| Abstrakt: |
Hormonal control of ovulation timing is an effective tool to optimize reproductive management and reduce costs in equine breeding programs. Few studies have evaluated the efficacy of GnRH analog histrelin as an ovulation inducer agent. This study aimed to compare the efficacy of human chorionic gonadotrophin (hCG) and histrelin as ovulation inducers in young, adult, and old mares during spring and summer. Reproductive records of 321 estrous cycles of 125 mares, mean age 9.8±0.37 years, range 1.5–24 years, between 360-600 kg body weight, and body condition ≥3 (1/5), were evaluated during spring (151 cycles) and summer (170 cycles). Mares were kept in the field and fed alfalfa hay, balanced concentrate feed and ad-libitum water. The ovaries, uterus, and cervix underwent transrectal examination and ultrasonography daily. When only one dominant follicle of 35 mm and endometrial edema compatible with estrus were reached, ovulation was induced. Each cycle was monitored every two to six hours until ovulation, 24h after induction. Cycles were randomly allotted in two groups; G1 (n=106 cycles): 1500 IU hCG (IV); G2 (n=215 cycles): 250 μg histrelin acetate (IM). A total of 119 cycles were from young (<8 years), 93 from adults (8-15 years), and 109 from old mares (>15 years). Cycles of mares ovulating within 24-48hafter treatment were considered to have responded to the inducer, and those ovulating before 24h and after 48h were excluded from the experiment. Inducer agents, season (spring or summer), and mare age were independent factors, and ovulation between 24-48h was considered the dependent factor. Data were analyzed through Fisher's exact test. The significance level was defined as P<0.05. From the 321 induced cycles, 254 (79.1%) ovulated within 24-48h, 20 (6.2%) before 24h, and 47 (14.6%) after 48h. There were no differences (P=0.2414) in the average response time between G1 (37.2h±3,5) and G2 (39.3h±4,5). The ovulatory response between G1 and G2 did not differ in spring (84.1% versus 90.7%, P=0.2627) and summer (79.2% versus 85.4%, P=0.3534). Independent of the inducer, the season did not influence the ovulation response in the different mare ages (spring P=0.1489; summer P=0.2992). No differences (P=0.896) were found between drugs in young and adult mares. However, old mares had a higher percentage of ovulatory response in spring and summer to histrelin (n=76) than to hCG (n=24) (89.5% versus 45.8%, P<0.0001). In conclusion, histrelin is more effective and accurate in inducing ovulation in old mares (>15 years) than hCG throughout the breeding season. [ABSTRACT FROM AUTHOR] |
Full Text from ScienceDirect