| The effects of four rations with different concentrate-to-forage ratios on rumen fermentation, nutrients intake and their whole-tract digestibility, behavioral science, performance and several blood parameters in the jugular vein were evaluated using 4 primiparous Holstein cows that were surgically and permanently fitted ruminal, duodenal top, and ileum bottom T-shaped cannulas in a 4×4 Latin square design with four 21-d periods. The concentrate-to-forage ratios for the ration 1, 2, 3, and 4 were 30:70, 30:70, 50:50, 65:35, respectively. The forage of the ration 1 was only Chinese wildryegrass hay. The forage of the ration 2, 3, and 4 comprised of Chinese wildryegrass hay, alfalfa hay, and corn silage. Cows averaged of 482.9±21.2 (mean ±SD) kg body weight, 175 ±6d days in milk and 16.3 ±1.96kg milk yield at the beginning of the experiments.The results showed that: 1 Effect of dietary concentrate-to-forage ratio on rumen fermentation of lactating cows: When cows were fed different rations, the average ruminal pH values that declined in response to increased concentrate-to-forage ratio ranged between 6.26 and 6.56 and the single value of every time dot remained above 6.0. And the ration 4 was lower significantly (P<0.05) than other rations. The average ruminal pH values was not correlated to neutral detergent fiber and physical effective neutral detergent fiber content of the rations and the ruminating and chewing times of cows. When cows were fed different rations, the average ruminal concentrations of ammonia-N ranged between 8.58 and 18.57mg/dl and increased with increased content of dietary crude protein. And the ration 3 and 4 were higher significantly (P<0.01) than the ration 1 and 2. When cows were fed different rations, the average ruminal concentrations of total volatile fatty acids, acetate, propionate, and butyrate ranged between 103.94 and 110.59, 68.66 and 71.73, 21.22 and 27.34, 10.86 and 14.37mmol/ml, respectively. With increased concentrate-to-forage ratio, the average ruminal concentrations of total volatile fatty acids, propionate and butyrate increased, but that of acetate decreased. For the average ruminal concentrations of total volatile fatty acids, the ration 1 and 2 were lower significantly (P<0.05) than the ration 4; for that of acetate, no differences between the dietary treatments were significant (P>0.05); for that of propionate, no differences between the rations 3 and 4 were significant (P>0.05), but significant (P<0.05) differences existed among the ration 3, 4 and the ration 1 or 2; for that of butyrate, the ration 3 and 4 were higher significantly (P<0.01) than the ration 1 and 2. The average ruminal values of acetate/propionate and (acetate + butyrate)/propionate that bothl declined in response to increased concentrate-to-forage ratio ranged between 2.53 and 3.42, 3.05 and 3.94, respectively. And no differences between the rations 3 and 4 were significant (P>0.05), but significant (P<0.01) differences existed among the ration 3, 4 and the ration 1 or 2. The average ruminal values of acetate/propionate was highly and positively correlated with the ratio of neutral detergent fiber intake/organic matter intake, and the linearly regressive equality was y=1.274+3.872x(R=0.884, p=0.000). And the average ruminal values of acetate/propionate and (acetate + butyrate)/propionate were both medially and positively correlated with the ruminating and chewing times of cows. When cows were fed different rations, the average values of ruminal fil-papase, xylanase, CMCase, salicinase activity that were not affected by the dietary treatments significantly (P<0.01) ranged between 1.84 and 1.94IU, 10.04 and 10.74IU, 2.62 and 2.89IU, 2.36 and 2.75IU, respectively. 2 Effect of dietary concentrate-to-forage ratio on intake and whole-tract digestibility of dry matter, organic matter, neutral detergent fiber and acid detergent fiber of lactating cows: Dry matter intake when cows were fed the ration 2 was lower significantly (P<0.01) than that when cows were fed the ration 1, 3, and 4...
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