PKE still a useful supplement

PKE can be useful in a season when cow welfare and milk production must be ensured, it says.

Fonterra recommends a PKE maximum of 3kg/day/per cow as a voluntary guideline for its suppliers.

"PKE is a dry, gritty meal with a soapy smell and has low palatability until cows get a taste for it. However, PKE has reasonable levels of energy (ME) and protein, and is relatively easy to introduce to cows over a range of farm systems.

"The profitability of PKE depends on its price relative to milk price and the utilisation of PKE and pasture."

Palm kernel extract (PKE) is a by-product of the palm oil industry in South East Asia.

It is derived from the nut of the palm fruit after the oil is either mechanically extracted (as is most PKE imported to NZ) or solvent extracted (lower nutritive value).

Is palm kernel a low digestibility feed and should it matter?

DairyNZ says there is no single, ideal measure of feed quality. However, in NZ metabolisable energy (ME) is the factor limiting milk production in most situations. Therefore, ME content (MJ/kg DM) is the best measure of feed quality for most farmers. It does not matter whether a supplement contains fibre, starch or sugar. The cost of each MJ ME should dictate how a farmer decides which supplement to buy.

Palm kernel extract contains about 11.0 - 11.5 MJ ME (mechanically extracted) and is therefore a reasonable quality feed for dairy cows when pasture is short.

DairyNZ quashes suggestions that PKE should be avoided as a feed for dairy cows because it has a low digestibility (about 50%) and, as a result, will not promote the growth of rumen microbes.

It says cows survive and produce on:

a. The waste products of rumen fermentation (volatile fatty acids)

b. The micro-organisms that have grown during rumen fermentation

c. Feed that was not fermented (ie bypasses the rumen).

As a result, there are multiple measures of feed quality, including:

1. How much is digested (digestibility)

2. How much energy is available for production (metabolisable energy or net energy)

3. How much protein is in the feed (crude protein, true protein, soluble protein)

4. How much fat is in the feed

Minerals and vitamins.

All these are important in varying degrees, depending on what is lacking from the diet.

Digestibility

The digestibility of the feed refers to how much of the feed is digested in the rumen (rumen digestibility or rumen degradability) or along the entire digestive tract (dry mater digestibility).

The rumen digestibility of a feed is important for determining the growth of rumen micro-organisms. These supply protein and some energy to the cow.

However, there is a long digestive system after the rumen, in which proteins, fats and some sugars are digested and absorbed. Therefore, dry matter digestibility is a better measure of feed quality as it takes into account the whole digestive system and not just the rumen. Metabolisable energy is estimated from some measure of dry matter digestibility.

Protein

Protein is important because it provides the rumen micro-organisms with nitrogen to grow, the protein that bypasses the rumen is used directly by the cow, and because it also provides some energy.

Fat

Fats and oils cannot be used by the rumen micro-organisms and therefore do not promote microbial growth. They are instead used directly by the cow as an energy source.

What about PKE?

DairyNZ says PKE is not very digestible in the rumen. Estimates of rumen digestibility range from 50 to 60%.

However, this does not accurately portray the feed value of PKE for dairy cows.

The feed value in PKE comes from the ruminal digestion of fibre, some ruminal digestion of protein (55 to 60%), the protein digested in the small intestine (40 to 45%), and the fat – although the minerals are also important.

In most situations, grazing dairy cows are short of ME. They are only rarely short of metabolisable protein (protein that reaches the small intestine). Therefore, changing supplement to increase the growth of rumen micro-organisms to further increase metabolisable protein will not be beneficial.