A fertile mule and hinny in China

Anecdotal reports of fertility in female mules (jack donkey x mare) and hinnies (stallion x jenny donkey) have appeared in the literature over the years, but scientists have generally regarded them with scepticism. The fact that some of these hybrids can come into estrous and ovulate makes fertility conceivable, given that opportunity for mating arises. In China, where mules are bred extensively for work on the farms, a fertile female mule and a fertile female hinny have now been verified by chromosomal investigation. Each had mated with a donkey and produced a filly foal. The foals show unique hybrid karyotypes different from the mule's or hinny's and different from each other's. The studies make it clear that mule and hinny fertility, at least for the female hybrid, is a real possibility.     

Sex ratios in mule duck embryos at various stages of incubation

Mule duck hatcheries have long reported varying degrees of unbalance in the sex ratio, with a preponderance of male mules at hatching. The aim of the present study was to assess the distributions of sex ratios at various stages of development in embryos originating from intra- and intergeneric crosses between parental lineages (Muscovy male x Muscovy female, Pekin male x Pekin female, Muscovy male x Pekin female or Mule, and Pekin male x Muscovy female or Hinny). In Experiment I, embryo sexing was performed on Days 1 and 5 of incubation (by multiplex PCR) and at hatching (by vent observation). The sex ratio was not significantly modified during the early stages of embryo development whatever the genetic origin (P>0.05, Days 1 and Day 5) but our results in mule and hinny ducklings confirmed the preponderance of males among normally hatched ducklings originating from the intergeneric lineage (58.9 and 55.4% males in mules and hinnies, respectively; P<0.05 in both cases). Sex ratio (vent sexing) in second grade (cull) ducklings revealed that 68% of these ducklings were females (P<0.05). In Experiment II, the distribution of sex ratio was also performed in mule duck eggs from 6 batches (400,000 eggs/batch) first examined for fertility (candling) on Day 18 of incubation. These results indicate that the percentage of males present in the population of normally hatched ducklings increases when fertility decreases. In addition, this experiment also revealed that 83.7-90.5% of viable male mule embryos develop up to hatching, compared to only 43.0-51.0% of female mule embryos. Given that a deviation in sex ratio during the first stages of incubation is unlikely (Experiment I), it is concluded that the skewed sex ratio of mule ducks at hatching is primarily due to increased late mortality in female mule embryos occurring between egg transfer and hatching. This mortality originated, at least in part, from the intergeneric origin of female mules, and was marked to a greater or lesser extent depending on the initial success of fertilization in a given batch, a possible indication that the initial quality of gametes may selectively exert its influence at the later stages of embryo development.     

A mare mule--dam or foster mother?

A female, horse-like foal was apparently born to a mare mule from mating to a Shetland stallion. The presence of three pregnant Shetland mares in the same pasture, however, raised some questions about parentage, even though all three mares apparently gave birth to single foals within 6 weeks after the birth of the propositus. The transferrin system indicated that the foal was not born to the mare mule but was the offspring of one of the Shetland mares. Apparently one Shetland mare gave birth to twins 3 to 6 weeks apart, and the mare mule came into lactation spontaneously and adopted the first twin. The offspring was determined to be a horse by appearance, karyotype, blood type, and voice.     

Analysis of mechanisms regulating the expression of parental alleles at the GPD locus in mule erythrocytes

Erythrocyte glucose-6-phosphate dehydrogenase (G6PD) was examined by 13% starch gel electrophoresis in 74 mules (42 females and 32 males), 35 donkeys, and ten horses. The quantitative expression of the parental alleles at the Gpd locus varies greatly in female mules from the hemizygous expression of the maternal allele to that of the paternal. The data obtained indicate that the X chromosomes are randomly inactivated in female mules. No selective advantage of a cell population with a maternally (or paternally) derived X active was found in female mule erythrocytes. It is suggested that the phenotypic variability in the expression of the parental Gpd alleles is related to the random proportions established between cells having either a maternal or paternal X active in an initiator (stem) cell group giving rise to erythroid tissue. Initiator cell numbers estimated for erythroid tissue (six or seven) are close to those reported for human females and intergeneric fox hybrids. These numbers may vary depending on the duration of the time of determination and the division rate of initiator cells at determination.     

Characterization of a red blood cell antigen in donkeys and mules associated with neonatal isoerythrolysis

A red cell antigen of donkeys and mules was identified using antibodies in serum from a mare which produced a mule foal affected with neonatal isoerythrolysis (NI). Subsequently antibodies with similar activity were identified in the sera of other mares which had produced mule foals and were produced by immunization of horses with blood from donkeys. The antigen detected by these antibodies does not correspond to any recognized horse red cell alloantigen. This may be a xenoantigen since all donkeys (and mules) tested have shared this antigen and all horses tested have lacked the antigen. The results suggest that all mule pregnancies (donkey sire x horse dam) are incompatible with regard to this factor and a potential for neonatal isoerythrolysis exists in all cases.     

Comparative testis morphometry and seminiferous epithelium cycle length in donkeys and mules

The mule (Equus mulus mulus) is a sterile hybrid domestic animal that results from the breeding of a male donkey (Equus asinus) to a female horse (Equus caballus). Usually, spermatogenesis in mules does not advance beyond spermatocytes. In the present study, we performed a comparative and more accurate morphometric and functional investigation of the testis in donkeys and mules. Due to the smaller testis size, lower seminiferous tubule volume density, and fewer germ cells, the total length of seminiferous tubules in mules was significantly smaller than in donkeys. However, the percentage of seminiferous tubules containing germ cells (spermatogonia and spermatocytes) in mules was approximately 95%. The total number of Sertoli cells per testis observed in donkeys and mules was very similar. However, the total number of Leydig cells in mules was approximately 70% lower than in donkeys. At least in part, this difference was probably related to the lower number of germ cells present in mule seminiferous tubules. Although spermatogenesis in mules did not advance beyond secondary spermatocytes/newly formed round spermatids, germ cell associations in the seminiferous epithelium and pachytene spermatocytes nuclear volume in donkeys and mules were similar. The duration of spermatogenesis was estimated using intratesticular injections of tritiated thymidine. Each spermatogenic cycle in donkeys lasted 10.5 days. A similar value was found in mules ( approximately 10.1 days). Considering that the entire spermatogenic process takes approximately 4.5 cycles to be completed, its total duration in donkeys was estimated to last 47.2 days. The results found for mules suggest that the mechanisms involved in the determination of testis structure and function are probably originated from donkeys. Also, the data found for mules suggest that their seminiferous tubules are able to sustain complete spermatogenesis. In this regard, this species is a potential model for transplants of germ cells originated from donkeys and horses or other large animals.     

Estimating chronic wasting disease effects on mule deer recruitment and population growth

Chronic wasting disease (CWD), a prion disease of mule deer (Odocoileus hemionus), accelerates mortality and in so doing has the potential to influence population dynamics. Although effects on mule deer survival are clear, how CWD affects recruitment is less certain. We studied how prion infection influenced the number of offspring raised to weaning per adult (≥2 yr old) female mule deer and subsequently the estimated growth rate (λ) of an infected deer herd. Infected and presumably uninfected radio-collared female deer were observed with their fawns in late summer (August-September) during three consecutive years (2006-2008) in the Table Mesa area of Boulder, Colorado, USA. We counted the number of fawns accompanying each female, then used a fully Bayesian model to estimate recruitment by infected and uninfected females and the effect of the disease on λ. On average, infected females weaned 0.95 fawns (95% credible interval=0.56-1.43) whereas uninfected females weaned 1.34 fawns (95% credible interval=1.09-1.61); the probability that uninfected females weaned more fawns than infected females was 0.93). We used estimates of prevalence to weight recruitment and survival parameters in the transition matrix of a three-age, single-sex matrix model and then used the matrix to calculate effects of CWD on λ. When effects of CWD on both survival and recruitment were included, the modeled λ was 0.97 (95% credible interval = 0.82-1.09). Effects of disease on λ were mediated almost entirely by elevated mortality of infected animals. We conclude that although CWD may affect mule deer recruitment, these effects seem to be sufficiently small that they can be omitted in estimating the influences of CWD on population growth rate.     

Effectiveness of a redesigned vaginal implant transmitter in mule deer

Our understanding of factors that limit mule deer (Odocoileus hemionus) populations may be improved by evaluating neonatal survival as a function of dam characteristics under free-ranging conditions, which generally requires that both neonates and dams are radiocollared. The most viable technique facilitating capture of neonates from radiocollared adult females is use of vaginal implant transmitters (VITs). To date, VITs have allowed research opportunities that were not previously possible; however, VITs are often expelled from adult females prepartum, which limits their effectiveness. We redesigned an existing VIT manufactured by Advanced Telemetry Systems (ATS; Isanti, MN) by lengthening and widening wings used to retain the VIT in an adult female. Our objective was to increase VIT retention rates and thereby increase the likelihood of locating birth sites and newborn fawns. We placed the newly designed VITs in 59 adult female mule deer and evaluated the probability of retention to parturition and the probability of detecting newborn fawns. We also developed an equation for determining VIT sample size necessary to achieve a specified sample size of neonates. The probability of a VIT being retained until parturition was 0.766 (SE = 0.0605) and the probability of a VIT being retained to within 3 days of parturition was 0.894 (SE = 0.0441). In a similar study using the original VIT wings (Bishop et al. 2007 ), the probability of a VIT being retained until parturition was 0.447 (SE = 0.0468) and the probability of retention to within 3 days of parturition was 0.623 (SE = 0.0456). Thus, our design modification increased VIT retention to parturition by 0.319 (SE = 0.0765) and VIT retention to within 3 days of parturition by 0.271 (SE = 0.0634). Considering dams that retained VITs to within 3 days of parturition, the probability of detecting at least 1 neonate was 0.952 (SE = 0.0334) and the probability of detecting both fawns from twin litters was 0.588 (SE = 0.0827). We expended approximately 12 person-hours per detected neonate. As a guide for researchers planning future studies, we found that VIT sample size should approximately equal the targeted neonate sample size. Our study expands opportunities for conducting research that links adult female attributes to productivity and offspring survival in mule deer. © 2011 The Wildlife Society.     

Influence of interspecific competition on mule deer birthing and rearing site selection

Ungulates often alter behavior and space use in response to interspecific competition. Despite observable changes in behavior caused by competitive interactions, research describing the effects of competition on survival or growth is lacking. We used spatial modeling to determine if habitat use by female mule deer (Odocoileus hemionus) was affected by other ungulate species prior to, during, and after parturition. We conducted our study in the Book Cliffs region of eastern Utah, USA, during 2019 and 2020. We used resource selection function (RSF) analysis to model space use of 4 ungulate species that potentially competed with mule deer: bison (Bos bison), cattle, elk (Cervus canadensis), and feral horses. We incorporated RSF models for competing species into a random forest analysis to determine if space use by mule deer was influenced by these other ungulate species. We used survival and growth data from neonate mule deer to directly assess potential negative effects of other ungulates. Habitat use by elk was an important variable in predicting use locations of mule deer during birthing and rearing. The relationship was positive, suggesting interference competition was not occurring. Survival of neonate mule deer increased as the probability of use by elk increased (hazard ratio = 0.185 ± 0.497 [SE]). Further, probability of use by elk in rearing habitat had no influence on growth of neonate mule deer from birth to 6 months of age, suggesting that exploitative competition was not occurring.     

Demodicosis in a mule deer (Odocoileus hemionus hemionus) from Saskatchewan, Canada

Infestation of deer with Demodex spp. mites has been described in white-tailed deer (Odocoileus virginianus) and in Columbian black-tailed deer (Odocoileus hemionus columbianus) in North America, as well as in four species of deer in Europe. We describe Demodex sp. infestation in an adult female mule deer (Odocoileus hemionus hemionus) with skin lesions found dead near Saskatoon, Saskatchewan, Canada. This is believed to be the first report of demodicosis in mule deer.     

Fertility in an F1 male hybrid of white-tailed deer (Odocoileus virginianus) x mule deer (O. hemionus)

The fecundity of an F1 male hybrid deer, from a cross between a male Odocoileus virginianus (white-tailed deer) and a female O. hemionus (mule deer), was assessed by cytogenetic and flow cytometric techniques. Analysis of chromosome morphology, nucleolus organizer expression, meiotic chromosome pairing, sperm production, and nuclear gene inheritance revealed no genetic anomalies that could potentially impair normal fertility. These observations are discussed in relation to recent reports of hybridization between natural populations of these two species.     

Differential prey use by male and female cougars in Washington

Male and female predators are often assumed to have the same effects on prey. Because of differences in body size and behavior, however, male and female predators may use different species, sexes, and ages of prey, which could have important implications for wildlife conservation and management. We tested for differential prey use by male and female cougars (Puma concolor) from 2003 to 2008 in Washington State. We predicted that male cougars would kill a greater proportion of larger and older prey (i.e., adult elk [Cervus elaphus]), whereas females would kill smaller and younger prey (i.e., elk calves, mule deer [Odocoileus hemionus]). We marked cougars with Global Positioning System (GPS) radio collars and investigated 436 predation sites. We located prey remains at 345 sites from 9 male and 9 female cougars. We detected 184 mule deer, 142 elk, and 17 remains from 4 other species. We used log-linear modeling to detect differences in species and age of prey killed among cougar reproductive classes. Solitary females and females with dependent offspring killed more mule deer than elk (143 vs. 83, P < 0.01), whereas males killed more elk than mule deer (59 vs. 41, P < 0.01). Proportionately, males killed 4 times more adult elk than did females (24% vs. 6% of kills) and females killed 2 times more adult mule deer than did males (26% vs. 15% of kills). Managers should consider the effects of sex of predator in conservation and management of ungulates, particularly when managing for sensitive species. © 2011 The Wildlife Society.     

Condition of mule deer during winter: stress and spatial overlap with North American elk

We assessed body condition, diet quality (indexed by fecal nitrogen), and stress levels (using fecal glucocorticoid metabolites) in mule deer Odocoileus hemionus in southeastern Idaho, USA, during a mild (2007) and a harsh winter (2008) to evaluate spatial overlap and potential competition with North American elk Cervus elaphus. We used data from GPS telemetry to construct spatially explicit maps of local population density of elk for January–April. Loss of body condition over winter in yearling and adult female mule deer was not related to elk density but to winter severity. Fecal nitrogen increased as winter progressed in both winters, was significantly lower during 2008 than in 2007, but was not related to local population density of elk. In the mild winter of 2007, a significant positive relationship existed between local population density of elk and fecal glucocorticoid metabolite levels of mule deer, indicating increased physiological stress among mule deer wintering in close proximity to elk. Fecal glucocorticoid metabolite levels in deer were lower in 2008 than in 2007 and exhibited no significant relationship with elk density. Declining fecal glucocorticoid levels through winter may be typical of northern cervids. No difference existed in levels of fecal glucocorticoids between sexes of deer. A reduction in elk populations may not improve diet quality, physiological stress levels, or body condition of mule deer on winter range, especially during severe winters. Consequently, management and conservation of winter habitat are more likely to benefit mule deer than would altering density of elk.     

Birth sex ratios relate to mare condition at conception in Kaimanawa horses

Several hypotheses have been proposed to explain variation inbirth sex ratios, based on the premise that variation is expectedwhen the profitability of raising sons and daughters variesbetween individual parents. We tested the Trivers-Willard hypothesisthat mothers in better condition produce relatively more sonsand that mothers in poorer condition produce relatively more daughterswhen male reproductive success is more variable. We examinedbirth sex ratios in relation to mare body condition at conceptionin horses in which male reproductive success is differentiallyhelped by slight advantages in condition. Horses meet the assumptionsof the Trivers-Willard hypothesis better than many species onwhich it has been tested and in which sex ratio biases are notconfounded by sexual size dimorphism such that one sex is more likelyto die in utero in females in poor condition. Mares that hada female foal were in poorer condition at conception than thosethat had a male foal, and mares that had foals of differentsexes in different years were in significantly poorer conditionwhen they conceived their female foal. There was no relationshipbetween offspring sex and mid-gestation condition, and therewas no difference in foaling rates in relation to body conditionat conception. Consequently, sex ratio deviations are not explainedby fetal loss in utero. Furthermore, differential fetal lossof the less viable sex cannot explain the greater proportionof males produced by mares in better condition. Therefore, ourresults suggest that sex ratio modification occurs at conceptionin wild horses.     

The effect of terrain and female density on survival of neonatal white‐tailed deer and mule deer fawns

Juvenile survival is a highly variable life‐history trait that is critical to population growth. Antipredator tactics, including an animal's use of its physical and social environment, are critical to juvenile survival. Here, we tested the hypothesis that habitat and social characteristics influence coyote (Canis latrans) predation on white‐tailed deer (Odocoileus virginianus) and mule deer (O. hemionus) fawns in similar ways during the neonatal period. This would contrast to winter when the habitat and social characteristics that provide the most safety for each species differ. We monitored seven cohorts of white‐tailed deer and mule deer fawns at a grassland study site in Alberta, Canada. We used logistic regression and a model selection procedure to determine how habitat characteristics, climatic conditions, and female density influenced fawn survival during the first 8 weeks of life. Fawn survival improved after springs with productive vegetation (high integrated Normalized Difference Vegetation Index values). Fawns that used steeper terrain were more likely to survive. Fawns of both species had improved survival in years with higher densities of mule deer females, but not with higher densities of white‐tailed deer females, as predicted if they benefit from protection by mule deer. Our results suggest that topographical variation is a critical resource for neonates of many ungulate species, even species like white‐tailed deer that use more gentle terrain when older. Further, our results raise the possibility that neonatal white‐tailed fawns may benefit from associating with mule deer females, which may contribute to the expansion of white‐tailed deer into areas occupied by mule deer.     

Horse, ass, and mule chromosomes.

Karyotypes of the horse with 64 chromosomes, the ass with 62 chromosomes, and the mule with 63 chromosomes are presented. The chromosome complements of each species and their mule hybrid are analyzed and compared.     

Tularemia in a mule deer

A case of tularemia was confirmed in a 51-year-old man who acquired the disease from a mule deer, Odocoileus hemionus. Francisella tularensis was isolated from bone marrow of the deer carcass.     

Isolation and chemical composition of the leucocytes from donkey, horse, mule and pig.

1. Leucocytes from the blood of adult and young donkeys (Equus asinus L.), adult horses (Equus caballus L.), adult mules (Equus asinus x Equus caballus) and adult pigs (Sus scrofa L.) were obtained in a high degree of purity (99.9%) using Na2-EDTA-dextrans mixtures. 2. Sialic acids were released, purified, identified and determined from both non-delipided and delipided leucocytes. 3. N-glycolylneuraminic was the predominant sialic acid. N-acetylneuraminic acid and N,O-diacetyl-neuraminic acid were also found in all materials. Except in pig, other unidentified sialic acid(s) were also detected. 4. The concentration of total sialic acids (microgram/mg protein) is different according to the species, and in donkey species according to the age. 5. Galactose, glucose, mannose, fucose and (in a less amount) ribose were determined. Their total content is about 2-3-fold that of hexosamines. 6. There is a higher cholesterol content in adult donkey leucocytes than in those of young ones. 7. Total lipids, cholesterol or phospholipid contents are similar among the leucocytes of the above-mentioned species. 8. The similarities are marked in the electrophoresis patterns of proteins and glycoproteins for the donkey, mule and horse samples. 9. The molecular weights for leucocytes proteins were estimated as ranging between 230,000 and 20,000; and for the main protein bands, between 120,000 and 22,000.