日粮中不同比例小麦替代玉米对奶牛乳脂合成和乳脂脂肪酸组成的影响

选择8头泌乳时间为(84±17)d,体重为(569±47)kg的经产中国荷斯坦奶牛作为试验动物,研究了日粮中不同比例小麦替代玉米对奶牛乳脂合成和乳脂脂肪酸(FA)组成的影响。采用重复4×4拉丁方设计,分别饲喂含不同比例粉碎小麦(GW)和粉碎玉米(GC)的日粮,4个处理组分别为(DM基础):W0组(0%GW+27.9%GC),W9.6组(9.6%GW+19.2%GC),W19.2组(19.2%GW+9.6%GC)和W28.8组(28.8%GW+0%GC)。结果表明:随着日粮中小麦比例的增加,瘤胃p H值线性降低(P=0.01);产奶量未受显著影响,平均为27.1 kg/d;乳脂率(P=0.02)、乳脂产量(P=0.02)和3.5%乳脂校正乳(FCM)(P=0.05)产量呈线性降低趋势;乳脂FA(g/100 g总FA)中C16∶0呈线性(P0.01)和二次曲线增加(P0.01),而C18∶0和FAC16呈线性(P0.01)和二次(P=0.03和0.01)曲线降低;C8∶0(P=0.01)、C15∶0(P=0.06)、C16∶1(P=0.01)和C18∶1n9t(P=0.10)呈线性增加趋势,而C14∶0(P=0.09)和C18∶2n6c(P=0.08)呈线性降低趋势;与W0和W9.6组相比,W19.2和W28.8组乳脂C16∶0、C16∶1及C16∶0与C16∶1之和显著增加(P0.01),而C18∶0显著降低(P0.01)。结果提示:奶牛日粮中可用适当比例的粉碎小麦来替代玉米,替代比例不宜超过日粮DM的19.2%;高比例小麦日粮饲喂奶牛(W28.8组)可引起瘤胃p H值和乳脂率下降,进一步引起乳脂FA组成发生变化。

Effect of Different Levels of Wheat as Replacements for Corn in Diets on Milk Fat Synthesis and Milk Fatty Acid Profile in Dairy Cows

Eight multiparous Holstein cows (569±47 kg of BW; 84±17 DIM) , were used in a replicated 4×4 Latin square design to evaluate the effects of different levels of ground wheat (GW) as replacements for ground corn (GC) in diets on milk fat synthesis and milk fatty acid profile in dairy cows. The cows were allocated to the dietary treatments as follows (DM basis): 1) W0 diet: total mixed ration (TMR) containing 0% GW and 27.9% GC; 2) W9.6 diet: TMR containing 9.6% GW and 19.2% GC; 3) W19.2 diet: TMR containing 19.2% GW and 9.6% GC; 4) W28.8 diet: TMR containing 28.8% GW and 0% GC. Increasing dietary levels of GW, the daily mean ruminal pH decreased linearly (P=0.01); daily dry matter intake (DMI) tended to increase quadratically (P=0.07), meanSmilk production was not affected by treatments (27.1 kg/d), however, percentage (P=0.02) and yield (P=0.02) of milk fat, 3.5% fat-corrected milk (FCM) yield (P=0.05) tended to decrease linearly; the concentrations of milk C16:0 fatty acids (FA, g/100 g) increased linearly (P<0.01) and quadratically (P<0.01), while C18:0 (P<0.01 and P=0.03, respectively), FA>C16 (P<0.01 and P=0.01, respectively) increased linearly and quadratically; C8:0 (P=0.01), C15:0 (P=0.06), C16:1 (P=0.01), and C18:1n9t (P=0.10) tended to increase linearly, while C14:0 (P=0.09) and C18:2n6t (P =0.08) tended to decrease linearly; C16:0, C16:1 and the sum of C16:0 and C16:1 significantly increased (P<0.01), while C18:0 significantly decreased (P<0.01) in cows fed the W19.2 and W28.8 diets, comparedSwithSotherStwoSdiets. Results from this experiment indicated that dairy cows fed diets containing appropriateSamounts of ground wheat is feasible; the GW as a replacement for GC in dairy cow diets shouldSnotSexceededS19.2% of diet DM; high quantities of wheat could reduce mean ruminal pH and milk fat percentage, and as the result of changes of milk fatty acid profile.