Ovulatory response to GnRH agonist during early and late fall in mares

Strategic approaches to improve equine breeding and stud farm outcomes

This review explores advanced strategies for enhancing fertility and optimizing reproductive outcomes in equine breeding programs. Horses, being seasonal breeders, present unique reproductive challenges influenced by environmental and physiological factors such as photoperiods, hormone cycles, and aging. Key approaches discussed include hormonal therapies, artificial light manipulation, and nutritional supplementation to improve ovulation and conception rates during the breeding season. Specific hormones such as gonadotropin-releasing hormone analogs, equine follicle-stimulating hormone, and progesterone are analyzed for their roles in synchronizing estrus and increasing ovarian activity. The document also emphasizes the significance of dietary strategies, particularly the inclusion of omega-3 fatty acids, L-arginine, and essential vitamins, in improving reproductive health. In addition, the review underscores the importance of stallion management, addressing factors such as testicular health, age, and environmental stress. Practical methods to mitigate seasonal infertility and improve foaling rates through better reproductive management of mares and stallions are detailed. These insights aim to assist stud farm owners in maximizing breeding efficiency and achieving higher economic returns. The primary goal of this review is to provide a comprehensive guide to practical interventions that increase the productivity and sustainability of equine breeding operations.

The Temporal Associations of B-Mode and Power-Doppler Ultrasonography, and Ovarian Steroid Changes of the Periovulatory Follicle and Corpus Luteum During Luteogenesis and Luteolysis in Jennies

This study aimed to determine the associations between B-mode and Power-doppler ultrasonography and ovarian steroids of the periovulatory follicle and respective corpus luteum (CL) during luteogenesis and luteolysis in jennies. Twenty-four periovulatory follicles/estrus of correspondent one inter-ovulatory interval (n = 12 jennies) were assessed in the study. B-mode ultrasonography and teasing were carried out once day until the detection of a periovulatory follicle (≥28 mm, uterine edema, and signs of estrus). Thereafter, jennies were monitored at 4-hour-intervals by B-mode and Power-doppler ultrasonography. Closer to ovulation, jennies were hourly checked. Each CL was checked daily from luteogenesis to luteolysis. Plasma concentrations of estradiol and progesterone were assessed daily with chemiluminescence immunoassay. Granulosa echogenicity and thickness increased from -36 hour to -1 hour before ovulation in 70% of follicles (P < .05) and were strongly associated with impending ovulation (r = 0.80 and r = 0.70, respectively). The follicular-wall blood flow increased from -72 to -24 hour pre-ovulation, while the estradiol concentration declined from 42 pg/mL by -72 hour to 31.6 pg/mL by 24 hour before ovulation (P < .05). The vascularization of the periovulatory follicle decreased from 62% (-36 hour) to 37% (-1 hour) before ovulation (P < .05). The CL vascularization and progesterone concentration gradually increased, reaching the peak at 11- and 10-day after the ovulation, respectively (P < .05). The CL vascularization started to decline 3 day before luteolysis, while progesterone concentrations started to drop 4 day before luteolysis (P < .05). In conclusion, the structural changes of the periovulatory follicle detected on B-mode and Power-doppler can be used to detect impending ovulation in donkeys; however, Power-doppler, but not B-mode ultrasonography, can be used to assess CL function in jennies.

Pharmacokinetics and efficacy of a novel long-acting bupivacaine formulation for cornual nerve block in calves

Local anesthetics are commonly used in farm animals to provide analgesia for painful procedures but can cause adverse effects at high systemic concentrations. The pharmacokinetics and efficacy of a long-acting sucrose acetate isobutyrate (SAIB) bupivacaine formulation following cornual nerve block in calves were compared to lidocaine. Fourteen calves were randomly assigned to one of the treatment groups (i) 5% Bupivacaine-SAIB (BUP-SAIB), n = 7; or (ii) 2% lidocaine (LID), n = 7. Cornual nerve block was performed, and duration of effective analgesia was evaluated by nociceptive threshold testing using a hand-held pressure algometer. Blood samples were collected at various time points and plasma concentrations were analyzed by HPLC. Pharmacokinetic parameters were calculated using a non-compartmental model. The mechanical nociceptive thresholds showed that the novel formulation could desensitize the skin around the horn bud for 18.77 ± 8.88 h (range 8-36 h), compared to 0.79 ± 0.34 h (range 0.5-1.5 h) with lidocaine. The mean maximum plasma concentration (Cmax) of bupivacaine was 152.03 (SD 37.34) ng/mL and its Tmax was 0.39 (SD 0.13) h. The half-life of elimination was 32.79 ± 11.00 h and the rate of clearance was 0.12 ± 0.03 L h-1. No toxicity signs were seen after treatment in either group. The novel formulation produced long-lasting analgesia of several times greater duration than that produced by lidocaine. This study showed that the safety and efficacy of the SAIB formulation justifies further studies in a larger population of animals.

Luteal tissue area and immunoreactive concentrations of progesterone in plasma of bred and non-bred mares

Progesterone is pivotal to maintain pregnancy in the first trimester and low concentrations (<4 ng/mL) have been associated with early pregnancy loss. Measurement of progesterone is widely used in practice to determine whether a mare needs progestin supplementation. Therefore, the objective of the present study was to determine progesterone concentrations and the luteal tissue area in mares non-bred, and those bred becoming pregnant, and those failing to become pregnant. We hypothesized that pregnant mares have greater progesterone concentrations than non-pregnant mares. Fifty-two cycles of mares (n=14) were monitored by ultrasonography every other day until detection of a preovulatory follicle. Then deslorelin acetate was administered to induce ovulation. Twenty-four hours later, mares were bred (∼2 billion progressively motile sperm extended in 50 mL; n=37 cycles) or a sham-bred (50 mL of extender; n=15 cycles). Ovulation was confirmed and number of corpora lutea and the luteal tissue area were recorded daily until 10d post-ovulation. Progesterone concentrations were assessed daily from the day of the ovulation up to 10d post-ovulation. Pregnancy diagnosis was carried out at 10d and 13d post-ovulation. Of the bred mares, 20 of them became pregnant and 17 did not. Data were analyzed with a mixed model, Tukey test as post-hoc, and Pearson's coefficient of correlation. Progesterone concentrations and luteal tissue area varied with time (P=0.001) but not with group (P>0.05). Multiple ovulations were associated with greater progesterone concentrations and luteal tissue area (P=0.0001). There was a moderate positive association between the number of ovulations and luteal tissue area (r=0.54; P=0.0001). The lack of change in the progesterone concentration and luteal tissue area between bred and non-bred mares suggests that horse seminal plasma does not affect luteal function in mares. As all mares had progesterone above 4 ng/mL after 5d post-ovulation; it is possible that if mares with abnormal progesterone concentrations were used, the results could have been different. In conclusion, pregnancy was not associated with greater progesterone concentrations or luteal tissue area.