Epididymal Sperm Characteristics, Testicular Morphometric Traits and Growth Parameters of Rabbit Bucks Fed Dietary Saccharomyces cerevisiae and/or Zinc Oxide

ABSTRACT

The objectives of this twelve-week feeding trial were to determine the effects of dietary Saccharomyces cerevisiae and/or zinc oxide on epididymal sperm characteristics, testicular morphometric traits, and growth parameters of bucks. 16 (New Zealand White) bucks 16-wk-old, weighing 2.8kg were randomly allotted to one of 4 treatment groups. Each treatment was replicated four times, with 1 buck per replicate, in a completely randomized design (CRD). Each treatment group was randomly assigned to one of the four commercial experimental diets designated thus: T_A = control diet with no additives, T_B = 0.12g/kg Saccharomyces cerevisiae, T_C = 150mg/kg zinc oxide and T_D = 0.12g/kg Saccharomyces cerevisiae +150 mg/kg zinc oxide. Although treatment had no effect (p>0.05) on final body weight, average daily weight gain and feed conversion ratio, epididymal sperm characteristics and testicular morphometric traits differed significantly (p<0.05). Bucks on T_B(Saccharomyces cerevisiae-based diet) had improved (p<0.05) sperm concentration, motility and live sperm, tubule diameter, epididymal volume, volume fraction of duct, and total duct volume, but decreased testicular volume. Bucks fed T_A (control diet) had improved volume fraction of tubule but recorded the highest incidence of head and tail sperm abnormality. Though, T_C(zinc oxide-based diet) enhanced (p<0.05) seminal vesicle volume, sperm pH was better among bucks fed T_D (Saccharomyces cerevisiae + zinc oxide-based diet). It can be concluded that dietary inclusion of Saccharomyces cerevisiae at 0.12g/kg of feed improved epididymal sperm characteristics and testicular morphometric traits of rabbit bucks.

Keywords:
Nutrition; bucks; semen; Saccharomyces cerevisiae; zinc oxide

INTRODUCTION

Feeding is an integral component of livestock and poultry enterprises. As an essential resource in livestock production, feed not only supplies livestock with nutrients which they require for normal metabolic processes, but also, its intake by animals, culminate in the production of valuable products (Fink-Gremmels, 2004). Animal feed consists of major and minor essential nutrients that are fed with intention of bringing about increased productivity. In view of this, feed additives like antibiotic growth promoters became increasingly utilized in livestock production in order to sustain large-scale animal production, while ensuring improved growth, feed efficiency, health and well-being of animals, and also meeting the protein demand of teeming human population (Peterson et al., 1991; Dibner & Richards, 2005; Huyghebaert et al., 2011; Hamasalim, 2016).

Although, antibiotic growth promoters have remarkable growth promoting and prophylactic effects (Niewold, 2007), their long term-use portends deleterious impact on public health (Nanung, 2013). Even at low therapeutic doses, dietary inclusion of antibiotic growth promoters in animal nutrition has been linked to cases of gram-negative bacteria resistance in animals and humans (Butaye et al., 2003), carcinogenicity in human consumers of animal products (Torres et al., 2010), environmental degradation (Bekele & Ahanafi, 2010) etc. These concerns have prompted a widespread need and search for alternative feed additives that can bring about improved productive performance in the same manner as AGPs (Huyghebaertet al., 2011). Probiotics is among several extensively researched alternative feed additives that has received increased attention over the years (Yan & Kim, 2014). Probiotics are non-pathogenic live microbial feed additives that have been shown to improve productive capacity and immune status of animals by enhancing the composition and balance of the animal’s gut microflora (Hill et al., 2014). According to Scott (2012), trace minerals like zinc oxide have also gained prominence in recent times.

Saccharomyces cerevisiae are non-bacteria probiotic supplements (Bai et al., 2013) which when used as dietary additives in the nutrition of animals have potential to alter gut microflora by controlling pH (Leeson & Summers, 2008; Ng et al., 2009), suppress pathogenic bacteria growth (Stanley et al., 2004), modulate immunity (Shashidhara et al., 2003; Magalhaes et al., 2008), promote intestinal microflora growth (Spring, 2000), improve growth performance (Parks, 2001; Galvao et al., 2005), enhance nutrient digestibility and retention (Bradley et al., 1995; Ciorba, 2012), affect intestinal mucosal development (Zhang et al., 2005), and serve as alternatives in lieu of antibiotic-based drugs in the feed of broiler chicks, thus ensuring food safety for human consumers (Hooge et al., 2003; Song et al., 2012; Broadway et al., 2014) amongst other immense benefits. Zinc is a heavy metal increasingly used alongside other trace minerals in livestock nutrition. These minerals are needed for normal digestive, physiological and biosynthetic functioning of biological systems. The utilization of these trace mineral elements in the nutrition of food-producing animals has revealed their capacity to improve/maintain growth, immunity, and overall metabolic and physiological processes (Attia et al., 2012; Scott et al., 2012).

According to Richards et al. (2010), and Bhowmilk et al. (2012), zinc not only serves as a cofactor in a number of cellular enzymatic and transcription processes, it is also involved in maintaining immunity, controlling reproduction, regulating gene expression and cell proliferation, and providing protection against deleterious effect of reactive oxygen species (ROS). Zinc affects semen quality and quantity, particularly in terms of exerting a direct effect on sperm maturity and reproductive epithelium of male sexual glands (Peter et al., 2004). Zinc deficiency has been linked to delay in testicular development and spermatogenesis (Peter et al., 2004), decreased litter size in pigs (Hoekstra et al., 1967), low production levels of luteinizing hormone and follicle-stimulating hormones (Dillin et al., 2002), change in dietary preferences in rats (Kennedy et al., 1998) low birth weight and number of offspring in ewes (Masters & Fels, 1980). Even though several feeding trials have been done using Saccharomyces cerevisiae and zinc oxide in livestock and poultry, there is currently very limited literature on the effect of dietary Saccharomyces cerevisiea and zinc oxide inclusion in improving semen and testicular morphometric characteristics in rabbits. Therefore, this study was designed to determine the effect on gross epididymal semen characteristics and testicular morphometrism of rabbit bucks fed dietary inclusions of Saccharomyces cerevisiae and/or zinc oxide.

MATERIALS AND METHODS

Experimental location and management of experimental animals

The study was carried out at the Rabbit Unit of the Department of Animal Science Teaching and Research Farm, University of Nigeria, Nsukka. The rabbits were procured from reputable rabbit farms around Nsukka local government area, Nsukka, Nigeria. Before the arrival of the animals, the experimental rabbit hutches, feeding and drinking troughs were thoroughly disinfected using a disinfectant known as Izal^®. Upon arrival, the bucks were allowed an acclimatization period of 3 weeks, and subsequently dewormed with ivermectin by subcutaneous means.

Experimental design and diets

16 New Zealand White rabbit bucks that were 16-wk-old were randomly allotted to 4 dietary treatments with 4 bucks per treatment. Each treatment was replicated four times with 1buck per replicate in a completely randomized design (CRD) with treatment as main effect. Commercial rabbit grower’s mash was used for the feeding process. Zinc oxide and/or Saccharomyces cerevisiae were procured from an Agro-Chemical Company in Nsukka. Both feed additives were included in the diets at different levels. The four experimental diets formulated were as follows: T_A = control diet with no additives, T_B = 0.12g/kg Saccharomyces cerevisiae, T_C = 150mg/kg zinc oxide and T_D = 0.12g/kg Saccharomyces cerevisiae +150mg/kg zinc oxide.

Performance parameters

Average initial weight of bucks was taken when the experiment started and subsequently weekly. At the end of the experiment, average final buck weight was recorded per buck per replicate. Data collected was used to calculate average weight gain (ADWG) per buck. A weighed amount of feed was given to the bucks daily. Thereafter, daily feed intake per replicate (DFI) was recorded as the difference between feed offered the previous day and that left over in the feeding trough the next day. A summation of DFI per replicate gave the value for the weekly feed intake. Average daily feed intake (ADFI) was then calculated from these values. Feed conversion ratio (FCR) was calculated as feed intake divided by the weight gain.

Semen collection and evaluation of semen characteristics

At the 8^th week of the trial, semen collection commenced using well lubricated artificial vagina whose temperature was maintained at 37^oC. The collection was made on a weekly basis from all the bucks for the remaining four weeks of the feeding trial. Semen collected was taken to the laboratory and kept in a hot water bath to maintain the same temperature. The semen samples were thereafter used to determine sperm quality. Semen volume was measured directly from the calibrated tube used for semen collection. Semen pH was determined by dipping a litmus paper into the ejaculate and monitoring the corresponding colour changes. Semen motility was examined as quickly as possible after semen collection. A drop of semen sample was placed on a pre-warmed glass slide, covered with warm cover slip and examined using a microscope at x10 magnification. A scale (0-100) was used to rate the motility. The highest scale (100) reflected the number of sperm cells that showed vigorous and progressive forward motility, whereas, the lowest (0) reflected very minor or immobile cells. Sperm concentration was determined following the procedures described by Azawi & Ismaeel (2012) using Neubaeur haematocytometer. A cover slip was placed on the haematocytometer and two drops of dilute semen was placed under the cover slip. The haematocytometer was carefully placed in a pre-wetted chamber, the lid closed and left for 5 minutes. Thereafter, it was examined using a microscope at ×40 magnification. The sperm cells were counted in five Thoma square of the chamber (i. e. four corners and the center squares). Semen concentration was calculated as follows:

$\text{Spem}\text{concentration}=\frac{\text{number}\text{of}\text{spem}\text{cells}\text{counted}\times \text{dilution}\text{factor}\times {\text{10}}^{\text{6}}}{\text{area}\text{of}\text{the}\text{heamacytometer}\times \text{depth}\text{of}\text{the}\text{heamacytometer}}$

Where: area and depth of haematocytometer = 0.10mm. Percentage live sperm cells were determined using the method described by Esteso et al. (2006). A thin smear of semen was made on a clean grease-free slide and stained with two drops of eosin-nigrosin. This technique was based on the principle that eosin-nigrosin penetrates and stains dead sperm cells, while live sperm repel the stain. Dead spermatozoa stained pinkish or reddish, whereas live spermatozoa remained colourless. 100 stained and unstained sperm cells were counted, when the slides were dried using light microscope at ×40 magnification. Percentage of each live sperm cell was then estimated (Esteso et al., 2006). Sperm abnormality was determined by making a thin smear of semen sample mounted on clean grease-free glass slide and stained with eosin-nigrosin. 100 sperm cells were counted per slide using hand counter under light microscope (× 40 magnification).

Evaluation of testicular morphometric traits

At the end of the 12-week study, 8 bucks (2 per treatment) were selected randomly around the mean weight of bucks in each treatment group and used for determination of morphometric traits. The bucks were euthanized, after which, the pairs of testes and epididymis were carefully separated and freed of all adhering connective tissues. Using conventional point counting, fraction of the seminiferous tubules in the testis (epipidymal duct) was estimated. Volume per organ was calculated by multiplying the fraction by the volume of the organ. All testicular sections were observed again at low power magnification (×10) using compound microscope. Each testis round or elliptical profiles of the seminiferous tubules with an apparent lumen was sampled with the frame. Thereafter, the diameter of round profiles or the short axis of elliptical profiles was measured as the tubule diameter. The tubule length per testis was then calculated by dividing the total tubule volume per testis by the cross-sectional area of the tubules.

Statistical analysis

Data generated from the study were subjected to analysis of variance (ANOVA) procedures for a CRD experimental model. Using the Duncan’s multiple-range test as outlined by Obi (2002), significantly different means were separated, and differences were considered to be significant at p<0.05. The model for the experimental design was given as follows: $X_{ij}=\mu +T_i+{ϵ}_{ij}$. Where: X_ij = individual observation; µ = population mean or overall mean; T_i = treatment mean or effect due to treatment; ϵ_ij = experimental error.

RESULTS

Growth performance

Table 1 shows that average final body weight (AFBW), average daily weight gain (ADWG), average daily feed intake (ADFI) and feed conversion ratio (FCR) were not significantly ((p>0.05) affected by dietary treatments. It was observed that bucks fed varying dietary levels of Saccharomyces cerevisae had numerically higher values for AFBW and ADWG than those that received other dietary treatments.

Table 1
Composition of commercial feed used for the experiment.

Nutrient composition	Quantity	Unit
Crude protein	20.09	%
Crude fibre	7.39	%
Fat	3.04	%
Metabolizable energy	1970	Kcal/kg
Arginine	1.42	%
Glycine	1.16	%
Serine	1.02	%
Histidine	0.49	%
Isoleucine	0.89	%
Leucine	1.54	%
Methionine	0.35	%
Cystine	0.28	%
Phenylalanine	0.83	%
Tyrosine	0.72	%
Threonine	0.72	%
Tryptophan	0.24	%
Valine	1.03	%
Linoleic acid	1.07	%
Calcium	3.71	%
Potassium	1.05	%
Available phosphorous	0.41	%
Magnesium	0.42	%
Sodium	0.28	%
Sulphur	0.22	%
Chlorine	0.36	%

Epididymal sperm characteristics

As shown in Table 2, the effect of dietary treatments on gross epididymal sperm characteristics was significant (p<0.05). Bucks fed supplemental Saccharomyces cerevisiae (SC) had significantly (p<0.05) improved sperm concentration, progressive motility and percent live sperm compared with other treatments. Incidence of head and tail sperm abnormality was also significantly (p<0.05) reduced in bucks fed SC-based diets, and highest for control (Treatment A) fed bucks. Sperm concentration in SC supplemented groups was 7.28 compared with 7.10, 6.60 and 5.89 recorded in treatments C, D and A. Progressive motility in SC dietary groups was 80.05, compared with 40.05, 60.05 and 70.05 respectively in treatments C, D and A. Live sperm percent was also higher in SC-supplemented groups, being 94.21 compared with 92.41, 93.60 and 89.40 obtained in treatments C, D, and A. Sperm motility was significantly (p<0.05) reduced in bucks fed zinc oxide (treatment C) supplemented diets. There was an observed significant (p<0.05) reduction in sperm concentration and percent live sperm in bucks that received the control diet (Treatment A). Bucks fed diets supplemented with a combination of Saccharomyces cerevisiae and zinc oxide (Treatment D) had significantly (p<0.05) higher sperm pH compared with other treatments. Nevertheless, the least sperm pH value was recorded amongst bucks fed Saccharomyces cerevisiae-based diets (Treatment B).

Table 2
Performance of bucks fed dietary Saccharomyces cerevisiae and/or zinc oxide.

Treatments	A	B	C	D	SEM
Parameters
Initial Body Weight (g)	2850.00	2800.00	2850.00	2800.00	31.33
Final Body Weight (g)	4075.00	4425.00	4175.00	4290.00	84.96
Average Daily Weight Gain (g)	11.00	16.00	11.00	13.00	1.16
Average Daily Feed Intake (g)	30.50	30.50	31.00	31.50	0.29
Feed Conversion Ratio	2.75	2.00	2.82	2.31	0.19

• ^a,b,c,d; Row means with different superscripts differ significantly at p<0.05. SEM= Standard error of the mean. Treatment A: control diet with no additives. Treatment B: 0.12 g Saccharomyces cerevisia/kg feed. Treatment C: 150 mg Zinc oxide/kg feed. Treatment D: 0.12 g Saccharomyces cerevisiae + 150 mg Zinc oxide/kg feed.

Testicular morphometric traits

Dietary treatments had significant (p<0.05) effect on testicular morphometric traits of rabbit bucks (Table 3). Inclusion of Saccharomyces cerevisiae alone in the diet (Treatment B) resulted in significant improvement in tubule diameter, epididymal volume, volume fraction of duct, and total duct volume. Although, dietary supplementation of zinc oxide alone (Treatment C) significantly (p<0.05) improved seminal vesicle volume in bucks, volume fractions of tubules were better in bucks fed the control diets. Testicular tubule length and testicular volume was highest (p<0.05) for bucks fed treatments A and D while the least (p<0.05) testicular tubule length was recorded for treatments B and C. Meanwhile, testicular volume was lowest (p<0.05) for bucks fed dietary Saccharomyces cerevisiae (Treatment B).

Table 3
Epididymal sperm traits of bucks fed dietary Saccharomyces cerevisiae and/or zinc oxide.

Treatments	A	B	C	D	SEM
Parameters
Sperm concentration (× 109/ml)	5.89d	7.28a	7.10b	6.60c	2.03
Progressive motility (%)	70.05b	80.05a	40.05d	60.05c	5.59
Live sperm (%)	89.40d	94.21a	92.41c	93.60b	6.99
Head abnormality	50.50a	39.05d	46.95b	39.65c	1.83
Tail abnormality	47.55a	39.85d	41.05b	44.65b	1.14
pH	7.60b	7.50c	7.60b	7.81a	0.42

• ^a,b,c,d; Row means with different superscripts differ significantly at p<0.05. SEM= Standard error of the mean. Treatment A: control diet with no additives. Treatment B: 0.12 g Saccharomyces cerevisia/kg feed. Treatment C: 150 mg Zinc oxide/kg feed. Treatment D: 0.12 g Saccharomyces cerevisiae + 150 mg Zinc oxide/kg feed.

DISCUSSION

Growth performance

According to Gibson & Roberfroid (2008), supplementation of Saccharomyces cerevisiae (SC) in the diet of animals can improve the quality of their feed and also their performance and productive traits. However, as observed in the present study (Table 2), mean live weights of bucks at the end of the feeding trial were 4075 g, 4425 g, 4175 g, 4290 g for A (control), B (SC), C (zinc oxide-ZNO) and D (SC + ZNO) respectively. This indicates that dietary inclusion SC or ZNO alone or a combination of both feed additives did not exert any significant (p>0.05) effect on performance of bucks. The result of the present study on growth performance is in line with the work of Collins & Moran (1999), whose study revealed that supplementing zinc oxide in the diet of broiler birds did not significantly (p>0.05) enhance body weight and feed efficiency of the birds. The result however contradicts the reports of Ezema & Eze (2015), who reported that rabbits fed diets supplemented with SC had improved average weight gain and daily feed intake compared to those in the control group. The result also disagrees with the work of Alcicek et al. (2004), who found that dietary inclusion of 10ppm zinc oxide resulted in significant improvement in rabbit performance. Although, Yirga (2015) noted that results obtained on the growth promoting effects of probiotics in livestock nutrition are somewhat inconsistent, probiotic feed additives are largely capable of inducing improved growth responses in animals. Thus, the exact reason for the non-significant effect on growth performance in both the Saccharomyces cerevisiae and zinc oxide supplemented groups as observed in this study is not known. However, it may be due to factors associated with diet preparation and composition, quantity of feed additives used, feeding strategy, or other physiologic or environmental issues.

Epididymal spermcharacteristics

Cheng et al. (2002) pointed out that semen quality assessment is an important marker in selection of breeding males, and also for effective monitoring of the male’s reproductive capacity. Usually, sperm traits such as sperm motility, percentage of live or dead sperm, morphological features among others often determines the inseminating capacity of particular semen (Okoro et al., 2016). As shown in Table 3, supplemental SC had more pronounced (p<0.05) effect on gross epipidymal semen characteristics of rabbit bucks compared to their counterparts that received other dietary treatments. According to Wysokinska & Kondracki (2013), sperm motility is a vital ejaculate attribute that has an enormous impact on egg cell fertilization. The rate of motility of a sperm determines the extent it can gain entry into the vestments (the cumulus oophorus, zona pellucida, and other coatings) around the oocyte, in order to reach the site of fertilization as well as achieve fertilization (Hidiroglou et al., 1978). It is evident from the result on semen characteristics obtained in the present study that semen from bucks fed SC had superior motility, higher sperm concentration, higher percentage of sperm livability and lower number of abnormal spermatozoa. This improvement in semen characteristics may be attributed to the antioxidant property of SC as a probiotic-based feed additive (Uskova & Kravchenko, 2009; Spyropoulos et al., 2011). The result of the present study on epididymal sperm characteristics agrees with the findings of Mangiagali et al. (2012) whose study showed that inclusion of lycopene in the water of rabbits, particularly at 0.5g/L, significantly affected sperm motility, forward progressive motility, sperm viability and other sperm quality parameters. Nevertheless, Castellini et al. (2003) reported that supplemental antioxidants such as vitamin C and E had no significant effect on sperm parameters of rabbits.

As reported by Subeve t al. (2005) and Mourvaki et al. (2010) semen contains lipids as important constituents. Structurally, seminal lipids help to maintain membranous integrity, absorption, utilization and inseminating capacity of spermatic cells. Nonetheless, these lipids are prone to attack by ROS. Physiologically, ROS are needed during sperm capacitation and fusion of sperm to ova (Aggarwal et al., 2003). Again, when the body’s ability to neutralize free radicals is below the rate at which the radicals are produced, oxidative stress becomes the resultant effect (Khan, 2011). Hence, according to Castellini et al. (2003) the fertilizing ability of sperm cell depends largely on the ideal balance of polyunsaturated fatty acids and antioxidant effects. Unlike other mammals, sperm from rabbits have been shown to contain high concentrations of n-6 than n-3 polyunsaturated fatty acids (Gliozzi et al., 2009). This predisposes the spermatozoa to faster oxidative damage under storage conditions, with consequent damaging effect on quality of the sperm (Bansal & Bilaspuri, 2011). Nevertheless, there are scientific evidence (Castellini, 2008; Mourvaki et al., 2010) to corroborate the claim that compounds with antioxidant properties such as Saccharomyces cerevisiae have potential to inhibit oxidative damage in cell membrane of sperm cells and fragmentation of sperm DNA brought about by the harmful activities of free radicals. According to Aggarwal et al. (2004) these beneficial effects of antioxidants in turn helps improve sperm motility and other seminal traits.

It is notable that bucks fed zinc oxide (Treatment C) supplemented diets recorded the least sperm progressive motility compared to the control (treatment A), and other dietary treatments. Notwithstanding, the motility value of 40.05% recorded for zinc oxide fed bucks was still within the range reported by Pascual et al. (2004) as shown in Table 3. This result on decreased sperm motility associated with zinc oxide supplementation contradicts the findings of Kumar et al. (2006) whose work showed that at different levels of dietary zinc inclusion significantly improved mass and individual sperm motility of crossbred cattle bulls. Rahman et al. (2014) also reported significant increase in sperm motility in rabbit bucks fed zinc sulphate supplemented diets. It has been shown that zinc is actively involved in energy movement along the adenosine triphosphate energy pathway, basically by controlling phospholipid energy reserves, improving sperm oxygen uptake, and thus sperm motility (El-Masry et al., 1994). Zinc is also a potent antioxidant compound that scavenges superoxide radicals present in seminal plasma, and thus, improves sperm motility (Kumar et al., 2006). As reported by Negamine et al. (1990) and Kurmal et al. (2006) enzymes such as sorbitol dehydrogenase and lactose dehydrogenase are major biochemical constituents of zinc and increase in these enzymes led to increase in sperm motility. It is surprising though, that this was not the case in the present study. Zinc supplementation led to significant (p<0.05) decrease in motility of spermatic cells. This result is however similar to that obtained from the reports of Khallare & Shrivastav (2003) and Alvarez-Gomez et al. (2007) who attributed reduced sperm motility in animals fed neem leaf meal based diets to blockage in energy metabolic route.

Although, dietary treatments had significant (p<0.05) effects on sperm characteristics of rabbit bucks in the present study (Table 3), the percentage head and tail abnormal sperm cells obtained in all the supplemented dietary groups exceeded 20 %. Research showed that 20 % head and tail abnormality is the upper limit recommended as the lowest value of abnormal spermatozoa indicative of good reproductive and prolific functions in male animals used for either natural mating or artificial insemination purposes (Zemjanis, 1977; Oyeyemi & Okediran, 2007). More so, there are considerable evidence that supports the existence of positive genetic correlation between body weight gain and sperm concentration (Rodriguez-De Lara et al., 2015), and ejaculate volume (Lavara et al., 2011) in rabbits, and also between daily body weight gain and volume of ejaculate, abnormal sperm, and sperm pH in broilers (Ramamurthy et al., 1989). This implies that heavier animals tend to possess more sperm reserves. This was however not the case in the present study, as final body weight and average body weight gain did not differ among different treatment groups, and as a result, had no determining effect on reproductive performance of bucks. The results of the present study also showed a significant (p<0.05) reduction in pH in bucks on Saccharomyces crevisiae diet, whereas the pH of those on zinc supplemented and control diets were comparable (p>0.05). However, a marked significant improvement in pH was recorded among bucks fed a combined dietary mixture of Saccharomyces cerevisiae and zinc oxide. This showed that the combined effects of the probiotic (Saccharomyces cerevisiae) and zinc supplementation resulted in enhanced semen pH. The result obtained on pH does not agree with the findings of Attia et al. (2013) who reported that including either vitamin C, or vitamin E, combined with selenium or probiotic in the diets of rabbit bucks did not affect semen pH. The findings of Kumar et al. (2006) indicated that there was significant (p<0.01) reduction in semen pH values in bucks fed zinc sulfate supplemented diet.

Testicular Morphometric traits

According to Ewuola (2013), two important factors that guide breeders in selecting breeding males include the quantity of good quality spermatogenic cells with good livability produced by the testis, and its ability to effectively store the produced spermatozoa. Oyeyemi et al. (2002) also opined that having adequate information on the morphometric traits of the testis and other reproductive organs of a particular breeding male is a vital pointer to its breeding value and fecundity. This is due to the fact that the spermatozoa-storing ability of the testis of a male animal determines its fertility level. Tubular measurement is usually the traditional method employed in assessing spermatogenic activity in any investigation involving testicular functions (Silvaet al., 2006). As shown in Table 4,dietary Saccharomyces cerevisiae (SC) improved (p<0.05) testicular parameters of bucks, mainly tubule diameter, epididymal volume, volume fraction of duct, and total duct volume, compared to those on the control diet. This implies that SC promotes the growth and development of testicular glands and gonadal sperm reserve. Colenbrander & Kemp (1990) asserted that testicular weight and quantity of sperm produced are correlated. Morris et al. (1999) also stated that within a species of animals, there often exist positive correlation between spermatozoa production, testicular size and testicular length. Some authors (Oyeyemi & Okediran, 2007; Oyeyemi et al., 2002; Britto et al., 2004) have also shown through their reports that testes that are larger in size tend to possess more sperm producing ability than smaller ones. Larger testes weight of bucks fed SC based diet would be said to contain more seminiferous tubules, leydig cells, Sertoli cells, and thus, produce larger amount of sperm.

Table 4
Testicular morphometric traits of bucks fed dietary Saccharomyces cerevisiae and/or zinc oxide.

Treatments	A	B	C	D	SEM
Parameters
Testicular volume (cm3)	1.41a	1.28c	1.38b	1.41a	0.02
Volume fraction of tubules (%)	85.05a	82.65c	84.65b	84.75b	3.59
Testicular diameter (µm)	29.85c	30.45a	30.05b	28.65d	25.42
Total tubule length (m)	14.75a	14.35b	14.25b	14.55a	0.54
Epididymal volume (cm3)	0.26c	0.33a	0.29b	0.26c	0.11
Volume fraction of duct (%)	50.65b	68.90a	49.05c	43.60d	35.97
Total duct volume (cm3)	0.20b	0.21a	0.17c	0.11d	0.14
Seminal vesicle volume (cm3)	0.08c	0.12b	0.17a	0.06d	0.01

• ^a,b,c,d; Row means with different superscripts differ significantly at p<0.05. SEM= Standard error of the mean. Treatment A: control diet with no additives. Treatment B: 0.12 g Saccharomyces cerevisia/kg feed. Treatment C: 150 mg Zinc oxide/kg feed. Treatment D: 0.12 g Saccharomyces cerevisiae + 150 mg Zinc oxide/kg feed.

Mosenthin & Baller (2000) and Ewuola et al. (2011) reported that dietary supplementation of probiotics has been linked with enhanced intestinal mucosal development which has significant effect on improved nutrient digestibility. The improved intestinal mucosal development helps to promote the growth and concentration of Sertoli cells and seminal fluids. According to (Berndtson et al., 1987) testes with more Sertoli cells are larger in size and tend to produce more spermatozoa than those with less number of Sertoli cells. However, it was observed that bucks fed mixture of Saccharomyces cerevisiae and zinc oxide had reduced testicular diameter compared to the other treatment dietary groups. This may probably indicate that the synergistic effect of both additives had a depressing impact on testicular growth of rabbit bucks. Morton (1988) attributed decrease in testis size to extensive loss of seminiferous epithelial cells, invariably signifying lower levels of spermatozoa production. Ogbuewuet al. (2009) reported significant reduction in seminiferous tubule diameter of rabbit bucks fed 15% neem leaf-based diet. Whereas, testicular volume was significantly improved by dietary supplementation of zinc oxide + Saccharomyces cerevisiae, it was lowest among bucks on dietary Saccharomyces cerevisiae and zinc oxide. The work of Ansa et al. (2017) showed that supplementation of cadmium reduced testis volume and epididymal carrying capacity and length. El-Neweshy et al. (2013) attributed reduction in testicular volume to reduced testosterone levels, and this consequently results in low sperm production. However, this study recorded improved testis volume among zinc oxide +Saccharomyces cerevisiae supplemented groups. This aligns with the findings of Ansa et al. (2017) who reported that methanolic extract of Date palm (Phoenix dactylifera) resulted in significant improvement of testis volume and density among rabbit bucks exposed to cadmium inclusion.

Dietary supplementation of zinc oxide alone (treatment C) significantly (p<0.05) improved seminal vesicle volume in bucks. This result agrees with the findings of Amara et al. (2008) whose study showed that dietary inclusion of zinc not only reduced DNA oxidative damage, but also reversed reduction in sperm and testosterone production induced by cadmium exposure in the testis of Wistar rats. The work of Oteiza et al. (1999) had shown that zinc deficiency resulted in concomitant cell damage in the testis of rats. Results of the present study also revealed that seminal vesicle volume was markedly (p<0.05) reduced in bucks fed treatments D and A (S. cerevisiae + zinc oxide diet, and control diet). This result is in consonance with the reports of Predes et al. (2010) and Elgawish & Ghanem (2014) whose works revealed that there was significant reduction in seminal vesicle volume and prostate gland of Wistar rats exposed to 1.2 mg/kg cadmium supplemented diet.

CONCLUSION

Dietary inclusion of Saccharomyces cerevisiae at 0.12g/kg of feed, improved epididymal sperm characteristics and testicular morphometrism of rabbit bucks.

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Publication Dates

• Publication in this collection
  2019

History

• Received
  17 Apr 2018
• Accepted
  27 Aug 2018