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The objective of these studies was to investigate the efficacy of an intravaginal triptorelin acetate (TA) gel as an ovulation-inducing agent in mares. In Exp. 1, 24 mares were blocked using a combination of parity and age and randomly assigned to 1 of 3 treatment groups: 5 mL TA gel (TA5), 10 mL TA gel (TA10), or 5 mL vehicle gel only (CON). Following the appearance of a follicle ≥ 25 mm, a blood sample was obtained for measurement of LH from each mare every 24 h until treatment administration. When a follicle ≥ 35 mm was observed, treatments were administered intravaginally. Following treatment, blood samples were collected for measurement of LH and ovaries were scanned via ultrasonography every 12 h until 48 h post-ovulation. Mares in both TA5 and TA10 tended (P = 0.08) to experience a brief surge in LH by 12 h post-treatment. There was a treatment by time interaction (P < 0.005). The interval from treatment to ovulation was not different between groups (P > 0.05). We hypothesized that duration of elevated LH was not sufficient to induce ovulation in most mares. In Exp. 2, 23 mares were blocked by parity/age and randomly assigned to 3 treatment groups: the CON (n = 7) and TA5 (n = 8) treatment groups remained the same, but the TA10 treatment was split into two 5-mL doses administered 24 h apart (TA5×2; n = 8). Blood collection and ultrasonography occurred every 12 h on detection of a follicle ≥ 25 mm in diameter. Once a follicle ≥ 35 mm was detected, treatment was administered and ultrasonography and blood collection for measurement of LH occurred every 6 h until 48 h post-ovulation to get a more robust characterization of the effect of TA on LH and a more accurate timeframe in which ovulation was occurring. Mares in both TA5 and TA5×2 had an increase (P < 0.05) in LH by 6 h post-treatment, which was declining by 12 h post-treatment. Following the second dose in TA5×2, another rise in LH occurred, but to a lesser magnitude (P > 0.05) compared with the initial dose. Again there was a treatment by time interaction (P < 0.005) and in Exp. 2 the interval from treatment to ovulation was shorter in TA5 (61.5 ± 8.8 h) and TA5×2 (61.5 ± 9.6 h) compared with CON (123.1 ± 21.7 h; P < 0.01). In Exp. 2, administration of TA gel increased LH concentrations and hastened the interval from treatment to ovulation in mares, without an advantage in the timing of ovulation noted between the 5 or 10-mL doses, or administration of two 5-mL doses given 24 h apart. [ABSTRACT FROM AUTHOR]

Nine pregnant mares (18.2 ± 0.7 y; 493.82 ± 13 kg BW) were used to test the hypothesis that dietary supplementation of arginine would enhance placental vascularity and nutrient transport throughout gestation in aged mares. Mares were balanced by age, BW, and stallion pairing, and randomly assigned to one of two dietary treatments consisting of supplemental L-arginine (50 mg/kg BW; n=5) or L-alanine (100 mg/kg BW; n=4; isonitrogenous control). Mares were individually fed concentrate top-dressed with the respective amino acid treatment plus ad libitum access to Coastal bermudagrass hay. Treatments began on d 14 of gestation and were terminated at parturition. Mare BW, BCS, and rump fat were determined every 28 d and concentrate adjusted accordingly. Parturition was attended with foaling variables and placental measures recorded. Placental tissue from the pregnant horn underwent histological analyses to assess cell-specific localization of vascular endothelial growth factor (VEGF) and cationic amino acid transporter 1 (CAT1) proteins. Semiquantitative analyses were performed using 10 non-overlapping images per sample fixed in a 10X field (Fiji ImageJ v1.2). Data were analyzed using SAS PROC MIXED procedure. BW increased (P < 0.01) in all mares with advancing gestation. BW, BCS, and gestation length of mares were not influenced (P > 0.05) by supplemental arginine. Compared with argininesupplemented mares, control mares had a thicker rump fat layer (P < 0.01) at parturition. Body length, height, and BW of foals at birth, as well as placental weight, volume, and positive staining for VEGF and CAT1 at parturition were not affected (P > 0.05) by maternal arginine supplementation. These results indicate dietary arginine supplementation (50 mg/kg BW) is safe for gestating mares and promotes mobilization of white adipose tissue. A larger number of mares is required to determine effects of supplemental arginine on embryonic/fetal survival and growth in mares. [ABSTRACT FROM AUTHOR]

We present a study focused on those factors influencing dominance position in young horses, with emphasis on the role of the mother. Horses, as other group-living polygynous mammals, form stable linear dominance hierarchies based on agonistic interactions. Higher dominance positions are believed to be connected, in both sexes, to better condition and higher reproductive success. Many variables play a role in forming the dominant-submissive relationships between horses; however, the maternal effect on the dominance position of the offspring still remains unclear, as do the possible mechanisms of transference ("inheritance"). We hypothesized that the maternal dominance position, plus differences in suckling parameters or maternal style, may be responsible for later outcome of the offspring's dominance position, characterized by 2 variables: index of fighting success (CB); and rate of winning encounters (RW). Our study animals were 8 groups of Kladruby horses, loose-housed lactating mares with foals (n = 66 mare-foal pairs); and subsequently 4 groups of the same foals at 3 yr of age. Our results revealed the impact of age on the dominance position of the young horses (P < 0.001 for CB, and P< 0.01 for RW), and residence in the group {P < 0.01, P < 0.01, respectively); not the maternal dominance position. Older foals reached higher dominance positions, independent of the dominance position, age, or experience of the mother; therefore, we did not find support for direct inheritance of maternal rank. Nevertheless, the foals born to the same mare in 2 consecutive seasons (n = 16 mares) revealed fair repeatability in the dominance position they obtained at 3 yr of age (intraclass correlation coefficient = 0.46). This suggests an important constant effect of the mother on the social success of her progeny; however, we did not find a significant effect of any of the tested variables describing maternal characteristics or maternal care. Dominance position depended significantly on the foal's age at observation, and the residence in the herd formed via sequential introducing of later-weaned groups of foals. The most dominant horses were mainly recruited from the first-weaned group of the season, and thus were also the oldest individuals in the herd. Further research is needed to discover the role of foal personality and mare style, and their links to possible dominance behaviors in a herd. [ABSTRACT FROM AUTHOR]

Uterine and placental infections are the leading cause of abortion, stillbirth, and preterm delivery in the mare. Whereas uterine and placental infections in women have been studied extensively, a comprehensive examination of the pathogenic processes leading to this unsatisfactory pregnancy outcome in the mare has yet to be completed. Most information in the literature relating to late-term pregnancy loss in mares is based on retrospective studies of clinical cases submitted for necropsy. Here we report the development and application of a novel approach, whereby transgenically modified bacteria transformed with lux genes of Xenorhabdus luminescens or Photorhabdus luminescens origin and biophotonic imaging are utilized to better understand pathogen-induced preterm birth in late-term pregnant mares. This technology uses highly sensitive bioluminescence imaging camera systems to localize and monitor pathogen progression during tissue invasion by measuring the bioluminescent signatures emitted by the lux-modified pathogens. This method has an important advantage in that it allows for the potential tracking of pathogens in vivo in real time and over time, which was hitherto impossible. Although the application of this technology in domestic animals is in its infancy, investigators were successful in identifying the fetal lungs, sinuses, nares, urinary, and gastrointestinal systems as primary tissues for pathogen invasion after experimental infection of pregnant mares with lux-modified Escherichia coli. It is important that pathogens were not detected in other vital organs, such as the liver, brain, and cardiac system. Such precision in localizing sites of pathogen invasion provides potential application for this novel approach in the development of more targeted therapeutic interventions for pathogen-related diseases in the equine and other domestic species. [ABSTRACT FROM AUTHOR]

Four experiments were conducted 1) to assess the use of glucose responses to insulin injections as a means of estimating insulin sensitivity in horses and 2) to compare the insulin sensitivities of normal horses vs. those displaying hyperleptinemia (HL). In Exp. 1, HL mares and geldings (n = 4 each) and 4 mares and geldings with normal leptin concentrations (NL) were injected intravenously with 20 and 100 mU/kg of BW of bovine insulin on 2 separate occasions in December 2008. In Exp. 2, the experimental protocol was repeated in late April 2009. In Exp. 1, the 20 mU/kg of BW dose of insulin caused a greater (P < 0.05) decline in glucose concentrations in NL mares and geldings compared with HL horses. The response of HL mares to the 100 mU/kg of BW dose was less (P < 0.05) than for the other groups. In Exp. 2, responses of all groups to the 20 mU/kg of BW dose were small and similar among groups (P> 0.1), whereas the greater dose revealed differences (P < 0.05) in sensitivity among groups consistent with those observed with the smaller dose in Exp. 1. Experiment 3 was conducted in June and July of 2009 to further examine the dose-response relationship in mares of potentially different insulin sensitivities in an attempt to standardize the approach for studying a wide range of sensitivities. Recombinant human insulin was used at doses of 8, 20, 50, and 125 mU/kg of BW, as needed, to estimate (by linear regression) the dose of insulin causing a 50% decline in glucose concentrations (ED50). Five mares each of reduced leptin concentrations (LL) and small BCS (3 to 5), LL and larger BCS (6 to 7.5), and increased leptin concentrations and increased BCS were studied. The ED50 was similar (P> 0.1) for LL mares, regardless of BCS, and was less (P < 0.01) than for mares with increased leptin concentrations. It was concluded that a dose of 50 mU/kg of BW of recombinant human insulin could be used safely to start the dose-response curve; smaller or larger doses could then be applied as appropriate to get sufficient data for estimation of ED50. Experiment 4, conducted in October of 2009, assessed the repeatability of the estimates for ED50 obtained in Exp. 3. Six mares with LL vs. increased leptin concentrations received the 50 mU/kg dose of insulin; appropriate larger or smaller doses were used to obtain estimates of ED50. Estimates obtained were highly correlated (r = 0.91) with those obtained in Exp. 3, with an average within-mare CV of 8.9%; this is equal to or better than the repeatabilities of the currently used methods of assessing insulin sensitivity in horses. It was concluded that hyperleptinemic horses, which are also hyperinsulinernic and have exaggerated insulin responses to glucose injection, are indeed less sensitive to insulin than normal horses with reduced leptin concentrations of the same body condition. [ABSTRACT FROM AUTHOR]

Mares and geldings in good body condition selected for hyperleptinemia vs. normal leptin concentrations were studied to determine whether the hyperleptinemic condition affected various characteristics of the hematologic and hormonal systems after a challenge with lipopolysaccharide endotoxin. Four mares and 4 geldings that were determined to be hyperleptinemic (mean plasma leptin concentrations of 10.0 to 15.5 ng/mL) and 4 mares and 4 geldings with mean plasma leptin concentrations between 2.4 and 5.5 ng/ mL were administered Escherichia coli 055:B5 endotoxin (35 ng/kg of BW in 500 mL of saline over a 30-mm infusion), or saline only, in pairs in a single-switchback design, with horses and treatments randomly assigned for the first infusion. Physiological variables and blood components were monitored for 24 h after the onset of infusions. Treatments were switched and the second infusions were administered 8 d later. Relative to vehicle infusion, endotoxin infusion increased (P < 0.01) the rectal temperature, heart rate, respiration rate, plasma total protein concentration, and blood packed cell volume; there was an interaction of leptin status, endotoxin treatment, and time for heart rate (P = 0.039), respiration rate (P = 0.018), and plasma total protein concentration (P = 0.054). Blood concentrations of leukocytes, lymphocytes, and neutrophils all decreased (P < 0.001) after endotoxin infusion; there was an interaction (P = 0.0057) between sex and leptin status for blood platelet concentration. Plasma leptin concentrations increased (P = 0.013) after endotoxin infusion in both hyperleptinemic horses and those with reduced leptin concentrations. There were interactions (P < 0.037) of sex with endotoxin treatment and time for plasma concentrations of cortisol and prolactin, whereas plasma GH concentrations were affected (increased; P < 0.001) only by time after infusion. Given that the effects of hyperleptinemia were generally minor, it was concluded that the hyperleptinemic condition, and its associated type-2 diabetic symptoms, has a minimal impact on the components of the hematologic and hormonal systems studied. [ABSTRACT FROM AUTHOR]

We previously reported that a rise in plasma leptin concentrations followed the rise in insulin and glucose in meal-fed horses, whereas horses maintained on pasture had little fluctuations in hormonal patterns. We have also described a hyperleptinemic-hyperinsulinemic condition that occurs in about 30% of our light horse mares of high body condition maintained on pasture. The present experiment was designed to 1) study the effect of 3 common feeding- housing regimens on leptin and other metabolic hormones in mares and 2) determine whether the hyperleptinemic condition interacted with these regimens. Six light horse mares with high body condition (average score = 7) were assigned to 2 simultaneous 3 x 3 Latin squares, 1 with normal mares (leptin = 0.1 to 6 ng/mL) and 1 with mares displaying hyperleptinemia (>10 ng/ mL). Three feeding-housing regimens were compared: ad libitum pasture, ad libitum native grass hay in an outdoor paddock, and single morning feedings of a pelleted concentrate and hay at 0700 in a barn. Five days of acclimation to the feeding regimens were followed by a 36-h period of hourly blood collection to characterize the hormonal characteristics. Leptin concentrations were elevated (P < 0.001) in mares predetermined to be hyperleptinemic compared with normal mares, regardless of the feeding regimen. Leptin was greatest (P < 0.01) in mares on pasture and least in mares fed hay. Variations over time (P < 0.01) were present for all hormones and metabolites studied. Glucose and insulin concentrations were greatest (P < 0.01) in mares on pasture, with meal-fed mares exhibiting an immediate rise in plasma concentrations of both after feeding. Mares on hay had low and constant concentrations of glucose, insulin, and leptin, with no apparent fluctuations. Cortisol, prolactin, and IGF-I did not differ with leptin status, whereas GH differed due to feeding-housing regimen (P < 0.02); there was also an interaction of leptin status and feeding-housing regimen for GH concentrations (P = 0.094). It was concluded that 1) estimates of hormonal secretion in horses based on frequent sampling, depending upon the hormone in question, can be profoundly affected by the feeding-housing regimens, and 2) the hyperleptinemic condition persists under differing conditions of feeding-housing. [ABSTRACT FROM AUTHOR]

The aim of this study was to characterize concentrations of leptin, IGF-I, and thyroid stimulating hormone (TSH) in the blood serum of mares pre- and postpartum, in the milk serum of mares postpartum, and in the blood serum of their foals. Nine pregnant Quarter Horse mares and their offspring were used in this study. Once weekly between 1000 and 1200 h for 2 wk before their predicted parturition date, mares were weighed, assigned a BCS, and blood was sampled via jugular venipuncture. Within 2 h of parturition and before the foals nursed (d 0), blood samples were obtained from the mares and foals, and a milk sample was collected from the mares. Blood from the foals and blood and milk from the mares were collected again at 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 12, 19, 26, 33, and 61 d postpartum. Mares and foals also were weighed and assigned a BCS on d 0, 5, 12, 19, 26, 33, and 61. Additionally, on d 5, 33, and 61, ultrasound images of fat depth and area of the LM immediately cranial to and parallel with the last rib on the left side of the foals were measured to characterize changes in fat depth and LM area over time. There were no changes in mare blood concentrations TSH (P = 0.15), nor were there any changes in foal blood concentrations of leptin (P = 0.54) or TSH (P = 0.10) during the trial period. Mare blood concentrations of IGF-I tended to change over time (P = 0.07), whereas leptin changed over time (P < 0.001), initially decreasing and then remaining relatively stable after d 5. Foal blood concentrations of IGF-I increased initially, peaked at d 19, and stabilized thereafter (P < 0.001). Milk concentrations of leptin and TSH were greatest on d 0 and decreased over time (P < 0.007), reaching nadir concentrations at d 61. Milk concentrations of IGF-I also changed over time (P = 0.02), being greatest on d 0 and undetectable by d 12. There was no difference in BCS (P = 0.94) in mares over time, but there was a difference between pre- and postpartum BW (P < 0.001) due to foaling. However, no differences were detected in pre- (P = 0.70) or post- partum BW (P = 0.76) of mares over time. Mean ultrasonic fat depth and LM area increased (P < 0.04) as the foals aged, as did BCS and BW (P < 0.001). Recognizing changes in metabolic hormones surrounding the time of parturition in the mare and foal provides a basis for further determination of the role, if any, these hormones play in the milk, as well as in the neonate. [ABSTRACT FROM AUTHOR]

The article offers information on a study related to patterns of change in luteal function. Topics discussed include rise and fall of ovarian derived progesterone detected in peripheral blood; normal estrous cycle in the absence of estrus; and corpus luteum of pregnancy regressed at parturition and transition from anovulatory to ovulatory seasons.

The objectives of this experiment were to characterize the development of the foal fecal microbiome from birth to 4 mo and determine its relationship to mare milk and fecal bacteria. Mare milk, mare fecal, and foal fecal samples were collected from 9 mare and foal pairs at birth, d 0, 2, and 7 postpartum, and then monthly until 4 mo. Mare fecal samples were collected by rectal palpation and foal fecal samples were collected manually using sterile gloves. All samples were placed in sterile conical tubes and immediately frozen until further analysis. Mare udders were cleaned and milk samples were obtained according to aseptic procedures used with dairy cows to collect samples for microbial analysis. Next generation sequencing of the V4 region of the bacterial 16S rRNA gene was performed using the Illumina Miseq according to Earth Microbiome Project protocols. Sequencing data was analyzed using QIIME. Bacteria found in mare milk and mare feces were different in diversity (P < 0.001) and composition (P < 0.05) across all time points. Newborn foal meconium contained low species diversity and a bacterial composition similar to mare milk consisting of the genera Enterococcus, Bacillus, Pseudomonas and Lactococcus. The Firmicutes and Proteobacteria phyla comprised the majority of bacteria in mare milk and foal feces on d 0 and 2. At the genus level, the bacterial communities shifted within the first week in foal feces to be dominated by Bacteroides and Escherichia. By 1 mo the foal fecal microbiome did not differ in composition at the phylum level from mare feces; however, species diversity was still lower in foals and the relative abundance of several genera were different (P < 0.05). Firmicutes, Bacteriodetes, and Verrucomicrobia were the dominant phyla found in both foal feces older than 1 mo and mare feces. To our knowledge, this is the first study to report the bacteria taxa of equine milk using next generation sequencing. These results demonstrate the foal is born with fecal microbial communities similar to milk that rapidly change within the first week of life. Within the first month of life there is a gradual transition of the foal fecal bacterial structure until it resembles that of its dam, remaining constant over the next 3 months. This change is likely due to the introduction of solid feedstuffs, consumption of their dam's feces, and/or environmental exposure. [ABSTRACT FROM AUTHOR]

Fat supplementation of horse diets has traditionally utilized sources rich in n-6 fatty acids. The objective of this study was to evaluate the effects of supplementing mares with protected marine-derived n-3 fatty acids (JBS United) during late gestation and early lactation. Twenty Quarter-type mares were randomly assigned to one of three treatment groups. Beginning 60 d prior to the expected foaling date, mares were fed either a control diet (CON, concentrate base with added corn oil, n=6), a docosahexaenoic acid (DHA) supplemented diet (D, n=7), or a eicosapentaenoic acid (EPA) / DHA supplemented diet (ED, n=7). Diets continued after parturition through the first postpartum estrous cycle. Mare plasma was collected at the start of treatment, at parturition, and at wk 3 postpartum. Gas chromatography was used to analyze mare plasma for linoleic acid (LA), arachidonic acid (AA), alpha-linolenic acid (ALA), EPA, and DHA. Gestation length did not differ between treatment groups. The time from foaling to the first postpartum ovulation was increased (P<0.01) in the ED group (22.5±2.1 d) compared to both the CON (12.5±2.3 d) and D (13.3±2.3 d) groups. The length of time that mares in the ED group held a large (≥ 35 mm) follicle during the first postpartum estrous period was increased (P<0.05, 12.7±1.9 d) compared to the CON (6.3±2.0 d) or D (6.0±2.0 d) groups. Mare plasma LA and ALA concentrations were not affected by treatment. AA was elevated (P<0.05) in D mares at parturition and 3 wk postpartum compared to the CON mares. DHA was increased (P<0.01) in both the ED and D mares at parturition and 3 wk postpartum compared to the CON group. EPA was increased (P<0.01) in ED mares at parturition and 3 wk postpartum compared to both the D and CON mares. Feeding mares diets high in EPA may result in increased follicle retention and affect timing of ovulation in the early postpartum period. [ABSTRACT FROM AUTHOR]

Arabian mares, three primiparous (P) and three multiparous (M), were used to estimate milk and nutrient intake by foals and nutrient demand on mares. Milk intake was estimated on d 10, 20 and 30 of lactation by weigh-suckle-weigh. Milk was collected on d 11, 21 and 31. Digestible energy (DE) requirements (Mcal/d) were estimated based on milk E content derived from milk lactose, protein and fat concentrations and a conversion coefficient (CC) of 0.72. Digestible protein (DP) requirements (g/d) were estimated based on daily true milk protein (TP) and a CC of 0.65. Data were analyzed as repeated measures over d of lactation and relationships between d of lactation and response variables determined by linear and quadratic orthogonal contrasts. Milk yield (kg) did not change with d of lactation in P mares but tended to increase in M mares (linear, P = 0.12) (12.98, 12.86, and 12.85 vs 12.66, 14.62, and 14.31 ± 1.43, respectively). As a percentage of BW, milk yield over d of lactation was 3.05 and 3.40 for P and M mares, respectively. Concentrations of TP decreased (linear, P = 0.05) and lactose and total solids increased (linear, P = 0.05 and P ≤ 0.001, respectively) in P mares, but did not change in M mares. Milk fat of M mares decreased (linear, P ≤ 0.05) with d of lactation (3.2 to 1.7 %) but did not change in P mares (2.05 to 2.39 %). Fat and TP yield did not differ between parities, but lactose yield was higher (P ≤ 0.05 on d 30) in M compared to P mares. Day of lactation increased (linear, P ≤ 0.01) lactose yield in M mares. Estimates of DP (g/d) requirements in P mares decreased (linear, P ≤ 0.05) with d of lactation (625, 579 and 503 for d 10, 20 and 30, respectively), but did not change in M mares (564, 527 and 633 for d 10, 20, and 30, respectively). Estimates of DE (Mcal/d) did not differ between P and M mares or between d of lactation (26.8, 26.3 and 27.2 vs 29.5, 30.0, and 31.8 ± 3.3, respectively). Results suggest that decreasing milk TP yield with d of lactation and lower milk lactose yield in P mares may limit foal protein and carbohydrate intake compared to that of M mares. [ABSTRACT FROM AUTHOR]