Physiological and Growth Response of New Zealand Male Rabbits Fed Zinc Supplemented Diets

Anizoba, N.W.; Ugwoke, S.C.; Nwuju, P.P.; Ikeh, N.E.; Nwoga, C.C.; Machebe, N.S.

ABSTRACT

Background and Objective: Zinc is important for several biological processes which are required by different species of animals at different ages of their life for maximum production and reproduction. This study was conducted to evaluate the effect of dietary Zinc (Zn) oxide on physiological, reproductive performance and growth rate of growing rabbits. Materials and Methods: Thirty-six New Zealand white rabbit bucks aged 4 months and with an initial average body weight of 2440 g were randomly allocated into 4 treatment groups containing 9 rabbit and fed diets containing 0, 50, 100 and 150 mg of zinc oxide per kg diet, respectively, for ten weeks in a Completely Randomized Design (CRD). Results: That zinc oxide supplementation significantly affected (p<0.05) most of the growth performances parameters, testicular characteristics, serum antioxidant enzyme assay and haematological characteristics except initial weight, right testis length, left testis length, right testis weight Aspartate Aminotransferase (AST), Superoxide Dismutase (SOD) and white blood cells which were not significant (p>0.05). Conclusions: From these findings, we conclude that 100 mg of zinc oxide per kg diet supplementation was adequate to improve the physiological traits, productive and reproductive performance of rabbit buck while reducing the antioxidant stress factors in the semen thereby maintaining the integrity of the sperm without adverse effect on the animal.

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INTRODUCTION

The growing human population especially in developing countries coupled with insufficient supply of animal sources of protein from the main livestock species (cattle, sheep, goats, pigs and poultry) has made it essential that interest be shifted to other micro-livestock such as rabbits. This is because rabbit production has the potential to assuage the problem of insufficient animal protein supply in developing economies¹. Ghosh et al.² defined a rabbit as a mini-livestock with high reproductive potentials. It has a unique ability that serves as a flexible financial reserve. It has a short gestation length, exhibits early maturity, has high prolificacy, efficient food utilization, the meat of high nutritional value and additionally can be rebred shortly after parturition.

In Nigeria, there are problems encountered in rabbit production such as lack of proper awareness, little or no adoption of the enterprise, lack of capital, lack of interest and above all reproductive inefficiencies³. Reproductive inefficiencies are the major factor because it determines the sustainability of production. Increased environmental conditions predispose male rabbits to reduced reproductive performances such as reduced semen quality as well as, reduced ability of Leydig and Sertoli cells to respond to luteinizing hormone (LH)⁴. High ambient temperature stimulates the hypothalamo-pituitary-adrenal axis activity inducing the sympathetic system functions but also, in the same way, increases the levels of free radicals and imbalances in the antioxidant defence system^5,6. Accumulations of these free radicals have been associated with significant decreases in sperm motility and sperm plasma membrane integrity and significant increases in sperm abnormality and DNA damage leading to infertility⁷.

To this effect, zinc oxide remains the most frequently used zinc supplement with the growth-promoting ability and an antioxidative property⁸. Zinc performs important antioxidative functions in biological systems, mainly as a structural component of the antioxidant enzymes. Zinc up-regulates the synthesis of proteins with oxidant-scavenging capacity (e.g., thionein) and prevents the binding of redox-active metals to oxidation target cell molecules⁹. Hence, it serves as a dietary supplement to reduce the stress of breeding rabbits for higher reproductive performance. According to Richard et al.¹⁰ and Bhowmilk et al.¹¹ zinc does not only serves as a cofactor in several cellular enzymatic and transcription processes, but it is also involved in maintaining immunity, controlling reproduction, regulating gene expression and cell proliferation and providing protection against the deleterious effect of reactive oxygen species (ROS). Zinc affects semen quality and quantity, specifically in terms of exerting a direct impact on sperm maturity and the reproductive epithelium of male sexual glands¹². Zinc deficiency has been linked to delays in testicular development and spermatogenesis¹², low production levels of luteinizing hormone and follicle-stimulating hormones¹³and change in dietary preferences.

Under tropical conditions, ambient temperature is the major determining factor controlling animal productivity. To select males based on high fertility for breeding purposes, it is necessary to assess the growth and productivity of their reproductive organs and the probable role of supplemental levels of zinc may be necessary. With this in mind and despite the good potentials of zinc in bucks reproduction especially when it concerns testicular morphometry and zincs’ ability to reduce oxidative stress, it is equally important to quantify the amount that has the most efficient effect on the bucks. This in turn will attempt to achieve goals number one, two and three of Sustainable Development Goals (SDG) 2020 and 2030 of the United Nations which include no poverty, zero hunger and good health and well-being respectively. Hence, this study aimed at evaluating the physiological traits, productive and reproductive performance of rabbit bucks fed dietary levels of zinc.

MATERIALS AND METHODS

Study area: The study was carried out at the Rabbitry Unit of the Teaching and Research farm, Department of Animal Science, University of Nigeria Nsukka, Enugu State, Nigeria from January-March, 2021. The experiment was carried out by the provisions of the Ethical Committee (MUC271SOYE01) on the use of animals and humans for biomedical research of the University of Nigeria, Nsukka, Nigeria.

Experimental animal and management: The rabbits were procured from reputable commercial rabbit farms, J-Royal Affairs Integrated Farms, Nsukka, Enugu State, Nigeria. A total of thirty-six (36) New Zealand white rabbit bucks of 4 months old with an average body weight of 2440 g were randomly divided into four equal treatments (9 bucks each) and replicated four times with 3 rabbits per replicate. In the 1st treatment (T₁), rabbits served as control (0 mg ZnO supplement kg^–1 diet). In the 2nd, 3rd and 4th treatments (T₂, T₃ and T₄), rabbits were fed with basal diet containing 50,100 and 150 mg ZnO/kg diet, respectively for 10 weeks. The basal diet used in the experiment was formulated to meet or exceed the nutrient requirements recommended by the National Research Council¹⁴.

Table 1:

Formulation and chemical composition of the basal diet

Ingredients	Percentage
Maize	44.6
Wheat bran	31.1
Soybean meal	15.8
Palm kernel cake	5.5
Fish meal	2.0
Lysine	0.2
Methionine	0.2
Salt	0.3
Vitamin premix (ZnO-free)	0.3
Chemical composition
Dry matter (%)	83.60
Crude protein (%)	16.50
Crude fibre (%)	12.13
Ether extract (%)	5.51
Ash (%)	10.31
Metabolizable energy (Kcal kg^–1)	2500.35
*Vitamin and mineral premix per kg of diet, vitamin A: 1000000 IU, vitamin D₃: 2000 IU, vitamin B₁: 0.75 g, vitamin B₂: 5 g, nicotinic acid: 25 g, vitamin B₁₂: 0.015 g, K₃: 2.5 g, vitamin E: 25 g, biotin: 0.050 g, Folic acid: 1 g, calcium pantothenate: 12.5 g, choline chloride: 250 g, manganese: 64 g, cobalt: 0.8 g, copper: 8 g, iron: 32 g, Iodine: 0.8 g, DL-methionine: 50 g and Lysine: 120 g

The formulation and nutrient composition of the basal diet is presented in Table 1. Rabbits were housed in individual cages, receiving rations and water ad libitum and kept under the same managerial and hygienic conditions.

Growth performance parameters: Average initial weight of bucks was taken when the experiment started and subsequently weekly. Bodyweight was obtained by weighing rabbits individually from each cage weekly using a 10.1 kg capacity precision weighing balance (models A and D weighing GK-10K industrial balance) made in China. The mean of each group was taken (A) and that of the previous week (B) was subtracted from it (A-B). The difference between the two divided by seven days gave the daily weight gain for a particular day in a week i.e., (A-B)/7 = daily wt gain (DWG). Feed intake was determined by offering a known quantity of feed (X) to each cage, morning and evening and the leftover (Y) weighed the following morning. The difference between X and Y (X-Y) gave the quantity of feed consumed.

Average feed intake (g) = Quantity of feed given-leftover feed

Feed conversion ratio (FCR) was calculated as feed intake divided by weight gain.

Evaluation of testicular morphometric traits: At the end of the feeding trial (10 weeks), 12 bucks (3 per treatment) were selected randomly around the mean weight of bucks in each treatment group and used for the estimation of testicular morphometry. The bucks were euthanized after which, the pairs of testes were carefully separated and freed of all adhering connective tissues and were weighed individually by placing in a sterile Petri dish on a sensitive scale to the nearest 0.01 g. The lengths of the two testes were measured with the aid of a meter rule. The volume of the paired testis was recorded using Archimedes's principle of water displacement. The scrotal circumference was taken using a measuring tape calibrated in a centimetre. The density of the testis was derived using the Eq¹⁵:

Image for - Physiological and Growth Response of New Zealand Male Rabbits Fed Zinc Supplemented Diets

Serum antioxidant enzyme assay: Blood samples were collected from 2 rabbits per replicate (i.e. 6 rabbit per treatment) at the end of the experiment into plain sterile bottles (without EDTA) by auxiliary vein puncture with the aid of a hypodermic needle and syringe and kept overnight at 4°C. The samples were separated by centrifugation for 15 min at 3000 rpm to fix the blood and then kept frozen for processing. Serum biochemical indices such as Alanine Aminotransferase (ALT), Alkaline Phosphatase (ALP) and Aspartate Aminotransferase (AST) were determined using the spectrophotometric procedure of Randox commercial assay kits. Serum oxidative stress indicators such as Superoxide Dismutase (SOD), Catalase (CAT), Glutathione Peroxidase (GPx) and Malondialdehyde (MDA) were assayed using standard protocol¹⁶.

Haematological analysis: At the end of the experiment, blood samples were collected from 2 rabbits per replicate (i.e. 6 rabbits per treatment) into plastic bottles containing Ethylene Diamine Tetraacetic Acid (EDTA) by auxiliary vein puncture for haematological profile determinations. To determine the Red Blood Cell count (RBC) and White Blood Cell (WBC) counts, counting was done with a haemocytometer chamber¹⁷. Parked Cell Volume (PCV) and Haemoglobin (HB) were determined by conventional laboratory methods¹⁸.

Statistical analysis: Data were statistically analyzed with the help of statistical software (SAS/STAT version 20.0, 2012 edition SAS Institute, Cary, NC). One-way analysis of variance (ANOVA) using a general linear model procedure was applied to test the significance of four dietary treatments on the studied parameters. Means were separated by the Duncan multiple-range test.^. Differences were considered statistically significant at p<0.05. The results were expressed as least square means with their standard errors (l.s.m±s.e.).

RESULTS

Growth performance: Table 2 showed that dietary supplementation of zinc oxide had a significant effect (p<0.05) on the growth performance of the rabbits. A marked increase in final body weight and weight gain was observed in the zinc treated groups compared (p<0.05) to the untreated groups. Higher values for these growth parameters were recorded at 100 and 150 mg ZnO whereas the lowest values were shown at 0 mg ZnO (control group) inclusion. Our finding shows a decline in the average daily feed intake and feeds conversion ratio (FCR) of the rabbits as the amount of zinc in the diet increased from 50-150 mg ZnO. The average daily feed intake and feed conversion ratio were lower in rabbits fed the zinc diets unlike in the untreated rabbits (p<0.05).

Testicular characteristics: The results of the testicular characteristics of rabbit fed dietary supplementation of zinc oxide are presented in Table 3. There were noticeable significant (p<0.05) effects of the dietary zinc in right testis weight, paired testis weight, paired testis length, scrotal circumference and testis density in the treated groups while right testis length, left testis length, left testis weight and paired testis volume had no significant (p>0.05) effect among treatment. Rabbits fed 50 mg ZnO and 150 mg ZnO level of zinc had the highest (p<0.05) paired testis length while 0mg ZnO had the lowest paired testis length. Rabbits fed 0 mg Zn had the least (p<0.05) testis weight and scrotal circumference while bucks on 100 mg Zn level of zinc had the highest testicular weight and scrotal circumference even though, they are statistically similar to bucks on 50 and 150 mg ZnO. Rabbits fed 50 mg Zn and 100 mg ZnO level of zinc had the highest (p<0.05) paired testis density, paired testis volume and right testis weight while 150 mg ZnO had the lowest right testis weight, paired testis volume and paired testis density.

Serum antioxidant enzyme: The results of the serum antioxidant enzyme of rabbit fed dietary supplementation of zinc oxide are presented in Table 4. Significant (p<0.05) effects were recorded in ALT, ALP, CAT, GPx and MDA while AST and SOD recorded no significant (p>0.05) difference. MDA, ALP and ALT concentration was higher in the control groups of a rabbit but gradually declined with an increase in zinc concentration in the diet. The concentration of GPx increased (p<0.05) linearly in the treated group 50 mg ZnO, 100 mg ZnO and 150 mg ZnO level of zinc and then declined in group 0 mg ZnO which is the control.

Haematological findings: Table 5 showed that dietary supplementation of zinc oxide had a significant effect (p<0.05) on the haematology of the rabbits. A marked increase in the haematological parameters was observed in the zinc treated groups compared (p<0.05) to the untreated groups. In groups fed 50 and 100 mg ZnO, PCV and HBV concentration increased significantly (p<0.05), the concentration of PCV and HBV increased (p<0.05) linearly in treated group fed 50 and 100 mg ZnO and then the declined (p<0.05) in group 150 mg ZnO.

Table 2:

Effect of dietary levels of zinc oxide on growth performance of rabbit bucks (n = 9 per treatment)

Parameters

T₁

T₂

T₃

T₄

Initial weight (g)

2425.00±69.28

2422.50±41.86

2444.50±35.87

2440±79.38

Final weight (g)

3706.50±84.58^b

3873.50±55.14^b

3988.00±37.53^ab

4001±33.60^a

ADG (g)

17.91±1.55^b

17.89±1.50^b

22.02±1.37^a

22.61±1.94^a

ADFI (g)

106.44±1.88^a

109.14±2.88^a

90.35±1.27^b

95.41±1.99^b

FCR

5.94±0.11^a

6.10±0.48^a

4.10±0.52^b

4.21± 0.50^b

^abcdMeans within rows with different superscripts are significantly different (p<0.05), ADG: Average daily gain, ADFI: Average daily feed intake and FCR: Feed conversion ratio, T₁: 0 mg Zn kg^–1, T₂: 50 mg Zn kg^–1, T₃: 100 mg Zn kg^–1 and T₄: 150 mg Zn kg^–1

Table 3:

Effect of dietary levels of zinc oxide on testicular characteristics of rabbit bucks (n = 3 per treatment)

Parameters

T₁

T₂

T₃

T₄

Scrotal circumference (cm)

6.00±0.22^b

7.25±0.43^a

7.25±0.26^a

7.55±0.26^a

Right testis weight (g)

3.00±0.04^b

4.00±0.01^a

4.00±0.06^a

2.00±0.02^c

Left testis weight (g)

2.50±0.90

3.00±0.87

4.00±0.60

2.50±0.30

Paired testis weight (g)

4.50±0.29^a

6.00±0.00^a

8.00±1.12^a

6.50±0.87^ab

Right testis length (cm)

2.20±0.06

2.75±0.03

2.70±0.20

1.55±0.03

Left testis length (cm)

3.00±0.23

2.85±0.32

2.65±0.14

2.25±0.14

Paired testis length (cm)

2.80±0.12^c

4.60±0.29^a

3.70±0.29^b

4.85±0.08^a

Paired testis volume (cm³)

7.50±0.87^b

8.00±0.22^a

8.50±1.44^a

6.00±0.34^c

Paired testis density (g cm^–3)

0.07±0.02^b

0.09±0.01^a

0.09±0.05^a

0.07±0.03^b

^abcdMeans within rows with different superscripts are significantly different (p<0.05), T₁: 0 mg Zn kg^–1, T₂: 50 mg Zn kg^–1, T₃: 100 mg Zn kg^–1 and T₄, 150 mg Zn kg^–1

Table 4:

Effect of dietary levels of zinc oxide on serum antioxidant enzyme of rabbit bucks (n = 6 per treatment)

Parameters	T₁	T₂	T₃	T₄
ALT (mg dL^–1)	11.33±0.04^a	11.39±0.05^a	10.84±0.07^b	10.84±0.07^b
AST (mg dL^–1)	11.55±0.12	11.40±0.12	11.05±0.17	11.30±0.06
ALP (mg dL^–1)	9.25±0.72^a	8.50±2.02^b	8.25±2.45^bc	7.75±1.01^c
CAT (μ mL^–1)	1.02±0.08^c	1.24±0.06^b	1.27±0.03^b	1.52±0.04^a
GPx (μ mL^–1)	9.91±0.25^b	10.78±0.35^a	10.34±0.48^ab	10.78±0.45^a
MDA (μ mL^–1)	1.48±0.02^a	1.24±0.02^c	1.36±0.01^b	1.16±0.01^d
SOD (μ mL^–1)	11.34±0.06	11.31±0.03	11.38±0.01	11.41±0.04
^abcdMeans within rows with different superscripts are significantly different (p<0.05), ALT: Alanine aminotransferase, AST: Aspartate aminotransferase, ALP: Alkaline phosphatase, CAT: Catalase, GPx: Glutathione peroxidase, MDA: Malondialdehyde, SOD: Superoxide dismutase and T₁: 0 mg Zn kg^–1, T₂: 50 mg Zn kg^–1, T₃: 100 mg Zn kg^–1 and T₄: 150 mg Zn kg^–1

Table 5:

Effect of dietary levels of zinc oxide on haematological indices of rabbit bucks (n = 6 per treatment)

Parameters	T₁	T₂	T₃	T₄
RBCs count (×10⁶/mm³)	6.50±0.288^c	7.50±0.235^b	8.59±0.267^a	7.50±0.217^b
WBCs count (×10³/mm³)	7.10±1.722	7.40±1.154	7.00±1.154	6.80±1.309
PCV (%)	37.50±2.88^c	41.00±2.68^a	42.00±0.78^a	39.50±2.74^b
Hb (g dL^–1)	9.38±0.072^c	10.45±0.087^a	10.25±0.144^a	9.88±0.072^b
^abcdMeans within rows with different superscripts are significantly different (p<0.05), RBC: Red blood cell, WBC: White blood cell, PCV: Packed cell volume, Hb: Haemoglobin concentration, T₁: 0 mg Zn kg^–1, T₂: 50 mg Zn kg^–1, T₃: 100 mg Zn kg^–1 and T₄, 150 mg Zn kg^–1

The groups supplemented with zinc had higher RBC compared to the control group and the best RBC level was observed in groups fed 100 mg ZnO. No significant change (p>0.05) was observed in WBC concentration.

DISCUSSION

In the present study, supplementation of zinc oxide to rabbit diets had a positive effect on the growth performance of rabbits. Improved performance in average final body weight, weight gain and feed conversion ratio was observed in rabbits fed 100 and 150 mg of zinc oxide per kg diet. These results were in agreement with Nessrin et al.¹⁹, who observed that dietary zinc levels had an effect (p<0.05) on body weight and feed conversion ratio (FCR) when adding Zn at the levels 50,100 or 200 mg kg^–1 diet. The positive results obtained in the performance traits may be because zinc plays an important role in growth and reproduction and can improve intestinal absorption²⁰ by participating actively in protein synthesis and carbohydrate metabolism²¹. The highest FCR of 5.94 and 6.10 was observed in 0 and 50 mg of zinc oxide per kg diet while the least FCR of 4.10 and 4.21 was observed in 100 and 150 mg of zinc oxide per kg diet, respectively. The improved FCR could be related to the immune-modulating properties of zinc which helped the rabbit use the nutrients properly and avoid losing them due to unnecessary stimulated immune system. The result observed in this study is in corroboration with Alcicek et al.²²and Ahmed et al.²¹. Dietary feed intake was lower for the zinc treated groups compared to the untreated group. This may be because of the antioxidant effect of zinc which protects nutrients from oxidation thereby improving feed utilization and better muscle accumulation. This result however contradicts the work of Dim et al.²³, who reported that supplementing zinc oxide did not exert any significant effect on the total feed intake of rabbit bucks. However, the differences observed in the results might be due to factors associated with diet preparation and composition, levels and sources of zinc used feeding strategy or other physiological or environmental issues.

Two essential factors that guide breeders in choosing breeding males consist of the quantity of good quality spermatogenic cells with good livability produced by the testis and its potential to effectively store the produced spermatozoa²⁴. Oyeyemi and Okediran²⁵ also opined that having ample information on the morphometric traits of the testis and the different reproductive organs of a particular breeding male is a fundamental pointer to its breeding value and fecundity. This is because the spermatozoa-storing ability of the testis of a male animal determines its fertility level. In the present study, dietary zinc oxide improved (p<0.05) testicular parameters of bucks compared to those on the control diet. This implies that zinc oxide promotes the growth and development of testicular morphometry.

Mohammed et al.²⁶ also stated that within a species of animals, there often exists a positive correlation between spermatozoa production, testicular size and testicular length. Some authors^25,27 have also shown through their reports that testes that are larger tend to possess more sperm-producing ability than smaller ones. Larger testes weight of rabbits fed zinc-based diet would be said to contain more seminiferous tubules, leydig cells, sertoli cells and thus, produce a larger amount of sperm thereby having better breeding and fertility potentials. The lower weight and volume of testis observed when the level of zinc increased to 150 mg shows that excess zinc significantly decreased the weight and volume of the testicles of the rabbit bucks. The reduction in the weight and volume of the testis is detrimental to breeding animals, since spermatogenic cells, leydig cells, seminiferous tubules and the surface area of spermatogenesis are likely affected by this phenomenon. The results of the current study confirm the reports of Ekuma et al.²⁸ who observed that morphometric traits, sizes and morphology are good indicators of present and future spermatozoa production, breeding and fertility potentials of a male animal.

Liver enzymes which include aspartate Aminotransferase (AST), Alanine Aminotransferase (ALT) and Alkaline Phosphatase (ALP) are found in many tissues throughout the body, including the liver, heart, muscles and kidney. The increment of the activities of ALT, AST and ALP in serum is mainly due to the leakage of these enzymes from the liver cytosol into the bloodstream which indicated liver damage and disruption of normal liver function²⁹. The result of the present study indicates that there was a significant decrease in the ALT and ALP concentrations as compared with the control after zinc supplementation. Zinc supplementation did not affect the AST concentration in the serum even though, numerically the concentration was reduced. Zinc decreased the elevation in the plasma AST, ALT and ALP activities by decreasing hepatocellular damage³⁰. These positive effects recorded after zinc supplementation could be attributed to the fact that zinc plays essential roles in many aspects of metabolism including the activity of more than 300 enzymes³¹. Zinc lowers the concentration of these hepatic enzymes in the blood plasma, prevents the oxidative damage of the liver by neutralizing the reactive oxygen species and improves the health condition of the liver.

Catalase reacts with generated hydrogen peroxide to form water and molecular oxygen thereby protecting the cells against hydrogen peroxide toxicity and lipid peroxidation³². According to Milinković-Tur, et al.³³ the activity of catalase and other antioxidant enzymes depend on the presence of antioxidants in the feed. In the present study, Catalase was observed to be highest in T₄ (150 mg Zn) while the lowest level was observed in T₁(0 mg Zn). This shows that the dietary supplementation of zinc up to 150 mg increase the concentration of catalase in the blood and this is due to the antioxidant effect of zinc. In the cellular membranes, GPx helps in protecting the cellular membranes from oxidative damage which enhanced the growth performance of rabbits under hot conditions. Glutathione peroxidase is an enzyme transforming the toxic and carcinogenic hydrogen peroxide into harmless water³⁴. In this study, there was a highly significant (p<0.05) increase in glutathione peroxidase level in the blood with the dietary supplement of zinc compared to the control group. This shows a positive effect of zinc in the reduction of hydrogen peroxide and lipid hydroperoxides formation. MDA considered a marker of oxidative stress, is one of the final products of cell polyunsaturated fatty acid peroxidation³⁵. In this study, there was a decrease in malondialdehyde level in the blood with the dietary supplement of zinc compared to the control group. This shows the positive effect of zinc as an antioxidant compound that reduces oxidative stress which was evident in the decrease in lipid peroxides formation. This result agrees with Sahin et al.³⁶, who stated that supplementing antioxidants can reduce the formation of lipid peroxides under heat stress conditions in broilers.

Determination of haematological parameters is important in farm animals because they indicate the physiological status of production and reproduction of animals³⁷. This goes in corroboration with Etim et al.³⁸ who said that the adjustments in haematological parameters are normally used to figure out the various status of the body and to determine stresses due to the environmental factor. According to the present study, the red blood cell count of rabbits supplemented with zinc was significantly higher than the control group (0 mg Zn) with T₂ (100 mg Zn) having the highest. This is in agreement with Abdel-Azeem et al.³⁹ and El Hendy et al.⁴⁰who reported that their haematological parameters which included red blood cells were significantly affected by zinc insufficiency in the zinc-sulphate supplemented diet of male rabbits. Similarly, Palmar et al.⁴¹ suggested that decreased red blood cell count reported in rats was either an indication of excessive damage to erythrocytes or inhibition of erythrocyte formation. In humans and animals, red blood cells formation (erythropoiesis) occurs in the bone marrow. The effect of zinc may be said to be due to its binding effect on 43-kDa zinc-binding protein that is present in the digestive tract of tissue and it is used as a signal to stimulate the formation of new red blood cells⁴². Packed cell volume is used as an index for the body’s physiological status. It is also the percentage of red blood cells in the circulating blood. In the present research study, supplementation of zinc oxide significantly improved the packed cell volume of the male rabbits compared to the control group. This agrees with Ogbu and Herbert⁴³ and

Abdel-Azeem et al.³⁹ who also reported a significant increase in the packed cell volume of zinc supplemented diets in the male rabbit. The increase in PCV obtained from the group supplemented with zinc was said to be obvious due to the increased cellular count in the blood that was zinc sufficient. Also, there was a significant increase among treatments in the haemoglobin of rabbit bucks fed zinc oxide. From the results, the increased haemoglobin content which is in corroboration with the El Hendy et al.⁴⁰ may be attributed to the increased rate of production in the rate of formation of erythrocyte as a result of the zinc oxide inclusion. The levels of haemoglobin were affected by zinc intake which is an indication of the sufficiency of oxygen to the body tissues resulting in an enhanced metabolism which may have increased the overall physiology of the rabbits. This result concurs with some authors who experimented on male rabbits and rats and equally reported an increase in haemoglobin after zinc supplementation^39,43,40. The addition of zinc oxide had an ameliorative effect since it minimized the antioxidant stress factors in the semen. The findings of this research work could be applied as a nutritional management practice to reduce stress and increase the growth and reproductive performance of the rabbit, especially in tropical environments where the animals are prone to stress.

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