b'Whats New in ESTRUS ManipulationHis team has also recently found thatRisks: Lumps, Doping, and Twinscombining histrelin or deslorelin acetateIts relatively safe to manipulate estrus, with hCG improves success rates in olderour sources say. But its not risk-free. Hor-mares or those at the beginning or end ofmone injection sites can swell, causing the breeding season. discomfort and lumps. Steroid hormones COURTESY DR. CARLOS GRADILGnRH agonists also help induce doublehave to be suspended in oil, and some ovulation, Alvarenga says, producing twomares really react to that, says Donnelly. embryos to remove and implant in sepa- As mentioned, for competing mares, rate mares to double productivity.its important that the drugs dont lead to positive doping testsfor them or The Anti-GnRH Vaccine the horses around them. This is a big One way to control estrus is to renderA magnetic IUD is safe and effective in mares. issue in sport horses in the U.S. because some of the mares hormones ineffective.of drug residues (in feed buckets, for Thats the principle of the anti-GnRH vac- pregnancy. It works, to an extent, butinstance), so were often asked for estrous cine. The brains hypothalamus releasesthe marbles can break and damage themanagement strategies that dont involve GnRH, signaling the mares reproduc- reproductive organs, says Donnelly.detectable prohibited substances like tive system to cycle, says Aurich. TheA new, safer IUD might soon becomealtrenogest, Donnelly explains. Due to its anti-GnRH vaccine stimulates the maresavailable. Carlos Gradil, DVM, PhD,nature as a steroid and also as a neuroac-own antibodies to overact in response toDipl. ACT, professor in Tufts Universitystive agent, theres always a question of GnRH, killing its action. The hypo- Department of Veterinary and Animalwhether its performance-enhancing or if thalamus still sends out GnRH, but theSciences, in Amherst, Massachusetts, andit can make horses quieter, he says. reproductive organs no longer respond,adjunct associate professor at the schoolsAltrenogest is approved for mares in and estrus doesnt occur. Cummings School of Veterinary Medicine,United States Equestrian Federation and Its very effective, Donnelly says. Butin North Grafton, has designed a mag- Fdration Equestre Internationale com-it comes with a huge downside in thatnetic IUD. Its three shatterproof beadspetitions, provided handlers file a medica-mares might never cycle again. self-assemble into a ring after insertiontion form. However, its a controlled medi-That could explain its lack of FDAinto the uterus. Early research showed itcation in geldings and stallions.approval, he says, though the drug isextended diestrus by an average of 74 daysTheres also the risk that any therapeu-approved and in circulation in countriesand stayed in place without complicationstic approach could make a mares estrous across Europe and South America.for the 18-month study period. Gradilsbehavior worse, Donnelly explains. Each While the vaccine might stop cycling,team easily removed the IUD with a mag- mare is different and can have different it might not change performance-relatednetic retriever, after which all 29 studyreactions, he says.Ovariectomiesissues, says Alvarenga. mares conceived successfully.removal of the ovariesare a good example. Estrogen production stops, but Novel Nondrug Therapies Plant Oils: The New Marbles? so does progesterone release. We some-One of the oldest efforts to manipulateInfusing plant oils into the uterus hastimes remove ovaries in teaser mares, estrus involves keeping the barn light onshown some promise in delaying estrus,because then they show estrous behavior at night to stimulate estrus earlier in thesays Ellerbrock. Theres a researchall the time, says Donnelly. breeding season. Specialized retinal cellspublication (from 2011) indicating thatSome estrous suppression therapies in the eyes signal the brain to send mes- intrauterine plant oil infusions (fraction- might have long-term or permanent ef-sages about time and season to the restated coconut or peanut oil) can work infects on future fertility, Donnelly says.of the body, affecting hormone produc- up to 90% of mares short-term, she says.Still, theres no concrete evidence of tion. Longer artificial days trick theBut we dont know the mechanisms oflong-term effects, says Ellerbrock. mares brain into coming into estrus. Irishaction, short-term side effects, or long- As for breeding mares, speeding up researchers have found that blue light isterm effects on fertility at this time. estrus or inducing ovulation can risk more effective than typical fluorescent orThe principle is probably similar tothe chance of double ovulation, creat-incandescent lights because its abun- that with marbles, in that the oil mimicsing twins in a single gestationwhich is dant in natural daylight. They designedgestation, says Donnelly. Hes used themdetrimental to the health of the mare and blue-light masks that manipulate estrussparingly, cautious of yet-unknown sideusually deadly for the foals, Aurich says, more effectively while letting mares geteffects but fairly confident in their efficacy.if youre not transferring these embryos. out of the barn and roam on pasture, saysMore recently, though, in a 2016 study Barbara Murphy, PhD, assistant professorCanadian and Brazilian researchersTake-Home Messagein University College Dublins School ofindicated that these approaches are notChanging your mares estrous cycle Agriculture and Food Science.effective at all, says Aurich. Evidence ispatterns can facilitate your breeding and Then there are intrauterine deviceslacking to show that either marbles or oilperformance plans. As research advances (IUDs). For decades vets have used a suppresses estrus or estrous behavior, shein this field, your mare can benefit from technique whereby they insert a glasssays. If owners notice a difference in theirimproved safety and efficacy, all while marble into the uterus to mimic mares, it might be purely a placebo effect. helping ensure her long-term fertility.h26May 2020The Horse|TheHorse.com'