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EFfect of Trypanosoma vivax infection on semen characteristics of Yankasa rams
Br . vet . f. (1992) . 148, 5 0 1
EFFECT OF TRYPANOSOMA VIVAX INFECTION ON SEMEN CHARACTERISTICS OF YANKASA RAMS
V . O . SEKONI National Animal Production Research Institute, Ahmadu Bello University, P. M . B. 1096, Shika-Zaria, Nigeria
SUMMARY Twelve Yankasa rams aged between 2 and 3 years with good semen characteristics were used in this 15-week study . Six rams were infected with Trypanosoma vivax, while six served as controls . The infected rams developed chronic trypanosomosis accompanied by fluctuating pyrexia, lethargy, anaemia, scrotal oedema and cachexia . There was a drastic and progressive deterioration in semen quality in all infected rams manifested by a decrease in volume or cessation of semen production, oligozoospermia, a sharp decrease in progressively motile sperm, elevated numbers of dead (eosinophilic) sperm and 100% morphological abnormalities of sperm in most animals . The rams were all deemed unfit for breeding by 3 weeks post-infection . Uninfected rams were healthy and had good semen characteristics throughout the investigation . The results show that rams infected with T. vivax may become infertile within a short interval due to rapid deterioration of semen characteristics and this trypanosome species may be an important causative agent of infertility in endemic areas .
INTRODUCTION Trypanosomosis caused by T. vivax, T. rongolense, T . brucei and T. simiae is an important disease of livestock in Africa and a major constraint to the livestock industry in Nigeria and many other African countries (Ikede, 1981 ; Morrison et al., 1981 ; Agu, 1983 ; Breinholt, 1983 ; Kanyari et al., 1983 ; Joshua & Kayit, 1984) . In Nigerian sheep T. vivax is a major problem (Isoun & Anosa, 1974 ; Anosa, 1983) . Reproductive disorders have been reported in both female (Ogwu et at., 1984 ; Llewelyn et at., 1988 ; Mutayoba et at., 1988) and male animals (Sekoni et at., 1988, 1990a, 1990b) and some studies have been undertaken to examine the effects of trypanosomosis on ram reproduction . Changes in semen characteristics have been reported in bucks and rams infected with 7'. vivax by Isoun & Anosa (1974), Anosa & Isoun (1980), and Agu et at. (1986) . Akpavie et at. (1987) infected rams with 7'. vivax and T. brucei and found the latter to he more pathogenic . There was a decline in the semen characteristics of infected animals although there was no appreciable change in the semen volume and sperm concentration of 7'. vivax-
502
BRITISH VETERINARY JOURNAL, 148, 6
infected rams . Some of the results reported are conflicting and confusing . For example, Isoun & Anosa (1974) reported a drastic reduction in sperm counts in control rams, while those of infected rams remained normal throughout the duration of their investigation . The investigators made mention of lack or depletion of epididymal sperm reserve of infected rams while their results indicated normal sperm counts for the infected rams . The aim of the present study was to carry out a detailed study of the effect of 7'. vivax infection on the semen characteristics of Yankasa sheep which are the most widely distributed and common breed in Nigeria (Adu & Ngere, 1979) .
MATERIALS AND METHODS Twelve indigenous healthy Yankasa rams, negative for haemoparasites, aged 2z 3 years with good semen characteristics were used for the 15-week study . Pre-infection baseline data were collected over a period of 6 weeks . The animals were randomly divided into two groups . Each group was housed in a separate flyproof room within the same building to prevent the transmission of infection by haematophagous flies to the control group . The animals were fed concentrates, fresh pasture, hay, salt licks and water ad libitum . Group A was inoculated with the Y 58 strain of T. vivax, isolated from a natural infection in cattle in northern Nigeria . One ml of heparinized blood from a donor goat containing approximately lx10' trypanosomes was inoculated into the jugular vein of each ram . The second group of rams served as control . Parameters monitored post-infection were rectal temperature, parasitaemia, packed cell volume and haemoglobin concentration measured three times weekly according to Coles (1967) and Woo (1969) . The scrotum and scrotal contents were palpated and semen collected by electroejaculation weekly . Semen was evaluated according to Hancock (1957) and Roberts (1971) . Characteristics evaluated were volume, sperm concentration, live/dead spermatozoa and progressively motile spermatozoa . Morphological abnormalities of the acrosome, detached heads, cytoplasmic droplets, midpiece, and the tail were estimated following dilution with buffered formal saline and counting at least 500 sperm per slide by scanning under the phase contrast microscope (Hancock, 1957 ; Rao, 1971 ; Sekoni et al., 1981) . Semen samples stained with eosin-nigrosin were used to determine the morphological abnormalities of the sperm head (Lagerlof, 1934 ; Rao, 1971 ; Sekoni et al., 1981) . Five hundred spermatozoa were counted per slide . Student's t-test was used to compare differences between the infected group and the control . The degree of significance is denoted by one, two or three asterisks (*P<0 .05 ; **P<0 .01 ; ***P<0 .001) .
RESULTS
Clinical findings Trypanosomes were present in the peripheral circulation of all infected rams by
5( 6
OVINE TRYPANOSOMOSIS AND INFERTILITY
3 days post-inoculation . There was fluctuating parasitaemia throughout the period of investigation . All infected rams developed chronic trypanosomosis characterized by intermittent pyrexia, rapid weight loss, lethargy, dullness, pale mucous membranes, scrotal enlargement and oedema and enlarged superficial lymph nodes . The rams in the control group were negative for trypanosomes and remained healthy throughout the investigation .
Semen characteristics All animals had good semen characteristics prior to the experiment . Before infection, semen samples collected from all rams were opaque and creamy . In the control rains, these characteristics were present throughout the investigation . In contrast, in the infected group, semen samples became milky then watery and transparent and there was a progressive deterioration in the semen characteristics of all the infected rams throughout the 9 weeks post-infection (p .i .) . Detailed results are shown in Table I . The pre-infection baseline value of the volume of semen in all the rams was normal with a mean of 3 ml . After infection, there was a progressive reduction in the volume of semen of all the infected rams and towards the end of the investigation most of them were unable to ejaculate . At 9 weeks p .i ., infected rams had a mean volume of 0 .1 ml of semen which differed significantly (***P<0 .001) from the mean of 3 .4 ml for controls . The pre-infection baseline value for sperm concentration in the semen of all the rams was normal with a mean value of'
Table I Mean values for semen characteristics of T. vivax infected and control rams
Weeks p.i. 1 2 3 4
6 7 8
Volume (ml) 2 .55 (2 .88) 2 .47** (3 .38) 1 .50** (2 .75) 1 .25*** (2 .58) 1 .00*** (2 .75) 0 .58*** (2 .65) 0 .38*** (2 .70) 0 .15*** (2 .90) 0 .11*** (3 .40)
Sperm X10, /ml 2250 .0 (2550) 2233 .33 (2423 .33) 1700 .0** (2633 .33) 1100 .0*** (2650 .0) 525 .0*** (2651 .0) 341 .67*** (2566 .67) 191 .67*** (2483 .33) 116 .67*** (2458 .33) 13 .33*** (2483 .33)
% Live sperm 90 .33 (93 .83) 82 .00** (92 .50) 75 .67*** (92 .60) 64 .33*** (93 .67) 54 .83*** (92 .50) 51 .67*** (92 .17) 44 .17*** (90 .50) 25 .00*** (91 .67) 15 .33*** (92 .67)
% Motile sperm 83 .17 (85 .50) 74 .17* (89 .0) 71 .67** (89 .17) 57 .50*** (86 .18) 45 .83*** (87 .67) 34 .17*** (88 .00) 16 .67*** (89 .17) 8 .33*** (86 .67) 3 .33*** (90 .83)
% Abnormal sperm 5 .38 (3 .97) 26 .29*** (4 .87) 43 .73*** (4 .02) 63 .50*** (3 .93) 88 .94*** (3 .97) 97 .41*** (3 .43) 98 .95*** (3 .82) 98 .96*** (3 .63) 99 .67* :* (3 .90)
p .i ., Post-infection, Values for control rams are in parentheses . Significant differences between infected group and corresponding control are denoted by one, two or three asterisks : *P<0 .05, **P<0 .01, ***P<0 .00 1 . Number of rams in each group=6 .
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BRITISH VETERINARY JOURNAL, 148, 6
2698 .6x10') ml . After infection, there was a decrease in the sperm concentration of all infected rams and their semen became oligozoospermic . At 9 weeks p .i ., infected rams had a sperm concentration of 13 .3x10''/ml which differed (***P< 0 .001) from 2483 .3xl0e/ml for the control group . The pre-infection baseline value for live sperm in all the rams was normal, (mean value 93 .2%) . As the infection progressed in the infected group, live sperms decreased, while dead (eosinophilic) sperms increased . By 9 weeks p .i ., the mean value of live sperm in the infected group was 15 .3% which differed (***P<0 .001) from the control (mean value 92 .7%) . Progressively motile sperm in all rams were normal (mean value of 85 .5%) and as infection progressed, sperm motility of infected rams decreased and at 9 weeks p .i ., the mean value for progressive sperm motility for infected rams was 3 .3% which differed (***P<0 .001) from the mean value of 90 .8% for the control group . Total sperm morphological abnormalities were low pre-infection and normal in all the rams with a mean value of 4 .2% . After infection, there was a progressive elevation of total sperm morphological abnormalities in all the infected rams . The mean value for total sperm morphological abnormalities at 9 weeks p .i . was 99 .7% which differed (***P<0 .001) from the mean value for the control group of 3 .9% .
DISCUSSION Trypanosomosis due to T. vivax infection severely affected the semen characteristics of Yanakasa rams . Significant deterioration in semen characteristics was recorded within 2 weeks of infection . By 3 weeks p .i ., infected rams were no longer good for breeding due to poor semen quality . This progressive deterioration in semen characteristics and eventual cessation of semen production in infected animals may be attributable to damage done to the genitalia of the infected animals by the infection . Mechanisms leading to tissue and organ damage could reflect endocrinological or physiological disturbances, blood, circulatory and immunological disorders and the production by the trypanosomes of biologically active and toxic substances (Boreham & Cox, 1978 ; Morrison et al., 1978, 1981 ; Ikede, 1979 ; Anosa & Isoun, 1980) . The results obtained in this study, unlike those reported by other investigators (Isoun & Anosa, 1974 ; Anosa & Isoun, 1980 ; Agu et al., 1986), show that T. vivax infection has more severe pathogenic effects on ram semen characteristics, possibly due to differences in pathogenicity of the strains of trypanosomes . Infertility problems in small ruminants caused by chronic trypanosomosis may therefore be of considerable socioeconomic significance in sheep in areas of Africa south of the Sahara where pathogenic trypanosomes and their tsetse fly vectors occur .
REFERENCES Anu, 1 . F . & NGERE, 15(3),51-62 .
L.
0 . (1979) . The indigenous sheep of Nigeria . World Rev. anim. Prod.
OVINE TRYPANOSOMOSIS AND INFERTILITY
5 i15
Act,, W. E . (1983) . Animal trypanosomiasis in Nigeria . ACIARProc . 4,70-5 .
Acu, W . E ., IcE, K . & OIATUNDE, D . S . (1986) . Evaluation of semen quality of rams infected with Trypanosoma vivax. Anim . rep rod . Sci . 11, 123-7. AKPAvIE, S . 0 ., IKFDE, B . O . & EGRUNIKE, G . N . (1987) . Ejaculate characteristics of sheep infected with Trypanosoma brucei and T. vivax. changes caused by treatment with diminazene aceturate . Res. vet. Sci. 42, 1-6 . ANOSA, V . 0 . (1983) . Diseases produced by Trypanosoma vivax in ruminants, horses and rodents . Zbl. Vet.-Med. 30, 717-41 . ANOSA, V. O . & Isoux, T . T. (1980) . Further observations on the testicular pathology in 7 1 rypanosoma vivax infection of sheep and goats . Res . vet. Sri . 28, 151-60 . BoRFnAM, P . F . L . & Cox, F . E . G . (1978) . Mechanism of cellular injury : blood and circulatory system . Discussion summary, pathogenicity of trypanosomes . In Proceedings of a Ilo,kchop held at Nairobi, Kenya, 20-23 Nov ., pp . 120 . BRFJNHOI,r, K . A . (1983) Production performance of an imported herd of Friesian cattle subject to trypanosome challenge in the humid lowlands tropics of Nigeria . last Afi . agile. for. /. 4, 355 . Coi,rs, H . E . (1967) . Veterinary Clinical Pathology, pp . 72-165 . Philadelphia and London : W . B . Saunders Company . I-IANCOCK, J. L . (1957) . The morphology of boar spermatozoa . J. roy . Micr. Soc . 76, 84-97 . IKEDE, B . O . (1979) . Genital lesions in experimental chronic Trypanosoma brucei infection in rams . Res. vet . Sci. 26, 145-51 . IKEDE, B . O . (1981) . The understanding of the pathogenic effects of trypanosomiasis in ruminants as basis for diagnosis . Paper presented at the First National Conference on Tsetse and Trypanosomiasis Research and Control . Aug . 9-12, Kaduna, Nigeria . ISOCN, T . T . & ANOSA, V. O . (1974) . Lesions in the reproductive organs of sheep and goats experimentally infected with Trypanosoma vivax. Z . Tropenmed. Parasit . 25, 469-76 . JOsnt , R . A. & KAVrr, Y. S . (1984) . The course of fatal Trypanosomaa sirniaeinfection in domestic sheep . Acta trop . 41, 91-2 . KANNARI, P . W . N ., AI .tANBY, E . W ., Wn .SON, A . J . & MuNYA, W . K. (1983) . Some economic effects of trypanosomiasis in goats . Trop . anim . hlth Prod. 15, 153-60 . 1 .AGERLOF, N . (1934) . Researches concerning the morphologic changes in the testicles of sterile or subnormally fertile bulls . Acta path . microbiol. scand suppl. 19, 254 . I .ILE.wEa .vN, C . A ., MUNRO, C . D ., LUCKINS, A. G ., JoRDT, T ., MI - RP_-"N, M . & Lt)RFNZINI, E . ( 1988) . The effects of Trypanosoma congolense infection on the oestrous cycle of the Boran cow . Br. vet .]. 144, 379-87 . MORRISON, W . I ., MURRAY, M . & SAVER, P . D . (1978) . Pathogenesis of tissue lesions in 7'. brucei infections . In Pathogenicity of Trypanosomes . Proceedings of a Workshop held at Nairobi, Kenwr, 20-23 Nov., 171-8 . MORRISON, I ., MiTRAY, M . & MCINTYRE, I . (1981) . Bovine trypanosomiasis . FAD/SIDA followup seminar on Veterinary Pathology, Faculty of Veterinary Medicine, University of Nairobi, 7-27 Sept . M 1AyoBA, B . M ., GoMBE, S ., KARYA, G . P . & WAIND1, E . N . (1988) . The effects of chronic experimental T. congolense infection on the ovaries, pituitary, thyroid and adrenal glands in female goats . Res. vet. Sri. 44, 140-6 . Ocwu, D ., N,joKU, C . 0 ., OSORI, D . I . K ., EZEOKott, C . D . & KL Mi-DIARA, J. (1984) . Effects of experimental Trypanosoma vivax infection on fertility of heifers . Theriogenology 22(6), 625-33 . RAO, A. R . (1971) . Changes in the morphology of sperm during their passage through the genital tract in bulls with normal and impaired spermatogenesis . PhD thesis . Royal Veterinary College, Stockholm, Sweden . ROBERTS, S . J . (1971) . Infertility in male animals . In : Veterinary Obstetrics and Genital Diseases, pp . 604-97 . Ann Arbor, Michigan : Edwards Brothers, Inc . SEKONI, V . 0 ., GUSrAFSSON, B . K. & MATHER, E . C. (1981) . Influence of wet fixation, staining techniques and storage time on bulls sperm morphology. Nord . Vet.-Med. 33, 161-6 . SEKONt, V . 0 ., KUMr-DIAKA, J., SAROR, D . & NIOKU, C . (1988) . The effect of Trypanosoma vivax
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BRITISH \ F 1 ERINARY . JOURNAL ., 148, 6
and Trypanosoma congolense infection on the reaction time and semen characteristics in the Zebu bull. Br. vet . J. 144, 388-94 . SixoNi, V . 0 ., N1oKU, C . 0 ., Kt sai-DIAK,s, J . & SsRoR, D . I . (1990a) . Pathological changes in male genitalia of cattle infected with Trypanosoma vivax and J rypanosoma congolense . Br. vet . J. 146, 175-80 . SEKoNI, V . 0 ., N1oKc, C . 0 ., S,skOk, D ., S .ANNcsi, A., ONEJOIs, B . & Kt'M]-DtaxA,,J . (1990b) . Effect of chemotherapy on elevated ejaculation time and deteriorated semen characteristics consequent to bovine trypanosomiasis . Br. vet. J. 146, 368-73 . Woo, P. T . K. (1969) . The haematocrit centrifuge technique for the detection of trypanosomes in blood . Can . J. Zool. 47, 921-3 . (Arrepted fm publiralion 21 .91n)l 1992)
EFFECT OF TRYPANOSOMA VIVAX INFECTION ON SEMEN CHARACTERISTICS OF YANKASA RAMS
V . O . SEKONI National Animal Production Research Institute, Ahmadu Bello University, P. M . B. 1096, Shika-Zaria, Nigeria
SUMMARY Twelve Yankasa rams aged between 2 and 3 years with good semen characteristics were used in this 15-week study . Six rams were infected with Trypanosoma vivax, while six served as controls . The infected rams developed chronic trypanosomosis accompanied by fluctuating pyrexia, lethargy, anaemia, scrotal oedema and cachexia . There was a drastic and progressive deterioration in semen quality in all infected rams manifested by a decrease in volume or cessation of semen production, oligozoospermia, a sharp decrease in progressively motile sperm, elevated numbers of dead (eosinophilic) sperm and 100% morphological abnormalities of sperm in most animals . The rams were all deemed unfit for breeding by 3 weeks post-infection . Uninfected rams were healthy and had good semen characteristics throughout the investigation . The results show that rams infected with T. vivax may become infertile within a short interval due to rapid deterioration of semen characteristics and this trypanosome species may be an important causative agent of infertility in endemic areas .
INTRODUCTION Trypanosomosis caused by T. vivax, T. rongolense, T . brucei and T. simiae is an important disease of livestock in Africa and a major constraint to the livestock industry in Nigeria and many other African countries (Ikede, 1981 ; Morrison et al., 1981 ; Agu, 1983 ; Breinholt, 1983 ; Kanyari et al., 1983 ; Joshua & Kayit, 1984) . In Nigerian sheep T. vivax is a major problem (Isoun & Anosa, 1974 ; Anosa, 1983) . Reproductive disorders have been reported in both female (Ogwu et at., 1984 ; Llewelyn et at., 1988 ; Mutayoba et at., 1988) and male animals (Sekoni et at., 1988, 1990a, 1990b) and some studies have been undertaken to examine the effects of trypanosomosis on ram reproduction . Changes in semen characteristics have been reported in bucks and rams infected with 7'. vivax by Isoun & Anosa (1974), Anosa & Isoun (1980), and Agu et at. (1986) . Akpavie et at. (1987) infected rams with 7'. vivax and T. brucei and found the latter to he more pathogenic . There was a decline in the semen characteristics of infected animals although there was no appreciable change in the semen volume and sperm concentration of 7'. vivax-
502
BRITISH VETERINARY JOURNAL, 148, 6
infected rams . Some of the results reported are conflicting and confusing . For example, Isoun & Anosa (1974) reported a drastic reduction in sperm counts in control rams, while those of infected rams remained normal throughout the duration of their investigation . The investigators made mention of lack or depletion of epididymal sperm reserve of infected rams while their results indicated normal sperm counts for the infected rams . The aim of the present study was to carry out a detailed study of the effect of 7'. vivax infection on the semen characteristics of Yankasa sheep which are the most widely distributed and common breed in Nigeria (Adu & Ngere, 1979) .
MATERIALS AND METHODS Twelve indigenous healthy Yankasa rams, negative for haemoparasites, aged 2z 3 years with good semen characteristics were used for the 15-week study . Pre-infection baseline data were collected over a period of 6 weeks . The animals were randomly divided into two groups . Each group was housed in a separate flyproof room within the same building to prevent the transmission of infection by haematophagous flies to the control group . The animals were fed concentrates, fresh pasture, hay, salt licks and water ad libitum . Group A was inoculated with the Y 58 strain of T. vivax, isolated from a natural infection in cattle in northern Nigeria . One ml of heparinized blood from a donor goat containing approximately lx10' trypanosomes was inoculated into the jugular vein of each ram . The second group of rams served as control . Parameters monitored post-infection were rectal temperature, parasitaemia, packed cell volume and haemoglobin concentration measured three times weekly according to Coles (1967) and Woo (1969) . The scrotum and scrotal contents were palpated and semen collected by electroejaculation weekly . Semen was evaluated according to Hancock (1957) and Roberts (1971) . Characteristics evaluated were volume, sperm concentration, live/dead spermatozoa and progressively motile spermatozoa . Morphological abnormalities of the acrosome, detached heads, cytoplasmic droplets, midpiece, and the tail were estimated following dilution with buffered formal saline and counting at least 500 sperm per slide by scanning under the phase contrast microscope (Hancock, 1957 ; Rao, 1971 ; Sekoni et al., 1981) . Semen samples stained with eosin-nigrosin were used to determine the morphological abnormalities of the sperm head (Lagerlof, 1934 ; Rao, 1971 ; Sekoni et al., 1981) . Five hundred spermatozoa were counted per slide . Student's t-test was used to compare differences between the infected group and the control . The degree of significance is denoted by one, two or three asterisks (*P<0 .05 ; **P<0 .01 ; ***P<0 .001) .
RESULTS
Clinical findings Trypanosomes were present in the peripheral circulation of all infected rams by
5( 6
OVINE TRYPANOSOMOSIS AND INFERTILITY
3 days post-inoculation . There was fluctuating parasitaemia throughout the period of investigation . All infected rams developed chronic trypanosomosis characterized by intermittent pyrexia, rapid weight loss, lethargy, dullness, pale mucous membranes, scrotal enlargement and oedema and enlarged superficial lymph nodes . The rams in the control group were negative for trypanosomes and remained healthy throughout the investigation .
Semen characteristics All animals had good semen characteristics prior to the experiment . Before infection, semen samples collected from all rams were opaque and creamy . In the control rains, these characteristics were present throughout the investigation . In contrast, in the infected group, semen samples became milky then watery and transparent and there was a progressive deterioration in the semen characteristics of all the infected rams throughout the 9 weeks post-infection (p .i .) . Detailed results are shown in Table I . The pre-infection baseline value of the volume of semen in all the rams was normal with a mean of 3 ml . After infection, there was a progressive reduction in the volume of semen of all the infected rams and towards the end of the investigation most of them were unable to ejaculate . At 9 weeks p .i ., infected rams had a mean volume of 0 .1 ml of semen which differed significantly (***P<0 .001) from the mean of 3 .4 ml for controls . The pre-infection baseline value for sperm concentration in the semen of all the rams was normal with a mean value of'
Table I Mean values for semen characteristics of T. vivax infected and control rams
Weeks p.i. 1 2 3 4
6 7 8
Volume (ml) 2 .55 (2 .88) 2 .47** (3 .38) 1 .50** (2 .75) 1 .25*** (2 .58) 1 .00*** (2 .75) 0 .58*** (2 .65) 0 .38*** (2 .70) 0 .15*** (2 .90) 0 .11*** (3 .40)
Sperm X10, /ml 2250 .0 (2550) 2233 .33 (2423 .33) 1700 .0** (2633 .33) 1100 .0*** (2650 .0) 525 .0*** (2651 .0) 341 .67*** (2566 .67) 191 .67*** (2483 .33) 116 .67*** (2458 .33) 13 .33*** (2483 .33)
% Live sperm 90 .33 (93 .83) 82 .00** (92 .50) 75 .67*** (92 .60) 64 .33*** (93 .67) 54 .83*** (92 .50) 51 .67*** (92 .17) 44 .17*** (90 .50) 25 .00*** (91 .67) 15 .33*** (92 .67)
% Motile sperm 83 .17 (85 .50) 74 .17* (89 .0) 71 .67** (89 .17) 57 .50*** (86 .18) 45 .83*** (87 .67) 34 .17*** (88 .00) 16 .67*** (89 .17) 8 .33*** (86 .67) 3 .33*** (90 .83)
% Abnormal sperm 5 .38 (3 .97) 26 .29*** (4 .87) 43 .73*** (4 .02) 63 .50*** (3 .93) 88 .94*** (3 .97) 97 .41*** (3 .43) 98 .95*** (3 .82) 98 .96*** (3 .63) 99 .67* :* (3 .90)
p .i ., Post-infection, Values for control rams are in parentheses . Significant differences between infected group and corresponding control are denoted by one, two or three asterisks : *P<0 .05, **P<0 .01, ***P<0 .00 1 . Number of rams in each group=6 .
504
BRITISH VETERINARY JOURNAL, 148, 6
2698 .6x10') ml . After infection, there was a decrease in the sperm concentration of all infected rams and their semen became oligozoospermic . At 9 weeks p .i ., infected rams had a sperm concentration of 13 .3x10''/ml which differed (***P< 0 .001) from 2483 .3xl0e/ml for the control group . The pre-infection baseline value for live sperm in all the rams was normal, (mean value 93 .2%) . As the infection progressed in the infected group, live sperms decreased, while dead (eosinophilic) sperms increased . By 9 weeks p .i ., the mean value of live sperm in the infected group was 15 .3% which differed (***P<0 .001) from the control (mean value 92 .7%) . Progressively motile sperm in all rams were normal (mean value of 85 .5%) and as infection progressed, sperm motility of infected rams decreased and at 9 weeks p .i ., the mean value for progressive sperm motility for infected rams was 3 .3% which differed (***P<0 .001) from the mean value of 90 .8% for the control group . Total sperm morphological abnormalities were low pre-infection and normal in all the rams with a mean value of 4 .2% . After infection, there was a progressive elevation of total sperm morphological abnormalities in all the infected rams . The mean value for total sperm morphological abnormalities at 9 weeks p .i . was 99 .7% which differed (***P<0 .001) from the mean value for the control group of 3 .9% .
DISCUSSION Trypanosomosis due to T. vivax infection severely affected the semen characteristics of Yanakasa rams . Significant deterioration in semen characteristics was recorded within 2 weeks of infection . By 3 weeks p .i ., infected rams were no longer good for breeding due to poor semen quality . This progressive deterioration in semen characteristics and eventual cessation of semen production in infected animals may be attributable to damage done to the genitalia of the infected animals by the infection . Mechanisms leading to tissue and organ damage could reflect endocrinological or physiological disturbances, blood, circulatory and immunological disorders and the production by the trypanosomes of biologically active and toxic substances (Boreham & Cox, 1978 ; Morrison et al., 1978, 1981 ; Ikede, 1979 ; Anosa & Isoun, 1980) . The results obtained in this study, unlike those reported by other investigators (Isoun & Anosa, 1974 ; Anosa & Isoun, 1980 ; Agu et al., 1986), show that T. vivax infection has more severe pathogenic effects on ram semen characteristics, possibly due to differences in pathogenicity of the strains of trypanosomes . Infertility problems in small ruminants caused by chronic trypanosomosis may therefore be of considerable socioeconomic significance in sheep in areas of Africa south of the Sahara where pathogenic trypanosomes and their tsetse fly vectors occur .
REFERENCES Anu, 1 . F . & NGERE, 15(3),51-62 .
L.
0 . (1979) . The indigenous sheep of Nigeria . World Rev. anim. Prod.
OVINE TRYPANOSOMOSIS AND INFERTILITY
5 i15
Act,, W. E . (1983) . Animal trypanosomiasis in Nigeria . ACIARProc . 4,70-5 .
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