G.L. Heusner

Hypothalamic-Pituitary-Adrenal Axis Assessment in Healthy Term Neonatal Foals Utilizing a Paired Low Dose/High Dose ACTH Stimulation Test

BACKGROUND Hypothalamic-pituitary-adrenal (HPA) axis function is dynamic in the neonatal foal. The paired low dose/high dose cosyntropin (ACTH) stimulation test allows comprehensive HPA axis assessment, but has not been evaluated in neonatal foals. HYPOTHESIS Foal age will significantly affect cortisol responses to a paired 10 and 100 microg dose cosyntropin stimulation test in healthy neonatal foals. ANIMALS Twenty healthy neonatal foals. METHODS HPA axis function was assessed in 12 foals at birth and at 12-24, 36-48 hours, and 5-7 days of age. At each age, basal cortisol and ACTH concentrations were measured and cortisol responses to 10 and 100 microg cosyntropin were assessed with a paired ACTH stimulation test protocol. Eight additional 36-48-hour-old foals received saline instead of 10 microg cosyntropin in the same-paired ACTH stimulation test design. RESULTS At birth, foals had significantly higher basal cortisol and ACTH concentrations and higher basal ACTH : cortisol ratios compared with foals in all other age groups. A significant cortisol response to both the 10 and 100 microg doses of cosyntropin was observed in all foals. The magnitude of the cortisol response to both doses of cosyntropin was significantly different across age groups, with the most marked responses in younger foals. There was no effect of the paired ACTH stimulation test design itself on cortisol responses. CONCLUSIONS AND CLINICAL IMPORTANCE A paired 10 and 100 microg cosyntropin stimulation test can be used to evaluate HPA axis function in neonatal foals. Consideration of foal age is important in interpretation of HPA axis assessment.

Serum Free Cortisol Fraction in Healthy and Septic Neonatal Foals

BACKGROUND Relative cortisol insufficiency occurs in septic foals and impacts survival. Serum free (biologically available) cortisol concentration might be a better indicator of physiologic cortisol status than serum total cortisol concentration in foals. HYPOTHESES In septic foals, (1) low free cortisol concentration correlates with disease severity and survival and (2) predicts disease severity and outcome better than total cortisol concentration. ANIMALS Fifty-one septic foals; 11 healthy foals; 6 healthy horses. METHODS In this prospective clinical study, foals meeting criteria for sepsis at admission were enrolled. University-owned animals served as healthy controls. Basal and cosyntropin-stimulated total cortisol concentration and percent free cortisol (% free cortisol) were determined by chemiluminescent immunoassay and ultrafiltration/ligand-binding methods, respectively. Group data were compared by ANOVA, Mann-Whitney U-tests, and receiver operator characteristic curves. Significance was set at P < .05. RESULTS Basal % free cortisol was highest in healthy foals at birth (58 ± 8% mean ± SD), and was higher (P ≤ .004) in healthy foals of all ages (33 ± 6 to 58 ± 8%) than in adult horses (7 ± 3%). Cosyntropin-stimulated total and free cortisol concentrations were lower (P ≤ .03) in foals with shock (total = 6.2 ± 8.1 μg/dL; free = 3.5 ± 4.8 μg/dL versus total = 10.8 ± 6.0 μg/dL; free = 6.9 ± 3.3 μg/dL in foals without shock) and in nonsurvivors (total = 3.8 ± 6.9 μg/dL; free = 1.9 ± 3.9 μg/dL versus total = 9.1 ± 7.7 μg/dL; free = 5.5 ± 4.4 μg/dL in survivors). Free cortisol was no better than total cortisol at predicting disease severity or outcome in septic foals. CONCLUSIONS AND CLINICAL IMPORTANCE Serum free cortisol is impacted by age and illness in the horse. There is no advantage to measuring free over total cortisol in septic foals.

Advancements in Large Animal Embryo Transfer and Related Biotechnologies

Embryo transfer has been an inherent part of cattle breeding for more than 35 years and has also gained remarkable interest from the equine industry after several breeds allowed registration of more than one foal per year. In both large animal species, non-surgical embryo recovery and transfer are well-established techniques. However, success rates after superovulation and cryopreservation of embryos in horses are still lagging behind those of cattle, and more research is needed to address these areas. To address the problem of freezing large equine embryos, we offer a preliminary demonstration of a new cryopreservation method which involves reduction of the blastocoelic volume and microinjection of cryopreservative. Successful cryopreservation will improve the ability of practitioners to preserve and implant embryos in recipient mares. Recent advances in the use of equine FSH to induce superovulation in mares brings to the forefront the issue of how to best preserve the large number of embryos that are produced. Finally, the use of sexed semen after superovulation will provide the bovine and equine breeding industry the offspring of the desired sex.

Synthetic adrenocorticotropic hormone stimulation tests in healthy neonatal foals

BACKGROUND Cosyntropin (adrenocorticotropic hormone [ACTH]) stimulation tests are used to evaluate adrenal function. Low-dose ACTH stimulation tests are the most accurate method for diagnosing relative adrenal insufficiency in critically ill humans but have not been evaluated in foals. HYPOTHESIS Peak serum cortisol concentrations in healthy foals will not be significantly different after intravenous administration of 1, 10, 100, and 250 microg of cosyntropin. ANIMALS 14 healthy neonatal foals, 3-4 days of age. METHODS A randomized cross-over model was used in which cosyntropin (1, 10, 100, or 250 microg) was administered intravenously on days 3 and 4 of life. Blood samples were collected before and 30, 60, 90, 120, and 150 minutes after administration of cosyntropin for determination of serum cortisol concentration. RESULTS Serum cortisol concentrations did not significantly increase after administration of 1 microg of cosyntropin. Cortisol concentration peaked 30 minutes after administration of 10 microg of cosyntropin and 90 minutes after 100 and 250 microg of cosyntropin. There was no relationship between cosyntropin dose and serum cortisol concentration at 30 minutes. Compared with the 10-microg dose, 100 and 250 microg of cosyntropin induced significantly greater cortisol concentrations at 90 minutes, at which point the 10-microg cosyntropin-dose cortisol values were indistinguishable from baseline. There was no significant difference in the area under the cortisol concentration curve between the 100- and 250-microg doses. No effect of day of testing or foal weight on peak cortisol concentration was detected. CONCLUSIONS AND CLINICAL IMPORTANCE The results of this study suggest that 10- and 100-microg doses of cosyntropin would be appropriate for evaluating adrenal function in neonatal foals.

Freezing equine semen: the effect of combinations of semen extenders and glycerol on post-thaw motility.

OBJECTIVE We evaluated combinations of two commercial semen extenders and three concentrations of glycerol to determine the combination that yielded the highest post-thaw sperm motility. DESIGN A randomised 2 x 3 block design was used. PROCEDURE Semen was collected from four stallions (6 collections per stallion). The sample was diluted with either a dried skim-milk glucose extender (EZ Mixin Original Formula) or a chemically defined, milk-free diluent (INRA 96), and each was used in combination with 2%, 3% or 4% glycerol in standard commercial freezing medium. Sperm motility was assessed by microscopy in fresh and post-thaw semen. RESULTS There was a significant difference between the two extenders in the motility of spermatozoa after cryopreservation (48.9% for INRA 96; 38.6% for EZ Mixin OF; P < 0.0001). Glycerol at 4% in freezing medium yielded the highest post-thaw motility, significantly better than 2% (P < 0.05). Three of four stallions had significantly higher post-thaw motility using INRA 96 relative to EZ Mixin OF (P < 0.01), and two of four stallions had significantly higher post-thaw motility using 4% glycerol (P < 0.05). The combination of INRA 96 and 4% glycerol in freezing medium gave the highest average post-thaw motility of 51.5%. CONCLUSION In this study, INRA 96 combined with 4% glycerol yielded an average recovery of progressively motile sperm consistently above the 35% target.

Growth rate, diet digestibility, and serum proclactin of yearling horses fed non-infected and infected tall fescue hay

Summary To determine to effect of feeding tall fescue hay infected with endophyte on growth rate, diet digestibility, and serum prolactin, 17 Quarter Horse yearlings were fed a diet of 60% concentrate and 40% tall fescue hay for 5 months. Diets were formulated to meet 1989 NRC recommendations for moderate growth. The dietary treatments included either non-infected (E-, n=9) or infected (E+, n=8) tall fescue hay. Field sampling determined a 52% infection rate of the E+ hay with the endophyte Acremonium coenophialum . Initially and at 29-day intervals, yearlings were weighed and measured for skeletal growth including: (1) height at the withers, (2) length of bone between knee and fetlock, (3) length of bone between hock and fetlock, and (4) the circumference of fore and rear cannon bones. Total fecal collection from the 10 geldings during the last month of the trial permitted the calculation of diet digestibility. Serum samples were taken throughout the trial to determine prolactin response to dietary treatments. The E+ fescue hay did not affect (P>.05) growth rate of yearling horses. Yearlings gained .40 and .38 kg/d when consuming the E− and E+ based diets, respectively. Geldings gained more (P E+ fescue hay diets tended to be lower in dry matter, apparent energy, and crude protein digestibility, but values were not statistically different. Fiber digestibility was lower (P