Use marginal feed rate to avoid costly mistakes

Dairy farmers considering pushing for extra litres to chase extra milk income must use marginal feed rate instead of average feed rate to calculate if it’s financially viable.

Marginal feed rate is the amount of concentrates fed relative to any litres over and above what are already being produced by the cow on her current ration.

It is a very different rate to that needed to produce the cow’s normal yield.

Promar International’s senior consultant Tim Harper says average feed rate can be misleading and instead advises farmers considering increasing production to use marginal feed rate.

“For a cow producing an average yield of 30 litres on 10kg of cake, her average feed rate is 0.33kg/litre. If a farmer decides to increase concentrates by 2kg, calculations based on the average feed rate will lead him to believe he will get a further six litres from the feed.

“In reality the farmer will likely only get two extra litres from 2kg of additional concentrates, so the marginal feed rate is much higher at 1kg/litre in this example,” he says.

Based on a current milk price of 32p/litre and a concentrate price of £250/t, the producer could seriously overestimate the margin over additional concentrate costs, which would total 144p, or 24p/litre when using the average feed rate calculation.

This compares to a total of just 14p/litre, or 7p/litre on the more accurate marginal feed rate (see below).

“By using marginal feed rates, farmers can make a more pragmatic judgement as to whether additional feed will be cost effective. If they’re using average feed rate they will come to the wrong conclusion,” adds Mr Harper.

He stresses there’s no such thing as a “standard” marginal feed rate and therefore each farm must carry out an individual assessment as there are so many variable factors.

Effect of higher concentrates

Mr Harper says feeding increasing amounts of concentrates will replace intake of other parts of the diet, such as forage.

He believes this has two key effects on milk production. Firstly the cow will eventually reach a point where she can’t physically increase her dry matter intake any further, limiting milk production.

And secondly the cow becomes unhealthy due to an unbalanced ration, causing yield to drop. But there is usually a negative financial effect before cow health is endangered, he warns.

He says close monitoring is essential. The bigger the change the more gradually it needs to be made, he says.

When monitoring the success of these alterations, simple overnight changes should be trialled for seven to 10 days, whereas changes taking two weeks to make should be closely scrutinised for 10-14 days after adjustments have finished, he explains.

Mr Harper says farmers should not be captivated by milk prices and should liaise with their nutritionist or adviser and a vet before making any decisions to increase yield. He also warns not to look simply at feed costs minus milk price when assessing viability.

“Farmers will have extra milk to cool and need extra labour to milk. The cows will also take longer in the parlour to eat more feed and there may be vet costs with potential health issues,” he warns.