean testicular length and width |
| Table 1: |
Derivations from testicular morphometry and seminiferous tubule
diameter of white fulani bulls (Mean±SEM) |
 |
| PTW: Paired testes weight (g), P.ep.wt: Paired epididymal
weight (g), P. Tunica: Paired tunica albuginea weight (g) |
| Table 2: |
Volumetric proportions (%) and absolute weights (gm) of testicular
elements of White Fulani bulls (Mean±SEM) |
 |
| H: Volumetric proportions of testicular elements. †:
Absolute weights of testicular elements, spg: Spermatogonia, spc: Spermatocytes,
spd: Speronatios, R: Round, El: Elongated, Spz: Spermatozoa, B: Basement,
Int: Interstitial |
Tunica and epididymal weights: The mean group values of paired epididymal
weight and paired tunica albuginea weight are shown in Fig. 2.
The mean values of group IV bulls were significantly (p<0.05) higher than
all the other groups, which did not differ significantly (p>0.05) from one
another in the two measurements.
Derivations from testicular morphometry: The mean group gonadal index
(relative weight of testes to live weight), the relative weight of paired epididymal
weight to live weight and the relative paired tunica albuginea weight to paired
testes weight are shown in Table 1. The gonadal index did
not differ significantly (p>0.05) between groups except group IV, which was
significantly (p<0.05) higher in value than all other groups. There was no
significant (p>0.05) difference between groups in the relative epididymal
weights. However the mean relative weight of paired tunica albuginea to the
paired testes weight decreased insignificantly (p>0.05) from group I-IV.
Testicular histometry
Seminiferous tubule diameter (STD): Table 1 shows
the mean group values of the seminiferous tubule diameter. There was no significant
(p>0.05) difference between the groups.
Volumetric proportions and absolute weights of cellular elements: Table
2 shows the live weight related changes in the volumetric proportions and
absolute weights of cellular elements in the seminiferous epithelium. There
was a relative marginal decrease in the spermatogonial volume percent along
with increasing live weight groups. The proportion of spermatocytes and spermatids
did not show a relative increase with liveweight groups. The volumetric proportion
of Sertoli cell did not show a fixed pattern but tended to increase unlike the
basement membrane, which increased up to group II and decreased thereafter.
The cellular cytoplasm tended to increase with live weight groups but the tubular
lumen decreased in volumetric proportion. However, the absolute weights of cellular
elements of bulls in group IV with the mean value of group I bulls being significantly
higher than in group IV bulls, were significantly higher than in all the other
groups.
Stages in the cycle of seminiferous epithelium: There was no significant
(p>0.05) difference between live weight groups in each of the stagesin the
cycle of seminiferous epithelium, which appeared stable irrespective of live
weight (Table 3).
Epididymal histometry
Tubular diameter: Figure 4 shows the mean group values
of epidiymal tubule diameter for the different segments of the epididymis. There
was no significant (p>0.05) difference between the groups in this parameter.
| Table 3: |
Live weight related changes in the stages in the cycle of
seminiferous epithelium of white fulani bull extensively managed in the
humid tropics |
 |
|
| Fig. 4: |
Epididumal tubule diameter |
|
| Fig. 5: |
Mean variation of epithelial height of epididymal tubule diameter
among live weight groups |
Epithelial height of epididymal tubule: Figure 5 shows
the mean group epithelial heights of the caput, corpus and cauda epididymal
tubules. Apart from the epithelial height of the caput epididymal tubule, which
showed an increasing tendency from group I-III with a decrease in group IV,
the epithelial height showed no fixed pattern with increasing live weight groups.
DISCUSSION
The study revealed a positive relationship between scrotal circumference, testes weight and live weight, which could lead to adequate prediction of the reproductive status of the bull in the absence of birth records as long as the live weight is known. Live weight can be estimated in practical terms from hearth girth measurement.
The similar pattern observed for the different morphometric characteristics along with the live weight groups, with a non-significant (p>0.05) increasing trend from group I through to group III but with a significant (p<0.05) increase in group IV, indicates some consistency in the pattern of growth of these characteristics. That the mean paired testes weight of group III bulls was significantly higher than the group I bulls in line with the scrotal circumference, confirms the reports in literature (Pant et al., 2003; Park et al., 2003; Vasquez et al., 2003; Togun et al., 2006; Togun, 2006; Hamilton and Stark, 1997) that scrotal circumference is a basis for estimating testes size as well as selecting breeding bulls. This is important since testis size has been reported as a good indicator of the present and future capacity of spurn production and breeding quality of bulls (Togun et al., 2006; Ezekwe, 1998; Perry and Petterson, 2001; Togun and Egbunike, 2006). Testicular weight has been reported to vary with age and body weight (Ezekwe, 1998; Togun et al., 2006; Togun and Egbunike, 2006) but according to Hahn et al. (1969), the scrotal circumference reaches a maximum at 5-6 years, when it remains relatively stable. It is thus expected that the testis size would also reach its maximum at probably a period not too far from this time in view of the established relationship between scrotal circumference and testicular size (Togun et al., 2006; Ezekwe, 1998; Perry and Petterson, 2001; Togun and Egbunike, 2006).
From the report of Olaloku (1972), the White Fulani breed reached its mature weight at about 348 kg on an experimental station, under the semi-intensive management system. Such system would offer a more conductive environment to the animals than the extensive system of management by the nomadic Fulani herdsmen typified in this study. From the observation in this study, the morphometric characteristics of the White Fulani bulls approached the plateau of their growth curve at around the live weight range of 260-330 kg. It would be expected that increases in morphometric measurements would be low or non existent from this stage of growth in the WF bull.
The volumetric proportion of cellular elements studied dealt with the relative
volume occupied by each element within the testis. The inconsistency in the
pattern of the relative increase in germ cell nuclei volume with increasing
live weight would not seem to indicate that heavier bulls in this study have
a grater capacity per unit volume of the testis to produce sperm cells than
the smaller bulls. This is in spite of the fact that the heavier bulls paraded
larger testes and scrotal circumference. The spermatocyte and spermatid population
have been positively linked with sperm production rate just as the Sertoli (Berndtson
et al., 1987) and Leydig (Abbasi et al., 1980) cells in cattle.
However, one valid observation is that with the bulls in this study, active
spermatogenesis was still taking place with most of the spermatogenic cells
attaining maturation to sperm cells. The significantly (p<0.05) higher mean
values of absolute weight observed for all the cellular elements of the seminiferous
epithelium in group IV bulls than all the other groups is a ready explanation
for the significantly (p<0.05) heavier tests of the group IV bulls. This
observation can further be extended to suggest the possibility of lager number
of cells to enhance relative total sperm production.
The non_significant difference between groups in the eight stages of the seminiferous epithelial cycle supports earlier observation (Swierstra and Foote, 1963) that the kinetic of spermatogenesis is species specific being, similar in pubertal and adult, irrespective of the site or the testis of sampling (Swierstra, 1968; Egbunike et al., 1983; Togun and Egbunike, 2005).
The non significant (p<0.05) difference between the epididymal tubule diameters (caput, corpus and cauda) and the epithelial heights of the epidymal tubules, point to the fact that the White Fulani bulls in the live weight range involved in this study, have very similar testicular and epididymal histometry. This suggests that a plateau state in testicular and epididymal functions are imminent at this stage or have been reached, having attained a physiological stable state of development. This is complemented by the result of other parameters studied above.
It is thus obvious from the above results that it was only in the scrotal circumference and the testes weight that there were significant (p<0.05) differences between the live weight groups studied. This would point to an apparent superiority of the larger animals in spermatozoa production. However the association of spermatogenic cells, as well as other histomorphometric characteristics, did not indicate a similar conclusion but pointed to the probability that sperm production capacity, quality and efficiency between the groups might not be significantly different. The only possible difference would thus be accounted for through the differences conferred by testicular size and scrotal circumference, both of which have been established to have highly, significant correlation with each other and with total sperm producing capability of an animal.
It can therefore be concluded that the live weight range in this study corresponds to the stage of physiological stability of the bulls.
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