Effect of genotype on the morphometric differentiation of the reproductive organs and sperm reserves in the Nigerian local chicken

U K Oke and C Ihemeson

Department of Animal Physiology and Breeding, College of Animal Science and Animal Production, Michael Okpara University of Agriculture, Umudike, Umuahia, Abia state, Nigeria, West Africa
dumukal@yahoo.com

Abstract

Fifty-four adult Nigerian local cocks (18 normal, 18 frizzle, and 18 naked-neck feathered birds) aged 20 weeks old were used to determine the effect of genotype on morphometric differentiation of the reproductive organ and sperm reserve in a complete randomized design experiment. Semen was collected once per week using massage technique for six weeks and examined for semen volume, concentration and motility. The reproductive organs were also evaluated.

The result showed no statistical difference (P>0.05) in the total reproductive organ mean weight values of the three genotypes, normal (14.1g), naked neck (11.2g) and frizzle (11.6g) respectively. There was no genotype effect (P>0.05) on body weight of the birds. However, the normal feathered bird had higher (P<0.05) semen volume (0.25±0.02ml) than frizzle (0.15±0.03ml). Percent sperm motility was significantly higher for normal (77.9%) and naked neck (65.8%) and least for frizzle (52.5%) cocks. Significant difference (P<0.05) were also noted for the three genotypes for sperm concentration with frizzle having the least value. The mean weight of the testis of the frizzle cocks (7.07g) showed a significantly lower (P<0.05) value from the normal (11.7g) and naked-neck (10.1) cocks respectively. The genotypes showed as positive and significant correlation between semen concentration and motility. However, there was a negative correlation between semen concentration and semen volume. 

Therefore, normal feathered cock and naked neck cock may be considered as potential candidate for use in either natural mating or artificial insemination programmes aimed at improving the reproductive performance of the local chicken.

Keywords: Indigenous cock, plumage reducing genes, semen characteristics, sex organs

Introduction

Nigerian local chicken have small body size, poor growth, small egg size and poor reproductive performance. These characteristics make them an undesirable stock in a complete economic situation (Oke et al 2007). However, local chickens are known to have some desirable traits such as tolerance and resistance to certain tropical diseases. Horst (1988) observed that the genetic resource base of the indigenous chicken in the tropics is rich and should form the basis for genetic improvement and diversification to produce a breed adapted to the tropics.

Three distinct genotypes can be identified in the local chicken (Oke et al 2007). It is necessary to evaluate the reproductive performance of tropical birds to help in selecting those males that could be used in breeding programmes and for sustainable meat and egg production in Nigeria. There are differences between species in the volume of semen concentration and total number of spermatozoa in an ejaculate. Differences in volume and sperm concentration depend largely on the relative contribution of the various reproductive glands (Hafez 1987). The reproductive traits of a male chicken consist of the paired testes, the Epididymis, the vas deference and the rudimentary penis (Lake et al 1985). However, basic morphometric data of the reproductive organs and sperm reserve of the three genotypes (frizzle, naked-neck and normal feathered chicken) are limited. The efficiency of this study will help in improving breeding practices, since a baseline for assessment of the reproductive organs in relation to the sperm reserves of the genotypes will be established. Therefore, the experiment was designed to evaluate the ejaculate quality and the sperm reserve of the testes in the three genotypes.

Materials and methods

The experiment was conducted at the poultry unit of the Teaching and Research farm, Michael Okpara University of Agriculture, Umudike, Abia State, Nigeria. A total of 54 adult local chicks (18 frizzle, 18 naked neck, and 18 normal feathered birds) aged 20 weeks were evaluated. The cocks were quarantined for a period of three weeks. During this period the cocks were vaccinated against Newcastle disease. At the end of the quarantine period, each group of cocks were housed separately, each genotype was replicated three times with 6 cocks per replicate in a deep litter and was fed commercial poultry ration containing 16.5% C.P, 2400 kcal/kg M. E and water offered ad libitum.

Prior to actual semen collection, cocks were trained daily for semen collection by the massage technique described by (Hafez 1987). This was considered necessary not only for effective semen collection but also to make the cocks familiar with the semen collector. Actual semen collection lasted for six weeks at which one ejaculate was collected weekly from each replicate. Weights of the cocks were recorded before semen collection with a weighing scale. Ejaculates were subjected to physical evaluation of semen colour (visual observation), semen volume (calibrated tube), and sperm concentration (Haemocytometer count, Ayorinde  and Ayeni 1984). Semen motility was estimated on microscopic stage at temperature of 37-39^oC under x4 magnification. Sperm morphology was assessed by differential staining according to White (1971).

Two birds from each genotype were slaughtered for assessment of the reproductive organ and sperm reserve at the end of the semen collection. The testes as well as all the accessory organs were weighed separately after carefully freed from fat. Their weights were determined by using sensitive weighing scale.

Experimental design and statistical analysis   

The cocks were assigned to three groups in a completely randomized design  The statistical model used was

Y_ij = µ + T_i + e_ij

Where:

Y_ij = the j^th observation in i^th treatment (genotype)

µ = common mean

T_i = effect of the treatment (genotype)

E_ij = experimental error, which was assumed to be independently, identically and normally distributed with zero mean and homogenous variance.

Analysis of variance was carried out on rooster traits and correlations between male trait at 24 and 28 weeks of age was done.

Results and discussion 

The total reproductive organ weights of the genotypes are shown in Table 1.

There were no statistical difference (P>0.05) within the mean values of the three genotypes reported in this study for normal (14.1± 0.85g), naked-neck (11.3 ± 1.69g) and frizzle (11.7 ±3.69g), respectively. This result indicates that the total organ weight were quantitatively similar. The range of values here recorded falls below the range of values (62.3±0.60) for a starcross broiler strain and for a warren-rose  broiler strain (57.4±0.20) reported by Onuora (1985).The role of these portions (vas deferens testes and Epididymis )  in semen output in domestic fowl is well known (Hafez 1987). The sizes of these organs are related to semen output and that is why birds which have large size of reproductive organ may produce larger quantity of semen. The testes of the frizzle cock showed a significantly (P<0.05) lower value from normal and naked neck cocks respectively. The values for the three genotypes were lower than the value recorded by Onuora (1985) in hyperco goldlink strain (42.1±6.3 g) and starcross broiler strain (43.3±5.20g) respectively. No significant difference was recorded in the mean values of right vas deferens, left vas deferens and epididymis of the three genotypes. In view of the low organ weight, it may not be the best for selection rather crossbreeding may be more advantageous.

Semen quality traits and body weight of different genotypes are presented in Table 2.  Normal and naked-neck individuals had significantly (P<0.05) higher semen volume than their frizzle counterparts.

The normal birds which had higher mean value of reproductive organ had higher semen volume. This result agrees, with the reports of Nwachukwu et al (2006) and varied with the reports of Ezekwe and Machebe (2004) who observed that naked-neck and frizzle cocks produced more semen than the normal cock in the humid tropics. The range of semen volume (0.15-0.25ml) recorded in this study falls below the range of values (0.25-0.35ml) in domestic fowl reported by Burke (1984).

Percent sperm motility was significantly higher for normal and naked-neck and least for the frizzle cock. Significant differences (P<0.05) were noted for the three genotypes for sperm concentration with frizzle having the least value.

The study did not detect any genotype effect (P>0.05) on body weight. However, the higher semen volume of the normal and naked-neck cocks could probably be a result of the larger body size.

Live body weights, reproductive organ weight relative to body weight of the genotypes are shown in Table 3.

The result of this study shows that in general, distribution of sperm within the genital tract was similar for the three genotypes. The general trend in the proportional distribution of sperm shows that testes in all the genotypes contains more sperm with regard to their mean genital weights followed by epididymis and vas deferens which has the least content of sperm. Mean values of these organs recorded was slightly higher than values reported by Onuora (1985) in Warren Rose broiler strains.

The sperm morphology of the genotypes is shown in Table 4.

Means of the bent tails of frizzle cocks were significantly (P<0.05) different from normal and naked neck. Normal and frizzle cocks produced ejaculates with highest percent bent tails while the least percent were obtained from naked-neck cocks. The mean percent bent tails were however, within the range of values reported by Oguike et al (2000). Means of the abnormal heads of frizzle cocks were significantly (P<0.05) different from normal and naked neck. Sperm abnormalities were not significantly (P>0.05) different with cytoplasmic droplets and tailess of the three genotypes. The results indicate that inclusion of frizzle cock for breeding may not be more suitable for either natural mating or artificial insemination purposes aimed at improving the reproductive performance of the local chicken.

The correlation among the traits measured on the genotypes at week 24 is shown in Table 5.

The genotypes showed a positive correlation between semen concentration and motility. This implies that as one trait increases the other increases. This corresponds with the findings of Mc Daniel et al (1995) who noted that the evaluation of the male for breeding soundness must be based on motility and concentration Correlations among fowl traits at 26 and 28 weeks of age followed the same trend as in week 24, except for a negative correlation between semen concentration and semen volume at 28 weeks of age, with -0.86 in normal and -0.39 in frizzle respectively. This is an indication that volume may not be a good indicator of semen viability and fertility.

The results of this study suggest that the three genotypes studied namely, normal, naked-neck and frizzle cocks were really distinct on their morphometric characteristics. This is an indication that assessment of reproductive organ is important from the point of view of primary breeding. Selection of genotype with large testicular size and better semen quality will be good for breeding programme. Therefore, inclusion of normal cock and naked-neck cocks are more suitable for breeding and therefore may be considered as potential candidate for use in either natural mating or artificial insemination programmes aimed at improving the reproductive performance of the local chicken.

Conclusion

• There is an indication that assessment of reproductive organ is important from  the point of view of primary breeding. 

  
  

• Inclusion of normal feathered cock and naked neck cock are more suitable for breeding and therefore may be considered for use in either natural mating or artificial insemination.

References

Ayorinde K. L and  Ayeni J S O 1984 Improving fertility in the exotic guinea fowls in Nigeria through artificial insemination. Kanji Lake research Institute Annual report Pg203-208

Burke W H 1984 Avian Reproduction. In: Dukes physiology of domestic animals 10^th Edition. M I Sirenson (Editor) Cornel University Press, New York. Pp 847-862.

Ezekwe A G and N S Machebe 2004 Effect of dry season on the ejaculate characteristics of three genotypes of local cocks in the humid tropics. Proceedings of the 9^th Annual Conference of the Animal science Association of Nigeria (ASAN) September 13^th-16^th, 2004, Ebonyi State University, Abakiliki, Nigeria. Pp 239-241.

Hafez E S E 1987 Techniques for improving reproductive efficiency. In: reproductive in farm Animals. 5^th Edition. Philadelphia, PA, USA. Lea and Febifer. Pp 455-497.

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Oke U K, Herbert U, Ebuzoeme C and Nwachukwu E N 2007 Effect of genotype on heamatology of Nigerian local chicken. In: Proceedings of the 32^nd Animal Conference of the Nigerian Society of Animal Production NSAP Calabar, Nigeria. Pp 123-125.

Onuora G I 1985 The effect of semi-castration on sperm reserve of cockrels on a restricted dietary intake, sperm resources and deposition of sperm in different starins of cockrels. Animal Reproduction Science 9 (3): 285-293.

Nwachukwu E N, Ibe S N and Amadi U 2006 Effect of genotype and frequency of semen collection on semen characteristics of local chicken cocks in the humid tropics. Journal of Animal Science and Veterinary Advances  5 (7): 562-565 http://www.medwellonline.net/fulltext/java/2006/562-565.pdf

WhiteI G 1971 Physiology of mammalian semen. In: Reproduction in farm Animals. 3^rd edition. Philadelphia. Lea and Febiger. Pp 113-114.

Received 30 September 2009; Accepted 5 January 2010; Published 1 March 2010

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