Ultrasonographic study of ovarian activities in the tropical jenny during the seasons of high and low sexual activity

doi:10.1016/j.jevs.2005.09.015

Journal of Equine Veterinary Science

Volume 26, Issue 1, January 2006, Pages 18-22

https://doi.org/10.1016/j.jevs.2005.09.015 Get rights and content

Abstract

The ovarian activities of 7 jennies were studied by serial ultrasonography during seasons of higher and lower sexual activity to determine if follicular development also corresponds to this pattern. The current study showed a seasonal pattern of ovarian activities related to the local environmental factors associated with each season rather than photoperiod, which is the widely known environmental cue determining seasonality in most equines. Jennies produced large numbers of follicles (11.3 follicles) during the long rainy season, compared with the 7.3 and 9.6 follicles during the dry and short rainy seasons, respectively. However, production of larger preovulatory follicles (37.8 ± 1.7 mm vs 31.0 ± 2.7 mm of the dry and 33.2 ± 2.7 mm of the long rainy seasons) and higher incidence of ovulation (77.8%) occurred during the short rainy season. Jennies had shorter interovulatory intervals during the season of higher (short rainy) than the season of lower (dry season) sexual activity. The short rain transition is characterized by higher follicular activity compared with the long rainy transition, indicating the presence of additional factors stimulating ovarian activity other than the mere availability of forage during the short rainy season.

Introduction

Several studies confirm that equines in the temperate region exhibit reproductive seasonality.¹ Although information is scarce for tropical jennies, a number of studies support the existence of varying degrees of seasonal differences in follicular activity in animals around the tropics, including mares,² camels,³ and ewes.⁴ Though jennies are believed to be less affected by seasons compared with mares, anecdotal observations show the existence of seasonality in estrus and mating probably related to the level of ovarian activity.

Donkeys in central Ethiopia usually show the highest sexual activity (demonstrated by the incidence of overt signs of estrus and mating) during the short rainy season and the lowest during the dry season of the year. However, it is not known whether ovarian activities also correspond to this seasonal pattern of sexual activity, hence whether a true seasonality exists. There is a general paucity of information on the characteristics of ovarian activity in the tropical jennies. The objective of this study is to describe the ovarian activities during the seasons of high and low sexual activity.

Section snippets

Materials and methods

This study was carried out in central Ethiopia at Debre Zeit, at an altitude of 1990 meters above sea level. The mean minimum temperature was 16°C (60.8°F) and the maximum temperature was 27°C (80.6°F).

Annual rainfall and mean relative humidity are 825 mm (32.5 in) and 52%, respectively. The climate is characterized by bimodal rainfall. The short rainy season occurs from March to May and is preceded by a long dry season occurring between October and February. The long rainy season occurs from

Distribution of follicles

The mean numbers of total follicles were 7.3, 9.6, and 11.3 follicles during the dry, the short rainy, and the long rainy seasons, respectively. There was a highly significant difference (P < .001) in the number of total follicles among the three seasons (Figure 1).

The number of small follicles (2–5 mm and 6–10 mm) was significantly higher (P < .05) during the long rainy season compared with the dry and short rainy seasons, while the number of medium follicles (16–20 mm) was significantly

Distribution of follicles

Seasonality of follicular development in jennies has been previously reported.⁸ On the other hand, studies in both domestic and feral donkeys⁹ show that ovarian activities, pregnancy, and parturition are less affected by season. However, these seasonal variations were due primarily to the effect of photoperiod. Contrary to the inactive ovaries and reduced follicular population observed in equines during anestrus, the ovaries of all jennies in this study were active during all seasons. Because

Conclusion

In this study, a distinct seasonal difference in the patterns of ovarian activity was observed. Higher follicular growth (both in number and diameter of follicles) and higher incidence of ovulation were associated with the short rainy season (period of higher sexual activity). Reduced follicular activities, higher incidences of anovulation, and irregularities in cycling observed during the dry season were most probably attributed to factors such as poor nutrition and/or management rather than

Acknowledgments

The authors would like to acknowledge the German Academic Exchange Service for sponsoring the study and the Faculty of Veterinary Medicine, Addis Ababa University for providing a working place.

References (12)

SquiresEL et al.
Use of ultrasound in reproductive management of mares
Theriogenology
(1988)
GintherOJ et al.
Reproductive seasonality of the jennies
Theriogenology
(1987)
BlanchardTL et al.
Oestrous cycle characteristics and response to oestrus synchronization in mammoth assess (Equus asinus americanus)
Theriogenology
(1999)
GintherOJ
Selection of the dominant follicle in cattle and horses
Anim Reprod Sci
(2000)
LöfstedtR
Reproductive physiology of mares. Web edition
SaltielA et al.
Ovarian activity in the mare between latitude 15 degrees and 22 degrees N
J Reprod Fertil
(1982)

There are more references available in the full text version of this article.

Cited by (6)

Ovarian dynamics and estrous cycle length in the donkey (Equus asinus)
2017, Theriogenology
Citation Excerpt :
Since a single observation is needed to know the diameter of the largest follicle at day 18, and since at least two days (2–12 days) remain before ovulation at the time that this recording is made, the high predictive value of this variable could be of clinical importance. The mean IOI is similar in most reports in donkeys [4–16,23]. Thus, it is possible that the diameter of the largest follicle at day 18 could be used as a reliable predictor of IOI in different donkey breeds.
Nine jennies were monitored daily by ultrasonography during three complete ovarian cycles in order to evaluate if the timing of luteolysis and the growth pattern of the ovulatory follicle (OVF) before, during and after luteolysis are related to the length of the interovulatory interval (IOI). Blood samples for progesterone determination were obtained daily during one of the cycles of each jenny. The cycles were classified according to the length of the IOI into three groups: Short IOI (21.2 ± 0.3 d, n = 10), medium IOI (23.9 ± 0.4 d, n = 7), and long IOI (26.2 ± 0.3 d, n = 10). Neither the time of luteolysis onset nor the time of luteolysis completion were significantly different between groups. The length of the IOI was mainly determined by the duration of the follicular phase, as the intervals from luteolysis onset to ovulation and from luteolysis completion to ovulation were directly correlated with the length of the IOI (p < 0.001 and p < 0.01 respectively). Multiple regression analysis revealed that the length of the IOI was negatively correlated with the size of the OVF at day 13 (p < 0.01), with its growth rate from day 13 to day 15 (p < 0.05) and with its growth rate from day 15 to day 18 (p < 0.01), and positively correlated with the final diameter of the OVF (p < 0.01). The correlation between the observed IOIs and those predicted by the multiple regression equation was highly significant (r = 0.91, p < 0.001), but the predictive ability of a simplified equation using only the diameter of the OVF at day 18 was almost as good (r = 0.89, p < 0.001). Estrus signs lasted longer and were more intense as the length of the IOI increased, and this was associated with a longer period of low progesterone concentrations during the follicular phase of jennies with longer cycles. It is concluded that the length of the luteal phase in jennies is relatively constant, and that most of the variation in the length of the IOI is associated with differences in the size of the OVF at the time of luteolysis onset and with its growth rate during the following five days.
Effects of breed, age, season, and multiple ovulations on cyclic, PGF2α-induced, and postpartum estrus characteristics in Spanish jennies
2016, Theriogenology
Citation Excerpt :
Here, single ovulation was observed in 46.54% of cases, whereas MO attained 53.46% (of which 47.09% double, 5.82% triple, and 0.55% quadruple). Strikingly, a low MO rate of only 8.8% is reported in tropical jennies [16], presumably because of the influence of climate conditions and nutrition regime. The ovulation rate here was significantly lower in first postpartum estrus, whereas jennies treated with PGF2α displayed an increase of ovulations per cycle.
This retrospective, population-based, cross-sectional study analyzed data for a total of 104 jennies reared in southern Spain over the period 1995 to 2014. Intervals to ovulation and incidence of multiple ovulation and pregnancy were charted for spontaneous, PGF2α-induced, and postpartum estrous cycles. In spontaneous estrous cycles, the interovulatory interval varied as a function of breed (P < 0.03) and month of ovulation (P < 0.01), and duration of estrus signs was longer in older jennies (0.04). Spontaneous cycles were also associated with higher ovulation rates from September to January (P < 0.006). When PGF2α was used to induce the estrus, not only did estrus signs last longer in old (P < 0.004) and in polyovular (0.02) jennies but old jennies also displayed significantly higher ovulation rates (P < 0.03). In postpartum jennies, no variations were observed as a function of any of the independent variables analyzed. Comparison of ovulation rates between different types of cycle revealed that postpartum jennies exhibited significantly lower ovulation rates (1.32 ± 0.07) and a lower incidence of multiple ovulation (30.4%) than spontaneous (1.62 ± 0.04, 55.0%) and PGF2α-induced (1.74 ± 0.08, 65.5%) groups. No differences were observed in the incidence of ovulation or pregnancy depending on the location of ovulation in polyovular cycles, and ovulation occurred at similar rates in the right and left ovaries. These findings shed further light on reproductive physiology in jennies and may be of value in improving animal management.
Factors affecting gestation length and estrus cycle characteristics in Spanish donkey breeds reared in southern Spain
2010, Theriogenology
Citation Excerpt :
Although in mares a relation has been postulated between number of ovulations and breed, genetic predisposition and reproductive status [16], no information has been found for jennies. The average interovulatory interval was slightly lower than that reported by other authors [13,25]. Year-on-year variations were noted in this interval, suggesting that annually-changing factors such as nutrition, environment, social interaction, and others, might be involved in determining the length of this interval.
This paper investigated gestation length and estrus cycle characteristics in three different Spanish donkey breeds (Andalusian, Zamorano-Leones, and Catalonian) kept on farm conditions in southern Spain, using data for ten consecutive breeding seasons. Gestation length was measured in 58 pregnancies. Ovarian ultrasonography was used to detect the ovulation, in order to ascertain true gestation length (ovulation-parturition). Pregnancy was diagnosed approximately 14–18 d after ovulation and confirmed on approximately day 60. Average gestation length was 362 ±15.3 (SD) d, and no significant differences were observed between the three different breeds. Breeding season had a significant effect (P < 0.01), with longer gestation lengths when jennies were covered during the early period. Breed, age of jenny, year of birth, foal gender, month of breeding, and type of gestation had no significant effect on gestation length.
After parturition, foal-heat was detected in 53.8% of the postpartum cycles studied (n = 78), and ovulation occurred on day 13.2 ± 2.7. The duration of foal-heat was 4.7 ±1.7 d, with a pregnancy rate of 40.5%.
When subsequent estrus cycles were analyzed, the interovulatory interval (n = 68) and estrus duration (n = 258) were extended to a mean 23.8 ± 3.5 and 5.7 ± 2.2 d, respectively. Both variables were influenced by the year of study (P < 0.03 and P < 0.001), whereas month and season of ovulation (P < 0.005 and P < 0.009, respectively) affected only interovulatory intervals. Estrus duration was significantly longer than that observed at the foal-heat (P < 0.006), and the pregnancy rate was 65.8%.
This study provides reference values for true gestation length and estrus cycle characteristics in Spanish jennies. Breeding season affected gestation length in farm conditions. Also, seasonal influence was observed on the length of the estrus cycle (i.e., interovulatory interval), although foal-heat was not affected by environmental factors.
Structural and Functional Dynamics of the Ovary and Uterus during the Estrous Cycle in Donkeys in the Eastern Caribbean
2023, Animals
Characteristics of follicular dynamics and reproductive hormone profiles during oestrous cycles of jennies over an entire year
2021, Reproduction in Domestic Animals
Follicular size predicts success in artificial insemination with frozen-Thawed sperm in donkeys
2017, PLoS ONE

: Refereed

View full text

Scientific PapersUltrasonographic study of ovarian activities in the tropical jenny during the seasons of high and low sexual activity

Abstract

Introduction

Section snippets

Materials and methods

Distribution of follicles

Distribution of follicles

Conclusion

Acknowledgments

Theriogenology

Theriogenology

Theriogenology

Anim Reprod Sci

Reproductive physiology of mares. Web edition

Ovarian activity in the mare between latitude 15 degrees and 22 degrees N

J Reprod Fertil

Scientific Papers
Ultrasonographic study of ovarian activities in the tropical jenny during the seasons of high and low sexual activity