Reproductive efficiency of Thoroughbred and Standardbred horses in north-east Victoria

Review of Pseudomonas aeruginosa and Klebsiella pneumoniae as venereal pathogens in horses

Three bacteria extensively acknowledged as venereal pathogens with the potential to induce endometritis include Taylorella equigenitalis, the causative agent of contagious equine metritis (CEM), specific strains of Pseudomonas aeruginosa, and certain capsule types of Klebsiella pneumoniae. The United Kingdom's Horserace Betting Levy Board recommends pre-breeding screening for these bacteria in their International Codes of Practice and >20 000 samples are tested per annum in the United Kingdom alone. While the pathogenesis and regulatory importance of CEM are well established, an evaluation of the literature pertaining to venereal transmission of P. aeruginosa and K. pneumoniae was lacking. The aim of this review was to evaluate published literature and determine the significance of P. aeruginosa and K. pneumoniae as venereal pathogens in horses. Literature definitively demonstrating venereal transmission was not available. Instead, application of molecular typing methods suggested that common environmental sources of contamination, such as water, or fomites be considered as modes of transmission. The presence of organisms with pathogenic potential on a horse's external genitalia did not predict venereal transmission with resultant endometritis and reduced fertility. These findings may prompt further investigation using molecular technologies to confirm or exclude venereal spread and investigation of alternative mechanisms of transmission are indicated.

Late gestation maternal overnutrition alters gene expression and histomorphology in neonatal foal testes

Reproductive health of male offspring following perturbations in maternal nutrition is not well-described in the horse; therefore, the objective of this study was to determine the effects of maternal overnutrition on neonatal foal testicular development. Sixteen Quarter Horse mares were used in a completely randomized design and stratified by expected foaling date, body weight, and body condition score into 1 of 2 dietary treatments beginning on gestational day 235: control (CON; n = 8) fed to meet nutrient requirements and overfed (HIGH; n = 8) fed 40% above CON. At 5 h postpartum, foals were euthanized, and testes from male foals were harvested, weighed, and stored for analyses. Samples were numerically coded in a blinded fashion and processed randomly to eliminate bias. Histomorphometric evaluations were performed following a hematoxylin & eosin stain and evaluated using ImageJ. All data were analyzed using the MIXED procedure in SAS v9.4. Horse within treatment served as a random effect, with a main effect of treatment. For RNA sequencing, differential gene expression analysis used DESeq2 1.20.0 R package to compare gene expression levels between CON and HIGH, and P-values were adjusted using the Benjamini-Hochberg correction. The threshold for significance was set at P ≤ 0.05 with trends toward significance at 0.05 < P ≤ 0.10, with sequencing data using adjusted P-values. Stringency was set to include differentially expressed genes with an unadjusted P-value < 0.05 for pathway enrichment analysis. Testes from HIGH foals (n = 4) were 61% heavier than testes from CON foals (n = 4; P < 0.01). There was no difference in individual seminiferous tubule area (P = 0.76) or Sertoli cell number within tubule (P = 0.57); however, testes from HIGH foals had 2.3 times fewer tubules per 10× magnification field than CON foals (P = 0.01). Further, tubules represented a lesser percentage of image area relative to interstitial tissue in testes from HIGH foals (P = 0.05). RNA sequencing revealed 56 differentially expressed genes between HIGH and CON testes (P-adjusted < 0.05). Differentially expressed genes represented biological processes related to steroidogenesis, cell regulation, and energy metabolism. Thus, late gestation maternal overnutrition alters fetal testicular development with potential long-term implications for reproductive function.

Changes in characteristics of spermatogonial stem cells in response to heat stress in stallions

Spermatogonial stem cells (SSCs) are essential for the maintenance of male fertility and survival of species. Environmental conditions, notably heat stress, have been identified as important causes of male infertility and have a negative impact on SSCs. Animals with cryptorchid testes (CT) are optimal models for the study of long-term heat stress-related changes in germ cells. The effect of heat stress on germ cells differs depending on the spermatogenesis stage. Thus, verifying whether the specific phase of spermatogenesis is dependent or independent of heat stress in stallions is important. We evaluated the heat stress-related response of SSCs by comparing the relative abundance of mRNA transcripts and expression patterns of the undifferentiated embryonic cell transcription factor 1 (UTF-1) and deleted in azoospermia-like (DAZL) in the seminiferous tubules of CT and normal testes (NT) of stallions using reverse transcription-quantitative polymerase chain reaction (RT-qPCR), immunofluorescence, and western blotting. We also analyzed the relative abundance of mRNA of different proliferative markers, including minichromosome maintenance 2 (MCM2), marker of proliferation Ki-67 (MKI-67), and proliferating cell nuclear antigen (PCNA). Testicular tissues from four Thoroughbred unilateral cryptorchid postpubertal stallions were used in this study during the breeding season. The relative abundance of the mRNA transcripts of UTF-1 and MCM2 was significantly upregulated in the CT group than that of those in the NT group. In contrast, the relative abundance of the mRNA transcripts of DAZL was significantly downregulated in the CT group than that of those in the NT group. Western blot quantification showed that the relative intensity of UTF-1 protein bands was significantly higher, while that of DAZL protein bands was significantly lower in the CT group than in the NT group. Immunofluorescence studies showed that the number of germ cells immunostained with UTF-1 was significantly higher while immunostained with DAZL was significantly lower in the CT group than that in the NT group. The higher expression level of UTF-1 in the CT group shows that undifferentiated SSCs are not affected by long-term exposure to heat stress. These results also indicate that germ cells after differentiation phase are directly affected by heat-stress conditions, such as cryptorchidism, in stallions.

Twin management in the mare: A review

Twin gestation in the mare is undesirable and can have disastrous consequences. As in many cases, the key to success in twin management lies in a thorough follow-up and accurate recording of clinical findings in the pre-breeding examination. A pregnancy diagnosis in the mobility phase is imperative for a good outcome in the event of twin reduction. If a twin gestation is not diagnosed during this early pregnancy stage, several other procedures exist for managing post-fixation twins (>16 days) with varying degrees of success. Most twin pregnancies are the result of multiple ovulations (dizygotic twins). However, monozygotic twins are also sporadically diagnosed, due to the increasing number of transferred in vitro produced equine embryos. In these cases, the most optimal treatment strategy still needs to be determined. This review provides an overview of the various twin reduction techniques described with the expected prognosis as well as of some less reported techniques with their results. In addition, physiological events and the reduction techniques are demonstrated to the user in virtual 3-dimensional illustrations.

Reproductive performance of a cohort of Standardbred mares under a commercial breeding system

BACKGROUND

Despite being a large commercial breeding industry, there is little published data on the reproductive success of Standardbred mares.

OBJECTIVES

To quantify the reproductive performance of Standardbred mares under artificial breeding systems in a commercial setting and determine the incidence of early embryonic and other pre-partum losses.

STUDY DESIGN

Retrospective cohort study.

METHODS

Data from four commercial farms were collected across four breeding years, and all mares were bred via artificial insemination. A total of 3995 mares contributed 7229 mare years. First-cycle pregnancy rate (FCPR) and end of season pregnancy rate (SPR) were analysed in mixed-effects logistic regression models. Time-to-conception interval was analysed in a Cox regression model.

RESULTS

The mean FCPR was 61.4% (confidence interval [CI] 60.3%-62.6%), the mean end of SPR was 84.7% (CI 83.8-85.5%), the mean live foal rate (FR) was 73.1% (CI 72.1%-74.2%). Mares located on-farm were more probable to be pregnant in terms of both FCPR (odds ratio [OR] 1.168, CI 1.018-1.340, p = 0.026) and SPR (OR 2.026, CI 1.673-2.454, p < 0.001), mares inseminated with thawed-frozen semen were less probable to be pregnant in terms of FCPR (OR 0.598, CI 0.457-0.783, p < 0.001) and SPR (OR 0.479, CI 0.354-0.647, p < 0.001) compared with insemination with fresh-extended semen. Older mares (14 years and older) were less probable to be pregnant in terms of FCPR (OR 0.795, CI 0.688-0.919, p = 0.002) and SPR (0.435, CI 0.352-0.538, p < 0.001) compared with young mares (3- to 8-year old).

MAIN LIMITATIONS

Retrospective data relied on accurate record keeping of stud farms and no mare-treatment or ovulation induction records were available. Live FRs relied mostly on annual foaling returns so fetal/foal deaths may be underrepresented.

CONCLUSION

This study provides substantial baseline data on reproductive performance for Standardbred mares managed under a commercial artificial breeding system.

Diagnostic Approach to Equine Testicular Disorders

Management of breeding stallions is crucial to equine reproduction. The longevity of the breeding career is the ultimate objective, whether the stallion is used for natural cover or for semen collection and artificial insemination. Stud farm veterinarians should be aware of the techniques used to evaluate testicular function and the diagnostic approach to testicular disorders in cases of emergency. This paper presents the clinical methods used to evaluate testicular health, including palpation, ultrasonography, biopsy, and fine-needle aspiration. The discussion of testicular disorders is broken down into four categories: congenital disorders (cryptorchidism, monorchidism, and testicular hypoplasia), differential diagnosis of scrotal enlargement, differential diagnosis of causes of progressive testicular enlargement, and differential diagnosis of testicular asymmetry or reduction in size with an emphasis on testicular degeneration. The sudden increase in testicular size is often accompanied by severe clinical signs and is a major cause for referral of stallion for surgery. Testicular disorders are illustrated with clinical cases seen by the authors.

Expression pattern of germ cell markers in cryptorchid stallion testes

Cryptorchidism affects spermatogenesis and testis development, often resulting in stallion subfertility/infertility. This study aims to identify the specific germ cells impacted by cryptorchism in stallions. In a previous study, we found that PGP9.5 and VASA are molecular markers expressed in different germ cells within stallions. Herein, we assessed the heat stress-induced response of spermatogonial stem cells (SSCs) in the seminiferous tubules (ST) of cryptorchid stallion testes (CST) and normal stallion testes (NST). This goal was accomplished by comparing PGP9.5 and VASA expression patterns through reverse transcription quantitative PCR and immunofluorescence assays. We also compared the cross-sectional ST area between groups. Six post-pubertal Thoroughbred unilateral cryptorchid stallions were used. The relative abundance of the mRNA transcripts of PGP9.5 and VASA was significantly upregulated in the NST group than in the CST group. Additionally, the cross-sectional ST area and localization of PGP9.5 and VASA in germ cells were significantly higher in the NST group than in the CST group. Regarding Leydig cells, PGP9.5 staining was observed in both groups. Spermatogonia, primary spermatocytes and secondary spermatocytes were immunostained with VASA in the NST group, while immunostaining was only observed in spermatogonia in the CST group. These results indicate long-term exposure to heat stress conditions, such as cryptorchidism, directly impacts germ cell proliferation and differentiation, leading to impaired spermatogenesis and compromised fertility in stallions.

Use of Doppler ultrasonography for selection of recipients in embryo transfer programs in horses

We aimed to evaluate the impact of corpus luteum (CL) and uterine characteristics accessed by B-mode and Color-Doppler ultrasonography in recipient mares at the time of embryo transfer (ET) on pregnancy outcomes. Recipient mares (n = 110), between days 3-9 after spontaneous ovulation, received a fresh embryo. Immediately before ET, the reproductive system was assessed by transrectal palpation for the following parameters: uterine tone (0-3), CL echogenicity (0-6), CL type (homogeneous, trabecular or anechoic center), luteal area (cm2), uterine echogenicity (0-3), uterine edema (0-3), luteal blood perfusion (0-100%) and uterine blood perfusion (1-4). Additionally, a blood sample was collected by puncture of the jugular vein for plasma P4 dosage. Retrospectively, recipients were classified according to the luteal area (small [≤ 6 cm2] or large [> 6 cm2]), luteal blood perfusion (low [≤ 55%] or high [> 55%]), and plasma concentration of P4 (low ≤ 9.98 ng/mL or high > 9.98 ng/mL). Pregnancy diagnosis was performed at 12 and 30 days of gestation. Luteal blood perfusion was significantly higher (P = 0.04) in pregnant recipients (n = 83) than in non-pregnant recipients (n = 27). Overall P/ET was higher (P ≤ 0.02) in mares with high luteal blood perfusion and high P4. Luteal blood perfusion was the most adequate significant (P = 0.01) predictor of pregnancy compared with the luteal area and plasma P4 concentration. Only luteal blood perfusion showed a linear (P = 0.03) and cubic (P = 0.004) effect on P/ET. In conclusion, CL blood perfusion determined by color-Doppler can be used in real-time to select recipients with the greatest chance of maintaining pregnancy in equine ET programs.

Heat stress and stallion fertility

The threat posed by increased surface temperatures worldwide has attracted the attention of researchers to the reaction of animals to heat stress. Spermatogenesis in animals such as stallions is a temperature-dependent process, ideally occurring at temperatures slightly below the core body temperature. Thus, proper thermoregulation is essential, especially because stallion spermatogenesis and the resulting spermatozoa are negatively affected by increased testicular temperature. Consequently, the failure of thermoregulation resulting in heat stress may diminish sperm quality and increase the likelihood of stallion infertility. In this review, we emphasize upon the impact of heat stress on spermatogenesis and the somatic and germ cells and describe the subsequent testicular alterations. In addition, we explore the functions and molecular responses of heat shock proteins, including HSP60, HSP70, HSP90, and HSP105, in heat-induced stress conditions. Finally, we discuss the use of various therapies to alleviate heat stress-induced reproductive harm by modulating distinct signaling pathways.

Genome-Wide Assessment of Runs of Homozygosity by Whole-Genome Sequencing in Diverse Horse Breeds Worldwide

In the genomes of diploid organisms, runs of homozygosity (ROH), consecutive segments of homozygosity, are extended. ROH can be applied to evaluate the inbreeding situation of individuals without pedigree data and to detect selective signatures via ROH islands. We sequenced and analyzed data derived from the whole-genome sequencing of 97 horses, investigated the distribution of genome-wide ROH patterns, and calculated ROH-based inbreeding coefficients for 16 representative horse varieties from around the world. Our findings indicated that both ancient and recent inbreeding occurrences had varying degrees of impact on various horse breeds. However, recent inbreeding events were uncommon, particularly among indigenous horse breeds. Consequently, the ROH-based genomic inbreeding coefficient could aid in monitoring the level of inbreeding. Using the Thoroughbred population as a case study, we discovered 24 ROH islands containing 72 candidate genes associated with artificial selection traits. We found that the candidate genes in Thoroughbreds were involved in neurotransmission (CHRNA6, PRKN, and GRM1), muscle development (ADAMTS15 and QKI), positive regulation of heart rate and heart contraction (HEY2 and TRDN), regulation of insulin secretion (CACNA1S, KCNMB2, and KCNMB3), and spermatogenesis (JAM3, PACRG, and SPATA6L). Our findings provide insight into horse breed characteristics and future breeding strategies.

Influence of Intrauterine Fluid Detection, Number of Transfers and Age of the Recipient on Pregnancy Rate and Early Embryonic Loss in a Commercial Embryo Transfer Program

The selection of the recipient mare is one of the most important factors involved in the success of equine embryo transfer. The aim of this study was to determine whether the age of the recipient, the number of transfers and the detection of intrauterine fluid during the follicular phase or after ovulation can affect pregnancy rate at 14 and 45 days (PR 14 and PR 45) or early embryonic loss (EEL). A total of 1222 ETs were included in the study. Mares receiving the first embryo of the year had a higher PR 14 and 45 days compared to mares at the third transfer (78.8% and 70.1% vs. 65.6% and 54.1%, respectively). The detection of intrauterine fluid post ovulation negatively affected PR 14 (60.5% vs. 77.6%) and should therefore be considered an abnormal finding, probably being a sign of uterine inflammation or delayed uterine clearance. On the contrary, the age of the recipient mare and detection of fluid during follicular phase did not affect PR 14. Only the age of the recipient mare influenced the EEL, since mares aged 10-13 years had a higher EEL compared to mares aged 3-5 years (15.6% vs. 6.4%). Embryo size and grade affected PR 14 and 45.

Predicting the Outcome of Equine Artificial Inseminations Using Chilled Semen

This study aimed to determine whether an analysis of stallion ejaculate could accurately predict the likelihood of pregnancy resulting from artificial insemination in mares. This study involved 46 inseminations of 41 mares, using 7 standardbred stallions over a 5-week period at an Australian pacing stud. Semen quality was assessed immediately after collection and again after chilling at ~5 °C for 24 h. The assessment involved evaluating ejaculate volume, sperm concentration, and motility parameters using an iSperm^® Equine portable device. After the initial evaluation, a subpopulation of cells was subjected to a migration assay through a 5 µm polycarbonate filter within a Samson™ isolation chamber over a 15 min period. The cells were assessed for their concentration, motility parameters, and ability to reduce the membrane impermeant tetrazolium salt WST-1. The data, combined with the stallion and mare's ages, were used to predict the likelihood of pregnancy, as confirmed by rectal ultrasound sonography performed 14 days post ovulation. The criteria used to predict pregnancy were optimized for each individual stallion, resulting in an overall accuracy of 87.9% if analyzed pre-chilling and 95% if analyzed post-chilling. This study suggests that an analysis of stallion ejaculate can be used to predict the likelihood of pregnancy resulting from artificial insemination in mares with a high level of accuracy.

Lethal variants of equine pregnancy: is it the placenta or foetus leading the conceptus in the wrong direction?

Embryonic and foetal loss remain one of the greatest challenges in equine reproductive health with 5-10% of established day 15 pregnancies and a further 5-10% of day 70 pregnancies failing to produce a viable foal. The underlying reason for these losses is variable but ultimately most cases will be attributed to pathologies of the environment of the developing embryo and later foetus, or a defect intrinsic to the embryo itself that leads to lethality at any stage of gestation right up to birth. Historically, much research has focused on the maternal endometrium, endocrine and immune responses in pregnancy and pregnancy loss, as well as infectious agents such as pathogens, and until recently very little was known about the both small and large genetic variants associated with reduced foetal viability in the horse. In this review, we first introduce key aspects of equine placental and foetal development. We then discuss incidence, risk factors and causes of pregnancy loss, with the latter focusing on genetic variants described to date that can impact equine foetal viability.

Multivariable analysis to determine risk factors associated with abortion in mares

Risk factors associated with equine reproductive efficiency have been identified along with those associated specifically with early pregnancy loss (EPL). In contrast, no studies have reported risk factors associated with abortion (loss between day 70 and 300 post-cover). Given the causes of abortion differ to those of EPL, likely too will the risk factors. A retrospective cohort study was carried out to identify risk factors associated with abortion in UK and Irish based Thoroughbreds, collecting data on 20 exposure variables over a five-year period. A generalized linear mixed model was utilized to evaluate the associations between exposure variables and abortion, with clustering of observations accounted for at the mare and farm level. Variables with a likelihood ratio test (LRT) p value <0.2 were entered into the model in a forward stepwise approach. Pregnancy outcome was available on 4,439 pregnancies from 2,510 mares. Having had two or more prior abortions (odds ratio (OR) 7.91, 95% confidence interval (CI) 2.86, 21.88), conceiving on the second or subsequent covered estrous cycle (OR 1.84, 95% CI 1.22, 2.78) and conceiving multiple conceptuses (OR 1.68, 95% CI 1.02, 2.76) were associated with an increased risk of abortion compared to null parous, first estrous cycle covers and singleton conceptions respectively. Increasing paternal age (OR 0.95, 95% CI 0.90, 0.99) was associated with a decreasing risk of abortion. Mare and farm variance were not significant in the final model, LRT p=0.43. These findings provide evidence-based data to inform Thoroughbred breeding management practices to help mitigate abortion risk.

The correlation of endogenous progesterone concentration in diestrus on early pregnancy rate in Thoroughbred mares

AIM

The aim of this project was to test the hypothesis that progesterone concentration 5 days after ovulation did not differ between pregnant and nonpregnant Thoroughbred mares on stud farms located in the Waikato region of New Zealand.

METHODS

A prospective cohort study was performed involving five stud farms in the Waikato region of New Zealand during the 2018 breeding season. A total of 275 mares were enrolled in the study. Mares were served by 34 individual stallions. Blood samples were taken from each mare 5 days after ovulation (D0) and measured for progesterone concentration. Early pregnancy was confirmed at D14 by transrectal palpation and ultrasonography of the mares reproductive tract.

RESULTS

Progesterone concentration at Day 5 post-ovulation was higher in mares determined to pregnant at Day 14 of gestation than in mares determined to be non-pregnant at Day 14 (6.4 ± 3.0 ng/ml vs 5.5 ± 3.3 ng/ml respectively; P=0.02). A negative association between increasing mare age and pregnancy rate was found but mare age had no effect on progesterone concentration at D5.

CONCLUSIONS

In this study we found that although higher serum progesterone concentration at Day 5 post ovulation was associated with a higher pregnancy rate at Day 14, no predictive or definitive minimum required progesterone concentration could be identified. Additional studies are required to determine if a synthetic progestogens can serve to supplant natural progesterone to increase pregnancy rate in naturally bred mares.

Mixed-Effects Modelling of the Risk Factors Associated with Multiple Pregnancies in Thoroughbred Mares

Simple Summary

Multiple pregnancies (MPs), or twins/triplets, are commonly diagnosed in pregnant mares. Whilst some studies have identified factors associated with an increased risk of MPs, they have only looked at each factor individually and not accounted for the effects of factors when they occur together. This study used statistical modelling to identify risk factors for MPs, looking at 27 factors as well as the contribution of the mare, stallion (both proxies for genetics), farm, and veterinarian. We found that multiple ovulations and the use of a drug that mimics prostaglandin F2α to induce oestrus, both increased the risk of a mare having an MP. Mares that had a foal that same year, had a uterine cyst, or who did not get pregnant on the first cycle they were bred on were at a decreased risk of having an MP. Factors that impact the early embryonic environment are more important influences of multiple pregnancies when compared to the genetics of the mare. The increased incidence of MP but not MOs over the previous decades may well reflect improved management of the endometrium as opposed to selection of mares with increased risk for MPs. A limitation of the study is the reliance on clinical records being completed accurately.

Abstract

Multiple pregnancies (MPs) are commonly diagnosed during breeding management of mares. Whilst some studies have reported on factors associated with the risk of MPs, few have utilised multivariable data analysis to control for confounding variables. A prospective cohort study of Thoroughbred broodmares was conducted with information collected on 27 factors. Mixed-effects logistic regression was used to determine risk factors for MPs. Mare, stallion, stud, and veterinarian were evaluated as random effects. The prevalence of MPs in 1754 mares and 2245 pregnancies was 16.06% (95% confidence interval [CI] = 14.54, 17.58). Multiple ovulations (OR = 15.57, 95% CI = 11.88, 20.53) and treatment with cloprostenol (OR = 1.35, 95% CI = 1.015, 1.80) were associated with increased odds of MPs following multivariable analysis. Mares that foaled at the start of the breeding season (OR = 0.66, 95% CI = 0.47, 0.94), conceived at the second or more oestrus cycles (OR = 0.60, 95% CI= 0.43, 0.84), or identified with a uterine cyst (OR = 0.63, 95% CI = 0.40, 0.97) were at reduced odds of conceiving MPs. Mare, stallion, stud, and veterinarian were not associated with MPs. These findings provide possible explanations as to why the prevalence of MPs but not MOs have increased over the last decade.

Supplemental Nicotinic Acid Elevates NAD+ Precursors in the Follicular Fluid of Mares

Simple Summary

Miscarriage and embryonic death have been associated with a deficiency in NAD⁺ resulting from a lack of dietary niacin in women and mice. Mares often suffer from high rates of early embryonic loss, but the dietary requirement of niacin in pregnant mares remains unknown. The aim of this study was to determine the effect of supplementing nicotinic acid, a form of niacin often supplemented in horse diets, on the elevation of other NAD⁺ precursors in the blood and follicular fluid of mares. We orally administered nicotinic acid to mares over consecutive days and collected blood and follicular fluid at the end of the feeding period. The results show that multiple examined NAD⁺ precursors were elevated in the follicular fluid of mares at the end of the feeding period, which we propose will aid in reducing early embryonic loss in the mare by promoting good quality oocytes.

Abstract

A deficiency in NAD⁺ has previously been linked with increased occurrences of congenital abnormalities and embryonic death in humans and mice. Early embryonic death is a major factor involved in pregnancy loss in mares, and very little is known regarding the NAD⁺ requirements for optimum reproductive function in horses. The aim of this study was to determine the effect of supplementing the diet of mares with nicotinic acid (NA) on the composition of NAD⁺ metabolites in the blood and follicular fluid. Vehicle alone or NA (3 g per os) were administered to seven mares over a minimum of 3 consecutive days during the follicular phase of the oestrous cycle. Blood samples were collected immediately prior to supplemental feeding and follicular fluid aspiration. Follicular fluid was collected from the dominant follicle through transvaginal ultrasound-guided aspiration. Blood and follicular fluid samples were processed and analysed by mass spectrometry. The concentration of nicotinamide mononucleotide (NMN) in the follicular fluid of NA-fed mares was 4-fold greater than that in the corresponding plasma and 10-fold greater than that in the follicular fluid of vehicle-fed mares. The concentrations of NA, nicotinamide (NAM) and nicotinuric acid (NUR) tended to be greater in the follicular fluid of NA-supplemented mares than in the corresponding plasma. The results show that NA supplementation increased the bioavailability of NAD⁺ precursors in the follicular fluid of the dominant follicle, which is proposed to better promote the maturation of good quality oocytes, especially in older mares.

Proteomic analysis of spermatozoa reveals caseins play a pivotal role in preventing short-term periods of subfertility in stallions

Stallions experience transient fluctuations in fertility throughout the breeding season. Considering pregnancy diagnoses cannot be ascertained until ~14 days post-breeding, the timely detection of decreases in stallion fertility would enhance industry economic and welfare outcomes. Therefore, this study aimed to identify the proteomic signatures reflective of short-term fertility fluctuations, and to determine the biological mechanisms governing such differences. Using LC–MS/MS, we compared the proteomic profile of semen samples collected from commercially “fertile” stallions, during high- and low-fertility periods. A total of 1702 proteins were identified, of which, 38 showed a significant change in abundance (p ≤ 0.05). Assessment of intra- and inter-stallion variability revealed that caseins (namely κ-, α-S1-, and α-S2-casein), were significantly more abundant during “high-fertility” periods, while several epididymal, and seminal plasma proteins (chiefly, epididymal sperm binding protein 1 [ELSPbP1], horse seminal plasma protein 1 [HSP-1] and clusterin), were significantly more abundant during “low-fertility” periods. We hypothesised that an increased abundance of caseins offers greater protection from potentially harmful seminal plasma proteins, thereby preserving cell functionality and fertility. In vitro exposure of spermatozoa to casein resulted in decreased levels of lipid scrambling (Merocyanine 540), higher abundance of sperm-bound caseins (α-S1-, α-S2-, and κ-casein), and lower abundance of sperm-bound HSP-1 (p ≤ 0.05). This study demonstrates key pathways governing short-term fertility fluctuations in the stallion, thereby providing a platform to develop robust, fertility assessment strategies into the future.

Female age and parity in horses: how and why does it matter?

Although puberty can occur as early as 14-15months of age, depending on breed and use, the reproductive career of mares may continue to advanced ages. Once mares are used as broodmares, they will usually produce foals once a year until they become unfertile, and their productivity can be enhanced and/or prolonged through embryo technologies. There is a general consensus that old mares are less fertile, but maternal age and parity are confounding factors because nulliparous mares are usually younger and older mares are multiparous in most studies. This review shows that age critically affects cyclicity, folliculogenesis, oocyte and embryo quality as well as presence of oviductal masses and uterine tract function. Maternal parity has a non-linear effect. Primiparity has a major influence on placental and foal development, with smaller foals at the first gestation that remain smaller postnatally. After the first gestation, endometrial quality and uterine clearance capacities decline progressively with increasing parity and age, whilst placental and foal birthweight and milk production increase. These combined effects should be carefully balanced when breeding mares, in particular when choosing and caring for recipients and their foals.

Effect of advancing age on the reproductive performance of Japanese Thoroughbred broodmares

Many studies have reported that advancing age in broodmares has a negative impact on the reproductive performance of horses. However, although the ages at first and last mating vary among broodmares, it is unknown how this variation affects the correlation between age and reproductive performance in mares. Here, in order to examine the effects of the ages at first and last mating, we analyzed all recorded mating events for Thoroughbreds in Japan from 1997 to 2017. We found that the live foal birth rate of mares with a younger age at first mating indeed declined at an earlier age than those with an older age at first mating and that the number of years since the first mating also contributes to the decline in the birth rate. We also found that the live foal birth rate and mean earnings of the produced foals are much higher for mares with an older age at last mating compared with mares with a younger age at last mating. Our results should aid breeders in assessing the value of broodmares and designing breeding strategies.

A New Approach of Sperm Motility Subpopulation Structure in Donkey and Horse

This study aimed to characterize the sperm kinematic values with high frames per second, to define the subpopulation structure of a horse and a donkey and compare them. A total of 57 fresh semen ejaculates (26 Spanish and 16 Arabian horse breeds and 10 donkeys) were collected and subsequently analyzed for kinematic parameters using the Computer-aided sperm motility analysis ISAS®v1.2 system and using a Spermtrack® 10-μm depth counting chamber. Sequences were recorded at 250 frames per second, and eight kinematic parameters were automatically evaluated. All kinematic parameters showed significant differences between a donkey and a horse and between horse breeds. All ejaculates evaluated showed excellent semen motility characteristics, with significantly higher values for all kinematic parameters for donkeys compared with horses except for beat-cross frequency. Donkey sperm was faster and linear than the horse. Regarding horse breeds differences, the Spanish horse had higher average path velocity, curvilinear velocity, and beat-cross frequency compared with the Arabian horse. Spanish horse sperm was rapid, but Arab horse was more linear. The principal component analysis showed three sperm subpopulations in the ejaculate of donkeys and horses with a significantly different motility characteristic between them. The dominant subpopulation for both donkey and horse was for rapid, straight, and linear with a high beat sperm (38.2 and 41.7%, respectively), whereas the lowest subpopulation was for the slowest and non-linear sperms. This, plus slight differences in the distribution of these subpopulations between Arabian and Spanish horses, were found. In conclusion, higher frames permitted to have a new interpretation of motile subpopulations with species and breed differences. More so, future works on donkey and horse breed spermatozoa should take into account differences between breeds that may interfere and alter the real analysis performed.

The Yolk Sac of the Equine Placenta. Its Remnant and Potential Problems

This review details the current state of knowledge about the equine yolk sac and its remnant (YSR) in the pregnant mare, which, incidentally, is the only animal species known to exhibit large and/or ossified YSR. It also describes the clinical significance of the YSR and details a case of a strangulating YSR that caused fetal death and abortion.

Effect of age and of reproductive status on reproductive indices in horse mares carrying mule pregnancies

Mules (Equus mulus) are interspecific hybrids derived from crossing horse (Equus caballus) mares with jackasses (Equus asinus). In Italy, the production of mules is very important for the special environmental areas, where they are used as working animals, instead of the forbidden agricultural machines. Although many horse mares carry mule pregnancy successfully at term, low fertility of mares used for producing mules was reported, but limited data about reproductive efficiency in mares carrying mule pregnancy, especially when age and reproductive status are concerned, are available. Therefore, the present study aimed to assess the effect of age and of reproductive status on some reproductive indices of horse mares carrying mule pregnancy, in the final purpose to better clarify factors affecting reproductive performances in the valuable production of mules as working animals under special environmental areas in Italy.

The study, performed on 96 draft mares inseminated with Martina Franca donkey semen, showed a satisfactory 89.6% 14 days PO pregnancy rate, lower pregnancy losses (19.8%) than those previously reported for mule pregnancies, leading to satisfactory foaling rates (71.9%), similar to those reported for intraspecific horse pregnancies. A clear, significant detrimental effect of mare's age on pregnancy losses, foaling rate, and on number of estrous cycles needed to achieve pregnancy, was found. Reproductive status also affected the reproductive indices, with significantly higher pregnancy losses and lower foaling rate in barren mares, reopening the question about the possible lower reproduction efficiency in horse mares carrying mule pregnancy. The present study results, although mostly descriptive, add useful information about some factors affecting reproductive performances in the valuable production of mules as working animals under special environmental areas in Italy.

Fetal morphological features and abnormalities associated with equine early pregnancy loss

BACKGROUND

Early pregnancy loss (EPL) occurs in approximately 8% of equine pregnancies, although the aetiology is mostly unknown and embryonic/fetal morphological abnormalities associated with EPL are not defined.

OBJECTIVES

To compare the morphology of EPL to clinically normal embryos/fetuses and previously described embryonic/fetal developmental milestones. To identify morphological abnormalities associated with equine EPL.

STUDY DESIGN

Observational case-control study.

METHODS

Embryos/fetuses were obtained from clinically normal Thoroughbred and pony pregnancies (n = 11) and following EPL from Thoroughbred mares (n = 27). The crown-rump length (CRL) of embryos/fetuses was measured and macroscopic morphology and developmental age were determined independently by three blinded examiners. Sagittal sections of EPL (n = 13) and control (n = 6) embryos/fetuses were assessed microscopically. Fisher's exact test was used to determine significance (P < .05) and correlations were expressed by Pearson coefficient.

RESULTS

Age and CRL were strongly positively correlated in clinically normal Thoroughbred and reference (n = 15, R = .9 (95% CI: 0.8-1.0), R²  = .9, P < .0001) but not EPL embryos/fetuses (n = 19, R = .1 (95% CI: -0.4 to 0.5), R²  = .01, P = .75). Relative to controls, the CRL of EPL embryos/fetuses was smaller, with evidence of intrauterine growth retardation (IUGR) in 3/8 fetuses assessed. In 9/13 EPL embryos/fetuses, nonspecific neural tissue alterations were identified including disruption of developing pros-, mes- and rhombencephalon and the presence of haemosiderin, indicating premortem haemorrhage. Failed neural tube closure was identified in 1/13 EPL embryos/fetuses. Subcutaneous haemorrhage was present in 14/27 EPL embryos/fetuses.

MAIN LIMITATIONS

Autolysis significantly affected 15/27 EPL embryos/fetuses, excluding them from complete assessment. The IUGR reference cut-off values were based on a small number of controls.

CONCLUSIONS

Morphological features associated with equine EPL were a mismatch between embryonic/fetal size and age, and alterations of the developing neural tissue and localised subcutaneous haemorrhage. Failed neural tube closure was confirmed as a rare specific abnormality.

Harem stallion changes are not associated with diminished reproductive performance of females in semi-feral Konik polski horses (Equus caballus)

Infanticide, related to a stallion's aggression toward a foal sired by another stallion, and feticide related to a new stallion's aggression and/or pheromonal influence (the Bruce effect) inducing loss of a fetus sired by another stallion, a female's counteraction to infanticide, have been proposed for domestic horses (Equus caballus) in human-managed conditions. The aim of the present study was, in conditions close to natural, to investigate the influence of the natural succession of a harem stallion on the mares' subsequent reproductive performance. In a population of semi-feral Konik polski horses observed for 31 years (reproductive seasons) in 8 bands, harem stallion changed 10 times. These changes involved 26 out of 48 mares and 60 out of 609 observed mare-seasons (MS, a year in which a mare experienced a reproductive event). Binary distribution and log link function were assumed. The marginal model included the classification variable (SCH) and the continuous variables (age of the mare and calendar year of reproductive event (birth of a live foal, abortion, foals lost or barrenness) in a given MS was analyzed with generalized linear mixed model. The reproductive fitness of mares and their reproductive success (foal surviving ≥ 1 year), did not differ between MS with and without SCH. Older females were more likely to stay barren, with chances increasing by 21% with each successive year; and less likely to give birth to a foal (13% decrease of chance), and rear a foal to one year of age (12% decrease of chance). The age did not affect the probability of abortions. Of the 26 MS when mares were pregnant when the stallion had changed, there were 25 healthy foals born. For the entire 31 years of monitoring, no aggression toward any foal was observed and all foals that were born in the harem of a new, succeeding stallion successfully reached adulthood. Due to the lack of incidents of infanticide and the lack of evidence suggesting that the presence of a new harem stallion leads to the termination of pregnancies sired by another stallion, the Bruce effect was not confirmed as a biological strategy to reduce investment in pregnancy and potential infanticide in studied population of semi-feral horses.

Whole-genome sequence analysis reveals candidate genomic footprints and genes associated with reproductive traits in Thoroughbred horse

The primary objective of most horse breeding operations was to maximize reproductive efficiency and minimize the cost of producing live foals. Here, we compared individual horses from the Thoroughbred population (n = 17), known as a horse breed with poor reproductive performance, with other six horse populations (n = 28), to detect genomic signatures of positive selection underlying of reproductive traits. A number of protein-coding genes with significant (p-value <.01) higher F_ST values (616 genes) and a lower value for nucleotide diversity (π) (310 genes) were identified. The results of our study revealed some candidate genes such as IGFBP2, IGFBP5, GDF9, BRINP3 and GRID1 are possibly associated with functions influencing reproductive traits. These genes may have been under selection due to their essential roles in reproduction performance in horses. The candidate selected genes identified in this work should be of great interest for future research into genetic architecture of traits relevant to horse breeding programmes.

Commercial equine production in New Zealand. 1. Reproduction and breeding

The Thoroughbred and Standardbred studbooks are the largest in New Zealand, where the production of horses is pasture based. Each racing studbook is closed, and both have well structured systems in place for recording breeding data. There are significant pressures on the Thoroughbred and Standardbred breeding industries with declining broodmare numbers, and increasingly large book sizes for popular stallions. The breeding season for Thoroughbreds is very short, with disparity between the official breeding season and the physiologic breeding season for mares. These issues are confounded by variable gestation lengths of mares, making it difficult for mares to maintain yearly foaling patterns. However, the reproductive efficiency of Thoroughbred mares is improving, mainly due to veterinary and stud management practices such as those to ensure that dry mares are cycling at the start of the breeding season, foaling mares are bred on foal heat, and that mares are kept in good body condition at breeding. There is also a bias towards breeding younger mares with high fertility in preference to older mares, unless they have desired genetics or successful offspring. Careful management of popular Thoroughbred stallions ensures that large books of mares can be covered by natural service. In contrast, Standardbred stallions are collected every-other-day using an artificial vagina, allowing the breeding of mares at distant locations by artificial insemination, using chilled or frozen semen. Breeding horses kept at pasture under New Zealand conditions requires excellent stud management and veterinary management to achieve good outcomes.

Retrospective study of the reproductive performance of Barb and Thoroughbred stallions in Algeria

Background and Aim

The Barb horse occupies a prominent place in the history, culture, and equestrian traditions of the Maghreb (Algeria, Morocco, and Tunisia). Although many studies on the breed standard and morphometry have been published, there are no studies on its fertility and reproductive potential. Thus, this work aimed to study the fertility of Barb, Arabian Purebred, and Thoroughbred horses in Algeria.

Materials and Methods

A total of 168 stallions and 1202 mares at the Chaouchaoua Stud farm in Tiaret, Algeria, were included in the study. The reproductive performance during 1592 cycles over 10 consecutive mating seasons (2003-2012) was evaluated. Multivariate analysis with logistic regression was used to analyze the reproductive parameters such as the number of cycles operated, number of pregnant mares, pregnancy rate per cycle, seasonal pregnancy rate, and embryonic mortality rate, and to determine the influence of breed, stallion's age, and year of the study on reproduction.

Results

Statistical analysis showed that stallion breed was a significant influencing factor for the number of pregnant barren mares (Odds ratio [OR]=1.72; p=0.03; 95% confidence interval [CI]=1.05, 2.84) seasonal pregnancy rate (OR=1.40; p<0.001; 95% CI=1.29, 1.53). Additionally, the reproductive performance of the Barb stallion was superior to that of the Thoroughbred stallion. With regard to the significant influence of stallion's age of >5 years on the number of pregnant foaling mares and seasonal pregnancy rate, significant interactions were observed between the stallion's breed and age, and the pregnancy rate per cycle: in the Barb breed, the pregnancy rate per cycle increased with the age of the stallion, while in the Thoroughbred, it decreased with age. Moreover, a significant effect of the year of the study on the pregnancy rate per cycle and number of pregnant foaling mares was observed. In contrast, the number of cycles and embryonic mortality rate were not influenced by the breed and age of the stallion, or the year of the study.

Conclusion

The Algerian Barb horse attained a similar level of fertility compared with that of the Arabian Purebred and Thoroughbred stallions depending on its age and reproductive performance.

Factors Influencing the Popularity of Artificial Insemination of Mares in Europe

Simple Summary

The popularity of mare insemination as an element affecting the dynamic growth of breeding progress among horses in Europe is subject to various fluctuations. The success of this method of reproduction should be considered first of all in terms of the quality of semen available on the market, the types of semen storage technology, the profitability of its use resulting from the effectiveness of insemination with the selected type of semen, and factors affecting the success of artificial insemination. The purpose of this work was to present the factors determining the popularity of artificial insemination of mares in Europe. The presented statistics show that the popularity of the use of chilled semen has gradually increased in the group of sport mares, while in the group of breeding mares, the popularity of frozen semen has increased. In the remaining group of mares (not classified as sport or breeding), insemination with chilled semen was dominant. To talk about the success of artificial insemination of horses in Europe, it is necessary to look thoroughly at these aspects that affect the popularity of this reproduction biotechnology, and in particular to improve the quality of insemination doses.

Abstract

The purpose of this review was to analyze factors affecting the popularity of artificial insemination of mares in Europe in the context of sperm quality. Taking into account the prices of stallion semen on the world market, efficiency is important for the profitability of its use in artificial insemination programs in Europe. To increase the efficiency of a semen insemination facility, it is necessary to correctly and objectively assess the quality of semen. The available range of tools allows an effective evaluation of the potential fertility of a stallion. For several years, artificial insemination programs in Europe have been gaining popularity. However, the frequency of chilled or frozen semen use is still quite low. This is mainly due to the common, negative opinion about the effectiveness of the use of packaged insemination doses as opposed to natural insemination. Unfortunately, the quality of the semen offered often deviates from expectations, which results in unsatisfactory (and therefore unprofitable) pregnancy rates. This review presents the popularity structure of chilled and frozen semen use in European horse breeding as well as the current state of research on the effectiveness of semen production technology. It is shown that the popularity of using chilled semen in the artificial insemination of mares in Europe has been gradually increasing in the group of sport mares, while in the group of breeding mares, in recent years, frozen semen has been gaining popularity. In the remaining group of mares (not classified as sport or breeding), insemination with chilled semen has been dominant.

The Effect of Routine Postpartum Uterine Lavage on Endometrial Cytology, Culture, and Pregnancy Rates in Thoroughbred Broodmares

Minimizing the interval between parturition and successful rebreeding of thoroughbred broodmares is important in maintaining annual foal production and broodmare profitability. Routine postpartum uterine lavage may help achieve this by aiding uterine clearance and involution in the early postpartum period and increasing pregnancy rates. This retrospective study investigates the effect of postpartum uterine lavage in 32 thoroughbred mares housed on a single farm in Australia in 2014 and 2015. In the control year (2014), postpartum uterine lavage was not performed. In the treatment year (2015), all mares received a uterine lavage 3 days postpartum. In both years, endometrial swabs were obtained for culture and cytology at the first postpartum estrus (foal heat swab) and the second postpartum estrus (second heat swab), prior to the mare being bred by natural cover at the second postpartum estrus. There was no significant difference in bacterial culture rates from foal heat or second heat swabs between the control and treatment years. Assessment of endometrial cytology of the foal heat swab and second heat swab revealed a significantly higher proportion of polymorphonuclear cells (PMNs) in the control year compared with the treatment year. Positive culture and cytology rates were significantly higher at foal heat than at the second postpartum heat in both years. No association of year, cytology, or culture with pregnancy rates was identified. In conclusion, routine postpartum uterine lavage significantly reduces the presence of endometrial PMNs at first and second postpartum estrus but does not reduce endometrial culture rates or increase pregnancy rates.

Patterns of conceptus development and of progesterone concentrations in maternal blood preceding spontaneous early pregnancy failure in mares

Sixteen cases of spontaneous pregnancy loss (11 of singletons and five of pairs of twins) are described. The losses occurred between gestation Days 13 and 25 in 12 mares being monitored almost daily by transrectal ultrasonography (for measurement of conceptus growth) and blood sampling (for determination of maternal plasma progesterone concentrations as evidence of luteolysis) in experimental studies of early pregnancy. In 10 of the 16 cases the uterus was flushed and eight conceptuses were recovered for morphological assessment. Five of the 11 losses of singletons occurred before Day 16 and, with one exception, were preceded or accompanied by luteolysis. The remaining six singleton pregnancies failed after Day 16, with two cases evidencing luteolysis beforehand. Thus, overall, 6/11 singleton losses were associated with luteolysis while 5/11 were not. The five cases of simultaneous loss or degeneration of twin conceptuses all occurred on Day 19 or 20, preceded by luteolysis in only one case. These observations suggest that while the causes of spontaneous early pregnancy failure are multifactorial, luteolysis might contribute to the problem more often than has been previously contended.

Half a century of equine reproduction research and application: A veterinary tour de force

Over the past 50 years, per season pregnancy rate in Thoroughbred mares have risen from 70 to >90% and foaling rates from 55 to >80%. Some of the significant pharmacological treatments and diagnostic methods which have driven this marked improvement in breeding efficiency are reviewed. They include the application of artificial lighting to hasten the onset of ovulatory oestrous cyclicity in early Spring, rapid steroid hormone assays to aid in determining the stage and normality of the mare's cycle, prostaglandin analogues, synthetic progestagens and Gonadotrophin-releasing Hormone (GnRH) analogues to better control and manipulate her cycle to good effect, transrectal ultrasound scanning to monitor follicle growth, endometrial architecture and ovulation and to allow accurate, early pregnancy diagnosis thereby enabling successful ablation of one of twin conceptuses. Also, flexible videoendoscopy to monitor physiological and pathological changes in the uterine endometrium and rigid laparoscopy to apply prostaglandin to the oviducts to dislodge and clear suspected blockages of them to restore fertility. The outbreak of Contagious Equine Metritis in Newmarket in the spring of 1977 and the swabbing-related changes to mare and stallion management, plus the improved veterinary hygiene methods, which followed are also recounted. The past half century has witnessed many technical and therapeutic advances that have enhanced tremendously the diagnostic and treatment capabilities of studfarm veterinary surgeons. They, in turn, have improved greatly the efficiency of breeding Thoroughbreds and other types of horses.

Not just a number: effect of age on fertility, pregnancy and offspring vigour in thoroughbred brood-mares

Advancing age can adversely affect a thoroughbred brood-mare's reproductive efficiency and influence the commercial and athletic potential of her progeny. Causes for the decline in fertility include decreased oocyte and embryo quality, anatomical defects and endometrial degeneration. In addition, evidence exists that as the age of a dam increases, her foals will be at increased risk of morbidity and mortality during the neonatal period. Health issues can have lasting and deleterious effects on surviving foals, including decreased sale value and reduced athletic performance. The purpose of this review is to evaluate the association between mare age, fertility and offspring vigour in thoroughbred horses.

Advances in Stallion Semen Cryopreservation

The use of stallion frozen semen minimizes the spread of disease, eliminates geographic barriers, and preserves the genetic material of the animal for an unlimited time. Significant progress on the frozen thawed stallion semen process and consequently fertility has been achieved over the last decade. These improvements not only increased fertility rates but also allowed cryopreservation of semen from "poor freezers." This article reviews traditional steps and new strategies for stallion semen handling and processing that are performed to overcome the deleterious effects of semen preservation and consequently improve frozen semen quality and fertility.

Field fertility of liquid stored and cryopreserved flow cytometrically sex-sorted stallion sperm

REASONS FOR PERFORMING STUDY

The fertility of sex-sorted, cryopreserved stallion sperm must be improved for the sex-sorting technology to be applied commercially.

OBJECTIVES

To optimise the conditions used to liquid store stallion sperm prior to sex-sorting and assess the fertility of sperm following sex-sorting and cryopreservation.

STUDY DESIGN

Both in vitro experiment and randomised controlled trial in healthy, client-owned mares.

METHODS

Stallion ejaculates (n = 9) were diluted in either a skimmed milk (KMT) or BSA (I-BSA) based media to 25 × 10⁶ sperm/ml directly (+SP25) or washed to remove seminal plasma and diluted to 25 or 111 × 10⁶ sperm/ml (-SP25 and -SP111). Sperm were stored for 18 h at 10 to 15°C and -SP25 and +SP25 treatments were centrifuged and resuspended to 111 × 10⁶ sperm/ml. Sperm were incubated under H33342 staining conditions and motility, viability and acrosome integrity assessed. Semen was collected from stallions (n = 4), liquid stored at 10-15°C for up to 5 h and sperm either cryopreserved directly, sex-sorted and cryopreserved, or sex-sorted and returned to liquid storage until insemination. Low-dose hysteroscopic insemination was performed in 23 mares randomly allocated to the semen preparation group and pregnancy determined following embryo flushing on Day 9 after ovulation, or via transrectal ultrasonography on Day 14 after ovulation.

RESULTS

Skimmed milk was superior to I-BSA in maintaining motility, viability and acrosome integrity. Seminal plasma removal did not affect the parameters measured at the concentrations examined. Conception rates did not differ significantly between the groups, although a high incidence of pregnancy loss was observed in both the cryopreserved groups.

CONCLUSIONS

While the conception rates achieved are among the highest yet reported for sex-sorted, cryopreserved stallion sperm, the high incidence of pregnancy loss suggests that the development of the resulting embryos was significantly impaired by the sperm processing treatments.

The Impact of Sperm Metabolism during In Vitro Storage: The Stallion as a Model

In vitro sperm storage is a necessary part of many artificial insemination or in vitro fertilization regimes for many species, including the human and the horse. In many situations spermatozoa are chilled to temperatures between 4 and 10°C for the purpose of restricting the metabolic rate during storage, in turn, reducing the depletion of ATP and the production of detrimental by-products such as reactive oxygen species (ROS). Another result of lowering the temperature is that spermatozoa may be "cold shocked" due to lipid membrane phase separation, resulting in reduced fertility. To overcome this, a method of sperm storage must be developed that will preclude the need to chill spermatozoa. If a thermally induced restriction-of-metabolic-rate strategy is not employed, ATP production must be supported while ameliorating the deleterious effects of ROS. To achieve this end, an understanding of the nature of energy production by the spermatozoa of the species of interest is essential. Human spermatozoa depend predominantly on glycolytic ATP production, producing significantly less ROS than oxidative phosphorylation, with the more efficient pathway predominantly employed by stallion spermatozoa. This review provides an overview of the implications of sperm metabolism for in vitro sperm storage, with a focus on ambient temperature storage in the stallion.

Factors affecting live foal rates of Thoroughbred mares that undergo manual twin elimination

REASONS FOR PERFORMING STUDY

Mares diagnosed with twin vesicles at 13-17 days after ovulation commonly have one of 2 vesicles manually reduced. It is not known whether vesicle location (adjacent vs. nonadjacent), mare age, mare reproductive status, parity, month of breeding or mare plasma progesterone concentration affects live foal rates.

OBJECTIVES

To determine factors associated with a positive outcome (live foal) in mares undergoing manual twin reduction between 13 and 17 days post ovulation when performed by a single operator.

STUDY DESIGN

Retrospective case-control study.

METHODS

Breeding records and the Jockey Club records of registered Thoroughbreds were used to evaluate factors affecting the outcome of pregnancies in mares undergoing twin elimination and mares with singleton pregnancies. Thoroughbred mares with twin pregnancies (n = 129) were matched by age, parity, farm location and month bred with mares diagnosed with a singleton pregnancy (n = 127). The effects of location of embryonic vesicles, mare age, reproductive status, parity, month of breeding, vesicle size and plasma progesterone concentration at pregnancy diagnosis on live foal rate were examined.

RESULTS

Position of embryonic vesicles at time of manual elimination, parity and month bred had no effect on live foal rate. Live foal rates in mares >9 years of age were lower (71.8%) than in all mares ≤9 years (87.1%; P<0.05). Mares >9 years of age that had a twin reduced lost more pregnancies (34.8%) than age-matched control mares (20.0%; P<0.005). Mean plasma progesterone concentration of twin-reduced mares was greater than in control mares when compared on the same day post ovulation. Plasma progesterone concentrations did not differ between mares that lost their pregnancy and those that delivered a live foal.

CONCLUSIONS

Mare age of >9 years is associated with decreased pregnancy rate after twin reduction.

POTENTIAL RELEVANCE

Furthering the understanding of factors that affect live foal outcome following manual twin elimination in mares.