Blevins C A, Shirley J E, Stevenson J S
Department of Animal Sciences and Industry, Kansas State University, Manhattan 66506-0201, USA.
J Dairy Sci. 2006 Nov;89(11):4176-87. doi: 10.3168/jds.S0022-0302(06)72463-8.
Our objectives were to determine lactational and reproductive outcomes in response to increased milking frequency (MF), injection of estradiol cypionate (ECP), and treatment with bovine somatotropin (bST). Lactating dairy cows (n = 144) were blocked by lactation number (1 vs. 2+) and assigned randomly to a 2 x 2 x 2 factorial experiment consisting of 8 treatment combinations: 1) MF consisting of 4x daily milking (4x) for the first 30 d in milk (DIM) vs. 2x daily milking (2x), with all cows milked 2x after 30 DIM; 2) 10 mg of ECP given postpartum at 8 +/- 3 DIM versus controls that received ECP diluent (oil); and 3) biweekly bovine somatotropin (bST), starting sometime after 60 DIM, versus no bST. Ovulation before the first artificial insemination was synchronized by using Heatsynch (GnRH injection 7 d before PGF2alpha followed in 24 h by ECP), and cows were artificially inseminated after detected estrus or at 48 h after ECP, whichever came first. Pregnancy was assessed by transrectal ultrasonography 28 to 30 d after artificial insemination. Daily yield and weekly components of milk were measured during the first 90 DIM. Intervals to first and second postpartum ovulation were unaffected by treatment, but cows were in estrus earlier after 2x (24 +/- 4 d) than 4x (41 +/- 4 d) daily MF, and sooner after ECP (25 +/- 3 d) than after oil (39 +/- 4 d) treatment. Pregnancy rates among 4x cows increased for ECP versus oil (52.8 vs. 27.8%) more than for cows with 2x MF treated with ECP versus oil (50.0 vs. 39.4%). Increased MF increased daily milk yields and energy-corrected milk yields during the first 30 DIM. Although milk yields were increased acutely by ECP during the 10 d after its injection, subsequent milk yields were decreased for ECP-treated cows previously milked 4x daily. Treatment with bST increased overall daily milk yields most in cows previously milked 2x daily and treated with oil and those milked 4x daily and treated with ECP. We concluded that early postpartum ECP injection increased pregnancy rates, but generally had detrimental effects on milk yields after 30 DIM for ECP-treated cows previously milked 4x daily, unless those cows also were treated with bST.
我们的目标是确定增加挤奶频率（MF）、注射环丙孕酮（ECP）以及使用牛生长激素（bST）治疗后的泌乳和繁殖结果。将泌乳奶牛（n = 144）按胎次（1胎与2胎及以上）进行分组，并随机分配到一个2×2×2析因试验中，该试验包含8种处理组合：1）在产奶的前30天，MF为每天挤奶4次（4x）与每天挤奶2次（2x），所有奶牛在30天后均改为每天挤奶2次；2）产后8±3天给予10mg ECP，对照组给予ECP稀释剂（油）；3）从60天后的某个时间开始每两周注射一次牛生长激素（bST），对照组不注射bST。通过使用Heatsynch（在PGF2α前7天注射GnRH，24小时后注射ECP）使首次人工授精前的排卵同步，奶牛在检测到发情后或在注射ECP后48小时进行人工授精，以先到者为准。在人工授精后28至3天通过直肠超声检查评估妊娠情况。在产奶的前90天测量日产奶量和每周的奶成分。首次和第二次产后排卵的间隔不受处理影响，但每天挤奶2次（24±4天）的奶牛比每天挤奶4次（41±4天）的奶牛发情更早，注射ECP（25±3天）的奶牛比注射油（39±4天）的奶牛发情更早。与油处理相比，4x组奶牛中接受ECP处理的妊娠率增加幅度（52.8%对27.8%）大于2x MF组奶牛中接受ECP处理与油处理的妊娠率增加幅度（50.0%对39.4%）。增加MF可提高产奶前30天的日产奶量和能量校正奶量。虽然注射ECP后的10天内日产奶量会急剧增加，但对于之前每天挤奶4次的ECP处理奶牛，随后的产奶量会下降。对于之前每天挤奶2次且接受油处理以及每天挤奶4次且接受ECP处理的奶牛，使用bST处理能最大程度提高总体日产奶量。我们得出结论，产后早期注射ECP可提高妊娠率，但对于之前每天挤奶4次的ECP处理奶牛，在30天后通常会对产奶量产生不利影响，除非这些奶牛也接受bST处理。
