Carriquiry M, Weber W J, Dahlen C R, Lamb G C, Baumgard L H, Crooker B A
Department of Animal Science, University of Minnesota, St Paul 55108-6118, USA.
J Dairy Sci. 2009 Oct;92(10):4852-64. doi: 10.3168/jds.2008-1673.
Multiparous cows (n = 59) were blocked by expected calving date and previous milk yield and assigned randomly to treatments to determine the effects of bovine somatotropin (bST; Posilac, Monsanto Animal Agricultural Group, St. Louis, MO) and source of dietary fat on production responses. Diets were provided from calving and included whole, high-oil sunflower seeds [SS; 10% of dietary dry matter (DM); n-6:n-3 ratio of 4.6] as a source of linoleic acid (18:2) or a mixture of Alifet-High Energy and Alifet-Repro (AF; Alifet USA, Cincinnati, OH; 3.5 and 1.5% of dietary DM, respectively; n-6/n-3 ratio of 2.6) as a source of protected n-3 fatty acids. Diets contained 181 versus 188 g of crude protein and 183 versus 186 g of acid detergent fiber/kg of DM and 1.54 versus 1.66 Mcal of net energy for lactation at the actual DM intake for SS versus AF, respectively. Cows received 0 or 500 mg of bST every 10 d from 12 to 70 d in milk (DIM) and at 14-d intervals through 280 DIM. The 2 x 2 factorial combination of diet (SS or AF) with or without bST administration resulted in treatments designated as SSY, SSN, AFY, and AFN, respectively. Data were analyzed as repeated measures using mixed model procedures to determine the effects of diet, bST, and their interactions. Yield of 3.5% fat-corrected milk was not altered by diet, but was increased by 4.0 +/- 1.9 kg/d from 12 to 70 DIM and by 5.1 +/- 1.2 kg/d from 12 to 280 DIM by bST. Treatment did not affect DM intake or energy balance (EB) nadir. There was an interaction of bST and diet on EB because AF decreased the impact of bST on overall EB and allowed AFY cows to reach a positive EB earlier than SSY cows. Gross feed efficiency adjusted for body weight change was greater for bST-treated cows (1.03 vs. 1.15 +/- 0.03 kg of fat-corrected milk/Mcal of net energy for lactation). Circulating insulin-like growth factor-I concentrations were increased by bST (85 vs. 125 +/- 8 ng/mL). Body weight, body condition score, and backfat thickness were reduced by bST, but differences between treated and nontreated cows did not differ by 280 DIM. Results indicate cows responded to bST administration in early lactation, but the magnitude of the response was greater after 70 DIM. Source of dietary fat had a minimal effect on most production measurements, but relative to SS, AF decreased the impact of bST on overall EB. Results support the premise that bST administration prolongs the delay in postpartum tissue replenishment.
经产奶牛（n = 59）按预期产犊日期和先前的产奶量进行分组，并随机分配至各处理组，以确定牛生长激素（bST；重组牛生长激素，孟山都动物农业集团，密苏里州圣路易斯）和日粮脂肪来源对生产性能的影响。从产犊开始提供日粮，日粮包含整粒、高油向日葵籽[SS；占日粮干物质（DM）的10%；n-6:n-3比例为4.6]作为亚油酸（18:2）的来源，或Alifet-高能和Alifet-繁殖的混合物（AF；美国Alifet公司，俄亥俄州辛辛那提；分别占日粮DM的3.5%和1.5%；n-6/n-3比例为2.6）作为保护型n-3脂肪酸的来源。日粮中粗蛋白含量分别为181和188 g/kg DM，酸性洗涤纤维含量分别为183和186 g/kg DM，泌乳净能分别为1.54和1.66 Mcal/kg DM，实际DM摄入量下SS组和AF组的泌乳净能分别为上述数值。奶牛在产奶12至70天（DIM）期间每10天接受0或500 mg的bST，并在280 DIM之前每隔14天接受一次。日粮（SS或AF）与是否使用bST的2×2析因组合分别产生了标记为SSY、SSN、AFY和AFN的处理组。使用混合模型程序对数据进行重复测量分析，以确定日粮、bST及其交互作用的影响。3.5%乳脂校正乳产量不受日粮影响，但bST使12至70 DIM期间产量增加4.0±1.9 kg/d，12至280 DIM期间增加5.1±1.2 kg/d。处理对DM摄入量或能量平衡（EB）最低点无影响。bST与日粮在EB上存在交互作用，因为AF降低了bST对总体EB的影响，并使AFY组奶牛比SSY组奶牛更早达到正EB。根据体重变化调整后的总饲料效率，bST处理的奶牛更高（1.03 vs. 1.15±0.03 kg乳脂校正乳/Mcal泌乳净能）。bST使循环胰岛素样生长因子-I浓度升高（85 vs. 125±8 ng/mL）。bST使体重、体况评分和背膘厚度降低，但到280 DIM时，处理组和未处理组奶牛之间的差异不显著。结果表明，奶牛在泌乳早期对bST给药有反应，但70 DIM后反应幅度更大。日粮脂肪来源对大多数生产指标影响极小，但相对于SS，AF降低了bST对总体EB的影响。结果支持bST给药会延长产后组织恢复延迟的前提。
