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):4865-75. doi: 10.3168/jds.2008-1674.
Multiparous cows (n = 59) were blocked by expected calving date and previous milk yield and assigned randomly to treatments to determine effects of bovine somatotropin (bST; Posilac, Monsanto Animal Agricultural Group, St. Louis, MO) and source of dietary fat on milk fatty acid composition during the first 140 d in milk. Diets were provided from calving and included whole, high-oil sunflower seeds (SS; 10% of dietary dry matter; n-6/n-3 ratio of 4.6) as a source of linoleic acid or a mixture of Alifet-High Energy and Alifet-Repro (AF; Alifet USA, Cincinnati, OH; 3.5 and 1.5% of dietary dry matter, respectively; n-6/n-3 ratio of 2.6) as a source of protected n-3 fatty acids (15.7% 18:3, 1.3% 20:5, and 1.3% 22:6). Treatments were derived from a 2 x 2 combination of supplemental fat source (SS, AF) and with 0 (SSN, AFN) or 500 (SSY, AFY) mg of bST administered every 10 d from 12 to 70 d in milk and at 14-d intervals thereafter. Milk fatty acid composition was determined in samples collected from 32 cows (8 complete blocks) during wk 2, 8, and 20 of lactation. Data were analyzed as repeated measures using mixed model procedures to determine the effects of diet, bST, week of lactation, and their interactions. Proportions of 18:3 (4.02 vs. 3.59 +/- 0.16%), 20:5 (0.52 vs. 0.41 +/- 0.02%), and 22:6 (0.11 vs. 0.02 +/- 0.02%) were greater and the n-6/n-3 fatty acid ratio (7.40 vs. 8.80 +/- 0.30) was reduced in milk from cows fed AF compared with SS. Proportions of de novo-synthesized fatty acids increased and preformed fatty acids decreased as lactation progressed, but bST administration delayed this shift in origin of milk fatty acids. Transfer efficiency of 18:3, 20:5, and 22:6 from AF to milk fat averaged 36.2, 4.9, and 5.2%, respectively. These efficiencies increased as lactation progressed, but were delayed by bST. Apparent mammary Delta(9)-desaturase activity and milk conjugated linoleic acid (cis-9, trans-11 conjugated linoleic acid) content increased through the first 8 wk of lactation. Based on the product-to-substrate ratio of 14:1/14:0 fatty acids in milk, there was an interaction of diet and bST because bST decreased apparent Delta(9)-desaturase activity in SSY cows but increased it in AFY cows (0.10, 0.09, 0.08, and 0.09 +/- 0.01 for SSN, SSY, AFN, and AFY, respectively). Feeding Alifet-Repro increased n-3 fatty acids in milk and bST prolonged the partitioning of dietary fatty acids into milk fat.
经产奶牛（n = 59）按预期产犊日期和先前产奶量进行分组，并随机分配至各处理组，以确定牛生长激素（bST；Posilac，孟山都动物农业集团，密苏里州圣路易斯）和日粮脂肪来源对产奶前140天牛奶脂肪酸组成的影响。从产犊开始提供日粮，日粮包含全脂、高油向日葵籽（SS；占日粮干物质的10%；n-6/n-3比例为4.6）作为亚油酸来源，或Alifet-High Energy和Alifet-Repro的混合物（AF；美国Alifet公司，俄亥俄州辛辛那提；分别占日粮干物质的3.5%和1.5%；n-6/n-3比例为2.6）作为保护型n-3脂肪酸来源（18:3占15.7%，20:5占1.3%，22:6占1.3%）。处理组来自于补充脂肪来源（SS、AF）的2×2组合，且在产奶12至70天期间每10天给予0（SSN、AFN）或500（SSY、AFY）毫克bST，并在此后每隔14天给药一次。在泌乳第2、8和20周从32头奶牛（8个完整组）采集的样本中测定牛奶脂肪酸组成。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、泌乳周及其相互作用的影响。与饲喂SS的奶牛相比，饲喂AF的奶牛牛奶中18:3（4.02%对3.59±0.16%）、20:5（0.52%对0.41±0.02%）和22:6（0.11%对0.02±0.02%）的比例更高，n-6/n-3脂肪酸比例（7.40对8.80±0.30）更低。随着泌乳进行，从头合成脂肪酸的比例增加，预先形成的脂肪酸比例降低，但施用bST延迟了牛奶脂肪酸来源的这种转变。AF中18:3、20:5和22:6向乳脂肪的转移效率平均分别为36.2%、4.9%和5.2%。这些效率随着泌乳进行而增加，但被bST延迟。在泌乳的前8周，表观乳腺Δ9-去饱和酶活性和牛奶共轭亚油酸（顺-9，反-11共轭亚油酸）含量增加。基于牛奶中14:1/14:0脂肪酸的产物与底物比例，存在日粮和bST的相互作用，因为bST降低了SSY奶牛的表观Δ9-去饱和酶活性，但增加了AFY奶牛的该活性（SSN、SSY、AFN和AFY分别为0.10、0.09、0.08和0.09±0.01）。饲喂Alifet-Repro增加了牛奶中的n-3脂肪酸，bST延长了日粮脂肪酸向乳脂肪的分配。
