by Tamara Scully
When it comes to milk production, dry matter intake is key. Learning to balance the quality and availability of pasture forages with the protein and energy needed in the dairy cow diet is one of the challenges when grazing. Many variables occur when grazing that affect the nutritional quality of the pasture forages. Managing a grazing program can be rewarding, but challenging, for dairy producers.
“No matter if a cow is grazing or totally confined, her milk production will be largely based on the total amount of dry matter consumed,” Mike Thresher, dairy specialist with Morrison’s Custom Feeds said. “The more a cow can consume, the more that gets turned into milk production.”
The nutritional levels of pasture forage are limited by forage quality and availability, and many factors can affect the actual dry matter intake being consumed. As dairy producers add grazing to their operations, common mishaps with an increased forage diet occur, Thresher said. While pasture is usually sufficient in protein, it can be low in energy, requiring a supplemental source. For every one pound of protein consumed by the dairy cow, she will also require four units (Mcals) of energy. Beef cattle require a 1:5 ratio.
Even with this greater need for protein, you can get all the protein from pasture when grazing a dairy herd, Thresher said. Even when overgrazing the cows are probably getting enough protein, but not enough energy. “Young grasses and legumes can have the needed protein but the energy is not there.”
Overgrazed pastures mean that the forage plants become stressed, and cannot regrow normally. Regrowth becomes slower, and soon there is not enough forage to meet the expected DMI from the pasture. If the DMI is limited, the milk output will be, too.
“I see it quite often in summertime, often around July 10,” Thresher said. The bulk tank weight goes down because the paddocks are overgrazed, and no longer providing the DMI they should. It can be hard to recover from this, so producers should plan for reduced DMI in their pastures in July, and compensate by rotating in fresh pasture, leaving paddocks to rest longer, and adding feed to supplement the reduction in forage.
“If there is not enough forage from pasture when grazing, and when the cows come off of the pasture it looks like a golf green, then there was not sufficient dry matter intake,” he emphasized. “The more a cow can consume, the more that gets turned into milk production.”
Forage Management Issues
Often, cows are simply not grazing all of the available forage, resulting in a lower DMI. It is imperative for producers to know how much the animals are actually eating. Thresher explained that an accurate DMI is the first step to balancing the ration. What is left in the paddock after the cows have grazed? Often it is a wet or dry spot which is left ungrazed. Then, go to the next paddock in the rotation and see what is available based on what they are consuming in the prior paddocks.
“You really have got to go out and look around and see what the cows are eating,” he said. “See what they chose to eat.” Recognize the areas they will eat, “and send in a forage sample from those areas to be analyzed.”
One concern is extra moisture in the fields. Wet periods can cause reduced grazing. If cows are refusing to graze a pasture that is 8-10 inches in height, and are only nipping at the top growth, it may be because of the putrid smell of decaying matter.
“They just won’t graze it,” Thresher advised. “Mow it off and clean it off.”
Cows need to have adequate water intake, or their DMI will be impacted. In the very early spring, protein deficit in the forages can be a concern. The pasture may look green and lush, but the protein content may only be 15 percent, particularly if the weather has been dry.
If there is adequate protein, but inadequate energy, the Milk Urea Nitrogen level will rise. Decrease MUNS by grazing at a higher height, and by feeding dry hay, which will increase rumination and slow down digestion. Dry hay “goes better with pasture” and can make an excellent forage for the dairy cow diet, Thresher said. If MUNS are high, the cows will act slow and lethargic, the manure will be loose, and there can be weight loss and breeding problems.
Simple math will help determine how much protein and energy is needed from supplemental feed. The amount of crude protein for a dairy cow should be 25 percent. Any higher, it is too difficult to manage, Thresher said. A rough rule of thumb is 1 pound of protein per 10 pounds of milk. Once it is known how much protein is coming from pasture (DMI multiplied by the crude protein level of the forage), the actual protein consumed is known. Accurate calculation of the supplementation needed to provide the energy for optimal milk production can then occur.
A Net Energy Lactation of .68-.78 Mcals is the target. While .41 Mcals is the minimal acceptable amount, “not a lot of milk” will occur in levels below .68 Mcals, Thresher said. On well-managed pasture, it is possible to get energy levels of .7-.8 Mcals. Adding annual grass or grain forages via frost seeding will increase pasture energy levels through new growth.
Energy needs can be increased on pasture, as cows are walking and exerting themselves depending on the distance and terrain. Adding grains is the easiest way to increase energy. Corn silage is a good choice. Corn meal provides the highest energy level of .94 Mcals. Barley, oats, wheat or small grain silage are other options, as are beet pulp and molasses. Feeding grain will increase milk production, which often offsets the cost of purchasing any feed very quickly, Thresher said.
“The best supplement for a non-grain approach would be to have part of the grazing include the grazing of an annual crop such as oats, annual rye grasses, triticale, sorghum-sudan or millet,” Thresher said. “This would bring in great energy along with a good amount of protein. Oats and sorghum-sudan would be the lower protein options, but still bring in a good deal of energy.”
There are other considerations for proper forage management. Types of forage available have an impact on intakes, Thresher said. Weather can impact the energy available from forages rapidly, with hourly changes seen.
“To maximize the most out of pasture for both energy and protein, one must manage the pasture well. This would include keeping the pasture clipped — three or four times per year, keeping soil fertility at its best, introducing new seeds into the pasture, possibly considering irrigation if drier than normal,” Thresher said. Moving the cows to fresh pasture twice each day is optimal.
Dairy herd graziers need not only to manage their pastures for optimal forage, but to adjust the feed ration regularly to compensate for forage limitations. Any economic benefits seen from reducing feed purchases via grazing can be quickly offset by production drops in inadequately monitored or maintained pastures.
Balancing nutrition for grazing dairy herds
by Tamara Scully