Altering physically effective fiber intake through forage proportion and particle length: chewing and ruminal pH

Area of Science:

• Ruminant nutrition and metabolism
• Dairy cattle health and management
• Feed science and technology

Background:

• Ruminal acidosis is a metabolic disorder in dairy cows, often linked to high-concentrate diets.
• Physically effective neutral detergent fiber (peNDF) is crucial for maintaining ruminal health.
• Forage particle length (FPL) and forage-to-concentrate (F:C) ratio influence peNDF intake and ruminal pH.

Purpose of the Study:

• To evaluate if increasing dietary peNDF content reduces the risk of ruminal acidosis in lactating dairy cows.
• To assess the impact of forage particle length (FPL) and F:C ratio on ruminal pH and chewing activity.

Main Methods:

• A replicated 4x4 Latin square design with 8 ruminally cannulated lactating dairy cows.
• Treatments involved a 2x2 factorial arrangement of short and long FPL alfalfa silage with low (35:65) and high (60:40) F:C ratios (dry matter basis).
• Dietary peNDF was measured using the Penn State Particle Separator (2 or 3 sieves).

Main Results:

• Increasing F:C ratio and FPL increased peNDF intake.
• Higher F:C ratio increased chewing time; increased FPL increased chewing time only in high-forage diets.
• Mean ruminal pH increased with higher F:C ratio and FPL. Low F:C diets resulted in prolonged periods of low ruminal pH.

Conclusions:

• High risk of ruminal acidosis in cows fed low F:C diets, especially with finely chopped silage.
• Dietary peNDF intake is a reliable indicator of ruminal pH status in dairy cows.
• Increasing forage proportion effectively prevents acidosis via increased chewing, altered meal patterns, and reduced acid production.