Wz. Yang et al., Effects of grain processing, forage to concentrate ratio, and forage particle size on rumen pH and digestion by dairy cows, J DAIRY SCI, 84(10), 2001, pp. 2203-2216
Dietary factors that alter the intake of effective fiber were evaluated for
their effects on rumen fermentation, digestion, and milk production using
a double 4 x 4 quasi-Latin square design with a 2(3) factorial arrangement
of treatments. The dietary factors were extent of barley grain processing,
coarse (1.60 mm) or flat (1.36 mm); forage-to-concentrate (F:C) ratio, low
(35:65) or high (55:45) (dry matter basis); and forage particle length, lon
g (7.59 mm) or short (6.08 mm). Eight lactating cows with ruminal and duode
nal cannulas were offered ad libitum access to a total mixed diet and milke
d twice daily. Dry matter intake was increased by increasing the extent of
grain processing. Mean rumen pH was lower for cows fed flatly rolled barley
than for cows fed coarsely rolled barley, whereas F:C ratio or forage part
icle size had no effect on rumen pH. Rumen pH was not correlated with effec
tive NDF intake but tended to be correlated with digestibility of starch in
the rumen. Total tract digestibilities of dry matter, organic matter, star
ch, and neutral detergent fiber were increased by feeding flatly rolled bar
ley or low F:C ratio diets. Milk yield and milk protein content were higher
in cows fed flatly rolled barley or low F:C ratio diets. Milk fat content
tended to increase with high F:C ratio or long forage particle length but w
as reduced by feeding flatly rolled barley. In this study, extent of grain
processing and intake of ruminal available starch were the most influential
factors affecting milk production. Reducing the ratio of F:C improved tota
l digestion and actual milk production. Forage particle length had minimal
impact on digestibility and milk production.