Abstract
Simple SummaryAn understanding of the basic mechanisms of reproduction in donkeys is essential, for several reasons. Some donkey breeds are threatened or endangered, and efforts to save these species depend on improved knowledge of reproductive processes. In some parts of the world, donkeys continue to be valued for purposes of work, recreation, or even meat or milk production, as well as the breeding of mules, and reproduction is essential to maintain suitable populations. In others, donkey populations have become feral and represent a nuisance or even a danger to human populations, and improved contraceptive methods are required. Whether for enhancing or inhibiting reproduction, species-specific information is valuable. While the mare has been extensively studied, few studies have explored early pregnancy in jennies. Therefore, this study characterized early embryo development and differences in progesterone profile and changes in the corpus luteum between pregnant and non-pregnant jennies.We aimed to characterize early embryo development and changes in corpus luteum (CL) development and progesterone profile in pregnant vs. non-pregnant jennies. Eight jennies were enrolled in the study. In the first two cycles, the jennies were monitored by transrectal ultrasonography and had blood harvested for hormone profile assay. In the third cycle, jennies were bred by a jack of proven fertility. Jennies were then monitored and sampled for up to 30 days of pregnancy. Data were evaluated by random-effects multiple linear regression, and correlations were expressed as Pearson’s correlation coefficient. Progesterone concentration rose rapidly from ovulation (D0) until D7, plateaued until D12–14, then precipitously declined between D14 and 15, remaining low until the next ovulation in non-pregnant cycles. In the pregnant jennies, the progesterone concentration rose to maximal concentrations on D7–11, being higher at this stage than in non-pregnant cycles, then declined gradually up to D30. In all cycles, the volume of the CL increased steadily until D6, when it plateaued in pregnant jennies. For non-pregnant jennies, CL volume decreased slowly from D6 to D11 and then had a faster drop. Uterine tone increased following ovulation, becoming turgid around the day of embryo fixation (D15.0 ± 0.9). An embryonic vesicle (EV) was first detected on D9.3 ± 0.5 (2.4 ± 0.5 mm). The EV remained spherical until D18.6 ± 1.4. The embryo proper was first detected ventrally in the vesicle on D20.8 ± 1.1 and the embryonic heartbeat by D22.0 ± 0.9. The allantoic sac was identified at D24.0 ± 0.9, and at D30, the allantoic sac filled the ventral half of the EV. This study provides evidence that higher cumulative concentrations of progesterone are correlated to size of the EV, and there were changes in the luteal dynamics and progesterone profiles in pregnant vs. non-pregnant jennies.
Highlights
During particular life phases, such as pregnancy and lactation, female animals have to face physiological demands and adaptation
The published literature focuses on the significant differences between jennies, mares, and ponies, but one study has described some characteristics of early pregnancy in jennies [7]; none fully define the daily progression of jennies’ early pregnancy
A positive correlation between systemic progesterone concentration and preovulatory follicle (POF) has been previously reported in mares [29], only moderate to weak correlation was observed in the present study, which is in accordance with another study in mares [28]
Summary
During particular life phases, such as pregnancy and lactation, female animals have to face physiological demands and adaptation. Despite the action of homeostatic mechanisms to maintain blood parameters within physiologic levels, changes in metabolites and hormones occur as a result of increased metabolic demands in pregnant animals. These changes are not necessarily indicative of disease, but make animals physiologically unstable and more susceptible to a number of metabolic diseases at this stage than during other life periods, compromising health status, welfare, and productivity. The use of ultrasonography to evaluate pregnancy development and fetal wellbeing has been well described, since 1980 [10,11], and endocrinology during gestation has been extensively studied in mares [12,13]. There is a lack of information regarding jennies’ pregnancy, and horse guidelines are often applied for this species [14]
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