Quarter Horse Mares Research Articles

Successful equine in vitro embryo production by ICSI – effect of season, mares’ age, breed, and phase of the estrous cycle on embryo production

This retrospective study aimed at identifying factors that contribute to the success of equine in vitro embryo production by intracytoplasmic sperm injection (ICSI). A total of 7993 ovum pick-up (OPU) sessions were performed, totaling 2540 donor mares and semen from 396 stallions. Oocytes were aspirated at multiple sites in Brazil and were sent to the laboratory, within 6 h from OPU, in pre-maturation medium where they were in vitro matured (IVM) followed by ICSI and in vitro embryo culture for 7–8 days. The number of recovered oocytes, matured oocytes, cleaved embryos and blastocysts were used to explore the effect of age and breed of the donor mare, time of year in which the mare was aspirated and phase of the estrous cycle on the day of follicular aspiration. Mares between 6 and 15 years old were superior to other age groups in most parameters evaluated, including the average number of blastocysts per OPU. The impact of age was similar when evaluated within two breeds, American Quarter Horse (AQHA) and Warmblood mares. We observed that breed (AQHA, Warmblood, Crioulo, Lusitano and Mangalarga) had an important effect on most of the parameter evaluated, including number of oocytes recovered, blastocysts produced per OPU, and blastocyst rates. The overall impact of season was less pronounced than age and breed, with the only statistically significant difference being a higher rate of oocyte maturation during the summer season. Finally, most of the parameters evaluated were superior in follicular phase mares, with or without dominant follicle than luteal phase mares. In conclusion, this retrospective study revealed that breed, age, season and stage of estrous at the time of OPU are all important parameters for the success of equine embryo production by ICSI. This technology enables producing embryos all-year-round from mares of different breeds and ages from OPU-derived oocytes collected at multiple sites.

Characterization of lyophilized equine colostrum

Foals require maternal colostrum in the first hours of life to prevent failure of transfer of passive immunity (FTIP). Innovative storage methods such as lyophilization may enable conservation of colostrum immunoglobulins by a differentiated process of dehydration. The current study aimed to compare the quality of equine colostrum after freezing and after the lyophilization process. Thirty-one pregnant Quarter Horse mares were used. The IgG concentration of frozen and lyophilized colostrum was determined by simple radial immunodiffusion (SRID) and Brix refractometry. The physical-chemical composition (pH, total protein (TP), fat, lactose, salts, total solids (TS), and density) of the samples was evaluated and the lyophilized colostrum reconstitution test was performed. There were no significant differences (P > 0.05) in the variables IgG, fat, lactose, salts, TS, density, and pH between samples measured before and after lyophilization. There was a significant difference (P < 0.05) between the Brix average and the TP of the frozen and lyophilized colostrum samples. Lyophilization resulted in a small reduction (6.55%) in the IgG concentration measured by SRID. A strong positive correlation was observed between colostrum density and IgG concentration by SRID (r = 0.76) and between Brix and IgG concentration by SRID (r = 0.77). In the reconstitution test, the lyophilized colostrum was easily rehydrated in water, with full dilution, and remained stable. Lyophilization could be an alternative for the conservation of mare colostrum, since it is a very efficient process for retaining the physicochemical characteristics of the product, with minimal loss, particularly of IgG.

Efficacy of buserelin for induction of ovulation in mares

The rational and controlled management of equine reproduction in commercial programs promotes the development of drugs that help to regulate certain physiological processes in mares, such as luteolysis or ovulation. Human Chorionic Gonadotropin is used predominantly in commercial and experimental programs showing optimal ovulatory results in multiple studies. However, a lower inducing effect has been reported in old mares, which are highly represented in the commercial breeding population. Some studies with human formulations of buserelin, one of the oldest GnRH synthetic analogs, have demonstrated similar efficacy to other analogs in mares (Newcombe and Cuervo-Arango. Journal of Equine Veterinary Science. 2016; 41, 57). In Argentina, until now, there are no specific buserelin formulations for mares. The aim of this clinical prospective study was to compare the ovulation induction efficacy of two doses of a new buserelin formulation in mares of different age groups. The study was carried out in a commercial breeding program in the subtropical north of Argentina using healthy Quarter Horse and Criollo mixed breed mares randomly assigned to treatment groups. When uterine edema, a relaxed cervix and 35 mm follicles were detected, mares were induced once, with a single intravenous (IV) injection of 0.2mg of buserelin (Busereleq,Laboratorio CIMOL, Argentina) for group 1 (G1, n=77) and 0.4mg for group 2 (G2, n=54). The response was considered positive when absence of the dominant follicle and presence in the same ovary of a corpus luteum were detected by ultrasound, 48 hours after treatment. In both groups, mares were classified according to age in <10; 11-15; >15 years old (yo). The data were analyzed by the chi square test for categorized data using Infostat Software. The follicular size, degree of edema and age were compared in the different groups at the time of treatment by means of a non-parametric Kruskal-Wallis analysis of variance. The results showed that 87.01% of the G1 (0,2 mg) and 70.37% of G2 (0.4mg) mares responded positively (p<0.05). No significant differences were found between follicular size, degree of edema and age of the mares at the time of induction among treated groups (p >0.05). Efficacy of the different treatments by age group in G1 and G2 was 77% and 68% in <10 y.o; 96% and 71% in 10 -15 y.o; 90% and 73% in >15 y.o respectively. A significant difference among treated groups was detected in middle age (10-15 years) with more efficacy in G1 (p=0,017). Our results suggest that a low dose buserelin (0.2mg IV) can be used to induce ovulation with acceptable clinical efficacy, even in older mares.

8 Comparison of oxytocin and pro-inflammatory cytokines in saliva and plasma in the post-partum mare as potential biomarkers of well-being

Although evaluating cortisol concentrations is a common method to assess stress in many species including horses, interpretation of results in these studies has proven challenging. Therefore, researchers are investigating alternative analytes as biomarkers of well-being. Historically thought to serve primary roles in parturition and lactation, oxytocin (OT) has been shown to act as a neurotransmitter to promote prosocial behavior and buffer stress. Pro-inflammatory cytokines (PICs) have been shown in humans to influence production of neurotransmitters such as serotonin and dopamine, implicating their potential role in psychosocial stress. Analyte levels are often measured in blood, but this sampling procedure can result in acute stress responses that may influence experimental results and conclusions. Evaluating analytes in saliva can serve as a less-invasive method to assess biomarkers of well-being. The purpose of this study was to determine the feasibility of measuring OT and PICs in saliva as an alternative to plasma sampling in horses. As studies have demonstrated that OT and PICs are elevated during parturition and lactation, 4 postpartum Quarter Horse mares (15.0 ± 0.82 yr) were chosen for this study. Plasma (P) and saliva (S) samples were collected 30 min post-foaling (P1, S1) and 30 min post first suckling (P2, S2). Samples were analyzedfor OT, IL1-β, IL-8, IL-6, and TNF-α via electrochemiluminescent (ECL) assay (Salimetrics). Data were analyzed using the PROC GLM and PROC CORR in SAS v 9.4. Mean analyte concentrations, with the exception of IL-8, differed by sample type (S OT = 45.16 ± 36.65 pg/mL, P OT = 96.10 ± 41.0 pg/mL, P < 0.05; S IL1-β = 13.98 ± 2.03 pg/mL, P IL1- β = 1.01 ± 0.18 pg/mL, P < 0.01; S IL-6 = 0.35 ± 0.14 pg/mL, P IL-6 = 1.32 ± 0.46 pg/mL, P < 0.01, S TNF-α = 0.36 ± 0.16 pg/mL, P TNF- α = 3.40 ± 0.86 pg/mL, P < 0.01). There were no differences in analyte concentrations due to time point. Though not significant (P > 0.5), time point comparisons across sample type showed moderate to strong Pearson correlations among OT (S1-P1; r = −0.56; S2-P2; r = −0.47), IL-8 (S1-P1; r = −0.69), IL-6 (S1-P1; r = 0.82), and TNF-α (S1-P1; r = 0.48). The established roles of OT and PICs in prosocial behavior and psychosocial stress suggest that measurement of these analytes may provide a targeted approach to assess biopsychosocial responses. While this assay has not yet been validated for use in horses, this study illustrates that PICs can be quantified in equine saliva which supports this less-invasive approach for studying biomarkers of well-being in horses.

102 Influence of localized massage on biobehavioral responses of mature horses during exposure to unfamiliar stimuli

Exposure to unfamiliar stimuli can lead to increased heart rate (HR), an increased incidence of locomotor behaviors, and changes in facial expressions. Responses of horses to unfamiliar stimuli can have important consequences for both horse and human safety. Horses preferentially groom conspecifics along the base of the neck, in front of the shoulder blade and across the withers. Imitated grooming of horses in this location has been shown to decrease horse HR. The objective of this study was to determine if localized massage along the base of the horse's neck and withers would influence HR, behavior, and facial expressions during exposure to an unfamiliar stimulus (cordless hair clippers) Eleven Quarter Horse mares (11.6 ± 4.9 yr) were fitted with a Polar H10 Equine HR monitor and led by the same handler to an open-front, 3.1 × 3.1 m grooming stall in a barn. After a 5 min acclimation period (P1: pre-stimulus), the clippers were turned on and held approximately 30.5 cm from the horse's left ear for a 3 min interval that consisted of: stimulus/pre-massage (45 s; P2), stimulus/massage (90 s; P3) and stimulus/post-massage (45 s; P4). The clippers were then turned off and the horse remained in the stall for 5 min (P5: post-stimulus). HR and video recording occurred throughout the 13 min session. Scan sampling of video footage every 15 s (P1 and P5) or every 5 s (P2-P4) was used to determine counts. Data wereanalyzed using PROC MIXED in SAS v. 9.4. Significant differences in HR, locomotor behaviors, and facial expressions were observed between horses in the study, highlighting the role of individual variation among horses. Although HR decreased once localized massage was initiated, no significant differences were observed in HR during exposure to the stimulus, with or without localized massage, compared with the pre- and post-stimulus periods. No differences were observed in the movement of horses’ front feet during exposure to the clippers; however, horses moved their hind feet more frequently during exposure to the clippers once the localized massage stopped (P < 0.05). Although the frequency of ears facing the same or different directions in a relaxed position was greater when localized massage was performed during exposure to the unfamiliar stimuli (P < 0.01), no differences were observed in nostril dilation, inner brow movements, or eye white increase during exposure to the stimuli compared with the pre- and post-stimulus periods. Localized massage may reduce stress-related behaviors during exposure of horses to unfamiliar stimuli; however, more research in this area is needed

106 Use of biobehavioral responses during a novel object test to assess suitability of horses for equine assisted services

Many recent studies have demonstrated positive outcomes for human participants in a variety of equine assisted services (EAS). Horses by nature are highly sensitive and their responses to unfamiliar stimuli can have important consequences for horse and human safety. Individual variation in the personality characteristics of horses, including their reactivity, may not only create safety concerns but also influence therapeutic outcomes. To date, there are no available standardized guidelines for the selection of equine in EAS. Observation of horse behavior by equine professionals has historically been used to assess the potential suitability of equine participants. However, overall behavior of individual horses can be challenging to objectively measure. Novel object (NO) tests are often used to measure reactivity in many animal species. To our knowledge, no study has yet evaluated the reactivity of horses in response to a NO test to assess their suitability for groundwork-based EAS. The purpose of this study was to compare biobehavioral responses of 11 Quarter Horse mares (11.6 ± 4.9 yr) before, during, and after exposure to a NO (stationary flamingo pool float) as a potential measure of their suitability for participation in EAS. The experiment consisted of 3 consecutive 5 min periods: Pre-NO test (P1), NO test (P2), and Post-NO test (P3) in the same 27 × 26 mpaddock. HR was recorded using a Polar H10 equine HR monitor. Behavior was video recorded and scan sampling of video every 10 s was used to determine counts. Data were analyzed using PROC MIXED in SAS v 9.4. Horse HR differed by horse and decreased with time within all 3 periods (P < 0.01). During the NO test, locomotion increased with increasing proximity to the NO (P < 0.05). Standing alert and exploratory behaviors decreased during the NO test but were not influenced by the horse's location (P < 0.03). Interestingly, eating behaviors increased during and after the NO test (P < 0.05). This study illustrates that behavioral and physiological responses of horses are influenced by their individuality which may ultimately influence their interactions during EAS. The reduction in HR over time within each period suggests that horses can quickly acclimate to changes in their environment and the overall lack of differences in their behavioral responses across periods suggests low reactivity among this study population. However, future studies with additional novel objects and horses are needed to determine if the use of this methodology can serve to evaluate suitability for horses for participation in EAS.

134 Late-gestation maternal overnutrition alters gene expression and histomorphology in neonatal foal testes

While obesity has deleterious effects on metabolism, performance, lameness, and health in mature horses, little is known about the impacts to reproductive health in foals from overfed dams. The objective of this study was to determine the effects of maternal overnutrition on neonatal foal testicular development. To test this, 16 Quarter horse mares were used in a completely randomized design and stratified by expected foaling date, body weight, and body condition score into one of 2 dietary treatments offered twice daily beginning on gestation d 235: control (CON; n = 8) fed to meet 100% of nutrient requirements and overfed (HIGH; n = 8) fed to 140% of nutrient requirements. At 5 h postpartum, foals were humanely euthanized, and testes were harvested, weighed, and stored for analyses. Testicular weight included the tunica dartos with the epididymis removed. RNA was extracted using the PureLink RNA Mini Kit (Life Technologies, Austin, TX) and submitted for RNA sequencing (Novogene, Sacramento, CA). Histomorphometric evaluations were performed using a hematoxylin and eosin stain. Ten 10X images per animal were analyzed using ImageJ software for individual seminiferous tubule (ST) area, ST number, and % area of STs per 10X field relative to interstitial tissue. Sertoli cell numbers were determined at 40X using 20 seminiferoustubules per animal. Data were analyzed using the MIXED procedure in SAS. Testes from HIGH male foals (n = 4; LSMeans ± SEM; 32.93 ± 1.93 g) were 61% larger than testes from CON male foals (n = 4; 20.50 ± 1.93 g; P < 0.01). RNA sequencing revealed 56 differentially expressed genes between HIGH and CON groups (P-adjusted <0.05). These genes represent biochemical pathways involved in oxidative phosphorylation, fatty acid metabolism, and thermogenesis, which are integral for testicular development and function. Gene ontology analyses revealed differential gene expression was associated with biological processes relevant to reproductive function and spermatogenesis, including cellular respiration and mitochondrial function. Histological analyses revealed no difference in individual ST area (P = 0.76) or Sertoli cell number within STs (P = 0.57); however, testes from CON foals had 2.3x more STs per 10X field (21.68 ± 2.48) than HIGH foals (9.35 ± 2.48; P = 0.01) along with STs representing a greater percentage of the image area relative to interstitial tissue (CON 3.66% ± 0.61%; HIGH 1.60% ± 0.61%; P = 0.05). These data from the neonatal foal indicate that late-gestation maternal overnutrition alters fetal testicular development with potential long-term implications.

The use of prostaglandin applied in Bai Hui Acupoint on mare reproductive efficiency

SummaryProstaglandin F2α (PGF2α) is one of the most frequently used drugs for pharmacologic manipulation of the oestrous cycle in mares. Among its roles, PGF2α induces luteolysis, leading to an early oestrus return, which reduces the dioestrous phase and the inter‐ovulatory intervals. Interestingly, mares are more sensitive to PGF2α than other domestic species, hence lower doses are used; even so, the side effects are still adverse and inconvenient for animals and breeders. Recent studies of acupuncture, a traditional Chinese medicine technique, have been performed as an alternative to decrease the PGF2α dose for mares. The efficacy described of applying lower doses of PGF2α at specific acupoints is similar to that obtained with the regular dose. Therefore, the objective of this study was to analyse the reproductive performance and characteristics of oestrus in embryo recipient and donor mares using different doses at the Bai Hui—an acupoint located on the dorsal midline, also known as ‘the point of one hundred meetings’, as its region of effect encompasses many nerve trunks, nerve endings and vascular networks—a useful veterinary acupuncture treatment for ovarian disorders. For this study, 76 Quarter Horse mares were randomly assigned to three experimental groups: Control (CTR)—Intramuscular (IM) administration of 5 mg PGF2α; Bai Hui 5 mg (BH5)—application of 5 mg at the Bai Hui acupoint; and Bai Hui 2.5 mg (BH2.5)—application of 2.5 mg at the Bai Hui acupoint. In the results, there were no differences regarding uterine oedema, pregnancy rate or body condition score among the groups. However, oestrous expression was lower (p &lt; 0.001) in both BH groups compared with CTR. Lastly, the interval between application and ovulation was shorter in BH5 compared with CTR (p = 0.042). The results indicate BH5 and BH2.5 as viable alternatives to the IM administration.

Liposomal bupivacaine is both safe and effective when administered via local infiltration at surgical site and mesovarium for laparoscopic ovariectomy in mares.

Liposomal local anaesthetic solutions may provide extended-duration analgesia postoperatively but have not been assessed following intra-peritoneal local infiltration in any species. To evaluate two doses of 1.33% liposomal bupivacaine (LB) versus 0.75% bupivacaine HCL (BHCl) for analgesia following laparoscopic ovariectomy in mares. Prospective cohort study. Fifteen healthy Quarter Horse mares (age 2-20 years) with normal bilateral ovarian palpation and appearance were enrolled. Horses were restrained in standing stocks and administered an α-2 agonist, butorphanol, and flunixin meglumine, followed by a variable rate infusion of sedation with α-2 agonists. Bilateral paralumbar fossa ovariectomies were performed. Treatment with either 30 ml 0.75% BHCl followed by 20 or 40 ml LB 13.3% (LB20 and LB40) volume expanded with saline to 80 ml total (n=6/group) or 80 ml BHCl alone (n=3, BCHL) was infused around incision sites and each mesovarium (LB or BHCl) prior to ovariectomy. Horses were monitored for 72 h by physical examination, algometry, and pain scoring (composite pain scale by Bussieres et al., Horse Grimace Scale). Abdominocentesis with peritoneal fluid analysis was performed at 72 h. Analgesia achieved with all treatment protocols allowed completion of ovariectomy procedures. Pressure algometry scores were lower in BHCl-treated horses versus both LB groups overall. Pain scores were improved with LB-treated horses in a dose-dependent fashion (Horse Grimace Scale scores LB40 < LB20 < BHCL; composite pain scale scores LB40 < BHCL, LB20 < BHCL, BHCL, and LB20 did not differ). Peritoneal fluid total protein was lower in LB40 versus LB20 and BHCL horses. No complications from LB administration were appreciated. Small patient sample size, lack of follow-up past 72 h or histopathology. Analgesia duration was extended and pain scores improved postoperatively with LB versus BHCl in a dose-dependent fashion. Further clinical evaluation of extended-duration local anaesthetics in horses for improved postoperative pain management is warranted.

Tend and Befriend in Horses: Partner Preferences, Lateralization, and Contextualization of Allogrooming in Two Socially Stable Herds of Quarter Horse Mares.

Studies show that horses express favoritism through shared proximity and time and demonstrate unique affiliative behaviors such as allogrooming (mutual scratching) with favorite conspecifics. Allogrooming also occurs more frequently during stress and has been observed to occur more frequently in domestic herds than feral. The role of partner preference, lateralization, and duration of allogrooming as measures of social bonding has remained unclear. The present study looked at two socially stable herds of mares (n = 85, n = 115) to determine the frequency, duration, visual field of view and partner preference during allogrooming in both pasture settings (low stress) and confined settings (higher stress). One hundred and fifty-three videos for both herds were coded for allogrooming behaviors with 6.86 h recorded in confined conditions and 31.9 h in pasture settings. Six allogrooming sessions were observed in the pasture setting with an average duration of 163.11 s. In confined settings, a total of 118 allogrooming sessions were observed with an average duration of 40.98 s. Significant (p &lt; 0.01) differences were found between settings for duration (s), number of allogrooming pairs, and frequency of allogrooming (per min) for each herd. All observed allogrooming sessions involved pairs of favored conspecifics (one partner per horse). The current study suggests that horses may have friendships that can be observed through the demonstration of specific affiliative behaviors during times of stress with more frequent, but shorter affiliative interactions with preferred partners during times of stress. This context suggests that horses adhere to the "tend and befriend" principles of friendship in animals.

220 Effects of Total Equine Grain with Ascophyllum Nodosum Seaweed Extract and Chelated Minerals on Forage Intake, DM, NDF, and ADF Digestibility, in Quarter Horse Mares Under Performance Conditions

Abstract A study was conducted in fall 2019 at Sul Ross State University to evaluate the effects of Total Equine containing Ascophyllum nodosum seaweed and chelated minerals on intake and cecal digestibility in comparison with a product without Ascophyllum nodosum seaweed or chelated minerals. Six Quarter horse mares (avg 9yrs) were used in a complete randomized block study. Horses were offered an ad libitum Bermuda hay for a 2wk standardization period and then blocked into pairs based on weight, age, and fitness level. Horses were assigned randomly within block to the Ctrl or Trt diets for an 8wk study with ad libitum access to water. Hay was offered 2xd in port-a-grazer tubs to control for waste. Grain was offered at a rate of 0.005% BW (manufacturer suggestions) and divided into 2 equal feedings. Horses were weighed weekly and grain amounts were adjusted weekly. Hay orts were collected 2x daily and hay offered was adjusted daily for a 3% refusal rate. Horses were exercised 6d/wk on a hot-walker for 2hrs. Horses were conditioned prior to the study and speed and duration were increased throughout the study. Horses worked 30min at a walk and 1.5hrs at a trot broken into periods. Feed samples were collected 2xwk and dried for DM and ground for analysis for NDF, ADF, CP, EE, and Ash. A significant difference in total DMI was observed at 13.1 ± 0.14kg Ctrl versus 12.02 ± 0.11kg Trt (P=0.0001). When evaluating forage intake only 10.07 ± 0.13 kg Ctrl versus 9.04 ± 0.11 kg Trt (P=0.0001). DMd and NDFd were not significantly affected by trt (P=0.38). However, tendency horse*diet (P=0.07) was observed. Overall, it appears that the inclusion of the grain product with Ascophyllum nodosum and chelated minerals reduced forage intake and overall DMI without effecting fiber digestibility or animal performance.

216 Effects of Total Equine Grain Containing Ascophyllum Nodosum Seaweed Extract and Chelated Minerals on in-Vitro DMd &amp; Ndfd, Body Composition, and Post-Exercise Recovery in Mature Quarter Horse Mares

Abstract Supplements such as seaweed extracts and chelated minerals have been shown to positively affect animal health. However, these supplementation is not well-researched in equines. The purpose of this study was to assess the effects of an extruded grain (Total Equine) containing Ascophyllum nodosum seaweed extract with and without a chelated sulfur supplement (Total Equine-15 Natural) on in vitro DMd and NDFd, body composition, and post-exercise recovery. Six Quarter Horse mares were fed three different diets: Control (Ctrl), Total Equine (TM), Total Equine plus Equine-15 Natural (TM15) in a Latin square design study with a six-week washout period between each three-week experimental period. Grain was offered at 0.004% BW. A submaximal test (4 min at 4.3 mph, 14 min at 9.5 mph, 6 min at 13.5 mph) was conducted on days 0 and 21. Resting and post-exercise blood lactate, respiratory rate, heart rate, and rectal temperature were measured at the start and end of each experimental period. Fecal samples were collected during the last week of each experimental period and analyzed through Daisy ANKOM. Body weight and body composition were evaluated pre- and post-study. Analysis showed no effect (P=0.12) on Bermuda DMd and NDFd among treatments. However, the DMd and NDFd of alfalfa with TE15 were decreased significantly at 24 hr (P=0.0001 and 0.0003, respectively). The other only significant change observed was body composition. Horses on TE15 had greater loss of fat mass (p=0.005), followed closely by the TE. In conclusion, TE did not show any adverse effects on DMd, NDFd, body composition, and post-exercise recovery; TE15 did not change most nutritional and physiological parameters besides decreasing in vitro DMd, NDFd, and body fat mass. The simple effect of the chelated sulfur and Ascophyllum nodosum in equine should be further investigated.

Thirty-Two Weeks of Oral Supplementation with LinPro™ Increases Hoof Growth in Healthy Mares

LinPro™ (LP) is a commercial dietary supplement marketed to increase hoof growth and quality. Ten mature (5-15 years) non-pregnant Quarter Horse mares without existing hoof quality issues were used to test the hypothesis that 32 weeks of daily supplementation with 113 g of LP would increase hoof growth rates as compared to non-supplemented controls. Hooves were trimmed at the start of the study and every 8 weeks thereafter. A mark was applied on the hoof wall surface at 2.5 cm below the junction of the hoof wall and coronary band. At each trimming, the distance between the mark and coronary band was measured and a new mark placed. For front hooves, horses assigned to LP had greater total hoof growth over 32 weeks (2.65 ± 0.15 vs. 2.18 ± 0.12 cm; P=.048) and tended to have greater hoof growth per 8 weeks trimming cycle (0.64 ± 0.03 vs. 0.55 ± 0.03 cm; P=.085) than horses assigned to non-supplemented controls (CON). Horses assigned to LP had greater plasma biotin concentrations (2158 ± 69 vs. 636 ± 62 ng/L; P < .001) and proportions of erucic acid in hoof tissue (1.03 ± 0.08 vs. 0.76 ± 0.07 %; P=.049) as compared to CON. Further, the most abundant fatty acids in hoof tissue were stearic, palmitic, oleic, and linoleic acids. LinPro may provide an effective treatment to improve hoof growth rates in horses with otherwise healthy hooves.

Energy and mineral metabolism of peripartum mares and foals of the Quarter Horse breed.

Several studies have demonstrated variations in peripartum blood biochemical analytes used to monitor the health status of mares and their foals of different breeds. We aimed to characterize the physiologic changes of peripartum energy and mineral metabolism in healthy Quarter Horse mares and their neonatal foals. Blood samples were initially collected from 17 mares on days 60 and 30 prepartum, and from mares and their foals on the day of parturition (after colostrum ingestion), and on days 15, 30, and 60 postpartum. The serum concentrations of calcium, phosphorus, magnesium, total cholesterol (T-Cho), triglyceride, beta-hydroxybutyrate (BHBA), and nonesterified fatty acids (NEFA) were measured using commercial kits. Statistical differences were analyzed using one-way ANOVA followed by Tukey's test (parametric variables) or the Kruskal-Wallis test followed by Dunn's multiple comparison test (nonparametric variables). Fourteen of 17 healthy Quarter Horse mares and their neonatal foals remained in the study until termination. Serum BHBA, T-Cho, and calcium concentrations in mares showed significant differences during the observation period. Serum BHBA concentrations increased from 60days prepartum to 60days postpartum. Postpartum serum T-Cho and calcium concentrations significantly decreased until day-30 postpartum. In the foals, NEFA, T-Cho, calcium, and magnesium concentrations significantly differed between sampling times. In the foals, serum NEFA concentrations decreased from parturition until day-60 postpartum, while serum T-Cho, calcium, and magnesium concentrations were lowest at day-30 postpartum. The temporal changes observed in the blood biochemical analytes of this study could be used to improve the clinical evaluation of periparturient mare and neonatal foal Quarter Horses.

Effect of maternal overnutrition on predisposition to insulin resistance in the foal: Foal skeletal muscle development and insulin signaling

Skeletal muscle plays an integral role in the ability of a horse to perform at high levels. Shifts in skeletal muscle development in response to maternal plane of nutrition may have substantial and lasting impacts on athletic performance and whole-body metabolism. Therefore, sixteen Quarter Horse mares were used in a completely randomized design and maintained at a body condition score (BCS) 6 until start of third trimester. On d 235 of gestation, mares were randomly assigned to receive one of two dietary treatments with a diet formulated to meet requirements during late gestation (CON; n = 8), and an overfed diet (HIGH; n = 8) where mares received an additional 40% above CON. Five h after parturition, foals were euthanized, and gluteus medius, triceps brachii, and semitendinosus were harvested for analyses. Gene expression was determined by qPCR and western immunoblotting was used to quantify total and phosphorylated forms of proteins involved in skeletal muscle metabolism with tubulin as the loading control. All data were analyzed using PROC MIXED of SAS. Foals from HIGH mares exhibited larger skeletal muscle fibers by area (P <0.05), and a shift in muscle fiber development towards type I slow twitch muscle fibers (P <0.05). Relative expression of glucose transporter 4 (GLUT4) was lower in HIGH foals compared to CON in gluteus medius (P = 0.05). Insulin receptor isoform B (INSR-B) and insulin-like growth factor 1 receptor (IGF1R) were greater in triceps brachii of HIGH foals compared to CON (P ≤ 0.03). Insulin receptor isoform A (INSR-A), however, tended to be lower in triceps brachii of HIGH compared to CON (P = 0.10). Ratios of phosphorylated to total extracellular signal-regulated protein kinase 1/2 (ERK1/2) and c-June N-terminal kinase (JNK) were higher in HIGH foals compared to CON (P ≤0.04) in gluteus medius. There were no differences observed for phosphorylated to total protein ratios in semitendinosus and triceps brachii muscles; however, total ERK1/2 tended to be elevated (P <0.10) in semitendinosus from CON foals compared to HIGH. There was no difference in phosphorylated or total protein kinase B (AKT) (P >0.14). These data indicate hypertrophy of skeletal muscle fibers and a shift towards type I slow twitch fibers in HIGH foals. Furthermore, this study identifies muscle specific changes in gene expression and downstream insulin receptor signaling, which may contribute to future metabolic abnormalities in response to maternal overnutrition.

107 The effect of storage time on progesterone concentration in refrigerated whole mare blood

The majority of equine progesterone research is over 30 years old and data is lacking regarding the use of current laboratory analysis methods. The research objective was to evaluate the effect of storage time on progesterone concentrations in refrigerated whole mare blood. Mares were ultrasounded twice weekly to confirm follicular development, ovulation, and cycling status before enrollment into the study. Twelve cycling, Quarter Horse mares were enrolled into the study from March to July, and blood samples were collected during multiple estrous cycles for an average of 2 cycles per mare. Mares were ultrasounded daily once a 35 mm follicle was detected on an ovary until ovulation, and then every other day to monitor corpus luteum formation. Open mares were reenrolled into the study on a subsequent estrous cycle, allowing for 28 total blood collection periods. Blood collections occurred 5 d after the ovulation of a previously recorded follicle and confirmation via ultrasonography of a corpus luteum on the same ovary. On each sample collection day, 6 cc of whole blood was collected from the mare into 5 vacutainer serum blood collection tubes from a single venipuncture, for a total of 30 cc of whole blood. The 5 blood samples were stored under refrigerated conditions at 4°C for 0, 6, 12, 24, and 48 h. The 0-h treatment was centrifuged once an adequate blood clot had formed or 30 min post-collection. Following the assigned storage time, each blood sample was centrifuged for 15 min and then serum was frozen at −22°C until analyzed for P4 using solid phase radioimmunoassay kit reagents validated for equine plasma. Statistical analysis of progesterone data was analyzed as a repeated measures design using the GLM procedure of SAS. Progesterone concentrations were similar among the refrigerated storage times at 0 ( P = 0.278), 6 ( P = 0.230), 12 ( P = 0.198), 24 ( P = 0.243), and 48 ( P = 0.282) hours. In summary, refrigerated samples of whole blood from mares may be stored for up to 48 h without an effect on progesterone concentration analysis.

59 Late gestation supplementation of long chain fatty acids increases foal docosahexaenoic acid concentrations at birth

Maternal supplementation of omega-3 fatty acids during gestation has a variety of benefits on the dam and resulting offspring in several species, including reduced latency to stand and suckle. The objective of the study is to test the hypothesis that foals born to mares supplemented with marine-derived algae during late gestation will have greater plasma DHA concentrations than foals born to either control mares or mares supplemented with flaxseed-derived ALA. The current study utilized 13 American Quarter Horse mares and their foals, assigned to one of 3 dietary treatments: a control basal diet (CON, n = 5), the basal diet plus 242.4 g of a supplement providing marine-derived omega-3 fatty acids (DigestaWell Ⓡ Omega; MAR, n = 5), or the basal diet with the addition of 190 g of a flaxseed supplement (Smartpak Simple Flax; FLAX, n = 3). Supplements were fed twice daily and were designed to deliver 40 g of omega-3 fatty acids. Mares began treatments 30 d before expected foaling dates and continued through d 5 post-parturition (PP). Plasma was collected from mares before supplementation, and on d 0, 5, and 30 PP. Milk samples were collected from mares at d 0 and 5 PP. Plasma samples were collected from foals at birth, and on d 5 and 30 PP. Fatty acid compositions of samples were determined using lipid extraction and gas chromatography. Data were analyzed using MIXED procedure of SAS, using repeated measures for milk and plasma. Simple effect differences were detected via Tukey test, and α = 0.05. The CON diet provided 29 g of α-linolenic acid (ALA), 0 g of eicosapentaenoic acid (EPA), and 4.5 g of docosahexaenoic acid (DHA), the MAR and FLAX diets provided 27 and 34 g of ALA, 0 and 0.03 g of EPA, and 17.4 and 4.5 g of DHA to mares, daily. Fatty acids are represented as g of fatty acid per 100 g of lipid. DHA (1.9 ± 0.2 g/100g) and EPA (0.3 ± 0.1 g/100g) contributed to a greater percent of plasma lipids in foals born to MAR supplemented mares compared with CON foals (DHA = 0.6 ± 0.2; EPA = 0 g/100g; P < 0.05). These fatty acids were not different between FLAX and CON foals ( P > 0.1) Samples obtained from foals at birth before nursing had the highest DHA levels (1.90 ± 0.18 g/100g), compared with all other samples, and DHA declined at d 5 (0.6 ± 0.2 g/100g) and 30 (0.1 ± 0.2 g/100g; P < 0.001) PP. No differences were observed in mare plasma or milk. Maternal supplementation of marine-derived omega-3 fatty acids in late gestation increased foal plasma DHA concentrations more so than that of foals from mares fed flax.

Effect of maternal overnutrition on predisposition to insulin resistance in the foal: Maternal parameters and foal pancreas histoarchitecture

Results from previous studies indicate that maternal overnutrition during late gestation predisposes foals to metabolic disease, however, specific mechanisms resulting in disease remain unknown. Quarter Horse mares (n = 16), were randomly assigned to dietary treatments, beginning on gestational day 235, and consisted of a control group (CON- diet meeting nutrient requirement; n = 8) or an overfed diet (HIGH; n = 8) where mares received an additional 40 % above CON. On gestational days 285 and 315, an intravenous glucose tolerance test (FSIGTT) was conducted. Following parturition, foals were separated from the mare, prohibited from nursing, and an FSIGTT was conducted at 2 h postpartum. Foals were immediately euthanized and tissues preserved for analyses. There was no effect of treatment on foal BW (P = 0.50), pancreas weight (P = 0.60), or FSIGTT area under the curve for glucose (P = 0.80) and insulin (P = 0.70). Colocalization of α-amylase to isolate pancreatic islets of Langerhans indicated increased islet number and size in foals from HIGH mares (P < 0.01). Immunofluoresent analysis of insulin, glucagon, and somatostatin indicate no difference in intensity of staining (P> 0.10). Foals exposed to overnutrition during peak fetal growth had altered pancreatic islet development that may lead to adult-onset metabolic disease.

Behavior of horses kept in different types of stalls in the semiarid region of Minas Gerais, Brazil

The objective of this study was to evaluate the feeding and agonistic behavior of Quarter Horses kept in different types of stalls in the semiarid region of Minas Gerais. A completely randomized design with two treatments (two types of stalls) and seven replicates (seven days of evaluation) was used. Four Quarter Horse mares and four stallions were used per treatment. Behavioral observations were made at 10-minute intervals for 24 hours. The stall environment was characterized by the following variables: air temperature, relative humidity, and black globe temperature for subsequent estimation of the wet-bulb globe temperature. Feeding behavior variables included: time spent eating concentrate and time spent eating roughage (hours), bite rate (bites/min), and the number of daily bites (bites/day). Zinc-roofed stalls had higher air temperatures than clay-roofed stalls and the external environment, averaging 28.2, 27.0, and 27.4 ºC, respectively, while relative humidity was significantly lower in the external environment (65.80%). Horses housed in zinc-roofed stalls had longer feeding times (8.32 h) than animals kept in clay-roofed stalls (7.22 h). Approximately 94% of the total feeding time was spent eating roughage and 73% of the time was spent resting and walking, regardless of the covering type. Although environmental variables showed thermal discomfort, the roofing material did not alter the feeding behavior of stabled horses in the semiarid region of Minas Gerais, suggesting an adaptation to the studied conditions. The feeding frequency should be increased to avoid a long resting time.

106 The effects of Total Equine™ grain with Ascophyllum nodosum seaweed extract and chelated minerals on forage intake and cecal digestibility in mature Quarter horse mares under performance conditions

Abstract A study was conducted in fall 2019 at Sul Ross State University to evaluate the effects of Total Equine™ containing Ascophyllum nodosum seaweed and chelated minerals on intake and cecal digestibility in comparison to a product without Ascophyllum nodosum seaweed or chelated minerals. Six quarter horse mares (avg 9 yrs) were used in a complete randomized block study. Horses were offered an ad libitum Bermuda hay for a 2wk standardization period and then blocked into pairs based on weight, age, and fitness level. Horses were assigned randomly within block to the Ctrl or Trt diets for an 8wk study with ad libitum access to water. Hay was offered 2xd in port-a-grazer tubs to control for waste. Grain was offered at a rate of 0.5% BW (manufacturer suggestions) and divided into 2 equal feedings. Horses were weighed weekly and grain amounts were adjusted weekly. Hay orts were collected 2x daily and hay offered was adjusted daily for a 3% refusal rate. Horses were exercised 6 d/wk on a hot-walker for 2 hrs. Horses were conditioned prior to the study and speed and duration were increased throughout the study. Horses worked 30 min at a walk and 1.5 hrs at a trot broken into periods. Feed samples were collected 2xwk and dried for DM and ground for analysis for NDF, ADF, CP, EE, and Ash. Blood samples were collected for 3x (1 wk, 4 wk, 8 wk) pre/post exercise to be tested for cortisol levels. A significant difference in total DMI was observed at 13.1 ± 0.14 kg Ctrl versus 12.02 ± 0.11 kg Trt (P = 0.0001). When looking at forage intake only 10.07 ± 0.13 kg Ctrl versus 9.04 ± 0.11 kg Trt (P = 0.0001). Overall, it appears that the inclusion of the grain product with Ascophyllum nodosum and chelated minerals reduced forage intake and overall DMI without affecting weight or animal performance.