Effect of sorghum grain processing on the performance and metabolism of lactating dairy cows.

Abstract

Experiments were conducted to compare the effect of processing grain sorghum either by dry rolling or steam flaking on the performance and metabolism of high producing dairy cow. In an 80 d trial, following a 14 d pretrial for covariance adjustments, 36 Holstein cows divided in 4 groups were fed a total mixed ration (37 forage:63 concentrate) prepared with one of the following four grains: Steam-rolled corn (CORN), dry-rolled sorghum (DRS), steam-flaked sorghum (SFS) and an equal mixture of DRS and SFS (MIX). Grain comprised 42.2% of diet DM. In the last 14 d of the experimental period a digestibility trial was conducted. There was no difference (PS < .05) in milk, FCM or milk fat production across treatments. Because cows on SFS consumed less DM (P < .05) than those on MIX, the gross efficiency of FCM production was higher, (P < .05) for SFS. Other treatments were intermediate for DM intake and FCM efficiency. Milk protein percentage and production were higher (P < .05) for SFS compared to DRS, while lactose and SNF were higher (P < .05) for SFS compared to DRS, while lactose and SNF percentages were the highest (P < .05) for SFS compared to other diets. Apparent digestibility of starch from SFS was the highest (P < .01) and that from DRS was the lowest while apparent digestibility of the fiber components and of CP were lower (P < .05) for SFS compared to DRS. Improvement in FCM efficiency and milk protein production was probably due to increased starch degradability. In a second experiment, the same diets used in the lactation trial were fed to 4 duodenally cannulated cows in a 4 x 4 Latin square design. Total tract digestibility of starch was higher (P < .05) for SFS than MIX and DRS diets and tended to be more digested in the rumen than starch from other diets. Cows fed SFS also tended to more efficiently convert dietary CP digested in the rumen to BCP and to have higher BCP flow to the duodenum. Cows on the SFS diet had highest (P < .01) fecal pH, tended to have the lowest amount of fecal protein and the highest apparent digestion of N.