DIGEST Ca.Uky.Edu/Equine ❙ Thehorse.Com ❙ APRIL 2013

Bluegrass Equine DIGEST ca.uky.edu/equine ❙ TheHorse.com ❙ APRIL 2013

Genetic Basis for Establish- Articles of Interest ment of EAV Carrier State Gluck Center Researchers ew research from the Univer- Results of previous studies by Yun Study Ways to Advance sity of Kentucky (UK) suggests Young Go, DVM, MSc, PhD, a for- Breeding Season that genetic factors play a role mer graduate student in Balasuriya’s N AAEP Launches Equine in determining stallion susceptibility to laboratory, identified that horses can Parasite Control Guidelines equine arteritis virus (EAV) infection. be divided into two groups based on Results from the laboratory of Udeni in vitro (in the lab) susceptibility of Graduate Student Spotlight: Balasuriya, BVSc, PhD, professor of their lymphocytes (white blood cells) Krista Cotten virology at the UK Gluck Center, dem- to EAV infection. One group of horses onstrated a correlation between horse had lymphocytes susceptible to in vi- Nielsen Receives Grayson- genetic factors and establishment of tro EAV infection and the other group Jockey Club Grant for EAV carrier state in stallions. Genome- had lymphocytes resistant to in vitro Parasite Study wide analysis shows that equine chro- EAV infection. Based on this finding, mosome 11 (ECA11) carries genes that the investigators hypothesized that Weed of the Month: Spiny Pigweed are likely involved in cellular suscepti- there must be a genetic basis for this bility to the virus. phenomenon. Coat Color Genetics 101

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tools, they analyzed DNA from each group’s cells to determine which genes might contain markers involved in viral infection of the cell. Of the 310 horses, 167 had the susceptible lymphocytes and 143 had the resistant type. By breed, 95% of the Standardbreds and approximately 90% of the American Standardbreds had the courtesy Gluck equine research center courtesy susceptible type. Thoroughbreds and Based on Dr. Yun Young Go's studies, Dr. Udeni Balasuriya and other Gluck Center researchers hypothesized there must be a genetic basis for EAV infection. Quarter Horses had the lowest preva- lence of the susceptible type (23%). Equine viral arteritis (EVA) out- In their study, the researchers ran- Quarter Horses had evenly distributed breaks result in significant economic domly selected 310 horses representing resistant and susceptible cell types. losses to the equine industry due to four breeds (Thoroughbreds, American The genome-wide analysis of EAV high rates of abortions, death in young Standardbreds, Standardbreds, and susceptibility showed that Standard- foals, and establishment of the carrier Quarter Horses) from Kentucky farms. bred horses were most fixed for suscep- state in stallions. Persistently infected They collected blood samples and di- tibility markers, meaning that almost carrier stallions function as the natu- vided them into two groups according all Standardbreds have the genetic ral reservoir of EAV, and they dissemi- to the susceptible and resistant types of markers associated with cell suscepti- nate the virus to susceptible mares at lymphocytes to in vitro infection with bility to EAV. Of the four breeds, Thor- breeding. EAV. Then, using genome-wide analysis oughbreds had the lowest number of

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EAV Carrier State EAV might interact with some of these semen samples using the same tech- cellular proteins to evade the equine im- niques. To continue these studies, we mune response and establish persistent have recently been awarded a $2.9 mil- markers associated with the susceptible infection in some, but not all, stallions lion five-year grant by the United States type. infected with the virus, as only some Department of Agriculture-Agriculture Thoroughbreds have less diversity for stallions become persistently infected and Food Research Initiative to spe- genetic markers than other breeds. By carriers, according to the authors. Re- cifically identify the genetic factors analyzing this breed first, the researchers cently, the same researchers demon- responsible for establishment of the EAV were able to uncover a specific marker strated that stallions with lymphocytes carrier state in stallions.” for lymphocyte susceptibility indicating susceptible to EAV infection might have These papers are available at http://jvi. that EAV infection is highly associated a higher risk of becoming carriers. asm.org/content/85/24/13174 and http:// with the ECA11 chromosome. The genes “These studies can help us develop jvi.asm.org/content/86/22/12407. on this chromosome encode proteins working hypotheses about why horses that are involved in virus attachment become infected, and how persistent >Nancy Zacks is a horse lover and freelance and entry into the cells, the inflamma- infection is established in the stallion,” writer with an MS in Science Journalism from the tory response, and cellular immunity. said Balasuriya. “The next step is to test Boston University College of Communication.

Gluck Center Researchers The facemask consists of a leather headpiece Study Ways to Advance with a single blue LED fitted on the inside of a semi-rigid rubber eye cup over the right eye. Breeding Season The mask is equipped with adjustable Velcro down the center of the head piece. Equine Recombinant Fol- A mare’s transition from licle Stimulating Hormone reproductive inactivity dur- University of Kentucky ing the winter to the breeding Veterinarians have devel- and administered either 0.65 Gluck Equine Research Cen- season can be lengthy and oped various management mg of reFSH or a placebo by ter scientists recently stud- complicated. Increased day- and therapeutic strategies random selection. They moni- ied the use of recombinant light suppresses melatonin (a to shift a mare’s first ovula- tored the mares by ultrasound hormones to induce mares’ hormone preventing mares tion of the year from April to until a 35 mm or larger fol- reproductive cyclicity and from cycling in winter) and February. The most common licle developed, discontinued advance the breeding season. allows secretion of reproduc- management is light treat- reFSH treatment, and admin- The study, done in collabora- tive hormones necessary to ment, which should begin in istered human chorionic go- tion with the University of induce ovulation and repro- December for mares to begin nadotropin (hCG) to induce California and Colorado State ductive cycles. Mares under their reproductive cycles in ovulation. All mares treated University, aimed to deter- natural light do not enter the mid-February. with reFSH developed folli- mine the efficacy of an equine breeding season until late “Even housed under artifi- cles after a week, and 23 of 30 recombinant follicle stimulat- April. Their transition pe- cial barn light, the mares may mares in this group ovulated ing hormone (reFSH) in non- riod is characterized by an still experience normal length within 72 hours after receiv- cycling mares housed under increase in follicle develop- of transition period lasting 50 ing hCG. The control group natural light conditions. ment and uterine edema. to 70 days or more, prior to did not develop follicles dur- the first ovulation of the sea- ing the period. son,” said Mats Troedsson, While reFSH proved suc- DVM, PhD, director of the cessful stimulating early UK Gluck Equine Research dominant follicles and ovu- Center and chair of the de- lation in the seasonally an- partment of veterinary sci- estrous mares, a continued ence. Therefore, there might cyclicity failed to appear. be a need for alternative treat- “However, the treated mares ments of shorter duration. returned to anestrus follow- In their study, the re- ing the induced ovulation searchers employed 60 deep and followed the calendar of anestrous (wintertime, non- the control group,” Troeds- cycling) mares in California, son said. He suggested that Colorado, and Kentucky from continuous treatment might the end of January until one be necessary in mares that or more pre-ovulatory fol- fail to become pregnant fol- anne m. eberhardt anne m. Mares are often housed under artificial barn light to hasten their licles developed. They divided lowing breeding on induced transition period for breeding season. the mares into two groups ovulation.

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Breeding Season Studies MASTHEAD Mobile Light Therapy Efficacy Using artificial indoor light to speed up ■ University of Kentucky Ag Equine Programs mares’ transition to breeding season can Jenny Evans, Managing Editor, [email protected] be time-consuming and costly in electric- Holly Wiemers, Managing Editor, [email protected] ity, bedding, and labor. Researchers at the Gluck Center col- ■ Bluegrass Equine Digest Advisory Board laborated with Barbara Murphy, BSc, Nancy Cox, PhD, associate dean for research in UK’s College of Agriculture, Kentucky Agricultural PhD, a researcher at the University Col- Experiment Station director lege Dublin, Ireland, who recently devel- Ed Squires, PhD, Dipl. ACT (hon.), director of UK Ag Equine Programs and executive director of the UK Gluck oped a facemask with blue light directed Equine Research Foundation at a single eye to suppress melatonin Mats Troedsson, DVM, PhD, Dipl. ACT, director of the UK Gluck Equine Research Center and chair of the production in mares under natural light. department of veterinary science The team set out to determine if the facemask was as effective in advancing ■ Bluegrass Equine Digest Editorial Committee breeding season as traditional indoor Craig Carter, DVM, PhD, Dipl. ACVPM, director of the UK Veterinary Diagnostic Laboratory barn light. Bob Coleman, PhD, PAS, associate director for undergraduate education in equine science and management From mid-December to mid-February and extension horse specialist 2013, the researchers studied 59 Thor- Laurie Lawrence, PhD, professor in the department of animal and food sciences oughbred mares, ages 4 to 17, from Ray Smith, PhD, professor and forage extension specialist farms in Lexington, Ky. They divided the William W. Witt, PhD, researcher in the department of plant and soil sciences mares into three groups. One group was ■ The Horse: Your Guide to Equine Health Care stalled individually under indoor barn light (250 Lux) that remained on until 11 Alexandra Beckstett, Managing Editor p.m.; the second group was housed out- Brian Turner, Layout and Design side wearing the facemask with timed The Bluegrass Equine Digest is a registered trademark of the University of Kentucky Ag Equine Programs and Gluck light (50 Lux blue light) from 4:30 p.m. Equine Research Center. The Bluegrass Equine Digest is produced by the University of Kentucky in partnership with until 11 p.m. daily. The third group was TheHorse.com and sponsor PfizerA nimal Health. It is published monthly to provide up-to-date information on equine a control group maintained outside in research from the University of Kentucky’s College of Agriculture. Research material is meant to be shared. However, materials are copyrighted and require reprint permission from UK Ag Equine Programs. Past issues of the Bluegrass natural light. The researchers performed Equine Digest are available at www2.ca.uky.edu/equine/bed. transrectal ultrasound examinations of the mares’ reproductive tract to determine the presence and size of the folli- light treatment groups, but all treated can remain in pasture.” cles in conjunction with sampling serum horses had advanced reproductive cycles Troedsson added that the light face- progesterone to confirm ovulation. compared to the control mares. mask is an excellent alternative to in- Fourteen of 16 mares exposed to in- “We concluded that the timed low door barn light as it also allows the door barn light and 20 of 26 mares level blue light was as effective as tra- horse more outdoor time in its natural wearing the light masks exhibited repro- ditional indoor barn light in advancing environment. ductive activity. The control group only breeding,” Troedsson said. “In addition, showed four mares in activity. There was we emphasize that the mobile head gear >Shaila Sigsgaard is an editorial assistant for no statistical difference between the two saves electricity and labor as the horse the Bluegrass Equine Digest.

AAEP Launches Equine Science at the University of Kentucky Gluck Equine Research Center. Nielsen is chair of the subcommittee. Parasite Control Guidelines Nielsen explained that guidelines for parasite control in horses are highly needed to help veterinarians and their clients he first official set of guidelines for parasite control in hors- maneuver the challenging landscape between the many differ- Tes is now available on the American Association for Equine ent parasite species infecting horses and the increasing levels Practitioners’ (AAEP) website. An AAEP-appointed subcom- of drug resistance in several of these. Parasite control is not as mittee of researchers, clinicians, industry representatives, and straightforward as we once believed. veterinary practitioners spent the last sev- “We have long been emphasizing there eral years formulating the document. is no one-size-fits-all program for parasite “We are facing a significant paradigm “We are facing a signifi- control, which is a true statement but does shift in equine parasitology, and there has not provide much help for the veterinarian been lots of confusion and controversy in cant paradigm shift in in the field,” Nielsen said. our field in recent years,” said Martin K. equine parasitology.” The document states that the goal should Nielsen, DVM, PhD, Dipl. EVPC, assistant never be to eradicate a parasite. Not only professor in the Department of Veterinary Dr. Martin K. Nielsen is this impossible, but the inevitable result

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Parasite Control Guidelines treatments their first year. The guideline provides information about the timing Gluck Center’s and choice of anthelmintic drug. Veteri- is accelerated development of parasite narians should continue treating year- Nielsen Receives drug resistance. Instead, goals are to lings and 2-year-olds as “high” shedders minimize parasitic disease risk; control and administer approximately three year- Grayson-Jockey parasite egg shedding; maintain effective ly treatments with effective drugs. In all drug control; and avoid further develop- ages it is highly recommended to perform Club Grant for ment of anthelmintic (drugs used to treat routine screenings of anthelmintic effi- parasitic worm infections) resistance. cacy with fecal egg count reduction tests. Parasite Study For adult horses, the guidelines state “We hope these guidelines will reduce that one or two yearly treatments are the confusion and controversy about artin Nielsen, DVM, PhD, EVPC, sufficient to prevent large strongyles parasite control and hope to continue Massistant professor in the De- infection. Cyathostomin (small stron- to update this document as we generate partment of Veterinary Science at the gyle) parasites can be treated based on more information,” Nielsen said. University of Kentucky Gluck Equine strategically performed fecal egg counts. To read the complete guidelines, visit Research Center, received a one-year Tapeworm treatments should be includ- www.aaep.org/images/files/ParasiteCont grant from the Grayson-Jockey Club ed annually in most regions. rolGuidelinesFinal032413.pdf. Research Foundation to study the inter- The document recommends not bas- action between anthelmintic treatment ing foal treatments on egg counts. In- >Shaila Sigsgaard is an editorial assistant for and vaccines. stead, foals should receive about four the Bluegrass Equine Digest. The study will generate useful information about the interaction between deworming and vaccination in horses. The presence of intestinal worms and GRAD student spotlight the host reaction to deworming can po- tentially influence vaccination effects Krista Cotten through modulating inflammatory re- actions in the horse. In addition, the From: Amarillo, Texas study allows Nielsen to evaluate pos- Degrees and institute: B.S., Animal sible differences between two types of Science, University of Kentucky dewormer (ivermectin and pyrantel pamoate) in their effect upon vaccination Krista Cotten, a master’s student in Plant and Soil responses. Sciences at UK, came to the Lexington area with the Well-managed equine establishments Kentucky Equine Management Internship program. deworm and vaccinate their horses “I fell in love with the area and transferred to UK against infectious agents on a routine (from West Texas A&M University) to finish my under- basis—sometimes having a veterinar- grad degree,” Cotten said. “I ended up in Plant and ian administer both dewormer and Soil Sciences (PSS) because of a great opportunity vaccination(s) during one visit. Until that a friend knew about working with Dr. Ray Smith recently, practitioners considered this and the UK Horse Pasture Evaluation Program. So I practice unproblematic, but recent guess PSS found me.” findings have raised concerns whether Cotten’s research project focuses on the effects of the horse’s response to deworming tall fescue sample handling and storage on ergovaline might affect vaccination efficacy. De- concentrations in fresh material. Ergovaline (a toxin worming causes a mild and transient produced by the fungus that infects some tall fescue) inflammatory reaction in the horse, adversely affects many livestock species, including horses. which appears to depend on the type However, knowing how much ergovaline is present in a pasture at any given point is tricky of dewormer used. In addition, intesti- because ergovaline appears to be unstable in the fresh plant, Cotten said. nal worms have been shown to possess “The goal of my research is to determine the best method of sample handling and ideal stor- properties capable of modulating an in- age conditions of samples until the lab can process them,” she said. flammatory response. Cotten also works with the UK Horse Pasture Evaluation Program, which helps local horse In the grant proposal, Nielsen said, farms of all sizes improve pastures by providing detailed recommendations based on observa- “Deworming has been found to cause tions made in each field. The program also samples tall fescue on some farms to determine the disease in newly dewormed horses, risk present to late-term mares. Last year, the program worked with 18 farms for a total of more but usually the inflammatory reaction than 3,800 acres and expects to cover even more ground this year. is mild with no apparent symptoms. “My hope is that my research provides guidelines for more standardized tall fescue sample However, it is unknown whether this handling and storage so that results from both research and diagnostic cases can be compared reaction can possibly affect the result from across the country,” Cotten said. of vaccination. Our hypothesis is that Cotten plans to graduate in December 2013. deworming causes an inflammatory reaction that affects the response to >Shaila Sigsgaard is an editorial assistant for the Bluegrass Equine Digest. vaccination.”

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Nielsen’s Grayson-Jockey Club Grant Weed of the Month In the study Nielsen will evaluate three groups of ponies. Common name: Spiny pigweed, Spiny amaranth Each will receive different vaccinations. He will deworm two of the groups with two different dewormers (pyrantel pamoate Scientific name:Amaranthus spinosus L. and ivermectin) at the time of vaccination and maintain the Life Cycle: Warm season annual third group as an untreated control. He will then monitor the Origin: Tropical America ponies for 60 days to evaluate deworming effectiveness, inflam- Poisonous: No matory response, and generation of vaccine-specific antibody levels. Spiny pigweed is distrib- “This allows us to measure the effectiveness of the deworm- uted widely across the United ing, the antibody response to the vaccine, and the inflammato- States and grows most fre- ry reaction to vaccination with and without the accompanying quently along fence borders, deworming,” Nielsen said. feeding and watering areas, The Grayson-Jockey Club Research Foundation will and other compacted areas. fund 17 projects in 2013, totaling $874,024. The research Spiny pigweed can some- includes the launch of 12 new projects, the continuation of five times infest entire pastures projects entering their second year, and three Storm Cat Career that are overgrazed. Seed ger- Development Awards. For more information on all the grants, mination occurs in late spring visit http://grayson-jockeyclub.org/default.asp?section=2&area or early summer. Stems are =Research&menu=2. reddish, stout, and branched. Mature plants can grow 3 feet >Jenny Evans, a MFA candidate, is the Gluck Equine Research Foundation tall and are most noticeable in late summer. Sharp spines that inhibit coordinator at the Gluck Center. grazing are found in stem axils and are surrounded by dense clusters of female flowers. The male flowers are long terminal clusters. Spiny pigweed control is relatively easy with herbicides when ap- plied to plants less than 12 inches tall. Mowing and hand weeding are effective if done before flower production to prevent seed production. Equine Coat Color Genetics 101 Consult your local Cooperative Extension Service personnel for herbi- cidal control in your area. t the 2013 University of breed organizations. Oth- AKentucky (UK) Equine er groups like the Friesian >William W. Witt, PhD, a researcher in Plant and Soil Sciences, provided Showcase, held Jan. 18 in Horse Association of North this information. Lexington, Ky., Kathryn America and the Kentucky Graves, PhD, the director of Mountain Saddle Horse As- the UK Animal Genetic Test- sociation won’t allow horses ing and Research Laboratory, to be registered if they have to identify mutations for the with the lowercase letters reviewed the basics of equine certain amounts of white basic coat colors as well as indicating recessive genes, coat color genetics. patches, she said. Graves also modify genes for other coat and capital letters signifying Why should the average said some horsemen believe colors and spotting patterns, dominant) for that trait. If he horse owner care about the horses of certain coat colors Graves said. In her presenta- carries one dominant and one genetics behind their horse’s are easier to market and sell tion, Graves first reviewed recessive allele, then he is het- coat color? Graves explained than others. Some owners the key terms “dominant” erozygous (E/e) for the trait. that some breed registries even opt to have genetic tests and “recessive.” Dominant Moving forward, Graves are either based on horses’ run on horses to identify their means only one copy of the discussed the genetics behind coat colors or have color re- genotypes (the genetic make- mutation is needed for it to specific equine coatcolors. strictions. For instance, The up of a given physical trait), be expressed outwardly, while Base Coat Colors Horses American Paint Horse Asso- especially if the animals will recessive means two copies have three basic coat colors: ciation, the Appaloosa Horse be used for breeding. are needed. If a horse carries red (chestnut), bay, and black, Club, and the International The completion of the two copies of the same allele all of which are controlled Buckskin Horse Association, equine genome in 2007 for a gene, he is homozy- by two gene’s interactions. among others, are all color opened a door for geneticists gous (for instance, E/E or e/e, The Extension (or E) locus

Dr. Kathryn Graves discussed the genetics behind specific equine coat colors. Photos.com

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Equine Coat Color Genetics 101 Graves then discussed coat spotting patterns that, in most cases, produce horses gene is instrumental in al- Gray The gray coat color with a base color spotted with lowing black pigment to be (gene STX17) is represent- a variety of white patches. expressed, and the Agou- ed by a dominant genotype Tobiano The first spotting ti (or A) locus gene controls (G/G or G/g), Graves said. pattern Graves discussed the location of black in the These horses are born dark was the tobiano pattern—the horse’s coat. Specifically, and eventually lose their hair most popular genetic test her the E locus is located on pigment until they are all or laboratory carries out. To- gene MC1R and the A lo- nearly all white. To produce biano horses generally have cus is located on gene ASIP. a gray horse, at least one par- dark-colored heads with Graves said chestnut is a ent must contribute a domi- white legs and white patches recessive trait, meaning all nant G. Non-gray horses have breaking over their topline. chestnut horses have a ho- two recessive genes (g/g). Graves said chromosomal mozygous (e/e) genotype for that color. The E allele, which is dominant, permits “All equine coat colors and patterns Q&A the expression of black pig- stem from three base coat colors.” Trimming ment; therefore, all black and Feed Costs bay horses have at least one Dr. Kathryn Graves copy of the E allele, Graves During the 4th annual explained; they can be ei- UK Kentucky Breeders’ ther E/E or E/e. Roan Although gray and inversion on the KIT gene Short Course in In horses with E/E or E/e roan horses can look simi- helps produce this color pat- Lexington, TheHorse. genotypes, the A gene deter- lar in some cases, Graves tern. Horses with this domi- com news editor Erica mines whether those animals stressed that their genetics nant gene will always pro- Larson caught up with are bay or black. Bay is the are different. Instead of light- duce spotted horses, she said. Laurie Lawrence, PhD, dominant phenotype (the ening in color over time, roan Sabino Sabino is a sub- to discuss how horse physical expression of a ge- horses retain dark heads and class of the other main paint- owners can cut their netic trait) between the two, legs and have a mixture of ed coat color pattern: overo. feed costs without and its genotype is expressed white and colored hairs over These horses are generally cutting corners. by either E/Aa or E/AA. Black the rest of their body. The solid with white facial mark- is the recessive color, mean- exact mutation behind roan ings, white legs, and belly ing it is always homozygous coloring hasn’t been identi- spots. The KIT gene is also and expressed as E/aa. fied, but researchers know it’s involved with creating this View the short video at All other equine coat colors linked to the MC1R and KIT color pattern, she said. The TheHorse.com/31240 and patterns stem from these genes, which play a role in most important thing to know base coat colors. some pinto horses’ genetics. about this semidominant

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Kentucky Equine Youth Festival Celebrates the Horse and Kentucky’s Youth

More than 2,500 school-aged children at- This year’s festival built upon the first one tended the 2013 Kentucky Equine Youth Festival, held in 2010, where children packed the venue Celebrating the Horse, held March 27 at the Ken- to watch world-renowned elite equestrian ath- tucky Horse Park’s Alltech Arena. letes demonstrate the World Equestrian Games’ Hailing from 46 Kentucky counties and two disciplines. neighboring states, participants ranged in age New this year was an art contest with the from 4 to 18. The event featured several horse theme, “What Horses Mean to Kentucky.” Win- breeds that demonstrated equestrian sport in ners were revealed during the event, and book- a variety of disciplines, including jumping, stock marks featuring the winning art were distributed horse versatility, vaulting, driving, Arabian Horse to all participants. versatility, and gaited breeds, including those na- The Kentucky 4-H Horse Program staged tive to Kentucky. Other educational opportunities the event in conjunction with the University of included up-close-and-personal sessions about Kentucky’s Ag Equine Programs and in part- vaulting, horse dentistry, therapy horses, size nership with the Equine Academy at Lexington comparisons of different breeds, and Catholic High School, Equine Land Conservation biomechanics of jockeys and Resource, Kentucky Department of Educa- racehorses. tion, Kentucky Equine Educa- “This year’s festival was tion Project, Kentucky Horse an educational and rewarding Council, Kentucky Horse Park, experience,” said Jimmy Hen- Midway College, United States ning, PhD, associate dean for Equestrian Federation, and the extension and director of the United States Pony Clubs. Kentucky Cooperative Extension The event’s major sponsors Service. “The UK College of Agri- included the Bluegrass Palomino culture was happy to join with our Horse Association, North Ameri- partner organizations in celebrat- can Equine Ranching Information ing two of Kentucky’s signature Council, Race for Education, Unit- assets, the horse and our youth. ed States Equestrian Federation, We are happy to have been a part and the University of Louisville’s of this special day at the Kentucky Equine Industry Program. Horse Park, as well as every day and across the state through our 4-H >Holly Wiemers, MA, is communi- equine programs at our county exten- cations director for UK Ag Equine sion offices.” Programs.

The event included several breed and discipline demonstrations as well as educational opportunities. hotos courtesy matt barton; bookmark desi g n dennis duross barton; matt courtesy p hotos

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1 Data on file, sales report data from 2001 through October 2012, Zoetis Inc. All trademarks are the property of Zoetis, Inc., its affiliates and/or its licensors. ©2013 Zoetis Inc. All rights reserved. EQB13005 WestNileInnovator.com/Horse Bluegrass Equine Digest ❙ ca.uky.edu/equine ❙ TheHorse.com ❙ April 2013

Equine Coat Color Genetics 101 stallions to reduce the risk of which a mutated gene dilutes producing an affected foal. a base color into a variety of Dominant White These different colors. trait is that foals with a ho- APAX3 mutation (SW2) and horses (born white with dark Cream The cream dilution mozygous genotype can be another type of MITF muta- eyes) are produced by 14 to (a mutation on gene MATP) born all white and healthy tion (SW3) produce a similar 15 different mutations in produces palomino, buck- (unlike some other white phenotype but are thought to the KIT gene, Graves said. skin, cremello, perlino, and foals affected by the deadly be lethal in the homozygous She explained that research- smokey black coat colors, overo lethal white syndrome state. ers have identified mutations depending on the number [OLWS]; more on that in a Frame Overo This color specific to certain families of of dilution mutations—one moment). Thus, she stressed, pattern (characterized by a horses. Thus far, all of these or two—and the horse’s base test white foals suspected of mostly solid colored horse horses tested have shown a color, Graves said: having OLWS for the disease with white, horizontal patch- heterozygous genotype. ■ A palomino is a chestnut before euthanizing them. es on the side of the neck and/ Appaloosa The final spot- that is heterozygous for the Splashed White Another or belly; white rarely crosses ting pattern Graves discussed cream dilution mutation; type of overo coloring is the back between the withers was the appaloosa or leopard ■ A cremello is a chestnut the splashed white pattern, and the tail in frame overos) complex spotting (LP) pat- that is homozygous for the Graves said, which is char- is produced by a mutation tern. Researchers still aren’t cream dilution mutation; acterized by similar mark- on gene EDNRB, which re- sure what causes this spotted ■ A buckskin is a bay that is ings as the sabino pattern. searchers discovered while pattern, but they’ve traced the heterozygous for the cream Many splashed white horses searching for the lethal white mutation to the TRPM1 gene, dilution mutation; and have blue eyes, she said. This gene, Graves said. As men- she said. The LP pattern is an ■ A perlino is a bay that is color pattern is caused by tioned, two recessive frame incomplete dominant trait, homozygous for the cream multiple mutations in the overo genes can also produce meaning there is a dosage ef- dilution mutation. genes MITF or PAX3, she a foal with OLWS. In these fect if the horse has two cop- Graves noted that a black said, and these horses are horses, the colon does not ies of the mutation (horses horse heterozygous for the at risk for several different develop normally and foals with one copy of the muta- cream dilution mutation ap- types of health problems, in- are unable to pass manure; tion are typically a differ- pears black, but is known cluding deafness. One type affected foals die or are eu- ent color than a horse with as a smokey black; a black of MITF mutation (termed thanized within a few days of two copies of the mutation), horse homozygous for the SW1) has been identified birth. Because the mutation Graves said. cream dilution mutation ap- in several breeds, she said, that causes OLWS is known, Finally, Graves discussed pears perlino and is called a and homozygotes are viable. breeders can test mares and the dilution patterns, in smokey cream. p hotos.com A horse with the tobiano spotting pattern is generally characterized by a Dun is a dilution pattern affecting a horse's primary base color. All dun dark-colored head with white legs and white patches breaking over his horses have dorsal stripes, and many have zebra stripes on their legs.

9 Bluegrass Equine Digest ❙ ca.uky.edu/equine ❙ TheHorse.com ❙ April 2013

Equine Coat Color Genetics 101

Champagne The cham- Dun The mutation behind pagne dilution is caused the dun coat color is still un- by a mutation on gene SL- known, Graves said, so there C36A1 and is a dominant is currently no direct genetic trait, Graves said. This di- test. Researchers know, how- lution gene acts solely on ever, that it’s a dominant trait the horse’s base color and affecting the horse’s primary does not have a dosage ef- base color. A horse with a fect like the cream dilution black base and the dun mu- gene. It simply lightens the tation would have a grullo horse’s base color pigment. coat color; a chestnut base Horses with a black base would have a red dun color; coat will appear chocolate and a bay base would have in color, while chestnut or a yellow dun color. All dun lighter bay horses will ap- horses have dorsal stripes, pear gold. Graves said horses and many have zebra stripes with the champagne dilution on their legs, Graves said. frequently have blue eyes at Silver The final dilution birth that become amber- Graves described is the sil- colored in adulthood. ver dilution, a phenotype Pearl Graves said pearl commonly seen in Rocky dilutions (caused by a muta- Mountain Horses, which

tion on gene MATP) are often is caused by a mutation on p hotos.com referred to as the “Barlink gene PMEL17. This domi- Silver dilution produces a chocolate body color with flaxen mane and tail. factor,” as many horses of nant trait requires either a this color can trace their heri- bay or black base color; chest- desirable colors can have (eyeball enlargement); ho- tage back to a stallion named nut horses with the mutation other undesirable effects. mozygotes are more severely Barlink Macho Man. Graves will not appear any different Aside from OLWS, horses affected. Additionally, horses said one copy of the muta- than a chestnut without the with the silver dilution pat- homozygous for the appaloo- tion lightens the horse’s skin mutation. This dilution pro- tern have been known to sa mutation are affected by and might produce golden duces a chocolate body color develop multiple congenital congenital stationary night undertones to the coat, while with a flaxen mane and tail. ocular abnormalities, a non- blindness, causing a com- two copies of the mutation Graves concluded with progressive disease that complete lack of night vision. produces a diluted base color a caution to breeders seek- monly includes ciliary body and might enhance cream ing “fancy” coat colors: The cysts (a congenital uveal ab- >Erica Larson is the news editor and champagne colors. mutations that cause these normality) and megaloglobus for TheHorse.com.

Upcoming events Locust Trace Field Day May 9 More than 250 Fayette Kentucky Equine Networking Association (KENA) Meet- County middle school ing. Networking 6 p.m., dinner 6:30 p.m., Sheraton Hotel, students attended the Lexington, Ky. Locust Trace Agri- Science Farm field day April 23. UK Ag Equine Programs provided educational materials and an interactive display about different forages. UK Ag Equine Store Students visited various In response to requests for merchandise featur- stations to learn about different equine organi- ing University of Kentucky (UK) equine logos, UK Ag zations and topics. Equine Programs has launched an online store. Find Locust Trace Agri- UK Ag Equine or Gluck Equine Research Center logoed Science Farm is a career

and technical high university of kentucky courtesy items from T-shirts to coats to tailgating gear all in one school in Lexington, Ky., spot. Visit www.ukagequinestore.com and login as a that opened in 2011. Energy and environment are key factors in the facility design guest. Want some new UK Equine gear? Find jackets, and agriculture the educational focus. scarves, bags, and more!