Spring turnout is an exciting and dynamic time for graziers and dairy cattle. These lush, fast-growing, green pastures, however, can pose some challenges – notably, decreased butterfat.

Early grass is high in unsaturated fatty acids, like linoleic acid, and low in total fiber. When these two factors combine, they create a perfect storm in a cow’s rumen and disrupt the normal pathways used to produce butterfat.

“The cow ends up not having an adequate fiber mat and feed does not stay in the rumen long enough to be adequately digested. So, we get rumen acidosis. We also get that squirty spring manure representing not just an unhealthy rumen environment, but also that the feed is leaving before the cow gets all of the nutrients that it could,” said Greg Brickner at a Dairy Grazing Apprenticeship (DGA) roundtable.

Brickner is a Wisconsin-based veterinarian and the senior director of precision grazing at DGA. He has nearly three decades of managed grazing experience.

In a healthy rumen, linoleic acid from the feed is first converted into rumenic acid. Rumenic acid is also known as a conjugated linoleic acid (CLA), and it eventually becomes a saturated fat in milk.

On the other hand, if the rumen has an acidic environment, a different set of bacteria helps transform linoleic acid into a different form of CLA. Brickner referred to it as “bad CLA.” This “bad CLA” ends up in the udders’ milk-producing cells and turns off butterfat production.

“If we turn off that production of fat in the udder itself, that’s when we get this big drop in butterfat. We want to avoid the rumen conditions that contribute to this ‘bad CLA’ being made,” said Brickner.

Maintaining butterfat comes with some irony for Brickner. He recalled the low-fat craze of the 1990s (when he was milking a herd of Jerseys), when scientists had discovered this “bad CLA” and were actually feeding it to dairy cattle in an attempt to induce butterfat depression.

To avoid making “bad CLA” and reduced butterfat, graziers must take one of two approaches to transitioning onto pasture. First, they can limit the intake of spring pasture by allowing only 10% of dry matter intake (DMI) to come from pasture and increase that percentage as quickly as rumen adaptation allows.

The downside to this approach is that it requires extra labor since the cows must be moved between the pasture system and the barn.

“It won’t take them long to harvest 10% of their ration. Plus, they really crave this early spring grass, and they will actually graze faster than they will in the middle of the summer. We have to control both the area that we give them and the time they have on pasture,” Brickner said.

He is a big proponent of using a grazing plan to calculate the dry matter demand it takes to reach the 10% DMI from pasture and to appropriately size paddocks based on the projected amount of forage available.

The second approach is to wait until all of the pastures are at the three leaves per tiller stage. At this point, linoleic acid levels will have decreased and the total fiber will have increased.

With this transition method, there is no need to restrict access to pasture. There will, however, be fewer days of grazing before the grasses start to head out and lose quality. This means the farmer will probably have to harvest more pasture as first crop if they want to capture that pasture as high-quality feed.

Manure, according to Brickner, should be used as the proxy for understanding what’s going on in the rumen and how healthy the rumen environment is. Manure is scored on a 1 to 5 basis, with 1 being very fluid and 5 being extremely dry and segmented. The ideal score is a 3, where the manure starts to take on a normal pat form with a consistency similar to thick pancake batter.

If, for example, the herd has been getting 10% of their DMIF from pasture for a few days and their manure is at a 3, then it’s appropriate to increase grazing time.

One roundtable participant shared that they felt it was unrealistic for herds with an emphasis on grazing to make such a gradual transition to pasture. “The cow psychology is once we start grazing, we’re grazers. We’re not eating what you give us in the barn,” they said.

Brickner acknowledged this challenge and suggested providing the herd with super palatable forage in the barn. Dry hay may be a good option since it doesn’t contain as many of those unsaturated fatty acids. He also suggested diluting some molasses and sprinkling the mixture over the feed in the barn.

Brickner also thinks that buffers – sodium bicarbonate or a 3:1 mix of sodium bicarbonate to magnesium oxide – should be offered to dairy cattle during the transition to pasture or even year-round.

He recommended using sodium bicarbonate if the buffer is added free choice because magnesium oxide is bitter and could lower intake. If, however, a total mixed ration is being used, he suggested using a sodium bicarbonate and magnesium oxide combination.

“These buffers are going to help keep that rumen and pH in the right zone and avoid making those ‘bad CLAs,’” he said.

by Sonja Heyck-Merlin