Watch out for a drop in milk fat

Many regions are welcoming some rain and new grass growth after a dry spell that limited grass growth. But, Philip Ingram, Cargill’s technical specialist based in Northern Ireland warns that this new grass could impact milk fat.

“The long dry spell has resulted in a low average grass cover for the time of year, and when the rain comes and the grass starts to grow, cows are likely to hoover it up while it is in a very immature stage,” he says. “These lower covers with immature grass in its first leave stage have 20% more oil content than mature grasses and this can be the cause of milk fat depression.”

Young immature grass, which is more typical of spring and early summer, has a high oil content that’s 50% richer in unsaturated fats than a typical winter ration. Its structural fibre is also low, with sugar and highly digestible fibre high. This can cause a reduction in rumen pH, creating acidic conditions.

The high oil content and the acidic rumen conditions created by the ration pose the two biggest risks associated with milk-fat depression. “The combination of the acidic conditions and the high oil content in fresh grass creates a ‘perfect storm’ in the cow’s rumen and disrupts the normal pathways used by the cow to produce milk fat,” explains Dr Ingram.

cows grazing short cover of regrowth after long dry spell
cows grazing short cover of regrowth after long dry spell
cows grazing short cover of regrowth after long dry spell

In milk production, half of the milk fat is imported into the udder from dietary oil and the cow’s body reserves, and the remaining 50% of milk fat is manufactured in the udder from the acids produced from forage and concentrate fermentation.

“But under these conditions, where cows are eating young immature grass with low fibre content, dietary oil is converted to conjugated linoleic acid (CLA). This is an oil that disrupts the fat production pathways and causes a depression in milk fat.”

In order to take advantage of this new grass, and mitigate a milk fat depression, Dr Ingram says the nutrient content of the buffer or concentrate feed can be altered. “And it’s a good idea to include a targeted rumen buffer.”

“Equaliser Cream is a good example,” he adds. “It has a two-pronged approach, by working as a buffer in maintaining rumen pH, and has a buffering capacity that’s more than double that of sodium bicarbonate. It also reduces CLA production by normalising the oil conversion pathways, so treating the problem before it happens. It’s more effective, both in terms of performance and cost, compared to using C16 fats.”

Results from 10 farms, where Cream was introduced into the TMR or concentrate part of the ration in 2021, showed an uplift in milk fat of 0.31% in seven days and 0.52% in a month. The financial benefit from an increase in milk fat was seen within a month.

“With most payment schemes based on milk solids, a drop in milk fat represents a significant reduction in milk income, and more so as some contracts move towards higher prices for milk fat,” says Mr Macleod. “Adjusting the ration and including a bespoke rumen buffer that is proven to help promote milk fat in challenging situations will give a good return on investment.”