Feed Additives: A Veterinary Perspective

In an already volatile environment, dairy profit margins vary as milk prices and feed costs shift annually. Feed costs represent the largest input cost (an estimated 35 to 70% of the variable cost) in the production of milk. As a group of feed ingredients, feed additives can cause a desired physiological response in a non-nutrient way, such as pH shift, growth or metabolic modifier, and will usually be cost-beneficial.

- Dr Chris van Dijk

We, however, need to recognise the fact that feed additives are not always a requirement or guarantee for high productivity or profitability. This article will, in part, focus on some of the positive effects of feed additives, as well as some of the negative outcomes that we need to be aware of.

Buffers

Buffers, such as sodium bicarbonate, help to reduce rumen acidity and can increase dry matter (DM) intake, rumen microbial protein production, and fiber digestion, resulting in increased milk and milkfat production. Usually, a little excess will not have a major effect on the cow, but palatability could become an issue. Feeding excess sodium leads to an increase in excretion with the usual environmental concerns (soil salinity and toxicity to plants).

Magnesium oxide

Magnesium oxide helps to raise rumen pH, increases the uptake of plasma acetate and fat by the udder, and increases milk fat percentage. It is rarely recommended in place of sodium bicarbonate but is often fed in addition to it. Dietary magnesium should not exceed recommended levels, as cows are likely to get black diarrhoea.

Methionine

Methionine is often included as methionine hydroxy analog (MHA) in buffer packages for lactating cows, because of research shows that it increases milk fat production. Research indicates that 40% of liquid MHA escapes the rumen, when it is fed as a large single dose and, therefore, should be fed in more but smaller doses.

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