Changes in digestion and AA supply in dairy cows were studied when fresh grass was partly replaced by concentrate mixtures based either on corn starch or sugar beet pulp fiber. Treatments were tested in a Latin square utilizing three lactating cows' with ruminal and intestinal cannulas. Partial replacement of grass decreased CP digestibility. When high starch concentrate was fed, NDF digestibility was lower than that of the high fiber diet, mainly because of decreased ruminal digestion of NDF. For the high starch concentrate, 39% of the ingested starch escaped ruminal fermentation. Although less OM was fermented in the forestomachs on high starch concentrate, the duodenal AA N flow was higher than for the high fiber concentrate. The proportion of microbial protein was unaffected; thus, efficiency of microbial synthesis was estimated to be higher when high starch concentrate was fed.

In a 2 x 2 Latin square design trial 6 grazing dairy cows, with rumen cannula, were supplemented with high-starch concentrate, containing starch 248 g/kg DM, or low-starch concentrate (starch 15 g/kg DM). Cows were given daily 1 kg high-starch concentrate (1HS), 7 kg high-starch concentrate (7HS) or 7 kg low-starch concentrate (7LS) in equal meals fed at 0600 and 1600 h. After 3 weeks of adaptation, rumen samples were taken at 4-h intervals in two 24-h periods. In the first 24-h period samples from the swards (80-90% Lolium perenne) were taken immediately before rumen sampling. Total sugar content of herbage increased during daytime with the highest content directly before sunset. Patterns of ruminal pH values were not different between treatment and values were minimum at 2400 h. Volatile fatty acids (VFA) and ammonia peaked at 2400 h. Extra high- or low-starch concentrate decreased ruminal content of ammonia 19, 13 and 12 mmol/litre for treatments 1HS, 7HS and 7LS and also decreased branched-chain VFA. Acetate:propionate and non-glucogenic:glucogenic ratios within VFA and percentage of milk fat were lowest for treatment 7HS. (Abstract retrieved from CAB Abstracts by CABI’s permission)

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