Reproductive seasonality in the mare: neuroendocrine basis and pharmacologic control

Comprehensive analysis of the whole-transcriptome landscape of the ovarian cortex from Mongolian horses that reproduce seasonally

The reproductive cycle of equines tends to be seasonal and is influenced by factors such as light and temperature. The process and methods of regulating the mare oestrous cycle in the anestrus period are still immature. The effects of noncoding RNAs and mRNAs on the oestrous cycle have aroused much interest, but corresponding analyses of seasonal mare ovaries have not been reported. Here, we report a whole transcriptome analysis of the Mongolian horse ovarian cortex collected in anestrus and diestrus periods. In total, 1081 mRNAs, 205 lncRNAs, 54 circRNAs, and 13 miRNAs were upregulated in winter anestrus ovarian cortex (WAO), and 1261 mRNAs, 90 lncRNAs, 29 circRNAs, and 40 miRNAs were upregulated in summer diestrus ovarian cortex (SDO). The GO and KEGG enrichment analysis of differentially expressed mRNAs and target genes of differentially expressed lncRNAs, circRNAs, and miRNAs revealed some key functions and pathways that may be related to follicle and oocyte development. We found that estrogen-related pathways were enriched in different RNAs. Our data were used to generate miRNA, circRNA, lncRNA, and mRNA databases from the Mongolian horse ovary and differential expression profiles between WAO and SDO; these results provide clues for exploring methods of estrus regulation in mares during the anestrus period.

The usefulness of melatonin in the field of obstetrics and gynecology

Disorders of the female reproductive system, including those associated with hormone regulation, fertility rate and fetal health, are issues of great concern worldwide. More recently, melatonin supplementation has been suggested as a therapeutic approach in gynecological practice. In both animal models and in women, melatonin supplementation suggests a therapeutic and preventative potential, effects attributed mainly to its antioxidant properties and action as hormone modulator. The aim of this literature review is to further investigate the evidence available on the effects of melatonin supplementation in animal and human studies, focusing on its potential application to gynecology. Melatonin-containing supplements are easily found in online and high street retailers, and despite its supplementation deemed to be relatively safe, no consensus has been reached on effective dosage and supplementation period. Short term supplementation studies, of up to six months, suggest that a daily posology of 2-18 mg of melatonin may have the potential to improve fertility rate, oocyte quality, maturation and number of embryos. However, the evidence available so far on the effects of melatonin supplementation covering gestational age and gestational outcomes is very scarce. Clinical trials and longer-term supplementation studies are required to assess any clinical outcome associated with melatonin supplementation in the field of gynecology.

Animal and environmental factors associated with gestation length in the endangered Old Kladruber horse

Little is known about factors influencing gestation length in heavier types of horses. The objective was to assess the effects of the weight and age of mares, weight and sex of foals, lactation, month and year of conception, month of foaling, stallion and mare on gestation length in the endangered Old Kladruber breed that once served as a heavy coach horse for ceremonies of the Imperial Court in Vienna. The study was performed at the stud farm Slatinany, Czech Republic and reports data from foaling seasons between 2001 and 2018. A total of 649 gestations were included in the study. Gestation in mares weighing 680 kg and more was 1.9 days shorter than in those weighing up to 639 kg (P < 0.0001). Gestation in lactating mares was 3.9 days shorter than in non-lactating mares (P < 0.0001). Gestation was longest in mares conceiving in March (343.9 ± 0.60 days); thereafter it gradually shortened, with the shortest (P < 0.0001) in mares conceiving in July (334.9 ± 0.90 days). Gestation length in mares increased (P < 0.0001) from February foaling (340.4 ± 0.73 days) to March foaling (343.6 ± 0.55 days), and then decreased (P < 0.0001) up to the end of the breeding season in June (336.7 ± 0.92 days). Year of conception had an effect on GL (P < 0.02). Gestation in mares carrying male foals was 2.0 days longer than in those carrying female foals (P < 0.01). Gestation in mares delivering foals weighing 70 kg and more was 1.0 days longer than in those delivering foals weighing up to 60 kg (P < 0.01). Mare's age had no effect on gestation length. In conclusion, gestation length was associated with the weight of mares and foals, lactation, month and year of conception, month of foaling, and sex of foals.

Evaluation of environmental effects on reproductive characteristics of Mangalarga Marchador mares in a commercial embryo transfer program

The objective of this study was to evaluate the environmental effects on embryo recovery rate and pregnancy rate of Mangalarga Marchador mares. The reproductive characteristics of donor and recipient mares were evaluated during five years in Brazilian tropical environment. The mares were used throughout the year and seasons were classified as: October to April (breeding season - BS); May (autumn transition out of the breeding season - ATBS); June to August (non-breeding season - nBS); and September (vernal transition into the breeding season - VTBS). Daily temperature rainfall and hours of daylight (photoperiod) were measured during all months and years of evaluation. The embryo recovery rate (ERR) and the pregnancy rate (PR) were observed and frequencies were calculated. The effect of environmental variables, day of flushing, and hormonal treatments (estradiol benzoate and progesterone) were determined for the reproductive measures using the Chi-square and Kruskal-Wallis tests. Significant effects were noted of the year, season and temperature on ERR (P < 0.05), but no significant effects were observed of the environmental parameters (year, season, hormone treatment, rainfall and photoperiod) on PR (P > 0.05). The day of uterine flush affected ERR (P < 0.05) but did not affect PR (P > 0.05). In addition, hormone treatment also supported favorable results of PR in recipient mares during nBS. The conclusion is that mares of this breed can be used in reproduction all year long, with good pregnancy rates, in Brazil's tropical environment. The hormone treatment also supported favorable pregnancy rates in recipient mares during the non-breeding season. It seems that mares can have good pregnancy rates throughout the year in Brazil´s tropical environment.

Grass greenness flush can influence breeding phenology and fertility in equatorial thoroughbred mares in the absence of photoperiod variation

Reproductive phenology is an important trait subjected to natural selection. Current horses in America belong to the Palearctic original populations after being introduced by European colonizers. Photoperiod variation is the main environmental factor for the adjustment of reproductive timing in horses, but is absent in equatorial areas. Here we hypothesize that seasonality of green-grass availability may influence breeding phenology in equatorial regions. We used data of 929 services to mares from 2006 to 2011 in a thoroughbred equine exploitation in Ecuador that experienced strong grass seasonality. Actual births could not be used to infer natural phenology because they were influenced by management decisions. Instead, we used variations in the probability of pregnancy after a service as a measure of the natural tendency of mares to show breeding phenology. We found that although managers tended to schedule pregnancies in two periods within the year, mares were more prone to become pregnant after the increase in grass greenness that takes place at the beginning of the year (February). Our finding has potential applications to improve the success of services and the welfare of animals, by providing green-grass stimuli in the appropriate season.

Reproductive phenology of Creole horses in Ecuador in the absence of photoperiod variation: The effects of forage availability and flooding affecting body condition of mares

Horse reproduction tends to be seasonal. The main adjusting factor in their original temperate ranges is photoperiod variation, although it is absent in equatorial areas where horses were introduced by European colonizers. Hence, dates of reproduction in these areas may be influenced by factors affecting mares' conditions and the success of foaling. Here we study reproductive timing in Creole horses in Ecuador reared in an extensive production system. We found that foaling peaked in August. Mares' conditions showed one peak in June-July, before the start of the breeding season, and another in December, and it was highly variable along the year. Mares' conditions increased after a period of vegetation growth and thus appeared negatively associated with the increment of grass greenness (normalized difference vegetation index data). Seasonal flooding of some pasturelands during March and April appeared to seriously impair mares' conditions and probably influenced the timing of foaling toward the dry season. Our results evidenced that horse breeding in these equatorial areas tended to be seasonal and point to some key factors that influence phenology by affecting body condition of mares, which may have implications for horse biology and management.

Effects of central injection of anti-LPS antibody and blockade of TLR4 on GnRH/LH secretion during immunological stress in anestrous ewes

The present study was designed to examine the effect of intracerebroventricular (icv) administration of antilipopolysaccharide (LPS) antibody and blockade of Toll-like receptor 4 (TLR4) during immune stress induced by intravenous (iv) LPS injection on the gonadotropin-releasing hormone/luteinizing hormone (GnRH/LH) secretion in anestrous ewes. Injection of anti-LPS antibody and TLR4 blockade significantly (P < 0.01) reduced the LPS dependent lowering amount of GnRH mRNA in the median eminence (ME). Moreover, blockade of TLR4 caused restoration of LH-β transcription in the anterior pituitary decreased by the immune stress. However, there was no effect of this treatment on reduced LH release. The results of our study showed that the blockade of TLR4 receptor in the hypothalamus is not sufficient to unblock the release of LH suppressed by the immune/inflammatory challenges. This suggests that during inflammation the LH secretion could be inhibited directly at the pituitary level by peripheral factors such as proinflammatory cytokines and circulating endotoxin as well.