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Study on reproductive activity and evaluation of breeding soundness of jacks (Equus asinus) in and around Debre Zeit, Ethiopia

Alemayehu Lemma and Benti Deressa

Addis Ababa University, Faculty of Veterinary Medicine, Department of Clinical Studies; P. O. Box 34, Debre Zeit, Ethiopia


An evaluation of the reproductive performance and breeding soundness of jacks was carried out through a study on phenotypic traits (n=107), castrated jacks (n=22) and semen evaluation (n=3). Measurements including age, body condition score (BCS), body weight and testicular parameters were taken. Semen was collected using artificial vagina and was subjected to both gross and microscopic evaluation.


The overall mean (±SD) BCS, age, and body weight for the jacks in the phenotypic study were 3.32±0.8, 11.1±4.7years, and 126 ±14.6kg, respectively. There was a significant difference (p<0.05) in the mean scrotal circumference between the different BCS categories. A highly significant (p<0.001) difference was observed in scrotal circumference among the different age groups with adult animals having the largest scrotal circumference. The mean (±SD) testis weight of the castrates was 276±33g while the ratio of testis weight to body weight was 1:2.1. A significant correlation was found between testis weight and scrotal circumference (r=0.43, p<0.05), testis weight and BCS (r=0.47, p< 0.05), and testis weight and body weight (r=0.81, p<0.001). The mean (±SD) semen volume was 39.9±14.5ml. The mean (±SD) jell-free volume, motility and sperm concentration were 28.8±10.7ml, 85.4±8.6%, and 533 ± 33.1 x 106/ml, respectively. BCS, scrotal circumference and testis weight were significantly correlated to sperm concentration (p<0.05; r=0.69; r=0.85 and 0.80, respectively). The mean time to erection was 3.3 minutes while length to semen collection was 5.4 minutes.


The present study shows critical evaluation of the phenotypic traits to be important for stud selection and breeding soundness evaluation of jacks such as in artificial insemination.

Keywords: Ethiopia, jacks, reproductive performance, semen analysis, testicular parameters


Donkeys have been important to the subsistence strategies of many communities in semiarid regions where they are used for transport and other energy consuming tasks (Blench 1997). Particularly in rural areas Ethiopia, they are used on a daily basis to carry out numerous tasks from household chores to providing transport and draft in agricultural operations (Alemu et al 1997). With 5.2million donkeys, Ethiopia possesses the second largest donkey population in the world and nearly 40% of Africa’s donkey population.


Though there is increasing interest in use of donkeys as draft animals, there is little published information on their biology (Blackway 1994). The need to improve the reproductive performance of indigenous breeds of donkeys has not received the attention it deserves. Results of available studies indicate that male and female donkeys in Ethiopia generally reach puberty at 4years of age and females foal at about 5 or 6years of age (Lemma 2004). Breed characterization of donkeys in Ethiopia is virtually absent and no work has been initiated to consider the use of reproductive technologies like artificial insemination (AI). This technology is relatively well developed in horses and good results have been obtained (Loomis 2001, Squires 2005), it could also be applied to donkeys. This study was therefore, aimed at evaluating the reproductive activity as determined by phenotypic parameters and conducting semen analyses of jacks.


Materials and methods 

Study area


This study was conducted in Debre Zeit, located about 45km southeast of Addis Ababa at 8070N Latitude and 390E longitude, at an altitude of 1990 meters above sea level. The annual rainfall reaches 866m with the long rainy season extending from June to September accounting for 84% of the precipitation. The mean annual maximum and minimum temperature ranges are 260C and 140C, respectively.


Study animals


The study involved a total of 132 jacks (129 for phenotypic evaluation, and 3 for semen evaluation). The jacks were local donkeys (Equus asinus) most commonly found in central Ethiopia. The jacks for the phenotypic evaluation were brought to the Donkeys Health and Welfare Project (DHWP) clinic for routine deworming and castration. Only those jacks that were clinically examined and found to be apparently healthy were included in this study. For semen evaluation, three experimental jacks with a history of confirmed normal breeding ability were used. The experimental jacks were dewormed, housed and fed a daily diet of hay supplemented with concentrate.  Water was available ad libitum.


Study design


Phenotypic evaluation and study on castrated jacks


Observational study was conducted on all jacks (n=132). Testicular parameters namely scrotal circumference [cm], testis length [cm], testis width [cm], and other related information such as age [years], body weight [kg], body condition were measured and recorded on a pre-designed form. Measurements were taken using ordinary tape-measure; estimations of body weight were made using a nomogram and BCS was estimated on a scale of 1 - 5 as described in Svendsen (1997). Age was determined by dentition according to Crane (1997). Jacks that were brought for castration (n=20) were among the animals used in this study. Data from two jacks later castrated after the semen analysis study were also included. Variables such as age, body condition, body weigh, testis width, testis length, scrotal circumference were taken before castration. The testes of each castrated jack was collected and weighed individually on a laboratory scale.


Semen collection and evaluation


Experimental jacks (n=3) were subjected to breeding soundness examinations before semen collection. They were additionally allowed to individually interact with jennies on heat for 30 minutes on daily basis until females were anoestrus. Semen was collected according to the method described in Prudy (2005), using Missouri model Equine Artificial Vagina (EAV) twice a week for 2 weeks. Immediately after collection, the color and the total volume of the semen [ml] were recorded.  The semen was then filtered and the gel-fraction removed and placed in water bath at 370C. Aliquots were removed from the gel-free volume for microscopic evaluation: sperm concentration [Million/ml], progressive motility [%] and live to dead ratio [%]. The pH of the semen was determined using pH-meter. Sperm concentration was measured using hemocytometer according to the methods described by Macpherson (2001). Sperm cell concentrations were expressed as the number of cells per ml using the formula given in Bearden et al (2004).

Number of sperm/ml = Number of sperm in 0.1mm3 * 10 * Dilution rate * 1000


Data management and analysis


All data computations were performed using SPSS for Windows (Version 11, 2002 USA). Data obtained both from phenotypic evaluation and semen analyses were described using descriptive statistics. The age of jacks was arbitrarily categorized as young (≤ 6years), adult (6 – 12 years) and old (> 12 years) based on the most frequently reported average age at puberty of 4 years and an average life expectancy of 12 years (Lemma 2004). Body condition was also arbitrarily categorized as poor (<3), moderate (3) and good (>3) based on the average BCS of 2.5 frequently reported for central Ethiopia. Effects of age and body condition, were analyzed using ANOVA. Correlations between testicular parameters, body condition and body weight were calculated using product moment correlation. Results were considered statistically significant when p< 0.05.



Phenotypic evaluation


The overall mean (±SD) BCS, age, and body weight for the jacks in the phenotypic study (n=107) were in the order of 3.32±0.8, 11.1±4.7years, and 126±14.6kg, respectively. The mean (±SD) scrotal circumference [cm], testicular width [cm] and testicular length [cm] were 20.9±4.45, 7.74±7.87 and 14.0±3.33, respectively. The mean (±SD) scrotal circumference [cm] of jacks with poor (n=24), moderate (n=43) and good (n=40) BCS were 19.2±3.44, 19.9±3.99, 22.5±4.74, respectively. There was a significant difference (p<0.05) in the mean scrotal circumference between the BCS categories. Animals with poor body condition had the smallest scrotal circumference. BCS was positively correlated (r=0.27; p<0.05) with scrotal circumference (Figure 1).


Figure 1.  Relationship between body condition and scrotal circumference of jacks

A highly significant (p<0.001) difference was observed in scrotal circumference among the age groups with adult animals having the largest scrotal circumferences. Age was also positively correlated (r=0.36) with scrotal circumference.


Table 1 shows summary of the phenotypic evaluations for the castrated jacks.

Table 1.  Summary of the phenotypic evaluation of castrated jacks (n = 22)






Age, years










Body weight, kg





Scrotal Circumference, cm





Testis Width, cm





Testis Length, cm





Total Testis weight, g





The ratio of mean testis weight to body weight was 1:2.1. There was no significant (p>0.05) difference between the weights of the left and right testicles. A significant correlation was found between testis weight and scrotal circumference (r=0.43, p<0.05), testis weight and BCS (r=0.47, p< 0.05). Correlation between testis weight and body weight was also highly significant (r=0.81, p<0.001, Figure 2).


Figure 2.  Relationship between body weight and testes weight of jacks
(Testes Weight [g] = -24.8+2.3*Body Weight; 0.95 Confidence Interval)

Behavioral responses and semen evaluation


The most prominent sexual behavior included vocalization, sniffing of the vulva, flehmen reaction, mounting with and without erection, naso-nasal contact, and herding. Vocalization usually occurred immediately after visual marking of the female. Vocalization was more intense in the presence of a competing jack in the vicinity of oestrous female. Periodic vocalization appeared to attract the females while threatening the competing males. Results of analyses of the ejaculates are summarized in Table 2.

Table 2.  Result of semen analysis in the experimental jacks (n=3)
















Body weight, kg





Scrotal Circumference, cm





Testis Width, cm





Testis Length, cm





Sexual Drive, score





Time to Erection, min





Number of Thrust





Length to Semen Collection, min





Total Volume of Semen, ml





Jell-free Volume, ml





Motility, %





Sperm Concentration, Million/ml





pH of the semen





The color the semen varied from deep creamy to light creamy. The percentage of live spermatozoa was 83.5%. BCS, scrotal circumference and testis weight were significantly correlated to sperm concentration (p<0.05, r=0.69, r=0.85 and r=0.80), respectively



Generally the sizes of reproductive organs of jacks are different from those of stallions (Pugh 2002, Hagstrom 2004). The finding that increasing age also increases the scrotal circumference agrees with previous work (Prudy 2005). In this study a strong positive correlation between body condition score and scrotal circumference indicates that an increase in body condition increases scrotal circumference. Hence, it is implied that BCS and age are parameters that may influence scrotal circumference. These results are in agreement with other work conducted on stallions (Naden et al 1990, Blanchard et al 2001).


The study on castrated donkeys indicates that average testis weights were larger than those reported for stallions (Pugh 2002, Hagstrom 2004). The mean testis weight to body weight ratio could be a good indicator considering size differences among individual animals. The significant positive correlation between testis weight and body weight could also be used in selection of jacks for breeding programs such as when AI is used. Similarly, as in the present study different studies also confirm that testis weight and sperm concentration are positively correlated (Prudy 2005, Vidament et al 2007). Results for stallions (Pickett and Voss 1992, Blanchard et al 2001) also confirm that testicular size is a good indicator of sperm production capability. Various researchers (Kreuchausf 1984, Henry et al 1991, Gastal et al 1996) have reported sexual behavioral responses of jacks similar to the observations in the present study. Some strong and obvious sexual behavioral responses like vaginal sniffing and flehmna’s reaction were observed, similar to those reported by Gastal  et al (1996). The current finding on time to erection (3.25 minutes) was lower than earlier reports which ranged from 10 to 16 minutes (Henry et al 1991, Gastal et al 1996). The mean length to semen collection (5.42 minutes) in the present study is less than the 30 minutes recorded by Gastal  et al (1996) and the 10 to 33 minutes reported by Kreuchauf (1984). Since the experimental jacks in the current study were housed near the jennies that were in oestrus it could also be due to a prior stimulation before the actual semen collection. The color of the ejaculate is similar with previous reports for jacks and stallions (Blanchard et al 2001, Varner et al 1987). Some jacks, however, at times produced a light creamy ejaculate that is fewer in sperm count. This was due to inadequate sexual stimulation and low temperatures (below 420C) of the EAV.


Results of the semen analysis in the present study are generally similar to earlier reports for donkeys (Blanchard et al 2001, Prudy 2005, Vidament et al 2007). The mean sperm concentration of the ejaculates (533 ±38.2 billion) is within the range of previous reports by Henry et al (1991) and Prudy (2005). However, the maximum number of spermatozoa found in this study is higher than the report by Prudy (2005). Progressive motility recorded in this study is similar to earlier studies by Henry  et al (1991), Gastal  et al (1996) and Prudy (2005) that reported 83.7%, 95% and 80-90%, respectively. The mean pH of semen in this study is similar to report by Gastal et al (1996)  with an average value of 7.6.





The authors would like to acknowledge Sida/SAREC and the Swedish Government for generously funding the research. Thanks also to the Department of Clinical Studies, FVM and the Donkey Welfare and Protection Trust for the support provided during the laboratory and field data collection.



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Received 31 December 2008; Accepted 4 July 2009; Published 5 August 2009

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