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Department of Animal Science, University of Manitoba, Winnipeg, MB, Canada R3T 2N2
Corresponding author: J. C. Plaizier; e-mail: plaizier{at}Ms.UManitoba.CA.
Barley silage, cut at the early dough stage, was chopped long (19 mm) or short (10 mm), ensiled, and incorporated into total mixed rations (TMR). The TMR contained (dry matter [DM] basis) either 58.0 or 41.4% concentrate and either short- or long-chopped barley silage. Reducing chop length of barley silage decreased the proportion (asis basis) of TMR particles retained by the 8- and 19-mm screens of the Penn State Particle Separator (PSPS) from 66.9 to 52.7% in the high concentrate TMR and from 74.8 to 60.9% in the low concentrate TMR. Chop length reduction decreased dietary physically effective fiber, calculated as the NDF retained by the 8- and 19-mm screens of the PSPS, from 29.2 to 25.2% DM in the high concentrate TMR and from 34.9 to 30.6% DM in the low concentrate TMR. Reduction in chop length did not affect rumen pH, total rumen volatile fatty acids, milk yield, and milk composition, but increased DM intake from 19.4 to 20.1 kg/d at the high level of concentrate and from 16.9 to 17.7 kg/d at the low level of concentrate and increased rumen propionate. Increasing the concentrate inclusion rate reduced rumen pH from 6.52 to 6.35, did not affect total volatile fatty acids, reduced the acetate-to-propionate ratio from 3.1 to 2.7, increased milk yield from 28.7 to 31.3 kg/d, reduced milk fat content from 3.48 to 2.94%, and increased milk protein content from 3.11 to 3.27% across chop lengths.
Key Words: chop length • barley silage • physically effective neutral detergent fiber • dairy cow
Abbreviation key: ADIP = acid detergent insoluble protein, peNDF = physically effective NDF, peNDF>1.18 = peNDF measured as the proportion of DM retained by a 1.18-mm screen multiplied by dietary NDF, peNDFM = peNDF measured from tabular values of chewing time, peNDFNDF = proportion of dietary NDF retained by the 19- and 8-mm PSPS screens, peNDFPS = proportion of DM retained by the 19- and 8-mm PSPS screens multiplied by dietary NDF content, PSPS = Penn State Particle Separator
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