by Elizabeth A. Tomlin
“Milk fat depression (MFD) is an active process,” said Organic Valley Staff Veterinarian, Dr. Greg Brickner, keynote speaker at a recent Northeast Organic Farming Association of New York, Inc. (NOFA-NY) field day sponsored by Organic Valley and Maple Hill Creamery, and hosted by Huftalen Farm, Erieville, NY.
Brickner explained that MFD is a natural, seasonal process in dairy cows that is magnified in many cases by neglecting best pasture management practices in grass fed dairies.
He led an interactive presentation on avoiding additional MFD through good pasture management — and reducing heat stress in the herd.
Conjugated linoleic acid (CLA), which is an unsaturated fatty acid, takes two forms that impact milk quality; one form promotes healthy rumen fermentation, the other, undesirable CLA (which he refers to as “bad CLA”), causes abnormal rumen fermentation — and rumen acidosis.
Bad CLA is linked to milk fat depression.
“It works on the cells in the udder that are making butter fat and tells them to make less butterfat.” Brickner said.
Bad CLA is produced in the rumen by specific bacteria and Brickner emphasized the importance of avoiding this production.
He noted that although it only takes “bad” CLA 12-hours to begin MFD; it takes 10-21 days to recover.
“You can get a pretty quick change in butter fat with this,” remarked Brickner. “The problem is, like most problems on the farm, the accident happens quickly and the fix takes a long time. If we keep having bad episodes in the rumen, we’re going to drop in butter fat and stay low all through the grazing season.”
Grazing mature grasses at the right time is one key to avoiding MFD.
“Milk fat is made with compounds from fiber digestion,” explained Brickner.
While lush pastures may look good, Brickner said they may provide too much excess protein.
“A dairy cow needs about 17 to 17.5 percent crude protein in her overall ration.”
A lush pasture providing 23 or 28 percent protein will cause instability in the rumen, allowing bad CLA to develop.
“The cow has to do something with that excess protein, that’s when you get elevated MUNs and all of the complications that go along with it,” he said.
Over-grazed pastures contain forages too short to provide the proper nutrients required for rumen stability and higher butter-fat yield percentages.
“During the time of year after the grasses have set seed heads, we can use leaf count on grass tillers to get the nutrient quality of the grasses at the correct stage for the cows and to avoid overgrazing,” Brickner said.
Perennial cool season grasses were looked at during the discussion.
Brickner said perennial cool season grasses should be the basis of grass-fed farms. “There is still, among members of the organic community, a sense of undervaluing these perennial swards and overvaluing annuals — whether it’s corn or sorghum Sudan,” he remarked.
Well-established, perennial swards, given enough rest time and not over-grazed, will provide the nutritional values required to meet dairy cow demands for healthy rumen and high milk-fat components. “It’s key to keep that rumen stable.”
One of the challenges is when seed-heads are forming and quality rapidly declines on a day-to-day basis. Clipping and trampling “sooner than later” will benefit the nutritional value.
“I think the goal should be to try to get through the seed-head period in about 2 weeks with your lactating cows,” Brickner said.
When clipping the pasture, he advised letting it lay instead of raking, allowing the cows to feed on that forage they wouldn’t have eaten if it wasn’t cut.
Brickner said to cut at 4-inches in height, as cows will not graze lower. He also recommends cutting with a discbine as opposed to a brush-hog. “It is best to wait until the grasses are in early seed-head emergence stage or later, before clipping. If done too early, the grasses may try again to set seed heads. It might be worth noting that pastures can be clipped with a haybine before the cows enter a pasture and the cows will eat the clipped pasture in the windrows.”
Overstocking pastures will also quickly diminish pasture nutritional value. Brickner recommends no more than four cows per-acre.
“Monitoring manure becomes really important,” said Brickner. “We can look at the manure quality of cows on pasture to see if rumen fermentation is healthy. If it is too loose we can make adjustments to the ration in many ways: adding a few pounds of stored forages, adding buffers, changing the maturity of the pastures we are offering to the cows, etc.”
Brickner advises keeping about five pounds of good quality, dry hay in the rations.
“During the grazing season, hay provides a steady source of effective fiber to regulate the rumen’s speed of digestion,” he said.
Brickner said the idea of using grass tillers to estimate pasture nutrition was developed in New Zealand and Australia on perennial rye grass, but is able to be used on perennial grasses here as well. “A tiller is simply a grass stem, and the leaves develop off of that stem,” he explained.
The method involves simply pulling the tiller out of the ground at the base and counting the green leaves on the tiller. “What we want to see is a minimum of a three-leaf stage. At three leaves, that grass plant has enough energy stored to tolerate grazing, so we’re not going to stress that plant. This plant has close to that 18 to 20 percent protein and the fiber levels are closer to what that cow needs, as well. We’re going to use that as our minimum of what we want to see.”
Since different species of grasses develop leaves at different rates, looking at grass height alone will not provide accuracy when determining grass maturity level.
“The difference between 2-leaves and 3-leaves is going to be difficult to discern when you’re just walking up the pasture. So, again, we want to pull up some tillers and see if we’re at the right place,” he explained.
Brickner showed pictures of orchard grass that even at nearly 10-inches high, was still immature.
“It’s not the right quality for the cow,” he said.
Aim for pasture and forages with fiber digestibility over 55 percent.
Another key to pasture management with grass-fed dairies is providing relief from the hot summer sun.
“Providing relief from heat involves having areas like cool barns, portable shade, trees in pasture, or a combination of all three,” Brickner said. “It is important that cows still have close access to feed, even when they are under shade.”
Concentrate grazing into morning and night-time on hot days. “Move cows into shade for the hottest parts of the day,” he advised.
Anne Phillips, Organic Valley New York, East Regional Pool Manager, demonstrated how to monitor cow body condition using the 5-point Body Condition Scoring Method and instructed attendees on sampling forages and using a refractometer to measure the Brix, or sugar content.
“It is my understanding that healthy plants will have a high sugar content as one measure of their palatability, quality and energy,” said Phillips. “Usually the reading is higher with more sun due to the process of photosynthesis.”
Phillips said having a refractometer on farms makes sampling easy, instead of taking samples and sending them off, then waiting for results.
Contact your local cooperative extension for help with sampling.