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<p>This study evaluated the effects of equine chorionic gonadotropin (eCG) dose and application timing after progestogen-sponge removal on estrus characteristics and ovulation rate in ewe‑lambs of three hair‑sheep breeds under dry-tropical conditions. Two hundred sixteen ewe‑lambs (62 Dorper, 69 Katahdin, 85 Pelibuey; 8–10 months old) were studied during a high (<i>n</i> = 91) and a low (<i>n</i> = 125) breeding season. Animals received intravaginal progestogen sponges (Cronolone, 20&#xa0;mg) for 12 days and were assigned to a 2×2 factorial treatment: eCG 200 IU or 300 IU administered either 24&#xa0;h before (−24&#xa0;h) or at sponge withdrawal (0&#xa0;h). Estrus signs (mount acceptance and vulvar swelling) were recorded every 4&#xa0;h for 48&#xa0;h; ovulation was confirmed by laparoscopic corpora lutea (Cl) count eight days later. Overall, 82% of ewe‑lambs exhibited estrus within 48&#xa0;h. There were no main effects of eCG dose or application time on overall estrus rate. A significant dose×time interaction affected interval to estrus (<i>P</i> = 0.012): mean interval was shorter after −24&#xa0;h application (30.2 ± 1.0&#xa0;h) than after 0&#xa0;h application (34.6 ± 1.0&#xa0;h). Breed influenced estrus expression and silent ovulation: Dorper ewe‑lambs were more likely to exhibit estrus than Pelibuey (odds ratio (OR) = 9.74, 95% confidence interval (CI) = 1.93–49.19; <i>P</i> = 0.0059) and had lower silent ovulation (3.4% vs. 24.7%; OR = 0.56, 95% CI = 0.02–0.59; <i>P</i> = 0.0094). Mean ovulation rate exceeded 95% across groups and was higher for Pelibuey (2.4 ± 0.1 Cl) than Dorper (2.0 ± 0.1 Cl) and Katahdin (1.9 ± 0.1 Cl; <i>P</i> &lt; 0.05). Under the conditions tested, administering 300 IU eCG at −24&#xa0;h sponge removal provided a practical balance for synchronized estrus and high ovulation rates across seasons.</p>

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Effects of eCG dose and timing on estrus and ovulation in hair ewe-lambs of three breeds under dry-tropical conditions across two breeding seasons

  • 期刊论文

  • 发表日期：

    2026年6月1日

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  • Nazario Pescador-Salas,
  • Javier Hernández-Meléndez,
  • Daniel López-Aguirre,
  • Nicolás López-Villalobos,
  • Froylán A. Lucero-Magaña,
  • Francisco J. Trejo,
  • Hilario Del-Angel,
  • Arnoldo González-Reyna,
  • José F. Vázquez-Armijo

摘要

This study evaluated the effects of equine chorionic gonadotropin (eCG) dose and application timing after progestogen-sponge removal on estrus characteristics and ovulation rate in ewe‑lambs of three hair‑sheep breeds under dry-tropical conditions. Two hundred sixteen ewe‑lambs (62 Dorper, 69 Katahdin, 85 Pelibuey; 8–10 months old) were studied during a high (n = 91) and a low (n = 125) breeding season. Animals received intravaginal progestogen sponges (Cronolone, 20 mg) for 12 days and were assigned to a 2×2 factorial treatment: eCG 200 IU or 300 IU administered either 24 h before (−24 h) or at sponge withdrawal (0 h). Estrus signs (mount acceptance and vulvar swelling) were recorded every 4 h for 48 h; ovulation was confirmed by laparoscopic corpora lutea (Cl) count eight days later. Overall, 82% of ewe‑lambs exhibited estrus within 48 h. There were no main effects of eCG dose or application time on overall estrus rate. A significant dose×time interaction affected interval to estrus (P = 0.012): mean interval was shorter after −24 h application (30.2 ± 1.0 h) than after 0 h application (34.6 ± 1.0 h). Breed influenced estrus expression and silent ovulation: Dorper ewe‑lambs were more likely to exhibit estrus than Pelibuey (odds ratio (OR) = 9.74, 95% confidence interval (CI) = 1.93–49.19; P = 0.0059) and had lower silent ovulation (3.4% vs. 24.7%; OR = 0.56, 95% CI = 0.02–0.59; P = 0.0094). Mean ovulation rate exceeded 95% across groups and was higher for Pelibuey (2.4 ± 0.1 Cl) than Dorper (2.0 ± 0.1 Cl) and Katahdin (1.9 ± 0.1 Cl; P < 0.05). Under the conditions tested, administering 300 IU eCG at −24 h sponge removal provided a practical balance for synchronized estrus and high ovulation rates across seasons.