Intensively grazed pasture has high nutritional value. The entire ration must, however, be balanced properly to get the most economic advantage.
High-producing milking cows should graze vegetative plants. Variability between paddocks must be minimized.
Pasture does not provide much effective fiber. Rumen acidosis must be controlled. Feed long hay, a blend of rapidly and slowly fermentable carbohydrates, and buffers.
Complement pasture with palatable, energy-dense grains and forages.
Pasture protein supplements should contain less rumen degradable protein and more UIP than traditional protein supplements. Heat-treated soy products are a good source of rumen bypass lysine needed to complement microbial amino acids.
Provide adequate water.
(This article used to be called 'Pasture')
In the 1990’s intensively grazed pasture became somewhat popular, especially among smaller farms looking to reduce input costs, such as machinery costs. The key is to move cows among small paddocks at a fast enough rate so that the cows are always consuming plenty of high-quality forage. Although intensively grazed pasture is very high in quality, it must be understood nutritionally in order to get cows to make a significant amount of milk from it over the entire growing season.
What is High-Quality Pasture?
Most rotational grazers use a blend of grasses and legumes in their pastures. In cool climates, for example, orchardgrass with clover is popular. Others might use alfalfa, bromegrass or reed canarygrass. Of course, in warmer climates, warm season grasses like bermudagrass are more popular.
Regardless of the type of forage planted, it is imperative for grazing success to feed cows only the best, vegetative, highly nutritious plants and to minimize variability between paddocks. For example, with cool season grasses, it is usually best to start grazing when the plants are 6-8 inches (15-20 cm) high and take cows out of the paddock with the plants are 2-3 inches (5-8 cm) high. Often this means that cows will be in a paddock for as little as 12 hours up to 3 days. The paddock is then “rested” and allowed to re-grow for about 21-30 days, depending on forage type and growing conditions. Some farmers find it helpful to graze high producers in a paddock first and follow with low producers or heifers having lower nutrient requirements. The tops of the plant are usually considered the most nutritious. It is generally recommended that pastures be mechanically clipped after grazing and before re-growth to remove mature, low quality pasture and increase uniformity.
Variation in Pasture Nutrient Analysis:
Although it was mentioned above that farmers should work to maintain consistent quality among paddocks, changes in the nutrient analysis of pastures can be significant. The crude protein (CP) content of pasture can vary depending on maturity, weather, and types of grasses. In one dataset from a forage lab, pasture CP content ranged from 14% to 29%. The neutral detergent fiber (NDF), which has a large impact on the total intake of the cow, can vary significantly as well. In one dataset from a forage lab pasture, NDF content ranged from 35-60%. That’s a range in energy (NEl) from 0.80 to 0.60 Mcal/lb (1.76 – 1.32 Mcal/kg). The variation in mineral content of pasture can be of particular significance for dry cows. The nutritionist may be using a value of 1.5% potassium for the pasture in a dry cow ration but if the pasture is really 3.5% potassium, milk fevers may become a problem. Pastures need to be analyzed. Keep track of and date the analyses of different plots and note the maturity of each. It won’t be perfect but it will help to predict the nutrient analyses of the plot the next time the cows go into it.
It is best to estimate pasture quality, pasture intake, and intake of other forages and then use a computerized feeding program to balance the ration. Total dry matter intake can be estimated based on a cow’s weight and level of production. For example, a 1350 pound (614 kg) cow making 80 pounds (36 kg) of milk (4% FCM) per day should consume about 3.7% of her weight, or about 50 pounds (23 kg) of dry matter from pasture, other forages, and grain. Of course, since NDF content dictates rumen fill, pasture containing more NDF and/or less digestible NDF will be consumed at a lower level than high quality pasture.
Offer a Palatable Feed
Often, cows on pasture have little desire to eat grain. Offering very palatable grains can help. Try to hide unpalatable ingredients, such as animal proteins and bypass fats. Molasses, distillers, and soy products all usually help palatability.
Watch Out for Rumen Acidosis:
Pasture does not provide a lot of long fiber that will float on top of the rumen and form a cud for the cow to chew again. Chewing results in saliva production which buffers the rumen and reduces acidity. Without adequate effective fiber, acid will build up in the rumen.
The fiber (NDF) in good pasture is very digestible. This is good for providing energy to the cow, increasing microbial protein synthesis, and increasing total intake of the cow. But, highly digestible NDF will leave the rumen more quickly. Because of this, more forage and less grain should be fed to cows on good pasture in order to provide enough rumen effective NDF to combat acidosis.
Rumen acidosis results in a reduction in fiber digestion, a reduction in dry matter intake, lower milkfat, and lower milk production. The first signs of acidosis are: pasty, bubbly manure, inconsistent manure (some cows are tight, others are loose), inconsistent daily intakes, and inconsistent milk production. Three or four pounds (1.4-1.8 kg) of long hay per day fed prior to grain in the barn can help reduce acidosis. Also, feeding grain in many small meals throughout the day can help reduce acidosis. Of course, this is difficult in most pasture situations and may take some work and creativity. Slowly fermentable carbohydrate sources, such as cornmeal, will reduce the rate of acid production in the rumen and minimize daily swings in rumen pH. Also, don’t forget sodium bicarbonate (or an equivalent buffer). A cow making over 80 pounds (36 kg) of milk should have at least 8 oz. (0.23 kg) of added buffer in the ration. Buffer should also be offered to cows free-choice.
Complement Pasture with Energy-Dense Grains and Forages:
Cows on pasture tend to have less of an appetite for grain partially because they prefer the green grass. Also, it is good not to feed a lot of grain to avoid acidosis. Regardless of grain offered, high-producing cows on pasture with little effective fiber will be slightly acidotic and will eat less grain. For these reasons, it is beneficial to provide a high-energy grain. Increase the amount of energy per pound of grain and decrease pounds of grain. The price per ton of feed will be higher but not the price per unit of milk. Extra energy will be especially helpful in eliminating thin cows at the end of the grazing season and the accompanying breeding problems. Often, feeding about 20 pounds (9 kg) of corn silage to cows on pasture is helpful.
Provide Non-Fiber Carbohydrate to the Rumen Microbes at the Right Time:
The rumen microbes require non-fiber carbohydrates (NFC) and protein in combination throughout the day. Pasture contains a lot of rumen available protein. Pasture does not provide much non-fiber carbohydrate for the rumen microbes. A blend of non-fiber carbohydrates, including sugar, fast-digesting starch (from sources like bakery product, barley, corn silage or high-moisture corn), and slow-digesting starch (from sources like cornmeal), is usually helpful for providing the non-fiber carbohydrates that the rumen microbes need throughout the day. Unfortunately, sugars and fast-digesting starches must be fed with care because they can increase the risk of acidosis more than cornmeal. But, if acidosis is controlled, microbial protein production and milk production will be enhanced with a non-fiber carbohydrate blend. Be careful not to supplement fats prior to meeting the cow’s requirement for rumen available NFC, in an effort to simply increase grain energy density.
Complement Your Pasture with the Right Proteins:
Pasture provides a lot of rumen degradable protein. Any rumen degradable protein that is fed beyond what the cow requires for milk production will just be wasted. Too much rumen degradable protein, especially soluble protein (SIP), in the diet also leads to high Milk Urea Nitrogen (MUN). MUN over 16 mg/dl has been associated with reproductive problems, such as early embryonic death. It is usually evidenced by irregular heat cycles.
Pasture doesn’t contain much bypass protein (UIP). UIP escapes the rumen and is available at the intestine to drive the early lactation cow to higher peak milk. Pasture protein supplements should contain less rumen degradable protein and more UIP than traditional protein supplements.
It is also important to pay attention to the amino acids supplied by the UIP. Because of a potentially higher microbial protein yield in pasture based diets, it becomes especially critical to supply more lysine in the UIP to adequately complement the amino acid profile of the rumen microbial protein. Heat-treated soy products are considered to be a good source of rumen bypass lysine.
Provide Adequate Water for Cows on Pasture:
Cows on pasture need water for two reasons. It can get hot in the summer and they need extra water for heat stress. Also, cows need to get rid of the excess rumen degradable protein that they eat. They do this by converting the protein to urea and then getting rid of the urea in urine. Cows need water to make urine.
Pasture for Dairy Cattle: Challenges and Opportunities
D.M. Amaral-Phillips et al., University of Kentucky
Grass Intake of Dairy Cows
R&H Hall Technical Bulletin
Undersander and Combs, University of Wisconsin
Ryegrass Types for Pasture and Hay
D. Cosgrove et al.
Uses of brassica crops in grazing systems
Dan Undersander, Ph.D., University of Wisconsin
Frost Seeding Legumes and Grasses into Pastures
Establishment and Management of Switchgrass
Dan Undersander, Ph.D., University of Wisconsin