Livestock Research for Rural Development 21 (10) 2009 Guide for preparation of papers LRRD News

Citation of this paper

Reproductive and physiological traits of Egyptian Suffolk rams as affected by selenium dietary supplementation during the sub-tropical environment of Egypt

I F M Marai, A A El-Darawany, E I Abou-Fandoud* and M A M Abdel-Hafez*

Department of Animal Production, Faculty of Agriculture, Zagazig University, Zagazig, Egypt
* Department of Sheep and Goats, Institute of Animal Research, Ministry of Agriculture, Dokki, Egypt
profmarai@yahoo.co.uk

Abstract

A project of study was planned to investigate the reproductive traits of ewes and rams as affected by adverse conditions, under the sub-tropical winter and summer conditions of Egypt.

 

The estimated THI (Temperature-Humidity Index )values indicated absence of  heat stress during winter and exposure of the rams to very severe heat stress during summer. Exposure to heat stress (i.e. increase in perception of warmth during the hot climate) conditions was accompanied with significant  (P<0.01 or 0.05) increase in rectal, skin and scrotal-skin temperatures, reaction time, dead spermatozoa, sperm abnormality, acrosomal damage, scrotal length and plasma creatinine and cortisol levels, and significant (P<0.01 or 0.05) decrease  in sperm motility, sperm cell concentration, scrotal circumference, testes length, serum albumin, alkaline phosphatase, lactate dehydogenase,  SGOT and T3 hormone levels. Meanwhile, dietary supplementation of the same rams with selenium was accompanied with significant (P<0.01 or 0.05) decrease in rectal temperature, reaction time, semen pH, percentages of dead spermatozoa, sperm abnormalities and acrosomal damage and serum creatinine, and significant (P<0.01 or 0.05) increase in sperm motility, sperm-cell concentration, scrotal circumference, scrotal length and testes length. The interactions of season of the year with selenium treatment were significant (P<0.01 or 0.05) on sperm abnormalities, scrotal circumference, scrotal length, testes length and serum  SGOT (Serum GlutamoOxaloacetate Transferase) and SGPT (Serum GlutamoPyruvate Transferase) levels.

 

Selenium supplementation during winter showed the highest (P<0.05) values in scrotal circumference and testes length, and the lowest  (P<0.05) values in sperm abnormality and serum SGPT. The highest  (P<0.05) sperm abnormality and serum SGOT and the lowest scrotal length and testes length were shown without supplementation during summer.

Keywords: heat stress, physiological reactions, reproductive traits, selenium treatment


Introduction

Recently, it happened in a Statal farm that the conception rate reached 19% in a flock of Egyptian Suffolk (1/16 Ossimi.15/16 U.K. Suffolk of which the crossbreeding programme was begun in the year 1957, then inter se mating was carried out). In addition to that, it happened that the sheep which were kept in the sheds, suffered from selenium deficiency more than once, although the animals were fed on NRC (1985) requirements.

The common breeding season of sheep in Egypt is during May. The hot climate in Egypt fluctuates in March-April, becomes stable at May till September-October and fluctuates in November, each year. 

Under such conditions, a debate has arisen regarding the extent to which sheep can suffer from such adverse conditions, under the sub-tropical conditions of Egypt.

 

In this respect, a project of study was planned to investigate the reproductive traits of ewes and rams as affected by such unfavourable conditions and the methods of its alleviation.

Most of the results of the planned project of research concerned with the effects of the hot climate conditions on traits of ewes (Marai et al 2004, 2006a,c, 2009), were published. However, most of the results on rams are not published, yet. 

 

The objectives of the present investigation were to study the reproductive and physiological traits of Egyptian Suffolk rams as affected by the use of selenium dietary supplementation under winter and summer conditions of  Egypt.

 

Material and methods 

The present study was conducted in the Department of Animal Production, Faculty of Agriculture, Zagazig University, Zagazig, Egypt. The experimental work was carried out at El-Gemmaiza Experimental Station located in mid Nile Delta (30.5N) and the laboratory work was conducted in the Department of Sheep and Goats Research, both belonging to Animal Production Research Institute, Ministry of Agriculture, Egypt. The present study was a part of a project of study on the reproductive traits of sheep as affected by the unfavourable sub-tropical conditions of  Egypt.

 

A total number of 18 Egyptian Suffolk rams  was used: 8 during  December- February as winter season and 10 during May-July as summer season. Within each season, the animals were divided into  two groups of nearly equal average body weights. The first group was kept without treatment as control and the second was treated with selenium (0.1 ppm/kg DM as sodium salenate) orally. The animals  were of 1.5-2.5 years of age and 60-70 kg body weight in the two seasons and all were healthy and clinically free of external and internal parasites and were kept, maintained and treated in adherence to accepted standards for the humane treatment of animals.

 

The animals were offered their requirements according to NRC (1985). Additional diet was offered to  rams,  15   days   before and   after  beginning of the breeding season (35 days). The additional diet was composed of 1.0 kg concentrates, 0.25 kg barely and rice straw ad lib. Each kilogram of the concentrate contained: 450 g yellow maize, 350 g decorticated cottonseed meal, 150 g wheat bran, 3 g mollases, 1 g calcium carbonate and 1 g salt. The quantity of selenium determined in the experimental diet was 0.09 ppm/kg DM which was nearly similar to the requirements for sheep according to NRC (1985). Proximate analysis of the concentrates and roughages (Table 1) were carried out according to AOAC (1980).


Table 1.  Chemical analyses of the diets used in experimental trails

Items

DM, %

CP, %

CF, %

EE, %

NFE, %

OM, %

Ash, %

Sel., %

Car. %

Concentrates

90.46

18.50

13.46

4.85

53.69

90.50

9.50

0.095

1.46

Barley

90.00

7.78

10.00

2.23

76.56

96.57

5.34

0.097

2.00

Rice straw

92.30

3.47

35.10

1.41

39.65

79.63

20.37

0.084

2.00

Sel. = Selenium and Car.= Carotene


The animals had access to water daily four times in summer at 9.00, 12.00, 15.00 and 18.00 h and three times in winter at 9.00, 13.00 and 18.00 h.

 

The rams were housed in soil floored, partially wood roofed semi-open sheds during the experimental periods. The partitions of the rams were 3 x 8 metres. The surface area of each shed was surrounded by brick walls of  2 metres height.

 

Semen ejaculates were collected weekly during the experimental periods, by means of artificial vagina. The temperature of the inner liner rubber sleeve of the artificial vagina was adjusted to be 41-43oC at the time of collection. At each collection time, sterile inner liner and graduated collecting tube, were used. Two ejaculates were collected each time per ram, evaluated and the average of the two ejaculates was included in the data analysed. Similarly, libido (reaction time), pH, semen ejaculate volume, percentages of sperm motility, dead spermatozoa, sperm abnormalities and acrosomal damage, were measured at time of semen collection. Reaction time was assessed according to Chenoweth (1981). Each ewe was transferred to the buck found alone in a shed, then the ewe was returned  to its shed after copulation. Hydrogen ion concentration was tested with pH paper. Semen ejaculate volume was measured directly in millilitres to the nearest 0.1 ml in a transparent graduated glass tube. Mass motility percentage was assessed in a drop of fresh semen examined under low power microscope, using a hot stage adjusted at 37C. Mass motility was estimated as percentage score according to the procedure outlined by Melorse and Laing (1970). Live and dead sperm percentages were examined immediately after semen collection according to the method of Hancock (1951). For determination of percentage of abnormal spermatozoa, the slides of live sperm were used. Live and abnormal spermatozoa percentages were counted using hand counter. Acrosomal abnormalities were determined by using smears made from the raw semen and stained by Giemsa stain according to Watson (1975). Two hundred spermatozoa were examined for each sample. Sperm-cell concentration (x109/ml) was determined by using Spectrophotometer (Spectronic 20 machine, U.S.A. of set wave length at 550 millimicrons. A spectronic 20 tube containing 7.9 ml of 2.9 % sodium citrate solution was inserted into machine and adjusted to read 100 % transmittance, then removed and 0.1 ml semen was added to the tube by using serological pipette. The tube (containing 7-9 ml of 2.9 % sodium citrate and 0.1 ml semen) was inserted into Spectrionc 20 machine and the percentage of transmittance after 10 seconds was recorded.

 

Physiological measurements in rams (rectal, skin and scrotal-skin temperatures and scrotal measurements (scrotal circumference, abdominal scrotal tip distance and testes length) were estimated at 12.00 h in the same day of semen collection once every week, during the experimental periods. Rectal temperature was measured to the nearest 0.1C by inserting electronic telethermometer 13-166-11 Probe (designed for measuring rectal temperature) to the depth of 5-6 cm into the rectum. The skin and scrotal-skin temperatures were measured using 15–176–324 Probe which was of 30 mm long with a plate of 10 mm in diameter to be put between skin folds. Scrotal measurements such as testes length, scrotum circumference and scrotal length (distance between abdominal margin and scrotal tip), were measured with a flexible metal tape.

 

Blood samples (5 ml) were collected from the jugular vein at 12.00 h on the day at which the other measurements were estimated from 3 animals chosen randomly from  each group of rams. Each sample was divided  into  two 10cc evacuated glass tubes, one of which contained heparin as anticoagulant. The un-heparinized blood samples were refrigerated for 30 min and were allowed to clot. Then all the tubes were centrifuged at 3000 rounds/min for 15 minutes and the plasma (of heparinized samples)  and serum (of un-heparinized  samples) were stored at -10C until analyzed (within one week). Serum total proteins, albumin and creatinine concentrations were estimated by the colorimetric method using commercial kits (Diamond Diagnostic, Egypt). Globulin was estimated by subtraction of albumin from total proteins. Glucose was determined by using glucose oxidase method by Hugget  and Nixon (1957). Alkaline phosphatase (ALP) was detected kinetically and Lactate dehydrogenase (LDH) was measured using kits of Bio-Analytics (Stanbio Laboratory Inc., San Antonio, Texas, USA). SGPT and  SGOT enzyme activities were assayed using commercial kits of Diamond Diagnostics, Egypt. Plasma total testosterone, estradiol and triidothyroxine concentrations were estimated by the method of Jaff and Behrman (1974)  using coat-A-count I125 Radio-immunoassay (RIA) kits purchased from Diagnostic Products Corporation, Los Angeles, California, 90045, USA. Cortisol hormone was assayed using RIA technique by cortisol antibody coated tubes kit according to Henricks et al (1984).  Estimations of chemical analyses (Inorganic phosphorus and zinc) were carried out using spectrophotometer computer system (8500 Ultra violet-Visible Techcomp).

 

Ambient air temperature and relative humidity (RH%) were recorded within the shed at the times of carrying out the physiological and scrotal measurements and semen collection. Ambient air temperature was recorded using Mercury thermometer to the nearest 0.1C. Maximum and minimum temperatures were recorded using thermometer. Relative humidity was recorded using hair-hygrometer to the nearest 1%. The averages of ambient temperatures and relative humidity values estimated in the present study were 14.5oC and 79.5% and 28.2 oC  and 61.4% during winter and summer, respectively.

 

THI was estimated according to the following equation (Marai et al 2000):

            THI = dbC - {(0.31 - 0.31 RH) (dbC - 14.4)},


where:

dbC = dry bulb temperature in Celsius and
RH = RH % / 100.

 

Then the obtained values of THI were classified as follows: <22.2 = absence of heat stress, 22.2 - < 23.3 = moderate heat stress, 23.3 - <25.6 = severe heat stress and 25.6 and more = very severe heat stress (Marai et al 2000).

 

Statistically, the model used to study effects of season and treatment and their interactions on semen traits, physiological parameters, scrotal measurements and blood components in rams, was as follows:

yijk = + si + tj + stk + eijk,

where:

= overall mean,
si = effect due season (i = 1 and 2),
tj = fixed effect of jth treatment (j = l and 2),
stk = interaction between season and treatment and
eijk = unexplained variation assumed to be randomly and independently distributed.

 

The statistical analysis was computed using analysis of variance procedure described in SAS (1995).

 

Results 

Temperature-Humidity Index

 

The estimated THI values were 14.5 during winter and 25.6 in summer, indicating absence of  heat stress during winter and exposure of the rams to very severe heat stress during summer.

 

Effects of heat stress

 

The heat stress conditions affected adversely  many of the studied traits. Such conditions caused significant (P<0.01 or 0.05) increase in rectal, skin and scrotal-skin temperatures, reaction time, dead spermatozoa, sperm abnormality, acrosomal damage, scrotal length and plasma creatinine and cortisol levels. At the same time, a significant (P<0.01 or 0.05) decrease occurred in each of sperm motility, sperm cell concentration, scrotal circumference, testes length, serum albumin, alkaline phosphatase, lactate dehydogenase,  SGOT and T3 hormone levels (Tables 2 and 3).


Table 2.  Least square means (S.E) of physiological parameters, libido, semen characteristics and scrotal measurements in Egyptian Suffolk rams, as affected by season of the year (Winter and summer) and treatment  (Selenium)

 Variables

Seasons

 

Sign.

Selenium

 

Sign.

Winter

No 8

Summer

No 10

Without

Suppl. No 9

With Suppl.

No 9

Physiological parameters

 

 

 

 

 

Rectal temperature, C

38.7 0.09

39.8 0.09

**

39.4  0.09

39.1 0.09

*

Skin temperature, C

36.7   0.11

38.3 0.11

**

37.6 0.11

37.4 0.11

NS

Scrotal-skin temperature, C

28.2   0.34

32.5 0.34

**

30.5 0.34

30.2 0.34

NS

Libido and semen characteristics

 

 

 

 

 

Reaction time (Libido; seconds)

11.1 0.55

20.5 0.55

**

16.9 0.55

14.8 0.55

**

pH

6.81 0.02

6.85 0.02

NS

6.86   0.02

6.80 0.02

*

Ejaculate volume, ml

0.96 0.05

1.03   0.05

NS

0.94 0.05

1.05 0.05

NS

Sperm motility, %

75.6 1.21

69.3 1.21

**

70.1 1.21

74.8   1.21

**

Dead spermatozoa, %

15.1 0.82

23.9 0.82

**

21.8 0.82

17.2 0.82

**

Sperm abnormality, %

11.3 0.71

18.8 0.71

**

16.8  0.70

13.3 0.70

**

Acrosomal damage, %

7.85   0.62

15.0 0.62

**

12.8 0.70

10.0 0.70

**

Sperm cell concentration, x109/ml

1.69   0.16

0.99 0.16

**

1.06 0.16

1.62   0.16

*

Scrotal measurements

 

 

 

 

 

 

Scrotal circumference, cm

32.7 0.67

22.8 0.67

**

26.8 0.67

28.7 0.67

*

Scrotal length, cm

12.8 0.29

13.8 0.29

*

11.8 0.29

14.5 0.29

*

Testes length, cm

12.6 0.25

11.2 0.25

**

11.5 0.25

12.3 0.25

**

No = Number of animals, **P<0.01, *P<0.05, NS = Not significant and Sign.= Significance.



Table 3.  Least square means (S.E) of blood components in Egyptian Suffolk rams as affected by season of the year (Winter and Summer) and treatment (Selenium)

Variables

Season

Sign

Selenium

Sign

Winter

No 8

Summer

No 10

Without Suppl.  No 9

With Suppl. No 9

Total proteins, g/dl

21.5 2.08

22.8 2.08

NS

22.22.08

22.2 2.08

NS

Albumin, g/dl

4.53   0.27

3.56  0.27

*

7.450.52

7.71 0.52

NS

Globulin, g/dl

3.71 0.26

3.35 0.26

NS

3.470.26

3.59 0.26

NS

Glucose, mg/dl

11.3 1.60

8.59 1.60

NS

8.711.60

11.2 1.60

NS

Alkaline phosphatase, u/L

131469.9

572 9.87

**

99469.9

89269.9

NS

Lactate dehydrogenase, u/l

752 62.0

358 62.0

**

503 62.0

607 62.0

NS

SGOT, u/L

92.2   3.95

82.8   3.95

**

87.0 3.95

88.0 3.95

NS

SGPT, u/L

21.5 2.08

22.8 3.95

NS

22.2 2.08

22.2 2.08

NS

Creatinine, mg/L

19.0 0.96

25.5 .96

**

23.9 0.96

20.6  0.96

*

Inorganic phosphorus, ng/dl

9.34   2.08

3.64 2.08

NS

6.59 2.08

6.39 2.08

NS

Zinc, ug/dl

35535.3

29135.3

NS

30835.3

338 35.3

NS

Testosterone, ng/ml

6.77 1.63

3.27 1.63

NS

3.90 1.63

6.15 1.63

NS

Estradiol, pg/ml

19.3 3.56

12.7 3.56

NS

14.4 3.57

17.6 3.57

NS

T3, ng/dl

94.2 10.48

39.0 10.5

**

61.410.48

71.4 10.5

NS

Cortisol, g/100 ml

0.95    0.89

4.47 0.89

*

2.83 0.89

2.59 0.89

NS

No = Number of animals, *P<0.05,  NS = Not significant.and Sign. = Significance.

Means bearing different letter within the same raw, differ significantly (P<0.05)


Effects of selenium treatment

 

Dietary supplementation of the same rams with selenium was accompanied with significant decrease (P<0.01 or 0.05) in rectal temperature, reaction time, semen pH, percentages of dead spermatozoa, sperm abnormalities and acrosomal damage and serum creatinine. The traits that increased significanly (P<0.01 or 0.05) with selenium supplementation were sperm motility, sperm-cell concentration, scrotal circumference, scrotal length and testes length (Tables 2 and 3).

 

Effect of interactions

 

The effects of interactions of season of the year with selenium treatment were significant (P<0.01 or 0.05) on sperm abnormalities, scrotal circumference, scrotal length, testes length and serum  SGOT and SGPT. Selenium supplementation during winter showed the highest (P<0.05) values in scrotal circumference and testes length, and the lowest  (P<0.05) values in sperm abnormality and serum SGPT. The highest  (P<0.05) sperm abnormality and serum SGOT and the lowest scrotal length and testes length were shown without supplementation during summer (Tables 4 and 5).


Table 4.  Least square means (S.E) of physiological parameters, libido, semen characteristics and scrotal measurements in Egyptian Suffolk rams as affected by interaction between season of the year (Winter and Summer) and treatment (Selenium)

Variables

Winter

Summer

Sign.

Winter
No 8

Summer
No 10

Without Suppl. No 9

With Suppl.

No 9

Physiological parameters

 

 

 

 

Rectal temperature, C

38.8 0.12

38.6 0.12

40.0 0.12

39.6 0.12

NS

Skin temperature, C

36.7 0.15

36.7 0.15

38.5 0.15

38.2 0.15

NS

Scrotal-skin temperature, C

28.2 0.49

28.2 0.49

32.8 0.49

32.2 0.49

NS

Libido and semen characteristics

 

 

 

 

Reaction time (Libido, seconds)

12.6 0.78

9.58 0.78

21.1 0.78

20.0 0.78

NS

pH

6.82 0.03

6.80 0.03

6.91 0.03

6.79 0.03

NS

Ejaculate volume, ml

0.93 0.07

1.00 0.07

0.95 0.07

1.11 0.07

NS

Sperm motility, %

72.3 1.71

79.0 1.72

67.9 1.72

70.6 1.72

NS

Dead spermatozoa, %

18.4 1.17

11.7 1.17

25.2 1.17

22.6 1.17

NS

Sperm abnormality, %

14.0 b 1.00

8.58 c 1.00

19.5 a 1.00

18.8a 1.00

*

Acrosomal damage, , %

10.1 0.89

5.63 0.89

15.5 0.89

14.4 0.89

NS

 

Sperm cell concentration, x109/ml

1.26 0:23

2.110.23

0.86 0.23

1.12 0.23

NS

 

Scrotal measurements

 

 

 

 

 

 

Scrotal circumference, cm

30.3 b 0.95

35.2a 0.95

23.3c 0.95

22.2c 0.95

**

 

Scrotal length, cm

12.3 b 0.35

13.3a 0.35

11.3b 0.41

16.3a 0.41

**

 

Testes length, cm

12.3 b 0.35

13.3a 0.35

11.1b 0.35

11.3b 0.35

**

 

Suppl. = Supplemented with selenium., No = Number of animals,
 Sign. = Significance., **P<0.01, *P<0.05 and NS = Not significant.

Means bearing different letter within the same raw, differ significantly (P<0.05)



Table 5.  Least square means (S.E) of blood components in Egyptian Suffolk rams as affected by the interaction between season of the year (Winter and Summer) and treatment (Selenium)

Variables

Winter

Summer

 Sign

Suppl.-free diet No 4

Suppl.  diet No 4

Suppl.-free diet No 5

Suppl. Diet No 5

Total proteins, g/dl

8.65 0.74

7.83 0.74

6.25 0.74

7.59 0.74

NS

Albumin, g/dl

4.80 0.38

4.26 0.38

3.15 0.38

3.97 0.38

NS

Globulin, g/dl

3.85 0.37

3.57 0.37

3.10 0.37

3.62 0.37

NS

Glucose, mg/dl

10.3 2.26

12.3 2.26

7.12 2.26

10.1 2.26

NS

Alkaline phosphatase, u/L

129698.8

1332 98.8

691 98.82

45298.8

NS

Lactate dehydrogenase, u/l

688 87.73

81687.7

319 87.73

39887.73

NS

SGOT, u/L

75.3b 5.56

85.7ab 5.59

98.7 a 5.59

90.3ab 5.59

*

SGPT, u/L

25.7 ab 2.94

17.3 b 2.94

18.7 b 2.9

27.0 a 2.94

*

Createnine, mg/L

20.1 1.36

17.9 1.36

27.7 1.36

23.2 1.36

NS

Inorganic phosphorus, ng/dl

9.59 2.94

9.09 2.94

3.59 2.94

3.68 2.94

NS

Zinc, ug/dl

334 49.95

377 49.95

282 49.5

300 95.0

NS

Testosterone, ng/ml

4.37 2.30

8.82 2.30

3.07 2.30

4.47 2.30

NS

Estradiol, pg/ml

16.8 5.04

21.9 5.04

12.1 5.04

13.3 5.04

NS

T3, ng/dl

94.8 14.82

93.5 14.82

27.9 14.82

50.1 14.6

NS

Cortisol, g/100 ml

1.42 1.26

0.47 1.26

4.23 1.26

4.70 1.26

NS

No = Number of animals, Suppl.= Supplemented with selenium.,
Sign. = Significance., *P<0.05 and NS = Not significant.

Means bearing different letters within the same raw, differ significantly (P<0.05).


Discussion 

Effecst of heat stress

 

The results on rectal and skin temperatures increase with exposure to heat stress were in agreement with those obtained by Johnson (1987), Marai et al (1997) and El-Darawany (1999b) and those on scrotal-skin temperature agreed with that obtained by Curtis (1983) and El-Darawany et al (1999b). Exposure of rams to elevated temperature stimulates directly the peripheral thermal receptors which transmit nervous impulses that stimulate the central receptors of the hypothalamus to thermal polyponea to increase heat loss (Kamal 1975), in order to balance the excessive heat load by different means. Animals loose heat by evaporation of water from skin surface and respiratory tract (Curtis 1983), but peripheral vasodilatations, sweating and panting, are the major evaporative pathways of sheep, under heat stress conditions (Marai et al 2007). However, evaporation by panting (high respiration evaporation) becomes the most important avenue for heat dissipation, since sweating in sheep is much less important due to the presence of the wool coat. When environmental temperature rises to 36C, the ears and legs of sheep dissipate a high proportion of sensible heat, since they contribute to about 32 % of the body surface area. With more exposure to heat stress, the animals develop certain mechanisms to produce less heat (Johnson 1987). Rectal temperature rises if heat production exceeds heat dissipation due to failure in proper response of the peripheral receptors, hypothalamus, nurohumora, nervous system, endocrine glands or enzymes (Kamal 1975). Regulating scrotal-skin temperature of ram exposed to high environmental temperature occurs independently by feedback circuit involving scrotal thermo-receptors and effectors in the form of tunica dartos muscle and scrotal sweat gland  activities (Maloney and Mitchell 1999).

 

The decrease in sperm motility percentage and sperm-cell concentration and the increase in reaction time and percentages of dead spermatozoa, sperm abnormality and acrosomal damage as a function of heat stress were similar to the results of El-Darawany (1999b). Exposure to hot conditions alters the animals body temperature, energy input, hormonal and water balances with resultant adverse effects on production and reproduction (Johnson 1987). Elevated body temperature during periods of high ambient temperature, leads to testicular degeneration and reduction in percentage of normal and fertile spermatozoa in the ejaculate (Curtis 1983) and  a sharp increase in the proportion of morphologically abnormal spermatozoa in the ejaculate (Bradon and Mattner 1970) and damage of spermatozoa (e.g. head, tail and acrosome) in the testes (Williamson 1974). Curtis (1983) explained that environmental temperature influences reproduction function in the male by alteration of spermatogenesis and reduction of semen quality that result in a drop of male fertility.

 

The decrease in scrotal circumference and testes length during summer hot season agreed with the results obtained by Finch (1986) and Yarny et al (1990) and the increase in scrotal length during the same season agreed with the results of Curtis (1983) and El-Darawany (1999a; Marai et al 2006b). Finch (1986) and Yarny et al (1990) reported that scrotal circumference and testicular consistency, tone, size and weight, which are excellent indicators of sperm production capacity and spermatogenic functions, decrease during hot summer conditions. Reduction in testicular measurements (testes weight and length) by exposure to heat stress is due to degeneration in the germinal epithelium and to partial atrophy in the seminiferous tubules (Chou et al 1974). The tunica dartos muscle of the scrotum relaxes (scrotal length increases) at high environmental temperature, permitting the testicles to drop away from the body to increase heat dissipation, and the reverse occurs at low environmental temperature (Maloney and Mitchell 1999).

 

The suppressive effects of heat stress on albumin were in agreement with the results of Marai et al (1996) and Yousef et al (1996). The significantly decline in serum albumin with rising temperature seems to be due to dilution caused by the increase in water consumption, and decrease of protein synthesis as a result of the depression of anabolic hormonal secretion (El-Masry and Habeeb 1989) and to the decrease in feed nitrogen intake that occurs under heat stress conditions. The increase in creatinine and decrease of ALP by heat stress agreed with the results of Baumgartner and Pernthaner (1994). The increase in creatinine level under heat stress may be due to the increase in protein catabolism, decrease in protein anbolism, increase in glucocorticoids hormones such as cortisol and decline in T3 hormone (Habeeb et al 1997). The decrease in ALP during summer season may be attributed to reduction in thyroid hormones, which takes place under heat stress conditions (Habeeb et al 1992). The decrease in  Tby heat stress agreed with the results of Yousef and Johnson (1985) and Marai et al (1997). Thyroid hormones major role in regulation of overall heat production lies in the control of endothermic thermoregulation (Hagen 1983), although T3 is more concerned with thermogenesis. The decrease in thyroid hormones is due to the decrease in basal metabolic rate and muscle activity that decrease heat production during hot conditions (Curtis 1983). The increase in cortisol during summer was similar to the results of Yousef et al (1997). Activation of the hypothalamic-pitutary-adrenal axis and the consequent increase of plasma glucocorticoid concentrations are perhaps the most-important responses of animals to stressful conditions. Adrenal corticoids, mainly cortisol, elicit physiological adjustment that enable animals to tolerate stressful conditions (Christison and Johnson 1972).

 

Effects  of selenium treatment

 

The decrease in rectal temperature in rams supplemented with selenium may be due to a favourable effect of selenium on body thermoregulation. The increase in sperm motility  and sperm-cell concentration and the decrease in reaction time, semen pH, dead spermatozoa, sperm abnormality and acrosomal damage with selenium supplementation agreed with the results obtained by Dyachenko and Katroshenko (1990). Selenium is considered an essential nutrient for animals, since it is implied in the functions of the body. Particularly, it is a component of the metallo enzyme glutathion peroxidase (GSH-Px) that is involved in the breakdown of hydrogen peroxidase (H2O2) formed in the body. Such enzyme may serve as a defense against free radical damage and lipid peroxidation (Burtis and Ashwood 1996), although it acts mainly for protection of red cells (RBC) against heomoglobin oxidaxtion and hemolysis (Mills 1957). Selenium also may have a role in reproduction either directly by effecting interstitial cells of testes and/or as a structural component of sperm cells (Calvin 1978), or indirectly via the effect on the anterior pituitary hormones secretion (Yousef et al 1990). In addition, selenium is connected with immunity (Larsen 1993), protects the animal from the white muscle disease (Pehrson 1993) and it is implied in  metabolism of thyroid and other functions (Behne et al 1990). Selenium deficiency causes diseases that decline fertility of livestock in different parts of the world. In human, cardiac muscle is the most susceptible tissue to selenium deficiency, in which cell membrane is damaged and normal cells are replaced with fibroblast (Burtis and Ashwood 1996).

 

The favourable results regarding the increase in scrotal circumference, scrotal length and testes length with  selenium dietary supplementation may be due to the beneficial effect of selenium on the interstitial cells of testes and protection of testes cell from damage under hot conditions, similar to that reported by Yousef et al (1990) and Burtis and Ashwood (1996).

 

Decrease in plasma creatinine level in rams supplemented with selenium may by due to the favourable effect of selenium on protein synthesis (protein anabolism),  protection    of   cells  from   damage and protein catabolism (Burtis and Ashwood 1996) and on T3 formation (Behne et al 1990).

 

Effects of interactions

 

Significance of interactions of selenium treatment with season on the performance traits are due to alteration of the phenotype ranking of the two groups of the animals treated with the two levels of selenium by change of the season of the year. This phenomenon occurs as a result to the change  (deviation; response) in magnitude and direction  in  each trait with the two levels of selenium as a function of heat stress.

 

Within each season, selenium supplementation showed favourable effects on most of the traits studied, but these effects were punctuated in summer. Particularly, the traits that decreased  with selenium supplementation were temperatures of rectum, skin and scrotal-skin,  reaction time,  semen pH, dead spermatozoa, sperm abnormality and acrosomal damage, scrotal circumference and serum alkaline phosphatase, SGOT and creatinine, while all the other traits were increased, in summer. This means that selenium supplementation  can help the ability of the Egyptian Suffolk sheep to maintain expression of their inherited functional potential, when raised under hot conditions. In that respect, it will be beneficial to select the animals which are equipped morphologically and physiologically to withstand heat and drought and maintain expression of their highest  productive abilities under the heat stressful conditions.

 

>From another point of view, it was clear that sperm abnormality values were higher in summer than in winter, either without or with selenium supplementation and the lowest value was obtained with selenium supplementation in winter. Ram group supplemented with selenium in winter season surpassed the other groups in scrotal circumference and testes length. The SGOT and SGPT high values  recorded in ram group with or without selenium supplementation during summer season were in agreement with the results obtained by Okab et al (1993). The increase in SGOT and SGPT activities in the heat stressed animals may be due to the increase in stimulation of gluconeogenesis by corticoids (increase in cortisol, cortisone or adrenocorticotrophic hormones) Marai et al 1995).


Conclusions

 

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Received 15 April 2008; Accepted 13 April 2009; Published 1 October 2009

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