19 September 1997

UKRATIONING SYSTEM IN AMERICAN STYLE?

Could US technology give the UK a reliable rationing system for high yielding cows? Sue Rider reports

RESEARCH into new rationing systems for dairy cows is at least five to six years overdue.

Thats according to independent nutritionist Ivor Bending, who specialises in rationing high yielding dairy cows and whose clients include some of the top milk producing herds in the UK.

He predicted that the metabolisable protein system currently used to ration dairy cows in the UK would fail to work efficiently for feeding high yielders. Experience in the field and the results of extensive research have proved him correct. The MP system is underrating the protein requirements of cows averaging more than 25 litres.

Given that the increasing genetic merit of the national herd is driving yield upwards there is an urgent need for a reliable rationing system for such animals, he says.

The MP system is a step forward from previous rationing systems in that it recognises that the energy needs of the rumen bugs must be met to enable them to produce the all-important microbial protein. But Mr Bending has long felt such a system fails to address the dynamic nature of the cows metabolism and the different rates of carbohydrate break-down.

Mr Bending now uses the Cornell Net Carbohydrate and Protein System to formulate diets for his clients, many with herd averages of 9000 litres and above.

Developed in the US over the last 15 years, it is a new style of cow feeding which considers factors such as the physiology of the cow, the environment, effective fibre, degradable carbohydrate and protein, excess proteins, amino-acid balance and energy reserves. "Its looking more closely at whats happening in the cow, and especially the rumen," says Mr Bending (see panel on CNCPS).

He maintains that the key to rationing high yielders is maximising microbial protein. "There is nothing as good as the Cornell model for doing that," he says. Evidence comes from five years studies in the US, Israel and Italy, where Mr Bending and fellow nutritionists have formulated data from high yielding cows using the existing rationing system in each country and also the Cornell model.

"We found that the Cornell results were best able to fine-tune diets to improve microbial protein production – thereby reducing the total amount of protein fed and the cost of the ration. It worked in the field and can do a better job than us."

The National Research Council in the US has adopted the system for rationing beef cattle and is currently evaluating it for use as the national dairy cow rationing system. The model will also be evaluated in the UK alongside other worldwide rationing systems as part of a new research project – currently known as Project 42 – shortly to be commissioned by MAFF, the Milk Development Council and the feed industry and carried out by the SAC, DANI and ADAS.

Mr Bending believes its only time before the Cornell system is adopted in the UK – maybe after improvements to the model by UK scientists. Success of this new feeding model will depend on accurate forage description.

"The CNCPS system works when used by experienced nutritionists alongside laboratories providing accurate and comprehensive forage analysis," says Mr Bending, who stresses the urgent need for standardisation of forage analysis techniques in the UK.

"There are few commercial labs in the UK providing suitable data on forage for use in the latest computer models. Grass silage analyses are particularly inadequate, with greatest errors on the most important carbohydrate fraction – neutral detergent fibre – a key factor in determining grass silage intake."

It is maximising intakes of high quality forage that is the secret to feeding high or low yielding dairy cows, says Mr Bending. And the more forage in the diet the more important it is to get an accurate description of the nutritive value of that forage.

Mr Bending will be working with ADAS Bridgets, therefore, as part of Project 42, to evaluate UK feeds and forages for use in dairy cow rationing systems.

Two labs – one in UK and one in US – are using standard procedures laid down by the researchers for analysing the different nutritive values of forages such as NDF%, DM%, CP%, pH and amino acids

Forage samples are being collected annually based on a classification system developed by Mr Bending. After five years of data the classification will allow more accurate prediction of the intake potential and nutritive value of forages. "It recognises that plants are products of their own environment and the forage quality will vary from season to season depending on temperature, light and water availability," says Mr Bending.

Once the industry has an accurate description of UK forages for use in the Cornell model, the next step is to determine the rates of passage and digestion of the different carbohydrate fractions, such as NDF – the fibre – and the non-structural carbohydrates, starch and sugars.

This work is underway, at the ADAS Feed Evaluation Unit.

NEW RATIONING SYSTEM

&#8226 Improved model long-overdue.

&#8226 US Cornell system works well.

&#8226 Reduces total protein fed and ration costs

&#8226 New project will evaluate it.

The key to rationing high yielders is maximising microbial protein and there is nothing as good as the Cornell model for doing that.

WHAT IS THE CORNELL MODEL?

THE cows rumen, if working at full rate, can maximise dry matter intake and supply up to 75% of the protein needs of the milking cow through the production of large quantities of microbial protein. The Cornell Net Carbohydrate and Protein system is unique in that it tries to predict in detail, what happens in the rumen, says Rosemary Mansbridge, ADAS Bridgets, Winchester, Hants. It is, she says, the only practical dairy feeding system that includes a rumen model which considers the growth of the two major bacterial populations within the rumen – fibre and non-fibre digesting. The system describes feeds in terms of the amount of energy and protein supplied to the rumen bacteria which can be used for microbial growth. It goes further than current systems by sub-dividing energy and protein sources into different forms. Rumen energy sources are identified as either sugars, starch, or fibre and protein sources as either ammonia, soluble protein, or fibre-bound protein. Each form has a different fate within the rumen. Some forms of energy and protein are very slowly broken down in the rumen, and may pass into the rest of the digestive tract, before this breakdown is complete. Other forms – sugars, ammonia, soluble protein – break down very rapidly and rarely, if ever appear, beyond the rumen. The system uses the results of this more detailed rumen model to predict the amounts of nutrients available for maintenance and production. A better understanding of the processes occurring in the rumen, should allow a more efficient use of raw materials. Further testing of the system on commercial dairy farms is required, says Miss Mansbridge, but initial experience suggests that the model offers opportunities to better feed the high production dairy cow.