Seasonal variations in sperm production, gonadal and extragonadal sperm reserves in pubertal West African dwarf bucks in their native tropical environment

I I Bitto and G N Egbunike*

Department of Animal Breeding and Physiology, University of Agriculture, Makurdi, Nigeria
sibittos@yahoo.com
*Animal Physiology Laboratory, Department of Animal Science, University of Ibadan, Nigeria

Abstract

The effects of season on daily sperm production (DSP), daily sperm production /gram testis (DSPG), gonadal and extragonadal sperm reserves in pubertal West African Dwarf  (WAD) bucks were evaluated using 8 animals.

Both DSP and DSPG determined by quantitative testicular histology and from testicular homogenates were similar (P>0.05) between the rainy and dry seasons. There were no significant differences (P>0.05) between the methods of evaluation in both DSP and DSPG. Season likewise had no effect (P>0.05) on gonadal and extragonadal sperm reserves. There were numerical differences between the seasons in all parameters except in DSPG obtained from testicular histology. DSP was highly significantly positively related to total epididymal sperm reserves (r = 0.71; P< 0.001); caput reserves (r = 0.82, P< 0.01); corpus reserves (r = 0.82; P<0.001); ductus deferens reserves (r = 0.85; P<0.001) and gonadal sperm reserves (r = 0.90; P<0.001). Total epididymal reserves were highly correlated with caput (r = 0.90; P<0.001); corpus (r = 0.91; P<0.001); cauda (r = 0.90; P<0.001); ductus deferens (r = 0.93; P<0.001) and gonadal (r = 0.82; P< 0.001) reserves. The relationships between all epididymal sections and gonadal sperm reserves as well as among epididymal sections were all good.

It is concluded that the WAD buck would not be a seasonal breeder in its native environment. Semen could therefore be obtained all year round from superior sires for use in planned breeding programmes aimed at the improvement of this breed. Farmers could then benefit from such programmes at affordable rates.

Key words: Buck, goats, production, reserves, sperm, tropics

Introduction

The West African Dwarf (WAD) goat occupies an important place in subsistence agriculture in the West African sub - region, with a unique adaptation to its native humid tropical environment. Besides being the most popular of all breeds of goats in the humid zone of West Africa in general and Nigeria in particular, this genotype has the advantage of being trypanotolerant (Upton 1985) and is adjudged as one of the most prolific in the world with a remarkably high reproductive potential in terms of young produced per female per year (Wilson 1989;Gall et al 1992).

Even though these animals are reared mainly for meat, providing a flexible financial reserve for the rural population (Sumberg and Cassaday 1985), milk production as a secondary function is common with many owners. The WAD goat however has been reported to be generally unimproved with a poor genetic potential for growth. As the demand for these animals in the sub region is constantly high and as the extraction rates for goats generally are high in the tropics and subtropics (Devendra 1982), the prospects for increasing the numbers and productivity of these animals need to be utilized.

Devendra (1982) suggested the effective use of genetic resources among the avenues for increasing productivity in small ruminants in the tropics. He also attributed the low performance of several breeds of goats in the tropics and subtropics including the WAD partly to low genetic quality. The genetic improvement of the WAD goat will require the selection of superior breeding stock and the application of artificial insemination (Al) technique. Al in goats in France has been reported to play an important role in the milk production system to control reproduction and in conjunction with progeny testing to improve milk production (Leboeuf et al 1998). The successes of Al in goats generally and in the WAD in particular will depend on a knowledge of sperm production rates, gonadal and extragonadal sperm reserves, the ejaculate characteristics as well as the efficiency in semen collection, evaluation, preservation and insemination techniques.

Preparatory to programmes aimed at the improvement of these animals in their native environment, some aspects of the physiology of reproduction in the male have been documented (Akusu et al 1984; Ugwu and Orji 1984; Bitto et al 1988; Bitto et al 2000a and Bitto et al 2000b). There is however at present no information on the reproductive capacity of the WAD buck, thus constituting a hindrance to their improvement. Moreover in the absence of planned breeding programmes for these animals here in the humid tropics, pubertal bucks have been known to successfully serve does on range as these animals are allowed to roam and scavenge for food. Bucks moreover, have been reported to exhibit sexual aggressiveness, penile development, and permit intromission with good libido under tropical conditions at a very young age (Bongso et al 1982). A sampling programme for young Al bucks has also been reported to be of immense benefits to a scheme that is in operation in France, aimed at improving milk protein yield and protein content (Leboeuf et al 1998).

A successful improvement programme for the WAD goat in the humid zone of West Africa will however require a linkage between the research stations, agricultural extension and the farmers as is the case in France, so that semen from superior sires will be used to bring about the improvement of this breed.

With no clearly defined breeding season for these animals but with significant differences in ambient temperatures between seasons in their native environment, we undertook this study to provide base line information on the influence of season on DSP, DSPG, gonadal and extragonadal sperm reserves in pubertal bucks born and raised in their native humid tropical environment.

Materials and methods

Location and climate

The study took place at the Teaching and Research Farm of the University of Ibadan, Nigeria. Ibadan is located at latitude 07^o 20¹ N and longitude 03^o 50¹ E, with a hot humid equatorial climate divided into four three monthly seasons namely: the early rainy season (April - June), the late rainy season (July - September), the early dry season (October - December) and the late dry season (January - March) (Egbunike and Steinbach 1979). The seasons in this study were limited to only two - the early rainy season (April - June) and the early dry season (October - December).

Animals and management

Eight healthy kid bucks, 4 in each season were randomly selected for the study. They were all weaned between 35 and 40 days of age and were housed in a standard goat barn with concrete floor and adequate protection from prevalent ambient temperature and other climatic conditions. They were fed a maize - based concentrate ration supplemented with forage ad libitum and also supplied with salt lick and cool clean drinking water always.

Puberty

The preputial smear technique described by Vandenberg (1971) in male golden hamsters and Egbunike (1979) in boars was applied to the animals to determine the onset of puberty. The cotton buds used in the present study were the bel de luxe - Hartmann Ltd, brand. The bucks in the rainy season attained puberty at an age of 153.95±4.08 days and weighed between 8.86 and 11.00kg while these in the dry season attained puberty at 154.62 ±5.04 days and weighed between 8.40 and 11.97 kg.

Sperm production and sperm storage capacity

The animals in each season were all sacrificed on the same day after which their reproductive tracts were obtained intoto and immediately taken to the laboratory. The testes and epididymis were carefully trimmed free of adhering fat and connective tissue and weighed. Known weights of both left and right organs were homogenized as reported by Igboeli and Rakha (1971).

Sperm concentration was determined haemocytometrically after a (1: 40v/v) dilution in 0.154M NaCl (Egbunike et al 1976).

DSP by quantitative testicular histology

Testicular tissues were fixed in aqueous Bouins' fixative for 24 hours after which they were dehydrated in graded levels of ethyl alcohol, cleared in chloroform, embedded in paraffin and sectioned in a microtone at 7µ thick. The slides were stained with haematoxylin - eosin (H & E) for histological evaluations.

The predicted maximum DSP was determined using the formula proposed by Swierstra (1966).

The volume percent of round spernatids and seminiferous tubules were determined by Chalkley's (1943) technique using a 25-point occular graticule (Zeis Oberkochen). All observations were made at 800-x magnification using oil immersion.

Correction was made for tissue shrinkage due to fixation, dehydration, clearing and paraffin impregnation using the Archimedes principle with water and xylene for the initial and final volumes respectively.

It was assumed that the mediastinum composed 1% of the testis volume Swierstra (1968). A Shrinkage factor of 0.55, a volume % of round spermatid nuclei of 5.25 and a life span of round spermatids (calculated from the kinetics and duration of spermatogenesis) of 6.35 days were obtained for the pubertal buck in this study.

DSP from testicular homogenates

DSP was obtained by dividing the gonadal sperm reserves by a time divisor of 3.56 proposed by Amann (1970).

DSPG

The efficiency of sperm production was obtained by dividing the DSP values obtained by either method by the corresponding testicular parenchyma weights.

Statistical analysis

Data were subjected to the student 't' test and correlation analyses (Steel and Torrie 1980).

Results and discussion

The effects of season on DSP and DSPG are presented in Table 1.

The influence of season on gonadal and extraganadal sperm reserves as well as the relationships between sperm production, gonadal and extragonadal sperm reserves are presented in Tables 2 and 3 respectively.

Season had no effect (P>0.05) on the parameters investigated even though there were numerical differences. There were also no significant differences (P> 0.05) between the methods of evaluation and in the ratios or left to right organs in terms of DSP and DSPG.

DSP values obtained in the present study by both quantitative histology and from testicular homogenates are higher than values reported by Carew and Egbunike (1980) for adult Red Sokoto Maradi bucks. These results confirm breed differences in Sperm production rates and also suggest a higher sperm production potential in the WAD buck at an earlier age. Also, even though Bongso et al (1982) did not report on sperm production rates, the onset of spermatogenesis they obtained as from 159 days of age in crossbred Saanen x Local Jumnapari x Local bucks shows an earlier attainment of puberty in the pubertal WAD buck in its native environment.

Although season had no significant effects on DSP, DSPG, gonadal sperm reserves as well as extra gonadal sperm reserves, major numerical differences were observed between the seasons with an apparent superiority of the early rainy season over the early dry season in the parameters. These numerical differences may be related to the differences between the seasons in the quality of the supplement pasture as the animals in both seasons were fed the same basal diet (concentrate). Van Soest (1992) reported that feeds are not equal in their capacity to support the animal functions of maintenance, growth and reproduction.

The non effect of season on gonadal and extragonadal sperm reserves suggests that sires could be used for breeding purposes all year round. Gonadal sperm reserves in both seasons in the present study are also higher than values reported for Red Sokoto Maradi bucks by Ogwuegbu et al (1985) and Butswat and Zaharaddeen (1998) and the Kano brown buck by Butswat and Zaharaddeen (1998) in the same environment. The same trend was observed in the extragonadal sperm reserves, thus confirming our earlier observation that the WAD buck might have a higher reproductive capacity in this environment them other breeds of goats.

Going by the mean sperm production and the mean total epididymal sperm reserves obtained in this study for all animals, it would mean that the epididymis of the pubertal buck is large enough to accommodate the equivalent of 6.34 days of sperm production.

With regard to the linear relationships, the good correlations between sperm production and sperm reserves obtained in the present study agree with earlier reports of Egbunike et al (1976) and Weisgold and Almquist (1979).

Conclusions

• We conclude from these results that the WAD buck in its native environment would not be a seasonal breeder

• Selected superior sires could therefore provide good quality ejaculates through out the year to sustain Al programmes in this breed. Farmers would then have their does inseminated at subsidized rates to rapidly spread superior genes widely in the sub - region.

Acknowledgment

We are grateful to Professor M O Akusu of the Department of Veterinary Reproduction and Surgery, University of Ibadan, Nigeria for his assistance.

References

Akusu M O, Agiang E A and Egbunike G N 1984 Ejaculate and seminal plasma characteristics of West African Dwarf (WAD) buck. 10^th International Congress on Animal Reproduction and A. I. University of Ilinois Volume II pp. 50 - 52.

Amann R P 1970 Sperm production rates. In A D Johnson, W R Gomes and N L Van Demark, editors. The Testis. Volume 1. Academic press. New York pp 433-488.

Bitto I I, Akusu M O, Egbunike, G.N. and Akpokodje, J.U. 1988 Comparative studies of the physical and micrometric characteristics of Ovine and Caprine semen in the humid tropics. 11^th Congress on Animal Reproduction and A. I., Dublin, Ireland, Volume 3:230 + pp. 3.

Bitto I I, Akusu M O, Egbunike G N and Akpokodje J U 2000a A comparative study of spermatozoal abnormalities and some Biochemical characteristics of Ovine and Caprine semen in the humid tropics. Tropical Journal of Animal Science 3 (1) 169 - 174.

Bitto I I, Egbunike G N, Nduka E U O and Akusu M O 2000b The effects of season on the circulating testosterone level in the pubertal West African Dwarf buck in its native environment. Tropical Journal of Animal Science. 3 (1): 157 - 161.

Bongso T A, Jainudeen M R and Siti Zahrah A 1982 Relationship of scrotal circumference to age, body weight and onset of spermatogenesis in goats. Theriogenology 18 (5): 513 - 524.

Butswat I S and Zaharaddeen D T 1998 Comparisons of some reproductive parameters in Red Sokoto and Kano Brown breeds of bucks. Nigerian Journal of Animal Production 25 (1): 1-5.

Carew B A and Egbunike G N 1980 Sperm production rates in Maradi goats extensively managed in a tropical environment. Proc. 9^th Congress on Animal Reproduction and A. I., Madrid, Volume V, 608-611.

Chalkley H W 1943 Method for quantitative morphologic analysis of tissues. National Cancer Institute, 4: 47-53.

Devendra C 1982 Prospects for increasing productivity from sheep and goats. In Animal Production in the Tropics. M K Yousef editor, Praeger Publishers. CBs Educational and Professional Publishing. New York, U.S.A pp123 - 147.

Egbunike G N and Steinbach J 1979 Seasonal variations in the sperm production rates of boars in a humid tropical environment. Nigerian Journal of Agricultural Science 1:21 - 26.

Egbunike G N 1979 Development of puberty in Large White boars in a humid tropical environment. Acta Anat. 104:400 - 405.

Egbunike G N, Holtz W and Smidt D 1976 Reproductive capacity of German Landrace boars. II: Sperm production rates as determined by quantitative testicular histology and from gonadal sperm reserves. Zuchthygiene 11:35 - 37.

Gall C H, Stier C H and Younan M 1992 Small ruminants in developing countries, Target for biotechnology. Symposium of potentials and limitations of biotechnology for livestock breeding and production in developing countries. Mariense, Germany 119 - 130.

Igboeli G and Rakha A M 1971 Gonadal and extragonaldal sperm reserves of indigenous Central African bulls. Journal of Reproduction and Fertility 25:107 - 109.

Leboeuf B, Manfredi E, Boue P, Piacere A, Brice G, Baril G, Broqua C, Humblot P and Terqui M 1998 Artificial insemination of dairy goats in France. Livestock Production Science 55 (3) 193-203.

Ogwuegbu S O, Oke B O and Akusu M O 1985 Gonadal and extragonadal sperm reserves of Maradi (Red Sokoto) goat. Bulletin of Animal Health and Production in Africa, 33: 139-141.

Steel R G D and Torrie J O 1980 Principles and Procedures of Statistics. Mc Grew-Hill Book Co. Inc. New York.

Sumberg J E and Cassaday K 1985 Sheep and goats in humid West Africa. Proceedings of the Workshop on Small Ruminant Production Systems in the Humid Zone of West Africa 23-26 January 1984 International Livestock Center for Africa, Addis Ababa, Ethiopia. J E Sumberg and K Cassaday editors, pp 3 - 5.

Swierstra E E 1966 Structural composition of Shorthorn bull testes and daily spermatozoa production as determined by quantitative testicular histology. Canadian Journal of Animal Science 46: 107.

Swierstra E E 1968 A comparison of spermatozoa production and spermatozoa output of Yorkshire and Lacombe boars. Journal of Reproduction and Fertility 17:459-469.

Ugwu S O C and Orji B I 1984 Ejaculate characteristics of West African Dwarf goats. Nigerian Journal of Animal Production 11 (1): 94.

Upton M 1985 Returns from small Ruminant Production in South West Nigeria. Agricultural Systems 17 (2): 65 - 84.

Vandenberg J G 1971 The penile smear: an index of sexual maturity in male golden hamsters. Biology and Reproduction 4:234 - 237.

Van Soest P J 1982 Quality of Feedstuffs. In Nutritional Ecology of the Ruminant. O and B Books. Inc. Corvallis, Oregon, U.S.A. pp23

Weisgold A D and Almquist J D 1979 Reproductive capacity of beef bulls VI. Daily spermatozoal production, spermatozoal reserves, dimensions and weight of reproductive organs. Journal of Animal Science 48: 351 -358.

Wilson R T 1989 Reproductive performance of African indigenous small ruminants under various management systems: a review. Animal Production Science 20:265 - 286.

Received 26 May 2006; Accepted 5 July 2006; Published 14 September 2006

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