Effectiveness of exposure to longday followed by melatonin treatment on semen characteristics of...

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Effectiveness of exposure to longday followed by melatonin

treatment on semen characteristics of Damascus male goats

during breeding and non-breeding seasons

T.A. Ramadan, T.A. Taha *, M.A. Samak, A. Hassan

Animal Production Department, Faculty of Agriculture (El-Shatby), Alexandria University, Alexandria 22545, Egypt

Received 17 December 2007; received in revised form 14 July 2008; accepted 26 July 2008

Abstract

Eight mature Damascus male goats were randomly divided into two equal groups. The first group served as control and the

second group was used to study the effect of exposure to longday (16L/8D) followed by melatonin treatment (2 mg/(animal/day)) on

semen characteristics and blood hormonal levels during breeding and non-breeding seasons. During breeding season, longday

exposure followed by melatonin treatments resulted in significant increases (P < 0.01) in means of sperm motility, ejaculate

volume, sperm concentration, total sperm output, total functional sperm fraction and blood testosterone concentration, while means

of reaction time, dead sperm, abnormal sperm and blood triiodothyronine (T3) concentration were significantly decreased

(P < 0.01). During non-breeding season, longday exposure followed by melatonin treatment exhibited improvements in some

reproductive parameters by reducing (P < 0.05) reaction time and percentage of dead sperm (P < 0.01) and increasing (P < 0.05)

total functional sperm fraction. Furthermore, longday exposure followed by melatonin treatment resulted in significant increases

(P < 0.01) in both of blood testosterone and T3 concentrations. It is concluded that longday exposure followed by melatonin

treatment successfully improve semen characteristics of Damascus male goats during breeding and non-breeding seasons. However,

the beneficial effects were more pronounced during the breeding season.

# 2009 Elsevier Inc. All rights reserved.

Keywords: Longday exposure; Melatonin; Semen characteristics; Blood serum hormones; Goats

1. Introduction

In most species, seasonal reproductive activity is

regulated by an endogenous rhythm. This rhythm is

synchronized with the geophysical year by environ-

mental stimuli, the most important of which is

photoperiod. Unlike temperature, availability of food,

rainfall or other environmental cues, photoperiod

provides information about the season and remains

constant from year to year. Photoperiodic stimuli are

transmitted via neuroendocrine pathways into hormonal

signals that regulate gonadal activity. Under subtropical

conditions in Egypt, ram [1], and goat [2], semen

qualities were found to be better during summer months

than during other months of the year. Sexual activity of

subtropical Mexican Creole bucks can be induced

during the non-breeding season by a longday treatment

followed by melatonin implantation [3]. In Mexican

bucks as in other subtropical breeds including

Damascus bucks, the breeding season takes place in

summer and autumn [4]. In these breeds, breeding

season starts during the natural increasing days, but in

controlled photoperiod conditions, longdays were found

to inhibit testosterone secretion in Creole goats [5], and

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Theriogenology 71 (2009) 458–468

* Corresponding author. Tel.: +20 35921960; fax: +20 35922780.

E-mail address: [email protected] (T.A. Taha).

0093-691X/$ – see front matter # 2009 Elsevier Inc. All rights reserved.

doi:10.1016/j.theriogenology.2008.07.029


in Merino and Suffolk rams [6]. In addition, Roca et al.

[7], found that semen quality of Murciano Grandina

goats was highest during summer and fall seasons in

Southern Spain (Mediterranean basin). Recently, the

best semen quality in Damascus bucks was obtained

during increasing photoperiod in spring and summer [8]

In sheep, marked seasonal variations in plasma

thyroid hormone concentrations have been described.

Low and high temperatures, respectively, are stimula-

tory and inhibitory to thyroid activity [9]. Photoperiod

also acts on thyroid activity, as triiodothyronine (T3)

plasma concentration followed the photoperiodic

changes, increasing during long days and decreasing

during short days in Alpine and Saanen male goats [10].

These seasonal cycles of circulating thyroid hormones

have been reported comparatively with testicular

endocrine activity in a broad variety of seasonal

breeders [11]. Plasma testosterone concentrations were

found to be negatively correlated with plasma thyroid

hormone concentrations in goats [12], and sheep [1].

Melatonin (N-acetyl-5-methoxytryptamine) is

synthesized by the pineal gland during the dark phase

of the photoperiod and it is rapidly released to the blood

stream where the highest levels reach nanomolar

concentrations [13]. Melatonin is a signal that conveys

photoperiodic information to synchronize cell physiol-

ogy with the dark–light cycle [13]. In addition, it is a

lipophilic agent that crosses lipid bilayers [14], and acts

as a free radical scavenger, neutralizing hydroxyl and

peroxyl radicals among others, preventing lipid

membrane peroxidation and apoptosis [15], and

protecting the DNA from the damage induced by free

radicals [16]. Moreover, melatonin stimulates gene

expression of antioxidative enzymes including super-

oxide dismutase, glutathione peroxidase, catalase and

glutathione reductase [17]. Studies dealing with the

antioxidative effect of melatonin on spermatozoa have

shown that melatonin significantly reduces the rate of

lipid peroxidation in sperm [18], and it can protect

sperm mitochondria from the damage induced by

reactive oxygen species (ROS) throughout its effective

antioxidative potential [19].

The objectives of the present study were to evaluate

the effect of longday exposure and melatonin treatment

on semen characteristics, and on blood serum con-

centrations of testosterone and T3 of Damascus male

goats during breeding and non-breeding seasons.

2. Materials and methods

The present study was conducted at the Agricultural

Experimental Station (318200N, 308E), Faculty of

Agriculture, Alexandria University, Egypt, on Damas-

cus male goats during the breeding season (from 9 July

to 22 November) and non-breeding season (from 8

January to 27 May).

2.1. Animals and management

Eight Damascus male goats aged 3–4 years and

weighed between 52 and 69 kg were used throughout

the present study. Animals were kept outdoors with

shelter during the daytime and housed in a semi-open

barn at night. They were offered roughage and

concentrate supplement according to their body weight

requirement [20]. Animals were given Egyptian clover

(Trifolium alexandrinum) in winter and spring and

chopped green maize in summer and autumn in addition

to hay. Each animal also received 500 g per day of a

pelleted concentrate mixture that contained 63% total

digestible nutrients (TDN) and 14% crude protein.

Water was offered in access to animals at all times.

Animals were free of any disease and were clinically

normal with a healthy appearance.

2.2. Photoperiod and melatonin treatment

Eight mature Damascus male goats were randomly

divided into two equal groups. The control group

remained in an open barn under natural day length and

ambient temperature throughout the experimental

period. Day length varied from 13 h 29 min during

the breeding season (summer) to 11 h 24 min during the

non-breeding season (winter). Animals from the

experimental groups were maintained at the same

conditions except for 3 months of photoperiodic

treatment (from 9 July, to 25 September) during the

breeding season. About 3.5 months later, the animals

were subjected to other 3 months of photoperiodic

treatment (from 8 January, to 1 April) during non-

breeding season. Photoperiodic treatment was carried

out in a light-proof building where animals were

exposed to longdays (16 h of light/day, lights on at

06:00 h, lights off at 22:00 h). Photoperiod was

regulated by an electric timer and light intensity was

at least 300 lx, positioned laterally to the eyes of the

animals. At the end of photoperiodic treatment, the light

treatment was stopped, and the males were exposed to

the natural day length until the end of the study.

Treatment with melatonin followed the photoperiodic

treatment in both breeding and non-breeding seasons

and was carried out at 18:00 h on the daytime. It

involved the oral administration of 2 mg melatonin

(Sigma Chemical Co., St. Louis, MO, USA) dissolved

T.A. Ramadan et al. / Theriogenology 71 (2009) 458–468 459


in 2 ml 50% ethanol/water (v/v) every day according to

Lincoln and McNeilly [21], during 2 months. The

corresponding control group received an equivalent

dose of the vehicle (50% ethanol/water). The experi-

ment layout is shown in Fig. 1).

2.3. Data collected

The following parameters were measured in all

experimental animals throughout the last 4 weeks of

photoperiodic treatment (prior to melatonin treatment)

and 8 weeks of melatonin administration.

2.3.1. Body weight, relative testes volume and

libido

Live body weight of each animal was recorded

weekly before access to feed and water. Scrotal sac

volume was measured by the water displacement

method described by Evans and Robinson [22], and

was divided by body weight to calculate the relative

testes volume. Sexual behavior of bucks was recorded

weekly by using the reaction time criteria. The time

elapsed between introducing the buck to a female doe at

estrus and semen collection was measured in seconds

using a stop-watch.

2.3.2. Semen evaluation

Semen collection by an artificial vagina was carried

out weekly from all animals throughout the experi-

mental period. The volume of sample was recorded

using a graduated collection tube. Determination of

semen initial fructose was carried out immediately after

collection according to Mann [23]. Ejaculates were

placed in a water bath adjusted to 38 8C. Sperm motility

(%) was subjectively estimated at 400� magnification

using a light microscope equipped with a warm stage.

Sperm concentration was counted by the hemocyt-

ometer method. Total sperm output was calculated by

multiplying semen ejaculate volume and semen con-

centration. The percentages of dead, live and abnormal

spermatozoa were assessed according to Blom [24]. The

total functional sperm fraction (TFSF; X 109) parameter

was calculated as the product of total sperm output by

progressive motility by normal morphology [25,26].

2.4. Blood collection

Blood samples were collected from the jugular vein

of animals every 2 weeks throughout the experimental

period. Blood samples were obtained in the morning

before access to feed and water. Serum was obtained by

centrifugation of samples at 3000 r.p.m for 20 min.

Serum was collected and stored at �20 8C until

analysis.

2.5. Hormonal assays

The concentration of T3 in blood serum samples was

measured using solid-phase enzyme immunoassay kits

obtained from Diatech Diagnostics Inc., Boston, USA.

The lower limit of detection (95% B/B8) was 0.16 ng/ml

serum, and the intra- and inter-assay coefficients of

variation (CV) were 6.4 and 5.1%, respectively based on

the means of low, medium and high quality control

samples measured in 12 assays. The concentration of

testosterone in sera was determined by solid-phase

enzyme immunoassay kits obtained from Bio Source

International, Inc., CA, USA. The lower limit of

detection (95% B/B8) was 0.05 (s.e.0.02) ng/ml serum,

and the intra- and inter-assay CVs were 7.2 and 6.9%,

respectively based on the means of low, medium and

high quality control samples measured in 20 assays.

2.6. Statistical analysis

Data were analyzed using generalized linear model

procedure [27], by two-way (treatments and weeks)

ANOVA. Comparisons among main effects were tested

T.A. Ramadan et al. / Theriogenology 71 (2009) 458–468460

Fig. 1. Experimental layout during breeding and non-breeding seasons.


using LSD.05 of SAS [27]. For the significance

interactions difference between the two treatments

within each week was tested using the LSD.05 for the

interaction.

3. Results

3.1. Effect of longday exposure followed by

melatonin treatment during breeding season

Effects of longday exposure followed by melatonin

treatment on overall mean semen characteristics and

blood hormonal levels of Damascus goats during

breeding season are displayed in Table 1 and their

weekly mean values are presented in Figs. 2 and 3.

Longday exposure followed by melatonin treatment

resulted in significant increases in sperm motility,

ejaculate volume, sperm concentration, total sperm

output, total functional sperm fraction and blood

testosterone (P < 0.01), and significant decreases in

reaction time, dead sperm, abnormal sperm and blood

T3 (P < 0.01). Relative testes volume and semen initial

fructose were not significantly affected.

3.2. Effect of longday exposure followed by

melatonin treatment during non-breeding season

Effects of longday exposure followed by melatonin

treatment on overall mean semen characteristics and

blood hormonal levels in Damascus goats during non-

breeding season are displayed in Table 1 and their

weekly mean values are presented in Figs. 4 and 5.

During non-breeding season, longday exposure fol-

lowed by melatonin treatment failed to exert any

significant effect on all semen characteristics except for

means of reaction time and dead sperm which were

significantly (P < 0.05 and P < 0.01) reduced and for

mean of total functional sperm fraction which was

significantly (P < 0.05) increased. Regarding hormonal

responses, blood testosterone and T3 concentrations

were significantly (P < 0.01) increased.

4. Discussion

4.1. Effect of longday exposure and melatonin

treatment during breeding season

Day length is the most important environmental

factor in determining the breeding season in small

ruminants within temperate latitudes [28]. The best

semen quality in Damascus bucks (at latitude 318N) was

obtained during increasing photoperiod in spring and

summer in Egypt [2], and in Jordan [8]. This trend

coincided with the results of the present study which

indicated that longday exposure followed by melatonin

treatment of male Damascus goats during breeding

season exerted significant improvements in semen

characteristics and testosterone concentration. How-

ever, relative tests volume and semen initial fructose

were not significantly affected (Table 1 and Figs. 2 and

3. It is of interest to note that control and treated groups

differed from the beginning of the study during the

breeding season; where treated bucks recorded ‘‘higher

values’’ of ejaculate volume and sperm motility and


Table 1

Changes in semen characteristics and blood hormones of Damascus male goats after exposure to longday followed by melatonin treatment

(LD + melatonin) during breeding and non-breeding seasons (means � S.E.)

Parameters Breeding season Non-breeding season

Control DL + melatonin Control DL + melatonin

Semen parameters

Relative testes volume (cm3/kg BW) 9.82 � 0.49 10.62 � 0.40 8.74 � 0.35 9.59 � 0.49

Reaction time (s) 23.69 � 2.04a 10.10 � 0.88b 26.25 � 2.56a 19.89 � 2.80b

Sperm motility (%) 55.94 � 2.06b 65.42 � 1.95a 57.05 � 1.78 58.41 � 2.45

Ejaculate volume (ml) 0.99 � 0.04b 1.26 � 0.07a 0.74 � 0.05 0.79 � 0.07

Sperm concentration (�109 ml�1) 0.97 � 0.06b 1.27 � 0.08a 0.88 � 0.02 0.93 � 0.04

Total sperm output (�109 per ejaculate) 1.02 � 0.08b 1.78 � 0.17a 0.67 � 0.05 0.82 � 0.09

Dead sperm (%) 41.69 � 2.19a 29.46 � 1.92b 33.51 � 1.13a 24.25 � 1.09b

Abnormal sperm (%) 17.37 � 0.51a 13.40 � 0.58b 15.51 � 0.62 13.62 � 1.14

Total functional sperm fraction (�109) 0.51 � 0.05b 1.19 � 0.15a 0.35 � 0.03b 0.51 � 0.08a

Semen initial fructose (mg/ml) 1.64 � 0.04 1.69 � 0.04 1.20 � 0.09 1.30 � 0.07

Blood hormones

Testosterone (ng/ml) 12.84 � 1.58b 20.01 � 1.94a 13.22 � 1.33b 17.97 � 2.59a

Triiodothyronine (ng/ml) 1.38 � 0.06a 1.09 � 0.05b 1.65 � 0.07b 2.12 � 0.10a

a,bWithin rows, within seasons, means with different superscript letters differ significantly (P < 0.05).


‘‘lower values’’ of reaction time and dead sperm. Indeed

these differences are mainly due to exposure of males to

longdays.

Longday exposure followed by melatonin treatment

during the breeding season of Damascus goats

showed opposite effects on serum concentrations of

testosterone and triiodothyronine; testosterone concen-

tration increased while triiodothyronine concentration

decreased (Table 1). This response of testosterone and

triiodothyronine in male Damascus goats has been

reported previously to coincide with the high semen

quality during summer (long photoperiod) [2]. In

addition, plasma testosterone concentrations were found

to be negatively correlated to plasma thyroid hormone

concentrations in goats [12]. Webster et al. [9], reported

that thyroid hormones play a key role in the expression of

the seasonal reproductive cycles in ewes, because they

increase responsiveness to estradiol negative feedback

that causes termination of the breeding season. Further-

more, the breeding season of ewes can either be extended


Fig. 2. Changes in relative testes volume (RTV), reaction time (RT), sperm motility (Sp. Mot.), ejaculate volume (E. Vol.), sperm concentration (Sp.

Conc.) and total sperm output (T. Sp. O.) during treatment of Damascus male goats with longday followed by melatonin during breeding season

[control (natural photoperiod) (*), longday (16L/8D) (~), melatonin (natural photoperiod) (*)]. *Significantly different from control in the same

time point (P < 0.05).


by lowering thyroxine secretion [29] or terminated

prematurely by injecting large doses of thryoxine [30].

These findings could be extrapolated to those of the

present study since the low T3 levels were associated with

the long photoperiod and with higher values of serum

testosterone level and better semen parameters.

In contrast, Todini et al. [10], found that T3 plasma

concentrations in Alpine and Saanen male goats follow

the photoperiodic changes, increasing during long days

and decreasing during short days. It is of interest to note

that their experiment was carried out in France (468Nlatitude), while the present experiment was carried out

at Alexandria, Egypt (318200 latitude). In addition, the

Damascus male goat is a long day reproductive breed in

latitudes near 308N [2,8]. Other breeds (Alpine and

Saanen) are short day reproductive breeds [31]. These

authors carried out their experiment in Greece

(408370N) and at this latitude, Damascus male goat

(in contrast to our results) behaved as a short day

reproductive breed.


Fig. 3. Changes in dead sperm (D. Sp.), abnormal sperm (Ab. Sp.), total functional sperm fraction (TFSF), semen initial fructose (IF) and blood

serum concentrations of testosterone and triiodothyronine (T3) during treatment of Damascus male goats with longday followed by melatonin during

breeding season [control (natural photoperiod) (*), longday (16L/8D) (~), melatonin (natural photoperiod) (*)]. *Significantly different from

control in the same time point (P < 0.05).


4.2. Effect of longday exposure and melatonin

treatment during non-breeding season

Previous studies indicated that melatonin adminis-

tration to goats during breeding season significantly

improved testes volume, ejaculate volume and sperm

concentration but sperm motility and abnormal sperm

were not affected [32]. Similar studies conducted on

ram by Hanif and Williams [33], indicated that

melatonin administration increased sperm motility, live

sperm, sperm concentration and decreased abnormal

sperm, but relative testes volume was not affected. Such

findings are similar to our results.

Langford et al. [34], reported that melatonin

stimulates spermatogenic activity of ram testes by

increasing the sensitivity of Leydig cells to luteinizing

hormone. The increase in the mean values of

testosterone in blood of rams after administration of

melatonin has also been attributed to the effect of

melatonin on the hypothalamus or hypophysis [35],


Fig. 4. Changes in relative testes volume (RTV), reaction time (RT), sperm motility (Sp. Mot.), ejaculate volume (E. Vol.), sperm concentration (Sp.

Conc.) and total sperm output (T. Sp. O.) during treatment of Damascus male goats with longday followed by melatonin during non-breeding season

[control (natural photoperiod) (*), longday (16L/8D) (~), melatonin (natural photoperiod) (*)]. *Significantly different from control in the same

time point (P < 0.05).


with the increase in both cases of the secretion of

luteinizing hormone. Receptors for melatonin are

located near the hypothalamus and adenohypophsis

[35], and have been found in Leydig cells indicating that

melatonin might also have a direct effect on the testes

[36]. Additionally, the effect of melatonin on sperm

quality might be direct, since there are melatonin-

binding sites in spermatozoa [37].

On the other hand, the antioxidant property of

melatonin has been demonstrated in vivo and in vitro

studies [38]. The total antioxidant capacity of blood

serum is closely related to melatonin levels, and a

reduction in melatonin level might indicate increasing

oxidative damage [39]. The plasma membranes of the

spermatozoa contain unsaturated fatty acids which are

highly sensitive to lipid peroxidaion leading to

membrane damage, particularly in the acrosomal

region, and consequently causing losses of motility

and viability [40,41]. Thus, in regard to studies dealing

with the antioxidative effect of melatonin on sperma-

tozoa, it has been reported that melatonin significantly

reduces the rate of lipid peroxidation in sperm [18], and


Fig. 5. Changes in dead sperm (D. Sp.), abnormal sperm (Ab. Sp.), total functional sperm fraction (TFSF), semen initial fructose (IF) and blood

serum concentrations of testosterone and triiodothyronine (T3) during treatment of Damascus male goats with longday followed by melatonin during

non-breeding season [control (natural photoperiod) (~), longday (16L/8D) (*), melatonin (natural photoperiod) (*)]. *Significantly different

from control in the same time point (P < 0.05).


it can protect sperm mitochondria from the damage

induced by reactive oxygen species (ROS) throughout

its effective antioxidative potential [19]. Furthermore,

melatonin implantation has been reported to improve

freezability of ram semen due to its antioxidant property

and protective effect against oxidative damage [42].

The beneficial effect of photoperiodic treatment

and melatonin administration on semen characteristics

during non-breeding season was not as obvious as it

was in the breeding season. This treatment exhibited

its improvement in semen characteristics as significant

decreases in reaction time and in the percentage of

dead sperm and significant increases in TFSF, while

other semen characteristics were not affected (Table 1

and Figs. 4 and 5). In agreement with the present

results, Rosa et al. [43], reported that melatonin

administration improved ram’s libido during non-

breeding season. However, previous studies dealing

with melatonin administration during non-breeding

season in goat and sheep yielded inconsistent results

where it ranged between no response to slight

improvement in some semen characteristics. Discre-

pancies between breeding and non-breeding seasons

in improving semen quality by melatonin treatment

could be explained on the basis of seasonal profile of

melatonin. Sheikheldin et al. [44], reported that

melatonin concentrations during summer and autumn

(breeding season) were significantly higher than those

in winter and spring (non-breeding season). Thus,

melatonin treatment during breeding season, where

the endogenous melatonin reached the maximum

level, represent an additive effect resulting in superior

improvement in semen quality compared to that of

non-breeding season where the endogenous melatonin

recorded the lowest level.

The percentages of dead sperm were ‘‘lower’’ in the

treated animals due to the beneficial effects of ‘‘longday

and/or melatonin’’ treatments. This was observed

during both breeding and non-breeding seasons

(Figs. 3 and 5). However, the percentages of dead

sperm were lower in non-breeding season than in

breeding season in both treated and control bucks. This

could be explained by the fact that after long sexual

arrest (during the non-breeding season), low semen

quality was noted at the beginning of breeding season,

hence it improved as ‘‘breeding season’’ advanced.

Thus, higher percentages of dead sperm were observed

at the beginning of the breeding season in both treated

and control bucks, but it tented to decrease sharply

throughout the breeding season (Fig. 3). On the other

hand, the percentages of dead sperm were lower at the

beginning of the non-breeding season in both control

and treated bucks than those of breeding season.

However, it failed to improve throughout the non-

breeding season in the control group, while dead sperm

decreased in the treated bucks as the season advanced

(Fig. 5).

Melatonin administration during non-breeding sea-

son also resulted in increases in serum concentrations of

testosterone and T3 hormones (Table 1). This finding

agrees with those reported in goats [3], and in sheep

[43]. The increase in mean values of blood testosterone

after administration of melatonin has been attributed to

the effect of melatonin on the hypothalamus or

hypophysis [35], which increases the secretion of

luteinizing hormone in both cases.

Naturally, seasonal variations in serum concentration

of T3 showed an increase in its level during winter and

spring (non-breeding time) in Damascus male goats [2].

As shown in the present study, melatonin treatment

caused a significant increase (P < 0.01) in T3 con-

centration (2.12 ng/ml) than that of control group

(1.65 ng/ml) (Table 1). It is known that thyroid

hormones accelerate the basal metabolic rate [45],

and may increase free radicals production and lipid

peroxide level [46]. Melatonin stimulates the activities

of some enzymes that metabolize reactive species and

also alters cell membrane fluidity, thereby reducing the

ability of damaging species to attack polyunsaturated

fatty acids in this structure [47]. The present study

suggests a protective role of melatonin in maintaining

normal sperm parameters, shown as significant reduc-

tions in reaction time and in the percentage of dead

sperm and significant increase in TFSF. However, the

melatonin-induced increase (P < 0.05) in T3 concen-

tration during non-breeding season did not reduce

sperm quality parameters due to the antioxidative effect

of melatonin on free radicals and on spermatozoal

membranes during that time.

5. Conclusions

The present study indicated that photoperiodic

treatment followed by melatonin administration

improved semen quality in Damascus male goats

during both of breeding and non-breading seasons.

However, this improvement was more pronounced

during breeding season compared with non-breeding

season and was suggested to be due to the antioxidative

effect of melatonin on spermatozoa. The divergent

responses of improvement of semen quality between

breeding and non-breeding seasons suggest that

Damascus goats are influenced by several environ-

mental factors in addition to photoperiod.



Acknowledgements

This research was partially funded by a research

grant awarded by the British Council, Egypt. The

authors wish to thank Dr. Mamdouh El-Rouby, Prof. of

Statistics, Faculty of Agriculture, Alexandria University

for his advice on the statistical analysis of data.

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