Gasser C L, Behlke E J, Grum D E, Day M L
Department of Animal Sciences, The Ohio State University, Columbus 43210, USA.
J Anim Sci. 2006 Nov;84(11):3118-22. doi: 10.2527/jas.2005-676.
Precocious puberty (<300 d of age) can be successfully induced in a majority of heifers with early weaning and continuous feeding of a high-concentrate diet. The objective of this experiment was to determine the relative effects of timing of feeding a high-concentrate diet on age at puberty in early-weaned heifers. Sixty crossbred Angus and Simmental heifer calves were weaned at 112 +/- 2 d of age and 155 +/- 3 kg of BW and were fed a receiving diet for 2 wk. Heifers were blocked by age and BW, and assigned randomly to receive a high-concentrate (60% corn; H) or control (30% corn; C) diet during phase 1 (mean age 126 to 196 d) and H or C during phase 2 (mean age 196 to 402 d), resulting in 4 treatments (HH, n = 15; HC, n = 15; CH, n = 15; and CC, n = 15). Blood samples were collected weekly beginning at a mean age of 175 d and assayed for progesterone concentration to determine age at puberty. After 56 d on the experimental diets, BW of heifers fed the H diet during phase 1 were greater (P < 0.05) than those of heifers fed the C diet (mean age of 182 d; treatment x mean age, P < 0.01). After 70 d on the new diets (mean age of 266 d), heifers fed the H diet during phase 2 reached heavier BW (P < 0.05) than heifers fed the C diet, when compared within phase 1 diet groups (HH > HC; CH > CC). Body weights in HC and CH treatments differed from a mean age of 169 through 238 d, after which BW did not differ between these treatments. The ADG over the entire experimental period was greatest for the HH treatment (1.2 +/- 0.04 kg/d; P < 0.05), followed by the HC and CH treatments (1.0 +/- 0.03 and 1.0 +/- 0.02 kg/d, respectively), which were not different, and the CC treatment gained the least (0.7 +/- 0.04 kg/d; P < 0.05). Precocious puberty occurred in 67, 47, 47, and 20% of heifers in the HH, HC, CH, and CC treatments, respectively (HH > CC; P < 0.05). Mean age at puberty for the HH and HC treatments (271 +/- 17 and 283 +/- 17 d of age, respectively) was earlier (P < 0.05) than for the CC treatment (331 +/- 11 d of age). Age at puberty in the CH treatment (304 +/- 13 d of age) was intermediate to and not different from the other treatments. Heifers fed the H diet during phase 1 attained puberty earlier (P < 0.05) than heifers fed the C diet during phase 1. In conclusion, increasing dietary energy intake in early-weaned heifers, through feeding a high-concentrate diet from 126 to 196 d of age, decreased age at puberty regardless of the diet fed after 196 d of age.
早熟（年龄<300天）可通过对大多数小母牛进行早期断奶并持续饲喂高浓缩日粮成功诱导。本试验的目的是确定在早期断奶小母牛中，饲喂高浓缩日粮的时间对青春期年龄的相对影响。60头杂交安格斯和西门塔尔小母牛犊在112±2日龄、体重155±3千克时断奶，并饲喂2周的过渡日粮。小母牛按年龄和体重进行分组，然后随机分配在第1阶段（平均年龄126至196天）接受高浓缩（60%玉米；H）或对照（30%玉米；C）日粮，在第2阶段（平均年龄196至402天）接受H或C日粮，从而形成4种处理方式（HH，n = 15；HC，n = 15；CH，n = 15；CC，n = 15）。从平均年龄175天开始每周采集血样，检测孕酮浓度以确定青春期年龄。在试验日粮饲喂56天后，第1阶段饲喂H日粮的小母牛体重比饲喂C日粮的小母牛重（P<0.05）（平均年龄182天；处理×平均年龄，P<0.01）。在新日粮饲喂70天后（平均年龄266天），在第1阶段日粮组内比较时，第2阶段饲喂H日粮的小母牛体重比饲喂C日粮的小母牛重（P<0.05）（HH>HC；CH>CC）。HC和CH处理组的体重在平均年龄169至238天期间存在差异，之后这两种处理方式的体重不再有差异。整个试验期内，HH处理组的平均日增重最高（1.2±0.04千克/天；P<0.05），其次是HC和CH处理组（分别为1.0±0.03和1.0±0.02千克/天，二者无差异），CC处理组增重最少（0.7±0.04千克/天；P<0.05）。HH、HC、CH和CC处理组中小母牛早熟的比例分别为67%、47%、47%和20%（HH>CC；P<0.05）。HH和HC处理组的平均青春期年龄（分别为271±17和283±17日龄）比CC处理组（331±11日龄）早（P<0.05）。CH处理组的青春期年龄（304±13日龄）处于中间水平，与其他处理组无差异。第1阶段饲喂H日粮的小母牛比第1阶段饲喂C日粮的小母牛青春期来得更早（P<0.05）。总之，在早期断奶小母牛中，通过在126至196日龄饲喂高浓缩日粮增加日粮能量摄入量，可降低青春期年龄，无论196日龄后饲喂何种日粮。
