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

Twin Pregnancy in the Martina Franca Donkey Breed Managed by Natural Reduction and Post-Fixation Manual Crushing

In Equids, undetected twin pregnancy represents the most important cause of abortion and is also associated with high neonatal mortality rates. Therefore, the detection and management of twin pregnancies is pivotal to allow the continuation of single pregnancies. Although pre-fixation manual crushing of one embryo is the most common management of twin pregnancies, and the impact of natural reduction has been reported in mares, very little is known about donkeys. The present study aimed to report results on the natural reduction occurrence and post-fixation manual crushing management of twin pregnancies in the Martina Franca donkey breed.

METHODS

Twenty-five twin pregnancies were detected at 11-13 days after ovulation. At 16 days after ovulation, twin pregnancies were classified as unilateral or bilateral and left untreated. The occurrence of natural reduction of one embryo was assessed at 20-21 days after ovulation, and post-fixation manual crushing of one embryo was performed in those cases in which natural reduction did not occur. The pregnancy rate at 28 days after ovulation and live foal rate were recorded.

RESULT

Sixteen out of 25 twin pregnancies were unilateral and nine bilateral. At 20-21 days after ovulation, the natural reduction of one embryo occurred in 87.5% of the unilateral and in none of the bilateral twin pregnancies. The remaining twin pregnancies were treated by post-fixation manual crushing of one embryo. The 28-days-after-ovulation single embryo pregnancy rate was 93.8% for unilateral twin pregnancies and 88.9% for bilateral twin pregnancies, with an overall pregnancy rate of 92%. The live foal rate was 87%.

CONCLUSIONS

The success rate of natural reduction within 20-21 days after ovulation, the 28-days-after-ovulation pregnancy rate, and the live foal rate suggest that waiting for the natural reduction of one embryo and choosing the post-fixation manual crushing of one embryo could be considered as an alternative to traditional early pre-fixation manual crushing in the Martina Franca donkey breed.

An Overview of Infectious and Non-Infectious Causes of Pregnancy Losses in Equine

Equine breeding plays an essential role in the local economic development of many countries, and it has experienced rapid growth in China in recent years. However, the equine industry, particularly large-scale donkey farms, faces a significant challenge with pregnancy losses. Unfortunately, there is a lack of systematic research on abortion during equine breeding. Several causes, both infectious and non-infectious, of pregnancy losses have been documented in equines. The infectious causes are viruses, bacteria, parasites, and fungi. Non-infectious causes may include long transportation, ingestion of mycotoxins, hormonal disturbances, twinning, placentitis, umbilical length and torsion, etc. In current review, we discuss the transmission routes, diagnostic methods, and control measures for these infectious agents. Early detection of the cause and appropriate management are crucial in preventing pregnancy loss in equine practice. This review aims to provide a comprehensive understanding of the potential causes of abortion in equines, including infectious agents and non-infectious factors. It emphasizes the importance of continued research and effective control measures to address this significant challenge in the equine industry.

Phenotypic Characterization of the Martina Franca Donkey: An Endangered Italian Donkey Breed

The Martina Franca (MF) donkey breed (Equus asinus) primarily inhabits the rural areas surrounding the homonymous municipality, as well as neighboring municipalities in the provinces of Bari and Brindisi, all located in the Apulia region of Italy. The objective of this study was to assess the current phenotype through the evaluation of 27 morphologic measurements. The study was conducted on 73 female and 18 male breeding animals from eight different herds located in central and southern Italy. Statistical analysis was performed in order to demonstrate statistical differences between males and females, as well as sexual dimorphism and uniformity of all measurements in both genders. The results demonstrated that the mean of three parameters used for the evaluation of an MF donkey (height at withers, circumference of thorax, and shin circumference) are highly representative of the population, with minimal dispersion Cv^ = 0.05-0.06 up to a maximum of 10%, as evidenced by relatively low standard deviations across observed measurements in both genders. Regarding sexual dimorphism, a statistically significant difference was found between males and females. This dimorphism is linked to reproductive activity and is useful during gestation. Overall, our findings suggest that the MF donkey phenotype has been largely preserved over time with high uniformity in males, slight inhomogeneity in the female population, and less variability in both genders.

Report on a Milking Mule: Milk Qualitative Characteristics during Lactation

Despite their inability to reproduce naturally, mules can host embryos and be surrogate dams. The aim of this investigation was to increase our knowledge of the qualitative composition of mule's milk and its variations throughout the whole lactation period-namely, from 6 h after foaling to 180 days in milk (DIM). Milk was obtained from a mule dam that had foaled after receiving a mule embryo transfer. For each sample, the gross, mineral, and fatty acid composition was evaluated. The average quality of the mule milk was as follows: protein 1.97 g 100 mL-1, fat 0.90 g 100 mL-1, and ash 0.39 g 100 mL-1. Saturated fatty acids made up, on average, 50.00 g 100 g-1 of fat. Monounsaturated and polyunsaturated fatty acids made up half of the total fatty acid content (31.80 g 100 g-1 and 18.2 g 100 g-1 of fat, respectively). Linoleic acid and linolenic acid were the main polyunsaturated fatty acids in the milk. The milk composition changed throughout lactation. Dry matter, protein, fat, and ash decreased significantly from early lactation (6 h to 14 DIM). The n3 polyunsaturated fatty acids decreased at the end of lactation. The changes in milk composition throughout lactation are probably due to adaptations to the growth requirements of the foal.

Mule embryos share identical morphological features to horse embryos

This study aimed to compare the morphometry of horse and mule embryos. The study's hypothesis was that the micronuclei and nuclear fragmentation indexes are higher in mule embryos than in horse embryos. Twenty-two mares were randomly assigned in a crossover design to receive semen from a horse and a donkey; thirteen horse and thirteen mule embryos were obtained. Embryos were recovered eight days post-ovulation and classified according to the stage of development and quality with a score from 1 (excellent) to 4 (degenerate). Embryos were stained with Hoechst33342, and images were acquired with a fluorescence microscope. Nuclei were categorized as compact, mitotic, or fragmented; the fragmented and mitotic indexes were calculated based on their proportion over the total amount of nuclei counted. Embryo size and nuclear morphometry were assessed through ImageJ. Data analyses were carried out with GraphPad using ANOVA and T-test; significance was set at P < 0.05. The number of positive flushes in cycles bred with donkey or stallion semen did not differ when compared per cycle or per ovulation (13 vs. 12) (P > 0.05). One set of twins was recovered from a mare bred to the stallion that had a double ovulation; a mule and horse embryos were both recovered from eight mares. There was no difference in size between mule and horse embryos (915.5 ± 288 μm vs. 575.8 ± 69.6 μm) (P > 0.05) size of the study. The mule embryos scored between grade 1 (n = 9) and grade 2 (n = 4); similarly, the horse embryos scored between grade 1 (n = 6) and grade 2 (n = 7). The evaluation of the nuclear morphometry revealed that horse and mule embryos have a similar number of compact nuclei per sector (148.7 ± 6.8 nuclei/sector in mule embryos vs. 156.5 ± 8.5 nuclei/sector in horse embryos) (P > 0.05); however, the number of mitotic nuclei tended to be higher in mule embryos (5.2 ± 0.82) than in horse embryos (3.3 ± 0.3) (P = 0.08). The fragmented nuclei index was similar between mule (0.25 ± 0.1%) and horse (0.22 ± 0.1%) embryos (P = 0.4); the mitotic nuclei index was higher in mule embryos (3.2 ± 0.4%) than in horse embryos (2.2 ± 0.2%) (P = 0.02). In conclusion, embryo morphology of mares bred to a donkey and a horse shares similar nuclear ultrastructure features, except that mule embryos have a higher mitotic index.

Seasonal absence of supplementary corpora lutea in pregnant mares and the relationship with pregnancy loss

Two experiments were conducted in the Northern (UK) and Southern (Brazil) hemispheres to determine the effect of season (month of conception) on the development of supplementary CL (SCL) and the relationship with pregnancy loss. In experiment 1, 199 pregnancies were followed between Day 14 and term, to determine the number of SCL and pregnancy viability (Northern Hemisphere). From the 199 pregnancies, 178 were obtained from inseminations during the breeding season (March-September), while the rest, 21 pregnancies resulted from conceptions in the non-breeding season (October to February). Pregnancies conceived in the breeding season were more likely (P < 0.01) to have at least 1 SCL (75.8 %, 135/178) than pregnancies from the non-breeding season (33 %, 7/21). However, the pregnancy loss between Days 35 and 120 of pregnancy in mares with no SCL was similar (3.5 %, 2/57; P >0.1) than from mares with SCL (1.4 %, 2/142). In Experiment 2 (Southern Hemisphere), three groups of recipients were used based on their ovarian activity at the time of embryo transfer: Anestrus (n = 8), transitional (n = 7) and cyclic (n = 7) recipient mares. While all transitional and cyclic mares developed at least 1 SCL, only 50 % of anestrous recipients (4/8) developed SCL by 120 of gestation. In conclusion, the development of SCL in pregnant mares is influenced by the time of season of conception, therefore it appears to be regulated by the photoperiod and the endogenous seasonal variation in gonadotropin concentrations. Mares with no SCL were not at increased risk of pregnancy loss.

Interspecific and Intraspecific Artificial Insemination in Domestic Equids

Horses and donkeys differ phenotypically and karyotypically, although they can interbreed freely. Eight Standardbred mares and nine Amiata donkey jennies were included in the study. Semen was collected from two horses and two donkey stallions of proven fertility. A first pregnancy diagnosis was performed on day 10 after ovulation and repeated every day until embryo detection or until day 16. Irrespectively of the sire species, pregnancy rates in horse females (20/30, 66.7%) were significantly higher than in donkey females (19/70, 27.1%) (p < 0.05), while horse and donkey males did not affect pregnancy rates. Comparing overall intraspecific and interspecific AI, pregnancy rates were 25/37 (67.6%) and 14/63 (22.2%), respectively (p = 0.0001). The lowest pregnancy rate was obtained when inseminating jennies with horse stallion semen (8/49, 16.3%). No statistical differences were found when comparing embryo diameters, day at first pregnancy diagnosis, or in vitro embryo morphological quality among groups. In this study, much poorer results were obtained with jennies than with mares. Interspecific AI resulted in lower pregnancy rates than intraspecific Al, and AI to produce hinny hybrids resulted in the lowest pregnancy rate. Further studies are required to better understand the mechanism involved in such different outcomes in relation to intra- and interspecific breeding in domestic equids.

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.