Silva Eduardo P, Wiltbank Milo C, Machado Amanda B, Gambin Laís S, Dias Marcelo M, Chaiben Márcio F C, Bernardi Mari L, Borges João B S
Unidade de Reprodução de Bovinos, Departamento de Medicina Animal, Faculdade de Veterinária, Universidade Federal Do Rio Grande Do Sul (UFRGS), Porto Alegre, RS, Brazil.
Department of Dairy Science, University of Wisconsin-Madison, Madison, WI, United States.
Theriogenology. 2018 Nov;121:7-12. doi: 10.1016/j.theriogenology.2018.07.019. Epub 2018 Jul 27.
This study compared estradiol cypionate (ECP) or GnRH as ovulation inducers at the end of a timed AI (TAI) protocol in Angus heifers. On day 0, heifers (n = 415), between 22 and 24 months of age, were treated with an intravaginal 1 g progesterone (P4) insert and 2 mg of estradiol benzoate. On day 8, heifers had P4 removed, received 500 μg cloprostenol, and were randomized into two groups: ECP [n = 214; 0.5 mg of ECP on day 8] or GnRH [n = 201; 25 μg of GnRH analog licerelin acetate on day 10]. All heifers received TAI on day 10; 48-50 h after P4 insert withdrawal. Estrus was determined by removal of tail paint. Ovaries of heifers were evaluated by ultrasound on day 0 to determine CL presence (with CL = 213, without CL = 202) and on day 10 to measure preovulatory follicle size. Heifers were divided into three categories based on preovulatory follicle diameter: <8.5 mm (smaller than deviation), 8.5-10.9 mm, or ≥11 mm. Pregnancy diagnosis was performed 32 days after TAI. Heifers treated with ECP had greater expression of estrus than GnRH-treated heifers (93.9% vs 67.7%; P < 0.0001), regardless of CL presence at beginning of protocol. Heifers with CL at beginning of protocol had larger preovulatory follicle diameter (10.4 mm vs 9.6 mm; P = 0.0058) and greater pregnancy per AI (P/AI; 61.0% vs 50.5%; P = 0.032) than heifers without CL at day 0. In heifers with CL at day 0, GnRH treatment increased P/AI compared to ECP treatment (68.0% vs 54.9%; P = 0.0498). Expression of estrus was greater in ECP-treated than GnRH-treated heifers that had small (<8.5 mm; 77.1% vs 5.6%; P < 0.001) or medium-sized (8.5-10.9 mm; 98.4% vs. 61.7%) follicles, but not in heifers with large follicles (≥11 mm; 97.9% vs 98.3%). The P/AI was very low in both treatments for heifers with follicles <8.5 mm (ECP-14.3% vs GnRH-16.7%). In heifers with medium-sized follicles (8.5-10.9 mm), ECP treatment tended to increase P/AI compared with GnRH-treated heifers (62.9 vs 46.7%; P = 0.074). In contrast, P/AI was greater for GnRH-treated than ECP-treated heifers with large preovulatory follicles (≥11 mm; 79.7% vs 60.4%; P = 0.032). Thus, the optimal inducer of ovulation in a TAI protocol for beef heifers appears to depend on the presence of a CL at beginning of protocol (GnRH > ECP if CL present) and size of the preovulatory follicle, with ECP increasing expression of estrus and tending to increase fertility in heifers with medium-sized follicles but GnRH increasing fertility in heifers having large preovulatory follicles.
本研究比较了在安格斯小母牛定时人工授精（TAI）方案结束时，环丙孕酮（ECP）或促性腺激素释放激素（GnRH）作为排卵诱导剂的效果。在第0天，对415头年龄在22至24个月的小母牛进行阴道内植入1克孕酮（P4）和2毫克苯甲酸雌二醇的处理。在第8天，取出P4，给小母牛注射500微克氯前列醇，并随机分为两组：ECP组（n = 214；第8天注射0.5毫克ECP）或GnRH组（n = 201；第10天注射25微克GnRH类似物醋酸利塞林）。所有小母牛在第10天接受TAI，即取出P4插入物48 - 50小时后。通过去除尾漆来确定发情情况。在第0天通过超声评估小母牛的卵巢以确定是否存在黄体（有黄体 = 213头，无黄体 = 202头），并在第10天测量排卵前卵泡大小。根据排卵前卵泡直径将小母牛分为三类：<8.5毫米（小于偏差）、8.5 - 10.9毫米或≥11毫米。在TAI后32天进行妊娠诊断。无论方案开始时是否存在黄体，接受ECP治疗的小母牛发情表现均高于接受GnRH治疗的小母牛（93.9%对67.7%；P < 0.0001）。方案开始时存在黄体的小母牛，其排卵前卵泡直径更大（10.4毫米对9.6毫米；P = 0.0058），且每次人工授精后的妊娠率（P/AI）更高（61.0%对50.5%；P = 0.032），高于第0天无黄体的小母牛。在第0天有黄体的小母牛中，与ECP治疗相比，GnRH治疗使P/AI增加（68.0%对54.9%；P = 0.0498）。对于卵泡小（<8.5毫米）或中等大小（8.5 - 10.9毫米）的小母牛，接受ECP治疗的发情表现高于接受GnRH治疗的小母牛（分别为77.1%对5.6%；P < 0.001和98.4%对61.7%），但对于卵泡大（≥11毫米）的小母牛则不然（97.9%对98.3%）。对于卵泡<8.5毫米的小母牛，两种治疗的P/AI都非常低（ECP组为14.3%对GnRH组为16.7%）。对于中等大小卵泡（8.5 - 10.9毫米）的小母牛，与接受GnRH治疗的小母牛相比，ECP治疗有使P/AI增加的趋势（62.9%对46.7%；P = 0.074）。相反，对于排卵前卵泡大（≥11毫米）的小母牛，接受GnRH治疗的P/AI高于接受ECP治疗的小母牛（79.7%对60.4%；P = 0.032）。因此，在肉牛小母牛的TAI方案中，最佳排卵诱导剂似乎取决于方案开始时是否存在黄体（如果存在黄体，GnRH > ECP）以及排卵前卵泡的大小，ECP可增加发情表现，并倾向于提高中等大小卵泡小母牛的繁殖力，而GnRH可提高排卵前卵泡大的小母牛的繁殖力。
