Evaluation and characterization of semen quality in rams of Menz, Dorper and Awassi crosses in different seasons in Ethiopia

S Goshme, S Banerjee¹, M Rekik², A Haile², E Yitagesu and T Getachew²

Debre Birhan Agricultural Research Center, P O. BOX 112, Debre Birhan, Ethiopia
shenkutegoshme@yahoo.com
¹ Hawassa University, Collage of Agriculture, P O. Box 05, Hawassa, Ethiopia
² International Centre for Agricultural Research in the dry Areas (ICARDA), Addis Ababa, Ethiopia

Abstract

The study was conducted at Debre Birhan Agricultural Research Center, with the aim to study season and genotype factors which influence semen quality traits of Awassi x Menz, Dorper and Menz rams using the artificial vagina collection technique. Semen quantity and quality were evaluated for 18 rams; 6 each of Menz, Dorper and Awassi x Menz (AXM) breed and cross. All semen quality traits were influenced by genotype and season, while mass motility of semen was similar across the genotypes. Semen taken from rams during short rain and dry seasons had higher number of live spermatozoa and lower number of abnormal spermatozoa than in long rain season. Dorper rams were superior for semen volume and concentration while Menz rams were superior in normal and live spermatozoa percentage. The correlation between semen quality with volume and concentration of semen was low (r = 0.22 and 0.23). By contrast, the correlation between volume and concentration was 0.77.

Key words: fertility, genotype, reproduction, season, sheep

Introduction

Small ruminants and specifically sheep are important for the subsistence, economic and social livelihood of small-holder farmers in the highlands of Ethiopia. Improvement in flock performance by selection of breeding rams based on phenotypic data is still the most practiced method for the genetic improvement of livestock in Ethiopia. However, evaluation of breeding rams on the basis of their reproductive traits has not yet been studied in Ethiopia although research on this topic has been reported from other countries (Salhab et al 2003; Mohammed et al 2006; Kridli et al 2007).

The objective of this research was to assess the effects of season and genotype factors on semen quality traits of rams of three breeds: Awassi x Menz, Dorper and Menz, using the artificial vagina collection technique.

Materials and methods

Description of the study area

The study was conducted at Debre Birhan Agricultural Research Center (DBARC) in the cool highlands of central-northern of Ethiopia, located at latitude of 9^ᵒ 36’N, longitude 39^ᵒ 38’E, and altitude of 2780m above sea level. The climate is characterized by bimodal rainfall of long rainy season (June-September), short rains (February-May) and dry season (October-January) (Table 1).

Animals and their management

Rams (n=18) of three genotypes (Menz, Dorper and Awassi x Menz) were purchased from farmers. Ages of the rams were 42-60 months. The average body weights for Menz, Awassi x Menz and Dorper were 38.4, 52.5 and 65.9kg, respectively. Corresponding body condition scores (Evans and Maxwell 1987) were 3.25, 3.5, and 3.9. Before semen collection, scrotal circumferences were 28.5, 29.3 and 32 cm for Menz, Awassi cross and Dorper, respectively. Ewes in estrus were used as teasers. Two rams of Dorper genotypes died during the study.

The rams were housed at night and grazed during the day with supplementation of commercial concentrate and hay in the morning and evening. Hay was fed ad libitum and concentrates based on body weight: 400, 500 and 600g/d for Menz Awassi cross and Dorper, respectively. The concentrate had 19.9% crude protein. The feeding started 56 days before the semen collection date. The pedigree animal data from research centers and ranches were used for genetic parameter estimation. The rams were trained on the artificial vagina collection method. The artificial vagina was prepared from smooth rubber with conical shape meant for small ruminants.

Data collection

The semen collection was undertaken for a period of twelve months encompassing all the seasons. About 393 ejaculations were collected from the rams. Annually the season was divided according to the methods suggested by Fekadu (2015). The parameters to assess the quality of the semen were ejaculation volume, color of semen, mass motility of semen, concentration of spermatozoa, live spermatozoa, normal and abnormal spermatozoa. Breeding soundness examination was by inspection of genital organ (e.g: prepuce, sheath and scrotal circumference).. Libido was assessed (Evans and Maxwell, 1987) during semen collection and scored from 1 to 5.

• Excellent (5); when the ram on introduction to the test pen is anxious to mount the teaser ewe such that the staff are unable to hold it still.
• Very good (4); the ram mounts immediately the teaser but the staff able to control it.
• Good (3); the ram when brought to the teaser sniffs around it and after 1-2 minutes it starts to mount.
• Poor (2); the ram sniffs around the teaser for a few minutes and mounts it within 3-4 minutes and collapses the artificial vagina, repeats mounting during which it ejaculates.
• Very poor (1); no interest to sniffing or mounting.

Semen was continued from all the rams every fortnight for 12 months according to the above-mentioned method. The color of semen was scored subjectively and classified as: milky, watery, thin creamy, creamy and thick creamy (Evans and Maxwell, 1987). After checking the color, the semen was immediately stored at 35°C temperature in a water bath to evaluate the quality of the fresh semen as follows:

1. Semen volume per ejaculation (ml),
2. Fresh sperm motility (score 0-5),
3. Sperm concentration and morphology.

The volume was measured in a graduated tube. Sperm cell concentration was measured using spectrophotometer (Evans and Maxwell, 1987). Sperm mass motility was estimated subjectively by using a phase contrast microscope. A micro-pipette was used place semen on a slide which was then covered with a cover slip and observed at magnification of 10x on the objective lens. The mass motility was graded from zero to five based on the intensity of wave motion as described by Evans and Maxwell (1987). According to these methods:

0. Zero; all spermatozoa are immotile (motionless)
1. Very poor; very few spermatozoa are active about 10% (weak movement around),
2. Poor (some movement of semen was visible about 20-40% of spermatozoa were live but poor motility),
3. Fair (small, slow moving wave 40-70% of sperm cells were active
4. Good (dense, vigorous wave movement 75-90% of sperm cells were active
5. Very good (cloudy, dense and rapidly moving waves more than 90% of spermatozoa were active.

The morphology of the sperm was assessed using stained slides with Eosin Nigrosin strain. The ratio of live and dead sperm cells and abnormality of the head, mid and tail was evaluated using a phase contrast microscope at the magnification of 100X. Percentage of live spermatozoa were estimated after smearing fresh semen on a slide using a pipette and putting a drop of fresh semen on a pre-warmed microscope slide and then staining with Eosin-Nigrosin staining methods and products (Evans and Maxwell, 1987). A drop of Eosin, four drops of Nigrosin and a drop of semen are placed on a clean, grease free slide, then the semen was mixed first with Eosin and then immediately with Nigrosin stain. The mixture is pt on the edge of a slide and pulled across the top of another slide, leaving a smear, thereafter it was air dried. Two hundred spermatozoa are counted under oil immersion at a magnification of 100X in different areas of the smear and classified as live spermatozoa, normal head, abnormal head, mid piece abnormal and tail abnormal (Evans and Maxwell 1987).

Statistical analysis

The effect of genetic, non-genetic factors and their interaction were determined for:

1. all the sperm quality criteria: volume, concentration, motility and other parameters;
2. libido, body weight and body condition of the rams

The statistical analysis was done according to the general linear model in the ANOVA program of the SAS 9.0 program. The model was as follows;

Y_ijkm = µ + B_i + S_j + W_k + E _ijkm

Y_ijkm = the dependent variable

µ= the overall mean

B_i= the fixed effect of i^th breed

S_j= the fixed effect of j^th season

W_k= the interaction effect of k^th breed and season

E_ijkm= the residual error

Results

Effect of genotype on semen quality parameters

There was no difference in mass motility of the ejaculate across the genotypes and seasons, whereas color, volume and concentration of spermatozoa all varied across the genotypes (Table 2). Percentage of live spermatozoa varied across genotypes but the differences were small. Abnormality of semen was higher in Awassi x Menz and Dorper when compared to the Menz rams.

Association between genotypes and season for semen quality traits

There were interactions among breeds and seasons on semen quality (Table 3). Abnormal spermatozoa were higher among the Dorper and AXM rams during all seasons. The color of the semen was higher in the Menz rams during the dry and short rainy season with no differences across seasons among the rams of the other two genotypes. Volume and concentration of semen were higher for AXM and Dorper in dry and long rain seasons.

Effect of season and genotype on body weight, body condition scrotal circumference and libido of rams

Body weight and body condition of Dorper rams were higher during the long rain seasons while AXM and Menz showed no differences in body weight and body condition across all the seasons (Table 4). There were no differences between AXM and Menz rams across all seasons on all the parameters studied except libido which was higher for Menz rams during the dry season. The results indicate that libido was highest among the Dorper and AXM rams during the long rainy season, while the scrotal circumference showed no differences across seasons among the rams of all genotypes.

Correlation between different semen quality traits

Body condition score of the rams was correlated with scrotal circumference and libido, whereas scrotal circumference was correlated with volume, concentration and abnormality of the semen (Table 5). Concentration of semen was positively correlated with volume and motility whereas color was negatively correlated with the volume and abnormality of semen.

Discussion

The color of the semen was influenced by the breed of the rams as was reported also by Salhab et al (2003). The volume of semen varied between breeds. The semen volume of Dorper, Awassi cross with Menz and Menz was relatively higher than in the report of Al-Samarra (2009) for Karradi and Arrabi breeds and comparable with other studies on Nari, Suvarna Pramenka rams (Tejaswi et al 2016). The average semen volume of Awassi rams in another report was 1.2ml (Salhab et al 2003) and 1.53ml (Oláh et al 2013) in growing and adult Awassi respectively. In the current study, ejaculation volume of Dorper rams was 1.14ml, which agrees with Malejane et al (2014), using different collection techniques (artificial vagina and electro ejaculator) to evaluate semen quality of Dorper rams. Our study indicated that season is not influencing the volume of semen of rams which, agrees with findings of Malejane et al (2014) concerning seasonal variation in semen quality in Dorper rams with different collection techniques.

Volume of ejaculate was correlated with scrotal circumference and semen concentration. The larger scrotal circumference had a large volume of ejaculated semen and high concentration of spermatozoa. This agrees with many findings (Malejane et al 2014: Kridli et al 2006; Tejaswi et al 2016) which reported on breed and seasonal variation on semen quality traits. The indigenous ram (Menz) ejaculation volume of semen was lower than other reports for Iraq cross breed rams (Moghaddam et al 2012); Awassi rams in Jordan (Kridli et al 2007); Dorper rams in South Africa (Malejane et al 2014); and Awassi in Syria (Salhab et al 2003).

The mass motility of spermatozoa was similar during the study period. This indicated that the motility of spermatozoa collected from different ram genotypes and in different seasons was not affected by breed and seasons which was similar to reports of Salhab et al (2003), David et al (2007) and Moghaddam et al (2012). Therefore, it may be concluded that the three breeds in the study area are not seasonal breeders as measured by sperm motility. Thus reproductive performance and semen characteristics were similar throughout the breeding season as well as during the year. However, these results disagree with those of Martin et al (2013), Kridli et al (2006) and Malejane et al (2014) who all reported that spermatozoa motility in different genotypes of rams are affected by season and genotype. High spermatozoa motility is suggested by many researchers as a good indication of high semen quality with acceptable fertilizing ability. In the study of Moghaddam et al (2012) in Iraq, cross breed rams (Ghezel x Baluchi and ArkharMerino x Ghezel) there was no significant difference in mass motility of ram semen in all seasons which agreed with the current finding, whereas progressive mass motility of ram spermatozoa wa higher during the breeding season (autumn and summer) (Kridli et al 2007; Mohammad et al 2006; David et al 2007). In addition, mass motility scoring greater than three is accepted as suitable for artificial insemination and cryopreservation (Malejane et al 2014; Martin et al 2013).

The current study on semen mass motility of Dorper was a score of 3.4 in all seasons and similar to the report of Malejane et al (2014) for different seasons for Dorper rams in South Africa. Our study further indicates the mass motility of ram semen is not influenced by ram body condition and body weight. This is a similar result with Kridli et al (2006) and Moghaddam et al (2012).

The spermatozoa concentration of semen was influenced by breeds and the seasons. The current result indicated that the dry season was the time for higher spermatozoa concentration than short and long rain seasons of Ethiopia. There was a significant genetic variation in semen concentration which is in agreement with many findings (Malejane et al 2014; Mohammad et al 2006; Martin et al 2013). Spermatozoa concentration of Menz rams was very low in contrast with Dorper and Awassi cross Menz, This might be due to the small size of the breed, but was much higher than Karradi and Arabia breeds of Iraq (Al-Samarrae, 2009). The Awassi cross with Menz has spermatozoa concentration of 3.34 x 10⁹ sperm/ml but was lower than the value of 4.9 x 10 ⁹ sperm/ml reported by Kridli et al (2006) for local Awassi rams in United Arab Emirate, and 4 x 10⁹ sperm/ml reported by Salhab et al (2003) for Awassi in Syria.

Spermatozoa concentration had a strong correlation with body weight and scrotal circumference of the ram and mass motility of the semen, whereas there were no correlations with other parameters like body condition, libido and color. The percentages of live spermatozoa varied between breeds and seasons.

Determination of live spermatozoa is important in assessing the semen meant for artificial insemination. The data in the current study are similar to those reported by Malejane et al (2014) for semen quality of Dorper rams in South Africa. in which collection techniques were compared. According to Malejane et al (2014), live spermatozoa of Dorper rams were affected by the seasons.

Our study revealed that there was significant genetic variation in proportions of sperm morphologically abnormal. This was higher in Dorper rams, followed by Awassi cross with Metz breed. Abnormal headless spermatozoa were recorded in the Menz rams. There was also a seasonal variation in sperm morphologically abnormal which was lower during the dry and short rainy season, whereas it was relatively high in the long rain season; this is supported by other findings (Moghaddam et al 2012; Martin et al 2013).

Conclusions

• Most semen quality traits were influenced by genotype and season
  
  
• Mass motility of semen was similar across the genotypes
  
  
• Semen taken from rams during short rain and dry seasons had higher number of live spermatozoa and lower number of abnormal spermatozoa than in long rain season
  
  
• Dorper rams were superior for semen volume and concentration while Menz rams were superior in normal and live spermatozoa percentage
  
  
• The correlation between semen quality with volume and concentration of semen was low (r = 0.22 and 0.23). The correlation between volume and concentration was 0.77

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