Effects of physically effective fiber on digestive processes and milk fat content in early lactating dairy cows fed total mixed rations.

Publication Type

Journal contribution

Authors

Zebeli, Q., Tafaj, M., Steingass, H., Metzler, B. and Drochner, W.

Year of publication

2006

Published in

Journal of Dairy Science

Band/Volume

89/2

Page (from - to)

651-668

Keywords

chewing activity, dairy cow, physically effective fiber, rumen pH, TMR-Fütterung

Data from recent research studies were analyzed quantitatively, and the random effect of experiment was assessed to define the physiological responses of dairy cows in early lactation to intake of physically effective neutral detergent fiber (peNDF). All studies were conducted with lactating Holstein cows (84.8 ± 3.54 days in milk) in Latin Square designs, and feeds were offered ad libitum as total mixed rations (TMR). The peNDF was estimated by 2 measurement techniques, the NDF content of TMR multiplied by amount of dry matter (DM) retained on a 1.18-mm screen (peNDF>1.18) and NDF content of TMR multiplied by the proportion of DM retained by 19- and 8-mm Penn State Particle Separator screens (peNDF>8). Other factors, including concentrations of NDF, forage NDF, non-fiber carbohydrates, the amount of digestible organic matter of forages (FDOM), and the intake of ruminally degradable starch (RDSI) from grain in the diet were also investigated. The studied animal response variables included feed intake, ruminal fermentation, chewing activity, fiber digestibility, and milk production and composition. The ruminal pH (day mean) in this study ranged from 5.30 to 6.59. Using peNDF>1.18 approach, the requirements for physically effective .fiber in high-yielding dairy cows fed TMR in an ad libitum intake were estimated to be about 19% of ration DM or 4.1 kg/d or 0.6 kg/100 kg of body weight to maintain a ruminal pH of about 6.0. When peNDF was measured as peNDF>8, ruminal pH responded in a quadratic fashion but the confidence of estimation was lower (R2 = 0.27) compared with the peNDF>1.18 approach (R2 = 0.67). Results of these data analyses showed that peNDF>1.18 is provided a satisfactory estimation of the mean ruminal pH (R2 = 0.67) and NDF digestibility (R2 = 0.56). Furthermore, peNDF>1.18 was poorly, although positively, correlated to daily chewing (R2 = 0.17), and rumination (R2 = 0.24) activity. On the other hand, results from these analyses showed that milk parameter