Influence on milk protein percentage of isocaloric infusions of glucose in the rumen, or propionate and acetate in the duodenum of cows fed dry rolled sorghum

摘要

Experiments were conducted to elucidate mechanisms of increased milk protein percentage in cows fed diets containing steam flaked (SFS) vs dry rolled (DRS) sorghum grains. In experiment 1 treatments were: DRS diet plus duodenal infusion of 30% sodium acetate (DA), or SFS diet plus duodenal water infusion (SFS). In the experiment 2 the DRS diet plus duodenal infusion of 23% sodium propionate (DP), was compared with the DRS diet plus ruminal infusion of 21% glucose (RG). Sorghum was 35% of DM in all diets and infusates were 5L/d. The SFS diet tended (P .19) to increase milk protein content and decrease ruminal pH. The DA infusion increased FCM, and tended to increase fat% and yield. The RG infusion increased milk protein percent and decreased ruminal pH, and the DP infusion tended to decrease DMI. In experiment 3 treatments were: (1) SFS, (2) DA, and (3) RG. Diets and infused amounts were similar to previous trials. No parameters was affected by treatment, but milk protein percent, yield of milk and milk protein were numerically higher SFS than DA, similar to the previous study. Milk composition and production for cows fed DRS plus RG were the same as for cows fed SFS. An in situ trial was conducted to better characterize ruminal starch degradation. The same (DRS and SFS) diets were used as in infusions trials. Treatments were divided into diets and grains as follows: (1) diet DRS, (2) diet SFS, (3) grain DRS, and (4) grain SFS. Material for incubation was ground to pass a 2 mm screen and placed in the rumen for 2, 4, 8, 12, 24 and 48h. DM degradability was not affected by treatment. Starch degradability at 4, 8 and 12h and were higher for the SFS than for DRS diets or grains. In situ data support the infusion data which of higher ruminal starch degradability with SFS than DRS. The studies suggest that increased milk protein content resulting from feeding SFS compared with DRS relates more to increased ruminal starch fermentability (as stimulated by RG) than to greater absorption of acetate or propionate.