The health, welfare and performance of cattle as ruminants depend largely on favourable conditions in the rumen. Feeding is of particular importance for rumen function and health. In bull fattening, the structural properties of the feed play a key role. This guide aims to cover the most important aspects of structural fibre provision in the feeding of fattening bulls.

Why is the provision of structurally effective fibre a problem in intensive bull fattening? Why is subacute ruminal acidosis becoming more prevalent?

• Very high proportions of maize silage (with high starch content and little structural effect) in the ration, often even as the sole roughage
• Intensive feeding with a high proportion of concentrate in the ration to enable high growth rates
• Additional structural components such as straw or hay are easily rejected in TMR

• a feed structure that promotes rumination and the salivation of the feed (saliva also has a buffering effect),
• a ration composition that leads to pH values in the rumen that are as stable as possible (normal range between pH values of 5.8 and 6.5) and
• a stratification of the rumen contents

• Rumination is significantly reduced in duration and intensity
  • less salivation
  • low pH values resulting from the conversion of rumen-degradable starch (sugar) into acids, which are insufficiently buffered
  • pH levels in the rumen fall below critical levels

→ Subacute ruminal acidosis (over-acidification) with adverse effects on health

• reduced feed intake
• poorer feed conversion (particularly in fibre digestion)
  • Poorer adhesion of bacteria to the fibres at lower pH levels
  • Shift in the microbial community towards lactate-producing (lactic acid-producing) bacteria
  • Damage to the mucous membrane of the rumen wall
• Deficiency in water-soluble B vitamins
  • At low pH: decrease in B-vitamin-producing bacteria alongside a high demand for B-vitamins for carbohydrate digestion
• Restlessness in bulls, stress
• Reduced performance
• Health problems
  • As certain bacteria die off, toxins (endotoxins) are released, which enter the bloodstream in increased quantities via the damaged rumen mucosa. This can lead to diseases throughout the entire organism. Diseases promoted by these toxins include, for example, the development of laminitis and tail tip necrosis (Heers et al. 2017)

_{Click on the individual graphics to view the necessary measures.}

Use of chopped straw

• Even small amounts (200–500 g per animal per day) are effective
• Cut only short (max. 3–4 cm, theoretical cut length shorter), mix in thoroughly

Use of alfalfa, clover-grass and grass silage

• Test the grass silage and calculate the ration! Note: The effect of texture is often overestimated!
• is readily eaten, provides additional crude protein
• Only the best quality for high weight gains
• Proportion of roughage DM depends on energy content

Use of shredded silage

• Chop length 20–30 mm with intensive processing of the plant residues.
• Intensive grain processing can improve the utilisation of starch from the maize grain.
• Predominantly positive results in trials (Bunk, 2021), but no final assessment for practical application yet
• Requires more silage space, higher compaction and greater feed-through during removal!
• Note: Chopping technology only available regionally
• Avoid feed selection
  • Observe feeding behaviour
  • Mix thoroughly without turning the feed into a paste, adding water if necessary
  • Replace pellets with meal feed (results in a more homogeneous mixture)
  • Check for feed residues
• Use of rumen buffers (e.g. sodium bicarbonate)
  • Only as a ‘last resort’ to alleviate symptoms
  • The cause of ruminal acidosis must be addressed separately