High-level competition exercise and related fatigue are associated with stride and jumping characteristics in eventing horses.

BACKGROUND: Fatigue and related injuries to the musculoskeletal system are among the most frequent reasons for the withdrawal of high-level eventing horses from the sport. The safety of both horse and rider is very important, and early detection of fatigue is crucial. OBJECTIVES: To investigate elite eventing horses in competitive events focusing on biomechanical, cardiovascular and metabolic variables across the cross-country test and to identify their potential associations with fatigue. STUDY DESIGN: Prospective observational exploratory field study. METHODS: Observations on 54 cross-country tests of 33 horses at five competitive, high-level events were evaluated using sternal accelerometric analysis of stride parameters between and at the jumps. Blood lactate concentration and heart rate were determined 10 min after finishing. The differences in kinematic parameters between the course start and end were analysed with mixed models for repeated measures. Associations between blood lactate and heart rate recovery with the kinematic variables were quantified with Pearson correlation coefficients. RESULTS: We observed numerous stride characteristics between the jumps and the jumps changing over time during the courses. Blood lactate concentrations were positively correlated with the mean maximal strike power at the jumps in the last minute of the course (r = 0.41; p < 0.001), and the latter was negatively correlated with the mean stride height over the jumps (r = -0.41; p = 0.003). MAIN LIMITATIONS: The sample contained horses of varying breeds, sexes and ages, and different horses participated in different events. CONCLUSIONS: We identified several kinematic changes during a cross-country test depending on event, speed and fatigue.

Age and treatment on the day of embryo transfer in recipient mares affect likelihood of pregnancy.

OBJECTIVE: This retrospective evaluation of data from a large commercial embryo transfer facility aimed to determine the extent to which age and treatment on the day of embryo transfer in recipient mares influence the likelihood of pregnancy. MATERIAL AND METHODS: Embryo recovery was carried out on days 8-10 post-ovulation using transcervical uterine flushing. Recipient mares grouped according to their age were treated once on the day of embryo transfer (Day 3-8 post ovulation) and were assigned randomly to 1 of 3 groups: Mares in Group A (n=101) received antispasmodic, antimicrobial, and anti-inflammatory drugs. Mares in Group B (n=100) received gentamicin and flunixin meglumine. Group C (control) (n=103) did not receive any treatment. Detomidine (0.008 mg/kg bwt i.v.) was administered to all recipients before transfer of the embryo. The influence of treatment and recipient´s age was calculated using binary logistic regression. RESULTS: Day 16 post-transfer pregnancy rates were highest in Group A (74/101, 73.3a%), when compared to Group B (60/100, 60%), and Group C (57/103, 55.3b%) (a vs b, p<0.05). Pregnancy loss rates at D45 were not different between groups, A (8/74, 10.8%), B (5/60, 8.3%), and C (6/57, 10.5%), respectively (p>0.05). Pregnancy losses were increased in recipient mares 17-22 years (33.3a%) compared to younger recipient mares (2-6 years 7b%, 7-11 years 10%, 12-16 years 8b%) (a:b p<0.05). The regression model showed that the predicted probability for pregnancy after embryo transfer decreased as the age of the recipient mare increased for treated recipients in Group A (p=0.012), there was no effect of treatment and recipient´s age in Group B, and a decreased likelihood of pregnancy in recipients of advanced age (≥12 years of age) in untreated recipients (group C). CONCLUSIONS AND CLINICAL RELEVANCE: Likelihood of pregnancy increased following single administration of antispasmodic, antimicrobial, and anti-inflammatory drugs at the time of embryo transfer in recipients 2-12 years of age. Likelihood of pregnancy in recipients decreased in recipients≥12 years of age. These results, obtained under the conditions of a large commercial embryo transfer program, offer an opportunity to improve pregnancy rates in recipient mares≤12 years of age.

Increase of Body Temperature Immediately After Ovulation in Mares.

To successfully inseminate mares, precise detection of ovulation time is crucial, especially when using frozen-thawed semen. Monitoring body temperature, as has been described in women, could be a noninvasive way to detect ovulation. The objective of this study was to investigate the relationship between the time of ovulation and the variation of body temperature in mares based on automatic continuous measurements during estrus. The experimental group included 21 mares for 70 analyzed estrous cycles. When the mares showed estrous behavior, they were administered intramuscular deslorelin acetate (2.25 mg) in the evening. At the same time, monitoring of body temperature using a sensor device fixed at the left lateral thorax was started and continued for over 60 hours. In 2-hour intervals, transrectal ultrasonography was performed to detect ovulation. Estimated body temperature in the 6 hours following ovulation detection was on average 0.06°C +/- 0.05°C (mean +/- SD) significantly higher when compared with body temperature at the same time on the preceding day (P = .01). In addition, a significant effect of PGF2α administration for estrus induction on the body temperature was found, being significantly higher until 6 hours before ovulation compared to that of uninduced cycles (P = .005). In conclusion, changes in body temperature during estrus in mares were related to ovulation. The increase in body temperature immediately after ovulation might be used in the future to establish automatized and noninvasive systems to detect ovulation. However, the identified temperature rise is relatively small on average and hardly identifiable in the individual mares.

Increase of skin temperature prior to parturition in mares.

Prediction of impending foaling is highly desirable as early intervention may improve mare and foal outcomes. However, monitoring the peripartum mare is a time-consuming challenge for breeders and many foaling prediction systems have limitations. "Heating up" of the mare is empirically used by breeders as a sign of upcoming parturition in mares. The purpose of this study was to investigate if an increase in skin temperature shortly before parturition is detectable and to determine whether such physiological changes could be an additional valuable parameter to predict foaling. For that, 56 foalings of 14 Warmblood mares, 5 Arabian mares, 27 Thoroughbred mares, and 2 mares of other breeds were analyzed in this 2-year-study. Eight mares were monitored in both years. Mares were between 4 and 22 years old (average: 10 ± 5.5 years) and the mean pregnancy length was 342 days (±9 days), resulting in 14 births from primiparous mares and 42 multiparous mares. For monitoring the periparturient mares, the Piavet® system (Piavita AG, Zurich, Switzerland) was fixed daily when the mares had returned from the field between 4:00 and 6:00 p.m. and collected the next morning between 6:30 and 7:30 a.m. until the time of foaling. Nocturnal rhythms of the skin temperature with the highest values at the start of measurements and a nadir at 6:00 a.m. were observed. On the foaling night, we found a rise in skin temperature starting on average around 90 min prepartum. Skin temperatures recorded at 50 min before parturition and at each 5 min time point until rupture of the allantochorion were significantly higher (p < 0.05) than the mean temperatures measured in the 5 nights before parturition at the same time, reaching a difference of approximately 0.5 °C. There was a significant effect of parity (p = 0.04) on skin temperature during the last hours before foaling where primiparous mares showed a higher mean temperature than uni- or pluriparous mares as early as from 180 min on before parturition. In conclusion, our study shows an increase in skin temperature in most mares within 90 min before birth. Using new biomechanical and digital technologies, this finding could generate an additional potential parameter for the detection of impending parturition. However, skin temperature cannot be used as the only predictive diagnostic of impending parturition in the absence of other parameters.

Quantitative Gait Analysis Before and After a Cross-country Test in a Population of Elite Eventing Horses.

Early recognition of lameness is crucial for injury prevention. Quantitative gait analysis systems can detect low-grade asymmetries better than the human eye and may be useful in early lameness recognition. The aims of this study were (1) to investigate the frequency of gait asymmetries based on head and pelvic movement in elite eventing horses using inertial mounted measurement units and (2) to assess the association between asymmetries and muscle enzymes and blood lactate (LA) levelspost-exercise. Movement asymmetry of the head, wither, and pelvis were quantified in 33 elite eventing horses prior to and one day after the cross-country test of three Concours Complet International (CCI3* and CCI4*) events held three weeks apart. The effects of LA concentration immediately after completion of the cross-country course and of serum levels of creatine kinase (CK) and aspartate amino-transferase (AST) four hours post-exercise on gait asymmetry parameters were tested with linear models. A total of 58% and 77% of the 33 horses exhibited gait asymmetries that exceeded published threshold values before and after the cross-country course, respectively. The magnitude of pre-existing gait asymmetries was not significantly increased after the cross-country test and no associations with post-exercise levels of CK, AST, or LA were detected. The stride duration was significantly shorter the day following the cross-country test and was associated with LA, the age and the weight of the horses. In conclusion, a majority of the horses studied presented gait asymmetries and strenuous exercise resulted in decreased stride duration but did not worsen gait asymmetries.

A Novel QTL and a Candidate Gene Are Associated with the Progressive Motility of Franches-Montagnes Stallion Spermatozoa after Thaw.

The use of frozen-thawed semen is an important reproduction tool to preserve the biodiversity of small, native horse breeds such as the Franches-Montagnes (FM). However, not all stallions produce cryotolerant semen with a progressive motility after thaw ≥ 35%. To improve our understanding of the genetic background of male fertility traits in both fresh and frozen-thawed semen, we performed genome-wide association studies (GWAS) on gel-free volume, sperm cell concentration, total sperm count, and progressive motility in fresh and frozen-thawed semen from 109 FM stallions using 335,494 genome-wide single nucleotide polymorphisms (SNPs). We identified one significant (p < 1.69 × 10-7) quantitative trait locus (QTL) on ECA6 within the SCN8A gene for progressive motility after thaw, which was previously associated with progressive motility in boars. Homozygous stallions showed a substantial drop in progressive motility after thaw. This QTL could be used to identify cryointolerant stallions, avoiding the costly cryopreservation process. Further studies are needed to confirm whether this QTL is also present in other horse breeds.

Active immunisation against GnRH as treatment for unilateral granulosa theca cell tumour in mares.

BACKGROUND: Stallion-like or aggressive behaviour in mares affected by unilateral granulosa theca cell tumour (GTCT) is well-known, but use of a GnRH-vaccine as an alternative to surgical removal of the neoplastic ovary has not been investigated. OBJECTIVES: To determine the effect of immunisation against GnRH on ovarian size, testosterone concentration, Anti-Müllerian hormone (AMH) concentration, and owner-reported behaviour in four mares affected by unilateral GTCT. STUDY DESIGN: Retrospective case report. METHODS: A presumptive diagnosis of GTCT was made in four mares based on clinical signs, behavioural changes, transrectal palpation, and ultrasonography. All mares were vaccinated twice with the GnRH-vaccine Improvac® on day 0 and on day 13-33. Further booster vaccinations were administered if aggressive behaviour recurred between days 15 and 498. Before and parallel to the vaccinations, serum levels of oestradiol, progesterone (P4), testosterone, and AMH were evaluated and transrectal ultrasonography was performed. RESULTS: In all horses, analysis of serum levels of oestradiol, progesterone, testosterone, and AMH confirmed the clinical diagnosis of GTCT. Serum levels of testosterone dropped to baseline levels following the first two of three vaccination in all mares. In addition, AMH serum values decreased shortly after the second vaccination in three of four mares, and in one of the four mares returned to baseline levels. No further GTCT linked behaviour was reported by the owners and the affected ovaries diminished in size in all four cases. MAIN LIMITATIONS: This report is a case series with a limited number of animals, no controls and no standardised immunisation protocol. CONCLUSIONS: Repeated vaccinations with the GnRH-vaccine Improvac® mitigated owner-reported behavioural abnormalities and stopped tumour growth in four mares affected by unilateral GTCT over the entire observation period which extends to 7 years in one mare.

Effects of breed, management and personality on cortisol reactivity in sport horses.

Sport horses need to fulfill high physical and psychological requirements during training and competition. These as well as certain conditions of modern husbandry may affect their wellbeing. Here we aimed to (1) evaluate effects of demographic and management factors as well as personality traits on stress reactivity of sport horses, (2) investigate if elite sport horses have elevated stress levels compared to amateur sport horses, and (3) assess whether different equestrian disciplines differentially influence equine adrenal cortex responsiveness. For this purpose, we visited 149 healthy elite (n = 94) and amateur (n = 54) sport horses in Switzerland and performed an adrenocorticotropic hormone (ACTH) stimulation test. Additionally, a person who was familiar with the horse completed a questionnaire about demographic and management factors and their horses' personality traits. Linear models were calculated to assess associations between the questionnaire data and salivary cortisol 60 (T60) and 90 (T90) minutes after ACTH stimulation. While the model at T90 was not significant, post-stimulatory cortisol after 60 minutes appears most informative in line with a previous study and was significantly affected by the breed and by three management factors: "number of riders", "hours spent outside" and "group housing" (adjusted r2 = 15%, p<0.001). Thoroughbred and Warmblood horses displayed an increased adrenal response compared to Franches-Montagnes horses. Horses with several riders had a less pronounced reaction than horses with one rider, and horses that spent more time outside had a decreased response compared to horses that were stabled most of the time. Horses living in groups showed higher post-stimulatory cortisol values than horses that were housed singly. However, no significant associations of cortisol responsiveness with personality traits were found, and neither the use as elite or as amateur sport horses nor the discipline had an effect on the cortisol response. This suggests that optimizing husbandry conditions may be more important for improving equine welfare than changing their use.

Herbal yeast product, Equi-Strath®, alters the antioxidant status of stallion semen.

Effects of a plasmolysed yeast product enriched with herbs, malt, honey and orange syrup on semen characteristics and oxidative status in stallions were evaluated. Twenty stallions (mean age ±â€¯standard deviation = 9.5 ±â€¯4.5 years) were randomly divided into a treatment group (n = 10) receiving 0.06 mL/kg bodyweight of plasmolysed herbal yeast, and a control group (n = 10) receiving the same amount of placebo daily in the feed for 10 weeks. Ejaculates were collected weekly from all stallions starting at Week 0. Volume, sperm concentration, motility, and velocity were evaluated immediately, 24 and 48 h after cooled storage at 5 °C. At the two storage time points, membrane lipid peroxidation was determined using the BODIPY-C11. Additionally, blood samples were collected at Weeks 0, 1, 5 and 9, and analysed for antioxidant status, consisting of superoxide dismutase, cholesterol, thiobarbituric acid reactive substances, and non-esterified fatty acids. Due to the nature of the data, the Mann-Whitney U test was applied as preliminary analysis. The BODIPY-C11 in the semen was less at 24 h and greater at 48 h after collections in Week 1 to 3 (P < 0.01) and Week 1 to 10 (P <  0.05) compared with Week 0 in the treatment compared to control group. There were no significant differences between groups for all values for other seminal and blood variables evaluated. In conclusion, feed supplementation with plasmolysed herbal yeast temporarily improved the antioxidant status of stallion semen, which might be of benefit for preservation of cooled semen.

Correction: Mutations in MITF and PAX3 Cause "Splashed White" and Other White Spotting Phenotypes in Horses.

[This corrects the article DOI: 10.1371/journal.pgen.1002653.].

Increase of pregnancy rate after multiple periovulatory inseminations in mares.

OBJECTIVE: There exist differences in the reproductive behavior of stallions and mares under free-running and domestic in-hand breeding conditions. Contrary to artificial insemination programs, a stallion mates a mare multiple times per estrus under natural conditions. The objective of this study was to determine if multiple periovulatory artificial inseminations (MI), four times in two different time intervals instead of two, would result in increased pregnancy outcome or higher incidences of breeding induced endometritis. MATERIAL AND METHODS: Eighty-two estrous mares were allocated randomly to one of three experimental groups. They were administered intramuscular deslorelin (1.25 mg) to induce ovulation, and 24 hours later, they were inseminated either twice (group DI), four times in relatively short intervals (group MISI) or four times in relatively long intervals (MILI), after division of one commercial insemination dose (either frozen-thawed or chilled-warmed semen) into two or four portions, respectively. Uterine sampling for bacteriological and cytological analysis was conducted directly before the first insemination and 24 hours after the last insemination. RESULTS: Mares of the MI groups showed a higher pregnancy rate with frozen-thawed semen than mares of the DI group. There was no difference in bacteriological and cytological results between the three groups. In addition, mares of the MISI group showed less intrauterine fluid accumulation 24 hours after the last insemination than mares of the DI and MILI groups. CONCLUSION AND CLINICAL RELEVANCE: We suggest that multiple periovulatory inseminations with frozen-thawed semen in a close time frame to ovulation lead to an increase of pregnancy results per cycle, and that they do not lead to impaired inflammatory reactions of the uterus in healthy fertile mares.

Antibody response to Influenza booster vaccination in Franches-Montagnes stallions supplemented with Equi-Strath® : a randomized trial.

Bio-Strath® is a plasmolyzed yeast product enriched with herbs, malt, honey and orange juice. In this study, the effect of Equi-Strath® , the adapted product for horses, on the equine immune system was evaluated. A routine influenza booster vaccination was used as a model to study the effects of Equi-Strath® supplementation on the immune response. Twenty healthy Franches-Montagnes stallions with pre-existing antibody levels were randomly divided into a study group (SG, n = 10) receiving 0.06 mL/kg bodyweight of Equi-Strath® , and a control group (CG, n = 10), receiving the same amount of placebo, daily. The supplement and placebo were given from week 1 until week 14 of the trial. After 10 weeks, the horses were vaccinated with a commercial vaccine containing equine influenza strains of the H3N8 subtype. Antibody titres in blood were measured at day 0 before vaccination, and 14 and 32 days after vaccination. In addition, a complete blood count (CBC) was performed on day 0 and day 32. A linear increase of haemagglutination inhibition titres in both groups was observed after vaccination, but with no difference between treatment groups. CBC components remained unaffected by treatment. In conclusion, daily Equi-Strath® supplementation did not affect the adaptive immune response in stallions after a routine commercial H3N8 influenza booster vaccination.

Effects of mares' age and day of gestation on efficacy of transvaginal ultrasound-guided twin reduction.

OBJECTIVE: Transvaginal ultrasound-guided aspiration (TUA) is a procedure which can be used for the reduction of twins post-fixation in the mare. The aim of this study was to evaluate the effect of the age of mares and the day of gestation on the outcome of TUA treatment. MATERIAL AND METHODS: In 88 mares, diagnosed pregnant with twins, TUA of the yolk sac or allantoic fluid was performed between day 30 and 62 of gestation. Mares were aged 3-22 years. Ultrasonographic examination for a viable singleton pregnancy was performed by referring veterinarians 5-7 days and 4 weeks after TUA. Based on reported findings, effects of age and day of gestation on pregnancy rates were evaluated. RESULTS: Four weeks after TUA, 67% of the cases resulted in a viable singleton pregnancy. Five to 7 days after TUA treatment, the success rate was 74%. The gestational period did not affect the outcome, irrespective of the age of the mare. In contrast, success rates decreased with increasing age of the mares (84% ≤ 7 years vs. 67% 8-14 years vs. 57% ≥ 15 years). In mares aged 8-14 years, a decrease in singleton pregnancies was observed, if TUA was performed after day 35 of gestation. Success rates were slightly higher, if twin vesicles were localized within separate uterine horns (73%) as compared to the same horn (66%). Differences in singleton pregnancy rates were not statistically significant (p > 0.05). CONCLUSIONS AND CLINICAL RELEVANCE: TUA was found to be an effective procedure for reduction of twin pregnancies performed at days 30-62 of gestation. Success rates for singleton pregnancies were high for young mares ≤ 7 years old (84%) and middle aged mares treated before day 36 of pregnancy (74%). Duration of pregnancy at the time of TUA did not have a major impact on the outcome. Nevertheless, the procedure should optimally be performed around days 32-35 of pregnancy to allow for the possibility of natural reduction before treatment and rebreeding in case of a total pregnancy loss after TUA.

Cycle-specific female preferences for visual and non-visual cues in the horse (Equus caballus).

Although female preferences are well studied in many mammals, the possible effects of the oestrous cycle are not yet sufficiently understood. Here we investigate female preferences for visual and non-visual male traits relative to the periodically cycling of sexual proceptivity (oestrus) and inactivity (dioestrus), respectively, in the polygynous horse (Equus caballus). We individually exposed mares to stallions in four experimental situations: (i) mares in oestrus and visual contact to stallions allowed, (ii) mares in oestrus, with blinds (wooden partitions preventing visual contact but allowing for acoustic and olfactory communication), (iii) mares in dioestrus, no blinds, and (iv) mares in dioestrus, with blinds. Contact times of the mares with each stallion, defined as the cumulative amount of time a mare was in the vicinity of an individual stallion and actively searching contact, were used to rank stallions according to each mare's preferences. We found that preferences based on visual traits differed significantly from preferences based on non-visual traits in dioestrous mares. The mares then showed a preference for older and larger males, but only if visual cues were available. In contrast, oestrous mares showed consistent preferences with or without blinds, i.e. their preferences were mainly based on non-visual traits and could not be predicted by male age or size. Stallions who were generally preferred displayed a high libido that may have positively influenced female interest or may have been a consequence of it. We conclude that the oestrous cycle has a significant influence on female preferences for visual and non-visual male traits in the horse.

Repeatability of gait pattern variables measured by use of extremity-mounted inertial measurement units in nonlame horses during trotting.

OBJECTIVE To determine repeatability of gait variables measured by use of extremity-mounted inertial measurement units (IMUs) in nonlame horses during trotting under controlled conditions of treadmill exercise. ANIMALS 10 horses. PROCEDURES Six IMUs were strapped to the metacarpal, metatarsal, and distal tibial regions of each horse. Data were collected in a standardized manner (3 measurements/d on 3 d/wk over a 3-week period) while each horse was trotted on a treadmill. Every measurement consisted of a minimum of 20 strides from which a minimum of 10 strides was selected for analysis. Spatial and temporal variables were derived from the IMUs. Repeatability coefficients based on the within-subject SD were computed for each gait analysis variable at each week. RESULTS Most of the temporal and spatial variables had high repeatability (repeatability coefficients < 10), and the repeatability coefficients were consistent among the 3 weeks of data collection. Some spatial variables, specifically the symmetry variables (which were calculated from other variables), had somewhat higher repeatability coefficients (ie, lower repeatability) only in the last week. CONCLUSIONS AND CLINICAL RELEVANCE With the exceptions of some symmetry variables, which may reflect individual variations during movement, the extremity-mounted IMUs provided data with high repeatability for nonlame horses trotting under controlled conditions of treadmill exercise. Repeatability was achieved for each instrumented limb segment with regard to the spatial relationship between 2 adjacent segments (joint angles) and the temporal relationship among all segments (limb phasing). Extremity-mounted IMUs could have the potential to become a method for gait analysis in horses.

Ejaculate Characteristics Depend on Social Environment in the Horse (Equus caballus).

Sperm competition theory predicts semen characteristics to be affected by the social environment. We used the polygamous horse (Equus caballus) to experimentally study within-subject plasticity in response to different social environments. Stallions were sequentially exposed, over a period of 8 weeks each, to other stallions and then singly to mares, or vice versa (in adjacent boxes separated by grills). Ejaculates were collected to determine semen characteristics. Highest sperm numbers were found in stallions that were first exposed to other stallions and then to mares, while lowest sperm numbers were observed in stallions that had been exposed to mares but not yet to other stallions. One of three sperm velocity measures (curvilinear velocity) was consistently elevated in stallions that were first exposed to stallions and then to mares. Sperm number after exposure to mares and curvilinear sperm velocity after exposure to stallions were both positively correlated to average blood testosterone levels during the corresponding period of exposure. We conclude that ejaculate characteristics are plastic traits affected by the social environment in horses.

Influence of transrectal and transabdominal ultrasound examination on salivary cortisol, heart rate, and heart rate variability in mares.

Pregnancy diagnostics in equine reproduction are routinely performed using transrectal ultrasonography, although it is also possible to visualize the fetus by transabdominal ultrasound examinations from the 90th day of gestation onward. We hypothesized that ultrasound examinations may stress the mare and that the gestational stage status and lactation may influence the mare's stress reaction. To investigate the stress reaction, 25 thoroughbred mares of different age, pregnancy and lactational status underwent a transrectal examination. In pregnant mares, an additional transabdominal examination was performed. Salivary cortisol concentration, mean heart rate, and heart rate variability of mares were assessed to evaluate the reactions of hypothalamic-pituitary-adrenal (HPA) axis and of the autonomic nervous system. Significant differences were observed between lactating and nonlactating mares; with a lower responsiveness to stress in lactating mares. The transrectal ultrasound examination in nonlactating mares induced a significant increase in salivary cortisol (P < 0.05), and in the heart rate variability parameter, ratio of low to high frequencies (P < 0.05). This reflects an activation of the HPA axis and a shift to more sympathetic dominance. In contrast, a transabdominally performed pregnancy check did not induce an activation of the HPA axis over basal level but increased the mean heart rate and low to high frequency ratio. The results of this study indicate that checks of advanced pregnancies can be easily performed by transabdominal ultrasonography. With regard to animal welfare, this technique should be preferred during midgestation in nonlactating mares.

Congenital hepatic fibrosis in the Franches-Montagnes horse is associated with the polycystic kidney and hepatic disease 1 (PKHD1) gene.

Congenital hepatic fibrosis has been described as a lethal disease with monogenic autosomal recessive inheritance in the Swiss Franches-Montagnes horse breed. We performed a genome-wide association study with 5 cases and 12 controls and detected an association on chromosome 20. Subsequent homozygosity mapping defined a critical interval of 952 kb harboring 10 annotated genes and loci including the polycystic kidney and hepatic disease 1 (autosomal recessive) gene (PKHD1). PKHD1 represents an excellent functional candidate as variants in this gene were identified in human patients with autosomal recessive polycystic kidney and hepatic disease (ARPKD) as well as several mouse and rat mutants. Whereas most pathogenic PKHD1 variants lead to polycystic defects in kidney and liver, a small subset of the human ARPKD patients have only liver symptoms, similar to our horses with congenital hepatic fibrosis. The PKHD1 gene is one of the largest genes in the genome with multiple alternative transcripts that have not yet been fully characterized. We sequenced the genomes of an affected foal and 46 control horses to establish a comprehensive list of variants in the critical interval. We identified two missense variants in the PKHD1 gene which were strongly, but not perfectly associated with congenital hepatic fibrosis. We speculate that reduced penetrance and/or potential epistatic interactions with hypothetical modifier genes may explain the imperfect association of the detected PKHD1 variants. Our data thus indicate that horses with congenital hepatic fibrosis represent an interesting large animal model for the liver-restricted subtype of human ARPKD.

A chromosomal region on ECA13 is associated with maxillary prognathism in horses.

Hereditary variations in head morphology and head malformations are known in many species. The most common variation encountered in horses is maxillary prognathism. Prognathism and brachygnathism are syndromes of the upper and lower jaw, respectively. The resulting malocclusion can negatively affect teeth wear, and is considered a non-desirable trait in breeding programs. We performed a case-control analysis for maxillary prognathism in horses using 96 cases and 763 controls. All horses had been previously genotyped with a commercially available 50 k SNP array. We analyzed the data with a mixed-model considering the genomic relationships in order to account for population stratification. Two SNPs within a region on the distal end of chromosome ECA 13 reached the Bonferroni corrected genome-wide significance level. There is no known prognathism candidate gene located within this region. Therefore, our findings in the horse offer the possibility of identifying a novel gene involved in the complex genetics of prognathism that might also be relevant for humans and other livestock species.

Accumulating mutations in series of haplotypes at the KIT and MITF loci are major determinants of white markings in Franches-Montagnes horses.

Coat color and pattern variations in domestic animals are frequently inherited as simple monogenic traits, but a number are known to have a complex genetic basis. While the analysis of complex trait data remains a challenge in all species, we can use the reduced haplotypic diversity in domestic animal populations to gain insight into the genomic interactions underlying complex phenotypes. White face and leg markings are examples of complex traits in horses where little is known of the underlying genetics. In this study, Franches-Montagnes (FM) horses were scored for the occurrence of white facial and leg markings using a standardized scoring system. A genome-wide association study (GWAS) was performed for several white patterning traits in 1,077 FM horses. Seven quantitative trait loci (QTL) affecting the white marking score with p-values p≤10(-4) were identified. Three loci, MC1R and the known white spotting genes, KIT and MITF, were identified as the major loci underlying the extent of white patterning in this breed. Together, the seven loci explain 54% of the genetic variance in total white marking score, while MITF and KIT alone account for 26%. Although MITF and KIT are the major loci controlling white patterning, their influence varies according to the basic coat color of the horse and the specific body location of the white patterning. Fine mapping across the MITF and KIT loci was used to characterize haplotypes present. Phylogenetic relationships among haplotypes were calculated to assess their selective and evolutionary influences on the extent of white patterning. This novel approach shows that KIT and MITF act in an additive manner and that accumulating mutations at these loci progressively increase the extent of white markings.