Herbage intake and ruminal digestion of alfalfa: a comparison between strip and zero grazed dairy cows

Abstract

Twelve Argentine Holstein dry cows under two alfalfa feeding regimes, direct grazing (DG) and swath grazing (SG, wilted to 35–40% dry matter (DM) content) were used to study dry matter intake (DMI), rumen physical breakdown of forage particles and its digesta kinetics. Distribution of rumen particle size was described using the log of its standard deviation. Fractional rate of passage was estimated using Cr-mordant as neutral detergent fiber (NDF) marker. The in vitro DM digestibility in DG was consistently higher than in SG (70.2 vs. 65.6%). However, DMI and organic matter intake (OMI) was higher in SG than in DG ( P<0.05). Animals in DG ate 16% more crude protein and 13% less NDF than those in SG. Due to the DMI difference, energy intake in DG was 17.6% lower. Except for molar proportion of volatile fatty acids, there were no differences ( P>0.05) for any other rumen variable. Analysis of the distribution of mean particle size showed no significant main effects. Mechanical mowing and wilting of alfalfa increased the efficiency of pasture utilization and voluntary DMI and produced no changes in the rate of passage. Under DG, dry matter intake of alfalfa in autumn was more influenced by forage moisture content than by the rate of fermentation and fractional passage through the reticulo-rumen.