Strategies for increasing energy density of dry cow diets'

The objective of this trial was to compare the effects of increasing dietar y energy density from 1.51 to 1.65 Mcal/kg of dry matter (DM) by replacing forage with concentrate or by further increasing concentrate via the substi tution of corn silage and alfalfa silage by a mixture of straw, starch, and soybean meal. Our hypothesis was that the latter diet would be more glucog enic while increasing rumen fill and be potentially desirable for transitio n cows. Nine far-off dry cows (greater than 3 wk before parturition at the end of the trial) were fed three diets: low energy diet, [LE, 1.51 Mcal/kg of DM, 14.0% crude protein (CP) and 35% non-fiber carbohydrates (NFC)], hig h energy diet, (HE, 1.65 Mcal/kg of DM, 13.9% CP and 39.5% NFC) and high en ergy diet, where a portion of alfalfa and corn silage was replaced by straw , soybean meal, and cornstarch (HES, 1.65 Mcal/kg of DM, 13.5% CP and 40.5% NFC). The experiment was a replicated 3 x 3 Latin square design with 21-d periods. Six cows from two squares were used to examine kinetics of DM disa ppearance from nylon bags suspended in the rumen. Two contrasts of interest were: LE versus HE, HES (effects of energy density) and HE versus HES (met hod of increasing energy density). Increasing energy density increased the potentially degradable (B) and decreased the undegradable (C) DM fractions of the diets. Because HES had greater B and a faster rate of degradation of fraction B (k), effective rumen degradable DM (ERDDM) was higher in HES co mpared to HE. Cows fed high energy diets had greater DM intake. No differen ces in DM intake were observed between HE and HES. Rumen volume or DM pool sizes were not affected by treatment. High energy diets increased total rum inal fluid volatile fatty acid concentration compared with LE. Propionate c oncentration was higher in cows fed high energy diets compared with cows fe d LE. The partial replacement of alfalfa and corn silage by straw, soybean meal, and cornstarch further increased propionate concentration. The greate st increase in serum insulin concentration following feeding was observed i n cows fed HE. Cows consuming high energy diets had lower plasma nonesterif ied fatty acids (NEFA) before and after feeding. The HES diet was less effe ctive in decreasing plasma NEFA concentration after feeding compared to HE. In conclusion, increasing diet energy density of far-off dry cows positive ly affected DMI, ruminal propionate, serum insulin, and plasma NEFA. Increa sing energy density with a blend of feeds that represent extremes in rates of carbohydrate fermentation may be a strategy to provide greater amounts o f glucogenic precursors. Applicability of this strategy should be examined in transition cows.