3 August 2001

Rumen pH the key calculation

A SYSTEM to predict how different feeds will act in the cows rumen to ensure its function is not compromised should prove a useful ration check, believes SACs Nick Offer.

As part of the Feed into Milk project, a computer program which calculates the likely rumen pH when a ration is fed has been developed.

Dr Offer says the system is based on Belgian research, modified to suit typical UK feeds. For each feed included in the ration it predicts a potential acid load (PAL). This PAL value is based on its buffering capacity.

Buffering capacity varies because of the way feeds ferment in the rumen, he says. "Cereals have a high PAL because they ferment, but ingredients with high mineral content ferment less, so have a low PAL." PAL values for concentrates have been predicted in the lab for the computer model and values for silages are based on forage analysis results.

When a cow chews feed, she produces saliva which controls rumen pH. The amount she chews is influenced by fibre content of feeds, so this is also an important factor, he adds.

"The model looks for the promotion of chewing from the fibre content of feeds and balances it with the PAL to give a single figure indicating rumen stability."

What figure is adequate for the cow on the diet will depend on her yield and how the diet is fed. "When a total mixed ration is fed the Rumen Stability Value requirement is lower than when concentrates are fed twice a day in the parlour," says Dr Offer. &#42