C.A. Cavinder

Sexual Behavior and Blood Hormone Profiles Around the Time of Ejaculation and Subsequent Sperm Characteristics in Stallions

In the stallion, inconsistent sexual behavior and variable semen quality are common, and this variability has been attributed, in part, to differences in circulating hormone concentrations. The objectives of this study were to quantify blood plasma concentrations of testosterone (TE), cortisol (CO), and estrone sulfate (ES) around the time of ejaculation, and to determine potential correlations with sexual behavior and sperm characteristics. Results indicate that both ES and CO increased (P < 0.05) at the time of semen collection, whereas TE did not increase. Estrone sulfate (r = −0.42, −0.34, and −0.42 at times −15, +30, and +60, respectively) and the ratio of ES to TE (r = −0.40, −0.41, and −0.39 at times −15, +30, and +60, respectively) were negatively correlated with libido scores at multiple times around ejaculation (P < 0.05). Additionally, a positive relationship was found between ES and reaction time (r = 0.41 and 0.34 at times −15 and +60, respectively), as well as between CO and libido scores (r = 0.38 and 0.45 at times −15 and +15, respectively; P < 0.05). No relationship was observed between TE and sexual behavior; however, TE was positively correlated with progressive motility (r = 0.40), whereas the ES:TE ratio was negatively correlated with progressive motility (r = −0.35; P < 0.05). No other association was detected between the ejaculate parameters and hormone concentrations analyzed. These results further characterize the hormone profiles of stallions around the time of ejaculation while providing additional insight into the potential interaction the endocrine system may play in relation to stallion sexual behavior and sperm production.

Body fat of stock-type horses predicted by rump fat thickness and deuterium oxide dilution and validated by near-infrared spectroscopy of dissected tissues

Body condition score and percent body fat (BF; %) of horses are positively correlated with reproductive efficiency and are indicative of metabolic issues. However, BF in horses may be poorly predicted because current procedures are either subjective or dependent on one anatomical location. Therefore, the objectives of the current study were to compare 2 methods of predicting BF using rump fat thickness (RFT) and deuterium oxide (DO) dilution with actual tissue fat analysis by near-infrared spectroscopy (NIRS) in stock-type horses and to identify the relationship between BF and BCS. Twenty-four stock-type horses were selected to be humanely euthanized based on 3 primary criteria: geriatric, crippled, and/or unsafe. Approximately 20 h before slaughter, horses were weighed and BCS assessed to be 1 ( = 1; 433 kg), 2 ( = 1; 415 kg), 3 ( = 1; 376 kg), 4 ( = 7; 468 ± 13 kg), 5 ( = 10; 455 ± 11 kg), and 6 ( = 4; 493 ± 12 kg) and RFT was measured using ultrasonography. Blood samples were collected immediately before and 4 h after DO infusion (0.12 g/kg BW). Deuterium oxide concentration of plasma was determined by gas isotope ratio mass spectrometry. Horses were housed in a dry lot overnight before being individually sedated (1.1 mg xylazine/kg BW) and anesthetized using a jugular venipuncture (2.2 mg ketamine/kg BW), and potassium chloride (KCl) solution was administered to cease cardiac function before exsanguination. After euthanasia, horse carcasses were processed and dissected and tissues were collected for NIRS analysis. Body fat predicted by DO dilution was correlated with BF measured by NIRS analysis on various weight bases ( = 0.76 to 0.81, < 0.001), whereas no correlation was observed for BF predicted by RFT. A paired -test indicated that both DO dilution and RFT overestimated BF by 2.48 to 3.26% ( < 0.001) and 5.81 to 6.59% ( < 0.001), respectively, compared with NIRS analysis. Body condition scores affected BF measured by NIRS analysis ( ≤ 0.038) and predicted by DO dilution ( < 0.001) and RFT ( = 0.042). The current study provided evidence that DO dilution was a better prediction method for BF than RFT and that BCS may serve as a BF predictor in stock-type horses.