Hamernik D L, Males J R, Gaskins C T, Reeves J J
J Anim Sci. 1985 Feb;60(2):358-62. doi: 10.2527/jas1985.602358x.
Seventy-five crossbred heifers (mean weight 304 kg) were stratified by weight and source and placed in eight pens. Four duplicate treatments were randomly assigned to pens as follows: (1) intact-control (n = 19), (2) intact + melengestrol acetate (MGA, n = 20), (3) hysterectomy (n = 17) and (4) ovariectomy (OVX, n = 19). All heifers were preconditioned for 2 mo before beginning the finishing study. Surgery was performed through a high lumbar incision approximately 3 wk before the finishing study began. Group 2 heifers were fed .4 mg X head-1 X d-1 MGA. Blood samples were collected at 28-d intervals throughout the 112-d finishing phase. Ovaries were collected at slaughter and carcass data were obtained 24 h after slaughter. On d 112, progesterone was higher (P less than .05) in hysterectomized heifers than in other treatment groups. Serum progesterone concentration was nondetectable (less than .35 ng/ml) in OVX and MGA heifers. There were no differences (P greater than .05) in feed efficiency or carcass characteristics among the four treatments. Hysterectomized and MGA heifers had similar (P greater than .05) average daily gains, which were higher (P less than .15) than control and OVX heifers. These data suggest that the elevated levels of progesterone from the maintained corpora lutea and the subsequent absence of estrous activity in the hysterectomized heifers are advantageous for promoting growth in feedlot heifers.
75头杂交小母牛（平均体重304千克）按体重和来源分层，放入8个围栏中。将四种重复处理随机分配到围栏中，如下所示：（1）完整对照（n = 19），（2）完整 + 醋酸美仑孕酮（MGA，n = 20），（3）子宫切除术（n = 17）和（4）卵巢切除术（OVX，n = 19）。在开始育肥研究之前，所有小母牛都经过了2个月的预处理。在育肥研究开始前约3周，通过高腰部切口进行手术。第2组小母牛每天每头饲喂0.4毫克MGA。在112天的育肥期内，每隔28天采集一次血样。在屠宰时采集卵巢，并在屠宰后24小时获得胴体数据。在第112天，子宫切除的小母牛体内孕酮水平高于其他处理组（P < 0.05）。OVX和MGA小母牛的血清孕酮浓度检测不到（低于0.35纳克/毫升）。四种处理之间的饲料效率或胴体特征没有差异（P > 0.05）。子宫切除的小母牛和MGA小母牛的平均日增重相似（P > 0.05），均高于对照和OVX小母牛（P < 0.15）。这些数据表明，子宫切除的小母牛体内因黄体维持而导致的孕酮水平升高以及随后发情活动的缺失有利于促进育肥牛的生长。
