Is your Diet in good physical shape?

Dairy farmers should pay as much attention to the physical composition of the diet as they do to the nutrient analysis if they want to get the most from their cows this winter according to NWF Agriculture Technical Manager Tom Hough.

“Ask a dairy farmer what the most important aspect of rationing cows is and you will get answers like maximising dry matter intakes, providing enough energy and protein for the expected yield levels, feeding plenty of forage and keeping the cost down,” observes Mr Hough.

“Few, if any, will comment on making sure the physical structure of the diet is correct, but new research from Frank Wright suggests that farmers should pay as much attention to the physical composition of the diet to produce cost effective, nutritionally sound rations.”

All diets, whether silage and cake in the parlour or a full-blown TMR are made up of a number of ingredients with different particle sizes. According to Mr Hough the importance of diet physical composition is not just the particle size in the diet as fed, but the size of the particles that end up in the rumen. This determines the extent of rumination, chewing and rumen pH and in turn influences dry matter intakes.

“If a diet contains too many long particles the effect will be to slow down the rate of digestion and depress dry matter intakes. If the ration contains too many fine particles the outcome will be a rapid fermentation and the onset of acidosis. The aim is to get the correct balance of particles.”

“It is impossible to determine the particle sizes a diet will produce based on visual inspection but sieving the diet can give a good approximation of how the ration will arrive in the rumen,” Mr Hough explains.

For many years farmers in America have been sieving diets based on work carried out at Penn State University which provides a target profile for the proportion of different sized particles in the diet. The research by Frank Wright has taken the Penn State system and adjusted it for UK diets and conditions. The result is a mechanism to assess the physical breakdown of diets and to compare what is being fed to targets and to modify diets accordingly.

The system also predicts what the breakdown of particle sizes will be when the diet is formulated which mean diets can be developed to deliver both the chemical and physical formulation to drive optimum performance.
“NWF worked with Frank Wright to evaluate this system last winter and we were able to fine tune diets based on the results. The target is to have 45% - 55% of the diet in the top two, coarser sieves.

“Where diets fell below this target we were able to increase the long fibre, often by adding chopped straw to offset the effects of acidosis. In diets where there was excess long fibre it was possible to increase the proportions of maize or wholecrop silage to speed the passage of feed through the gut and promote higher intakes.”

Mr Hough adds that the principle of sieving diets is also useful as a way to check for ration sorting and the accuracy of the mixer wagon. He recommends farmers sieve the ration at several points along the feed fence directly after the mix has been put out. If the distribution of particles is inconsistent along the feed fence then there may be a problem with the mixer or how it is being used.

“Similarly if you sieve a sample of the diet four hours after it has been put out and find too much in the long particle sieve and too little in the fine fragment one, then it is likely that the cows are sorting the diet which can quickly lead to poor feed efficiency and even acidosis.

“Assessing diets on physical composition is a technique which will help farmers get the most from their diets. It does not replace formulations based on chemical composition but is a valuable additional tool,” Mr Hough concludes.