Late-Season Pasture Quality Decline Poses Nutritional Challenge for Grazing Herds

As summer gives way to autumn, grazing dairy cows face a hidden nutritional hurdle. The same leafy regrowth that follows the grass heading phase can pack a higher oil concentration, triggering a rumen response that mirrors early-spring butterfat depression. Declining dry matter intakes and reduced energy density combine to erode milk yield, just when many herds are already stretched.

According to Dr. Richard Kirkland, global technical manager at Volac Wilmar Feed Ingredients, the challenge is one of energy delivery without upsetting rumen balance. ‘Late-season grazing isn’t simply about adding more energy,’ he explains. ‘It’s about delivering enough energy to maintain milk production without compromising rumen health. Once rumen function is disrupted, feed efficiency falls, and performance quickly follows.’

The typical farmer’s response—increasing cereal in the buffer diet—can backfire. High-starch feeds ferment rapidly, raising rumen acid production and lowering pH. That impairs fibre digestion, raises the risk of subacute ruminal acidosis, and ultimately hits both milk volume and milk fat content. Instead, Dr. Kirkland advocates shifting the energy source to rumen-protected fats, which bypass fermentation, deliver around 2.5 times the energy density of cereals, and do not add to the rumen acid load.

Trials at the Tasmanian Institute of Agriculture’s Dairy Research Centre back the approach: cows given 250 grams per day of rumen-protected fat produced up to 2.1 kg of extra milk at peak lactation, and still held a 1.5 kg/day advantage at 200 days in milk while maintaining high fertility. The supplement effectively narrows the energy gap that opens as late-season grass quality declines.

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What the Research and Expert Guidance Reveal About Rumen-Protected Fats

Seasonal Grass Changes and Rumen Health

The oil content of grass climbs as it moves out of the reproductive heading phase, creating a leafier, higher-oil pasture. Dr. Kirkland notes that this late-summer regrowth can trigger the same rumen responses seen at turnout, when butterfat depressions are common. The result is a nutritional tightrope: maintain energy intake without disrupting the delicate rumen fermentation that drives both milk volume and milk fat synthesis.

Why Rumen-Protected Fats Are Gaining Traction in Buffer Feeding

Unlike cereals, rumen-protected fats do not break down in the rumen; they travel intact to the small intestine, where the cow absorbs the energy directly. This avoids the acid spike that accompanies starch fermentation, preserving fibre digestion and rumen pH. Because the supplement packs roughly 2.5 times the energy of cereals, a relatively small inclusion rate can offset the energy shortfall without crowding out forage. That dual benefit—energy density plus rumen stability—makes it a sharper tool than simply feeding more grain.

What the Trial Data Shows

The Tasmanian Institute of Agriculture’s grazing trials provide a concrete illustration. With 250 grams of rumen-protected fat daily, cows at peak lactation gave up to 2.1 kg more milk, and a 1.5 kg/day advantage persisted at 200 days in milk, all while fertility held steady. Such sustained responses matter to producers who need to protect milk cheques through to housing, not just fix a short-term dip.

How Dairy Producers Can Incorporate Rumen-Protected Fats Into Buffer Feeding Strategies

  • Assess pasture quality weekly from late summer onward. As grass enters the leafy regrowth phase, watch for early signs of milk fat depression—a signal that rumen energy balance may be slipping.
  • Where buffer feeding is required, limit cereal inclusion. High-starch feeds increase acidosis risk; replace a portion of the cereal energy with rumen-protected fat to maintain total energy without compromising rumen pH.
  • Target a supplement rate of around 250 grams per cow per day. This level, used in the Tasmanian grazing trial, delivered a measurable milk-yield response without harming fertility.
  • Combine the supplement with sound grazing management. Rotational grazing and adequate residual covers still underpin intake; the fat supplement fills the energy gap, it does not replace basic pasture husbandry.
  • Monitor milk yield and butterfat through the transition to housing. The carry-over benefits seen in the trial suggest that strategic late-season supplementation can help cows enter the winter period in better condition.