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

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

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(P<0.01)和二次曲线增加(P<0.01),而C18∶0和FA>C16呈线性(P<0.01)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(P<0.01),而C18∶0显著降低(P<0.01)。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。

8 multiparous Holstein cows（ 569 ± 47 kg of BW; 84 ± 17 DIM） have been applied in a replicated4 × 4 Latin square design to evaluate the effects of ground wheat（ GW） at different levels on milk fat synthesis as well as milk fatty acid profile in dairy cows（ as substitution for ground corn（ GC） in diets）. The cows have been allocated to the dietary treatments as follows（ DM basis） ： 1） W0 diet： total mixed ration（ TMR） containing 0% GW and27. 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. Along with the increasing dietary levels of GW,the daily mean ruminal p H was decreased linearly（ P = 0. 01）; daily dry matter intake（ DMI） tended to increase quadratically（ P = 0. 07）; no effect on mean milk production was found 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,compared with other two diets. Results from this experiment indicated that dairy cows fed diets containing appropriate amounts of ground wheat was feasible; the GW as a replacement for GC in dairy cow diets could not exceeded 19. 2% of diet DM; high quantities of wheat had the ability to reduce mean ruminal p H and milk fat percentage as a result of changes of milk fatty acid profile.