"Horses" is a broad topic that encompasses various aspects of equine biology, behavior, and management. This category includes studies on the anatomy, physiology, and genetics of horses, as well as their behavior, nutrition, and care. Research in this area may also cover the historical and cultural significance of horses, their roles in agriculture, sport, and therapy, and the challenges associated with their conservation and welfare. The page aggregates peer-reviewed research articles and scholarly studies that explore the multifaceted relationships between humans and horses, examining both scientific and socio-economic perspectives.
Moreno-Millan M, Delgado Bermejo JV, Lopez Castillo G.An X-trisomy has been detected in an intersexuality Spanish-bred horse by using G- and C-banding methods. The external characteristics and the behavioural and physiological irregularities of the horse are described. This is the first time that an association between an X-trisomy and a case of intersexuality has been reported in any domestic animal.
ter Laak EA, Fennema G, Jaartsveld FH.Contagious Equine Metritis (CEM) was detected in the Netherlands for the first time in 1987. A total number of five mares (Dutch saddle-horse) were infected in three separate outbreaks. The origin of the infection could not be determined in any of the cases. As the isolates of the causal organism, Taylorella equigenitalis, showed auto-agglutination, diagnosis was difficult. Therefore, an indirect immune fluorescence test as used to diagnose the second isolate. Five strains were isolated, which all were resistant to streptomycin. The prevalence of CEM since 1981 is summarised. The importance of...
Mendoza L, Marin G.Antigens and rabbit-antisera from holotypes of Pythium insidiosum and P. destruens were prepared to elucidate their antigenic relationship. The antigens and rabbit-antisera of P. insidiosum as well as P. destruens used as a reference system showed that both shared three precipitin bands in common. The antigen and rabbit-antisera of P. destruens and P. insidiosum used as a reference system against other strains isolated from humans and animals with pythiosis, also showed three precipitin bands in common. When we used sera taken from horses with proven pythiosis against antigens of P. insidiosum...
Higuchi T, Ichijo S, Osame S, Ohishi H.In order to clarify the cause of white muscle disease (W.M.D.) in foals, tocopherol and selenium concentrations in serum and glutathione peroxidase activities in blood were measured. Examination was made on the samples from horses affected with W.M.D., the foal kept with them in the same stable, the foals kept in the stables without affected foals, and respective mares. The heavy-breed horses in Fukuoka prefecture and Tokachi district were also examined for comparison. Serum tocopherol levels of these foals were normal because after intake of colostrum. Mares of affected foals showed lower toc...
Dumasia MC, Houghton E, Jackiw M.After homogenization of testicular tissue from stallions aged 1, 2 and 5 years, the unconjugated and conjugated steroids were isolated by a combined solvent-solid extraction procedure. The conjugates were further separated into glucuronides and sulphates by chromatography using Sephadex LH-20. After enzyme hydrolysis and solvolysis of the respective conjugate classes, the three extracts, unconjugated steroids, aglycones and solvolysed sulphates, were purified by chromatography using Kieselgel 60H columns. Five fractions were resolved from each extract; an aliquot of each fraction was derivatiz...
Gibson KT, McIlwraith CW, Turner AS, Stashak TS, Aanes WA, Trotter GW.A retrospective study was made of 58 horses with open joint injuries admitted to the veterinary teaching hospital. Twenty-five (43%) were admitted within 24 hours of injury, 15 (26%) were examined 2 to 7 days after injury, and 18 (31%) were evaluated a week or more after the initial injury. The joints of the lower portions of the limbs most commonly were affected, with injuries that varied from puncture wounds to severe lacerations with soft tissue deficits. Diagnosis was made on the basis of clinical signs and results of synovial fluid analysis and radiography. Radiography was found to be an ...
Bernard WV, Reef VB, Reimer JM, Humber KA, Orsini JA.Small-intestinal intussusceptions were diagnosed in 3 foals. Cross-sectional ultrasonography through the apex of the intussusceptum revealed a target-like pattern with a thick hypoechoic rim. The thick hypoechoic rim was caused by severe edema of the entering and returning walls of the intussusceptum. At the more proximal portion of the intestines, where parietal edema was less severe, the image appeared as 2 concentric rings and an inner circular area. The outer ring and inner circular area were hypoechoic and represented the returning and the entering wall of the intussusceptum. An additiona...
Parks AH, Guy BL, Rawlings CA, Constantino MJ.A 5-year-old mare was evaluated for lameness and swelling of the right forelimb. Clinical findings, including peripheral edema, venous pulsation, palpable thrill in the cephalic vein, disparate arteriovenous oxygen tension differences between the left and right forelimbs, and Branham sign, were suggestive of arteriovenous fistula. Failure to identify the fistula by angiography was attributed to closure of the shunt during anesthesia. Surgical exploration of the affected limb to identify the shunt also was unsuccessful.
Holland RE, Sriranganathan N, DuPont L.Enterotoxigenic Escherichia coli was isolated from a 3-day-old foal with diarrhea. The isolate was distinguished from nonpathogenic E coli by determining the presence of pili and enterotoxin production. A standard slide agglutination test was performed, using pooled antisera that contained antibodies against K99 and F41 pilus antigens, K87 capsular antigen, and 0101 somatic antigen. Agglutination of the antisera occurred in the presence of the isolate. Piliation was verified by use of negative-contrast electron microscopy. Further, the isolate produced a heat-labile enterotoxin-like antigen th...
Voss KA, Norred WP, Plattner RD, Bacon CW.Currently there is no convenient bioassay to determine the potential toxicity of corn naturally contaminated with Fusarium moniliforme. A short-term bioassay would be useful for future investigations aimed at isolating as yet unidentified toxins produced by this fungus. Two groups of five male Sprague-Dawley rats were each fed one of two F. moniliforme contaminated corn samples, designated CS-1 and CS-2, that were associated with separate field cases of equine leukoencephalomalacia (ELEM). A control group, also consisting of five male rats, was fed uncontaminated seed corn. All animals survive...
Shamis LD, Bramlage LR, Gabel AA, Weisbrode S.Arthrotomies of middle carpal joints were done on 13 horses, and a 1-cm partial thickness, round defect was made on the radial facet of both third carpal bones. In one joint, 1-mm diameter 1-cm deep holes were drilled within the defect, and one joint was used as a control. horses were assigned to 2 groups--group 1 (n = 6 horses), 5 drill holes; group 2 (n = 7 horses), 11 drill holes. At 1 and 3 weeks after surgery, differences between joints in synovial fluid total protein values, WBC counts, or results of mucin precipitate tests were not significant (P = 0.005). Physically and radiographicall...
Cymbaluk NF, Christison GI, Leach DH.Eighteen weanling horses were assigned to two treatments: limited or ad libitum feed intake. Growth and feed utilization were evaluated over a 78-wk period. Ad libitum-fed horses gained 24% more (P less than .05) weight than limit-fed horses. Total BW was distributed into 57% fore and 43% hind weight and did not differ between groups regardless of dietary treatment or age. Net gain and ADG in wither height of ad libitum-fed horses exceeded (P less than .05) that of limit-fed horses over 78 wk. Ad libitum-fed horses consumed 19, 44 and 34% more digestible energy (DE) than indicated in 1978 NRC ...
Ray AC, Kyle AL, Murphy MJ, Reagor JC.In addition to the 3-striped blister beetles (Epicauta temexa and E occidentalis), other sources of equine cantharidin toxicosis were identified at the Texas Veterinary Medical Diagnostic Laboratory and included E albida and E attrivittata and the previously incriminated E pardalis and E pennsylvanica. Improved methods for diagnosing cantharidin or blister beetle toxicosis involve partial purification of urine and gastric content extracts, using silica cartridges, followed by analysis, using capillary gas chromatography/mass spectrometry. During a 26-month period, 53 episodes of cantharidin to...
Furuoka H, Ito H, Hamada M, Suwa T, Satoh H, Itakura C.The endocrine cell components in the pancreatic islets of the following 4 pancreatic regions of the horse were investigated by immunohistochemical methods: lobus pancreatis sinister (left lobe); lobus pancreatis dexter (right lobe); and 2 regions of Corpus pancreatis (body), the duodenal lobe which lies along the cranial duodenal flexure and descending duodenum, and the intermediate lobe which is situated around the portal vein. The islets in the left and intermediate lobes contained a central mass of glucagon cells surrounded by insulin cells, a few somatostatin cells and sporadic pancreatic ...
Sweeney CR, Leary HJ, Ziemer EL, Spencer PA.Water vapor-saturated air was delivered to 12 healthy, housed horses for 2 hours daily for 5 days. Treatment had no effect on tracheal mucus transport rate, bronchoalveolar lavage total and differential cell counts, blood cell counts, or plasma fibrinogen concentration.
Rossmanith W, Horvath E.After electrophoretic separation in SDS-PAGE structural proteins of the virus of Equine Infectious Anemia (EIA) were easily blotted by the semi-dry-blotting method onto nitrocellulose filters. Strips of these filters were used for antibody demonstration, and positive reactions thereof were intensified by a biotin-avidin-peroxidase system. Sensitivity of this system was so high as to allow readable interpretation of bands up to the dilution of 1:6,400 of a strongly positive serum. Frequently this procedure allowed to make a firm diagnostic Western-Blot diagnosis on far weaker equine sera. Inter...
Henry M, Prasse K, White S.Multiple myeloma was diagnosed in a 3-month-old Quarter Horse foal with chronic weight loss, chronic bronchopneumonia, and epistaxis. The foal had pancytopenia, thrombocytopenia, and monoclonal beta-globulinemia. Bone marrow aspirates contained between 80 and 90% plasma cells.
Abrahamsen E, Hellyer PW, Bednarski RM, Hubbell JA, Muir WW.Arterial hypertension developed in a horse anesthetized for arthroscopy and lavage of an inflamed right carpal joint. Anesthesia was induced with xylazine HCl, butorphanol, guaifenesin, and thiamylal Na and was maintained with halothane in oxygen. Arterial hypertension and tachycardia developed within 15 minutes after a pneumatic tourniquet was placed 8 to 10 cm proximal to the right carpus and inflated to 800 mm of Hg. The surgical procedure was expedited, halothane was discontinued and anesthesia was maintained with guaifenesin to facilitate bandaging. Heart rate decreased from 72 to 42 beat...
Matsui K, Sugano S.Intrinsic heart rate (IHR) and autonomic nervous tone (ANT) were measured using the young and the adult of horses, cows, pigs, goats and chickens in order to elucidate species differences in a decrease of resting heart rate (RHR) with growth or age. The IHR and ANT were estimated from the changes in heart rate after the administration of atropine and/or propranolol. The IHR in all species decreased progressively with an increase in body weight from young to adult, and moreover the ANT altered toward the direction of parasympathetic predominance by a decrease in sympathetic tone and/or an incre...
Cymbaluk NF, Christison GI, Leach DH.Eighteen Quarter Horse and Paint weanling colts were assigned to two treatments, either limit or ad libitum feeding. Nutrient digestibilities of diets were evaluated between 6 and 12 mo, 12 and 18 mo and 18 and 24 mo of age. From 6 to 12 mo, energy digestibility (64 to 68%) was unaffected by feed intake level. Ad libitum-fed horses had energy digestibilities 9 to 10% greater (P less than .05) than limit-fed horses between 12 and 24 mo of age, but adjustment for DM intake removed these differences. Limit-fed, mature ponies used dietary energy similarly to growing horses from 6 to 18 mo of age, ...
Doonan GR, Brown CM, Mullaney TP, Brooks DB, Ulmanis EG, Slanker MR.Several hundred Michigan horses were accidentally exposed to varying levels of monensin. Severity of effects was proportional to the level of feed contamination; sudden death resulted on at least two premises. Acute signs of cardiovascular impairment occurred on one premises having received feed containing over 200 grams of monensin per tonne. Gross and histological postmortem lesions consisted of acute myocardial necrosis. Although only circumstantially confirmed, investigations led to the suspicion that the source of poisoning was a ration formulation error in a feedmill in southwestern Onta...
Troyer D, Howard D, Leipold HW, Smith JE.Southern blot analysis of equine DNA's digested with the restriction endonuclease Hinfl hybridized with a 32 PdCTP labeled human VNTR probe revealed a highly polymorphic pattern of restriction fragments upon autoradiography. The horses were unrelated individuals of the quarter horse breed. This heterologous probe can thus be used in the equine species for individual identification and pedigree analysis.
Edwards DJ, Brownlow MA, Hutchins DR.Urine and blood samples were taken at the same time from normal adult horses presented for routine investigations to establish reference values for a variety of parameters reported to be useful in the clinical evaluation of renal function. Blood biochemical values were consistent with previous studies and had well-defined normal ranges. Parameters representing urine concentration and electrolyte excretion however, varied widely reflecting the ability of the healthy kidney to change the composition of urine in response to differences in environment and management. Percent creatinine clearance r...
Bertone AL, van Soest PJ, Stashak TS.Nutritional alterations were evaluated in 9 horses before surgery and 3 weeks, 3 months, and 6 months (4 total trials) after sham operation (group 1; n = 3) or extensive large colon resection (group 2; n = 6). Feed and fecal analyses were performed to determine apparent digestion of dry matter, organic matter, crude protein, calcium, phosphorus, magnesium, potassium, manganese, zinc, copper, and iron, and true digestion of dry matter, organic matter, crude protein, total plant cell wall, hemicellulose, cellulose, and lignin. Additional fecal and metabolic variables included the percentage of f...
Prater PE, Patton CS, Held JP.Pleural effusion, secondary to a metastasis from a malignant hepatoblastoma, was diagnosed in a 3-year-old Appaloosa gelding. Severe hemorrhagic transudate in both pleural cavities resulted in acute onset of labored breathing, tachypnea, tachycardia, and jugular vein pulsation. Results of ultrasonography and radiography of the ventral lung field and cranial portion of the abdomen initially were nondiagnostic, as were results of cytologic examination of peritoneal fluid and tracheal wash specimens. Moderately high serum gamma-glutamyl transferase and alkaline phosphatase activities, despite nor...
Wood T, Tai CL, Taylor DG, Woods WE, Wang CJ, Houtz PK, Tai HH, Weckman TJ, Yang JM, Sturma L.Detomidine is a potent non-narcotic sedative agent which is currently in the process of being approved for veterinary clinical use in the United States. Since no effective screening method in horses is available for detomidine, we have developed an 125I radioimmunoassay for detomidine in equine blood and urine as part of a panel of tests for illegal drugs in performance horses. Our 125I radioimmunoassay has an I-50 for detomidine of approximately 2 ng/ml. Our assay shows limited cross-reactivity with the pharmacodynamically similar xylazine, but does not cross-react with acepromazine, epinephr...
Schmidt AR.A 5-MHz transducer was used transrectally to image palpable structures in the caudal portion of abdominal and pelvic cavities of 12 horses. In 8 healthy horses, structures scanned transrectally included the left kidney, spleen, urinary bladder, urethra, accessory sex organs in the male, portions of the intestinal tract, caudal portion of the aorta, and iliac arteries, and, in small horses, the cranial mesenteric artery. The transrectal technique was used to evaluate these structures in 4 horses with clinical signs indicating intrapelvic or intra-abdominal disease. Seemingly, transrectal ultras...
Johnston JK, Divers TJ, Reef VB, Acland H.Ten horses with clinical signs consistent with cholelithiasis were evaluated. Fever, icterus, mild intermittent colic, and weight loss were reported. Clinical laboratory abnormalities included leukocytosis, hyper-proteinemia, and hyperfibrinogenemia. Gamma glutamyltransferase and liver isoenzyme of lactate dehydrogenase activities also were high. Choleliths were observed via ultrasonography of the liver in 5 of the 8 horses evaluated, and increased echogenicity of the hepatic parenchyma and dilated bile ducts were observed in all horses. Seven horses were treated medically, 5 of which died or ...
Whalley JM, Robertson GR, Scott NA, Hudson GC, Bell CW, Woodworth LM.A gene in equine herpesvirus 1 (EHV-1; equine abortion virus) equivalent to the gB glycoprotein gene of herpes simplex virus (HSV) has been identified by DNA hybridization and nucleotide sequencing. A 4.3 kbp EHV-1 PstI-ClaI sequence (0.40 to 0.43 map units) contained an open reading frame flanked by appropriate control elements and was capable of encoding a polypeptide of 980 amino acids. This had 50 to 60% identity over a 617 amino acid conserved region with the gB gene products of HSV and three other alphaherpesviruses, and 20 to 30% identity with those of human cytomegalovirus and Epstein-...
Martin Giménez T, Aguirre Pascasio CN, de Blas Giral I.Andalusian horses have been proposed as a breed predisposed to equine metabolic syndrome (EMS) phenotype [1] because they are prone to exhibiting regional, generalised adiposity and tendency to laminitis [2]. Insulin dysregulation represents the main pathophysiological cause for all the features of EMS, however there are no epidemiological studies in this breed. Objective: To assess insulin dysregulation through insulin proxies in Andalusian horses with different levels of obesity. Methods: Cross-sectional study. Methods: One hundred and sixty-four Andalusians (78 stallions and 86 mares, 2-15 ...
Respondek F, Lallemand A, Julliand V, Bonnaire Y.Presence of drugs is completely prohibited in post racing urine samples by most of racing and competition authorities, even if environmental contamination might occur. Objective: To assess the daily dose of several contaminants absorbed through the diet that would result in detectable concentrations in urine. Methods: Caffeine, theobromine, theophylline, atropine, scopolamine, bufotenine, DMT or morphine were administered orally to 6 horses, in different dosages, for 3 days before their urine was sampled for regular anti-doping tests. Results: Theobromine, theophylline, bufotenine and morphine...
Cassotis NJ, Stick JA, Arnoczky SP.A 4-month-old Quarter Horse colt was admitted for repair of an open, comminuted fracture of the proximal portions of the diaphyses of the left second, third, and fourth metatarsal bones. Initial repair included internal fixation and cancellous bone graft. However, the third metatarsal bone became infected and failed to heal. After removal of infected portions of the bone, a 5-cm, fullthickness cortical allograft was placed in the defect. Rigid internal fixation provided stability for the allograft and remaining fracture fragments so that the horse was able to bear weight on the second and four...
Breukink HJ, Németh F, van Dieten JS.The clinical examination, anaesthesia and surgery in a gelding with an incarcerated scrotal hernia are described. The results of examination of the blood at regular intervals are shown in a table. Surgery was performed without enterectomy. The postoperation course was uneventful. It is concluded that the possibility of scrotal hernia should be borne in mind, even in geldings with colic. The incarcerated portion of the small intestine is usually found to be the jejuno-ileal junction. The anaesthesiological and surgical features of equine scrotal hernia are discussed.
Goulden BE.Any condition which leads to a diminution in the size or alteration of the shape of the lumen of the respiratory tract in the horse may result in the production of abnormal respiratory noises at exercise.
Schamhardt HC, Hartman W, Lammertink JL, Badoux DM.Strain tracings obtained from the tibial cortex of walking ponies reveal peaks in the principal tension and compression strains occurring immediately before and after the support phase. Evidence is presented that the presupport peak is caused by inertial forces.
Hawkes CS, Easley J, Barakzai SZ, Dixon PM.There is minimal published information on equine oromaxillary fistulae that are unrelated to cheek teeth (CT) repulsion or on the conservative treatment of these atypical fistulae. Objective: To report equine oromaxillary fistulae unrelated to CT extraction and describe their management in standing horses. Methods: Case details of oromaxillary fistulae of atypical aetiology occurring at 2 referral centres between 2002-2006, including their treatment and response to treatment were examined. Results: Nine cases of oromaxillary fistula were recorded, mainly in aged horses (median 22 years). Fistu...
Escabias MI, Santisteban R, Rubio MD, Tovar P.The correlations between different electrocardiographic variables and plasma concentrations of K, Na and Ca ions were studied in foals of 1 to 14 days of age. The results obtained are only significant in neonate individuals of 1 day of age. Whilst the PQ segment and R wave duration showed a positive linear correlation (p less than or equal to 0.05) with plasma concentrations of Na and Ca ions respectively, the amplitude of the T wave showed a negative linear correlation (p less than or equal to 0.05) with the K ion. Moreover, the variability in duration of the QT and ST intervals can be explai...
Sarasola P, McKellar QA.Ampicillin is an antibiotic commonly administered to horses by both the intramuscular (i.m.) and the intravenous (i.v.) route. Its physicochemical properties restrict its absorption after oral administration and explain its rapid elimination from the body. To prolong the effects of ampicillin in the horse, attempts have been made to alter its elimination and absorption rates. The alteration of urinary pH did not change the plasma disposition of the antibiotic but when probenecid was administered concurrently with ampicillin, a significant reduction of total body clearance was achieved. Ampicil...
Wernette KM, Hubbell JA, Muir WW, Sams RA.The cardiopulmonary effects of 3 dosages of doxapram hydrochloride (0.275 mg/kg, 0.55 mg/kg, and 1.1 mg/kg, IV) were studied in 6 adult horses. Doxapram given IV significantly (P less than 0.05) decreased PaCO2 and increased respiratory rate, cardiac output arterial blood pressures (systolic, mean, and diastolic) arterial pH, and PaO2 at 1 minute after each dose was administered. Heart rate and mean and diastolic pulmonary arterial blood pressure were significantly (P less than 0.05) increased 1 minute after the 2 larger dosages of doxapram were given (0.55 mg/kg and 1.1 mg/kg, IV), but not af...
Bhavnani BR, Martin LJ, Baker RD.A mixture of 1-14C-isopentenylpyrophosphate and 3H-dehydroisoandrosterone was injected into a horse fetus intramuscularly during laparotomy, after which maternal urine was collected for 4 days. Steroid conjugates in the urine were extracted with Amberlite XAD-2 resin, hydrolysed and separated into phenolic and neutral fractions. From the phenolic fraction estrone, 17alpha-estradiol, equilin and equilenin were isolated. Only estrone and 17alpha-estradiol contained both 3H and 14C, while the ring B unsaturated estrogens contained only 14C. From the neutral fraction 14C-labeled 3beta-hydroxy-5alp...
Campbell TM, Studdert MJ.An inactivated equine adenovirus type 1 (EAdV1) vaccine was administered to 4 horses. The horses had virus-neutralizing (VN) antibody titers before they were vaccinated, but developed higher VN antibody titers in response to vaccination. Nonvaccinated control horses did not show increases in VN antibody during the study, indicating that any increase in antibody titer in vaccinated horses was a result of vaccination and not due to an EAdV1 epizootic during the study. Specific EAdV1 in vitro lymphocyte blastogenesis (LB) was evaluated, using lymphocytes from 4 vaccinated and 2 control horses. Ho...
Pilsworth RC, Head MJ.The differential diagnoses of tarsal joint infection, fracture and peritarsal focal infection are of particular importance in practice. The objective of the present report is to provide additional clinical data to assist in the understanding of one of these conditions. The haematological parameters, clinical signs, treatment and outcome of 10 cases of severe lameness associated with peritarsal infection are reviewed. All horses had a significant rise in rectal temperature. The majority of cases (6/10) had haematological changes consistent with acute bacterial infection on the day of first exam...
Clark ES, Gantley B, Moore JN.The effects of intravenous (iv) infusion of endotoxin for 60 mins at a cumulative dosage of 0.03 micrograms/kg bodyweight on systemic arterial, right atrial and pulmonary arterial pressures, heart rate, cardiac output, and derived pulmonary vascular resistance and total peripheral vascular resistance were compared to the effects of iv infusion of saline solution in four healthy horses. Heart rate was increased significantly after endotoxin infusion, although diastolic arterial pressure, systolic arterial pressure, electronically averaged arterial pressure, cardiac output, total peripheral resi...
Koekemoer JJ, Paweska JT, Pretorius PJ, van Dijk AA.We present the first VP2-gene phylogenetic analysis of African horsesickness (AHS) viruses within a serotype. Thirteen AHSV 7 isolates were obtained from cases that occurred in South Africa during 1998-1999, and three were historical AHSV 7 isolates. The goals were to start a database of isolates of known location and time of isolation and to determine if we could identify the origin of an AHS outbreak in the surveillance area in the Western Cape. We prepared full-length cDNA copies of the VP2-genes of the isolates. Nucleic acid sequence data of a 786 bp region was used to characterize the gen...
Agrawal K, Ebel JG, Bischoff K.Most antidoping method development in the equine industry has been for plasma and urine, though there has been recent interest in the analysis of synovial fluid for evidence of doping by intra-articular corticosteroid injection. Published methods for corticosteroid analysis in synovial fluid are primarily singleplex methods, do not screen for all corticosteroids of interest and are not adequately sensitive. The purpose of this study is to develop a rapid and sensitive liquid chromatography-tandem mass spectrometry (LC-MS-MS) screening method for the detection of four of the most common intra-a...
Kozawa Y, Mishima H, Sakae T.During the evolution of the Equoidea, the histological structures of the teeth have become more complex as the molars have become hypsodont in form. The straight Hunter-Schreger bands of Hiracotherium have evolved into a more complex pattern in Equus. The enamel prisms changed from an arched form (about 5μm in diameter) with an alternating pattern in Hiracotherium to an oval form (about 2 μm width) arranged in straight rows in Equus. In Equus the rows of prisms are separated by interprismatic sheets. This pattern may have increased the architectural strength of the enamel, and is related to ...