By Lorna MacPherson, Dairy consultant, SRUC, and Jennifer Flockhart, Dairy nutrition researcher, SRUC

BY-products from the food and drink industry can play a significant and cost-effective role in dairy herd nutrition.

However, their use in keeping costs down must not be allowed to affect milk quality. Increasingly, milk contracts are rewarding kg of fat and protein produced and to maximise the milk price producers must strike a balance between optimising milk yield, composition and feed costs.

Different industry by-products can influence levels of milk solids when included in the ration at appropriate levels.

Distillery by-products include wet feeds, such as draff, brewers grains and Trafford Gold, or liquid pot ale syrup; or dry material, such as distiller’s dark grains (based on barley, maize or wheat).

Wet by-products and distillers dark grains contain unsaturated oils or fatty acids which, when fed at high levels, can depress milk fat by suppressing rumen function and reducing fibre digestion. However, their protein and energy content are useful in encouraging milk yield.

Of the dark grains available, maize-based products contain the highest fat content – up to 12% on a dry matter basis.

The key to using distillery co-products is to avoid depressing milk fat. Feeds that are known to promote milk fat content include sugar beet pulp, soya hulls and citrus pulp.

Dairy rations should contain no more than 6% fat on a dry matter basis and unsaturated fatty acids should make up less than 3% of the total diet.

There are also some by-products available that can have a positive effect on milk protein, which is influenced by increasing the supply of rumen fermentable energy. This can come from by-products such as biscuit meal, bakery and bread waste.

Whey permeate, a sugary liquid co-product from cheese manufacture, has also been proven to increase milk protein content.

Different co-products from food-oil manufacture (for example soya bean meal, rapeseed meal, and maize germ meal) are sources of protein, both rumen-degradable and by-pass (undegradable) protein. These are good ingredients for promoting milk yield.

When feeding certain by-products, especially at high levels it is vital to manage rumen pH and minimise the risk of acidosis if you want to reduce the risk of depressed milk fat. Rumen microbes require a pH over 6 to thrive and effectively digest fibre to produce acetate, the precursor for milk fat production.

Below pH6, fibre digesting bacteria start to die off and the end products of fermentation can depress milk fat production in the udder.

Many factors related to nutrition and nutritional management are involved in managing rumen pH:

• Avoid feeding too much starch and sources of starch that are rapidly degradable (eg bakery and cereal by-products and finely ground cereals, especially wheat).

• Minimise sorting of the TMR (common in dry rations over 50% dry matter). This leads to cows eating less effective fibre, favouring finer particles of concentrate/grain, reducing cud chewing. Process forages adequately and add liquid feeds or water. Compact feeding, where the concentrate portion of the ration is soaked in water for 12 hours before mixing in forage, can eliminate sorting.

• Provide sufficient effective fibre to promote good cudding behaviour and saliva production. This will increase the supply of natural buffer from sodium bicarbonate in saliva to the rumen. Avoid over processing forages and aim for a minimum forage to concentrate ratio of 40:60, with NDF from forage a minimum of 20%.

• Avoid slug feeding when cows consume large volumes of feed. This not only applies to parlour cake but also the TMR, if the cow has been unable to access feed for an extended period of time. Once the cow starts eating again and consumes a large volume of feed, her rumen is not as full or as well buffered, leading to a drop in pH. Ensure feed is available for at least 22 hours/day, push up feed regularly (every two hours during the day), minimise time away from the feedbunk and ensure adequate feeding space (30-35 inches for milking cows).

* For further advice on feeding by-products and nutrition of your dairy herd, please contact your local SAC consultant.