Livestock Research for Rural Development 28 (9) 2016 Guide for preparation of papers LRRD Newsletter

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Effect of age and season on semen traits and serving capacity of Pelibuey rams under tropical conditions

J R Aké-López, N Y Aké-Villanueva, J C Segura-Correa, J R Aké-Villanueva and R C Montes-Pérez

Departamento de Reproducción Animal y Mejoramiento Genético, Facultad de Medicina Veterinaria y Zootecnia, Universidad Autónoma de Yucatán, Mérida, Yucatán, México.


The objective of this study was to evaluate the effect of age  of the ram and season of the year on scrotal circumference, semen traits and serving capacity. Six Pelibuey rams were allocated to two age groups: young (n=3; 9.2 ± 0.3 months) and adult (n=3; 34 ± 6.9 months). Rams were ejaculated once a week, during fall (September-December) and winter (December-March), and semen evaluated. Also, service capacity of the rams were tested during 10 minutes. Scrotal circumference (SC) was evaluated each month. Data on response variables were analyzed using analysis of variance with or without repeated measures, where the fixed effects were breed, season and the interaction breed x season.


There was no breed x season interaction effect (P > 0.05) for all traits. Age and season had effects on SC, sperm concentration and individual motility (P < 0.05). Age had also effect on time at first mating (P < 0.05). In conclusion, most of the traits studied were influenced by age and season of the year; these results may allow to take better decisions in the management to improve reproductive performance of Pelibuey rams.

Key words: hair sheep rams, seminal characteristics, sexual behavior

Efecto de edad y época sobre las características seminales y capacidad de servicio en ovinos Pelibuey bajo condiciones tropicales


El objetivo de este estudio fue evaluar el efecto de la edad del carnero y la época del año en la circunferencia escrotal, características del semen y la capacidad de servicio. Seis carneros Pelibuey fueron asignados a dos grupos de edad: jóvenes (n = 3; 9,2 ± 0,3 meses) y adultos (n = 3; 34 ± 6,9 meses). Los carneros fueron eyaculados una vez por semana, durante el otoño (septiembre-diciembre) y el invierno (diciembre-marzo), y el semen fue evaluado. Además, la capacidad de servicio de los carneros fue evaluada durante 10 minutos. La circunferencia escrotal (CE) se evaluó cada mes. Los datos sobre las variables de respuesta se analizaron mediante análisis de varianza con o sin medidas repetidas, donde los efectos fijos fueron la raza, la época y la interacción raza x época.

No hubo efecto de interacción raza x época (P> 0,05) para ninguno de los rasgos estudiados. La edad y la época tuvieron efecto en la CE, la concentración de espermatozoides y la motilidad individual (P <0,05). La edad también presentó efecto sobre el tiempo al primer servicio (P <0,05). En conclusión, la mayoría de los rasgos estudiados fueron influenciados por la edad y la época del año; estos resultados pueden permitir tomar mejores decisiones en el manejo para mejorar el rendimiento reproductivo de los carneros Pelibuey.

Palabras clave: carneros de pelo, conportamiento sexual, reproducción


In the tropics, the reproductive ability of the ram is eventually evaluated, and commonly only includes the evaluation of the semen quality but not the sexual behavior. For a ram to pregnant a ewe, not only is necessary a good quality and quantity of semen, but the ability of the ram to deposit the semen in the reproductive tract of the ewe (Chenoweth 1981; Silva 2009); low fertility and prolificacy in some flocks could be attributed to low mating behavior of the ram (Stellflug et al 2006; Alexander et al 2012).


Even though Pelibuey rams are known to produce semen and mate all year round, the effect of season on semen quality and quantity and on sexual behavior have been reported (Aguirre et al 2007; Zamiri et al 2010; Cárdenas-Gallegos et al 2012). Also, the inability of young rams to pregnant the ewes when they are introduced the first time to the breeding flock is a common problem. In spite of that, semen quality and quantity of rams is not carried out in a routinely way, and the evaluation of libido and serving capacity is rare (Ibarra et al 1999; Silva 2009). The knowledge of ram reproductive ability under specific conditions will allow technicians and farmers to take management decisions on rams to improve reproductive parameters of the flock (Stellflug et al 2006).


The objective of this study was to evaluate the effect of age and season of the year on the scrotal circumference, semen traits and serving capacity of Pelibuey rams under the tropical conditions of Southern Mexico.

Materials and methods

The study was carried out in the central region of Yucatan, Mexico (20º 58’ N and 89º 37’ W), where the climate is subhumid tropical (Aw0) with rain in summer. The annual temperature average varies from 26 to 27.8 ºC, the relative humidity from 63 to 83%, and the annual rain from 940 to 1132 mm (Orellana et al 2009).


Animals and samplings


Six Pelibuey rams, three young rams with age and body weight averages of 9.2 ± 0.3 months and 38.1 ± 2.7 kg; and three adults rams with age and body weight averages of 34.0 ± 6.9 months and 55.5 ± 4.1 kg, respectively, were used. The body condition score for both age groups was 3, in the scale of 0 to 5 (Russel 1984). The rams were clinically healthy and were fed based on grass (± 6 hours/day) in irrigated paddocks of Star grass (Cynodon plectostachius) plus 400 g/day of a commercial feed (14% crude protein).


The study was carried out from September 2010 to March 2011, in two season periods: Fall (September 21 to December 20) and winter (December 21 to March 20). Semen was collected and evaluated once a week (two ejaculates per ram per day) for a total of 168 ejaculates in fall and 156 in winter. Also, serving capacity of the rams was evaluated. Once a month scrotal circumference was measured using a scrotal tape, and measures taken at the portion with the greatest testicle circumference.


Semen traits evaluation


Semen was collected using an artificial vagina, every Monday from 08:00 to 10:00 hours. The traits measured were volume (VOL), sperm concentration (SpC), spermatic mass motility (MM), progressive sperm motility (IM) and abnormal sperm (Abnormalities). VOL was measured using a graduated collector tube; SpC was carried out counting the number of spermatozoa in a Neubauer chamber and expressed in millions per ml (x106/sperm/ml); MM was evaluated in a semen drop (at 37 ºC), in a scale from 0 to 5, where 5 indicated the presence of dense and fast waves and 0 no waves and spermatozoa moving; IM was determined in a drop of semen diluted in sodium citrate at 2.9%, at 37 ºC and using a scale of 0 to 100%; for abnormalities semen smear stained with Eosin-Nigrosine was used, counting 100 spermatic cells in a scale from 0 to 100% (Aké-López et al 2013).


Serving capacity test


Service capacity was evaluated during semen collection, registered as a mating when the ram mounted, penetrated and ejaculated into the artificial vagina (Stellflug and Berardinelli 2002; Aguirre et al 2007; Cárdenas-Gallegos et al 2015). Once a week (84 test in fall and 78 in winter) the rams were individually exposed to ewe in estro (restrained) in a breeding crate per 10 min in a 3 m x 3 m pen. The number of matings given, the time in seconds taken by the ram to give the first mating (reaction time), the time between the first and the second mating (latency to second mating) and the time between the second and third mating (latency to third mating) were also evaluated.


Statistical analysis


Data on VOL, SpC, MM, IM, abnormalities, scrotal circumference (SC) and serving capacity (Number of mating, reaction time, and latency at the second and the third mating) were analyzed using repeated measure analysis of variance, where the fixed effects were age group (Young and adult rams), season of the year (fall and winter) and their interaction, plus the experimental error, which was the effect of ram nested within age group-season combinations. All statistical analysis were carried out using the SAS package (SAS 2003).

Results and Discussion

There was not interaction effect of age group by season of the year for any of the traits studied; however, age group and season had significant effects (P<0.05) on SC (Table 1). SC was lowest for the young rams and in the fall. These results disagree with those of Chi et al (2009) who working with hair sheep did not find differences between young (1 to 2 years) and adult (3 to 4 years of age) rams. Also, the results disagree with those of Cárdenas-Gallegos et al (2012), who under tropical conditions did not find effect of season in SC of hair sheep (P > 0.05). On the other hand, Kafi et al (2004) in Karakul rams found larger SC in fall (33.3 cm) compared with winter measured rams (31.1 cm; P < 0.05).


Differences in SC between young and adult rams, in this study, could be due to the size or body weight of the rams, because the adult rams weighed 17 kg more than the young rams. Many researchers have shown that body weight is positively correlated with SC of the ram (Salhab et al 2001; Fourie et al 2005). The greater SC found in winter, could be cofounded with a growing effect, because the study started in September and finished in March of the next year. Therefore as the body weight of young and adult rams increased with time so did the SC, as was found also by Sarlós et al (2013).


Age and season in this study, had significant effects (P < 0.05) on sperm concentration. Adult rams and rams measured in winter had a high sperm concentration (Table 1). Similar results were reported by Osinowo et al (1988) in Yankasa rams, who found that as age increased (1.4, 2.4 and 3.4 years of age), the sperm concentration increased (3,421, 4,025 and 4,673 x 106/ml, respectively). Cárdenas-Gallegos et al (2012) found that the sperm concentration was higher in the hot-dry season (3,295.1 ± 93.9 x106/ml; P < 0.05) than in the fresh-humid season (2,755.4 ± 90.9 x106/ml) and hot-humid season (2,615.4 ± 90.7 x106/ml). The highest sperm concentration, found in this study, for the adult rams and in the winter was possibly due to a major testicular volume of the adult rams in winter. Some studies have demonstrated that at a greater testicular size, greater sperm concentration (Gouletsou and Fthenakis 2010; Zamiri et al 2010).


For progressive sperm motility, age effect was significant and was highest in young rams (P < 0.05) (Table 1). This result is similar to that of Osinowo et al (1988) who reported that sperm motility decreased (83.2, 84.6 and 74.0%) as the age of males increased (1.4, 2.4 and 3.4 years of age). With respect to sperm abnormalities, age effect was not significant, but the percentage was greater in fall than in winter (P < 0.05; Table 1), which disagree with the results of Sarlós et al (2013) who found a higher percentage of abnormalities in winter (18.48 ± 3.23 %) and lower in fall (7.95 ± 1.58%; P<0.05).

Table 1. Means (± EE) by age group and season of the year for scrotal circumference and semen traits in Pelibuey rams.


Age group






Scrotal circumference (cm)

29.4 ± 0.83b

31.9 ± 0.83ª

29.4 ± 0.65b

31.9 ± 0.65ª

Volume (ml)

0.63 ± 0.35a

0.48 ± 0.35a

0.53 ± 0.27a

0.58 ± 0.27ª

Sperm concentration (x106/ml)

2535 ± 60.7b

2849 ± 60.7ª

2435 ± 47.3b

2969 ± 47.9ª

Spermatic mass motility (0-5)

4.75 ± 0.11a

4.46 ± 0.11a

4.60 ± 0.08ª

4.60 ± 0.09ª

Progressive sperm motility (%)

88.0 ± 0.86ª

84.8 ± 0.86b

86.4 ± 0.67ª

86.4 ± 0.68ª

Abnormalities (%)

3.81 ± 0.96a

6.12 ± 0.96ª

5.66 ± 0.74ª

4.23 ± 0.75b

a,b Mean in rows with different literals by factor are different at p < 0.05.

In spite of the differences found between the age groups and seasons here studied, the averages of SC and semen traits were within the range of values reported in the literature for sheep and particularly Pelibuey rams (Cárdenas-Gallegos et al 2012, Aké-López et al 2013).


Age had not effect on serving capacity measures except for time at first mating (Table 2) where young rams used a longer time for the first mating (P < 0.05). Chi et al (2009) reported that young rams took longer time to give the first mating than adult rams (91.4 vs 69.8 seconds, respectively). The longer time used by young rams may be associated to a lack of experience in mating the ewes than adult rams. Simitzis et al (2006) comment that both breed and age influence the sexual behavior in Chios rams, adult rams showing a better sexual behavior than young rams. The lack of season effect on serving capacity could be explained by the fact that Pelibuey rams mate during all year round (Arroyo et al 2007; Gündoğan 2007) and to the fact that, this study, was carried out during the fall/winter seasons which correspond to the highest reproductive period for this type of sheep (De la Isla-Herrera 2010; Arroyo 2011). The number of service was not affected by age nor season; the average being similar to that reported by Cárdenas-Gallegos et al (2015) who found a value of 2.71±0.5 matings in Pelibuey rams.

Table 2. Means (± SE) by group of age and season of the year for number of mating and time needed for the first, second and third mating in Pelibuey rams.


Number of

time (s)

Latency to
second mating (s)

Latency to
third mating (s)

Age group


2.8 ± 0.11a

29.1 ± 1.33a

87.0 ± 31.5a

143 ± 62.8a


2.9 ± 0.11a

18.4 ± 1.33b

67.0 ± 31.5a

141 ± 70.2a



2.9 ± 0.08a

24.2 ± 1.03a

67.5 ± 24.4a

136 ± 50.3a


2.8 ± 0.08a

23.2 ± 1.03a

87.2 ± 25.0a

150 ± 53.7a

a,b Mean in columns of different sub-groups without ommon letter are different at P < 0.05



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Received 2 March 2016; Accepted 10 August 2016; Published 1 September 2016

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