Mike Gamroth, Oregon State University
High-producing cows early in lactation often cannot consume enough forage to meet their nutritional needs. Therefore, all the feed they consume must be of the highest quality if you're going to maintain production.
Dairy cows prefer grazing grasses rather than legumes and will graze the most palatable species first. For example, they'll graze ryegrass before tall fescue.
Pasture intake is directly affected by the amount of feed allocated in the paddock. You allocate feed when you control the height of the pasture presented to the animals, the size of the pasture, and the percentage of the forage in the pasture they're forced to consume.
Forage height is a good indication of the amount of dry matter (DM) available. Each inch of pasture height is about 300 pounds DM per acre. Meters such as the "floating plate" meters are available to help more accurately estimate DM in the pasture. The floating plate meter is made of a flat disk that slips around a measuring stick. To measure the forage, you place the measuring stick vertically in several representative areas of the pasture, allowing the disk to rest on top of the forage. By reading the stick, you can estimate the DM per acre. More expensive electronic meters that estimate the forage density and display a reading of the DM estimate are also available.
Cattle on pasture will graze a maximum of 8 to 12 hours per day and spend an additional 3 to 4 hours ruminating the feed they've consumed while grazing.
Pasture intake is controlled by biting rate. The ease with which the cow can tear off and consume the pasture plants greatly influences biting rate. Quality or maturity of the pasture also affect intake. Coarse, mature grasses reduce intake. Feed intake is also reduced if you do not control the cow's tendency to walk considerable distances while grazing.
Research studies show that a cow will take about 36,000 bites and consume a maximum of about 28 pounds of dry matter per day given ideal conditions. Under less than ideal conditions, the amount of pasture dry matter consumed will be considerably less. Pasture allowances for high-producing, lactating dairy cattle need to be generous if they are to consume the 20 or more pounds of pasture dry matter required daily. If you maintain forage quality, the height of the pasture determines how much feed the animal can consume and how much milk she will produce.
High milk production from pasture requires low forage use at any one grazing. A good rule of thumb is the 50/50 rule which means 50% or less of the available forage should be consumed during each grazing period. When dairy cattle are forced to use more than half the available forage, intake is limited, even though it may be of high quality. At the end of the grazing period, you should have "leftover" forage in the pasture.
For pasture forage to support the first 35–40 pounds of milk per day, graze pastures to a residual dry matter level of not less than 1,400 pounds of DM per acre. This requires strip grazing—moving cows daily or twice daily to graze from 2,400–2,800 pounds of DM per acre down to 1,500–1,600 pounds. However, leaving more than 1,800 pounds of DM per acre after grazing will reduce the quality of the grass for future grazing.
Pastures allowed to grow over 3,000 pounds of DM per acre become coarse and of lower quality even though total production is high. If you offer this feed to high-producing dairy cows, production will suffer.
The ideal situation is to keep pastures growing in Phase 2 by grazing them from 2,400 to 2,800 pounds of dry matter growth per acre down to 1,400–1,600 pounds. You can use dry cows, heifers, or mowing equipment to clip the pastures and remove the remaining forage evenly to about 4.5 inches (1,400 pounds of DM per acre).
Intensive grazing improves the quality of regrowth in pastures, but you must manage the rate of regrowth and, thus, the yield from the pastures. Table 1 shows a sample feed budget for pasture systems, based on Oregon growing conditions.
|Total forage in pasture (8 inches)||2,400 lb DM/A|
|Subtract residual pasture desired (about 5 inches)||- 1,500 lb DM/A|
|Feed available||= 900 lb DM/A|
|Daily feed allowance for 100 cows at 24 lb DM/day||2,400 lb DM|
|Pasture needed for one day (2,400 lb DM daily feed allowance divided by 900 lb feed available)||2.7 acres|
|Days required before re-grazing (growth at 35 lb DM/A/day)||26 days|
|Area needed for a 26 day rotation||70 acres|
For information on estimating the nutritional value of your grasses, legumes, and weeds, as well as supplementing later season pastures, consider the ATTRA publication, Ruminant Nutrition for Graziers by Rinehart (2008).
References and Citations
- Rinehart, l. 2008. Ruminant nutrition for graziers [Online]. ATTRA publication #IP318. National Sustainable Agriculture Information Service. Available at: https://attra.ncat.org/attra-pub/summaries/summary.php?pub=201 (18 March 2010).
- Milligan, K. G. 1983. Controlled grazing systems. Aglink FPP 681, New Zealand Ministry of Agriculture and Fisheries, Wellington.