Mathematical nutrition models have been developed for beef and dairy cattle to estimate dietary energy intake needed to change BCS. Similar technology has not been used to improve nutrition and feeding strategies for horses. An accurate equine nutrition model may enhance feeding management and reduce the costs of unnecessary overfeeding and promote an optimal level of fatness to achieve reproductive efficiency. The objectives of this study were to develop and evaluate a mathematical nutrition model capable of accurately predicting dietary energy changes to alter BW, rump fat (RF) thickness, and overall body fat (BF), which is needed to maximize profitability and productivity of mares. Model structure was similar to a previously developed model for cattle, and literature data for Quarter Horse mares were used to parameterize the horse model in predicting DE requirement associated with BCS changes. Evaluation of the horse model was performed using an independent dataset comprising 20 nonlactating Quarter Horse mares. Pretrial BCS was used to assign mares to 1 of 4 treatment groups and fed to alter BCS by 1 unit as follows: from 4 to 5 (Group 1), 5 to 4 (Group 2), 6 to 7 (Group 3), and 7 to 6 (Group 4). The BCS, RF thickness, and BW were measured for each mare before the commencement of the feeding trial and once per week thereafter for the duration of a 30-d feeding trial. Initial and target BCS, percent BF, and BW data were collected from each mare and inputted into the model. Mares were individually fed according to the DE suggestions proposed by the model to achieve the targeted BCS change within 30 d. The coefficient of determination of observed and model-predicted values (model precision) was 0.907 (P < 0.001) for BCS, 0.607 (P < 0.001) for percent BF, and 0.94 (P < 0.001) for BW. The BCS was highly correlated to percent BF (r = 0.808; P = 0.01). We concluded the reparameterized model was reliable to predict changes in BW and BCS, but more work is needed to improve the predictions of initial and final body composition.

Background: Both graying and melanoma formation in horses have recently been linked to a duplication in the STX17 gene. This duplication, as well as a mutation in the ASIP gene that increases MC1R pathway signaling, affects melanoma risk and severity in gray horses.Objective: To determine if melanoma susceptibility in gray Quarter Horses (QH) is lower than gray horses from other breeds because of decreased MC1R signaling resulting from a high incidence of the MC1R chestnut coat color allele in the QH population.Animals: A total of 335 gray QH with and without dermal melanomas. Methods: Blood or hair root samples were collected from all horses for DNA extraction and genotyping for STX17, ASIP, and MC1R genotypes. Age, sex, and external melanoma presence and grade were recorded. The effect of age and genotype on melanoma presence and severity was evaluated by candidate gene association.Results: Melanoma prevalence (16%) and grade (0.35) in this QH cohort was lower than that reported in other breeds. Age was significantly associated with melanoma prevalence (P = 5.28 9 10

Chair of Advisory Committee: Dr. Clay A. Cavinder Studies performed on stallions have characterized detrimental effects on semen quality resulting from thermal stress by testicular insulation, but few have investigated the effects of exercise-induced increases in core body temperature on stallion semen parameters. To our knowledge, this is the first study that correlates subcutaneous scrotal temperature and stallion spermatozoa quality using a subdermal scrotal thermal sensory device. Stallions were assigned to a non-exercised (non-ex; control; n=4) or exercised (ex; n=4) group. A motorized equine exerciser was used to work stallions 30 min/d for 4 d/wk during a 12-wk period from July through October. Temperatures (subcutaneous scrotal, subcutaneous neck, rectal, and ambient) were recorded before exercise, immediately after exercise, and 60 and 120 min post-exercise. Humidity data were obtained later to determine THI.No deleterious effects were observed from implantation of thermal sensorydevices. An interaction of treatment and time (P < 0.0001) was evident for rectal and neck temperatures. The relationship between scrotal and rectal temperatures was highest (r s =0.761), and other correlations existed between scrotal, neck, and ambient iv temperatures, as well. Mean rectal temperature in the ex group increased 1.9°C (P < 0.0001), while there was a slight increase in scrotal temperature of 0.8°C (P > 0.05) from 0 min to 22 min. Although an increase in core body temperature was successfully induced by exercise protocol, scrotal temperatures were not significantly affected, and no treatment effects were found in any of the semen parameters measured (P > 0.05).Therefore, no significant changes in fresh or cooled semen parameters resulted from exercise or increases in core body temperature resulting from exercise protocol used in this study.Results of this study indicate that thermal sensory devices are a safe and effective way to measure subcutaneous scrotal and neck temperatures. Although an increase in core body temperature was successfully induced by exercise protocol, scrotal temperatures were not significantly affected, indicating efficient thermoregulation of the testes by the scrotum. Since the testes experienced no significant thermal insult during the exercise protocol, no significant changes in fresh or cooled semen parameters were evident as a result of exercise or elevated core temperature.v DEDICATION This thesis is dedicated to the two people I admire most, my parents. They forged the career path that I have chosen in life by providing me the opportunity to grow up with horses. Although this path has taken me far from home and family, I know that no matter the distances I travel, the unwavering love and support of my parents will always sustain me. Mom and Dad, I will forever be grateful for the sacrifices you have made to see me achieve my goals. Thank you; I love you; and I miss you every day.To my beloved horse and friend of only 5 short years: you will always be the horse to which I will compare ...

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Stallions (n = 8) were implanted with a thermal sensory device in the muscle of the neck and the subcutaneous tissue of the scrotum and then assigned to either a nonexercise (Non-EX; n = 4) or exercise (EX; n = 4) group. A motorized equine exerciser was used to work EX stallions 30 min/d for 4 d/wk during a 12-wk period from July through October 2010. Temperatures (subcutaneous scrotal, intramuscular neck, and rectal) were recorded at 0, 22, and 30 min after the start of exercise, as well as 60 and 120 min post-exercise. Hourly ambient temperature and relative humidity data were also obtained. Semen was collected at 0, 4, 8, and 12 wk and analyzed for volume, sperm concentration, total sperm numbers, percentages of total and progressively motile sperm, sperm morphologic characteristics, and sperm DNA quality. No effect (P > 0.05) of exercise was observed on any of the measured semen variables. Implantation of thermal sensory devices had no demonstrable acute or chronic effects on the scrotal or neck tissue, indicating that the thermal sensory devices are a safe and effective way to measure subcutaneous scrotal and neck temperatures. At 22 and 30 min of exercise, rectal and neck temperatures increased (P < 0.0001) approximately 1.9 and 2.4°C, respectively, and scrotal temperatures simultaneously increased, although not significantly (P = 0.33), approximately 0.8°C. Correlations existed between scrotal, neck, rectal, and ambient temperatures, with the correlation between scrotal and rectal temperatures being greatest (r(s) = 0.76; P < 0.0001). Although moderate exercise for a short duration in extreme heat and humidity did significantly increase core body temperatures in stallions, scrotal temperatures did not significantly increase, and sperm parameters were unaffected.

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Mean (± SD) ambient temperature (AMBT) and temperature heat index (THI) in the shade and in the sun during exercise………………………... 2 Mean (± SD) ambient temperature (AMBT) in the shade and in the sun during exercise over the 12 wk of the exercise…………………………... 3 Mean (± SD) neck (NT) and subcutaneous scrotal (SQST) temperatures for exercising (EX) and non-exercising (CN) stallions during exercise period………………………………………………………….

Lactating mares were assigned as controls or fed altrenogest (.044 mg.kg body wt-1.d-1) for 15 d after foaling. Mares (n = 6) fed altrenogest were inseminated during the first estrus after treatment and mares (n = 6) in the control group were inseminated during the second postpartum estrus. Ovulation during the estrus in which mares were inseminated occurred 26 +/- 1 d postpartum for treated mares and 36 +/- 1 d postpartum for control mares. The percentage of mares conceiving was not different for control (67%) and alternogest-treated (100%) mares. No differences were observed in tone and size of the uterus or size of the ovulatory follicle between treated and control groups. Uterine cultures and biopsies collected on d 7 and 15 postpartum were similar between treatment and control groups in bacterial populations or endometrial epithelial cell height. Blood was collected on d 7, 11, 15, 19 and 23 postpartum, and concentrations of estradiol-17 beta in serum were determined by radioimmunoassay. Mean concentrations of estradiol-17 beta across days were 10 +/- .8 and 12 +/- .6 pg/ml for control and treated mares, respectively. Concentrations of serum estradiol-17 beta were higher (P less than .05) in treated mares on d 23 postpartum. Daily milk yields, determined by the weigh-suckle-weigh method, and milk composition were similar between treatment groups on each collection day. Altrenogest can be used to predictably delay estrus in the postpartum mare without altering fertility, yield and composition of milk, or foal growth.