Equine Science Research


Effects of Thermal Stress on Reproductive Function
Clay Cavinder, Martha Vogelsang, Dennis Sigler, Terry Blanchard, Dickson Varner, Charles Love and Steven Brinsko

In the mare, a significant decrease in the number of embryos collected and a lower average embryo quality was observed when mares were used in moderate exercise which was sufficient to raise the body temperature by just a few degrees (°C). An ongoing study demonstrated little change in preovulatory follicle size or interovulatory interval in mares in a similar exercise regimen and analyses of the effect on reproductive hormones was completed in 2010.

Also, effect of exercise-induced thermal stress on the stallion was studied with placement of a thermal sensor in the scrotum and subsequent evaluation of semen parameters and endocrine profile. The primary finding is that moderate and even heavy workloads during extreme heat do not seem to influence sperm quality.

Influences of Body Condition on Growth and Reproduction
Clay Cavinder, Dennis Sigler and  Martha Vogelsang

Studies have shown that keeping mares in an excessively fleshy body condition does not increase their reproductive performance over that seen when they are in a more moderate condition.  One study utilized a mathematical model to identify the daily digestible energy required to increase body condition in mares by one score. More recent research incorporated exercising horses into the model with preliminary results showing strong correlations between what the model predicts and actual changes in sedentary horses body fat percent, body condition score, and even weight.

As a follow-up to a previous study in which mares were maintained at different body conditions during gestation, adrenal function of their offspring during the subsequent (yearling) year showed no detrimental or beneficial effects.

Controlling Seasonal Breeding in Mares
Gary Williams and Marcel Amstalden

Project is designed to understand the fundamental mechanisms that control seasonal breeding in the mare and to develop practical pharmacological strategies for controlling this phenomenon. Studies include:
1) Use of subcutaneously-administered gonadotropin releasing hormone (GnRH) for 14-28 days to stimulate the development of a large ovarian follicle and ovulation for early breeding of non-cycling mares in February and March. Currently, we are searching for a method to allow convenient injection of a subcutaneous depot of GnRH that would elicit desired responses without the need for a surgically-applied implant or pump device.
2) Roles of the RF-amide, RFRP3 (also called gonadotropin-inhibiting hormone; RFRP3) and its antagonist (RF9) in regulating hormones that control reproductive seasonality.


Thorson, J.F., C.C. Allen, M. Amstalden, and G.L. Williams.  2014. Pharmacologic application of native GnRH in the anovulatory mare, I: Frequency of reversion to the anovulatory state following ovulation induction and cessation of treatment. Theriogenology 81:579–586.

Thorson, J.F., L.D. Prezotto, R.C. Cardoso, C.C. Allen, B.R.C. Alves, M. Amstalden, and G.L. Williams.  2014.Pharmacologic application of native GnRH in the winter anovulatory mare, II: Accelerating the timing of pregnancy. Theriogenology 81: 625–631

Thorson, J.F., L.D. Prezotto, R.C. Cardoso, S.M. Sharpton, J.F. Edwards, T.H. Welsh, Jr., P.K. Riggs, A. Caraty, M. Amstalden, and G.L. Williams.2014. Hypothalamic distribution, adenohypophyseal receptor expression, and ligand functionality of RF-amide-related peptide 3 in the mare during the breeding and non-breeding seasons. Biol. Reprod. 90(2):28, 1–9.

Dexamethasone Effects on Testis Gene Expression
Nancy Ing, Tom Welsh, Penny Riggs, David Forrest, Martha Vogelsang and Clay Cavinder

Dexamethasone is an anti-inflammatory drug with side effects that may include impairment of fertility. The effects of glucocorticoids and stress on spermatogenesis and steroidogenesis is being evaluated using several laboratory procedures including microarray to screen the gene products, quantitative RT-PCR to quantify gene products and in situ hybridization to localize gene expression to specific testis cells In stallions treated with Dex, there was a 50 percent decrease in expression of gene involved in steroidogenesis.

RNA Markers in Stallion Sperm that Correlate with Fertility
Nancy Ing, Penny Riggs and David Forrest

The purpose of this research is to identify regulatory microRNAs and protein encoding RNAs in sperm and compare their concentrations in high and low density sperm.  Protamine 1 & 2 expression is linked to fertility and the high density sperm had the highest gene expression.  This type of testing could prove beneficial in assessing fertility in stallions.  Additionally, function of the NMES1 gene function is being determined.


Spermatozoal Function
Clay Cavinder, Dickson Varner, Charles Love and Steven Brinsko

Utilizing omega-3 fatty acid dietary supplements did not improve spermatozoa characteristics in miniature horse stallions. The relationship between seminal characteristics and libido was evaluated to try to identify potential therapeutic regimens for stallions with low libido. Most recently, the relationship between sperm chromatin and pregnancy rates was analyzed. Data for this study was collected at a commercial farm and includes information from approximately 150 stallions. Identification of blood hormone markers during times of excitation was found for stallions.

Equine Gastric Ulcer Syndrome
Dennis Sigler and Clay Cavinder

Several studies a have been conducted to further identify factors leading to equine gastric ulcer syndrome (EGUS) in horses and to develop management strategies to reduce the incidence of EGUS.  Comparison of hay type showed that young horses on alfalfa hay had lower EGUS scores than those on grass hay.  In a second study, there was no difference in ulceration of young horses fed an organic versus an inorganic trace mineral supplement, however, as previous studies indicated, horses on alfalfa hay had lower EGUS scores.  In a third study, high dietary Ca levels had no effect on reducing EGUS scores.  A final study showed significant reduction in EGUS scores when horses were fed a textured grain plus hay diet vs. a pelleted grain plus hay.  This research work produced 3 MS graduates.


Effect of Dietary Magnesium on Muscular Dysfunction
Dennis Sigler

Studies evaluated the effect of low dietary Mg levels on muscular dysfunction and the possible role of Mg in tying-up syndrome in strenuously exercised horses.  Results indicated a possible connection of low dietary Mg to certain muscular enzyme levels indicative of muscle damage after intense exercise.

Effect of Dietary Starch Load on Muscle Glycogen Depletion and Repletion in Exercising Horses
Dennis Sigler and Clay Cavinder

Studies are being conducted on the effect of low-starch diets on muscle glycogen during and after intense exercise.  Results show a significant reduction in muscle glycogen repletion rate for up to 48 hours after intense exercise in horse fed a commercial low-starch concentrate.  Further research is continuing to further define dietary starch requirements for horses undergoing multiple bouts of intense exercise over a several day period.

Rider Energy Expenditure During High Intensity Horse Activity
Dennis Sigler, Martha Vogelsang, Clay Cavinder, James Fluckey and Steve Crouse

Using a COSMED K4b2 Portable Telemetric Gas Analysis System, the goal of this project is to examine rider energy expenditure during high intensity horse activity. Results of this project will provide data on energy expenditure during certain high intensity rides and form a prediction equation that can be used to provide riders with much needed information on caloric requirements and the health benefit of horseback riding as a form of exercise.  The implications to human health and therapeutic riding activities are enormous.

Development of a Mathematical Model for Predicting Dietary Energy Intake to Meet Desired Body Condition Parameters in Exercising Horses
Dennis Sigler, Clay Cavinder, Luis Tedeschi, James Fluckey and July Harlin

The main objective of this study is to utilize a novel computer nutrition modeling program, recently developed by the Department of Animal Science (Cavinder et al., 2011) to provide more accurate feeding recommendations which will minimize resources spent in managing horses and ultimately improve the health and welfare of the horse.  In order to refine the current model to include the exercising horse, the energy expended during exercise needs to be measured through indirect calorimetry using a COSMED K4b2 Portable Telemetric Gas Analysis System.


Determining Endocrine and Immune Factors For Survival in Septic vs Healthy Neonatal Foals
Tom Welsh, Lisa Caldwell Maple and Noah Cohen

The leading cause of mortality in neonatal foals is bacterial septicemia; therefore, our long-term goal is to develop intervention procedures to improve foal survival and to enhance the health of neonates.  The adaptive response of the body to the pathophysiologic stress created by acute severe sepsis causes activation of both the neuroendocrine and immune systems.  Therefore, we conducted a prospective clinical study that compared endocrine and immune factors in 11 healthy and 15 septic neonatal foals. The purpose of this study was 3-fold: (1) to determine whether there was an association between adrenal axis and cytokine expression in hospitalized full-term, septic and nonseptic neonatal foals, (2) to compare temporal changes in secretion of ACTH and cortisol between septic and nonseptic foals, and (3) to compare temporal changes in expression of cytokines among septic and nonseptic foals of the same ages. At each time point examined, ACTH and cortisol concentrations were greater in septic than nonseptic foals. The observation that anti-inflammatory cytokine gene expression was decreased in septic foals relative to nonseptic foals suggests dysfunction of the immune system among septic foals. Another key finding was an association between the adrenal axis and pro-inflammatory gene expression among septic foals. How cytokines, adrenal axis hormones and the innate immune system interact to impact the clinical response to sepsis warrants further review.


Transport of Commercial Slaughter Horses – Dehydration
Ted Friend

The existing regulations for the transport of commercial slaughter horses in the United States and Canada are largely based on a series of studies conducted at Texas A&M funded by the USDA Veterinary Services. Also, these studies have been featured in federal litigation and state hearings on the issue. Past studies conducted at two other universities had found that stalled horses could be deprived of feed and water for 5 to 7 days and recover with no lasting problems.  However, our studies found that detectable dehydration starts occurring during transport in hot conditions after 24 hours, with significant dehydration and fatigue occurring after 28 hours.  Although providing horses with water during transport moderated dehydration, fatigue still became significant after 28 hours.

Transport Stress of Horses – Rest
Ted Friend

Applied studies conducted at A&M demonstrated that the European Council’s proposal for regulations requiring frequent off vehicle rest stops and the associated unloading and reloading of food animals were detrimental to the wellbeing of most agricultural animals.  Horses and sheep did not actually “rest” during rest stops, but explored and remained active until they became fatigued.  Although many animals ate and drank water during stops, there is a tradeoff between getting the trip over as soon as possible and greatly prolonging the transport event when, for example, 6 hour rest stops are mandated at 8 hour intervals.  The European Council then revised and implemented more reasonable regulations, although some aspects of their regulations are still poorly researched.  When determining duration of transport for horses, “rest stops” should often be included as time spent in transport. The optimum duration for a rest stop to be useful in mitigating transport stress has not been determined, but 12 hours is not enough time for normal rest patterns to be re-established.

Horses Feeders for “Sloppy Eaters”
Ted Friend and Josie Coverdale

Horse owners are often faced with the dilemma of having one or more “sloppy eaters”.  These horses typically take up large amounts of feed in their mouths, raise their heads out of the feeder to apparently look around, and then much of the feed falls out of their mouths as they start mouthing and chewing the feed.  Much of their feed ends up on the floor of their stall or into the dirt or sand when fed outdoors.  In addition to wasting a good portion of the feed, such horses also then try to eat the contaminated feed after what was in their feeder ends up on the floor.  The contaminated feed is mixed with sand, manure, and other debris which are eaten by the horse and can cause major health issues for the horse.  Studies at A&M evaluated four different types of feeders, and determined that feeders with 8 cups molded into the bottom greatly increased time horses spent eating and significantly reduced the amount of feed dropped on the floor. The most wasteful horse on the study lost 32.8% of his ration when fed from a conventional bucket, but that was reduced to 8.7% when fed from the feeder with the molded cups in the bottom.  This type of feeder would be especially useful when managing sloppy eaters, but it is more expensive and requires more cleaning.

Transporting Horses in Groups or Individual Stalls
Ted Friend

Whether it is better to transport horses in loose groups or in individual stalls has been a controversial issue. Studies at A&M have indicated that transport in loose groups is comparable or in some situations preferable than individual stalls, as long as the groups are observed in pens prior to loading and aggressive stallions or mares are removed from the group and transported individually.  The European Union, however, implemented regulations that all horses being transported to slaughter be transported in individual stalls.  The individual stall requirement has created a host of “unexpected” welfare problems for the horses that welfare groups have exposed and are campaigning to remedy, but there appears to be little interest among European regulators to revise the regulations.

Transporting Horses in Groups
Ted Friend

There has long been a myth that when horses are transported in groups, they should be loaded very tightly so that they “hold each other up”.  Studies conducted at A&M have shown that horses do not hold each other up, but impede each other’s ability to maintain balance.  High density transport is also associated with more injuries and it makes a horse that does lie down during transport more likely to be trampled.  Horses also avoid contact with walls and others horses during rough roads, turns and abrupt stops.  When loose groups of horses are being transported, they should be given more room during shipments of 24 hours or longer than during shorter hauls.

On-truck Watering System for Groups
Ted Friend

An on truck watering system for horses being transported in loose groups in commercial semi-trucks was developed and tested. A float valve plastic waterer that was mounted on a bracket that could be inserted into the animal compartments was utilized by horses when the truck drivers stopped at truck stops for a meal and rest brakes.  Most of the horses readily drank and did so within the first 30 minutes of access to the water, so the system appears to be practical in delaying dehydration during long shipments.  Implementing this or a similar watering system will require changes in our current regulations, which is not likely at present.


Whole-Genome sequencing and genetic variant analysis of a Quarter Horse mare
Jason Sawyer, Ryan Doan, Noah Cohen, Noushin Ghaffari, Charles Johnson and Scott Dindot

The first sequencing of a horse genome by next-generation sequencing and the first genomic sequence of an individual Quarter Horse mare was conducted, unlocking the secrets of what makes this breed so unique. This information can be used to study genetic disorders and distinctive traits leading to diseases and syndromes.


Doan, R., N.D. Cohen, J. Sawyer, N. Ghaffari, C.D. Johnson, and S.V. Dindot. Whole-Genome Sequencing and Genetic Variant Analysis of a Quarter Horse Mare. 2012. BMC Genomics 13:78.

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