5 June 1998

KNOWING DIGESTION RATES…

UPDATES to the Cornell University cow rationing programme will include an improved prediction of dry matter intake and fibre digestibility, and it will become easier to use.

According to researcher Alice Pell of Cornell University, Ithaca, New York State, they have tried to solve the digestion rate issue, so that the Cornell Net Carbohydrate and Protein System (CNCPS) can predict DM intake more accurately. This also involves predicting the rate of passage of feed through the cow and rumen availability.

She accepts that this feeding programme is more complicated than some. "It is mostly used for trouble-shooting in herds where you cannot identify whats going wrong," she says, "but is widely used by nutritionists around the world to fine-tune rations for high yielding cows.

"There is a constant debate about whether to simplify or add more biology. But we want the programme to be used. The current programme is more of a ration evaluator; the new one will have a linear programme to act as a ration balancer, and as such will be more user friendly."

Unlike many rationing systems, to form its predictions the Cornell feeding model requires a lot of information on feeds, cows in the herd and herd environment. For example, climate and housing inputs are needed so the programme can allow for increases in cow maintenance requirements. It also helps to input an idea of actual cow intakes achieved on their current ration, she adds.

Another major factor that determines what cows achieve from a ration is the digestibility rates of different fractions of carbohydrates. These fractions include sugars and organic acids, starch and pectin, digestible and undigestible fibre.

It has taken five years to develop a method to assess digestion rates, she says.

This involves culturing samples of feed in rumen fluid and measuring the gas generated as methane and carbon dioxide. Forages take 48 hours to assess and concentrates 24-48 hours.

"This wont reveal the different fractions, but by pre-extracting digestible fibre and incubating it or leaving in the starch, pectin and fibre we can get information for three of the four carbohydrate fractions."

The nutritive value of the forage, therefore, can be assessed more accurately – using the information on the different fractions allows more accurate rationing.

It has taken five years to develop a method to assess digestion rates, says

Alice Pell.