Effects of dietary concentrate-to-forage ratio on rumen fermentation and performance of dairy cows

صينى. 选择4头安装有永久性瘤胃瘘管的泌乳奶牛，按4×4拉丁方设计，分别饲喂精粗比约为30∶70的“高低质粗料型”日粮、30∶70的混合型高青贮日粮、50∶50的精粗料比例相当的日粮及65∶35的高精料日粮等4种不同精粗比日粮,研究日粮精粗比对奶牛瘤胃发酵及泌乳性能的影响。结果显示，日粮精粗比对奶牛瘤胃pH值，氨氮质量浓度，总挥发性脂肪酸、丙酸、丁酸的浓度和乙酸/丙酸、（乙酸+丁酸）/丙酸有显著（P0.05）或极显著（P0.01）影响，而对瘤胃乙酸浓度影响不显著（P0.05）；饲喂不同精粗比日粮，奶牛乳产量、4%标准乳产量均有显著（P0.05）或极显著（P0.01）差异，而乳脂、乳蛋白、乳糖、非脂固形物及总固形物的含量差异均不显著（P0.05），但其产量随乳产量的增加而增加，存在显著（P0.05）或极显著（P0.01）差异。结果表明，4种精粗比日粮能使瘤胃发酵和乳成分含量保持稳定，但影响瘤胃挥发性脂肪酸浓度和乳产量；低质和优质粗料的合理搭配有利于稳定瘤胃内环境和乳脂含量，且能改善泌乳性能。

إنجليزي. Effects of dietary concentrate-to-forage ratio on rumen fermentation and performance were evaluated by using four primiparous Holstein cows with permanently ruminal cannula in a 4×4 Latin square design with four 20 d periods. Dietary concentrate-to-forage ratios were 30∶70, 30∶70, 50∶50, and 65∶ 35, respectively. The forage of the ration 1 was only Chinese wildryegrass hay. The forage of the ration 2, 3, and 4 is comprised of Chinese wildryegrass hay, alfalfa hay, and corn silage. The results showed that: significant (P0.05) differences existed among four diets for rumen pH, the concentrations of ammonia N, total volatile fatty acids, propionate, and butyrate, and the ratios of acetate to propionate and acetate plus butyrate to propionate, but differences among them were not significant (P0.05) for acetate concentration; there were significantly difference (P0.05) for the yields of milk and 4% of fat corrected milk among four diets, showed no significant differences (P0.05) among them for milk contents of fat, protein, lactose, no fat solid and total solid.In addition, the yields of every composition increased with increasing of milk yield and significant (P0.05) differences existed among four diets. The results indicated that four diets with different concentrate-to-forage ratios could make rumen fermentation and milk compositions content stable though the concentrations of volatile fatty acids and milk yield were influenced and the appropriate association of forage with high and low quality could make rumen environment and milk fat content stable and improve performance.