By Rainey Rosemond
In Pennsylvania, many dairies utilize grazing as a management tool for dairy cow nutrition. Organic and grass-fed dairies intensely manage pastures as a component of milking cow diets, and many conventional dairies will allow dry cows and heifers to graze. When properly managed, pasture can provide a low fiber, high protein feed for lactating and dry cows or heifers. However, when improperly managed, utilizing pasture could be detrimental to milk yield or the efficient growth and productive life of heifers.
Intensive grazing systems require a detailed pasture management plan, accurate estimates of available dry matter intake (DMI) in a paddock, and close attention to pasture quality and weed control.
Pasture Management Plan
A detailed pasture management plan allows producers to stretch forage inventories with similar labor input to many stored forages. The first step in designing a pasture management plan is understanding the land available for grazing and the areas that should not be grazed. Mapping programs, like PA One Stop, are available to help determine the boundaries of fields and where streams, tree shade, or other natural objects might be. Once you know the boundaries of your pastures, you can determine the size and number of paddocks necessary to support your animals’ needs, based on stage of lactation and current nutrition goals for your herd. The ability of an individual paddock to support forage needs will be influenced by soil quality and health, current dominant grasses, frequency of inter-seeding, and fertilizer application. Calculations for determining pasture production and ability to support animal numbers are described in Four Steps to Rotational Grazing .
Estimations of Dry Matter Intake
Dry matter intake is a critical component of dairy production, as it is a main driver of milk production, animal growth, and animal health. The inclusion of pasture in lactating dairy rations can limit milk production if expected pasture DMI is lower than actual pasture DMI. Reduced dry matter intake can lead to body stores being used as an energy source, potentially leading to underconditioned cows, lower fertility, and reduced milk production. If heifers are permitted access to pasture without sufficient forage, heifer growth could be limited by limited intake.
Grazing sticks are an easy method to estimate pasture dry matter availability. Grazing sticks utilize plant height to estimate available dry matter throughout a pasture. It is important to frequently re-evaluate the dry matter availability of pastures as it changes season to season. Measurements of pasture height should be taken in 10 to 20 spots evenly spread throughout the pasture at spots representative of forage availability. As pasture size increases, more samples will be necessary to accurately reflect pasture productivity. Samples should not be taken in only low or tall forage height areas. Once available pasture forage is known, producers can determine what percentage of that pasture is actually grazed to estimate animal intake.
In Pennsylvania, formulated rations typically range from 48 to 52 pounds of DMI. For organic operations a minimum of 30% of this intake is expected to be from pasture. Before putting animals out to pasture, knowing how much forage is available can help producers more accurately estimate the contribution of pasture to DMI and determine how much supplementation is needed. See the example below to determine the appropriate pasture supplementation necessary.
Example:
A paddock has an estimated available forage yield of 1,700 lbs as fed and will be grazed for 2 days by 10 cows.
85 lbs/cow of pasture consumed * 20% dry matter (DM) = 17 lbs of pasture consumed
Formulated dry matter intake = 50 lbs/cow/day
50 lbs/cow/day – 17 lbs = 33 lbs of pasture supplementation needed
Other factors may further influence animal intake including the availability of fresh, clean drinking water and heat abatement provided while out on pasture.
Weed Control
Pasture quality and accurate estimates of DMI go hand-in-hand when managing pastures. Pasture, especially in the spring, can look lush, green, and readily available. However, in some pastures, weed growth or unappetizing grasses can contribute to an increased estimated DMI, but may drastically inhibit actual DMI. Weed pressure is more likely to occur with non-intensively managed pastures or with pastures that are not periodically mowed.
Some considerations for weed management (Comerford and Glazier, 2014; Anderson, 2021; Sellers and Devkota, 2022):
- Weeds generally outcompete desirable pasture plants.
- Pastures should be scouted frequently to determine the number of weeds and the species present.
- Control dominate species and prevent the spread of less common weeds. When left unattended less common weeds can become the dominate species.
- Fall is one of the best times for managing perennial and biennial weeds due to biological processes that occur as weeds prepare for winter.
Additional considerations specific to animal grazing would be the toxicity of weeds and the availability of control measures suitable for lactating animals. Toxic weeds should be removed from pastures and controlled in a timely manner. In forage limiting pastures or management systems, animals might resort to eating toxic weeds they might otherwise sort against (Lingenfelter and Curran, 2001). Even in systems where forage is not limited, animal behavior is unpredictable and consumption of toxic weeds might occur, potentially resulting in unthrifty animals, reduced milk production, or even death.
Weed control is frequently done through mowing, hand removal, or herbicides (Lingenfelter and Curran, 2001). Which management practice that is selected is dependent upon weed species and organic certification. Organic dairies cannot use herbicides and must control weeds through mowing, hand removal, or other pasture management techniques such as inter-seeding, improving soil quality, and proper fertilization. Inter-seeding established pastures can increase stand density and improve dry matter availability. Patchy paddocks after being grazed, portions of a pasture not regrowing, and reduced yields or quality could all be signs that inter-seeding is necessary. Soil quality should be tested at least once every three years to ensure that nutrients in the soil are available to support pasture quality and quantity. Mowing and hand removal of weeds are excellent practices that reduce the ability of weeds to out compete established grasses. These practices additionally reduce seed dispersal and incidence of new growth.
For non-organic dairies, herbicides can be an effective weed management tool. Choosing an herbicide with a proven track record for successfully eliminating the identified species in your pastures is important. Before using herbicides pay close attention to label specifications on when and what concentrations the herbicide should be applied. Ensure that all herbicides are safe for grazing animals and determine appropriate use according to the label instructions.
The effectiveness of any grazing operation is based on having an updated grazing plan that accounts for animal nutrient and dry matter requirements, animal numbers, and forage productivity. Effectively managing pastures to maintain forage quality, quantity, and reduce competition with weeds will lead to greater success with pasture incorporation into an operation.
Source : psu.edu